A non-destructive approach for assessing the integrity and performance of waterproofing membranes in bridge decks

Abstract

A scanning apparatus for non-destructively locating waterproofing membrane damage in a bridge deck having an uncoated carbon steel rebar mesh, an asphalt overlay and a waterproofing membrane. A frame alignable over a measurement area of the asphalt carries a counter electrode for physical contact with the asphalt around the measurement area, and one or more reference electrodes to measure a rebar overlay potential of the bridge deck at discrete points within the measurement area when a DC power source is connected between the rebar mesh and the counter electrode to apply a counter electrode potential thereto. A controller takes a respective rebar overlay potential measurement at each discrete position, and determines whether a potential difference between any individual one or more of the rebar overlay potential measurements and the counter electrode potential exceeds a predetermined threshold that signifies the presence of waterproofing membrane damage.

Description

[0001] A NON-DESTRUCTIVE APPROACH FOR ASSESSING THE INTEGRITY AND PERFORMANCE OF WATERPROOFING MEMBRANES IN BRIDGE DECKS CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority benefit of U.S. Provisional Application No. 63 / 644,703, filed May 9, 2024, the entirety of which is incorporated herein by reference.

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to non-destructive techniques for assessing the integrity of waterproofing systems in reinforced concrete bridge decks.

[0005] BACKGROUND

[0006] Using water-proofing membrane under an asphalt overlay is one of the common technologies for increasing the service life of steel-reinforced concrete bridge decks. It is designed to prevent the penetration of water and chloride ions from the road surface to the embedded steel reinforcement. Early detection of the membrane failure before the start of corrosion is crucial as it provides a low-cost intervention opportunity for bridge deck maintenance.

[0007] The deterioration of the water-proof membrane is very complex. The current prediction model used in the previous deterioration model (Li et al., 2022) is purely statistical and depends on a reliable field survey of the membrane’ s condition. However, a destructive survey needs to be carried out to find the broken membrane or resultant delamination and corrosion hot spots that indicate a hidden membrane rupture. In this research project, a non-destructive method has been developed to identify and locate damage in the water-proofing membrane installed in concrete bridge decks.

[0008] Chloride salts such as CaCh, MgCh and NaCl are typically used to deice roadways during sub-zero conditions to improve the skid resistance of the roadway. These salts and their ions penetrate components of adjacent structures such as a bridge and initiate chloride-induced corrosion when they reach a certain concentration at the rebar depth. Once initiated, corrosion will create concrete delamination, spalling and reduction of structural capacity.

[0009] Various approaches have been developed to address this deterioration process. This includes the use of non-corrodible reinforcement and high-performance concrete designed to limit the ingress of moisture and chloride. However, these techniques are costly and can create several construction issues that may compromise the system before it is placed into service. For example, the use of high-performance concrete typically results in a high-strength concrete that is stiffer than the adjacent element to which it is attached. This difference in stiffness results in more frequent cracking, which negates the benefit of the high-performance concrete used. Therefore, many jurisdictions implement a further level of protection by applying waterproofing membranes or sealers overtop of the element to prevent the penetration of water and chloride ions from the road surface and thus prolong the service life.

[0010] Many types of waterproofing systems are available such as preformed sheets, hot- applied rubberized membranes, or spray-on liquids. All these systems are applied to the concrete surface which is then protected by a wearing surface when exposed to wheeled traffic. In Canada, the most common type of membrane used on bridge decks is the hot-applied rubberized asphalt membrane which according to a report from the Transportation Association of Canada (John Emery, 2010) is standard practice in much of Canada since the early 2000s. Similarly, for other elements, the most common type of waterproofing system is silane sealer.

[0011] The failure of the membrane or sealer is dependent on many factors, such as membrane / sealer type, method of application, traffic load, stiffness of the supporting element, and exposure to abrasion. For bridge decks covered with an asphalt overlay, the membrane performance was found to be highly dependent on the overlay condition (Sohanghpurwala, 2006) as cracking and ravelling of the overlay allows more water to access the membrane below.

[0012] As such, premature failure of a membrane / sealer system means a loss of the extra protection afforded by this system from chloride-induced corrosion which can drastically reduce the life of the element. As well, because the membrane failure is often localized, it can produce localized corrosion cells that accelerate concrete delamination, and pop-outs further deteriorate the element condition. In the extreme, pitting corrosion on the embedded reinforcement can reduce the load capacity of the element without visible damage on the deck surface.

[0013] According to a survey conducted by the National Cooperative Highway Research Program (NCHR) on deck test guidelines, there is no specific test concerning the condition assessment of a membrane although mostDOTs (U.S. and Canadian Departments of Transportation) acknowledge that membrane application is a common practice and that the repair / application of membrane is one of their rehabilitation options after the removal of the chloride-contaminated concrete (Krauss et al., 2009). As such, there is a lack of reliable non-destructive test information for assessing the membrane condition under service conditions without which, it is very difficult to implement proactive measures before the concrete is so contaminated that severe corrosion has initiated and caused damage to the surrounding concrete.

[0014] Driessen and Raupach (Driessen & Raupach, 2019) reported a proof-of-concept study on a possible large-scale moisture monitoring method. They simulated the resistance between two carbon meshes where the mortar with artificial water leakage was sandwiched in between. They attempted to use the total resistance to indicate water leakage. However, their parametric study identified limitations with this method for the leakage to be detectable that the water penetration depth must reach a certain level, and it requires a significant resistivity difference between the leakage and the matrix mortar. Since this resistance is dependent on temperature and moisture in the bulk mortar matrix, further calibration under service conditions is required. This method could be useful for assessing the presence of damage in waterproofing membranes provided that the damage causes significant leakage. However, there was no proposed method to locate the leakage and likely the sensitivity is questionable when the leakage is minor.

[0015] Other non-destructive methods such as ground-penetrating radar (GPR) and infrared thermography (Gucunski et al., 2012), can be used to detect membrane failure as these systems incorporate the dielectric constant of concrete to signify a change in characteristics within the surveyed volume. This change occurs when embedded reinforcement is encountered a fracture point within the concrete, so these tests are used to identify reinforcement and delamination that are not visible on the surface. However, this dielectric constant is also sensitive to the liquid water content of the mass concrete so when voids are filled with water or air, they stand out with different dialectic constants and heat capacity, which can be identified by the GPR and thermography techniques. However, while both techniques can detect the change in moisture conditions within the concrete, their sensitivity to the quantity of water accumulation is not clear.

[0016] Therefore, the inventors of the present application sought to develop novel methodology and equipment to achieve improved sensitivity over the existing GPR technique for water leakage detection due to membrane failure.

[0017] SUMMARY OF THE INVENTION

[0018] According to a first aspect of the invention, there is provided a scanning apparatus for locating waterproofing membrane damage in a bridge deck having an uncoated carbon steel rebar mesh, an asphalt overlay and a waterproofing membrane, said apparatus comprising: a frame alignable over a measurement area of the asphalt overlay of the bridge deck; a counter electrode arrangement attached to the frame to make physical contact with the asphalt overlay at locations around said measurement area when the scanning apparatus is placed atop said asphalt overlay; a DC power source configured for connection between the rebar mesh of the bridge deck and the counter electrode arrangement to apply a counter electrode potential thereto; one or more reference electrodes supported or supportable by the frame at a plurality of discrete positions thereon to measure a rebar overlay potential of the bridge deck at respectively discrete points within the measurement area; and a controller configured and operable to perform measurement and analysis steps that comprise at least the following:

[0019] (a) from the one or more reference electrodes, take a respective rebar overlay potential measurement at each of said discrete positions; and

[0020] (b) determine whether a potential difference between any individual one or more of the respective rebar overlay potential measurements and the counter electrode potential exceeds a predetermined threshold, denoting detection of waterproofing membrane damage.

[0021] According to a second aspect of the invention, there is provided a method of scanning a bridge deck, having an uncoated carbon steel rebar mesh, for waterproofing membrane damage, said method comprising:

[0022] (i) placing a scanning apparatus atop an asphalt overlay of the bridge deck at a measurement area thereof; and

[0023] (ii) with a counter electrode arrangement of said scanning apparatus in physical contact with the asphalt overlay of the bridge deck at locations around said measurement area, and with a DC power source apply a counter electrode potential to said counter electrode arrangement: taking a respective rebar overlay potential measurement at a plurality of discrete points within the measurement area; and determining whether a potential difference between any individual one or more of the respective rebar overlay potential measurements and the counter electrode potential exceeds a predetermined threshold, denoting detection of waterproofing membrane damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Preferred embodiments of the invention will now be described in conjunction with the accompanying drawings in which:

[0025] Figure l is a 2-D representation of a rectangular domain of a section of a bridge deck with membrane defects.

