1. A method for testing initial damage of a cemented filling body material is characterized by comprising the following steps:

step one, manufacturing a plurality of groups of cemented filling body sample materials, and doping air entraining agents with different percentage contents in the pouring process;

step two, carrying out uniaxial compression test on the cemented filling body sample material;

calculating the effective secant elastic modulus of the cemented filling body sample material in the initial damage state through test data;

calculating the initial damage of the cemented filling body sample material;

and fifthly, observing the morphology and the structural performance of the cemented filling body sample materials with different air entraining agent contents by adopting a scanning electron microscope, and analyzing and verifying.

2. The method for initial damage testing of cementitious filler material as claimed in claim 1 wherein in step one the cementitious filler sample material concentration is 68%, the ratio of sand to ash is 1:8 and the dimensions are 70.7mm x 70.7 mm.

3. The method for testing the initial damage of the cemented filler material according to claim 1, wherein the air entraining agents in different percentage contents in the first step are: the mixing amount of the air entraining agent respectively accounts for 0 percent, 0.05 percent, 0.1 percent, 0.2 percent and 0.4 percent of the using amount of the cement.

4. The method for testing the initial damage of the cemented filling body material according to claim 1, wherein the specific process of calculating the effective secant elastic modulus of the cemented filling body sample material in the initial damage state through the test data in the step three comprises the following steps:

according to the formulaCalculating the effective secant elastic modulus of the cemented filling body sample material in a given initial damage stateWhere σ (D) is the stress at a given initial damage state D and ε (D) is the strain at a given initial damage state D.

5. The method for testing initial damage of cemented filling body material according to claim 4, wherein the specific process of calculating initial damage of cemented filling body sample material in step four comprises:

according to the formulaCalculating initial damage D of cemented filling body sample material_iniWherein E is_iniIs the elastic modulus in the initial damage state, i.e. at initial damage D_iniEffective secant modulus of elasticity in the state; e₀The modulus of elasticity in the intact state.

6. A method for initial damage testing of cementitious filler material as in claim 5, characterised in that said method is carried out in a non-destructive mannerModulus of elasticity E of₀The determination is carried out by fitting the relation between the elastic modulus and the air entraining agent in the experimental data.

Background

In the mine filling engineering practice, a cemented filling body material is fully mixed by a stirrer and then is transported to an underground goaf by a pipeline, the cemented filling body is usually used for temporarily or permanently supporting the goaf, the mechanical properties of the cemented filling body are similar to those of concrete, for example, initial defects such as air bubbles, holes, microcracks, micropores and the like are easily caused in the filling body material due to water seepage, drying shrinkage, hydration heat of cement and the like in the preparation process and the hardening process of the cemented filling body, and the initial defects control the damage mechanism of the brittle material and determine the structural strength of the brittle material. Therefore, the initial defect test of the cemented filling material has important theoretical and practical significance on the stability of the goaf of the underground mine.

In the prior art, when a study is made on brittle materials such as rock and concrete, the materials are generally treated as if no initial defect exists inside the materials. As can be seen from the theory of continuous damage mechanics, direct measurement of the initial damage variable is very difficult, and no one has done detailed quantitative measurement of the distribution of the initial defects of brittle materials, and a learner has been able to estimate a single parameter such as defect rate, damage variable, etc. from the external appearance of concrete. On the other hand, no study was made by the researchers for measuring the amount of initial defect damage of the filler material.

Disclosure of Invention

The invention aims to solve the technical problem that the method for testing the initial damage of the cemented filling body material is provided aiming at the defects in the prior art, has the advantages of simple steps, reasonable design and convenient realization, can be effectively applied to the mechanical property analysis of the cemented filling body sample material, can provide scientific reference basis for mine enterprises to more effectively utilize the tailing cemented filling body to maintain the stability of gob surrounding rocks and guarantee safe production, has obvious effect and is convenient to popularize.

In order to solve the technical problems, the invention adopts the technical scheme that: a method for testing initial damage of a cemented filling body material comprises the following steps:

step one, manufacturing a plurality of groups of cemented filling body sample materials, and doping air entraining agents with different percentage contents in the pouring process;

step two, carrying out uniaxial compression test on the cemented filling body sample material;

calculating the effective secant elastic modulus of the cemented filling body sample material in the initial damage state through test data;

calculating the initial damage of the cemented filling body sample material;

and fifthly, observing the morphology and the structural performance of the cemented filling body sample materials with different air entraining agent contents by adopting a scanning electron microscope, and analyzing and verifying.

In the method for testing the initial damage of the cemented filling body material, in the first step, the concentration of the cemented filling body sample material is 68%, the ratio of the ash to the sand is 1:8, and the size is 70.7mm × 70.7mm × 70.7 mm.

