Method for testing self-drying effect of cement-based material with low water-binder ratio

Abstract

The invention discloses a method for testing the self-drying effect of a low-water-binder-ratio cement-based material, which comprises the following steps of: dividing the shrinkage process of the low-water-binder-ratio cement-based material into three stages, namely a stage before staged expansion, a stage of staged expansion and a stage after staged expansion, and respectively testing the self-shrinkage of the cement-based material and the negative pressure and humidity of an internal capillary tube, so as to test the self-drying effect of the cement-based material. And representing the relative humidity before staged expansion, the relative humidity at the staged expansion stage and the relative humidity after the corrected staged expansion in stages, and integrating the relative humidity at the three stages to draw a complete relative humidity curve graph. By means of the testing method, the relative humidity change in the staged expansion stage is corrected, the influence of external factors on the relative humidity testing result is reduced, and the relative humidity change curve of the low-water-binder-ratio cement-based material in the whole shrinkage period can be truly reflected; the method is better used for shrinkage mechanism analysis and theoretical prediction based on relative humidity.

Description

Technical Field

[0001] The present invention relates to the technical field of performance testing of cement-based materials, and particularly relates to a method for testing the self-drying effect of cement-based materials with a low water-binder ratio. Background Art

[0002] The chemical reaction between cement and water is a process of overall volume reduction, that is, the overall volume of hydration products is less than the overall volume of reactants. When the internal skeleton of the cement-based material is basically formed and the solid-phase particles lose the ability of free deformation, further hydration will cause the water inside the cement-based material to change from a saturated state to an unsaturated state, thereby resulting in a decrease in the internal relative humidity (less than 100%), which is the self-drying effect. The self-drying effect is the main reason for the self-shrinkage of cement-based materials. The lower the water-binder ratio (the mass ratio of water to binder) of the cement-based material, the more obvious the self-drying effect and the greater the self-drying shrinkage generated. Taking concrete in actual engineering as an example, the self-drying shrinkage of concrete with a water-binder ratio of 0.30 can account for more than 50% of the total shrinkage, and the self-drying shrinkage of concrete with a water-binder ratio of less than 0.20 can account for more than 80% of the total shrinkage. Self-drying shrinkage has become one of the important reasons for shrinkage cracking of cement-based materials with a low water-binder ratio.

[0003] Precisely testing the change of internal relative humidity of cement-based materials is the key to studying the self-drying effect and establishing a self-drying shrinkage model. In terms of specific humidity testing, currently, a hygrometer is mainly used for testing. However, since the internal humidity of concrete is at a very high stage in the early stage, it is difficult for the hygrometer to test the humidity change at this stage, especially in the stage before the final setting of the cement-based material (the relative humidity in this stage is usually above 99%). Testing the early relative humidity and how to effectively connect the early relative humidity with the results of later hygrometer testing are key problems that need to be solved urgently.

[0004] The Chinese invention patent with the publication number CN101539566B discloses a method for testing the early capillary negative pressure of concrete based on the principle of a tensiometer, providing a technical approach for exploring the self-drying shrinkage mechanism of high-performance concrete at the earliest stage. On this basis, the Chinese invention patent with the publication number CN102539475B discloses a method for testing the self-drying effect of cement-based materials. During the period from the time when the cement-based material is formed by adding water to the final setting, the capillary negative pressure is measured by a capillary negative pressure tester, and then the capillary negative pressure is converted into relative humidity by using relevant formulas; during the period from after the final setting of the cement-based material to 1 day after adding water for forming, the dew point temperature inside the cement-based material is measured by a dew point thermometer, and then the relative humidity inside the cement-based material is calculated by using relevant formulas; during the period after 1 day of adding water for forming the cement-based material, the relative humidity inside the cement-based material is measured by a hygrometer.