[0026] Figure 2 illustrates wetting and drying boundary conditions for moisture transport on a surface of the bridge deck.

[0027] Figures 3 graphically shows initial water saturation of the bridge deck before the wetting and drying cycle starts.

[0028] Figure 4 graphically shows waterfront penetration in a concrete domain of the bridge deck that occurs through the membrane defects after one-day wetting.

[0029] Figure 5 illustrates waterfront penetration in the bridge deck’s concrete domain through the membrane defects after one-day wetting using a cut-off value of 0.8 of water saturation.

[0030] Figure 6 graphically illustrates time-dependent change in waterfront penetration depth for three types of membrane defects.

[0031] Figure 7 graphically illustrates time-dependent change in waterfront penetration spread width for three types of membrane defects (a) actual spread width, (b) relative to the defect size.

[0032] Figure 8 schematically illustrates use of a non-invasive TDR (Time Domain Reflectometry) probe on the bridge deck.

[0033] Figure 9 graphically shows water saturation in the bridge deck’s concrete domain after a one-day wetting followed by one-week drying period.

[0034] Figure 10 graphically shows simulated moisture measurement with different non- invasive TDR (Time Domain Reflectometry) probe lengths, in the instance of a one-week drying period after the one-day wetting cycle.

[0035] Figure 11 graphically shows distribution of chloride content in the deck under the membrane defects when the critical chloride content (0.6% by weight of cement) is reached at the rebar depth.

[0036] Figure 12 graphically shows potential distribution in the deck when rebar under the membrane defects corrodes.

[0037] Figure 13 graphically shows potential versus adjacent reference electrode on top rebar, concrete cover, and overlay surface of the bridge deck when the rebar under the membrane defect is actively corroding.

[0038] Figure 14 graphically shows potential versus adjacent reference electrode on the top rebar, concrete cover, and overlay surface when there is a combination of active and passive rebar under the membrane defect.

[0039] Figure 15 schematically illustrates setup and use of a counter electrode and cooperating reference electrode on the bridge deck, and flow of electrons during said use.

[0040] Figure 16 graphically shows potential distribution in the concrete and overlay when a counter electrode is applied at x=l m.

[0041] Figure 17 graphically shows potential distribution on the asphalt overlay under the excitement of a counter electrode when all rebars are in a passive corrosion state.

[0042] Figure 18 graphically shows potential contour of the membrane defect area with various counter electrode scenarios, and compares use of four discrete electrodes (left) and a continuous framing counter electrode (right), with (a) showing an ideal scenario and (b) showing a non-ideal scenarios.

[0043] Figure 19 schematically shows rebar potential measured from the overlay directly above the rebar segment under various conditions, in which each gradient bar denotes a spectrum of the rebar corrosion condition.

[0044] Figure 20 schematically illustrates symmetric layout of four rebar potential measurement locations within a framed measurement area for membrane damage / defect attention according to the present invention.

[0045] Figure 21 graphically shows a potential difference A reading as a function of the applied potential at the pre-set rebar potential measurement locations of Figure 19 for three worstcase scenarios (a) a membrane defect at the center of the framed measurement area of Figure 19; (b) a membrane defect at a location laterally offset to one side of the framed measurement area of Figure 19; and (c) a detectable membrane defect at location diagonally offset toward one comer of the framed measurement area of Figure 19.

[0046] Figure 22 schematically illustrates overlapping arrangement of four measurement areas of the same type as Figure 19 (with a minor shift illustrated to reveal the overlap).

[0047] Figure 23 illustrate stepwise location of a membrane defect, first with multiple counter electrodes at squares of a larger measurement area, then further refined using a framing counter electrode of full continuous span around a smaller measurement area.

[0048] Figure 24 shows schematically illustrated plan and elevation views of a rebar mesh layout in a reinforced concrete deck section used in experimental validation of the present invention.

[0049] Figure 25 schematically depicts intentional defects implemented in the reinforced concrete deck section of Figure 24 for said experimental validation of the present invention.

[0050] Figure 26 is a top plan view of the actual reinforced concrete deck section schematically shown in Figure 25, with the defect locations marked on the asphalt overlay thereof.

[0051] Figure 27 schematically demonstrates a dielectric constant reading setup for water leakage detection on a bridge deck.

[0052] Figure 28 shows a non-invasive TDR probe.

[0053] Figure 29 shows a GPR scanner, characterized by a 2700 MHz antenna.

[0054] Figure 30 shows a different model GPR scanner, characterized by a 2600 MHz antenna.

[0055] Figure 31 shows a normal GPR line scan image.

[0056] Figure 32 shows a characteristic line scan image for water accumulation in the concrete cover under the membrane defects, featuring a curved reflection line on the membrane surface and poor signal strength underneath.

[0057] Figure 33 is another top plan view of the reinforced concrete deck section of Figure 26, with markup of the asphalt overlay thereof to show water accumulation detected by GPR scan from the asphalt overlay.

[0058] Figure 34 illustrates potential distribution of a three-electrode setup (rebar, counter electrode, and reference electrode) in demonstrating of an operating principle of the membrane damage / defect detection apparatus and methodology of the present invention.

[0059] Figure 35 schematically illustrates side elevation and top plan views of a frame and counter electrode assembly of novel scanning apparatus of the present invention, with a singular framing counter electrode spanning around a square measurement area of the apparatus.

[0060] Figure 36 schematically setup and use of a single-channel scanning apparatus, featuring the frame and counter electrode assembly of Figure 25, on a bridge deck to detect membrane damage / defects therein.

[0061] Figure 37 is a top view of a prototyped embodiment of the scanning apparatus of Figure 36 in place atop the reinforced concrete deck section of Figure 26.

[0062] Figure 38 is another top plan view of the reinforced concrete deck section of Figure 26, with markup of the asphalt overlay thereof to show detection of the intentional membrane defects therein by the scanning apparatus of Figure 37.

[0063] Figure 39 schematically illustrates side elevation and top plan views of a four- channel embodiment of the scanning apparatus, using the same frame and counter electrode assembly found in Figures 35 and 36.

[0064] Figure 40 is a block diagram of the electronic components of the four-channel scanning apparatus of Figure 39.

[0065] Figure 41 schematically illustrates side elevation and top plan views of an eightchannel embodiment of the scanning apparatus, using the same frame and counter electrode assembly found in Figures 35, 36 and 39.

[0066] Figure 42 is a block diagram of the electronic components of the eight-channel scanning apparatus of Figure 42.

[0067] Figures 43A and 43B are side elevational views of a full-scale embodiment of the scanning apparatus that integrates a similar eight-channel scanner to that of Figures 41 and 42 into a wheeled framework by which the apparatus is rollable over the bridge deck, and on which the scanner is raisable and lowerable between travel and working positions.

[0068] Figures 44A and 44B are top plan and side elevational views of the eight-channel scanner of the full-scale embodiment of the preceding figure, shown in isolation from the wheeled framework thereof.

[0069] Figures 45A and 45B are vertically cross-sectioned side elevational views of a spring-loaded reference electrode assembly from the scanner of the preceding figure, of which Figure 45A shows a fully extended state of the spring-loaded reference electrode and Figure 45B shows a partially collapsed state thereof.

[0070] DETAILED DESCRIPTION

[0071] The present invention focuses on a non-destructive approach for assessing the integrity of waterproofing systems in reinforced concrete bridge decks. The achieved utility includes the ability to detect membrane failures early to prevent corrosion and mitigate costly repairs. Through extensive numerical simulations, two innovative test procedures where developed: a moisture test and a potential test, both of which effectively detect membrane defects. These methods are based on the early indicators of the damaged membrane: water accumulation under the membrane, possible active corrosion of the rebar due to chloride accumulation and the uneven potential distribution on the overlay due to localized active corrosion or externally applied potential via the electrical continuity of the damaged membrane.

[0072] Numerical models were undertaken to simulate two physics: unsaturated water transport and secondary current density distribution. The former simulates the water content distribution in concrete and the latter simulates the current and potential field excited by the corroding rebar mesh with or without externally applied potential. Various prescribed wetting-and- drying cycles were implemented to explore the proper testing window and test setting parameters so that the experimental measurables (moisture and potential readings) could effectively detect the membrane defect or damage location. Based on numerical studies, two test procedures were proposed: a moisture test and a potential test. Numerical simulations were used to determine the proper test parameters.

[0073] To validate the effectiveness of the test methods, experiments were conducted on a physical deck model. The results confirm that both the moisture test and potential test are highly successful in identifying membrane defects at their early stages, offering valuable insights to address potential corrosion issues promptly.

