Method for detecting expansion rate of RAP-steel slag emulsified asphalt cold recycled mixture

Abstract

The invention relates to the technical field of steel slag asphalt material detection, in particular to an RAP-steel slag emulsified asphalt cold-recycled mixture expansion rate detection method, which comprises the following steps: firstly, curing a prepared RAP-steel slag emulsified asphalt cold-recycled mixture Marshall test piece, and in the curing process, enabling a resistance strain gauge adhered to the test piece to deform so as to detect the expansion rate of the RAP-steel slag emulsified asphalt cold-recycled mixture. The resistance value is changed; then, calculating a strain value according to the working principle of a resistance strain gauge, and analyzing the expansion strain condition of the test piece at the position; and finally, accurately and efficiently detecting the expansion rate of the RAP-steel slag emulsified asphalt cold recycled mixture according to the calculated strain values at different positions. The method for detecting the expansion rate of the RAP-steel slag emulsified asphalt cold recycled mixture solves the problems that measurement positions of a vernier caliper are different before and after a test piece is soaked in water and measurement is inaccurate due to the fact that water intrudes into a dial indicator in the maintenance process, overcomes the defect of single measurement of soaking expansion, and has the characteristics of high precision, real-time detection and multi-latitude measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of steel slag asphalt material detection, and particularly relates to a method for detecting the expansion rate of RAP–steel slag emulsified asphalt cold recycled mixture. Background Art

[0002] In recent years, due to the comprehensive coverage of highway infrastructure construction and road maintenance, problems in aspects such as economy, environment, and society have become increasingly prominent. At present, the annual output of natural aggregates is about 20 billion tons, among which the demand for aggregates in highway construction is the largest. However, over-exploitation of sand and gravel will lead to results such as shortage of natural resources, mountain damage, and environmental degradation, triggering problems such as short supply and rising prices of aggregates. At this stage, in view of the dilemma of shortage in the exploitation of natural aggregates, the effective utilization of recycled aggregates and waste has become an effective way to solve this problem. On the one hand, this can reduce environmental damage and resource waste caused by waste stacking, and on the other hand, it can also enrich the raw material sources for transportation infrastructure construction and solve the problem of shortage of road materials. In addition, the steel industry is an upstream power industry in the infrastructure construction industry, and the by-products generated during steel smelting contain solid waste steel slag, the output of which accounts for 10%–15% of the original steel. At present, the utilization rate of steel slag resources is low, and it is usually treated by stacking or burying underground. The steel slag cannot be effectively utilized, resulting in serious land pollution and resource waste.

[0003] At this stage, the applied research on cold recycled asphalt mixtures has gradually matured. The comprehensive utilization of steel slag and reclaimed asphalt pavement (RAP) materials can prepare cold recycled asphalt mixtures with excellent performance, with obvious advantages in energy conservation and environmental protection and good application prospects. Steel slag has excellent mechanical properties and good adhesion to asphalt. After being incorporated into asphalt mixtures, it can significantly improve the structural stability of cold recycled mixtures. Adding steel slag to recycled asphalt mixtures can also increase the utilization rate of reclaimed asphalt pavement materials and make full use of waste materials. However, steel slag also has certain limitations as a road construction material. The self-expansion characteristic of steel slag causes diseases such as uplift and cracking in the paved roadbed. This is mainly because fluxes such as quicklime and dolomite are added during the steelmaking process and are not completely consumed, forming free calcium oxide (f–CaO) and free magnesium oxide (f–MgO). The hydration reactions of f–CaO and f–MgO generate Ca(OH)2 and Mg(OH)2, resulting in local expansion pressure and volume expansion, which in turn leads to instability in the road use performance and structure of asphalt pavements. The complete digestion of f–CaO and f–MgO in steel slag at normal temperature takes a long time and has potential volume expansibility. Since there is no dedicated method for detecting the expansion rate of RAP–steel slag emulsified asphalt cold recycled mixture in the current specifications, it is very necessary to seek an effective method for detecting the expansion rate of RAP–steel slag emulsified asphalt cold recycled mixture.

