Concrete water-retaining property testing system and testing method

Abstract

The concrete water-retaining property testing system comprises a sample cylinder, a filter element arranged in the sample cylinder, a clamping cavity formed between the inner wall of the sample cylinder and the filter element, an oscillator used for oscillating concrete in the clamping cavity, a liquid collecting hopper arranged at the lower end of the filter element in the sample cylinder, a measuring cylinder and a negative pressure system, and the water outlet valve, the measuring cylinder and the negative pressure system are sequentially communicated, so that the problem that the test period of the existing concrete mixture water retention performance test is long is solved.

Description

Technical Field

[0001] The present invention relates to the field of concrete water retention testing, and in particular to a concrete water retention testing system and method. Background Art

[0002] Concrete water retention generally refers to the ability of a concrete mix to retain moisture during construction. A concrete mix with good water retention prevents water from separating from the mix during transportation, placement, and vibration. Concrete with good water retention ensures adequate hydration of the cement, thereby improving the concrete's strength and durability.

[0003] When concrete has poor water retention, bleeding can occur. For example, after concrete is poured, moisture will gradually rise to the concrete surface and accumulate, forming a layer of water. This not only increases the water-cement ratio on the concrete surface, resulting in reduced strength, but also affects the surface quality of the concrete, such as looseness and sandiness. Water loss can also increase the number of capillaries within the concrete, reducing its impermeability and durability. In structures with high waterproofing requirements, such as basements and pools, poor concrete water retention can easily lead to leakage.

[0004] However, current methods for evaluating the water retention of concrete mixes generally rely on the slump test and the bleeding rate test. The slump test evaluates slump, stickiness, cohesion, and water retention through a slump test. Water precipitation from the mix is ​​graded into three levels: "Excessive," "Small," and "None." This evaluation is highly subjective and cannot quantitatively measure or evaluate the degree of water retention. The bleeding rate test is only suitable for detecting surface moisture and takes a long time, typically requiring more than two hours for concrete, but some special concretes may require observation for four to six hours or even longer. Summary of the Invention

[0005] The present invention provides a concrete water retention test system and test method, which solves the problem of long test period for the existing concrete mixture water retention performance test.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a concrete water retention test system, including a sample cylinder, a filter element is provided in the sample cylinder, a cavity is provided between the inner wall of the sample cylinder and the filter element, and an oscillator is provided. The oscillator is used to oscillate the concrete in the cavity. A liquid collecting hopper is provided at the lower end of the filter element in the sample cylinder, a water outlet valve is provided at the lower end of the liquid collecting hopper, a measuring cylinder and a negative pressure system are also provided, and the water outlet valve, the measuring cylinder and the negative pressure system are connected in sequence.

[0007] In a preferred embodiment, the filter element comprises a ceramic filter sleeve, a polyester fiber layer is provided on the outside of the ceramic filter sleeve, and a nanofiltration membrane is provided on the inside of the ceramic filter sleeve.

[0008] In the preferred embodiment, the filter element also includes a hollow cover, the ceramic filter sleeve is sleeved on the outside of the hollow cover, the upper end of the hollow cover is open and provided with a core cover, the other end of the hollow cover is provided with a bottom plate end, and a plurality of hollow inner covers are provided on the bottom plate end. The inner covers are detachable, the nanofiltration membrane is sleeved on the outside of each inner cover, and the inner side of the inner cover is connected to the liquid collecting bucket.

[0009] In the preferred solution, a connecting port is provided on the core cover, and a positive pressure system is also provided. A first pressure regulating valve is provided at the connecting port, and the negative pressure system and the positive pressure system are respectively connected to the connecting port. An openable sample tube cover is also provided at the upper end of the sample tube, and the sample tube cover is provided with an air connection hole and a second pressure regulating valve. The positive pressure system is connected to the air connection hole through the second pressure regulating valve.

[0010] In a preferred solution, an annular bottom cover is further provided, the inner wall of the annular bottom cover is sleeved with the outer wall of the bottom plate end, and the polyester fiber layer and the bottom end of the ceramic filter sleeve are against the annular bottom cover.

[0011] In the preferred solution, a frame is provided at the upper end of the sample tube, a shelf ring frame is provided in the center of the frame, a hollow structural mesh sleeve is provided at the lower end of the shelf ring frame, a fine mesh sleeve is provided on the outside of the structural mesh sleeve, the lower end of the structural mesh sleeve is against the bottom end of the clamping cavity, and the filter element is provided in the structural mesh sleeve.

[0012] In the preferred embodiment, a plurality of upward concave covers are provided along the circumferential direction at the bottom end of the cavity, and an opening is provided at the lower end surface of the bottom of the cavity. The oscillator is provided with a plurality of oscillation rods along the circumferential direction, and each oscillation rod is attached to the inner wall of the concave cover and inserted into the concave cover.

[0013] Test methods included: Concrete for mixing tests; Prepare multiple sets of test devices and number them; Place the concrete specimen into the clamping cavity of each test device and turn on the oscillator; Start the negative pressure system, connect the negative pressure to the measuring cylinder, and adjust the pressure of the gas line; Read the volume of water in the measuring cylinder at set intervals, and weigh the total mass of the precipitated water in the measuring cylinder after the test is completed; Calculate the water extraction rate and water extraction rate of concrete; The arithmetic mean of the test values ​​of multiple samples is used as the test result to evaluate the water retention of the concrete.

[0014] In a preferred embodiment, after the negative pressure system is turned on, the connection port is simultaneously connected to the negative pressure so that the pressure in the clamping cavity, the inner cavity space of the filter element and the measuring cylinder decreases in sequence; After maintaining the pressure for the set time, cover the sample tube cap and switch the air hole and connection port to connect to the positive pressure system; Adjust the first pressure regulating valve and the second pressure regulating valve to reduce the pressure in the clamp cavity, the inner cavity space of the filter element and the measuring cylinder in sequence. The beneficial effects of the present invention are as follows: by establishing a negative pressure system, the evaluation of the water retention performance of concrete can be completed in a shorter period, which saves a lot of time and improves the test efficiency; not only the water separation rate of concrete can be measured, but also the water separation velocity can be measured, and the water retention performance of concrete can be evaluated using multiple indicators; by adding a positive pressure system, the pressure difference on both sides of the nanofiltration membrane can be increased, the efficiency of water separation of the nanofiltration membrane can be multiplied, and the test period can be further reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be further described below with reference to the accompanying drawings and examples.