[0074] Numerical Study

[0075] In the numerical models, the deck cross-section was modelled as a 2-D geometric object. As shown in Figure 1, the rectangular domain consisted of an asphalt overlay and concrete. The membrane and rebars were modelled as line edges. The membrane line was discontinued at the three defects: dot defect, area defect and debonding defect. Those defects were the openings in the membrane allowing the water and chloride ions to transport through. The dot defect and area defect represented different opening sizes: 1 cm and 10 cm. The debonding defect had a small opening (rupture) in the membrane and a deboned area underneath the adj acent membrane with compromised water tightness.

[0076] The moisture transport model simulated the water accumulated under the membrane due to leakage through the defects. The top asphalt surface was subject to a wetting and drying boundary condition; the remaining external surfaces were exposed to ambient dry air conditions, and the sound membrane was set as impermeable (Figure 2). The initial moisture condition was the simulation result from an 80% saturated concrete slab followed by one-month air drying in the ambient environment, and a no-flow condition on the top surface for one month where the membrane is installed. The wetting and drying conditions were described as hydraulic pressure heads summarized in Table 1. Table 1 Moisture boundary condition parameters

[0077] ,,, . Ambient

[0078] Wetting . . .

[0079] . air-drying condition .. . ° condition

[0080] Hydraulic pressure head [m] -50 -16971

[0081] Concrete saturation level in equilibrium [-] 0.99 0.3

[0082] The initial moisture condition is plotted in Figure 3. The deck cross section exhibited a significantly drier surface layer, with a thickness of approximately 2 cm. The depth near the corner was greater, measuring around 5 cm. The concrete beneath the membrane displayed a water saturation level comparable to the internal concrete. The wetting and drying cycle periods were explored. In the practical on-site application, the wetting phenomenon can be from rainy weather or water spray. It should be noted that concrete is known for faster wetting and slower drying. Herein, consideration is made to both a shorter period (one day) and longer period (three days) of wetting.

[0083] It was found that the simulated defect sizes did not significantly affect the penetration depths. As shown in Figure 4, a one-day wetting period was sufficient to allow the waterfront to reach a similar depth (30 mm) among the different defects. For the dot defect, which was one-tenth of the cross-sectional size of the area defect, the water penetration depth was slightly smaller. For the debonding defect, the waterfront had a raindrop shape with deeper penetration leaning towards the membrane rupture location. The waterfront horizontal spread inside concrete was significantly affected by the defect type and size. The ratio of water spread size to the defect size was 5, 1.4, 0.95 for dot, area, and debonding defects respectively. The increase in the defect size did not proportionally increase the horizontal spreading size. For the dot and area defects, the horizontal spread size can be approximated by the summation of the defect size and a constant (20 mm). For the debonding defect, this spread size was about the average value of the dot and area defect cases. Using 0.8 saturation as a cut-off value (Figure 5), the water penetration front can be accurately quantified (Figure 6). The penetration depth and spread size are plotted against the length of the wetting period.

[0084] The progress of the water penetration depth slowed down after one day wetting period. It can be seen from Figure 7, the water spread width was determined by the defect size, the greater the defect size, the larger the spread area. For the same defect size, the area defect had a greater water spread width than the debonding defect. When the defect size is subtracted from the spread size (Figure 7b), it was found that the relative spread size was similar for dot and area defects, and they were both significantly greater than the debonding defect. It was concluded that for dot and area, the defect size did not significantly affect the water spread speed, but the debonding defect caused a slower spread speed.

[0085] The waterfront penetration propagated most rapidly in the first 24 hours. The one- day wetting time is also practical for rainwater or water spray. In the following drying period, the moisture in the overlay evaporates quickly, leaving the water trapped under the membrane defect. The non-invasive TDR probe can be used to test the dielectric constant which is sensitive to the moisture content. The sampling volume of the TDR probe is approximately half of the cylinder with the length of the probe and the radius of the probe spacing (Figure 8). The sampling volume should be restricted above the top rebar since the steel rebar interferes with the TDR signal. Therefore, an adequate wetting period is selected such that the moisture occupies the concrete cover and does not significantly spread horizontally. This criterion allows the TDR test to detect the location of the moisture accumulation. Since the cover considered ranged from 30 cm to 70 cm, a one-day wetting period was selected, which corresponded to 20 mm to 30 mm penetration depths with up to 30 mm of relative horizontal spread. Considering the thickness of the asphalt overlay is 50 mm, appropriate probe spacing was selected as 80 mm.

[0086] Figure 9 shows the water distribution after a one-day wetting followed by a one- week drying period. The sampling volume shown in the figure contains the water trapped between the top rebar mesh and the membrane, from which the TDR reader registers a data point. Figure 10 shows that a shorter TDR probe length gives a better contrast in the water saturation profile. A 15- cm probe can be used to account for both spatial precision and dielectric measurement accuracy.

[0087] The chloride penetration phenomenon was simulated using diffusion and advection (Li et al., 2024). Chloride ions were transported from the deck surface into the asphalt and concrete domain through advection during the wetting cycle, while in the drying cycle, the chloride transport boundary condition was set as no-flux. Chloride diffusion was implemented in the asphalt and concrete domain in both wetting and drying cycles. In the simulation study, multiple wetting and drying cycles were used to facilitate the chloride penetration, such that the chloride content reached the critical value at the rebar depth to initiate active corrosion on the affected rebar.

[0088] When the rebar section under the damaged membrane had a chloride content that is high enough to cause active corrosion (Figure 11), it created an electrical potential field pattern. This pattern can be mapped from the cover surface. The potential distribution was simulated with the secondary current density distribution with the electrode corrosion kinetics on the rebar (Li et al., 2023b, 2023a, 2025). Figure 12 shows a typical potential distribution in the concrete deck with the corroding rebar. When the chloride content at the rebar depth reached the critical chloride content (0.6% by weight of cement), the rebar in the affected region was activated to more negative corrosion potential. The potential will be polarized towards the positive direction when the active rebar couples with the remaining passive / less active rebars. This created a potential field in the concrete and overlay domain. However, due to the membrane insulation, the potential profile on the asphalt overlay surface was not as sensitive to the potential on the corroding rebar or as the potential on the concrete cover surface underneath the membrane (Figure 13). The potential on the overlay approximately only registered the concrete cover potential in the membrane defect area, with a linear transition in between. The same conclusion also holds for the case where there is a combination of active and passive rebar under the membrane defect (Figure 14). Therefore, in a half-cell test, without an externally applied potential, a defect will not be detectable based on the mapped potential from the overlay when it has a similar potential as its neighbouring location.

[0089] When the external potential is applied with a counter electrode, the electrolyte potential on the deck surface is altered. The gridded potential readings can be used to locate the defect locations. The rebar under the membrane defect could be actively corroding or remains passive. Its intrinsic corrosion potential ranges approximately from -600 mV (active) to -100 mV (passive) with respect to a saturated calomel reference electrode (SCE). The counter electrode can be set to maintain a 1000 mV electrolyte potential on the overlay surface. It reads -1000 mV for the electrode potential, which equals electric potential (0 mV) minus the electrolyte potential. Figure 15 illustrates the flow of electrons and possible electrode reactions. This setup will not accelerate rebar corrosion. Instead, it offers a cathodic protection effect that suppresses possible corrosion on the rebar.

[0090] Consideration was made starting from an early-stage membrane damage case with all passive rebar (transport model on Day 2), then verifying the observation for the case where the rebar under the membrane damages is active or active and passive combined. The simulated potential distribution in the concrete and overlay is presented in Figure 16, where the counter electrode was applied at x=l m as an example. The potential gradient was concentrated at the membrane defect, the great potential difference existed in the overlay while the potential was more uniform in the concrete under the membrane. The potential distribution on the overlay was then explored for various counter electrode locations along the x-axis in the 2-D model (Figure 17). With the imposed voltage, the electrode potentials of the rebar measured at the neighbouring membrane defect locations became different, depending on the defect size and distance from the counter electrode. In the 2-D model, there was a linear transition between these different potentials and the potential remains constant outwards from the counter electrode when there was no more membrane defect. For example, in Figure 17, when the counter electrode was positioned at x = 0.1, 0.5, 1 m, the potential remained at various constant values for positions x>1.4 m. In addition, the potential gradient (if it exists) diminishes with the distance from the counter electrode.

[0091] Therefore, it was concluded that using a counter electrode overcomes the shortcoming in the half-cell test setup, where the rebar potential measured at a neighboring membrane defect location may appear similar, rendering the membrane defect undetectable. With this discovery, it was decided that a group of counter electrodes should be used to locate the membrane defects in the confined area to improve the abovementioned issues.