[0004] In view of the above defects, the creator of the present invention has finally obtained the present invention through long-term research and practice. Summary of the Invention

[0005] The object of the present invention is to solve the problems such as the difference in the measurement positions of the vernier caliper before and after the specimen is immersed in water and the inaccurate measurement caused by the intrusion of water into the dial indicator during the curing process, and to make up for the deficiency of single measurement of immersion expansion, and provides a method for detecting the expansion rate of RAP–steel slag emulsified asphalt cold recycled mixture.

[0006] In order to achieve the above object, the present invention discloses a method for detecting the expansion rate of RAP–steel slag emulsified asphalt cold recycled mixture, including the following steps:

[0007] S1, making the RAP–steel slag emulsified asphalt cold recycled mixture into Marshall specimens, setting metal foil waterproof strain gauges on the specimens, connecting a resistance strain gauge, and measuring the initial transverse resistance value R in the diameter direction 0,d and the initial longitudinal resistance value R in the height direction 0,h ;

[0008] S2, using a vernier caliper to measure the initial diameters of the top, middle and bottom parts of the specimen, denoted as D1, D2, D3, taking the average diameter value D0, and measuring the initial height of the specimen at intervals of 120°, denoted as H1, H2, H3, taking the average height value H0, and then putting the specimen into a curing box for curing;

[0009] S3, curing the specimen for 7 days, measuring and recording the transverse resistance value R of the resistance strain gauge d and the longitudinal resistance value R h every day, and the measurement method is to collect once every 1 h in the initial stage, extend to once every 3 h in the middle stage, and extend to once every 6 h in the later stage;

[0010] S4, according to the formula wherein, the resistance change value: ΔR = R - R0, R is the transverse resistance value R d or the longitudinal resistance value R h , R0 is the initial transverse resistance value R 0,d or the initial longitudinal resistance value R 0,h , K is the sensitivity coefficient, calculating the strain value ε, and respectively obtaining the transverse strain ε d and the longitudinal strain ε h ;

[0011] S5, calculating the initial volume of the specimen The expanded diameter D = D0(1 + ε d ), the expanded height H = H0(1 + ε h ), calculating the volume of the specimen after expansion According to the formula Calculate the volume expansion rate δ of the RAP - steel slag emulsified asphalt cold recycled mixture V 。

[0012] In the step S1, four strain gauges are placed at the top, middle, and bottom of the specimen respectively, and the interval between adjacent strain gauges is 90°, and an epoxy resin protective layer is covered.

[0013] In the step S2, the temperature of the curing box is 60°C and the humidity is 95%.

[0014] In the step S3, the initial stage is 1 - 2 days, the middle stage is 3 - 4 days, and the later stage is 5 - 7 days.

[0015] In the step S4, considering the different conductive characteristics of the specimen in the diameter and height directions, the transverse sensitivity coefficient K d and the longitudinal sensitivity coefficient K h need to be calibrated respectively. Calibration is carried out by applying a known strain to the specimen, and according to the formula Record the linear relationship between ΔR and ε and fit the sensitivity coefficient K d and K h 。

[0016] According to the resistance strain technology and the requirements of volume expansion rate detection, aiming at the anisotropic expansion characteristics of the RAP - steel slag emulsified asphalt cold recycled mixture, the present invention proposes a directional calibration method. By arranging multi - dimensional strain gauges on the Marshall specimen and dynamically collecting data, long - term stable detection is realized, overcoming the disadvantages that traditional strain gauges can only detect in the short term and have high requirements for material uniformity. Compared with the traditional method, the present invention realizes continuous and non - contact measurement in the temperature and humidity curing environment, and has obvious advantages in long - term stable detection. The present invention overcomes technical obstacles such as complex detection materials and difficult data correlation.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1. The present invention applies a known strain load (such as a micro - displacement device) to the emulsified asphalt cold recycled mixture with different steel slag contents, records the relationship between the resistance change (ΔR) and the true strain (ε), and fits the sensitivity coefficient K d (transverse) and K h (longitudinal), solving the problem that the properties (conductivity, thermal expansion coefficient) of steel slag and emulsified asphalt cold recycled mixture are different, affecting the sensitivity of the resistance strain gauge;

[0019] 2. The present invention respectively establishes strain formulas for the transverse and longitudinal directions through the calibration method, solving the problem that the difference between transverse strain and longitudinal strain is unclear;

