A goaf filling cementitious material, a filling test block and a preparation method thereof

Abstract

The application discloses a kind of goaf filling cementitious material, filling test block and preparation method thereof, and the mass ratio of the goaf filling cementitious material is as follows: stone coal vanadium extraction tailings 50-70%, stone coal vanadium extraction neutral residue 5-20%, smelting slag 0-15%, cement clinker 10-30%, and activator 2-8%.The filling test block also includes full tailings filling material and tap water, the mass percentage of the tap water is 18-30%, and the mass ratio of the goaf filling cementitious material to the full tailings filling material is 1:12-1:4.The goaf filling cementitious material uses stone coal vanadium extraction tailings as the main raw material, can be applied to mine tailings filling nearby, helps to large-scale, stable absorption of vanadium tailings, avoids the problems caused by tailings accumulation, and has a positive effect on the green development of mine and the friendly development of mining industry and social environment.The preparation method of the goaf filling cementitious material is simple, the main raw materials used can be obtained nearby, which helps to reduce the production cost of the cementitious material.

Description

Technical Field

[0001] This invention relates to the field of industrial waste resource utilization technology, specifically to a goaf filling cementitious material, a filling test block, and its preparation method. Background Technology

[0002] Currently, domestic research on the utilization of vanadium extraction tailings from coal shale mainly focuses on the preparation of building materials such as cement clinker, non-fired or sintered bricks, microcrystalline glass, ceramics, or ceramsite. In the preparation of cementitious materials from solid waste (including tailings and slag), research has been conducted on the preparation of cementitious materials by adding powdered materials such as steel slag, blast furnace slag, fly ash, and gypsum to solid waste.

[0003] For example, Chinese patent application number CN202110249119.3 discloses an activator for red mud-based cementitious materials and a red mud-based goaf filling material. This application uses red mud as the main raw material to prepare cementitious materials. Although this reduces material costs, it requires the addition of powdered materials such as steel slag, blast furnace slag, fly ash, and gypsum, resulting in a large amount of raw materials required. This makes it inconvenient to source materials locally, increases grinding costs, and is not conducive to the local and low-cost utilization of tailings. At the same time, since vanadium extraction tailings from shale are low-activity solid wastes with high SiO2 content and low CaO and Al2O3 content, the activation of vanadium extraction tailings from shale is difficult during the preparation of goaf filling materials. Therefore, the amount of vanadium extraction tailings incorporated in this application is relatively small. Summary of the Invention

[0004] The first aspect of this invention provides a goaf filling cementitious material, which is prepared using vanadium extraction tailings from coal shale as the main raw material. This cementitious material can be applied locally to mine tailings filling and helps to dispose of vanadium tailings on a large scale and in a stable manner.

[0005] The second aspect of the present invention provides a filling test block prepared from the above-mentioned goaf filling cementitious material, which can be applied to the filling of goaf in mines, can dispose of tailings nearby, avoid the problems caused by tailings accumulation, and play a positive role in the green development of mines and the environmentally friendly development of mining.

[0006] The third invention provides a method for preparing the above-mentioned cementitious material for filling goaf areas. This method fully activates the chemical activity of low-activity solid waste such as vanadium extraction tailings from shale coal, which has high SiO2 content and low CaO and Al2O3 content, by using a special activator to prepare a cementitious material with better performance. This method overcomes the shortcomings of the prior art in the preparation of cementitious materials from vanadium extraction tailings from shale coal and similar tailings.

[0007] The fourth aspect of the present invention provides a method for preparing the above-mentioned filling test block. This method allows for compressive strength testing in the early and late stages of preparing the filling test block, thereby evaluating the mechanical properties of the goaf filling cementitious material. This helps to ensure initial stability and safety during the filling process of the goaf in the mine.

[0008] The technical solution provided by this invention is as follows:

[0009] The first aspect of the present invention provides a goaf filling cementitious material, wherein the mass ratio of the goaf filling cementitious material is: 50-70% vanadium extraction tailings from coal stone, 5-20% neutralized vanadium extraction tailings from coal stone, 0-15% smelting slag, 10-30% cement clinker, and 2-8% activator.

