Rapid evaluation method of compressive toughness of tailings cementing material based on fiber content-concentration effect

Abstract

The application discloses a method for rapidly evaluating the compressive toughness of tailing cementing material based on the fiber content-concentration effect, and the method comprises the following steps: tailing and cement are mixed to form a base material; a non-fiber tailing cementing material test piece is prepared by using the base material with a mass concentration of 65% as a standard test piece; non-fiber tailing cementing material test pieces with mass concentrations of 68% and 72% are prepared by using the base material; a tailing cementing material test piece with a fiber content of 0.5% is prepared; and a tailing cementing material test piece with a fiber content of 0.7% is prepared; the uniaxial compression test is performed on the test pieces to obtain the ultimate strain values of the test pieces; and the tailing cementing material test piece with the highest increment of the defined ultimate strain factor K is the best tailing cementing material.

Description

Technical Field

[0001] This invention belongs to the field of solid waste comprehensive utilization technology of tailings cementing materials, specifically involving a rapid evaluation method for the compressive toughness of tailings cementing materials based on the fiber content-concentration effect. Background Technology

[0002] Tailings cementing materials are composed of a certain proportion of cementitious materials, water, and tailings. Using tailings cementing materials as roadbed materials, building structural materials, and materials for filling mined-out areas and backfilling pits is a comprehensive utilization of solid waste resources. This not only mitigates the environmental pollution caused by tailings but also addresses the decreasing availability of ordinary sand. However, compared to ordinary sand cementing materials, tailings cementing materials have lower strength and are more brittle, which can affect the safety of engineering projects.

[0003] Currently, increasing the cement content in tailings cementitious materials can improve their strength, but high cement usage significantly increases costs. Fiber, as a cheap and readily available additive, can improve both the strength and toughness of tailings cementitious materials. Patent CN114813336A defines the compressive toughness of tailings cementitious materials based on the ratio of the area enclosed by the curves at ultimate load and peak load to the horizontal axis, defining the compressive toughness index. This index evaluates the influence of different types of fibers on the compressive toughness of the filler. It allows for the selection of the optimal fiber for enhancing compressive toughness from a fixed mix. However, the only variable is the type of fiber incorporated into the filler, making it a single-variable control. Changes in the filler mix ratio and concentration can prevent the fiber from achieving its intended performance enhancement. In practical engineering applications, different concentrations of tailings cementitious materials are typically used based on the site and surrounding environmental factors. Furthermore, research indicates that higher fiber content does not necessarily lead to better material performance optimization; each material has an optimal fiber content. Therefore, further research is needed to evaluate the effect of the coupling effect of fiber content and concentration on the compressive toughness enhancement of tailings cementitious materials, so as to provide a rapid and accurate reference for their application in roadbed materials, building structure materials, goaf filling and pit backfill materials. Summary of the Invention

[0004] To address the shortcomings of the prior art, this invention provides a method for evaluating the compressive toughness of tailings cementing materials under the coupled effect of fiber content and concentration using the limiting strain factor, thus providing a faster and more accurate theoretical basis for the engineering application of tailings cementing materials.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A rapid evaluation method for the compressive toughness of tailings cementitious materials based on the fiber content-concentration effect includes the following steps:

[0007] Step 1: Prepare tailings cementing material specimens

[0008] The tailings cementitious material specimens were prepared by mixing tailings and cement to form a base material. A fiber-free tailings cementitious material specimen was prepared using a base material with a mass concentration of 65% as a standard specimen. Then, fiber-free tailings cementitious material specimens, tailings cementitious material specimens with a mass concentration of 68% and 72%, tailings cementitious material specimens with a fiber content of 0.5% and 0.7% were prepared using the same base material.

[0009] Step 2: Conduct uniaxial compression tests on the tailings cementing material specimens described in Step 1 and plot stress-strain curves to obtain the ultimate strain value of each specimen.

[0010] Step 3: Define and calculate the limiting strain factor of the tailings cementing material specimen described in Step 1.

[0011] Define the limiting strain factor K as:

[0012]

[0013] Where: ε (m,n) ε represents the ultimate strain value of the tailings cementitious material specimen when the mass concentration of the base material is n% and the fiber content is m%, and ε0 represents the ultimate strain value of the standard specimen.

