Method for preparing high-activity auxiliary cementitious material by washing sand mud and increasing calcium and hot activation

Abstract

The application discloses a method for preparing high-activity auxiliary cementitious material by washing sand mud calcium-increasing thermal activation, and belongs to the technical field of comprehensive utilization of solid waste. The method comprises the following steps: uniformly mixing dried washing sand mud, calcium carbonate and a mineralizer, and placing the mixture into a high-temperature furnace; and cooling the calcined powder to room temperature to obtain the auxiliary cementitious material. The auxiliary cementitious material prepared by washing sand mud calcium-increasing thermal activation has a high activity of more than 90%; and the calcined powder does not need to be ground, and the process is simple. The application can not only high-value utilize washing sand mud, but also reduce production energy consumption and pollution, and has important economic and environmental benefits.

Description

Technical Field

[0001] This invention belongs to the technical field of building materials and comprehensive utilization of solid waste, specifically relating to a method for preparing highly active auxiliary cementitious materials by thermal activation of washed sand and mud with calcium addition. Background Technology

[0002] During the production of manufactured sand, the generation of powder particles (stone powder and mud powder) is inevitable, negatively impacting the quality of concrete made from it. To obtain high-quality manufactured sand, it is necessary to remove these powder particles through water washing during the preparation process. Statistics show that washing 1m³ of sand... 3 The manufactured sand requires 4m 3 The wastewater produced generates large quantities of sand washing sludge that are difficult to dispose of. Whether directly discharged or dumped into landfills, it will cause serious environmental pollution. Therefore, finding effective methods for the safe management and resource utilization of sand washing sludge is an urgent problem to be solved.

[0003] With the deepening implementation of major national development strategies such as "Building a Strong Transportation Nation" and "Urban Renewal," the demand for cement concrete is enormous, leading to a shortage of traditional auxiliary cementitious materials such as fly ash, slag, and silica fume. In some areas, there are even situations where no auxiliary cementitious materials are available. Therefore, the huge market for auxiliary cementitious materials provides a new approach for the high-value utilization of washed sand sludge. In building materials, auxiliary cementitious materials can be used as cement admixtures in cement preparation or as concrete admixtures in concrete preparation. Invention patent CN112960919A discloses a method for preparing cement admixtures using washed sand sludge. This method involves mixing 5-15% quicklime with washed sand sludge, adding 0.05-0.1% grinding aid and 2-5% activator to the mixture, calcining at 700-900℃, and then grinding the mixture until it passes through a 45μm sieve to produce the cement admixture. The activity of the washed sand and cementitious mixture prepared by this method is no higher than 76%, and it requires the addition of grinding aids and activators during calcination. After calcination, it needs to be ground, which increases the cost and difficulty of industrial production. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention provides a method for preparing highly active auxiliary cementitious materials by calcium-enriching and thermal activation of washed sand and mud. The auxiliary cementitious material obtained by this invention has an activity greater than 90%, and requires no grinding after calcination, greatly reducing production energy consumption.

[0005] The present invention discloses a method for preparing highly active auxiliary cementitious materials by calcium enrichment and thermal activation of washed sand and mud, comprising the following steps:

[0006] Step 1: Mix the dried washed sand mud, calcareous materials and mineralizer to obtain mixture A;

[0007] Step 2: The mixture A obtained in Step 1 is fed into a high-temperature furnace, heated to 800-900℃, and held for 60-120 minutes to obtain a fully reacted calcined product;

[0008] Step 3: After cooling the calcined product obtained in Step 2 to room temperature, the auxiliary cementitious material is obtained.

[0009] Preferably, the particle size of the washed sand mud is ≤150μm, and the particle size of the calcareous material is ≤75μm.

[0010] Preferably, the calcium material is selected from limestone powder, dolomite powder, and calcium carbonate.

[0011] Preferably, the mineralizing agent is selected from calcium fluoride, calcium chloride, and gypsum.

[0012] Furthermore, the mass percentage of calcareous material to washed sand mud is: 15-30% calcareous material and 70-85% washed sand mud, with the sum of their masses being 100%.

[0013] Furthermore, the added mineralizer is 1-5% of the total mass of the calcareous material and the washed sand mud.

[0014] The technical principle of this invention is as follows:

[0015] By adding calcium-based materials and mineralizers to washed sand and calcining it at 800–900℃, the clay minerals in the washed sand first dehydrate and transform from a crystalline ordered structure to an amorphous structure. Secondly, during the decomposition of calcium carbonate, the uniformly distributed mineralizer is already in a molten state, promoting the low-temperature decomposition of the phases and the bonding of calcium oxide to the surface of the washed sand particles, accelerating the destruction of the silicon-oxygen and aluminum-oxygen structures of the mineral phases. Finally, calcium oxide reacts with the active silica and alumina in the system to form silicate minerals, enhancing the reactivity. Furthermore, due to the expansion and destruction of some mineral structures and the volatilization of components during the calcium-addition thermal activation process, the minerals decompose, significantly reducing the particle size, thus eliminating the need for further grinding of the activated washed sand.

[0016] The beneficial effects of this invention are reflected in:

[0017] (1) The auxiliary cementitious material obtained by the calcium-increasing thermal activation method of the present invention has an activity index of over 90%, which can realize the high-value utilization of washed sand mud.