[0016] Figure 1 It is a schematic diagram of the present invention.

[0017] Figure 2 It is a schematic diagram of the erection of the present invention.

[0018] Figure 3 It is a system connection diagram of the present invention.

[0019] Figure 4 It is a cross-sectional view of the sample tube.

[0020] Figure 5 This is a partial enlarged view of the sample tube.

[0021] Figure 6 This is a schematic diagram of the sample tube with the cover opened.

[0022] Figure 7 This is an exploded view of the sample tube.

[0023] Figure 8 It is a filter element diagram.

[0024] Figure 9 This is an exploded view of the filter element.

[0025] Figure 10 This is a structural diagram of the hollow cover.

[0026] In the figure: sample tube 1; clamping cavity 101; bracket 102; concave cover 103; frame 2; shelf ring 201; structural mesh sleeve 202; fine mesh sleeve 203; filter element 3; polyester fiber layer 301; ceramic filter sleeve 302; nanofiltration membrane 303; hollow cover 304; bottom plate end 305; inner cover 306; flange 307; core cover 308; connection port 309; annular bottom cover 310; liquid collecting hopper 4; water outlet valve 5; oscillator 6; oscillating rod 601; measuring cylinder 7; negative pressure system 8; positive pressure system 9; air circuit switching valve 10; first pressure regulating valve 11; sample tube cover 12; air connection hole 1201; second pressure regulating valve 13; switch valve 14. DETAILED DESCRIPTION

[0027] Example 1: like Figure 1-10A concrete water retention test system is disclosed, comprising a sample cylinder 1, a filter element 3 provided in the sample cylinder 1, a cavity 101 provided between the inner wall of the sample cylinder 1 and the filter element 3, an oscillator 6 for oscillating the concrete in the cavity 101, a liquid collecting hopper 4 provided at the lower end of the filter element 3 in the sample cylinder 1, a water outlet valve 5 provided at the lower end of the liquid collecting hopper 4, a measuring cylinder 7 and a negative pressure system 8, the water outlet valve 5, the measuring cylinder 7 and the negative pressure system 8 being connected in sequence.

[0028] After the concrete sample is placed in the clamping cavity 101, the oscillator 6 is turned on, and the negative pressure system 8 provides negative pressure to the inside of the filter element 3, continuously filtering the moisture in the concrete into the liquid collecting hopper 4 in the filter element 3 and then pumping it into the measuring cylinder 7. The moisture content of the concrete sample is evaluated based on the amount of water collected in the measuring cylinder 7 within the set time.

[0029] A bracket 102 is provided at the lower end of the sample tube 1 to raise the position of the water outlet valve 5 for easy connection of the pipeline.

[0030] If a cover is added to the upper end of the clamping chamber 101, a vent hole needs to be reserved to maintain communication with the atmosphere.

[0031] In a preferred embodiment, the filter element 3 includes a ceramic filter sleeve 302 , a polyester fiber layer 301 is sheathed on the outside of the ceramic filter sleeve 302 , and a nanofiltration membrane 303 is provided on the inside of the ceramic filter sleeve 302 .

[0032] The filtration pores of the polyester fiber layer 301 , the ceramic filter sleeve 302 , and the nanofiltration membrane 303 decrease in sequence. After multiple filtrations, the water in the concrete reaches the inner side of the nanofiltration membrane 303 and is collected by the liquid collecting bucket 4 .

[0033] In the absence of negative pressure, it takes a long time for water molecules to naturally penetrate through the three filter layers, so negative pressure is needed to speed up the test process.

[0034] Since the nanofiltration membrane 303 has small pores and slow permeation, it is difficult to clean the contact surface between the nanofiltration membrane 303 and the ceramic filter sleeve 302. Conventional practice is to remove the polyester fiber layer 301, the ceramic filter sleeve 302 and the nanofiltration membrane 303 in turn for cleaning or replacement, which is quite troublesome.

[0035] In addition, due to the negative pressure, if the nanofiltration membrane 303 is only attached to the inner wall of the ceramic filter sleeve 302, it is easy to fall off. Therefore, the nanofiltration membrane 303 needs a fixed structure to resist the negative pressure.

[0036] In the preferred embodiment, the filter element 3 also includes a hollow cover 304, a ceramic filter sleeve 302 is sleeved on the outside of the hollow cover 304, the upper end of the hollow cover 304 is open and provided with a core cover 308, and the other end of the hollow cover 304 is provided with a bottom plate end 305, and the bottom plate end 305 is provided with multiple hollow inner covers 306, the inner covers 306 are detachable, the nanofiltration membrane 303 is sleeved on the outside of each inner cover 306, and the inner side of the inner cover 306 is connected to the liquid collecting bucket 4.

[0037] Core cap 308 is threadedly connected to the open end of hollow cover 304. Thus, the inner side of ceramic filter sleeve 302 and the outer side of nanofiltration membrane 303 form the inner cavity of filter element 3. Inner cover 306 serves as the framework of nanofiltration membrane 303. When negative pressure from negative pressure system 8 is drawn through the inner side of nanofiltration membrane 303, air in the inner cavity of filter element 3 gradually permeates through nanofiltration membrane 303 and is drawn away, creating a negative pressure environment. This accelerates the penetration of moisture from cavity 101 into the inner cavity of filter element 3. Since concrete only loses a small amount of moisture, only a small amount of water remains at the lower end of the inner cavity of filter element 3. Therefore, the height of inner cover 306 does not need to be too high.

[0038] The water in the inner cavity of the filter element 3 is filtered by the nanofiltration membrane 303 at the same time, enters the inner side of the nanofiltration membrane 303 from the outside and falls into the liquid collecting bucket 4 and is sucked into the measuring cylinder 7 by negative pressure.