In the method for testing the initial damage of the cemented filling body material, the air entraining agents with different percentage contents in the step one are as follows: the mixing amount of the air entraining agent respectively accounts for 0 percent, 0.05 percent, 0.1 percent, 0.2 percent and 0.4 percent of the using amount of the cement.

In the method for testing initial damage of cemented filling body material, the specific process of calculating the effective secant elastic modulus of the cemented filling body sample material in the initial damage state through the test data in the third step includes:

according to the formulaCalculating the effective secant elastic modulus of the cemented filling body sample material in a given initial damage stateWhere σ (D) is the stress at a given initial damage state D and ε (D) is the strain at a given initial damage state D.

In the method for testing initial damage of cemented filling body material, the specific process of calculating initial damage of cemented filling body sample material in the fourth step includes:

according to the formulaCalculating initial damage D of cemented filling body sample material_iniWherein E is_iniIs the elastic modulus in the initial damage state, i.e. at initial damage D_iniEffective secant modulus of elasticity in the state; e₀The modulus of elasticity in the intact state.

In the method for testing the initial damage of the cemented filling body material, the elastic modulus E in the nondestructive state₀The determination is carried out by fitting the relation between the elastic modulus and the air entraining agent in the experimental data.

Compared with the prior art, the invention has the following advantages:

1. the method has simple steps, reasonable design and convenient realization.

2. According to the method, the air entraining agents with different percentage contents are doped in the pouring process of the cemented filling body sample material, the influence of the initial damage of the cemented filling body sample material is reflected, different initial damage degrees of the cemented filling body sample material are reflected through different doping amounts of the air entraining agents, and therefore the initial elastic modulus of the cemented filling body sample material under different initial damages is obtained through tests and calculation.

3. The method quantitatively calculates the initial damage of the cemented filling body sample material according to the sample data, has a simple calculation formula, and can quickly and accurately obtain the elastic modulus and the initial damage value of the cemented filling body sample material.

4. The method can be effectively applied to the mechanical property analysis of the cemented filling body sample material, can provide scientific reference basis for mine enterprises to more effectively utilize the tailing cemented filling body to maintain the stability of the surrounding rock of the goaf and guarantee the safe production, and has obvious effect and convenient popularization.

In conclusion, the method provided by the invention has the advantages of simple steps, reasonable design and convenience in implementation, can be effectively applied to mechanical property analysis of cemented filling body sample materials, can provide scientific reference basis for mine enterprises to more effectively utilize the tailing cemented filling body to maintain stability of goaf surrounding rocks and guarantee safe production, and is remarkable in effect and convenient to popularize.

The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.

Drawings

FIG. 1 is a flow chart of a method of the present invention;

FIG. 2 is a plot of modulus of elasticity versus air entraining agent for the present invention;

figure 3 is a microstructure diagram of sample cemented fill materials of varying air entraining agent content in accordance with the present invention.

Detailed Description

As shown in fig. 1, the method for testing initial damage of cemented filling material of the invention comprises the following steps:

step one, manufacturing a plurality of groups of cemented filling body sample materials, and doping air entraining agents with different percentage contents in the pouring process;

in this example, the cemented filling material sample had a concentration of 68%, a sand-lime ratio of 1:8, and dimensions of 70.7mm by 70.7 mm. The sample material of the cemented filling body is divided into 5 groups, and the mixing amount of the air entraining agent in each group respectively accounts for 0 percent, 0.05 percent, 0.1 percent, 0.2 percent and 0.4 percent of the using amount of the cement in the pouring process. In specific implementation, in order to reflect the influence of initial damage of the cemented filling body sample material, the air entraining agent is doped, different initial damage degrees of the cemented filling body sample material are reflected through different doping amounts of the air entraining agent, and therefore the initial elastic modulus of the cemented filling body sample material under different initial damages is obtained through subsequent tests and calculation.

Step two, carrying out uniaxial compression test on the cemented filling body sample material;

during specific implementation, a single-axis compression test is carried out on the cemented filling body sample material by adopting an MTS microcomputer control electronic universal testing machine, the maximum MTS output is 50kN, a displacement control mode is adopted for test loading, and vaseline is coated at a contact position in order to eliminate the end effect of the cemented filling body sample material and a loading table in the loading process.

Calculating the effective secant elastic modulus of the cemented filling body sample material in the initial damage state through test data;

according to the formulaCalculating the effective secant elastic modulus of the cemented filling body sample material in a given initial damage stateWhere σ (D) is the stress at a given initial damage state D and ε (D) is the strain at a given initial damage state D.