[0092] The simulation study examined the effectiveness of using a set of four discrete counter electrodes and a singular continuous counter electrode spanning around a measurement area bound thereby, and thus “framing” this measurement area. Figure 18 shows the surface and contour plot for the potential on the overlay. It was observed that a four-electrode setup was able to lay out the membrane defect locations, but the interference from the neighbouring defect could not be disregarded (Figure 18b). This suggests the need for denser data points to tell determine if the outstanding potential gradient is a result of interference from a remote defect. On the other hand, the framing counter electrode clearly shields the potential interference from the neighbouring membrane defect. For the practical application, it was proposed to use discrete cathodes to screen large areas and then use frame cathodes to locate individual membrane defects.

[0093] For practical operations, it is necessary to establish a criterion to designate the framing counter electrode guarded area as a “membrane defect”. As previously discussed, a potential can be measured within the guarded area and compared to the potential adjacent to the counter electrode. This potential difference is dependent on many factors: the membrane defect size and its distance from the counter electrode, the rebar condition, applied potential, and concrete and overlay moisture condition. The moisture condition can be set as one-day wetting same as the moisture test setup. The rebar corrosion condition can be active, passive or anywhere in between. Figure 19 illustrates the potential measurement on the overlay by a reference electrode and a voltmeter with a wired connection to the embedded rebar. When the counter electrode is used to apply a more negative potential, the rebar potential shifts in the negative direction. For a given position (e.g., directly above the rebar section as shown in Figure 15) The potential difference, is a positive value, defined as

[0094] = rebar’s overlay potential — counter electrode potential

[0095] For a given position on the overlay near the rebar section, reaches its minimum value when the rebar segment is in an active state. Therefore, an active rebar setting was used in the numerical model to determine the threshold Acf>threshold at the targeted locations within the framing counter electrode where the rebar potential from the overlay is measured. When A > <pthresoid the counter electrode framed area can be marked as “defect positive”.

[0096] In the preferred but non-limiting embodiment illustrated in the drawings, four data points within the framed measurement area (Figure 20) are collected to capture the potential difference. The remaining objective is to find a <pthresoid such that if any of the four readings is greater than this value, it indicates the presence of a defect within the framed area. Note that the potential field is affected by the location of the membrane defect within the counter electrode frame. In addition, for a given geometric configuration of membrane defect and frame, the potential difference A decreases as the distance between the membrane defect and the potential reading location increases. It was necessary to find the worst-case scenario considering these two aspects to determine the minimum value of A< > at the pre-set potential reading locations to mark the area as “defect-positive”.

[0097] To do so, first the lower limit of test sensitivity was set as a 1 cm2membrane defect with 1 cm2active rebar under it. Three cases were simulated: In Case 1, the measurement points had the longest distance from the defect; in Case 2, the defect was close to the frame at the middle of the side, and in Case 3, the defect was close to the frame at the corner. The results of the measured the potential difference at the pre-set locations for these three cases are shown in Figure 21. The A< > increased with the applied potential at the location of the counter electrode. Using an applied potential 2 V as an example, the threshold <pthresoid foreachcasewere approximately 100 mV, 40 mV, and 14 mV. If a smaller A< > were used as the threshold, the test would be more prone to have type one errors (false positives) caused by noise, while a larger value would lead to type two errors (false negatives). To use a larger threshold value without compromising the test quality, an overlay sampling method can be used (Figure 22). In this method, Case 2 (side) and Case 3 (corner) become Case 1 (center) in the neighbouring sampling areas. For the sampling area that is on the edge of the deck the 40-mV threshold value should be used.

[0098] Table 2 Potential test setting parameters

[0099] Conclusions of the simulation results included that, for the moisture test, moisture data of a 10 cm resolution is adequate to detect a 1 cm defect after one-day of wetting and one-week of drying. For a potential test with no external excitement, half-cell potential readings from the overlay reflect the potentials on the concrete cover at the membrane defect locations. The potential distribution has a linear transition between these locations. As a result, only neighbouring defect locations with dissimilar potential readings (corrosion state) are detectable.

[0100] For a potential test with external excitement, when an external voltage is applied using a cathode it artificially creates a dissimilar (very negative, e.g. -2 V) potential, which is more negative to both active and passive rebar potential. The membrane defect next to the counter electrodes becomes detectable according to the same logic for the no external excitement case. Therefore, as summarized in Figure 23, a membrane defect can be identified in the area confined by multiple electrodes. By zooming in on the electrode-confined area and scanning with a framing electrode, the defect areas can be further pinpointed. Once the framed overlay area is marked with “membrane defect”, there is no need to pursue the exact location of the defect, as the framed area can be made small enough (0.5 m x 0.5 m). The marked overlay area is rectangular, so it is easy to remove and repair the membrane underneath it. Table 2 summarizes the potential test setting parameters, including deck conditions, counter electrode frame size, applied potentials, and thresholds for potential differences, as well as membrane defect size limits.

[0101] Experimental Validation

[0102] A reinforced concrete deck section was used to validate the proposed test method. This deck sample had a membrane with predetermined membrane damage. The dielectric constant and potential reading test procedures were carried out with the selected test setting variables such as wetting-and-drying window, applied voltage, and data sample spacing. The test results were evaluated based on the effectiveness of finding the location of the membrane damage.

[0103] The reinforced concrete deck section had a dimension of 2 m x 1 m x 0.2 m, reinforced with two layers of No.10 rebar mesh. The rebar spacing was 20 cm in both longitudinal and transversal directions. Two concrete top cover thicknesses were used: 70 cm and 30 cm. Figure 24 shows the schematics of the rebar mesh layout. The structure included two electrically isolated rebar cages corresponding to the two cover thicknesses. Four non-conductive GFRP (glass fibre reinforced polymer) rebars connected the bottom mesh to ensure adequate bending capacity during demolding Four rebar hooks extended out of the top cover providing electrical connectivity to the rebars. The concrete was mixed at the following proportions

[0104] Table 3 Concrete mix proportion

[0105] Cement Water Fine Coarse aggregate aggregate

[0106] 1 0.5 2.78 4.08

[0107] The deck sample was cured for 28 days. A cold-applied rubberized asphalt waterproofing membrane was applied to the deck sample. A 50 cm asphalt overlay was applied on top of the membrane. Two 1x1 cm2dot defects of and two 10x10 cm2debonding defects were introduced in the membrane. The dot defect was an open cut of the membrane. The debonding defect was fabricated by layering down a plastic film on the deck when applying the membrane and adding an open cut in the membrane when it is cured. The protection board was eliminated as the trial tests suggested that the cold-applied membrane and asphalt overlay would not stick to the board properly and without the protection board, the asphalt overlay would not damage the cured membrane during the construction in the current lab setting. The schematic of the membrane defect layout can be found in Figure 25. The finished deck sample is shown in Figure 26. The defect areas were guarded by PVC pipes which can hold standing water in the wetting phase without flooding the whole deck.

[0108] Moisture Testing

[0109] Figure 27 shows the schematic of the moisture testing setup. The moisture-sensitive dielectric constant can be tested by a TDR tester with a non-invasive waveguide or a GPR. The TDR tester (signal generator) was found not powerful enough to penetrate the membrane and protection board with the non-invasive TDR probe (Figure 28). Therefore, a GPR was used instead. GPR devices with 2700 MHz and 2600 MHz antennas (Figure 29 and Figure 30) were used to scan the surface of the deck sample with the purposely staged water saturation scenarios: water saturation for 24 hours and drying for one week. The settings parameters are listed in Table 4.

[0110] Table 4 GPR setting parameters

[0111] The line scan data (Figure 31) shows the barrier between the asphalt and the concrete, the reinforcement and the different elevations in the reinforcement, and the thickness of the deck. Figure 32 shows the effect of the water accumulation underneath the membrane on the line scan images. The wet concrete underneath the membrane had a much higher dielectric constant and conductivity, which caused a curved reflection line on the membrane surface and poor signal strength underneath. The area of the water saturation visible with the GPR was marked on the deck sample in yellow chalk (Figure 33). The marked area encompassed all four membrane defects, but it was significantly greater than the actual defect sizes and the sizes of the simulated water spreads (defect size + 30 mm). This may have been caused by the increased channel flow along the membrane due to the possible imperfect membrane bonding. As a result, the area of water accumulation detected by the GPR provides a conservative estimate of the size and location of the membrane damage. Potential Testing

[0112] A simple rebar-counter electrode system was used to demonstrate the proof of concept for the rebar polarization in Figure 19. The rebar was embedded in the moist sand and a graphite rod was used as a counter electrode. The applied -1000 mV potential dragged the rebar’s electrode potential (as measured by an adjacent reference electrode) from -228 mV to -450 mV with a potential gradient laying between the distance from the rebar and the counter electrode. Figure 35 shows a design of a scanning apparatus embodying the framing counter electrode that is used to frame a 0.5 m X 0.5 m area on the overlay. Figure 36 shows the schematic of the potential testing setup. The voltmeter registers the potential with a saturated calomel reference electrode (SCE).