[0020] 3. The present invention adopts a metal foil type waterproof strain gauge, covered with an epoxy resin protective layer, which isolates moisture erosion, improves long-term stability, and reduces environmental interference;

[0021] 4. By adjusting the acquisition data frequency, the phased changes in the expansion rate are captured, solving the problem that the immersion expansion method cannot dynamically capture the phased changes in the expansion rate and making up for the deficiency of single measurement;

[0022] 5. The method for detecting the expansion rate of the RAP–steel slag emulsified asphalt cold recycled mixture provided by the present invention measures the expansion rate by using the principle of the resistance strain gauge and the mechanical property relationship of the material, and efficiently, accurately and intuitively obtains the expansion strain data. It solves the problems of large detection errors in the conventional methods in the past and insufficient applicability in composite materials such as RAP–steel slag emulsified asphalt cold recycled mixtures. Detailed implementation manners

[0023] The following, in combination with the embodiments, further elaborates on the above and other technical features and advantages of the present invention in more detail.

[0024] Embodiment 1

[0025] (1) Prepare RAP–steel slag emulsified asphalt cold recycled mixtures with different steel slag dosages (the dosages are 10%, 20%, and 30% respectively), make the mixtures into standard Marshall specimens, place 4 strain gauges at the top, middle, and bottom of each specimen, with a 90° interval between adjacent strain gauges, cover them with an epoxy resin protective layer, connect a resistance strain gauge, and measure the initial transverse resistance value R in the diameter direction 0,d and the initial longitudinal resistance value R in the height direction 0,h ;

[0026] (2) Use a vernier caliper to measure the initial diameters (denoted as D1, D2, D3) of the top, middle, and bottom parts of the specimen, take the average diameter value D0, and measure the initial height of the specimen (denoted as H1, H2, H3) at intervals of 120°, take the average height value H0, place the specimen in a curing box for curing, set the temperature of the curing box to 60°C and the humidity to 95%;

[0027] (3) During the curing process of the specimen, measure and record the transverse resistance value R of the resistance strain gauge d and the longitudinal resistance value R h every day for 7 consecutive days. The measurement method is to collect once every 1 h in the initial stage (1 - 2 d), extend to once every 3 h in the middle stage (3 - 4 d), and extend to once every 6 h in the later stage (5 - 7 d);

[0028] (4) According to the formula where the resistance change value: ΔR = R - R0, R is the transverse resistance value R d or the longitudinal resistance value R h, where R0 is the initial transverse resistance value R 0,d or the initial longitudinal resistance value R 0,h , K is the sensitivity coefficient, calculate the strain value ε, and obtain the transverse strain ε d and the longitudinal strain ε h ; Considering the different electrical conductivity characteristics of the specimen in the diameter and height directions, it is necessary to calibrate the transverse sensitivity coefficient K d and the longitudinal sensitivity coefficient K h respectively. Calibration is carried out by applying a known strain to the specimen. According to the formula Record the linear relationship between ΔR and ε and fit the sensitivity coefficients K d and K h , so as to calculate the volume expansion rate of the RAP–steel slag emulsified asphalt cold recycled mixture more accurately;

[0029] (5) Calculate the initial volume of the specimen The expanded diameter D = D0(1 + ε d ), the expanded height H = H0(1 + ε h ), calculate the volume of the specimen after expansion According to the formula Calculate the volume expansion rate δ of the RAP–steel slag emulsified asphalt cold recycled mixture V ;

[0030] (6) According to the requirements of the current "Test Method for the Stability of Steel Slag (GB / T 24175–2009)", conduct immersion expansion detection on the expansion rate of the RAP–steel slag emulsified asphalt cold recycled mixture. Through error analysis, further optimize the resistance detection method to ensure accurate measurement of the strain at the key parts and achieve a more accurate measurement effect, thereby proposing an accurate and efficient detection method for the expansion rate of the RAP–steel slag emulsified asphalt cold recycled mixture.