[0005] The main problems existing in the above method during application are as follows: The capillary negative pressure test results are less affected by ions in the pore solution of cement-based materials, while the test results of dew point thermometers and hygrometers are more affected by ions in the pore solution. It is relatively difficult to connect the test results of the three methods; for cement-based material systems with a water-binder ratio less than 0.30, there is a stage of expansion during the autogenous drying shrinkage test, and the existing test methods are difficult to solve the above phenomenon. In addition, near a capillary negative pressure of 100 kPa, a gasification effect will occur inside the cement-based material (under the action of negative pressure, the liquid water in the pores is converted into gas phase), and the capillary negative pressure test value will rapidly decrease, making it difficult to characterize the capillary negative pressure during the above-mentioned stage of expansion. Summary of the Invention

[0006] To solve the above problems, the present invention provides a test method for the autogenous drying effect of low water-binder ratio cement-based materials, which can accurately characterize the autogenous drying effect inside low water-binder ratio cement-based materials with a water-binder ratio of 0.30 and below. By combining methods such as autogenous drying shrinkage of cement-based materials, capillary negative pressure, and humidity measurement by hygrometer, it realizes the effective connection of the capillary negative pressure test results and the hygrometer test results. At the same time, it corrects the stage of expansion during the autogenous shrinkage process of cement-based materials, reduces the influence of external factors on the phase, and truly reflects the relative humidity change curve of the entire shrinkage cycle.

[0007] The present invention adopts the following technical solutions: A test method for the autogenous drying effect of low water-binder ratio cement-based materials, comprising the following steps: S1. Mold at least two groups of cement-based material test specimens with the same size and composition, which are respectively used to test the autogenous shrinkage of the specimens, the capillary negative pressure inside the specimens, and the humidity of the specimens; S2. Determine the stage of expansion according to the test results of the autogenous shrinkage rate of the specimens, and determine the moment when expansion starts and the moment when the expansion reaches the peak ; S3. Determine the capillary negative pressure at the moment according to the test results of the capillary negative pressure inside the specimens, and calculate the relative humidity at the moment and at the moments before ; the moment ; S4. Determine the capillary negative pressure at the moment and the relative humidity at the moment, and calculate the relative humidity during the stage of expansion between the moment and the moment ; S5. Set a relative humidity adjustment coefficient, and correct the relative humidity at the moments after according to the specimen humidity results measured by the hygrometer and the adjustment coefficient; S6. After setting the relative humidity adjustment coefficient, correct the relative humidity at the moments after S6. Time and the relative humidity at the previous time, to the relative humidity at the time, time and the relative humidity at the subsequent time are integrated to obtain a complete relative humidity curve.

[0008] The autogenous shrinkage of the cement-based material test specimen is tested to form an autogenous shrinkage curve graph. According to the autogenous shrinkage test results, the stage of periodic expansion is determined. This stage is mainly manifested as follows: during the test, the cement-based material first shows shrinkage; at a certain time point , the cement-based material begins to show a certain amount of expansion. At time, the expansion reaches the peak. After that, the cement-based material further shows shrinkage; the stage from when the cement-based material begins to show expansion to when the expansion reaches the peak is the stage of periodic expansion.

[0009] Preferably, the method for testing the capillary negative pressure inside the specimen is as follows: when forming the test specimen, a capillary negative pressure test probe is buried inside the cement-based material to test the change of the capillary negative pressure inside the test specimen.

[0010] Preferably, the autogenous shrinkage and the internal capillary negative pressure of the specimen can be tested on the same test specimen or on different specimens separately. When tested on different specimens separately, the specimens are formed separately and uniformly.

[0011] Preferably, the method for testing the humidity of the specimen is as follows: a test specimen identical to the above autogenous shrinkage test specimen is formed. At the initial setting time, the specimen is taken out and broken, and the broken fragments are placed into a container. A humidity sensor is inserted and sealed to test the humidity of the specimen.

[0012] Specifically, the fragments are screened with a sieve to select fragments of 2.36 - 4.74 mm, and the fragments are placed into a metal container. Then a humidity sensor is inserted and sealed for humidity testing.

[0013] Preferably, according to the autogenous shrinkage test results of the cement-based material, the time period before the cement-based material begins to undergo periodic expansion is selected. According to the capillary negative pressure test results in this stage, the capillary negative pressure at time is determined. The relative humidity RH(t0) at this time is calculated using the following formula (1): The relative humidity RH(t) at the previous time is also calculated according to formula (1): (1); wherein, is the relative humidity value at is time and Previous moment; is the capillary negative pressure test value; is the molar mass of water; is the density of water; is the universal gas constant; is the absolute temperature.

[0014] Furthermore, according to the autogenous shrinkage test results of cement-based materials, determine the moment of the stage expansion stage, and set the capillary negative pressure at the moment, and calculate the relative humidity at the moment through formula (1), and then calculate the relative humidity at the moment of the stage expansion stage through the following formula (2): (2); wherein, is the relative humidity at the moment; is the relative humidity at the moment; is the relative humidity at the moment; is the autogenous shrinkage value at the moment; is and the moment between; , are respectively the moment, the autogenous shrinkage values at the moment.

