Method for calibrating expiration degree of expired cement

Abstract

The invention provides a method for calibrating the expiration degree of expired cement, which is used for calculating and calibrating the expiration degree of the cement by simulating the expiration condition of the cement and measuring the mass, the particle size and the uniaxial compressive strength of the cement. According to the calibrated expiration degree, the optimal use amount of the active material can be determined, the optimal recovery effect on the expired cement strength is achieved, and the pollution of construction waste to the environment is effectively reduced. The method has the advantages of realizing the maximum utilization of the active material, reducing the economic cost, realizing the optimal optimization, reducing the environmental pollution and the like.

Description

Technical Field

[0001] This invention relates to the field of expired cement treatment and expired cement degree calibration, and particularly to a method for treating expired cement and a method for calibrating the expired cement degree. Background Technology

[0002] Cement, as a crucial building material, possesses characteristics such as corrosion resistance, high-temperature resistance, and earthquake resistance, and is widely used in industrial and civil construction, transportation engineering, water conservancy projects, port engineering, national defense construction, and other emerging industrial and engineering projects. However, most cement on the market has a shelf life of only three months. Expired cement experiences a decrease in strength, viscosity, and hardness, rendering it unusable and leading to significant waste. Furthermore, when cement absorbs moisture, the surface of the particles hydrates and clumps, resulting in reduced strength and even loss of its binding capacity. Even under good storage conditions, cement absorbs moisture and carbon dioxide from the air, undergoing slow hydration and carbonization, further reducing its strength. This unusable cement, having lost its energy efficiency, becomes construction waste, causing significant environmental damage.

[0003] Currently, my country suffers from severe pollution from discarded construction materials. It is estimated that the annual amount of urban construction waste generated in my country exceeds 2 billion tons, approximately eight times the amount of household waste, accounting for about 40% of the total urban solid waste. This construction waste not only occupies a large amount of land, but improper disposal can also pollute groundwater, soil, and air. To effectively mitigate construction waste pollution, we considered utilizing the properties of reactive materials to restore the mechanical properties of materials and enhance the strength of expired cement. However, the addition of reactive materials should not be indiscriminate. Reactive materials are relatively expensive, and considering economic costs, their indiscriminate addition is not advisable. Furthermore, the addition of reactive materials requires an appropriate dosage; too much or too little will not achieve the optimal strength restoration effect for expired cement. Summary of the Invention

[0004] The purpose of this invention is to provide a method for calibrating the degree of expiration of expired cement. Based on the calibrated degree of expiration of the cement, an appropriate amount of active material can be selected, which is conducive to achieving the best restoration effect on the strength of expired cement, effectively reducing the pollution of construction waste to the environment, and maximizing benefits.

[0005] To achieve the above objectives, the following technical solution will be adopted: a method for calibrating the degree of expiration of expired cement, including weighing unexpired cement and measuring the mass M and uniaxial compressive strength f(u) of the unexpired cement.

[0006] Unexpired cement was mixed with n different masses of water and left in a dry environment for a predetermined number of days to obtain n groups of expired cement. The mass M of the i-th group of expired cement was measured. iThe maximum particle size d of the granulated particles of the i-th group of expired cement. i , i = 1, 2, ..., n.

[0007] Cement was prepared into specimens, and the uniaxial compressive strength X of the i-th group of expired cement was determined. i , i = 1, 2, ..., n.

[0008] Calculate and label the degree of expiration A(0) of expired cement according to the following formula. <A<1):

[0009] A*f(u)=(a+b)X i

[0010] Where a represents the correlation coefficient of expired cement quality, b is the correlation coefficient of particle size, and a = (M i -M) / M, b=d i a<1, b<1 and a+b<1; the unit of mass is g, the unit of uniaxial compressive strength is MPa, and the unit of maximum particle size is m.

[0011] The value of A reflects the proportional relationship between the strength change of expired cement and the strength of unexpired cement. The closer A is to 1, the closer the strength of the expired cement is to its strength before expiration, indicating a lower degree of expiration. Conversely, the smaller A is than 1, the greater the difference between the strength of the expired cement and its strength before expiration, indicating a higher degree of expiration. The degree of expiration of expired cement is categorized into the following ranges: 0.8 ≤ A ≤ 1.0, indicating a mild degree of expiration; 0.6 ≤ A < 0.8, indicating a moderate degree of expiration; and A < 0.6, indicating a severe degree of expiration.