[0031] The implementation effect data is shown in Table 1 below:

[0032] Table 1 Comparison of expansion rates under different steel slag dosages

[0033] Steel slag content (%) Volume expansion rate (%) Error of immersion expansion method (%) Error of resistance method (%) 10 0.7 ±0.13 ±0.05 20 1.2 ±0.21 ±0.08 30 1.4 ±0.24 ±0.10

[0034] As can be seen from Table 1, the volume expansion rate shows an increasing trend with the increase of the steel slag content, but the increasing trend of the amplitude gradually slows down, indicating that there is an optimal content of steel slag. By comparing and analyzing the errors between the immersion expansion method and the resistance method, it can be known that the errors of both detection methods increase with the increase of the steel slag content, but the error of the resistance method is significantly lower than that of the immersion expansion method. The main reason is that the immersion expansion method relies on the macroscopic measurement of volume change and is easily affected by operation errors, while the error of the resistance method is always lower than that of the immersion expansion method. The main reason is that the resistance method avoids the accumulation of errors caused by single measurement of the immersion expansion method by dynamically adjusting the data acquisition frequency, and realizes the accurate measurement of local strain through the real-time detection of multi-dimensional strain gauges, avoiding the overall measurement ambiguity of the immersion expansion method.

[0035] The above are only the preferred embodiments of the present invention, which are illustrative rather than restrictive to the present invention. Those skilled in the art understand that many changes, modifications and even equivalents can be made within the spirit and scope defined by the claims of the present invention, but all of them will fall within the protection scope of the present invention.

Claims

1. A method for detecting the expansion rate of a RAP - steel slag emulsified asphalt cold recycled mixture, characterized in that, It includes the following steps: S1. Make the RAP - steel slag emulsified asphalt cold recycled mixture into Marshall specimens, set metal foil waterproof strain gauges on the specimens, connect the resistance strain gauge, and measure the initial transverse resistance value R in the diameter direction 0,d and the initial longitudinal resistance value R in the height direction 0,h ; S2, Use a vernier caliper to measure the initial diameters at the top, middle, and bottom of the specimen, denoted as D1, D2, and D3, take the average diameter value D0, and at intervals of 120°, measure the initial height of the specimen, denoted as H1, H2, and H3, take the average height value H0, and then place the specimen in a curing box for curing; S3. Cure the test piece for 7 days, and measure and record the transverse resistance value R of the resistance strain gauge every day. d and the longitudinal resistance value R h . The measurement method is to collect once every 1 hour in the initial stage, extend to once every 3 hours in the middle stage, and extend to once every 6 hours in the later stage. S4. According to the formula where the resistance change value: ΔR = R - R0, R is the transverse resistance value R d or the longitudinal resistance value R h , R0 is the initial transverse resistance value R 0,d or the initial longitudinal resistance value R 0,h , K is the sensitivity coefficient, calculate the strain value ε, and respectively obtain the transverse strain ε d and the longitudinal strain ε h ; S5. Calculate the initial volume of the test piece The diameter D after expansion = D0(1 + ε d ), and the height H after expansion = H0(1 + ε h ). Calculate the volume of the test piece after expansion According to the formula Calculate the volume expansion rate δ of the RAP–steel slag emulsified asphalt cold recycled mixture V .

2. The expansion rate detection method of a RAP - steel slag emulsified asphalt cold recycled mixture according to claim 1, wherein, In step S1, place 4 strain gauges at the top, middle, and bottom of the specimen respectively, with an interval of 90° between adjacent strain gauges, and cover with an epoxy resin protective layer.

3. The expansion rate detection method of a RAP - steel slag emulsified asphalt cold recycled mixture as described in claim 1, characterized in that, In step S2, the temperature of the curing box is 60°C and the humidity is 95%.

4. The expansion rate detection method of a RAP - steel slag emulsified asphalt cold recycled mixture according to claim 1, characterized in that, In step S3, the initial stage is 1 - 2 days, the middle stage is 3 - 4 days, and the later stage is 5 - 7 days.

5. The expansion rate detection method of a RAP - steel slag emulsified asphalt cold recycled mixture according to claim 1, characterized in that, In the step S4, considering the different conductive characteristics of the specimen in the diameter direction and the height direction, the transverse sensitivity coefficient K d and the longitudinal sensitivity coefficient K h need to be calibrated respectively. The calibration is carried out by applying a known strain to the specimen. According to the formula Record the linear relationship between ΔR and ε and fit the sensitivity coefficients K d and K h .

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