[0015] Furthermore, set the capillary negative pressure at the moment to be constantly 100 kPa, and calculate that the relative humidity at the moment is 99.926% according to formula (1), and calculate the relative humidity at different moments of the stage expansion stage through formula (2).

[0016] When the capillary negative pressure reaches 100 kPa, a gasification effect will occur inside the cement-based material. However, due to the existence of ions, microbubbles, etc. in the pore solution, the capillary negative pressure at the time when gasification starts will decrease, that is, gasification starts when it is lower than 100 kPa, and the moment of occurrence corresponds to the moment in the present invention, and gasification ends when it reaches 100 kPa. The stage from the start of gasification to the end of gasification inside the cement-based material is the stage expansion stage. Therefore, set the capillary negative pressure at the moment to be constantly 100 kPa. This capillary negative pressure corresponds to the vertex of the stage expansion in time, that is, the time point when the gasification effect ends.

[0017] Further, based on the humidity test results measured by the hygrometer, the relative humidity at a subsequent moment is corrected according to the coefficient by the following formula (3): (3); wherein, is the relative humidity at moment is the subsequent moment; is the result of the humidity test by the hygrometer at moment; is the relative humidity at t1 moment; is the result of the humidity test by the hygrometer at moment, and the ratio of is the correction coefficient.

[0018] Particularly, being constantly 99.926%, formula (3) can be expressed as: (4).

[0019] Further, after calculating the relative humidity at the moment before the stage expansion, the relative humidity at the moment during the stage expansion, and the relative humidity at the moment after the stage expansion respectively, the relative humidity curve graphs of the three stages are integrated to draw a complete relative humidity curve graph, and the self - drying effect curve of the cement - based material in the whole cycle can be reflected by the corrected relative humidity curve graph.

[0020] Compared with the prior art by adopting the above technical solutions, the present invention has the following technical effects: 1. The method of the present invention divides the self - drying effect test process into three stages, namely before the stage expansion occurs, during the stage expansion, and after the stage expansion, which can realize the phased characterization of the relative humidity; and the humidity test results of the three stages can be well docked, and then a complete self - drying effect curve is drawn.

[0021] 2. The humidity test results of the first two stages of the present invention are all obtained by conversion or fitting based on the capillary negative pressure results, while the humidity test results of the hygrometer are corrected based on the stage expansion effect. Therefore, the obtained humidity test results reduce the influence of factors such as ion concentration on the relative humidity, and can be better used for the shrinkage mechanism analysis and theoretical prediction based on the relative humidity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram of the principle of the self - drying effect test method for low - water - binder - ratio cement - based materials of the present invention; Figure 2Flow chart of the self - drying effect test method for low water - binder ratio cement - based materials of the present invention; Figure 3 Self - shrinkage test results of concrete in the embodiment of the self - drying effect test method for low water - binder ratio cement - based materials of the present invention; Figure 4 Capillary negative pressure test results of concrete in the embodiment of the present invention; Figure 5 Relative humidity results measured by a hygrometer in the embodiment of the present invention; Figure 6 Complete curve of the internal humidity change of concrete drawn after correction in the embodiment of the present invention. Detailed implementation manners

[0023] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0024] Embodiment 1

[0025] In this embodiment, the ambient temperature is 20 ± 1 °C, and the cement - based concrete with a water - binder ratio of 0.30 (kg / m 3 ) raw material ratio (number "C0.30"), the cement is Anhui Conch P·Ⅱ 52.5 cement, the gravel is basalt gravel with a particle size of 5 - 10 mm, the sand is natural river sand with a fineness modulus of 2.60, and the water - reducing agent is a polycarboxylate water - reducing agent from Jiangsu Sobute New Materials Co., Ltd., as shown in Table 1 below.

[0026] Table 1

[0027] As Figure 1 shown, the relative humidity of the cement - based concrete is characterized in 3 stages, and the self - drying effect test of the low water - binder ratio cement - based material is carried out by the method of the present invention. The method is as Figure 2 shown, and the specific steps are as follows: Mold 5 test specimens with exactly the same size. Among them, 3 test specimens are used to test the self - shrinkage of the concrete according to the non - contact method of the shrinkage experiment in the national standard GB / T 50082 - 2009 "Standard for Test Methods of Long - Term Performance and Durability of Ordinary Concrete", and form a self - shrinkage curve graph as Figure 3 shown.