[0012] Preferably, during the preparation of expired cement, the amount of water added to different groups is arranged in a certain gradient to expire the previously unexpired cement. Because cement is sensitive to water, a small gradient range is set. Starting with the first group, the amount of water added to each subsequent group increases in a gradient of m. That is, the amount of water added to the first group is the initial amount, the amount added to the second group is the initial amount + 1m, the amount added to the third group is the initial amount + 2m, and so on, where m = 5g. Starting from the initial amount, the first group adds V1 water, mixes it with the previously unexpired cement, and places it in a dry environment for a predetermined number of days to obtain the first group of expired cement. Its mass M1 and the maximum particle size d1 after granulation are measured, and specimens are prepared to determine the uniaxial compressive strength X1. The second group adds V2 water, and the same process is followed to obtain M2, d2, and X2; and so on, until n groups of experiments are completed.

[0013] Preferably, the predetermined number of days is 7-10 days. This duration allows the unexpired cement to undergo sufficient physicochemical reactions with water, resulting in noticeable performance changes, without causing an excessively long experimental period. During these 7 days, the cement's hydration reaction continues, and the presence of moisture causes its internal structure to gradually change, thereby affecting the cement's various performance indicators.

[0014] A method for activating expired cement further includes adding different amounts of active material to the expired cement according to a specified degree of expiration, and determining the optimal amount of active material by measuring the performance of freshly mixed concrete specimens. Activation is performed using the method described in claim 1, based on calculation A.

[0015] Fly ash, mineral powder, silica fume, metakaolin, and other active materials can enhance the density and durability of concrete, and optimize its workability and mechanical properties. However, in improving the performance of expired cement, nano-magnesium hydroxide outperforms other active materials. Therefore, this study selected nano-magnesium hydroxide as the active additive. The amount of nano-magnesium hydroxide added was determined based on the calculated A value. When 0.8 ≤ A ≤ 1.0, it indicates a small decrease in cement performance, requiring the addition of 2%-3% of the expired cement mass as active material. When 0.6 ≤ A < 0.8, it means that the cement performance has decreased to some extent, requiring the addition of 3%-4% of the expired cement mass as active material. If A < 0.6, it indicates that the cement is severely expired, with hardening, component deterioration, etc., and even adding active materials will hardly restore its performance; its use should be prohibited to avoid affecting the quality of the project.

[0016] Preferably, the active material is nano-magnesium hydroxide.

[0017] After determining the degree of cement expiration, the expired cement is divided into different groups according to its expiration degree. Different amounts of the same magnesium hydroxide are added to each group to prepare fresh concrete, which is then used to make a certain number of test specimens. After the specimens have cured, various properties are measured. By comparison, the group with the best performance can be determined, thus establishing the optimal dosage of active material for that degree of expiration. Through extensive experiments, the optimal dosage of active material for different degrees of expiration in expired cement can be obtained.

[0018] Compared with the prior art, the present invention has at least the following advantages:

[0019] 1. Maximizing the utilization of active materials. Based on the specified degree of expiration of the expired cement, the optimal amount of active material at that degree of expiration was determined through experiments. This maximizes the advantages of the active material in restoring the mechanical properties of the repair material, achieving the best restoration effect on the strength of the expired cement and reducing the waste of active materials.

[0020] 2. Reduced economic costs of restoring the strength of expired cement. Reactive materials on the market are expensive, and indiscriminate use of them increases the economic cost of repairing expired cement. By determining the optimal dosage of reactive materials, the required amount can be precisely added, reducing waste and lowering the economic cost of repairing expired cement.

[0021] 3. Optimal optimization of the strength of expired cement was achieved. The remedial effect of the active material on expired cement has an optimal point. By calibrating the degree of cement expiration and conducting numerous experiments, the optimal dosage of the active material at the corresponding degree of expiration was obtained, thus finding this optimal point and achieving optimal optimization of the strength of expired cement.

[0022] 4. This invention enables the reuse of expired cement, reducing environmental pollution from construction waste. Expired cement ultimately becomes construction waste. This invention achieves optimal reuse of expired cement, which is of great significance in mitigating the environmental pollution caused by expired cement.