[0010] Furthermore, the activator is liquid and is composed of liquid water glass, calcium salt and early strength agent. The liquid water glass has a modulus of 2.9 to 3.2 and a Baume degree of 30 to 50°Bé. The calcium salt includes one or more of calcium hydroxide, calcium formate, calcium sulfoaluminate and calcium chloride. The early strength agent includes one or more of triethanolamine, calcium formate and sodium sulfate.

[0011] Furthermore, the chemical composition of the vanadium extraction tailings from the coal shale by mass percentage includes: SiO2 60-80%, Al2O3 1-8%, CaO 1-10%, Fe2O3 1-10%, MgO 0-2%, and LOI 4-15%.

[0012] Furthermore, the calcium sulfate content in the vanadium extraction neutralization residue from the coal is 78-95%.

[0013] Furthermore, the chemical composition of the smelting slag by mass percentage includes: SiO2 25-40%, Al2O3 3-10%, CaO 35-60%, Fe2O3 3-10%, MgO 1-5%, and LOI 1-3%.

[0014] A second aspect of the present invention provides a backfill test block prepared from the above-mentioned goaf backfill cementitious material. The backfill test block further includes tailings backfill material and tap water, wherein the tap water has a mass percentage of 18-30%, and the mass ratio of the goaf backfill cementitious material to the tailings backfill material is 1:12-1:4.

[0015] A third aspect of the present invention provides a method for preparing a goaf filling cementitious material, which includes the following steps:

[0016] Step S1: Weigh the materials. Grind the weighed vanadium extraction tailings and smelting slag from the coal shale to a particle size of ≤74μm to obtain tailings powder.

[0017] Step S2: Mix the tailings powder with the weighed vanadium extraction neutralization slag from the coal shale, cement clinker, and activator to obtain the first mixture.

[0018] Step S3: The first mixture is piled up for a period of time, and then the piled mixture is broken up to obtain the goaf filling cementitious material.

[0019] Furthermore, in step S2, the mixing time of the tailings powder with the vanadium extraction neutralization slag from the coal shale, cement clinker, and activator is ≥20 minutes.

[0020] In step S3, the first mixture is stockpiled for ≥16 hours.

[0021] A fourth aspect of the present invention provides a method for preparing a filling test block, for use in the aforementioned filling test block, comprising the following steps:

[0022] Step 1: Mix the goaf filling cementitious material and the tailings filling material at a mass ratio of 1:12 to 1:4 until they are evenly mixed to obtain the second mixture.

[0023] Step 2: Add 18-30% by mass of tap water to the second mixture while stirring the material to make it into a slurry.

[0024] Step 3: Place the slurry material into the mold, vibrate it to compact it, and place it in an environment with a temperature of (20±5)℃ and a humidity of ≥90% for curing. After solidification, remove the mold to obtain the filling test block.

[0025] Further, in step 3, the filled test block is cured in an environment with a temperature of (20±2)℃ and a humidity of ≥90% for 3 days and 28 days, respectively, and its early (3 days) and late (28 days) compressive strength is measured.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] 1. The goaf filling cementitious material provided by the present invention uses vanadium extraction tailings from coal shale as the main raw material, which can be applied to mine tailings filling nearby, which helps to dispose of vanadium tailings on a large scale and stably, avoids the problems caused by tailings accumulation, and plays a positive role in the green development of mines and the environmentally friendly development of mining.

[0028] 2. The goaf filling cementitious material provided by the present invention uses fewer types of raw materials, and the main raw materials, vanadium extraction tailings and vanadium extraction neutralization slag, are all from vanadium extraction mines. The raw materials are easy to source and manage, which can effectively reduce the preparation cost of cementitious materials.

[0029] 3. The method for preparing goaf filling cementitious material provided by the present invention uses liquid water glass, calcium salt and early strength agent as activators. The activator is liquid and is easy to react chemically during the mixing and stockpiling process. The synergistic effect of water glass and calcium salt can promote the activation of vanadium extraction tailings and other raw materials to form active hydrated calcium silicate and calcium aluminosilicate, thereby improving the mechanical properties of the cementitious material. The early strength agent can improve the initial strength of the cementitious material, which helps to ensure the initial stability and safety during the filling of goaf in the mine.

