Method for testing the setting time of a cementitious material with accelerator

Abstract

The application discloses a kind of test methods of the setting time of cement-based material with accelerator.The test method described in the application carries out capillary negative pressure test to the cement-based material with accelerator after forming using capillary negative pressure testing device, obtains capillary negative pressure value, obtains the capillary negative pressure growth rate value valley value result list by differential processing to test result, when the capillary negative pressure growth rate value reaches maximum valley value, corresponding acquisition time is the end point of hydration acceleration period, that is, the initial setting time of cement-based material with accelerator, and / or the capillary negative pressure growth rate value reaches the acquisition time of second major valley value corresponding, the start point of hydration induction period, that is, the final setting time of cement-based material with accelerator.The application embeds monitoring probe into cement-based material structure with accelerator, without screening coarse particles or damaging concrete structure when testing setting time.The application does not need to set threshold when testing setting time, and is simple to operate.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of cement-based materials, and particularly relates to a method for testing the setting time of a cement-based material mixed with a rapid hardening agent. BACKGROUND

[0002] Cement rapid hardening agent is one of the important components of shotcrete material, which has the functions of accelerating the setting and hardening of cement, improving the adhesion of concrete to the surface of surrounding rock or structure repair surface, and realizing the control of volume deformation performance of loose surrounding rock and rapid repair. Compared with ordinary cast-in-place concrete, the incorporation of cement rapid hardening agent will rapidly accelerate the cement hydration reaction and promote the rapid loss of solidification and fluidity of plastic cement paste within tens of minutes, so the setting and hardening process of cement-based material mixed with rapid hardening agent is significantly different from that of ordinary cast-in-place concrete.

[0003] GB / T 35159-2017 "Rapid Hardening Agent for Shotcrete" proposes a method for testing the cement paste mixed with rapid hardening agent by using a Vicat apparatus and a penetration method, and requires that the initial setting time of qualified rapid hardening agent product is not more than 5 minutes and the final setting is not more than 12 minutes. However, this method and index value cannot effectively evaluate the setting time of shotcrete mortar or shotcrete material containing coarse and fine aggregates. For concrete systems, the methods for evaluating the setting time of ordinary cast-in-place concrete include penetration resistance method, hydration heat curve method and capillary negative pressure method, among which the penetration resistance method is more common and is also the standard test method for testing cast-in-place concrete in laboratories or engineering. When using this method, the coarse aggregates larger than 5 mm in freshly mixed concrete need to be removed by a vibrating screen to obtain the remaining cement mortar. However, compared with shotcrete concrete mixed with rapid hardening agent, it is difficult to remove the rapidly hardened concrete after spraying in actual engineering or laboratory, and the test method has strong limitations. The hydration heat curve method refers to analyzing the hydration kinetics characteristics of cement paste, and taking a certain point after the hydration latent period to the acceleration period as the initial setting and a certain point after the hydration acceleration period to the stable period as the final setting. However, when this method is used for cement-based material mixed with rapid hardening agent, the evaluation is time-consuming, lagging and the hydration kinetics of cement paste mixed with rapid hardening agent is obviously different from that of traditional cement paste (literature: Influence of Liquid Rapid Hardening Agent on Early Hydration of Portland Cement, Journal of Building Materials, Zeng Luping, 2021), which causes the initial and final setting time results of cement paste mixed with rapid hardening agent tested by this method to have obvious deviation from the setting time index value of cement paste mixed with rapid hardening agent in standard GB / T 35159-2017, and cannot truly reflect the cement-based material mixed with rapid hardening agent containing coarse and fine aggregates.

[0004] Patent CN102590483B discloses a method for testing the setting time of cement-based materials, which is aimed at testing the capillary negative pressure value development law of cement-based materials under non-bleeding, sealed curing conditions, and when it reaches a certain threshold, it is judged as initial setting or final setting, but this method does not mention the use of accelerator, and the determination of the threshold also needs to pass through the penetration resistance method, which cannot be adapted to the sprayed concrete system with rapid setting and hardening. SUMMARY

[0005] Based on the above research status and the fact that few existing technologies are aimed at testing the setting and hardening of cement-based materials with accelerators, the present application provides a method for testing the setting time of cement-based materials with accelerators, which can be used for laboratory testing of the setting time of cement-based materials with accelerators, and can also be used for non-destructive, online monitoring of the setting time of actual underground engineering sprayed concrete.