[0113] A prototype embodying the framing counter electrode was built and used on the deck sample (Figure 37). The membrane defects were placed at the center of the frame so that they represented the least detectable case from the four A readings. The direct current power source was tuned to maintain a -2 V potential adjacent to the counter electrode. A wet sponge sheet was used to ensure electrolytic conductivity of the asphalt across the PVC pipe barrier (Note: In the actual deck, no PVC pipe exists, hence the use of this sponge is unnecessary). Four potential data points were read and A values were compared with the threshold A< > threshold, 100 mV- The framed area with a membrane defect should report at least one A< > value greater than A< > threshold- As shown in Figure 38, in the selected framed area with membrane defects, the expected A< > readings were observed except in the second frame where a 99-mV reading is just below the 100-mV threshold. We consider this 100-mV threshold to remain valid, as the defect size of 1 cm2is the lower limit for this threshold value.

[0114] Experimental Results

[0115] Having used the numerical models to simulate the water content distribution in concrete and the potential field excited by the corroding rebar mesh with / without externally applied potential, and having implemented various prescribed wetting-and-drying cycles to explore the proper testing window and test setting parameters to achieve effective detection of the membrane failure location, two test procedures were validated: a moisture test and a potential test.

[0116] In the moisture test, ground-penetrating radar (GPR) can be used to locate the accumulated water beneath the membrane defect following a wetting-and-drying cycle. One nonlimiting example of a working set of test setting parameters are summarized below.

[0117] The potential test applies an overpotential to the rebar mesh through the overlay using a counter electrode frame. The potential difference readings between the counter electrode frame and the four locations inside it are used to determine whether the framed area has a membrane defect. A defect in the framed area is indicated when the potential difference exceeds a predefined threshold. The test setting parameters are listed below.

[0118] The results of the validation experiments on the physical deck model unequivocally confirmed both the moisture test method and the potential test effectiveness in locating membrane defects at early stages before active corrosion initiation, providing valuable insights to implement timely and cost-effective preventive measures.

[0119] Novel Scanning Apparatus for the Potential Test

[0120] Embodiments of the scanning apparatus 10 usable to perform the potential test documented above are now described in more detail with reference to a particular subset of the drawings. Referring initially to Figures 35 and 36, the apparatus comprises a frame 12 having an outer perimeter 12A of fixed shape and size that denotes an overall horizontal footprint of the scanning apparatus that will occupy the asphalt overlay of the bridge deck when the apparatus is placed thereon for scanning. The outer perimeter of the frame, and thus the footprint of the apparatus 10, is square in the illustrated embodiments, but may vary in other embodiments, as contemplated in more detail below. A counter electrode arrangement 14 is attached to an underside of the frame 12 at an outer margin 12B thereof that is of inwardly adjacent relation to the outer perimeter 12A. An imaginary inner boundary of this outer margin 12B is denoted in the Figure 35 top plan view of the apparatus by a broken line.

[0121] The counter electrode arrangement 14 comprises one or more counter electrodes attached the frame 12 at this outer margin, and in the Figure 35 embodiment, consists of a singular continuous electrode spanning around an entirety of the frame’s outer margin 12B, thus constituting a “framing” counter electrode of the above described type that spans fully around a bounded area framed thereby. This counter electrode 14 is preferably composed of carbon felt, though other suitable electrode materials are also contemplated herein further below. The area bound within the electrode-occupied outer margin 12B denotes a measurement area of the scanning apparatus 10 at which measurements will be taken when the counter electrode(s) 14 is / are seated atop the asphalt overlay of the deck bridge, in which condition the counter electrode(s) reside(s) in physical contact with the asphalt overlay at locations around said measurement area. The apparatus further comprises a handle 16 standing upright from the frame 12 for grasping in the hand of a human operator of the apparatus during placement of the apparatus onto, and lifting of the apparatus from, the asphalt overlay before and after scanning of a given measurement area of the bridge deck.

[0122] In addition to the counter electrode(s) 14, the apparatus 10 further comprises one or more reference electrodes 18 supported or supportable by the frame 12 at a plurality of discrete measurement positions thereon, at locations within the measurement area, to enable measurement of a rebar overlay potential of the bridge deck at these respectively discrete measurement locations within the measurement area. In the Figure 35 embodiment, the frame 12 comprises a solid deck spanning the full footprint of the apparatus, with the handle 16 standing upright from a topside of the deck at a central point thereof. For the purpose of supporting the one or more reference electrodes at the discrete measurement locations within the measurement area, the solidly decked frame 12 of the Figure 35 embodiment features four scanning electrode support holes 20 arrayed around the centrally located handle 16, each such scanning electrode support hole 20 residing at a center point of a respective one of four equally sized quadrants of the measurement area, in this case four square quadrants of the square measurement area. Each scanning electrode support hole 20 denotes a respective one of the discrete measurement locations, of which there are four in this embodiment, though the quantity and layout of the discrete measurement locations may vary in other embodiments, as contemplated in more detail below.

[0123] In the prototype, a singular reference electrode 18 was used (Figure 36), and was manually relocated from one measurement location to location to another between measurements, to collectively achieve reference electrode measurements from all four discrete measurement locations using a singular reference electrode 18, though obviously this would not be the preferred implementation for commercially implantable embodiments, for which alternative designs are contemplated herein further below for more practical commercial use. Figure 37 illustrates the prototype, where instead of a solidly decked frame 12, the frame instead comprised a skeletal outer frame of square shape surrounding the measurement area, and a skeletal inner frame of square shape lying concentrically of the outer frame, but angularly offset therefrom by 45-degrees about a vertical axis of orthogonal relationship to the planes of these two frames, so that the four corners of the inner frame resided atop the four sides of the square outer framer at respective midpoints of those four sides. The singular reference electrode 18 was relocatable among the midpoints of the four sides of the inner frame 13, each of which denoted a respective one of four discrete measurements locations, each residing centrally of a respective quadrant of the square measurement area bound by the outer frame. The underside of the outer frame was equipped with the singular, continuous counter electrode 14 in this prototyped example of the scanning apparatus.

[0124] As shown in Figures 35 and 36, the scanning apparatus further includes a DC power source 24 that is configured for connection between the rebar mesh of the bridge deck and the counter electrode arrangement 14 to apply a counter electrode potential thereto. Figure 37 shows connection of one side of the DC power source 24 being to the rebar mesh via engagement of an alligator clip to an exposed rebar connection point. In commercial embodiments, the wire connection to the rebar mesh is typically accomplished by means of a compression-type ground clamp, brazing or welding a protruding rod, or by using a self-tapping screw in a hole drilled into the bar, as in routinely done during a standard half-cell mapping survey. In the prototype, similarly clipped connection of an offboard adjustable DC power source is made to the counter electrode 14, but in commercial embodiments, this connection may optionally be of a more permanent character, and the adjustable DC power source may be incorporated onboard the frame. In the prototype, a voltmeter 26 was connected between the rebar mesh and reference electrode 14 to take the reference electrode measurements, which were read and recorded manually by the experiment operator(s) for offboard analysis to derive the useful results derivable therefrom, but in commercial embodiments, a controller would instead be used to implement the measurement and analysis steps in at least a partially automated fashion.

[0125] The potential difference between the respective rebar overlay potential measurement taken at each of the discrete measurement locations positions and the counter electrode potential was compared against the potential difference threshold <pthresoid to see if the measured potential differences exceeded said threshold. A positive determination that the threshold was exceeded by any one or more of the potential differences measured at the four measurement locations denotes positive confirmation of membrane damage or defect within the measurement area. With the respective measurement area of the asphalt overlay having been scanned, that measurement area can be visually marked as such, and if a defect was positively detected, specifically marked as “positive” for a “located defect”. The scanning apparatus 10 is then moved to a neighbouring unscanned measurement area, and the scanning process repeated. The boundaries of the measurement areas can be visibly drawn onto the bridge deck before any scanning is performed, for example by drawing a grid on the asphalt overlay, which grid is composed of rows and columns of square spots of a size corresponding to the measurement area of the scanning apparatus, as denoted the inner perimeter of the frame margin 12 A, and the matching inner perimeter of the framing counter electrode 14 of the illustrated embodiments. Alternatively, a square can be drawn around the outer perimeter of the frame 12 of the scanning apparatus each time its placed on the bridge deck, thus marking the scanned measurement areas on the go, with the second and each subsequent placement of the apparatus involving overlap of the frame 12 with any previously scanned areas by at least the margin width of the frame to ensure no gaps between scanned areas.