[0030] 4. The method for preparing goaf filling cementitious material provided by the present invention has a simple process and the main raw materials used can be sourced locally, which helps to reduce the production cost of cementitious material. Attached Figure Description

[0031] Figure 1 Here is a physical image of the goaf filling cementitious material prepared according to the present invention;

[0032] Figure 2 A photograph of the filling test block prepared according to the present invention;

[0033] Figure 3 This is a flowchart illustrating the preparation method of the goaf filling cementitious material in an embodiment of the present invention;

[0034] Figure 4 This is a flowchart illustrating the preparation method of the filling test block in an embodiment of the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this application, not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0036] Therefore, the detailed description of the embodiments of this application provided below with reference to the accompanying drawings is intended merely to illustrate selected embodiments of this application and is not intended to limit the scope of protection claimed by this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0037] See Figure 1 This invention provides a goaf filling cementitious material, wherein the mass ratio of the goaf filling cementitious material is: 50-70% vanadium extraction tailings from coal shale, 5-20% vanadium extraction neutralization slag from coal shale, 0-15% smelting slag, 10-30% cement clinker, and 2-8% activator. The cement clinker is ordinary silicate cement clinker.

[0038] The goaf filling cementitious material provided by this invention uses vanadium extraction tailings from shale oil as the main raw material, which can be applied locally to mine tailings filling, and helps to dispose of vanadium tailings on a large scale and stably. This invention uses few types of raw materials, and the main raw materials, vanadium extraction tailings and vanadium extraction neutralization slag from vanadium extraction, both come from vanadium extraction mines, making raw material sourcing and management convenient and effectively reducing the preparation cost of the cementitious material.

[0039] Optionally, the activator is liquid and is composed of liquid water glass, calcium salt and early strength agent. The liquid water glass has a modulus of 2.9 to 3.2 and a Baume degree of 30 to 50°Bé. The calcium salt includes one or more of calcium hydroxide, calcium formate, calcium sulfoaluminate and calcium chloride. The early strength agent includes one or more of triethanolamine, calcium formate and sodium sulfate.

[0040] Optionally, the chemical composition of the vanadium extraction tailings from the coal shale, by mass percentage, includes: SiO2 60-80%, Al2O3 1-8%, CaO 1-10%, Fe2O3 1-10%, MgO 0-2%, and LOI 4-15%. It should be noted that LOI is the loss on ignition.

[0041] Optionally, the calcium sulfate content in the vanadium extraction neutralization residue from the coal shale is 78-95%.

[0042] The main component of the vanadium extraction neutralization slag from coal shale is calcium sulfate, with a calcium sulfate content of 78-95%. Using this neutralization slag can replace the addition of gypsum, which not only avoids the environmental pollution problems caused by the accumulation of neutralization slag, but also reduces the preparation cost of cementitious materials.

[0043] Optionally, the chemical composition of the smelting slag by mass percentage includes: SiO2 25-40%, Al2O3 3-10%, CaO 35-60%, Fe2O3 3-10%, MgO 1-5%, and LOI 1-3%.

[0044] This invention utilizes a special activator to fully activate the chemical activity of low-activity solid waste such as vanadium extraction tailings from shale coal, which has high SiO2 content and low CaO and Al2O3 content, and prepares a high-performance cementitious material. This invention overcomes the shortcomings of existing technologies in the preparation of cementitious materials from vanadium extraction tailings from shale coal and similar tailings.

[0045] Figure 2 The present invention provides a filling test block prepared from the above-mentioned goaf filling cementitious material. The filling test block further includes tailings filling material and tap water. The mass percentage of tap water is 18-30%, and the mass ratio of the goaf filling cementitious material to the tailings filling material is 1:12-1:4.

[0046] Figure 3A method for preparing the above-mentioned goaf filling cementitious material is shown, comprising the following steps:

[0047] Step S1: Weigh the materials. Grind the weighed vanadium extraction tailings and smelting slag from the coal shale to a particle size of ≤74μm to obtain tailings powder.

[0048] Step S2: Mix the tailings powder with the weighed vanadium extraction neutralization slag from the coal shale, cement clinker, and activator to obtain the first mixture.