[0023] 5. Quantifying the degree of cement expiration (A value) significantly improves the accuracy of judgment and the efficiency of resource utilization. This method calculates the A value in the range of 0 to 1, transforming subjective experience into a three-level objective standard of "relatively mild, moderate, and severe," eliminating ambiguity in judgment. Based on the grading results, the amount of active materials is accurately matched, avoiding waste and restoring the performance of expired cement. Detailed Implementation

[0024] The present invention will now be described in further detail.

[0025] Example 1: A method for determining the degree of expiration of expired cement, comprising the following steps: preparing a bag of unexpired cement, weighing n groups of cement, each with a mass of M, and placing them into n identical containers, adding volumes of V1, V2, V3, ... V1 to each group according to a 10g difference gradient. n Tap water.

[0026] After being placed in a dry environment for 7 days, n groups of expired cement were obtained. These n groups of expired cement were then weighed on an electronic scale to obtain the mass of the cement at different degrees of expiration. The mass of the first group was M1, the second group was M2, the third group was M3, and so on, with the nth group being M... n The unit is g.

[0027] By sieving each batch of expired cement (which has already produced particles) through a square-hole sieve, the maximum particle size d can be obtained. n (n represents the group), and the unit is m.

[0028] Expired cement was used to prepare specimens for each group, and after curing for 28 days according to the group number, the uniaxial compressive strength X of the specimens prepared with expired cement in each group was measured using a compressive strength tester. i , unit MPa.

[0029] Prepare 1-3 specimens of unexpired cement for each group, and cure them for 28 days according to the group number. After curing, measure the uniaxial compressive strength f(u) of the specimens prepared with unexpired cement in each group using a compressive strength tester, and calculate A using the following formula.

[0030] A*f(u)=(a+b)X i

[0031] Where 'a' represents the correlation coefficient of cement quality after its expiration, and 'b' is the correlation coefficient of particle size, a = (M i -M) / M, b=d i a<1, b<1 and a+b<1; the unit of mass is g, the unit of uniaxial compressive strength is MPa, and the unit of maximum particle size is m.

[0032] The degree of expiration of the cement can be determined based on the value of A.

[0033] Example 2: After determining the degree of cement expiration, the cement was grouped according to different expiration degrees, and experiments were conducted on the optimal dosage of active material for each group. Expired cement with a density of 0.6 ≤ A < 0.8 was evenly divided into 6 equal portions, each weighing m grams. The first portion served as a control group without the addition of nano-magnesium hydroxide; after adding an appropriate amount of water and mixing thoroughly, it was poured into a mold to form a specimen. From the second portion onwards, nano-magnesium hydroxide active material was added at 1%, 2%, 3%, 4%, and 5% of the cement mass, respectively, and then an equal amount of water was added as to the control group to form specimens. All specimens were then cured in a curing chamber for 28 days. After the curing period, the compressive strength of each specimen was measured using a pressure testing machine, and the data was recorded. By comparing the data, the amount of nano-magnesium hydroxide added corresponding to the specimen with the highest compressive strength was identified. This amount is the optimal dosage of nano-magnesium hydroxide for that degree of expiration. This method allows for the determination of the optimal dosage of active material for different degrees of expiration.

[0034] Example 3: First, weigh 10 equal portions of unexpired cement, each with a mass of M, and determine its uniaxial compressive strength f(u). Add tap water to the 10 portions of cement in increments of 5g: 20g for the first group, 25g for the second, and so on, up to 65g for the tenth group. Cure the cement with added tap water in a dry environment for 7 days, maintaining constant temperature and humidity during curing. After curing, measure the mass M of each group of expired cement. i (i = 1, 2, ..., 10), and after granulating each group of expired cement, the maximum particle size d of the particles is measured.i Each group of expired cement was used to prepare specimens, and their uniaxial compressive strength X was determined. i .

[0035] According to the formula A*f(u)=(a+b)X i (where a = (M) i -M) / M, b=d i Calculate the expiration degree A value of each group of cement, where a<1, b<1 and a+b<1.

[0036] When 0.8≤A≤1.0, it is judged as slightly expired; when 0.6≤A<0.8, it is judged as moderately expired; when A<0.6, it is judged as severely expired.

[0037] Example 4: Two different types of unexpired cement were selected and labeled Cement A and Cement B, respectively. Five portions of each type of cement were weighed, each with a mass of M, and their uniaxial compressive strength f(u) was measured. A and f(u) B Five experimental groups were set up for both cement A and cement B. Water was added in increments of 5g: 20g of tap water was added to the first group, 25g to the second, and so on, up to 40g for the fifth group. The cement with added water was cured in a dry environment for 7 days, ensuring stable curing conditions. After curing, the mass M of the expired cement in each group was measured. iA M iB The maximum particle size d after granulation iA d iB and uniaxial compressive strength X iA X iB .