[0028] A capillary negative pressure test probe was embedded in the 4th test specimen to measure the capillary negative pressure in the concrete. The capillary negative pressure test device and method are as follows: The capillary negative pressure test probe consists of a ceramic head, a gas collecting pipe, and a pipe plug. The ceramic head is installed at the bottom of the gas collecting pipe, and the pipe plug is provided at the top. The surface and interior of the ceramic head have tiny pores with a pore diameter of 0.01 - 0.035 μm. The capillary negative pressure test probe is connected to a measuring cylinder through a needle. The needle installed at the front end of the measuring cylinder passes through the pipe plug and extends into the gas collecting pipe. A pressure sensor is installed inside the measuring cylinder. The ceramic head, the needle, the measuring cylinder, and the pressure sensor form a tensiometer; the pressure sensor is connected to a computer through a transmitter and an A / D converter in sequence. The signal of the pressure sensor is transmitted to the A / D converter through the transmitter, and the signal output from the A / D converter is sent to the computer for analysis and processing.

[0029] The specific method for testing the capillary negative pressure is as follows: Fill the gas collecting pipe with water to wet the ceramic head, obtaining the initial pressure P0 inside the probe; Insert the ceramic head at the bottom of the probe into the cement-based concrete, and measure the pressure P1 inside the probe through the pressure test device. The difference between P1 and P0 is the capillary negative pressure of the concrete.

[0030] The capillary negative pressure test results are formed into a capillary negative pressure curve as Figure 4 shown.

[0031] After the 5th test specimen has initial set, break the test specimen into pieces, and then select the paste fragments of 2.36 - 4.74 mm using a square-hole sieve. Vertically insert a hygrometer into the center of a metal container with a diameter of 10 cm and a height of 10 cm, then pour the cement paste fragments around the hygrometer and seal them with a plastic film and aluminum foil to measure the humidity of the test specimen and form a humidity curve as Figure 5 shown.

[0032] The model of the hygrometer used is Rotronic HC2A-S, and the humidity test accuracy is not greater than 0.8%.

[0033] As Figure 3 the autogenous shrinkage test curve, according to the autogenous shrinkage test results, determine the stage of expansion and determine the start time of the stage of expansion ; the time when the stage of expansion reaches the peak .

[0034] As Figure 4 the internal capillary negative pressure test curve, according to the determined time points t0 and t1, determine that the capillary negative pressure at the moment is 82.43 kPa, and calculate according to formula (1) the relative humidity at the moment is 99.939%.

[0035] According to the capillary negative pressure test results, calculate the relative humidity at the time before t0 according to formula (1).

[0036] In the stage of staged expansion, according to Figure 3 the autogenous shrinkage curve, according to the determined and time points, determine the autogenous shrinkage value at the moment is -101.273×10 -6 , the autogenous shrinkage value at the moment is -105.179×10 -6 , substitute into formula (2) to obtain the following formula (5), and calculate according to formula (5) to the relative humidity values at different moments between the moments: (5).

[0037] At the moment after the stage of staged expansion, that is, the moment after, referring to Figure 5 , based on the relative humidity test results, read the humidity measured at the moment is 99.312%, and the correction coefficient is obtained as 1.006 according to formula (4), and multiply the humidity meter test results by this coefficient for correction.

[0038] As Figure 6 shown, integrate the corrected relative humidity curve before staged expansion, the relative humidity curve in the stage of staged expansion, and the relative humidity curve after staged expansion, and draw a complete relative humidity curve graph.

[0039] Example 2

[0040] In this example, the ambient temperature is 20±1°C, and the raw material ratio of cement-based concrete with a water-cement ratio of 0.17 (kg / m 3 ), silica fume is Elkem microsilica, cement is Anhui Conch P·Ⅱ 52.5 cement, crushed stone is basalt crushed stone with a particle size of 5~10 mm, sand is natural river sand with a fineness modulus of 2.60, and the water reducing agent is polycarboxylate water reducing agent of Jiangsu Sobute New Materials Co., Ltd., as shown in Table 2 below.

[0041] Table 2

[0042] Furthermore, the relative humidity of the cement-based concrete is characterized in 3 stages.