[0049] Step S3: The first mixture is piled up for a period of time, and then the piled mixture is broken up to obtain the goaf filling cementitious material.

[0050] Optionally, in step S2, the mixing time of the tailings powder with the vanadium extraction neutralization slag from the coal shale, cement clinker, and activator is ≥20 minutes.

[0051] In step S3, the first mixture is stockpiled for ≥16 hours.

[0052] The above-mentioned goaf filling cementitious material prepared by the present invention uses vanadium extraction tailings and neutralization slag from coal shale as the main raw materials. When applied to goaf filling in mines, this cementitious material can dispose of tailings nearby, avoid the problems caused by tailings accumulation, and play a positive role in the green development of mines and the environmentally friendly development of mining.

[0053] This invention uses a compound of liquid water glass, calcium salts, and an early-strength agent as an activator. This activator is liquid, facilitating chemical reactions during mixing and stockpiling. The synergistic effect of water glass and calcium salts promotes the activation of vanadium extraction tailings and other raw materials, forming active hydrated calcium silicate and calcium aluminosilicate, thus improving the mechanical properties of the cementitious material. The early-strength agent enhances the initial strength of the cementitious material, helping to ensure initial stability and safety during the backfilling of mined-out areas. The process for preparing the cementitious material using this invention is simple, and the main raw materials can be sourced locally, helping to reduce the production cost of the cementitious material.

[0054] Figure 4 A method for preparing the above-mentioned filling test block is shown, comprising the following steps:

[0055] Step 1: Mix the goaf filling cementitious material and the tailings filling material at a mass ratio of 1:12 to 1:4 until they are evenly mixed to obtain the second mixture.

[0056] Step 2: Add 18-30% by mass of tap water to the second mixture while stirring the material to make it into a slurry.

[0057] Step 3: Place the slurry material into the mold, vibrate it to compact it, and place it in an environment with a temperature of (20±5)℃ and a humidity of ≥90% for curing. After solidification, remove the mold to obtain the filling test block.

[0058] In step 3, the dimensions of the mold are 70.7mm × 70.7mm × 70.7mm. The filling test block prepared using a mold of these dimensions is a cube, such as... Figure 2 As shown.

[0059] Optionally, in step 3, the filled test block is cured in an environment with a temperature of (20±2)℃ and a humidity of ≥90% for 3 days and 28 days, respectively, and its early (3 days) and late (28 days) compressive strength is measured.

[0060] Example 1:

[0061] A goaf filling cementitious material prepared from vanadium extraction tailings of shale oil has the following mass ratio: 64% vanadium extraction tailings, 8% vanadium extraction neutralization slag, 5% smelting slag, 18% cement clinker, and 5% activator. The chemical compositions of the vanadium extraction tailings and smelting slag are shown in Table 1. The vanadium extraction neutralization slag contains 87.3% calcium sulfate, and the cement clinker is 42.5 grade ordinary Portland cement clinker. The activator composition is: 65% water glass, 29% calcium salt, and 6% early-strength agent; wherein the water glass has a modulus of 2.9 and a Baume degree of 36°Bé.

[0062] Table 1. Example 1: Chemical composition of raw materials for preparing goaf filling cementitious materials from vanadium extraction tailings from coal stone.

[0063] Components / % <![CDATA[SiO2]]> <![CDATA[Al2O3]]> CaO <![CDATA[Fe2O3]]> MgO LOI Vanadium extraction tailings from coal shale 64.82 7.37 8.68 4.72 1.66 9.51 Smelting slag 37.62 6.65 41.26 5.14 1.34 1.68

[0064] The above-mentioned vanadium extraction tailings and smelting slag from shale were mixed in proportion and ground to a particle size of ≤74μm. Then, they were mixed and stirred with vanadium extraction neutralization slag from shale, cement clinker and activator for 20 minutes, and then allowed to stand for 16 hours. Finally, the material was broken up to obtain the goaf filling cementitious material.