[0006] Based on a large number of experimental research results and the use of the setting time testing method proposed in patent CN102590483B, it is found that when the standard curing temperature and the surface of the test piece do not bleed, the penetration resistance of ordinary concrete or mortar and the capillary negative pressure value increase with the increase of curing time, but after the addition of accelerator, the penetration resistance of concrete increases with the increase of curing time, and there is still an induction period with gentle growth, while the capillary negative pressure value has begun to grow rapidly with the increase of curing time after the addition of accelerator, and the development laws of the two are obviously inconsistent, as shown in the accompanying drawings. Figure 1 and 2 Therefore, for cement-based materials with accelerators, the method of using capillary negative pressure method supplemented by penetration resistance correction threshold is not applicable, and the results of concrete obtained by using penetration resistance method are quite different from the results of initial and final setting time of cement paste with accelerator in GB / T 35159-2017 "Accelerator for sprayed concrete", which is widely recognized.

[0007] The present application is aimed at testing the setting and hardening performance of cement-based materials with accelerators, especially for sprayed mortar or sprayed concrete materials containing coarse and fine aggregates, the applicant has found that the development stage of hydration heat release rate of cement paste with accelerator is consistent with the development law of capillary negative pressure growth rate, and on this basis, the relationship between the capillary negative pressure growth rate of cement-based materials with accelerator and the hydration heat release stage under different cement varieties, accelerator types and water-cement ratios is studied, and a method for testing the setting time of cement-based materials with accelerator is proposed, which can be used for laboratory testing of the setting time of cement-based materials with accelerator, and can also be used for non-destructive, online monitoring of the setting time of actual underground engineering sprayed concrete.

[0008] Based on the above research status and technical principles, the technical solutions adopted by the present application are as follows:

[0009] The application provides a method for testing setting time of cement-based material doped with accelerator, and specifically comprises the following steps:

[0010] (1) Preparation before testing: firstly, before spraying the cement-based material doped with accelerator, the capillary negative pressure testing device is tied on the back of the steel arch or the vertical steel bar at the bottom of the sprayed structure by lead wire, and the probe on the capillary negative pressure testing device is placed on the back of the sprayed structure or fixed at the bottom of the cement-based material doped with accelerator, so as to avoid the continuous impact of the spraying equipment on the probe;

[0011] The probe is connected with a pressure sensor for testing the capillary negative pressure;

[0012] It is generally recognized that the cement-based material doped with accelerator is used together with the steel arch and the steel mesh as the tunnel supporting material, the steel arch or the steel mesh is used as the flexible support before spraying, and then the material is sprayed on the steel arch and the steel mesh;

[0013] (2) Preparation and molding of the cement-based material to be tested: the accelerator is doped into the cement-based material and the molding is completed;

[0014] (3) Testing of the capillary negative pressure: the capillary negative pressure testing device is used to test the capillary negative pressure of the cement-based material doped with accelerator after molding, and the capillary negative pressure value is obtained, and the differential processing of the test result is taken to obtain the capillary negative pressure growth rate value;

[0015] (4) Data collection: the capillary negative pressure testing device comprises a data collection device and a conveying device, the data collection device is first cleared, and then the spraying of the cement-based material doped with accelerator is completed, then the capillary negative pressure value of the cement-based material doped with accelerator is collected, and after the data collection time exceeds 6h, the capillary negative pressure growth rate valley value result list is fed back after program data processing, and is conveyed to the remote end through the conveying device;

[0016] In step (4), after the capillary negative pressure value of the cement-based material doped with accelerator is collected by the data collection device, real-time data analysis can be directly performed on the remote end, the first derivative of time is taken, and the capillary negative pressure peak and valley value result list is obtained;

[0017] (5) Initial and final setting time of the cement-based material: in the result list obtained in step (4), when the capillary negative pressure growth rate value reaches the maximum valley value, the collection time corresponding thereto is the end point of the hydration accelerator period, that is, the initial setting time of the cement-based material doped with accelerator, and / or when the capillary negative pressure growth rate value reaches the second largest valley value, the collection time corresponding thereto is the starting point of the hydration induction period, that is, the final setting time of the cement-based material doped with accelerator.

[0018] The technical scheme of the application is based on the following principles:

[0019] (1) When the cement accelerator is introduced into the cement paste, there is a significant hydration exothermic peak in the early hydration stage, which belongs to the hydration acceleration stage (see the attached figures in the description Figure 3 )(SALVADOR R P, CAVALARO S H P, SEGURAI, et al. Early age hydration of cement pastes with alkaline and alkali-free accelerators for sprayed concrete[J]. Construction and Building Materials, 2016, 111: 389-398.).

