A method for preparing a non-initiator single component cement

Abstract

This invention discloses a method for preparing activator-free single-component cement. The main technical method involves selecting raw meal containing silicon, aluminum, calcium, magnesium, potassium, and sodium oxides, grinding it into raw meal powder, oxidizing and calcining it at a temperature not lower than 1250°C until the phase is stable, and then rapidly cooling it to obtain clinker; the clinker is then ground into powdered cement. This cement has the characteristics of low carbon, energy saving, waste utilization, and environmental protection, and has good application prospects.

Description

Technical Field

[0001] This invention belongs to the field of cement-based building materials, and specifically relates to a method for preparing a single-component cement without activator. Technical Background

[0002] With economic development, the discharge of bulk solid waste is increasing. Its storage not only occupies large amounts of land but also poses serious geological disaster risks and pollutes the environment, soil, water systems, and air. Currently, the main method for effectively utilizing bulk solid waste is the preparation of building materials, including general-purpose cement. Current general-purpose cement is made from silicate cement clinker with a small amount of gypsum and other admixtures. Bulk solid waste is mostly aluminosilicates composed primarily of SiO2 and Al2O3. However, silicate cement, due to its high calcium and low silica-alumina chemical composition, has high carbon emissions, and the utilization rate of aluminosilicate waste is low. Furthermore, many aluminosilicate wastes contain excessive levels of alkali metal oxides and MgO, making them unsuitable for silicate cement production.

[0003] Developing a general-purpose cement that is low-carbon, environmentally friendly, and has a high capacity for disposing of aluminosilicate waste to replace silicate cement has been a long-term goal for scientists in the cement field. Alkali-activated cement has outstanding advantages such as early strength, corrosion resistance, and good freeze-thaw resistance. It can make extensive use of solid waste, is low-carbon, energy-saving, and environmentally friendly, and is one of the most likely new cements to replace silicate cement. Traditional alkali-activated cement is a two-component cement that is hardened by activating active amorphous aluminosilicate (calcium) salts with strong alkali. It still has many shortcomings: (1) Kaolin resources are scarce, and the prices of other main raw materials such as fly ash and blast furnace slag have increased due to their large-scale use as admixtures in silicate cement; (2) The large amount of industrial alkali activator (accounting for 3-14 wt% based on Na2O) also keeps its cost high and is prone to efflorescence, which affects durability; (3) The inherent variability in the composition of industrial waste makes it difficult to stably control and standardize the performance and preparation process of alkali-activated cement prepared with it as the main raw material.

[0004] Reducing or eliminating the use of alkali activators can effectively lower the cost of alkali-activated cement. Patents CN110371140A and CN110451827A disclose methods for preparing and using alkali-activated cement for room temperature curing and steam curing, respectively. Both methods involve mixing and grinding a small amount of industrial alkali with potassium aluminosilicate and calcareous raw materials, calcining the mixture at 1250–1300℃, and then rapidly cooling it to obtain clinker. The clinker is then finely ground and uniformly mixed with sodium silicate to obtain cement. The 28-day compressive strength of their cement pastes exceeds 80 MPa and 110 MPa, respectively. While these two types of cement use less alkali activator than commonly used two-component alkali-activated cement, the industrial alkali and potassium aluminosilicate used in calcining the clinker are not inexpensive, thus still affecting the cost of alkali-activated cement. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing activator-free single-component cement.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing activator-free single-component cement, comprising the following sequential steps:

[0007] (1) Select raw materials with suitable chemical composition to mix and obtain raw materials with chemical composition that meet the subsequent requirements. Grind the dried raw materials into uniform raw material powder.

[0008] (2) The raw meal powder is oxidized and calcined at a temperature of not less than 1250℃ until the phase state is stable, and then rapidly cooled to obtain clinker. The chemical composition of the clinker satisfies the following: the mass percentage of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O is not less than 95%, and based on the total mass of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O being 100, the mass of each component is as follows: SiO2: 24.6~34.3, Al2O3: 7.0~13.7, Fe2O3: 0~7.0, CaO: 32.5~57.8, MgO: 0~22.3, Na2O+K2O: 4.4~9.7.