[0065] Example 2:

[0066] A goaf filling cementitious material prepared from vanadium extraction tailings of shale oil has the following mass ratio: 60% vanadium extraction tailings, 8% vanadium extraction neutralization slag, 8% smelting slag, 20% cement clinker, and 4% activator. The chemical compositions of the vanadium extraction tailings and smelting slag are shown in Table 2. The vanadium extraction neutralization slag contains 87.3% calcium sulfate, and the cement clinker is 42.5 grade ordinary Portland cement clinker. The activator composition is: 64% water glass, 32% calcium salt, and 4% early-strength agent; wherein the water glass has a modulus of 2.9 and a Baume degree of 36°Bé.

[0067] Table 2. Example 2: Chemical composition of raw materials for preparing goaf filling cementitious materials from vanadium extraction tailings from coal stone.

[0068] Components / % <![CDATA[SiO2]]> <![CDATA[Al2O3]]> CaO <![CDATA[Fe2O3]]> MgO LOI Vanadium extraction tailings from coal shale 68.74 5.76 6.08 4.64 1.57 10.62 Smelting slag 29.36 3.46 53.41 7.55 2.19 2.18

[0069] The above-mentioned vanadium extraction tailings and smelting slag from shale were mixed in proportion and ground to a particle size of ≤74μm. Then, they were mixed and stirred with vanadium extraction neutralization slag from shale, cement clinker and activator for 20 minutes, and then allowed to stand for 16 hours. Finally, the material was broken up to obtain the goaf filling cementitious material.

[0070] Example 3:

[0071] A goaf filling cementitious material prepared from vanadium extraction tailings of shale oil has the following mass ratio: 55% vanadium extraction tailings, 10% vanadium extraction neutralization slag, 7% smelting slag, 22% cement clinker, and 6% activator. The chemical compositions of the vanadium extraction tailings and smelting slag are shown in Table 3. The vanadium extraction neutralization slag contains 92.0% calcium sulfate, and the cement clinker is 42.5 grade ordinary Portland cement clinker. The activator composition is: 70% water glass, 26% calcium salt, and 4% early-strength agent; wherein the water glass has a modulus of 3.2 and a Baume degree of 40°Bé.

[0072] Table 3. Example 3: Chemical composition of raw materials for preparing goaf filling cementitious materials from vanadium extraction tailings from coal.

[0073] Components / % <![CDATA[SiO2]]> <![CDATA[Al2O3]]> CaO <![CDATA[Fe2O3]]> MgO LOI Vanadium extraction tailings from coal shale 76.70 4.12 5.69 3.11 0.98 6.43 Smelting slag 29.36 3.46 53.41 7.55 2.19 2.18

[0074] The above-mentioned vanadium extraction tailings and smelting slag from shale were mixed in proportion and ground to a particle size of ≤74μm. Then, they were mixed with vanadium extraction neutralization slag from shale, cement clinker and activator for 20 minutes, and then allowed to stand for 16 hours. Finally, the material was dispersed using a dispersing machine to obtain the goaf filling cementitious material.

[0075] Comparative Example 1

[0076] Compared with Example 1, the only difference in this comparative example is that no early strength agent is added to the activator used.

[0077] Comparative Example 2

[0078] Compared with Example 1, the difference in this comparative example is that no activator is added, and only vanadium extraction tailings from shale, vanadium extraction neutralization slag from shale, smelting slag and cement clinker are mixed in proportions of 64%, 8%, 6% and 22%, respectively.

[0079] The cementitious materials prepared in Examples 1, 2, and 3, and Comparative Examples 1 and 2 were mixed with unground vanadium extraction tailings from coal shale at a mass ratio of 1:7. Tap water was then added at a mass percentage of 25%, and the mixture was stirred into a slurry. This slurry was placed into a 70.7mm × 70.7mm × 70.7mm mold, compacted, and cured in an environment with a temperature of (20±5)℃ and humidity ≥90%. After solidification, the mold was removed to obtain filled test blocks. The filled test blocks were then cured in an environment with a temperature of (20±2)℃ and humidity ≥90% for 3 days and 28 days to determine their compressive strength. The results are shown in Table 4.

[0080] Table 4 Compressive strength results of filled test blocks

[0081] Group 3d compressive strength / MPa 28-day compressive strength / MPa Example 1 0.47 2.44 Example 2 0.39 2.06 Example 3 0.43 2.21 Comparative Example 1 0.38 1.88 Comparative Example 2 0.35 1.79

[0082] As shown in Table 4, the filling test blocks prepared by the cementitious material of the present invention have relatively high compressive strength in both the early and late stages, which helps to ensure the stability of the cemented filling of the entire tailings.