[0020] (2) When the cement accelerator is introduced into the cement-based material, i.e. sprayed concrete, sprayed mortar or accelerator test neat paste, the internal early capillary negative pressure growth rate has two obvious valleys in the hydration acceleration stage, which respectively correspond to the end of the hydration acceleration period and the beginning of the hydration induction period (see the attached figures in the description Figure 4 ). The engineering construction time of the accelerator-doped cement-based material is not more than 3h, which is a common knowledge in the art, so the end of the hydration acceleration period and the beginning of the hydration induction period can be regarded as the key points of the setting and hardening of the accelerator-doped cement-based material, which are hereinafter referred to as the initial and final setting times of the accelerator-doped system, corresponding to the initial and final setting time of the accelerator-doped cement paste in GB / T35159-2017 standard.

[0021] Step (1) The accelerator is a common additive in the art, including liquid alkaline accelerator, liquid alkali-free accelerator or mixture of additives with hydration acceleration effect.

[0022] Step (1) The cement-based material is a mixture with cement as the cementitious material or the main cementitious material, mainly including cement paste, mortar and concrete, and the accelerator-doped cement-based material refers to sprayed mortar, neat paste and concrete.

[0023] Step (1) The forming device of the accelerator-doped cement-based material uses engineering spraying equipment or laboratory mixer; the laboratory mixer is a common term in the art, which is a mixing device with the function of mixing cement-based materials, including cement paste mixer, cement mortar mixer and horizontal concrete mixer; the engineering spraying equipment is a spraying equipment with accelerator adding space or pipeline device, including dry spraying machine and wet spraying machine.

[0024] The testing method of the capillary negative pressure in step (3) is the prior art, and the automatic testing device for the early capillary negative pressure of the cement-based material disclosed in the patent CN100510746C can be used. The automatic testing device for the capillary negative pressure comprises a pressure sensor, a ceramic head, a gas collecting pipe, a pipe plug, a measuring cylinder, a needle, a data acquisition and transmission device, the ceramic head is arranged at the bottom of the gas collecting pipe, the pipe plug is arranged at the top of the gas collecting pipe, the ceramic head has a plurality of micro pores on the surface and in the interior, the average pore diameter of the micro pores is 0.035-1.5 μm, the pressure sensor is arranged in the measuring cylinder, and the needle arranged at the front end of the measuring cylinder extends into the gas collecting pipe through the pipe plug. The data measured by the pressure sensor is analyzed and processed by the data acquisition and transmission device. The method for testing the capillary negative pressure comprises the following steps:

[0025] a. The ceramic head is inserted into the gas collecting pipe, and the ceramic head is wetted by water, so that the micro ceramic head, the gas collecting pipe and the water in the gas collecting pipe together form a probe, and the initial pressure P0 in the probe is obtained;

[0026] b. The ceramic head at the bottom of the probe is inserted into the cement-based material, the pressure P1 in the probe is tested by the pressure sensor, and the difference between P1 and P0 is the capillary negative pressure of the cement-based material.

[0027] In order to saturate the ceramic head with water, the ceramic head must be soaked in air-free water (ordinary tap water can be used, which is heated to boiling and then heated for more than 20 minutes to cool) for more than 24 hours before use; the gas collecting pipe is a soft plastic pipe with a diameter of about 3-5 mm, corresponding to the diameter of the ceramic head; the bonding between the ceramic head and the plastic soft pipe must be tight, and air leakage must be avoided; the plastic soft pipe needs to be filled with water before the ceramic head is buried, and the pipe plug needs to be tightly plugged to prevent air leakage.

[0028] Preferably, the range of the automatic testing device for the capillary negative pressure of the cement-based material doped with the accelerator is not higher than 50 kPa, and the accuracy is not less than ±1 kPa.

[0029] The data measured by the pressure sensor is analyzed and processed by the data acquisition and transmission device, and the capillary negative pressure growth rate data result is obtained after processing. The first two peak values in the output data result correspond to the testing time, and the result is transmitted to the remote end. The data acquisition and transmission device can be a wireless monitoring system or a wired monitoring system.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] (1) Non-destructive and remote online monitoring. The present application adopts a pre-embedded monitoring probe into the cement-based material structure doped with the accelerator, and does not need to screen the coarse particles of the concrete or cause damage to the concrete structure.

[0032] (2) No need to set threshold, simple operation. The application automatically feeds back the capillary negative pressure growth rate valley value list to the user end through the data acquisition and processing system, without setting threshold according to the indoor penetration resistance method, and the operation process is simple and efficient, and the test result and the corresponding time point error of the hydration heat release peak of the cement paste without adding accelerator are within ±5 min. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The development law of the penetration resistance value and the capillary negative pressure value of the cement-based material without adding accelerator with the curing time.

[0034] Figure 2 The development law of the penetration resistance value and the capillary negative pressure value of the cement-based material with the curing time.