Calculating the initial damage of the cemented filling body sample material;

according to the formulaCalculating initial damage D of cemented filling body sample material_iniWherein E is_iniIs the elastic modulus in the initial damage state, i.e. at initial damage D_iniEffective secant modulus of elasticity in the state; e₀The modulus of elasticity in the intact state.

In specific implementation, the elastic modulus of the cemented filling body sample materials with the air entraining agent doping amounts of 0, 0.05%, 0.1%, 0.2% and 0.4% were calculated and averaged, and the results are shown in table 1.

TABLE 1 mechanical Properties of Filler with different air entraining agent contents

The data in table 1 show that the mechanical property parameters of the cemented filling body sample material have a process of deterioration first, reinforcement then deterioration due to the incorporation of the air entraining agent, and the compressive strength and the compressive elastic modulus of the cemented filling body sample material doped with the air entraining agent are reduced first and then increased and then reduced compared with the cemented filling body sample material not doped with the air entraining agent, which indicates that the internal pore structure of the cemented filling body sample material can be improved and the pore characteristics can be optimized by adding a proper amount of the air entraining agent, so that the strength of the cemented filling body sample material can be improved.

In this example, the modulus of elasticity E in the nondestructive state₀The determination is carried out by fitting the relation between the elastic modulus and the air entraining agent in the experimental data.

In specific implementation, the relation between the elastic modulus and the air entraining agent is shown in FIG. 2, and the elastic modulus E in a non-destructive state₀Determined by the value at which x is 0 (i.e. zero bleed air dosage) in the figure, i.e. E₀The results of calculating the initial damage values for cementitious filler sample materials of different air entraining agent contents are shown in table 2, 187.007 MPa.

TABLE 2 initial damage values of cementitious filler sample materials at different air entraining agent loadings

And fifthly, observing the morphology and the structural performance of the cemented filling body sample materials with different air entraining agent contents by adopting a scanning electron microscope, and analyzing and verifying.

In the specific implementation, an MLA650F type field emission scanning electron microscope is adopted to observe the shape and the structural performance of cemented filling body sample materials with different air entraining agent contents, and the used model and parameters are as follows, ZeissSEM, resolution was 30nm and maximum acceleration voltage was 20 kV.

The macroscopic strength of the cemented filling body sample material is closely connected with the microstructure thereof, and depends on the strength of the tailings particles, the strength of hydration products and the bonding strength among the particles. The hydration product is mainly composed of 2 parts: one part is a hydrate phase which is a new phase generated after hydration reaction of cement and tailings; the other part is a residual phase which is an unreacted or unreacted phase; and other pores, microcracks, and the like. The main effect is a hydrate phase, also called a cementing phase, the characteristics of the type, the number, the relative size, the spatial distribution and the like of the cementing filling body sample material determine the strength characteristic of the cementing filling body sample material, and the hydration products can fill the gaps among particles to form a net structure, so that the compactness of the cementing filling body sample material is improved.

Under the observation of a scanning electron microscope, incomplete structures such as micropore cracks and holes appear in the cemented filling body sample material, and are mostly distributed dispersedly and independently. However, the internal structure of the cemented filling body sample material is denser and the internal integrity is better, as shown in fig. 3. As can be seen from FIG. 3, the gelled product produced by hydration is mostly combined in a filamentous line, has a silk-screen structure, and the microscopic morphology inside the sample material of the cemented filling body is loose. When magnified to a high power lens, the gelled product is mostly combined into flakes, and some pores are distributed around the flakes and arranged substantially randomly, as shown in fig. 3 (d). The micropores formed during the gelling and setting processes and the pores created by the air entraining agent are distributed around the gelled product, forming a complex microstructure within the cementitious fill sample material. This affects the mechanical properties of the cemented pack sample material, indicating that the cemented pack sample material is a heterogeneous, nonlinear complex.

It can be readily observed from figure 3 that the voids contained in the cementitious filler sample material gradually increased after the addition of the air entraining agent. The pore size increases with increasing air entraining agent content, so the higher the air entraining agent content, the higher the porosity of the cementitious fill sample material. As the volume of the cementitious fill sample material remains constant, more voids are connected, resulting in a decrease in strength of the cementitious fill sample material. Furthermore, the air-entraining agent has an inhibitory effect on the internal hydration reaction, and it is considered that the content of the hydration product decreases as the content of the air-entraining agent increases. Because the hydration product can fill the voids between the particles, the reduction in the amount of hydration product can affect the pore size and strength of the sample material of the cemented pack.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all simple modifications, changes and equivalent structural changes made to the above embodiment according to the technical spirit of the present invention still fall within the protection scope of the technical solution of the present invention.