[0009] (3) Grind the clinker to obtain powdered cement.

[0010] Preferably, the chemical composition mass ratio of the clinker satisfies (CaO+MgO) / (SiO2+Al2O3)=1.1~2.0.

[0011] Preferably, the chemical composition mass ratio of the clinker satisfies SiO2 / Al2O3 = 1.1 to 3.6.

[0012] Preferably, the chemical composition mass ratio of the clinker satisfies MgO / CaO = 0.0 to 0.6.

[0013] Preferably, the rapid cooling in step (2) is specifically blower cooling.

[0014] The method of using the cement is the same as that of silicate cement.

[0015] The present invention has the following beneficial effects:

[0016] (1) Compared with silicate cement, the amount of carbonate in the raw materials for preparing cement clinker is significantly reduced, which can reduce the carbon emissions of cement. Moreover, since the upper limit of magnesium oxide content in carbonate raw materials is much higher than that of silicate cement clinker, it can make full use of carbonate rocks with high magnesium content and save high-quality limestone resources.

[0017] (2) Compared with silicate cement, the cement clinker has a high alkali metal content, can utilize alkali metal-containing waste residue, and improve the utilization rate of aluminosilicate waste residue, thus having better waste utilization and sustainability.

[0018] (3) The clinker firing temperature of the cement can be as low as 1250℃, which is much lower than the firing temperature of silicate cement of 1450℃, resulting in better energy saving effect. Detailed Implementation

[0019] The present invention will be further described in two steps below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0020] (1) Clinker preparation and grinding

[0021] Based on their different chemical compositions, 12 kinds of raw materials, including potassium sodium aluminosilicate, kaolin, analytical grade sodium carbonate, calcium carbonate, iron oxide, and dolomite powder, were prepared. All raw materials were dried to constant weight at 105℃, and their chemical compositions were analyzed and detailed in Table 1. The raw material formulations for the 12 examples are shown in Table 2. The raw materials obtained by mixing according to the formulations in Table 2 were ground to obtain raw material powder, all of which achieved a fineness of no more than 10% residue on an 80-micron square-hole sieve. The raw material powder was placed in a corundum crucible and transferred to a silicon carbide muffle furnace for calcination at a heating rate of 10℃ / min. The temperature was maintained at 1250–1300℃ for 1, 2, and 3 hours, respectively. After the holding time, the crucible was immediately removed from the furnace and rapidly cooled by forced air to obtain clinker. The clinker was then ground to a fineness of no more than 5% residue on an 80-micron square-hole sieve. Powder X-ray diffraction analysis revealed that, among clinker samples obtained by holding at the highest calcination temperature for 2 hours and 3 hours, the phase characteristics were similar, but some differences were observed in the samples held at the temperature for 1 hour. Clinker used for cement hydration was selected from those calcined at the temperature for 2 hours. The total mass of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O in the clinker powder is greater than 95%. When the mass of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O is calculated as 100, the masses of each component are as follows: SiO2: 31.5~45.0, Al2O3: 10.0~20.0, Fe2O3: 0~6.2, CaO: 22.0~45.0, MgO: 1.2~16.0, Na2O+K2O: 1.0~8.3, and (CaO+MgO) / (SiO2+Al2O3)=0.6~1.0, SiO2 / Al2O3=2.0~4.0, MgO / CaO=0.04~0.66 (see Table 3 for details).

[0022] (2) Cement hydration and curing

[0023] Clinker powder was mixed with water and stirred for 2–5 minutes. The slurry was then transferred into a 40×40×40 cubic steel mold and vibrated to compact it. The mold and slurry were then transferred into a standard cement curing chamber and cured at 20℃ and ≥90% humidity for 1 day. After demolding, the cement paste specimens were immersed in 20℃ water and cured for 3, 7, and 28 days, respectively, and the unconfined compressive strength of the specimens at each age was tested. The water-cement ratio and compressive strength of the cement paste are detailed in Table 4. As shown in Table 4, this single-component cement that does not require an activator can cure with just water and has good compressive strength. The maximum compressive strength of the cement paste at 28 days exceeds 90 MPa.