[0035] Figure 3 The development law of the hydration heat release rate of the cement-based material with the curing time.

[0036] Figure 4 The development law of the capillary negative pressure growth rate of the cement-based material with the curing time. DETAILED DESCRIPTION

[0037] In order to better understand the application, the content of the application will be further described below in combination with examples, but the content of the application is not limited to the range described in the examples.

[0038] The following experiments or examples in this part all use the early capillary negative pressure automatic test device for cement-based materials shown in the patent CN100510746C. The data measured by the pressure sensor are analyzed and processed by the data acquisition and transmission device, and the capillary negative pressure growth rate data results are obtained after processing. The hydration heat release peak tested in the following experiments or examples in this part uses the cement paste under the same water-cement ratio and accelerator variety as the test sample. The method for testing the hydration heat release peak includes the following steps:

[0039] a. The mass of water, cement and mineral admixture and other cementitious materials is weighed according to the set water-cement ratio. If the cementitious material is cement and mineral admixture, the cement and mineral admixture should be mixed uniformly before preparing the paste. The mixing pot and stirring blade are first wiped with a wet cloth to avoid causing water-cement ratio error. The mixed water is poured into the cement paste mixing pot, and the weighed 500g of cementitious material is carefully added into the water within 5-10 seconds to avoid material splashing. The mixing method and device refer to the standard GB / T1346-2019 <Water requirement for standard consistency of cement, setting time and stability test method>, and the automatic stirring program is used.

[0040] b. The prepared cement paste is weighed and added to the hydration heat test container. The amount of accelerator is calculated based on the amount of cement paste and the accelerator is weighed. The accelerator is added to the cement paste using a medical syringe, and the mixture is placed in an isothermal microcalorimeter. The time corresponding to the hydration heat release rate peak of the cement paste with accelerator is recorded.

[0041] To ensure that the accelerator is fully mixed with the prepared cement paste, the test container is placed in an ultrasonic device for 10 seconds after the accelerator is added. The mass of the cement paste is between 20 and 28 grams.

[0042] Example 1: Investigate the relationship between the capillary negative pressure growth rate valley and the hydration heat release peak of different types of cementitious material systems after adding different liquid accelerators. See Table 1 (cement paste + different types and amounts of accelerators).

[0043] Table 1 Relationship between capillary negative pressure growth rate valley and hydration heat release peak of cement paste after adding different types and amounts of accelerators

[0044]

[0045]

[0046] Example 2: Investigate the relationship between the capillary negative pressure growth rate valley and the hydration heat release peak of shotcrete. See Table 2 (shotcrete).

[0047] Table 2 Relationship between capillary negative pressure growth rate valley and hydration heat release peak of shotcrete

[0048]

[0049] Example 3: Investigate the comparison of capillary negative pressure growth rate valley of different cement-based materials (paste, mortar, and shotcrete) with accelerators. See Table 3 (cement-based material with water-cement ratio of 0.40, accelerator dosage of 8%).

[0050] Table 3 Relationship between capillary negative pressure growth rate valley and hydration heat release peak of different cement-based materials with accelerators

[0051]

[0052] Example 4: Investigate the relationship between the capillary negative pressure growth rate valley and the hydration heat release peak under the influence of raw materials. See Table 4 (shotcrete of different cementitious material systems).

[0053] Table 4 Relationship between capillary negative pressure growth rate valley and hydration heat release peak of cement mortar with accelerators under the influence of raw materials

[0054]

[0055]

[0056] From Table 1 to Table 4, it is found that Examples 1-4 give the corresponding time results of the capillary negative pressure growth rate valley and the hydration heat peak of the cement-based material doped with accelerator under different influencing factors, and the results all show that there is a good similar corresponding relationship between the capillary negative pressure growth rate valley and the special point of the hydration heat curve. In the case of inconvenience of using hydration heat test to test the setting time of the cement-based material doped with accelerator, the capillary negative pressure growth rate valley result can be obtained through the capillary negative pressure acquisition device, and then the setting time of the cement-based material doped with accelerator can be obtained. The test method has the advantages of in-situ, online and non-destructive testing, and the error of the setting time test result is within ±5 min. From the results of Examples 1-4, it can be known that the above-mentioned test method has good adaptability to different varieties of accelerator, different water-cement ratio shotcrete, different cement-based materials doped with accelerator, different cementitious material systems and other test systems, and has high sensitivity and strong reproducibility.

[0057] Although the present application has been described in detail by the general description, specific embodiments and experiments above, some modifications or improvements can be made on the basis of the present application, which is obvious to those skilled in the art. Therefore, these modifications or improvements made on the basis of not deviating from the spirit of the present application all belong to the scope of the present application claimed.