[0039] The inner cover 306 is inserted into the inner cavity space of the filter element 3 from the lower end. The U-shaped structure can increase the contact area. The inner cover 306 is connected to the bottom plate end 305 through a threaded connection, which is easy to replace.

[0040] In the preferred embodiment, a connection port 309 is provided on the core cover 308, and a positive pressure system 9 is also provided. A first pressure regulating valve 11 is provided at the connection port 309, and the negative pressure system 8 and the positive pressure system 9 are respectively connected to the connection port 309. An openable sample tube cover 12 is also provided at the upper end of the sample tube 1, and the sample tube cover 12 is provided with an air connection hole 1201 and a second pressure regulating valve 13. The positive pressure system 9 is connected to the air connection hole 1201 through the second pressure regulating valve 13.

[0041] A gas circuit switching valve 10 is also provided. The main gas circuit connected to the connection port 309 is equipped with a first pressure regulating valve 11 and the gas circuit switching valve 10. The gas circuit switching valve 10 branches into two branch gas circuits, one of which is connected to the negative pressure system 8 and the other is connected to the positive pressure system 9. The gas circuit switching valve 10 can switch whether the main gas circuit is connected to positive pressure or negative pressure, and the first pressure regulating valve 11 can adjust the pressure.

[0042] When the gas circuit switching valve 10 is switched to the connection port 309 to connect to the positive pressure system 9, the sample tube cover 12 remains in a closed state.

[0043] In a preferred embodiment, an annular bottom cover 310 is further provided. The inner wall of the annular bottom cover 310 is sleeved with the outer wall of the bottom plate end 305 , and the bottom ends of the polyester fiber layer 301 and the ceramic filter sleeve 302 rest against the annular bottom cover 310 .

[0044] The polyester fiber layer 301 and the ceramic filter sleeve 302 can be directly placed against the bottom of the clamping cavity 101. However, when the filter element 3 is removed, the end is not connected and is prone to loosening and falling off. Therefore, an annular bottom cover 310 can be installed. A quick-connect connector is installed at the connection port 309. When the filter element 3 is removed, the connection port 309 can be connected to the waterway, and clean water enters the inner cavity of the filter element 3 to flush out impurities on the outer side of the nanofiltration membrane 303. Then, the clean water is flushed out from the ceramic filter sleeve 302 and the inner side of the polyester fiber layer 301 in reverse order, taking away the embedded impurities. Subsequently, the inner side of the nanofiltration membrane 303 at the lower end of the filter element 3 is flushed with clean water. Finally, the core cover 308 can be opened, and the inner cavity of the lower filter element 3 is flushed again to discharge the sewage. The filter element 3 is then cleaned.

[0045] Finally, the frame 2 is dismantled, the concrete in the sample tube 1 is poured out, and the clamping cavity 101 is rinsed with clean water and allowed to dry.

[0046] In the preferred embodiment, a frame 2 is provided at the upper end of the sample tube 1, a shelf ring 201 is provided in the center of the frame 2, a hollow structural mesh sleeve 202 is provided at the lower end of the shelf ring 201, a fine mesh sleeve 203 is provided on the outside of the structural mesh sleeve 202, the lower end of the structural mesh sleeve 202 is against the bottom end of the clamping cavity 101, and the filter element 3 is arranged in the structural mesh sleeve 202.

[0047] The structural mesh sleeve 202 and the fine mesh sleeve 203 can be made of steel, which is low in price, long in life and easy to clean. The structural mesh sleeve 202 serves as the force-bearing structure of the fine mesh sleeve 203, and the fine mesh sleeve 203 serves as the first layer of filtering structure, which can intercept large particles in concrete and extend the service life of the inner filter element 3.

[0048] The filter element 3 is provided with a flange 307 . The filter element 3 is inserted into the placement ring 201 , and the flange 307 is stopped on the placement ring 201 .

[0049] In the preferred embodiment, a plurality of upward concave covers 103 are provided along the circumferential direction at the bottom end of the clamping cavity 101, and the concave covers 103 are provided with an opening on the lower end surface of the bottom of the clamping cavity 101. The oscillator 6 is provided with a plurality of oscillation rods 601 along the circumferential direction, and each oscillation rod 601 is attached to the inner wall of the concave cover 103 and inserted into the concave cover 103.

[0050] The oscillator 6 is embedded in the bottom of the sample tube 1, and a wiring position is reserved. The oscillating rod 601 does not directly contact the concrete, eliminating the need for a cleaning process and extending the service life.

[0051] In the preferred embodiment, Concrete for mixing tests; Prepare multiple sets of test devices and number them; Place the concrete sample into the clamping cavity 101 of each testing device and turn on the oscillator 6; Start the negative pressure system 8, connect the negative pressure to the measuring cylinder 7, and adjust the pressure of the gas circuit; The volume of water in the measuring cylinder 7 is read at set intervals, and the total mass of the precipitated water in the measuring cylinder 7 is weighed after the test is completed; Calculate the water extraction rate and water extraction rate of concrete; The arithmetic mean of the test values ​​of multiple samples is used as the test result to evaluate the water retention of the concrete.

[0052] In the preferred embodiment, Before the water retention test, a variety of concretes with different formulations were prepared; Divide the concrete into two parts, one sample is tested for slump, and the other sample is tested in the same way as the water retention test; The concrete slump measured by the slump test is matched with the water extraction rate measured in the water retention test system and a comparison table is established; During the subsequent water retention test, the concrete water extraction rate obtained from the test was converted into slump.

[0053] Before the actual concrete sample test, multiple groups of preliminary tests are used to correlate the new water retention rate evaluation method with the old slump evaluation method, and a query table is established. After the concrete sample test, the slump corresponding to the calculated concrete water loss rate is queried in the comparison table, meeting various occasions that require the old evaluation system.