[0043] Five test specimens of exactly the same size were formed, of which three test specimens were tested for concrete shrinkage using the bellows method. The bellows method test device and method are as follows: the bellows method test device includes a magnetic suction cup, a non-contact displacement sensor, a bellows mold, a test bracket, a bellows packaging end, a hanging chain, a pressure-relief airbag, a plastic tube and a rubber plug; the magnetic suction cup and the non-contact displacement sensor are respectively mounted on the side panels on both sides of the test bracket, the bellows packaging end includes a fixed end packaging end and a movable end packaging end, which are respectively mounted on both sides of the bellows mold, the fixed end packaging end is provided with a vent hole, and when the bellows packaging end is matched with the bellows mold, the vent hole is connected to the inside of the bellows mold; the pressure-relief airbag is connected to one end of the plastic tube, and the other end of the plastic tube passes through the rubber plug, the rubber plug can form a tight fit with the vent hole of the fixed end packaging end, and the pressure-relief airbag, the plastic tube, the vent hole and the bellows mold form an internally connected structure; the hanging chain is suspended on the hanging rod of the test bracket.

[0044] The self-drying effect test of low water-binder ratio cement-based materials is carried out by the method of the present invention, and the specific steps are as follows: 1. Install the magnetic suction cup and non-contact displacement sensor on the test bracket, match 5 to 30 hanging chains of the same specifications with the hanging rod of the test bracket, and evenly distribute them according to the corrugation spacing of the bellows mold to ensure that the test bracket is firmly placed without shaking or vibration.

[0045] 2. Match the test end packaging terminal with the bellows mold, stand the bellows mold with the opening facing upward, and load the cement-based concrete slurry into the bellows mold. During the loading process, stretch the bellows mold by 20 to 40 mm. When the cement-based concrete sample is loaded to the bellows mold with a remaining height of 30 to 50 mm, match the fixed end packaging terminal with the bellows mold, and slowly put the stretched bellows mold back to its original length. During this process, the air in the bellows mold is discharged through the vent, and the remaining air inside is 10 to 20 mm. The pressure-relief airbag is matched with the vent through a plastic tube and a rubber plug. The pressure-relief airbag is connected to the inside of the bellows mold. Place the bellows mold horizontally with the vent at 12 o'clock. Gently vibrate to move the remaining gas in the bellows mold to the upper part of the bellows mold, so that the corrugations of the bellows mold are connected through the air at the upper part.

[0046] 3. Place the corrugated pipe mold containing the cement-based material sample on the hanging chain, and make sure that the vent is located at the 12 o'clock position. Adjust the magnetic suction cup up and down to form a magnetic link between the magnetic suction cup and the center of the fixed end package end. Fix the magnetic suction cup, and then adjust the non-contact displacement sensor up and down to align it with the center of the test end package end. Fix the non-contact displacement sensor and start the deformation test of the cement-based material.

[0047] 4. During the testing process, the pressure-relieving airbag will undergo varying degrees of volume change as the corrugated pipe mold contracts or expands, thereby keeping the internal air pressure of the corrugated pipe mold always equal to the test environment air pressure.

[0048] 5. Calculation of test results: Assume that the microstrain value of the cement-based material at time is A, the initial length of the corrugated pipe mold filled with the cement-based material is L, its initial test reading is A0, and the test reading is A1. Then A = (A1 - A0) / L·10 -6 .

[0049] Form the autogenous shrinkage test results into an autogenous shrinkage curve graph as Figure 3 shown.

[0050] According to the test method in Example 1, test the capillary negative pressure in the cement-based concrete and form a capillary negative pressure curve graph as Figure 4 shown.

[0051] According to the method in Example 1, use a hygrometer to test the internal humidity of the cement-based concrete.

[0052] As Figure 3 the autogenous shrinkage test curve, based on the autogenous shrinkage test results, determine the stage of expansion and the start time of the stage of expansion ; the time when the stage of expansion reaches the peak .

[0053] As Figure 4 the internal capillary negative pressure test curve, based on the determined time points t0 and t1, determine that the capillary negative pressure at time t0 is 81.10 kPa, and calculate according to formula (1) the relative humidity at time is 99.940%.

[0054] According to the capillary negative pressure test results, calculate the relative humidity at times before t0 according to formula (1).

[0055] During the stage of expansion, referring to Figure 3 the autogenous shrinkage curve, based on the determined and time points, determine that the autogenous shrinkage value at time is -390.577×10 -6 , the autogenous shrinkage value at -6 time is -406.443×10 to the relative humidity values at different times between (6)

[0056] At the moment after the stage of staged expansion, that is At the moment after that, referring to Figure 5 , based on the relative humidity test results, read The humidity value measured at the moment is 98.183%. According to formula (4), the correction factor is obtained as 1.018, and the test results of the hygrometer are multiplied by this factor for correction.