[0126] To enable calibration of the scanning apparatus to the particular bridge deck being tested, the solidly decked frame 12 of the Figure 35 embodiment includes not only the four discretely located scanning electrode support holes 20 situated at spaced distances inwardly from the margin 12A of the frame 12 and the counter electrode(s) 14 thereof, but also includes one or more calibration electrode support holes 22 each positioned immediately or closely adjacent to the outer margin 12A and its counter electrode(s) 14, which enables placement of the reference electrode 18 at any one of these calibration electrode support holes 22 for calibration purposes. In such calibration, the reference electrode 18 placed adjacent to the counter electrode 14 is used to measure the counter electrode potential, which is tuned to target value (e.g. 2 V) by adjusting the DC power source 24. This calibration procedure ensures that the potential difference threshold Ac|)threshoidis accurate for its purpose in the context of the particular bridge desk being tested. The counter electrode potential is uniform, as long as the reference electrode 18 on the overlay is close to the counter electrode 14, provided that there is no membrane defect immediately at the reference electrode location during this calibration. Given this, there are preferably a plurality of calibration electrode support holes 22, for example the illustrated quantity of four, optionally residing at the four inside comers of the frame margin 12A as shown, so that multiple calibration readings of the counter electrode potential can be taken to eliminate, or at least minimize, the possibility for calibration error.

[0127] Having detailed the prototyped example of the scanning apparatus used in the experimental validation of the invention, attention is now turned to other embodiments denoting possible alternatives, with particular attention to more commercial-ready implementations of the scanning apparatus 10. Figures 39 and 40 illustrate a multi-channel embodiment of the scanning apparatus 10’, and more particularly a four-channel embodiment in which the singular reference electrode of the Figure 35 embodiment is replaced with four reference electrodes 18, each selectively movable back and forth between a respective one of the scanning electrode support holes 20 for defect scanning of the bridge deck, and a respective one of the calibration electrode support holes 22 for calibrating the counter electrode potential. An onboard controller 28 is mounted somewhere on the frame 12 or handle 16, and is preferably embodied, at least in part, by a micro-controller with at least four analog inputs respectively connected to the four reference electrodes 18 to receive potential measurements from the four reference electrodes 18, which the microcontroller converts into digital measurement data via an analog / digital converter of the microcontroller.

[0128] The controller 28 preferably includes a mode toggle switch 32 connected to the micro-controller to switch between calibration and scanning modes, thus dictating whether the measurement data read from the four reference electrodes 18 is being inputted to the executed control logic as the measured counter electrode potential (in calibration mode), or as the measured rebar overlay potential for membrane defect detection (in scanning mode). A threshold selector switch 34 is also connected to the micro-controller, whose position dictates which one of two potential difference threshold values is used in the scanning control logic, according to whether the bridge deck area being scanned is a marginal area thereof situated adjacent to an edge of the bridge deck (e.g. <pthreshoid=40 mV for such marginal scanning of the bridge deck), or not (e.g. ^threshold = 100 mV for non-marginal scanning of the bridge deck at all other areas thereof further from the edge). A controller power supply 36 (e.g. 9V battery) provided on-board the scanning apparatus 10 supplies power to the controller 28, and one or more operation indicators 30 (LEDs, piezoelectric buzzer, small digital display screen) is / are also connected to the microcontroller to provide visual and / or audible operation status indications to the user. Among such status indications are preferably included alarm signals triggered in scanning mode when a membrane defect is positively detected (e.g. activation of a red LED or other visual alarm indicator and / or activation of a piezoelectric buzzer or other audible alarm), a mode status indicator indicative of whether the apparatus is in calibration or scanning mode (e.g. differently coloured LEDs, or different LED illumination patterns - solid, blinking, pulsing), and a calibration confirmation indicator activated in calibration mode once the counter electrode potential has achieved the targeted value.

[0129] The inclusion of a display screen as the sole, or one of multiple, operation indicator(s) may be particularly beneficial in embodiments relying on manual adjustment of the DC power source 24 in calibration mode. In such implementation, in calibration mode, the controller measures the counter electrode potentials at the four inside corners of the frame margin 12A on input channels respectively fed by the four reference electrodes 18 fixed or placed, at the four calibration electrode support holes 22, and displays these four counter electrode potential values on the display screen for visual reading thereof by the user, who manually adjusts the output voltage of the adjustable DC power source to achieve the targeted counter electrode potential (e.g. -2 V). In other embodiments, this calibration process can be automated by the controller 28, using a feedback loop from the reference electrodes 18 installed or placed closely beside the counter electrode 14 at the four calibration electrode support holes 22, and from the controller to the adjustable DC power source 24, allowing for automated adjustment of the applied DC power voltage by the controller 28. In such embodiments with automated calibration, where the user need not have a visual readout of the measured counter electrode potential, incorporation of a display screen may be less critical, and therefore optionally omitted. In embodiments with a display screen, additional LED indicators may be rendered unnecessary, and thus omitted. In Figure 40 , the schematic connection between the controller 28 and the adjustable DC power source 24 can thus be included for embodiments with automated calibration, or excluded for embodiments relying on user-performed counter electrode calibration.

[0130] Figures 41 and 42 illustrate an eight-channel embodiment as an alternative to the four-channel embodiment of Figures 39 and 40, the operation of which is generally same, but differs in that there are a total of eight reference electrodes 18, which in this embodiment are installed in eight fixed positions: four permanently occupying the scanning electrode support holes 20 used for membrane damage / defect scanning purposes, and four permanently occupying the calibration support holes 22 for counter electrode calibration purposes, so that the reference electrodes need not be relocated by the user depending on whether they are being used for calibration or scanning. In this embodiment, the controller selects which one of two sets of four reference electrode inputs it reads from depending on whether the controller is in calibration mode or scanning mode, as dictated by the status of the mode toggle switch. In embodiments with a display screen, the display screen may be embodied in a touch screen, in which case the mode toggle switch and the threshold selector switch may be embodied as on-screen toggles of the touch screen’s graphical user interface, as an alternative to hardware switches.

[0131] Having set forth the details of preferred embodiments of the apparatus, a brief summary of its typical method of use is now given. First, a grid will typically be marked out on the bridge deck to form a predefined roadmap of measurement areas to be scanned with the apparatus. Wetting of the deck with a water hose, or natural rainfall should conditions enable, is performed or permitted for a sufficient period (e.g. one day). Hardware setup of the apparatus is performed, involving at least wired connection of the adjustable DC power source 24 to the rebar mesh of the bridge deck, and for example further including wired connection of the adjustable DC power source to the counter-electrode, if a permanent predefined connection therebetween, or on-board integration of the adjustable DC power source, is not embodied in the given scenario. The scanning apparatus is switched into calibration mode, if not already set thereto by default or ahead of time, the counter electrode potential is calibrated to the targeted value (e.g. -2 V) through user adjustment, or automated controller adjustment, of the adjustable DC power source 24. The scanning apparatus is placed on a marked measurement area of the grid. If this marked measurement area is at a marginal region of the deck adjacent to an edge thereof, the threshold selection switch is set to its marginal setting, if not already set to such setting. Otherwise, the threshold selection switch is set to, or left in, its non-marginal setting, which may be a default setting of this threshold selection switch, given that the majority of a bridge deck’s overall surface area will be non-marginal (not immediately adjacent an edge of the bridge deck). The apparatus is now ready to scan the occupied measurement area of the bridge deck, and so a reading of the rebar’s overlay potential is taken from the four reference electrodes at the four discrete measurement positions occupied thereby (e.g. reference electrode holes 20).

[0132] The controller 28 of the scanning apparatus 10 may include a trigger switch for user actuation to trigger such a measurement reading when the apparatus has been appropriately placed and set in the appropriate mode and at the appropriate threshold. Via execution, by one or more processors of the controller 28, of executable logic embodied in statement and instructions stored in non-transitory computer readable memory of the controller, the controller checks whether the potential difference A< > between any individual one or more of the rebar overlay potential readings and the counter electrode potential (e.g. calibrated at -2 V) exceeds the predetermined potential difference threshold threshold- If so, this denotes detection of membrane damage or defect, and actuation of one or more of the alarm indicators (e.g. red LED and buzzer combination, and / or onscreen alarm) is triggered by the controller 28. The user marks this scanned area of the grid with an appropriate one or more markers indicative of its scanned status and its membrane damaged / defective status, if so found. The scanning apparatus is then moved to a next measurement area of the grid, and the scanning process repeated. The calibration process need not be repeated at every measurement of the grid, and may instead be performed once for the entire bridge deck, or periodically after scanning of a fractional portion of the overall bridge deck area.