[0054] Since the pores of the nanofiltration membrane 303 are relatively small, the rate at which water precipitates from the clamping cavity 101 to the inner cavity space of the filter element 3 is fast, while the rate at which water precipitates from the inner cavity space of the filter element 3 to the liquid collecting bucket 4 is much slower, which greatly restricts the total duration of the test. If only unilateral negative pressure suction is used, the rate of acceleration is limited because the maximum pressure difference is one atmosphere.

[0055] In a preferred embodiment, after the negative pressure system 8 is turned on, the connection port 309 is connected to the negative pressure so that the pressure in the clamping cavity 101, the inner cavity space of the filter element 3 and the measuring cylinder 7 decreases in sequence; After maintaining the pressure for the set time, cover the sample tube cover 12 and switch the air inlet 1201 and the connection port 309 to connect to the positive pressure system 9; The first pressure regulating valve 11 and the second pressure regulating valve 13 are adjusted to reduce the pressure in the clamping cavity 101, the inner cavity space of the filter element 3 and the measuring cylinder 7 in sequence. Initially, since there's no water accumulated in the filter element 3, if the inner cavity of the filter element 3 is directly connected to positive pressure, some of the positive pressure will be lost through the nanofiltration membrane 303. Furthermore, to ensure that the moisture in the clamping chamber 101 moves into the filter element 3, the air inlet 1201 must be connected to a higher positive pressure, which consumes a lot of energy. Therefore, the sample cylinder cover 12 can be opened to return the clamping chamber 101 to atmospheric pressure, creating a negative pressure within the filter element 3. Due to the relatively large pores between the polyester fiber layer 301 and the ceramic filter sleeve 302, moisture can quickly precipitate and enter the filter element 3. At this point, the on-off valve 14 is closed.

[0056] When the water in the filter element 3 submerges the upper end of the nanofiltration membrane 303, at this time, most of the precipitated water has entered the filter element 3 from the concrete. At this time, cover the sample tube cover 12 and open the switch valve 14. Adjust the first pressure regulating valve 11 and the second pressure regulating valve 13 so that the first pressure regulating valve 11 is at the set value required for the test and the second pressure regulating valve 13 is adjusted to a value slightly larger than the value of the first pressure regulating valve 11, ensuring that the water in the filter element 3 is difficult to reversely enter the clamping cavity 101.

[0057] Under the premise that the strength of the nanofiltration membrane 303 can support it, the pressure difference on both sides of the nanofiltration membrane 303 is increased as much as possible, and the pressure difference between the inside and outside of the nanofiltration membrane 303 is doubled to accelerate the rate of water precipitation from the inner cavity space of the filter element 3 to the vector cylinder 7. Example 2: A device for testing concrete water retention consists of two parts: a rigid metal cylinder with a base and handles on both sides, and a solid, watertight wall. A small hole is located in the center of the bottom of the cylinder, which is fitted with a fixed, rigid conduit. For mixtures with a maximum aggregate size of 31.5 mm or less, the following cylinder is used: an inner diameter and height of 210 mm ± 2 mm, a wall thickness of approximately 5 mm, and a cap.

[0058] The other part is the filter cartridge, which consists of a cartridge cover and filter elements. From the outside in, these are a stainless steel filter element, a polyester fiber filter element, a ceramic filter element, and an anti-fouling nanofiltration membrane. The stainless steel filter element has an outer diameter of 86 mm and an inner diameter of 78 mm. It features a tapered funnel at the bottom, which is integral to the stainless steel filter element. 2.36 mm circular holes are uniformly and densely distributed throughout the stainless steel filter element, ranging from 45 mm to 150 mm in height. The cone is hollow and connects to the central conduit of the sample cartridge. The polyester fiber filter element has an outer diameter of 78 mm and an inner diameter of 66 mm; the ceramic filter element has an outer diameter of 66 mm and an inner diameter of 54 mm. The anti-fouling nanofiltration membrane is 0.5 mm thick. A soft butylene rubber gasket is placed at each end of the filter cartridge. Each component is removable for easy cleaning after testing.

[0059] Preferably, the device selects suitable filter elements - stainless steel filter elements, polyester fiber filter elements, ceramic filter elements and anti-pollution nanofiltration membranes - based on the specific composition of fresh concrete, the required accuracy of filtration, flow rate, durability, convenience of replacement and cleaning, and cost; Preferably, the stainless steel filter is corrosion-resistant, suitable for use in concrete environments, can filter larger particles, and is easy to clean; Preferably, the polyester fiber filter element has a relatively low cost and can effectively remove solid particles and impurities in concrete. The moisture in the fresh concrete enters the filter element under pressure, and the tiny pores between the polyester fibers can prevent the concrete particles from passing through, allowing only moisture to pass through and be collected. Polyester fiber has been designed to resist pollution and has good chemical stability. It will not chemically react with the components in the concrete and affect the filtration effect. This type of filter element has strong corrosion resistance and can maintain good performance in alkaline concrete environments. Its filtration accuracy can be adjusted according to the thickness of the fiber and the weaving method. However, the hydrophilicity of the polyester fiber filter element is relatively weak, and it may take a certain amount of time to allow moisture to fully enter the filter element in the early stage of filtration.

[0060] Preferably, there are many tiny pores inside the ceramic filter element, and these pores can filter water by using capillary phenomena. When fresh concrete comes into contact with the ceramic filter element, water enters the pores of the ceramic filter element under the action of capillary force, while the solid particles in the concrete are blocked outside the filter element due to their large particle size. The filtration of the ceramic filter element is based on the dual effects of physical screening and adsorption. The advantages of the ceramic filter element are high temperature resistance, excellent chemical stability, and the ability to work stably in complex concrete environments. In addition, it has a long service life and can be reused many times after cleaning. However, the ceramic filter element is relatively brittle and should be avoided from being subjected to large impact forces during installation and use, otherwise it will be easily damaged. Preferably, the surface of the anti-fouling nanofiltration membrane undergoes a special modification treatment, resulting in strong anti-fouling capabilities. The nanofiltration membrane surface is coated with hydrophilic groups, such as hydroxyl (-OH) and carboxyl (-COOH). These hydrophilic groups reduce the adsorption of impurities on the membrane surface, making it difficult for impurities such as cement particles and admixtures, which are precipitated from concrete, to adhere to the membrane surface. Furthermore, the anti-fouling nanofiltration membrane has a relatively strong flux recovery capability. Once the membrane has become contaminated to a certain extent, simple physical cleaning (such as rinsing) or chemical cleaning (using mild acid or alkaline solutions) can effectively restore the membrane flux, thereby extending the membrane's service life.