[0014] Step 4: Set the K value of the standard specimen to 1 (set the K value of the fiber-free specimen with a mass concentration of 65% to 1). Compare the K value of the tailings cementing material specimen described in Step 1 with the K value of the standard specimen to obtain the increase in the K value of the tailings cementing material specimen described in Step 1. The larger the increase in the K value, the stronger the compressive toughness of the tailings cementing material.

[0015] Furthermore, the fiber is a mixture of glass fiber and polyacrylonitrile fiber in a mass ratio of 1:1, the fiber cross-section is circular, and the fiber length is 12mm.

[0016] Furthermore, the uniaxial compression test described in step two adopts a loading strain test with a loading rate of 0.5 mm / min.

[0017] The beneficial effects of this invention are:

[0018] This invention uses the increase of the limiting strain factor K to evaluate the compressive toughness of tailings cementing materials under the coupled effect of fiber content and concentration, and quickly selects the fiber-reinforced tailings cementing material with the best compressive toughness. This provides a faster and more accurate theoretical basis for preparing tailings cementing materials for engineering applications based on the concentration-fiber content of the fiber-reinforced tailings cementing material matrix, thus mitigating the environmental pollution caused by tailings and addressing the increasing scarcity of ordinary sand. Attached Figure Description

[0019] Figure 1 This is a stress-strain evolution curve of a tailings cementing material specimen according to an embodiment of the present invention. Detailed Implementation

[0020] The tailings cementing material specimen in this embodiment consists of tailings, cement, and fibers. The tailings were taken from a metal mine in Sanmenxia. The cement was a composite silicate cement with a grade of P.C32.5. The commercially available glass fibers and polyacrylonitrile fibers had circular cross-sections and a length of 12 mm. The tailings cementing material in this embodiment is a mixture of the above-mentioned cement and tailings at a weight ratio of 1:6, with fibers accounting for 0.5% of the total mass of cement and tailings. The glass fibers and polyacrylonitrile fibers in the fiber are a mixture at a weight ratio of 1:1.

[0021] A rapid evaluation method for the compressive toughness of tailings cementitious materials based on the fiber content-concentration effect includes the following steps:

[0022] Step 1: Prepare tailings cementing material specimens

[0023] Using a tailings cementing material with a mass concentration (solid concentration) of 65%, specimens were prepared with fiber-free tailings cementing material (specimen number: C1-0), tailings cementing material with 0.5% fiber content (C1-0.5), and tailings cementing material with 0.7% fiber content (C1-0.7). Similarly, using a tailings cementing material with a mass concentration (solid concentration) of 68%, specimens were prepared with fiber-free tailings cementing material (specimen number: C2-0), tailings cementing material with 0.5% fiber content (C2-0.5), and tailings cementing material with 0.7% fiber content (C1-0.7). Tailings cementing material specimens with % fiber content (C2-0.7) were prepared. Using a tailings cementing material mass concentration (solid concentration) of 72%, specimens were prepared as follows: fiber-free tailings cementing material specimens (specimen number: C3-0), tailings cementing material specimens with 0.5% fiber content (C3-0.5), and tailings cementing material specimens with 0.7% fiber content (C3-0.7). These specimens were then fabricated into a total of 9 groups of tailings cementing material specimens with dimensions of 70.7mm × 70.7mm × 70.7mm (length × width × height), as shown in Table 1.

[0024] Table 1. Specimens with different fiber contents prepared from tailings cementing materials of different concentrations.

[0025]

[0026] Step 2: Displacement loading was applied to 9 groups of tailings cementing material specimens described in Step 1 at a loading rate of 0.5 mm / min. Uniaxial compression tests were conducted on each specimen, and stress-strain curves were plotted to obtain the ultimate strain value of each specimen. The average value of the data from 3 specimens in each group was taken as the valid data.