[0024] Table 1. Summary of Chemical Composition of Raw Materials (Unit: wt%)

[0025] raw materials <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[TFe2O3]]> CaO MgO <![CDATA[K2O]]> <![CDATA[Na2O]]> other Potassium sodium aluminosilicate 1 65.9 12.6 7.4 3.0 0.8 0.9 9.5 0.0 Potassium sodium aluminosilicate 2 58.1 25.7 3.9 1.5 0.4 0.5 9.8 0.0 Potassium sodium aluminosilicate 3 46.7 21.2 5.8 4.0 8.5 1.6 12.3 0.0 Potassium sodium aluminosilicate 4 69.5 10.9 2.8 1.9 0.7 1.2 13.0 0.0 Potassium sodium aluminosilicate 5 72.4 8.8 1.0 3.2 0.8 0.8 13.2 0.0 Potassium sodium aluminosilicate 6 62.5 10.4 5.6 4.4 3.7 0.8 12.6 0.0 Potassium sodium aluminosilicate 7 62.4 20.3 3.1 1.4 0.7 2.2 9.9 0.0 Potassium sodium aluminosilicate 8 72.5 13.9 0.6 1.0 0.3 0.8 11.0 0.0 Potassium sodium aluminosilicate 9 46.6 42.7 1.5 0.4 0.4 0.5 7.9 0.0 Potassium sodium aluminosilicate 10 51.6 38.7 0.6 0.3 0.3 0.3 8.2 0.0 Potassium sodium aluminosilicate 11 48.1 27.0 4.9 0.4 0.6 6.2 12.9 0.0 Sodium potassium aluminosilicate 12 49.0 37.3 0.2 0.2 0.1 0.2 13.2 0.0 Kaolin 42.7 38.3 0.5 0.3 0.3 0.6 0.5 16.7 dolomite 31.6 20.2 48.3 Sodium carbonate 58.5 41.5 Calcium carbonate 56.0 44.0 iron oxide 100.0 0.0

[0026] Table 2. Cement raw material proportions and maximum calcination temperatures (Unit: wt%)

[0027]

[0028] Table 3 Chemical composition and ratios of clinker

[0029]

[0030] Note: The content of each oxide refers to the percentage when the sum of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O is 100%, and all chemical composition ratios are mass ratios.

[0031] Table 4. Water-cement ratio and compressive strength of cement paste under normal temperature curing

[0032]

Claims

1. A process for the preparation of a non-activator single component cement, characterized in that, The steps include the following sequence: (1) Select raw materials with suitable chemical composition to mix and obtain raw materials with chemical composition that meet the subsequent requirements of the clinker, and grind the dried raw materials into uniform raw material powder. (2) The raw meal powder is oxidized and calcined at a temperature of not less than 1250℃ until the phase state is stable, and then rapidly cooled to obtain clinker. The chemical composition of the clinker satisfies the following: the mass percentage of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O is not less than 95%, and based on the total mass of SiO2+Al2O3+Fe2O3+CaO+MgO+Na2O+K2O being 100, the mass of each component is as follows: SiO2: 24.6~34.3, Al2O3: 7.0~13.7, Fe2O3: 0~7.0, CaO: 32.5~57.8, MgO: 0~22.3, Na2O+K2O: 4.4~9.7; (3) Grind the clinker to obtain powdered cement.

2. The method for preparing a single-component cement without activator as described in claim 1, characterized in that: The chemical composition mass ratio of the clinker satisfies (CaO+MgO) / (SiO2+Al2O3)=1.1~2.

0.

3. The method for preparing an activator-free single-component cement as described in claim 1 or 2, characterized in that: The chemical composition mass ratio of the clinker satisfies SiO2 / Al2O3 = 1.1 to 3.

6.

4. A method for preparing an activator-free single-component cement as described in any one of claims 1 to 3, characterized in that: The chemical composition mass ratio of the clinker satisfies MgO / CaO = 0.0 to 0.

6.

5. The method for preparing a single-component cement without activator as described in claim 1, characterized in that: The rapid cooling described in step (2) is specifically blower cooling.

6. A method for preparing an activator-free single-component cement as described in any one of claims 1 to 5, characterized in that: The method of using the cement is the same as that of silicate cement.

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