[0061] Preferably, moisture is removed from the concrete by simulating on-site construction using a method that applies pressure to the top of the concrete and vibrates it with a high-frequency vibrator. Calculations show that the ring vibrator, weighing approximately 5.5 kg, exerts a unit area pressure of approximately 2 kPa on the top of the concrete. Combined with the unit area pressure of approximately 8 kPa caused by the concrete's own weight, this simulates the pressure of concrete poured 50 cm high on-site, i.e., a unit area pressure of 10 kPa. Since the vibrator has a diameter of 16 mm and is a micro vibrator, the frequency is controlled within the range of 150 Hz ± 1.5 Hz, and the vibration time is controlled within approximately 30 seconds, with the concrete surface showing slurry and no bubbles.

[0062] Preferably, negative pressure is applied to the device through a vacuum pump to keep the pressure of the device constant at -2.0 MPa, so that the moisture in the concrete quickly passes through the filtering device and is collected in the graduated cylinder, which can accelerate the test speed.

[0063] Preferably, the water retention detection method can detect the water release rate inside the concrete, which has guiding significance for optimizing admixtures and studying the concrete hydration process.

[0064] Preferably, the water retention detection method can detect the water precipitate situation inside the concrete, the test time is short, and the result is more objective.

[0065] The following steps are involved: S1. Install the anti-pollution nanofiltration membrane material, which can be customized in batches in advance. The size is determined by the inner diameter and length of the ceramic filter element. Before installation, make sure the inner wall of the ceramic filter element is clean and smooth. You can use a mild detergent and clean water to rinse the inner wall of the ceramic filter element, then blow it dry with clean compressed air or let it dry naturally to prevent impurities from affecting the installation and performance of the nanofiltration membrane. Use sealant (such as food-grade silicone) at both ends to seal the connection between the nanofiltration membrane and the ceramic filter element to prevent water leakage and ensure that the membrane can fit tightly against the inner wall of the filter element. S2. Mix an appropriate amount of concrete in a test room at a temperature of 20°C ± 2°C and a relative humidity of not less than 50%, with a volume of not less than 1.5 times the amount required for the test and not less than 25L; S3. Prepare three sets of devices, numbered 1#, 2#, and 3# respectively. Wet the inner wall of the sample tube and the filter element shell with a wet cloth and assemble them according to the diagram. Screw on the core tube cover and weigh them immediately. Record the mass m of the device before loading. 01 、m 02 、m 03 ; S4. Check the switch of the funnel at the lower end of the device and keep it closed. Stir the concrete sample evenly and then put it into the sample tube. The method of loading and compacting the concrete is as follows: (1) The slump should not exceed 90 mm. Use a vibrating table to compact the sample. Place the sample into the sample tube at once, turn on the vibrating table, and continue vibrating until the slurry appears on the surface. Avoid over-vibration. Make sure the concrete mixture is 30 mm ± 5 mm below the surface of the sample tube and smooth it with a trowel. After smoothing, immediately weigh and record the total mass of the device and the sample m1, m2, and m3. (2) If the slump is greater than 90mm, use a tamping rod to compact it. The concrete mixture should be loaded in two layers. For each layer of concrete mixture, use a tamping rod to tamp it evenly from the edge to the center in a spiral shape 25 times. When tamping the bottom layer, the tamping rod should penetrate the entire depth. When tamping the second layer, the tamping rod should penetrate the current layer to the surface of the next layer. After tamping each layer, use a rubber hammer to gently tap the outer wall of the container 5 to 10 times until the tamping holes on the mixture surface disappear. Make the surface of the concrete mixture 30mm±5mm lower than the surface of the sample tube and smooth it with a spatula. After smoothing, immediately weigh and record the total mass of the device and the sample m1, m2, and m3. S5. Slowly place the annular vibrator in the concrete so that the lower surface of the steel plate contacts the concrete surface, and tighten the test cylinder cover; S6. Turn on the switch of the funnel at the lower end of the device and start the vacuum pump to make the pressure in the device constant at -2.0 MPa. At the same time, start timing; S7. Read the volume of water every 10 minutes. Start the ring vibrator and vibrate for 30 seconds in the first 30 seconds of each 10-minute timer. Record the volume V every 10 minutes. w1i (1# sample in the first 10 minutes), V w2i (the first 10 minutes of sample 2#), V w3i (the first 10 minutes of sample 3#), accurate to 0.01ml, and end the test after 30 minutes. Weigh the total mass of the precipitated water in the measuring cylinder m w1 、m w2 、m w3 .

[0066] S8. Calculate the water separation rate of concrete:

[0067]

[0068]

[0069]

[0070]

[0071]

[0072]

[0073] 、 、 ——Represents the average volume of water precipitated by three samples in the first, second and third 10 min periods (ml); V w ——Total volume of water extracted (ml); m w ——Total mass of deionized water (g); S——water separation rate (ml / min), which can be used to calculate the average water separation rate in different time periods and 30 minutes; T ——water separation rate (%); B——water retention rate (%); m ——total mass of the mixture when mixing concrete (g); w——Total water required for mixing concrete (g); m1——total mass of the sample tube and sample before water analysis (g); m0——total mass of the device before loading (g); α, β, γ - correction factors for polyester fiber and ceramic filter element respectively, α=K α / 360, β=K β / 1.5,γ=K γ / 0.002; K α , K β , K γ ——The water permeability of polyester fiber, ceramic filter element and anti-pollution nanofiltration membrane using distilled water at -2.0MPa pressure is 360L / (cm 2 h) is the water permeability of the polyester fiber filter element using distilled water at standard atmospheric pressure, 1.5L / (cm 2 h) is the water permeability of the ceramic filter element using distilled water at standard atmospheric pressure, 0.002L / (cm 2 h) is the water permeability of the anti-fouling nanofiltration membrane using distilled water at standard atmospheric pressure.