[0038] According to the formula A*f(u)=(a+b)X i (a=(M i Given -M) / M, b=di, a<1, b<1 and a+b<1), calculate the expiration degree A of each group of cement A and cement B respectively. Ai A Bi .

[0039] Example 5: A method for activating expired cement. 600g of expired cement with an A value of 0.8 ≤ A ≤ 1.0 was taken and evenly divided into 6 portions, each weighing m grams. Magnesium hydroxide was selected as the active material and added sequentially at 0.5%, 1%, 1.5%, 2%, 2.5%, and 3% of the cement mass, i.e., 0.5g, 1g, 1.5g, 2g, 2.5g, and 3g of silica fume, respectively. After adding an appropriate amount of water and stirring evenly, the mixture was poured into molds to form specimens. All specimens were cured in a curing chamber for 28 days. After the curing period, the compressive strength of each specimen was measured using a pressure testing machine, and the data was recorded. By comparing the data, the amount of nano-magnesium hydroxide added corresponding to the specimen with the highest compressive strength was identified. This amount is the optimal dosage of nano-magnesium hydroxide for that degree of expiration. This method can determine the optimal dosage of the active material for different degrees of expiration.

[0040] Example 6: A method for activating expired cement. The expired cement was evenly divided into five portions, each weighing 450 grams. Fly ash was selected as the activating material and added sequentially at 10%, 20%, 30%, 40%, and 50% of the expired cement's weight. 180g of water was added to each portion, and the mixture was stirred thoroughly before being poured into molds to form specimens. All specimens were placed in a curing chamber and cured for 28 days. After curing, the compressive strength of each specimen was measured using a pressure testing machine, and the data was recorded. According to the test results, the specimen with 50% fly ash added exhibited the highest compressive strength of 42.3 MPa after 28 days.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for determining the degree of expiration of expired cement, characterized in that, This includes weighing out unexpired cement and determining the mass M and uniaxial compressive strength f(u) of the unexpired cement; Unexpired cement was mixed with n different masses of water and left in a dry environment for a predetermined number of days to obtain n groups of expired cement. The mass M of the i-th group of expired cement was measured. i The maximum particle size d of the granulated particles of the i-th group of expired cement. i , i = 1, 2, ..., n; Cement was prepared into specimens, and the uniaxial compressive strength X of the i-th group of expired cement was determined. i , i = 1, 2, ..., n; Calculate and label the degree of expiration A(0) of expired cement according to the following formula. <A<1): A*f(u)=(a+b)X i Where a represents the correlation coefficient of expired cement quality, b is the correlation coefficient of particle size, and a = (M i -M) / M, b=d i a<1, b<1 and a+b<1; the unit of mass is g, the unit of uniaxial compressive strength is MPa, and the unit of maximum particle size is m; The degree of expiration of expired cement is divided into the following ranges: 0.8≤A≤1.0, indicating a relatively mild degree of expiration; 0.6≤A<0.8, indicating a moderate degree of expiration; and A<0.6, indicating a severe degree of expiration.

2. The method for determining the degree of expiration of expired cement according to claim 1, characterized in that: In the process of preparing expired cement, starting from the first group, the amount of water added in each subsequent group increases in a gradient of m. Starting from the initial amount added, the first group is given V1 water, mixed with non-expired cement, and placed in a dry environment for a predetermined number of days to obtain the first group of expired cement. Its mass M1 and the maximum particle size d1 after granulation are measured, and specimens are prepared to determine the uniaxial compressive strength X1. The second group is given V2 water, and the same process is followed to obtain M2, d2, and X2. This process is repeated until n groups of experiments are completed.

3. The method for determining the degree of expiration of expired cement according to claim 1 or 2, characterized in that: The scheduled number of days is 7-10 days.

4. A method for activating expired cement, characterized in that: When 0.8≤A≤1.0, it indicates that the cement performance decline is relatively small, and 2%-3% of the expired cement mass of active material should be added; when 0.6≤A<0.8, 3%-4% of the expired cement mass of active material should be added. If A < 0.6, its use should be prohibited.

5. The method for activating expired cement as described in claim 4, characterized in that: The active material is nano-magnesium hydroxide.