[0027] from Figure 1As can be seen, in the pre-peak stage, the upward trend of the curves of each specimen is not regular with the changes in concentration and fiber content, and is quite discrete. That is, the degree of "concavity" in the compaction stage is not the same as the steepness of the curve in the elastic stage. At the same concentration, the curve evolution trends of the fiberless (0%) and fiber-containing (0.5%) specimens in the post-peak failure stage are different. The post-peak curve of the fiberless specimen has a faster downward trend, while the post-peak curve of the fiber-containing specimen has a gentler downward trend and a larger post-peak ultimate strain value, which increases with the increase of fiber content. At the same fiber content, the post-peak ultimate strain value of the specimen shows a trend of first increasing and then decreasing with the increase of concentration.

[0028] Step 3: Define and determine the ultimate strain factor for each specimen.

[0029] Quantitative analysis of the compressive toughness of tailings cementitious materials under the fiber content-concentration effect was conducted. Based on the good ductility characteristics of its post-peak curve, the limiting strain factor K was defined.

[0030]

[0031] Where: ε (m,n) ε represents the ultimate strain value of the tailings cementitious material specimen when the mass concentration of the base material is n% and the fiber content is m%. ε0 represents the ultimate strain value of the standard specimen. The ultimate strain and ultimate strain factor of each tailings cementitious material specimen are shown in Table 2.

[0032] Table 2 Ultimate strain and ultimate strain factor of each tailings cementing material specimen

[0033]

[0034] Table 2 shows that under the influence of a single factor, the K-value increases for specimens C1-0.5 and C1-0.7 (fiber content) were 27% and 48%, respectively; while the K-value increases for C2-0 and C3-0 (concentration) were -20.1% and 14%, respectively. Under the influence of a two-factor model, the K-value increases for specimens C2-0.5, C2-0.7, C3-0.5, and C3-0.7 were 41%, 104%, 18%, and 81%, respectively; the C2 group of fiber specimens showed the highest increase. This indicates that the two-factor model is more effective than the single-factor model in enhancing the compressive toughness of FRCM, and fiber content is the key factor influencing the fiber content-concentration effect on the compressive toughness of FRCM. The evaluation results are as follows: using tailings from a metal mine in Sanmenxia as the raw material for the tailings cementitious material, and mixing cement and tailings at a weight ratio of 1:6, the tailings cementitious material with a fiber content of 0.7% showed the strongest compressive toughness in the project.

[0035] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any equivalent variations made in accordance with the scope of the present invention are still within the scope of the present invention.

Claims

1. A rapid evaluation method for the compressive toughness of tailings cementitious materials based on the fiber content-concentration effect, characterized in that, Includes the following steps: Step 1: Prepare tailings cementing material specimens The tailings cementitious material specimens were prepared by mixing tailings and cement to form a base material. A fiber-free tailings cementitious material specimen was prepared using a base material with a mass concentration of 65% as a standard specimen. Then, fiber-free tailings cementitious material specimens, tailings cementitious material specimens with a mass concentration of 68% and 72%, tailings cementitious material specimens with a fiber content of 0.5% and 0.7% were prepared using the same base material. Step 2: Conduct uniaxial compression tests on the tailings cementing material specimens described in Step 1 and plot stress-strain curves to obtain the ultimate strain value of each specimen. Step 3: Define and calculate the limiting strain factor of the tailings cementing material specimen described in Step 1. Define the limiting strain factor K as: In the formula: ε( m,n ) represents the ultimate strain value of the tailings cementitious material specimen when the mass concentration of the base material is n% and the fiber content is m%, and ε0 represents the ultimate strain value of the standard specimen; Step 4: Set the K value of the standard specimen to 1. Compare the K value of the tailings cementing material specimen described in Step 1 with the K value of the standard specimen to obtain the increase in the K value of the tailings cementing material specimen described in Step 1. The larger the increase in the K value, the stronger the compressive toughness of the tailings cementing material.

2. The rapid evaluation method for the compressive toughness of tailings cementing materials based on the fiber content-concentration effect according to claim 1, characterized in that, The fiber is a mixture of glass fiber and polyacrylonitrile fiber in a mass ratio of 1:

1. All fibers have a circular cross-section and a length of 12 mm.

3. The rapid evaluation method for the compressive toughness of tailings cementitious materials based on the fiber content-concentration effect according to claim 1 or 2, characterized in that, The uniaxial compression test described in step two adopts a loading strain test with a loading rate of 0.5 mm / min.

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