[0018] (2) The auxiliary cementitious material prepared by the present invention through the calcium-enriched thermal activation of washed sand mud does not need to be ground after calcination, which can significantly reduce energy consumption.

[0019] Therefore, this invention not only makes high-value use of washed sand mud and provides a method for preparing highly active auxiliary cementitious materials, but also simplifies the preparation process, effectively reduces the consumption of resources and energy and the pollution to the environment caused by the production of auxiliary cementitious materials, and is conducive to promoting the green and sustainable development of the building materials industry. Attached Figure Description

[0020] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 The XRD patterns are of the auxiliary cementitious materials prepared in Comparative Examples 1 and 2 and Examples 1 and 2. Detailed Implementation

[0022] The specific embodiments of the present invention will be described in detail below with reference to examples. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0023] Example 1:

[0024] The dried washed sand mud, calcium carbonate and calcium chloride are thoroughly mixed in a mass ratio of 85:15:3 to obtain a mixture; then the mixture is placed in a high-temperature furnace, heated to 800℃, and held for 90 minutes to obtain a calcined product; the calcined product is cooled to room temperature to obtain the auxiliary cementitious material.

[0025] Example 2:

[0026] The dried washed sand mud, calcium carbonate and calcium chloride are thoroughly mixed in a mass ratio of 70:30:3 to obtain a mixture; then the mixture is placed in a high-temperature furnace, heated to 800℃, and held for 90 minutes to obtain a calcined product; the calcined product is cooled to room temperature to obtain the auxiliary cementitious material.

[0027] Example 3:

[0028] The dried washed sand mud, limestone powder and calcium fluoride were thoroughly mixed in a mass ratio of 70:30:3 to obtain a mixture. The mixture was then placed in a high-temperature furnace, heated to 900℃, and held for 60 minutes to obtain a calcined product. The calcined product was cooled to room temperature to obtain the auxiliary cementitious material.

[0029] Example 4:

[0030] The dried washed sand mud, dolomite powder and calcium chloride were thoroughly mixed in a mass ratio of 70:30:3 to obtain a mixture. The mixture was then placed in a high-temperature furnace, heated to 900℃, and held for 120 minutes to obtain a calcined product. The calcined product was cooled to room temperature to obtain the auxiliary cementitious material.

[0031] Example 5:

[0032] The dried washed sand mud, calcium carbonate and gypsum were thoroughly mixed in a mass ratio of 70:30:3 to obtain a mixture; then the mixture was placed in a high-temperature furnace, heated to 900℃, and held for 120 minutes to obtain a calcined product; the calcined product was cooled to room temperature to obtain the auxiliary cementitious material.

[0033] Comparative Example 1:

[0034] Unlike the above embodiments, this method provides a method for preparing auxiliary cementitious materials through thermal activation of washed sand mud. The dried washed sand mud is placed in a high-temperature furnace, heated to 800°C, and held at that temperature for 120 minutes to obtain a calcined product. The calcined product is then cooled to room temperature to obtain the auxiliary cementitious material.

[0035] Comparative Example 2:

[0036] Unlike the above embodiments, the dried washed sand mud is used as an auxiliary cementing material.

[0037] The auxiliary cementitious materials obtained in the above examples were tested according to the activity index testing standards of commonly used auxiliary cementitious materials such as fly ash and steel slag. The test results are shown in Table 2.

[0038] Table 2 Activity index of each group of samples

[0039]

[0040]

[0041] As shown in Table 2, the activity index of the auxiliary cementitious materials prepared using Examples 1-5 of this invention is greater than 90%, which is superior to the 76% in invention patent CN112960919A, and far exceeds the qualification standards of commonly used auxiliary cementitious materials such as fly ash and steel slag. Furthermore, this invention not only produces highly active auxiliary cementitious materials, but also eliminates the grinding process, reducing production costs and thus providing social and environmental benefits.

[0042] Depend on Figure 1 It can be seen that the intensity of the mineral phase diffraction peaks of the auxiliary cementitious material prepared by this invention is significantly weakened, indicating that the disordered structure of the activated sand-washing mud is significantly enhanced. At the same time, due to the decomposition of calcareous materials and mineralizers, new active silicate minerals are generated with active SiO2 and Al2O3 in the sand-washing mud, which enhances the activity of the auxiliary cementitious material.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-activity supplementary cementitious material from sand washing slurry by calcium-increasing thermal activation, characterized in that Includes the following steps: Step 1: Mix the dried washed sand mud, calcareous materials and mineralizer to obtain mixture A; Step 2: The mixture A obtained in Step 1 is fed into a high-temperature furnace, heated to 800~900℃, and held for 60~120 min to obtain a fully reacted calcined product; Step 3: After cooling the calcined product obtained in Step 2 to room temperature, the auxiliary cementitious material is obtained without grinding; the activity index of the auxiliary cementitious material is ≥90%. The calcareous material is selected from one of limestone powder, dolomite powder, and calcium carbonate; the mass percentage of the calcareous material to the washed sand mud is: 15-30% calcareous material, 70-85% washed sand mud, and the sum of their masses is 100%. The mineralizing agent is selected from calcium fluoride and calcium chloride; the added mass of the mineralizing agent is 1-5% of the total mass of the calcareous material and the washed sand mud; The particle size of the washed sand mud is ≤150 μm, and the particle size of the calcareous material is ≤75 μm.

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