[0133] The preceding description reflects preferred embodiments, among which certain features are believed to be optimized for various parameters, such as performance, ease of use, and computational and cost efficiency, but there are also workable, albeit perhaps less optimal, alternatives, some of which are now elaborated on, not with the intent of serving as an exhaustive list of possible implementations, but rather as a non-exhaustive listing examples intended to be explicitly captured under the broadest claims presented herein.

[0134] Instead of a continuous “framing” counter electrode spanning fully and continuously around the margin 12A of the frame 12, a set of discrete counter electrodes could instead be arrayed at spaced intervals around the margin 12A of the frame 12, for example a set of four discrete counter electrodes at the four corners of the frame’s square margin 12A, or a set of eight discrete counter electrodes including such four corner reference electrodes, plus another four counter electrodes respectively residing at midpoints of the four respective sides of the frame’s square margin. In alternative implementations of the continuous “framing” counter electrode, the shape thereof (and thus likewise the perimeter / margin shape of the frame) may vary from the square shape of the preferred embodiments detailed above and shown in the drawings, which alternative shape may instead, for example, be a circle or oblong rectangle. The continuous “framing” character of the preferred embodiment’s singular counter electrode is preferred to reduce the likelihood of false positives may be more likely to arise in embodiments with an array of discrete counter electrodes, at least absent a notably dense array of notable electrode quantity that may denote added complexity. The square shape of the continuous framing electrode of the preferred embodiment avoids unnecessary complexity that arises in the determination of threshold potential differences for oblong rectangle embodiments. While the symmetry of a circular embodiment would avoid such complications, the mapping, scanning and marking of round measurement areas on the bridge deck, and the cutting out and repairing of damaged areas found, is less preferable to the use of gridded working space characterized by straight-line quadrilateral boundaries.

[0135] The counter electrode(s) is / are preferably composed of a carbon material, such as graphite, carbon felt, or other carbon fiber fabrics, which are conductive and versatile, though alternative embodiments could employ a noble metal, for which one option is platinum-coated titanium, which is as a high-end, durable material with excellent conductivity and corrosion resistance. Materials that are inert in the operating environment or noble enough to withstand corrosion are ideal as they do not degrade when functioning as an electrode where anodic reactions (e.g., oxidation of H2O or other species) occur. Carbon felt was chosen for its cost-effectiveness, chemical stability, and flexibility, which ensures proper contact with the overlay surface.

[0136] While the preferred embodiments employ four discrete measurement locations each centered in a respective one of four equal quadrants of the square measurement area, the quantity and location of the four discrete measurement locations where the rebar overlay potential is measured may be varied. For example, in another four-location example, the four measurement locations may reside off center of their respective quadrants and nearer to the outer comers of the overall measurement area. That said, such configuration may present challenges in accurately assessing the uniformity of the potential across the measurement area. For example, a damaged spot at the center of the measurement area would be notably far from all four corner-adjacent potential reading points, making it hard to detect. This would require a lower potential threshold to make it detectable, which could lead to an increase in false positives. The preferred embodiment with its quadrant-centered measurement locations denotes a symmetric layout of even distribution throughout the measurement area for balanced potential measurements across the entirety thereof. A more densely packed array of measurement locations could be used, for example a 3 x 3 array of nine measurement locations centered in respective nonants 3 x 3 of the measurement area, instead of the illustrated 2 x 2 array in respective quadrants. While a denser array of reading points could provide a higher number of data points for damage detection, it also adds to the device’s complexity. The preferred implement of four measurement locations is simpler and more efficient. Good contact with the asphalt overlay is also easier to ensure with the lesser quantity of four reference electrodes (2 x 2 quadrant based layout vs. 3 x 3 nonant based layout), which optimizes the balance between system reliability and operational complexity.

[0137] Regarding the calibrated counter electrode potential and the potential difference threshold (p threshold, the calibration value for the counter electrode was chosen as -2 V with respective to a saturated calomel electrode (SCE). This applied voltage polarizes the rebar mesh to a potential more negative than its original corrosion potential. The potential difference between the rebar and the counter electrode generates a potential gradient across the overlay through a damaged membrane. This gradient is detected as the potential difference between the rebar’s overlay potential, read by the reference electrodes, and the counter electrode potential. The established potential difference thresholds are critical for identifying variations in the potential gradient which indicates membrane damage within the measurement area. While the selection of the counter electrode potential is somewhat arbitrary and other calibration potentials may be effective, the corresponding thresholds would need to be reevaluated according to the methodology explained herein. The appropriate thresholds are influenced by several factors including the configuration of the counter electrode frame, the location of the placement of reference electrodes, and the electrochemical properties of the rebar.

[0138] Figures 43 to 45 illustrate a full-scale embodiment of the present invention, which incorporates an eight-channel scanning apparatus 100 like that of Figures 41 and 42 into a rollable testable station 200 composed of a wheeled cart 202 that carries not only the scanning apparatus 100, but also the power supply 36 (e.g. 9V battery) and the controller 28, and can further host a laptop or tablet computer 300 (or any other comparably mobile computing resource) that is connectable to the controller 28 and useable in cooperation therewith for real-time data display during scanning, processing of the acquired potential measurements from the controller channels during such scanning, and storage of the resultant data of each scan. The controller in this particular example is responsible for acquisition of the potential measurements from each channel, and also for control of the battery output potential during calibration mode. The wheeled cart features a rectangular, and more specifically square, base 204 composed of four base rails connected end-to-end at right angles to one another to frame an open rectangular, and more specifically square, space between them. The base 204 is elevated off the bridge deck by a set of wheels 206 attached to the base 204 at the four comers thereof where the base rails meet one another. The scanning apparatus 100 (hereinafter “scanner” for short) is movably supported on the cart 202 in a manner movable upwardly and downwardly thereon between a raised transport position (Figure 43 A) in which the frame 112 and counter electrode 114 of the scanner 100 are elevated off the bridge deck in aligned and elevated relationship over the square opening of the base 204 of the cart 202, and a lowered position lowered through the square opening of the base 204 and placing the counter electrode 114 into contact with the asphalt overlay of the bridge deck, on which the wheels 206 also reside for rollable support of the cart 202. In the raised transport position of the scanner 100, the cart 202 can be wheeled from one measurement area of the bridge deck to another, during which the raised scanner 100 lacks any contact with the bridge deck to prevent damage to any of the electrodes. With the cart stopped in alignment over any given measurement area, the scanner 100 is then lowered down into working contact with the asphalt overlay of the bridge deck to performing the scanning operations described above.

[0139] A header 208 of the cart 202 is supported in elevated relationship above the base 204 by a set of upright supports 210 anchored to the base 204, typically at the four comers thereof. The scanner 100 is movably suspended from the header 208, and raisable and lowerable relative thereto between the raised transport and lowered working positions, for example by a threaded vertical rod 212 that hangs downwardly from the header 208 and is actuated in rotational fashion about its central lengthwise axis. Such driven actuation of the threaded vertical rod 212 may be implemented through a hand crank 214 mounted atop the header 208 of the cart 204, though other variants could alternatively employ electric drive of the threaded vertical rod 212 (in equivalence to an electric linear actuator). A travelling nut 216 of threaded engagement to the threaded vertical rod 212 is affixed to the scanner 100, for example on a stanchion 116 of the scanner 100 that stands upright from the frame 112 thereof at a typically central location thereon, in place of the handle 16 of the earlier handheld embodiments from the preceding figures. Driven rotation of the threaded vertical rod 212 in opposing rotational directions via the crank 214 or other drive source is thus operable to drive vertical displacement of the traveling nut 216 upwardly and downwardly along the threaded vertical rod 212, thereby lifting and lowering the scanner 100 between the raised transport position and lowered working position.

[0140] In this embodiment, the frame 112 of the scanner 100 may be of metal composition, in which case it is electrically isolated from the counter electrode 114 (e.g. carbon felt) by an intervening insulation layer 115 that lines the underside of the metal frame 112 and hosts the counter electrode beneath the insulation layer 115. The eight channel example shown in the drawings features eight reference electrodes 118 disposed symmetrically within the framed measurement area in matching relationship to the eight electrodes of the handheld eight-channel scanner 41 of Figure 41. With reference to Figure 45, each reference electrode 118 may be a spring-loaded reference electrode assembly featuring a protective outer casing 118A and an electrode 118B partially housed within the outer casing 118A, and a spring 118C that acts between a closed upper end of the outer casing 118A and an upper stop shoulder of the electrode 118B to bias a bottom end the electrode 118B outwardly from a bottom end of the outer casing 118A.