[0057] As Figure 6 shown, the corrected relative humidity curve before staged expansion, the relative humidity curve during the staged expansion stage, and the relative humidity curve after the staged expansion are integrated to draw a complete relative humidity curve graph.

[0058] Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can make many specific transformations in form without departing from the spirit of the invention and the scope protected by the claims. All of these fall within the protection scope of the present invention.

Claims

1. A test method for the self-desiccation effect of cement-based materials with a low water-cement ratio, characterized in that, Including the following steps: S1. Mold at least two groups of cement-based material test specimens with the same size and composition, which are respectively used to test the autogenous shrinkage of the specimens, the capillary negative pressure inside the specimens, and the humidity of the specimens; S2. Determine the phased expansion stage based on the test results of the self-shrinkage rate of the sample, and determine the moment when expansion begins and the moment when the expansion reaches its peak ; S3. Determine the capillary negative pressure at according to the test results of the capillary negative pressure inside the sample, and calculate the relative humidity at this moment and the moments before S4. Determine the capillary negative pressure at the moment and the relative humidity at the moment, and calculate the relative humidity during the phased expansion process from the moment to the moment; S5. Set the relative humidity adjustment coefficient and correct the relative humidity at a subsequent moment based on the humidity result of the sample measured by the hygrometer and the adjustment coefficient. The relative humidity at a subsequent moment; S6. Integrate the relative humidity at the moment and the relative humidity at the moment before, from the relative humidity at the moment to the moment and the relative humidity at the moment after to obtain a complete relative humidity curve.

2. The self-desiccation effect test method for low water-binder ratio cement-based materials according to claim 1, wherein The method for testing the capillary negative pressure inside the specimens is as follows: When molding the test specimens, bury capillary negative pressure test probes inside the cement-based materials to test the capillary negative pressure inside the specimens.

3. The test method for the autogenous drying effect of a low water-binder ratio cement-based material according to claim 2, characterized in that The capillary negative pressure inside the specimens and the autogenous shrinkage of the specimens are tested on the same cement-based material test specimen.

4. The test method for the self-desiccation effect of the low water-binder ratio cementitious material according to claim 2, wherein The capillary negative pressure inside the specimens and the autogenous shrinkage of the specimens are respectively tested on separately molded and identical different cement-based material test specimens.

5. The self-desiccation effect test method for low water-binder ratio cement-based materials according to claim 1, wherein, The method for testing the humidity of the specimens is to mold the test specimens. When the cement-based materials start to set, take out the specimens and break them. Place the broken fragments into a metal container, insert a humidity sensor and seal it to test the humidity of the specimens.

6. The self-desiccation effect test method for low water-binder ratio cement-based materials according to claim 5, characterized in that The size of the selected fragments is 2.36~4.74 mm.

7. The test method for the autogenous drying effect of a low water-cement ratio cementitious material according to claim 1, characterized in that In step S3, calculate the relative humidity at the moment and at the previous moment, and the formula is: ； Among them, is the relative humidity value at the moment, is the moment and the moments before; is the capillary negative pressure test value; is the molar mass of water; is the density of water; is the universal gas constant; is the absolute temperature.

8. The test method for the self-drying effect of the low water-binder ratio cement-based material according to claim 7, wherein, In step S4, determine the relative humidity at the moment: Set the capillary negative pressure at the moment to 100 kPa. The gasification effect occurs inside the cement-based material, generating a phased expansion. According to the method in step S3, calculate the relative humidity at the moment.

9. The self-desiccation effect testing method for low water-binder ratio cement-based materials according to claim 8, characterized in that In step S4, calculate the relative humidity during the phased expansion process from the moment to the moment, and the formula is: ； Among them, is the relative humidity at time is the relative humidity at time is the relative humidity at time is the autogenous shrinkage value at time is and the time between and are respectively the autogenous shrinkage values at time and time 10. The test method for the self-desiccation effect of the low water-binder ratio cement-based material according to claim 9, characterized in that, In step S5, correct the relative humidity at a later time, and the formula is: ； Among them, is the relative humidity at a moment, is the moment after that; is the result of humidity measurement by the hygrometer at the moment; is the relative humidity at the moment t1; is the result of humidity measurement by the hygrometer at the moment, and the ratio of is the correction coefficient.

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