Claims

1. A method of testing the setting time of a set accelerator doped cementitious material, characterized in that, Specifically comprises: (1) the preparation before test: first, before the spraying construction of the cement-based material mixed with accelerator, the capillary negative pressure test device is tied on the back of the steel arch or the vertical steel bar at the bottom of the spraying before spraying, and the probe on the capillary negative pressure test device is placed on the back of the structure affected by spraying or fixed at the bottom of the cement-based material mixed with accelerator, and the probe is connected with a pressure sensor; (2) preparation and molding of the cement-based material to be tested: mixed accelerator into cement-based material and molding is completed; (3) capillary negative pressure test: capillary negative pressure test device is used to test the capillary negative pressure of the mixed accelerator cement-based material after molding, and the capillary negative pressure value is obtained, and the test result is differentiated to obtain the capillary negative pressure growth rate value; (4) data acquisition: the capillary negative pressure test device includes data acquisition device and conveying device, first, the data acquisition device is cleared, then the mixed accelerator cement-based material is sprayed, then the capillary negative pressure value of the mixed accelerator cement-based material is collected, after the data acquisition time is more than 6h, the capillary negative pressure growth rate valley value result list is fed back after program data processing, and is conveyed to the remote end through the conveying device; (5) initial and final setting time of cement-based material: in the result list obtained in step (4), when the capillary negative pressure growth rate value reaches the maximum valley value, the collection time corresponding to the maximum valley value is the end point of the hydration accelerator period, that is, the initial setting time of the cement-based material mixed with accelerator, and / or the collection time corresponding to the second largest valley value of the capillary negative pressure growth rate value is the starting point of the hydration induction period, that is, the final setting time of the cement-based material mixed with accelerator.

2. The method for testing the setting time of a cementitious material doped with accelerator according to claim 1, characterized in that, The accelerator in step (1) is a liquid alkaline accelerator, a liquid non-alkaline accelerator or a mixture of external additives with hydration accelerator effect.

3. The method for testing the setting time of a cementitious material doped with accelerator according to claim 1, characterized in that, The cement-based material in step (1) is a mixture of cement as cementitious material or main cementitious material, and the mixed accelerator cement-based material is sprayed mortar, sprayed neat cement paste or sprayed concrete.

4. The method of claim 1, wherein the method is characterized by: The molding device of the mixed accelerator cement-based material in step (1) uses engineering spraying equipment or laboratory mixer, the laboratory mixer is a mixing equipment with mixed cement-based material function, and the engineering spraying equipment is a spraying equipment with accelerator adding space or pipeline device.

5. The method of claim 4, wherein the method is characterized by: The laboratory mixer includes cement paste mixer, cement mortar mixer and horizontal concrete mixer; the engineering spraying equipment includes dry spraying machine and wet spraying machine.

6. The method of claim 1, wherein the method is characterized by: The capillary negative pressure automatic test device used in the capillary negative pressure test method in step (3) includes pressure sensor, ceramic head, gas collecting pipe, pipe plug, measuring cylinder, needle and data acquisition and conveying device, the ceramic head is installed at the bottom of the gas collecting pipe, and the pipe plug is arranged at the top of the gas collecting pipe; the pressure sensor is installed in the measuring cylinder, and the needle installed at the front end of the measuring cylinder penetrates through the pipe plug and extends into the gas collecting pipe; the capillary negative pressure test method comprises the following steps: a. fill the gas collecting pipe with water to wet the ceramic head, and the completely water-saturated micro ceramic head, the gas collecting pipe and the water in the gas collecting pipe together constitute the probe, and the initial pressure P0 in the probe is obtained; b. Insert the ceramic head at the bottom of the probe into the cement-based material, test the pressure P1 in the probe through the pressure sensor, and the difference between P1 and P0 is the capillary negative pressure of the cement-based material.

7. The method of claim 6, wherein the method is characterized by, The range of the automatic capillary negative pressure testing device for the cement-based material doped with the accelerator is not higher than 50 kPa, and the accuracy is not lower than ±1 kPa.

8. The method according to any one of claims 1 to 7, wherein the method is a method for testing the setting time of a cementitious material doped with a set accelerator, characterized in that, The data acquisition and transmission device is a wireless monitoring system or a wired monitoring system.

9. The method of claim 1, wherein the method is characterized by: After the capillary negative pressure value of the cement-based material doped with the accelerator is acquired by using the data acquisition device in step (4), the remote end is directly connected for real-time data analysis, the first derivative of time is taken, and a peak-valley value result list of the capillary negative pressure is obtained.

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