[0141] Figure 45 A shows the spring-loaded reference electrode assembly 118 with the spring 118C in a defaulted extended state with the spring 118C uncompressed and the electrode 118B maximally extended from the outer casing, in which state the assembly resides reside in the raised transport position of the scanner 100. Figure 45B instead shows the spring-loaded reference electrode assembly 118 in a partially collapsed state with the spring 118C partially compressed, which collapse and compression occurs under forced contact of the electrode 118B with the bridge deck in the lowered working position of the scanner 100. This spring-loaded character of the electrode 118B encourages full and consistent contact of the electrode with the asphalt overlay of the bridge deck, at relatively consistent pressure, when the scanner 100 is in the lowered working position. Use of such spring-loaded reference electrodes accommodates minor surface elevation differentials in the asphalt overlay of the bridge deck among the points thereof respectively engaged by the wheels 206, the counter electrode 114 and the various reference electrodes 118 to ensure proper bridge deck contact by the totality of the reference electrodes.

[0142] Since various modifications can be made in the invention as herein above described, and many apparently widely different embodiments of same made, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense. REFERENCES:

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Claims

CLAIMS:

1. A scanning apparatus for locating waterproofing membrane damage in a bridge deck having an uncoated carbon steel rebar mesh, an asphalt overlay and a waterproofing membrane, said apparatus comprising: a frame alignable over a measurement area of the asphalt overlay of the bridge deck; a counter electrode arrangement attached to the frame to make physical contact with the asphalt overlay at locations around said measurement area when the scanning apparatus is placed atop said asphalt overlay; a DC power source configured for connection between the rebar mesh of the bridge deck and the counter electrode arrangement to apply a counter electrode potential thereto; one or more reference electrodes supported or supportable by the frame at a plurality of discrete positions thereon to measure a rebar overlay potential of the bridge deck at respectively discrete points within the measurement area; and a controller configured and operable to perform measurement and analysis steps that comprise at least the following:(a) from the one or more reference electrodes, take a respective rebar overlay potential measurement at each of said discrete positions; and(b) determine whether a potential difference between any individual one or more of the respective rebar overlay potential measurements and the counter electrode potential exceeds a predetermined threshold, denoting detection of waterproofing membrane damage.

2. The apparatus of claim 1 wherein the controller is further configured to, in response to said detection of waterproofing membrane damage in step (b), trigger a notification signal indicative thereof.

3. The apparatus of claim 2 comprising at least one alarm indicator operably coupled to the controller for activation of said indicator by said notification signal to inform an operator of said detection of water proofing membrane damage.

4. The apparatus of claim 3 wherein said at least one alarm indicator comprises a visual indicator.

5. The apparatus of 3 or 4 wherein said at least one alarm indicator comprises an audible indicator.

6. The apparatus of any one of claims 3 to 5 comprising a display screencommunicatively coupled to the controller and operable display a visual alarm notification in response to said notification signal.

7. The apparatus of any one of claims 1 to 6 wherein the controller is switchable between at least two functional modes, including a scanning mode in which said measurement and analysis steps are executed, and a calibration mode, and the controller is also configured, and operable in the calibration mode, to measure the counter electrode potential of the counter electrode arrangement during adjustment of the de power supply to achieve a targeted counter electrode potential, and monitor for achievement of said targeted counter electrode potential, denoting successful calibration of the apparatus to the bridge deck.

8. The apparatus of any preceding claim wherein the controller is operable to switch between at least two different scanning modes characterized by different threshold values for said predetermined threshold.

9. The apparatus of claim 8 wherein said at least two different scanning modes comprise a marginal scanning mode for scanning the bridge deck at edge-adjacent margins thereof, and a non-marginal scanning mode for scanning the bridge deck at non-marginal areas thereof situated inwardly from said edge-adjacent margins.

10. The apparatus of claim 9 wherein the marginal scanning mode is characterized by a lower threshold value than said non-marginal scanning mode.

11. The apparatus of any one of claims 8 to 10 comprising a scanning mode selection switch that is user-operable to switch between said at least two different scanning modes.

12. The apparatus of any preceding claim wherein the counter electrode arrangement comprises a continuous electrode spanning fully around the measurement area.

13. The apparatus of claim 12 wherein the continuous electrode spans four sides of a right-angled quadrilateral area.

14. The apparatus of claim 13 wherein said right-angled quadrilateral area is square.

15. The apparatus of any one of claims 1 to 12 wherein the counter electrode arrangement resides at four perimeter sides of a right-angled quadrilateral area that is of coincident relation to the measurement area of the bridge deck when the scanning apparatus is placed in a working position thereon.

16. The apparatus of any one of claims 13 to 15 wherein the discrete positions occupied or occupiable by the one or more reference electrodes comprise four discrete positionsrespectively situated in four quadrants of said right-angled quadrilateral area.

17. The apparatus of claim 16 wherein the four discrete positions are respectively centered in the four quadrants of said right-angled quadrilateral area.

18. The apparatus of any one of claims 15 to 17 wherein the counter electrode arrangement comprises four counter electrodes each occupying a respective one of the discrete positions.

19. The scanning apparatus of any preceding claim in combination with a wheeled base on which the scanning apparatus is hosted in a movable manner raiseable and lowerable relative to said wheeled base between a lowered working position placing the counter electrode arrangement against the asphalt overlay of the bridge deck, and a raised transport position withdrawing the counter electrode arrangement therefrom.

20. The scanning apparatus of 19 wherein the scanning apparatus is carried on a threaded rod whose driven rotation in opposing directions is operable to raise and lower the scanning apparatus.

21. The scanning apparatus of any preceding claim wherein each reference electrode is spring-loaded in a manner biasing the reference electrode in a downward direction to encourage contact thereof with the asphalt overlay of the bridge deck.

22. A method of using the scanning apparatus of any preceding claim to scan a bridge deck for waterproofing membrane damage, said method comprising:(i) placing the scanning apparatus atop the asphalt overlay of the bridge deck at a measurement area thereof; and(ii) executing the measurement and analysis steps to determine whether there is any waterproofing membrane damage within said measurement area thereof.

23. The method of claim 22 further comprising repeating steps (i) and (ii) in relation to each of one or more subsequent measurement areas of the bridge deck, thereby incrementally scanning an entirety or partially fraction of the bridge stage one measurement area at a time.

24. A method of scanning a bridge deck with uncoated carbon steel rebar mesh for waterproofing membrane damage, said method comprising:(i) placing a scanning apparatus atop an asphalt overlay of the bridge deck at a measurement area thereof; and(ii) with a counter electrode arrangement of said scanning apparatus in physicalcontact with the asphalt overlay of the bridge deck at locations around said measurement area, and with a DC power source apply a counter electrode potential to said counter electrode arrangement: taking a respective rebar overlay potential measurement at a plurality of discrete points within the measurement area; and determining whether a potential difference between any individual one or more of the respective rebar overlay potential measurements and the counter electrode potential exceeds a predetermined threshold, denoting detection of waterproofing membrane damage.

25. The method of claim 24 further comprising repeating steps (i) and (ii) in relation to each of one or more subsequent measurement areas, thereby incrementally scanning an entirety or partially fraction of the bridge stage one measurement area at a time.

26. The method of claim 23 or 25 comprising, after at least one instance of step (ii), recording a status update in relation to the measurement area scanned in said instance of step (ii).

27. The method of claim 26 wherein recording said status update comprises, after each and every instance of step (ii), recording a scanned status of said measurement area scanned in said instance of step (ii), to avoid inadvertent redundant rescanning thereof in subsequent repetition of step (ii).

28. The method of claim 26 or 27 wherein said at least one instance of step (ii) comprises a damage-detecting instance thereof, and said status update comprises recordal of a damaged status of the measurement area scanned in said damage-detecting instance thereof.

29. The method of any one of claims 26 to 28 wherein said recording of the status update comprises visibly marking of the asphalt overlay at the measurement area scanned.

30. The method of any one of claims 23 and 25 to 29 wherein the measurements areas are right-angle quadrilaterals whose boundaries collectively form a grid.

31. The method of any one of claims 22 to 29 wherein each measurement area is a right-angle quadrilateral.

32. The method of any one of claims 22 to 31 wherein boundaries of each measurement area are visibly drawn on the asphalt overlay.

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