[0074] S9. For water separation rate and water retention rate, the arithmetic mean of the test values ​​of the three samples shall be used as the test result, and the result shall be accurate to 1%. If the difference between one of the values ​​and the median value exceeds 10% of the median value, the median value shall be used as the test result. If the difference between the maximum and minimum values ​​and the median value exceeds 10% of the median value, the test shall be invalid. S10. When the water leaching rate exceeds 8%, the concrete is considered to have poor water retention, which has a significant impact on the durability of the concrete and should be used with caution. When the water leaching rate exceeds 5% but does not exceed 8%, the concrete is considered to have moderate water retention and should be optimized before use. When the water leaching rate exceeds 2% but does not exceed 5%, the concrete is considered to have good water retention. When the water leaching rate is less than or equal to 2%, the concrete is considered to have excellent water retention and can be used to evaluate special concretes such as high-performance concretes. S11. Calculate the water leaching rate with an accuracy of 0.01 L / min, analyze the average water leaching rate at different time periods, adjust the concrete water-binder ratio as needed, and optimize the admixture formula. Study the correlation between the concrete hydration process and the water leaching rate; S12. After the test, disassemble and clean the device promptly. Soak it in distilled water for 1 hour after cleaning. Chemically condition the anti-fouling filter membrane with sodium hexametaphosphate solution to reduce the flux drop caused by scaling. Then store it at a temperature of 20℃±2℃ and a relative humidity of not less than 95%. In order to verify the reliability of the test method, a correlation was established between the water extraction rate of concrete and its slump, water-binder ratio, 20-min yield stress and 20-min plastic viscosity, and further analysis was carried out.

[0075] S13. Evaluate the water retention of the concrete mixture sample based on the appearance of the mixture and the test results.

[0076] The tests involved in this scheme are simple, reliable and easy to operate, which greatly improves the efficiency of concrete water retention testing.

[0077] ① Reliability: The invented device can detect the water retention of concrete from the inside, which improves the objectivity and accuracy of the evaluation. After comparison and verification, the test results of the device are correlated with the test results of T0528-2005 cement concrete mixture bleeding test method in JTG 3420-2020 "Test Procedures for Cement and Cement Concrete in Highway Engineering" at a correlation of up to 99.95%, proving that the test is highly reliable.

[0078] ② Economical: The new device adopted in this invention has low cost and can be reused after cleaning.

[0079] ③ Efficiency: The test method in this invention can be completed in a relatively short time, and the water retention results can be evaluated quickly.

[0080] ④ Convenience: The test device involved in the invention is light in weight, detachable, easy to operate, safe and reliable.

[0081] ⑤Wide scope of application: It is suitable for the water retention evaluation of various types of concrete. It can not only detect the water separation inside the concrete, but also provide guidance for the optimization of admixtures and the study of concrete hydration process.

[0082] Example 3: A technical solution for a device for detecting the water retention of concrete is described in further detail below. It specifically includes the following steps: S1. Use distilled water to test the water permeability K of polyester fiber, ceramic filter element and anti-pollution nanofiltration membrane under -2.0MPa pressure difference. α =240×10-4 L / (cm 2 h), K β =60×10 -4 L / (cm 2 h), K γ =2.5L×10 -4 / (cm 2 After the test, the temperature should be kept at 20℃±2℃ and the relative humidity should not be less than 95%.

[0083] S2. Install the anti-pollution nanofiltration membrane material. Rinse the inner wall of the ceramic filter element with a mild detergent and clean water. Then blow dry with clean compressed air or let it dry naturally to prevent impurities from affecting the installation and performance of the nanofiltration membrane. Use sealant (such as food-grade silicone) at both ends to seal the connection between the nanofiltration membrane and the ceramic filter element to prevent water leakage and ensure that the membrane can fit tightly to the inner wall of the filter element. S3. Prepare three devices, numbered 1#, 2#, and 3#. Wet the inner wall of the sample tube and the filter element housing with a damp cloth and assemble as shown. Secure the core tube cap and check the funnel switch at the bottom of the device to ensure it is closed. Immediately weigh the three devices and record the masses before loading: m01 = 2.865 kg, m02 = 2.879 kg, and m03 = 2.893 kg. S4. Taking C30 ordinary concrete as an example, the amount of raw materials per cubic meter of concrete is shown in the following table:

[0084] S5. Control the test room temperature to 20℃±2℃ and the relative humidity to not less than 50%. According to the above mix ratio, the amount of concrete to be mixed for 25L is as shown in the following table:

[0085] S6. After the mixing is completed, turn the concrete sample over on the iron plate and mix it evenly. Start loading it into the sample tube within 5 minutes after adding water. Because the designed slump of the concrete is 180±20mm (greater than 90mm), the concrete loading and compacting method is as follows: compact with a tamping rod. The concrete mixture is loaded in two layers. For each layer of concrete mixture, use a tamping rod to tamp it evenly from the edge to the center in a spiral shape 25 times. When tamping the bottom layer, the tamping rod should penetrate the entire depth. When tamping the second layer, the tamping rod should penetrate the current layer to the surface of the next layer. After tamping each layer, use a rubber hammer to gently tap the outer wall of the container 5 to 10 times until the tamping holes on the mixture surface disappear and no large bubbles are seen. Make the surface of the concrete mixture 30mm±5mm lower than the surface of the sample tube and smooth it with a spatula. The loading time should not exceed 90s. Immediately weigh and record the total mass of the device and the sample: m1=14.577kg, m2=14.542kg, m3=14.654kg; S7. Slowly place the annular vibrator in the concrete so that the lower surface of the steel plate contacts the concrete surface, and tighten the test cylinder cover; S8. Turn on the switch of the funnel at the lower end of the device and start the vacuum pump to make the pressure in the device constant at -2.0 MPa. At the same time, start timing; S9. Read the volume of water every 10 minutes. Start the ring vibrator and vibrate for 30 seconds during the first 30 seconds of each 10-minute timing. Record the volume Vw1i (the i-th 10 minutes of sample 1), Vw2i (the i-th 10 minutes of sample 2), and Vw3i (the i-th 10 minutes of sample 3) every 10 minutes with an accuracy of 0.01 ml. Continue for 30 minutes before the end of the test. Weigh the total mass of the precipitated water in the measuring cylinder, mw1, mw2, and mw3.