[0083] As can be seen from Comparative Example 1, the addition of an early strength agent in the activator described in this invention can improve the early strength of the filled test block, and the later strength of the filled test block is also relatively high.

[0084] As shown in Comparative Example 2, the addition of the activator in this invention can effectively improve the compressive strength of the filled test block. The activator formulated in this invention is rationally selected, promotes the chemical reaction between the components, improves the chemical activity of vanadium tailings, and thus improves the mechanical properties of the cementitious material.

[0085] The above description is merely the preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A cementitious material for filling goaf areas, characterized in that: The mass ratio of the cementitious material used for filling the goaf is as follows: 50-70% vanadium extraction tailings from shale, 5-20% neutralized vanadium extraction shale from shale, 0-15% smelting slag, 10-30% cement clinker, and 2-8% activator. The chemical composition of the vanadium extraction tailings from the coal stone by mass percentage includes: SiO2 60~80%, Al2O3 1~8%, CaO 1~10%, Fe2O3 1~10%, MgO 0~2%, LOI 4~15%.

2. The goaf filling cementitious material according to claim 1, characterized in that: The activator is liquid and is composed of liquid water glass, calcium salt and early strength agent. The liquid water glass has a modulus of 2.9 to 3.2 and a Baume degree of 30 to 50°Bé. The calcium salt includes one or more of calcium hydroxide, calcium formate, calcium sulfoaluminate and calcium chloride. The early strength agent includes one or more of triethanolamine, calcium formate and sodium sulfate.

3. The goaf filling cementitious material according to claim 1 or 2, characterized in that: The calcium sulfate content in the vanadium extraction neutralization residue from the coal stone is 78-95%.

4. The goaf filling cementitious material according to claim 3, characterized in that: The chemical composition of the smelting slag by mass percentage includes: SiO2 25~40%, Al2O3 3~10%, CaO 35~60%, Fe2O3 3~10%, MgO 1~5%, LOI 1~3%.

5. A filling test block, prepared from the goaf filling cementitious material according to any one of claims 1-4, characterized in that: The filling test block also includes tailings filling material and tap water, wherein the tap water mass percentage is 18-30%, and the mass ratio of the goaf filling cementitious material to the tailings filling material is 1:12-1:

4.

6. A method for the production of a goaf filling cementitious material for the production of a goaf filling cementitious material according to any one of claims 1 to 4, characterized in that, Includes the following steps: Step S1: Weigh the materials. Grind the weighed vanadium extraction tailings and smelting slag from the coal shale to a particle size of ≤74μm to obtain tailings powder. Step S2: Mix the tailings powder with the weighed vanadium extraction neutralization slag from the coal shale, cement clinker, and activator to obtain the first mixture. Step S3: The first mixture is piled up for a period of time, and then the piled mixture is broken up to obtain the goaf filling cementitious material.

7. The method for preparing a goaf filling cementitious material according to claim 6, characterized in that: In step S2, the mixing time of the tailings powder with the vanadium extraction neutralization slag from the coal shale, cement clinker and activator is ≥20 minutes. In step S3, the first mixture is stockpiled for ≥16 hours.

8. A method for preparing a filling test block, used to prepare the filling test block as described in claim 5, characterized in that, Includes the following steps: Step 1: Mix the goaf filling cementitious material and the tailings filling material at a mass ratio of 1:12 to 1:4 until they are evenly mixed to obtain the second mixture. Step 2: Add 18-30% by mass of tap water to the second mixture while stirring the material to make it into a slurry. Step 3: Place the slurry material into the mold, vibrate to compact it, and cure it in an environment of 20±5℃ and humidity ≥90%. After solidification, remove the mold to obtain the filling test block.

9. The method for preparing the filling test block according to claim 8, characterized in that: In step 3, the filled test block is cured in an environment of 20±2℃ and humidity ≥90% for 3 days and 28 days, respectively, and its 3-day and 28-day compressive strength is measured.

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