[0086] S10. Calculate the water separation rate of concrete:

[0087]

[0088]

[0089]

[0090]

[0091]

[0092]

[0093] 、 、 ——Represents the average volume of water precipitated in the first, second and third 10 minutes of the three samples (ml). The weighing results are shown in the following table:

[0094] V w ——The average value of the total volume of water (ml), calculated as V w =41.29ml; S——water separation rate (L / min), which can be used to calculate the average water separation rate in different time periods and 30 minutes;

[0095] m w ——Total amount of dehydrated water (g), calculated as m w =41.33g; T - water separation rate (%), calculated as T1=5.62%, T2=4.97%, T3=5.24%; B——water retention rate (%); m ——When mixing concrete, the total mass of the mixture is 59.795 kg; w——Total water required for the mixture when mixing concrete (4kg); m1, m2, m3 - total mass of the sample tube and sample before water analysis: m1 = 14.577 kg, m2 = 14.542 kg, m3 = 14.654 kg; m 01 、m 02 、m 03 ——Total mass of the device before loading m 01 =2.865kg, m 02 =2.879kg, m 03 =2.893kg; α, β, γ——Correction factors of polyester fiber filter element, ceramic filter element, and anti-pollution nanofiltration membrane respectively, α=K α / 360, β=K β / 1.5,γ=K γ / 0.002; K α , K β , K γ ——The water permeability of polyester fiber, ceramic filter element and anti-pollution nanofiltration membrane using distilled water at -2.0 MPa pressure, 15×10 -4 L / (cm 2 h) is the water permeability of the polyester fiber filter element using distilled water at standard atmospheric pressure, 2.5×10 -4 L / (cm 2 h) is the water permeability of the ceramic filter element using distilled water at standard atmospheric pressure, 0.02×10 -4 L / (cm 2 h) is the water permeability of the anti-fouling nanofiltration membrane using distilled water at standard atmospheric pressure.

[0096] S11. For water separation rate and water retention rate, the arithmetic mean of the test values ​​of three samples shall be used as the test result, and the result shall be accurate to 1%. If the difference between one of the values ​​and the median value exceeds 10% of the median value, the median value shall be used as the test result. If the difference between the maximum and minimum values ​​and the median value exceeds 10% of the median value, the test shall be invalid. After calculation, we can get: The water extraction rate of this concrete sample is T = 5.28%; Water retention rate B = 94.72% S12. When the water leaching rate exceeds 8%, the concrete is considered to have poor water retention, which has a significant impact on the durability of the concrete and should be used with caution. When the water leaching rate exceeds 5% but does not exceed 8%, the concrete is considered to have moderate water retention and should be optimized before use. When the water leaching rate exceeds 2% but does not exceed 5%, the concrete is considered to have good water retention. When the water leaching rate is less than or equal to 2%, the concrete is considered to have excellent water retention and can be used to evaluate special concretes such as high-performance concretes. In order to verify the reliability of the test method, a correlation was established between the water extraction rate of concrete and its slump, water-binder ratio, 20-minute yield stress and 20-minute plastic viscosity, and the analysis is as follows:

[0097] Table 1 Concrete water separation rate at different slumps By comparing the data in Table 1, it can be concluded that without adding water reducing agent, if the amount of sand and gravel in the concrete remains unchanged and only the water-cement ratio and unit water consumption are adjusted, the greater the slump, the greater the water separation rate.

[0098]

[0099] Table 2 Water separation rate of concrete with different water-binder ratios The slump of fixed concrete is 180mm±10mm. By comparing the data in Table 2, it can be concluded that under the same slump, the larger the water-binder ratio of concrete, the greater the water separation rate.

[0100]

[0101] Table 3 Concrete water separation rate at different yield strengths

[0102] Table 4 Concrete water separation rate at different plastic viscosities Yield stress is the minimum shear stress required for concrete to begin to flow. The 20-minute yield strength, measured by a rheometer, reflects concrete fluidity. The 20-minute plastic viscosity, which correlates with the cohesiveness of the concrete paste, reflects the concrete's resistance to segregation. Comparing the data in Tables 3 and 4 shows that yield strength is not the primary factor affecting the bleeding rate; the plastic viscosity has a more direct impact on the degree of concrete bleeding. When the plastic viscosity is 36 Pa·s ≤ 74 Pa·s, the required water separation rate for ordinary concrete can be met.

[0103] In addition, the water separation rate and water separation speed of concrete are related to the type and fineness of cement, the water absorption rate of aggregate, and the dosage of admixtures such as water reducer and admixture. Generally speaking, for concrete with the same slump, the finer the cement fineness, the lower the water absorption rate of aggregate, and the higher the dosage of water reducer and admixture, the lower the water absorption rate of concrete. The water retention of different concretes can be further studied in combination with this patent.

[0104] S13. Calculate the water shedding rate to an accuracy of 0.01 L / min, analyze the average water shedding rate at different time periods, and adjust the concrete water-binder ratio and optimize the admixture formula as needed. Based on the above test, it is inferred that the water shedding rate of concrete decreases as the hydration process progresses. S14. After the test, the device should be disassembled and cleaned in time. The anti-fouling filter membrane should be chemically conditioned with sodium hexametaphosphate solution to reduce the flux drop caused by scaling. After cleaning, soak it in distilled water for 1 hour and then store it at a temperature of 20℃±2℃ and a relative humidity of not less than 95%. α <200×10 -4 L / (cm 2 h), K β <40×10 -4 L / (cm 2 h) or K γ <2.0×10 -4 L / (cm 2 ˙h), the filter element should be replaced; S15. Evaluate the water retention of the concrete mixture sample based on the appearance of the mixture and the test results.

[0105] It can be determined that the concrete homogeneity is poor. The cause should be analyzed and appropriate solutions should be taken until the concrete homogeneity meets the requirements.

[0106] While this water retention test device is removable, easy to clean, inexpensive, and reusable, it's important to note that the polyester fiber filter element is designed to resist contamination, making cleaning relatively simple. Blockages on the surface and within the pores can be removed through backflushing or chemical cleaning. However, after repeated cleaning, the fibers may wear or deform, affecting filtration accuracy and performance, limiting their reusability. Ceramic filter elements, on the other hand, have a longer service life and can be reused multiple times after cleaning. Cleaning methods typically involve physical cleaning (such as brushing) or chemical cleaning (using appropriate detergents) to remove blockages within the pores. However, care must be taken during the cleaning process to avoid damaging the ceramic filter element's structure, as this may reduce filtration accuracy. The anti-contamination membrane is chemically conditioned with a sodium hexametaphosphate solution to minimize flux loss caused by scaling.

[0107] The above embodiments are merely preferred technical solutions of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention shall be the technical solutions set forth in the claims, including equivalent alternatives to the technical features of the technical solutions set forth in the claims. In other words, equivalent alternatives and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A concrete water retention testing system, characterized by: The invention comprises a sample cylinder (1), a filter element (3) is provided in the sample cylinder (1), a cavity (101) is provided between the inner wall of the sample cylinder (1) and the filter element (3), an oscillator (6) is provided, and the oscillator (6) is used to oscillate the concrete in the cavity (101), a liquid collecting hopper (4) is provided at the lower end of the filter element (3) in the sample cylinder (1), a water outlet valve (5) is provided at the lower end of the liquid collecting hopper (4), a measuring cylinder (7) and a negative pressure system (8), and the water outlet valve (5), the measuring cylinder (7) and the negative pressure system (8) are connected in sequence.

2. The concrete water retention testing system according to claim 1, characterized in that: The filter element (3) comprises a ceramic filter sleeve (302), the outer side of the ceramic filter sleeve (302) is covered with a polyester fiber layer (301), and the inner side of the ceramic filter sleeve (302) is provided with a nanofiltration membrane (303).

3. The concrete water retention testing system according to claim 2, characterized in that: The filter element (3) further comprises a hollow cover (304), a ceramic filter sleeve (302) is sleeved on the outside of the hollow cover (304), the upper end of the hollow cover (304) is open and provided with a core cover (308), the other end of the hollow cover (304) is provided with a bottom plate end (305), and the bottom plate end (305) is provided with a plurality of hollow inner covers (306), the inner covers (306) are detachable, the nanofiltration membrane (303) is sleeved on the outside of each inner cover (306), and the inner side of the inner cover (306) is connected to the liquid collecting bucket (4).

4. The concrete water retention testing system according to claim 3, characterized in that: The core cover (308) is provided with a connection port (309) and a positive pressure system (9). A first pressure regulating valve (11) is provided at the connection port (309). The negative pressure system (8) and the positive pressure system (9) are respectively connected to the connection port (309). An openable sample cylinder cover (12) is provided at the upper end of the sample cylinder (1). The sample cylinder cover (12) is provided with an air connection hole (1201) and a second pressure regulating valve (13). The positive pressure system (9) is connected to the air connection hole (1201) through the second pressure regulating valve (13).

5. The concrete water retention testing system according to claim 3, characterized in that: An annular bottom cover (310) is also provided, the inner wall of the annular bottom cover (310) being sleeved with the outer wall of the bottom plate end (305), and the bottom ends of the polyester fiber layer (301) and the ceramic filter sleeve (302) resting against the annular bottom cover (310).

6. The concrete water retention testing system according to claim 1, characterized in that: The upper end of the sample tube (1) is provided with a frame (2), the center of the frame (2) is provided with a shelf ring frame (201), the lower end of the shelf ring frame (201) is provided with a hollow structural mesh sleeve (202), the outer side of the structural mesh sleeve (202) is covered with a fine mesh sleeve (203), the lower end of the structural mesh sleeve (202) is against the bottom end of the clamping cavity (101), and the filter element (3) is arranged in the structural mesh sleeve (202).

7. The concrete water retention testing system according to claim 1, characterized in that: The bottom end of the clamping cavity (101) is provided with a plurality of upward concave covers (103) along the circumferential direction, and the concave covers (103) are provided with an opening at the lower end surface of the bottom of the clamping cavity (101). The oscillator (6) is provided with a plurality of oscillation rods (601) along the circumferential direction, and each oscillation rod (601) is abutted against the inner wall of the concave cover (103) and inserted into the concave cover (103).

8. The testing method of the concrete water retention testing system according to claim 4, characterized in that: Concrete for mixing tests; Prepare multiple sets of test devices and number them; Place the concrete sample into the clamping cavity (101) of each test device and turn on the oscillator (6); Start the negative pressure system (8), connect the negative pressure to the measuring cylinder (7), and adjust the pressure of the gas line; The volume of water in the measuring cylinder (7) is read at set intervals, and the total mass of the precipitated water in the measuring cylinder (7) is weighed after the test is completed; Calculate the water extraction rate and water extraction rate of concrete; The arithmetic mean of the test values ​​of multiple samples is used as the test result to evaluate the water retention of the concrete.

9. The testing method of the concrete water retention testing system according to claim 8, characterized in that: After the negative pressure system (8) is turned on, the connection port (309) is simultaneously connected to the negative pressure so that the pressure in the clamping cavity (101), the inner cavity space of the filter element (3) and the measuring cylinder (7) decreases in sequence; After maintaining the pressure for the set time, cover the sample tube cover (12), and switch the air connection hole (1201) and the connection port (309) to connect to the positive pressure system (9); The first pressure regulating valve (11) and the second pressure regulating valve (13) are adjusted so that the pressures in the clamping chamber (101), the inner space of the filter element (3), and the measuring cylinder (7) decrease in sequence.

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