Method for calcining concrete expansive agent by adopting novel dry-process kiln

Abstract

The invention discloses a method for calcining a concrete expansive agent by adopting a novel dry-process kiln. The method comprises the following steps: respectively crushing limestone, bauxite and anhydrite, and warehousing; the preparation method comprises the following steps: weighing 60-90wt% of crushed limestone, 1-6wt% of bauxite and 8-35wt% of anhydrite, mixing and grinding to obtain a powdery material, namely a raw material; pre-decomposing the mixed raw material through a preheater, calcining in a rotary kiln, cooling to obtain an expanding agent clinker, and grinding the clinker to obtain the concrete expanding agent. The advantages of a novel dry method kiln are fully utilized, materials are heated more uniformly and calcined more sufficiently, the fired expanding agent clinker is uniform in size, the content and activity of free calcium oxide are stable, the structure is more compact, the activity of free calcium oxide and anhydrous calcium sulphoaluminate is more stable, and the comprehensive effect on the mechanical property and limited expansion rate of cement mortar is better.

Description

Technical Field

[0001] The invention relates to the technical field of concrete expansion agent preparation, and in particular to a method for calcining a concrete expansion agent by adopting a novel dry kiln. Background Art

[0002] The shrinkage of concrete materials is an inherent phenomenon that is prone to occur during the cement hydration and hardening process, among which drying shrinkage is one of the main causes of concrete cracking. Adding concrete expansion agents to compensate for the shrinkage of concrete is a common method. Commonly used expansion agents can be divided into sulphoaluminate expansion agents, lime expansion agents, magnesium oxide expansion agents and composite expansion agents according to their basic composition and expansion sources. Due to the increase in mineral admixtures in cement or concrete, concrete becomes "calcium-poor", and CSA expansion agents with CaO composite calcium sulfonate expansion sources have become the main research direction.

[0003] CSA expansion agent is usually produced by tunnel kiln, wet kiln, vertical kiln and hollow kiln. Tunnel kiln has large infrastructure investment and thermal system is not suitable for frequent adjustment; vertical kiln has large materials entering the kiln and single temperature control means, and the calcined clinker is often quite different from the mineral activity and uniformity required to be controlled; hollow kiln has low carbonate decomposition rate, high heat consumption, large amount of heat loss, and thermal efficiency of only about 20%; wet kiln has high heat consumption and low unit volume output. Wet rotary kiln calcination has strong adaptability to heterogeneous raw materials, uniform raw material composition, stable process, high quality of calcined clinker, high clinker strength grade, less dust during grinding, and less fly ash at kiln tail. However, evaporating 30% to 40% of the slurry water during wet production requires a large amount of heat consumption, and the energy consumption is higher than that of vertical kiln and dry rotary kiln. Wet production consumes a lot of energy and water during production, which consumes water resources, and wet production has been listed as a restricted and eliminated kiln type. The reactivity of anhydrous calcium sulphoaluminate and free calcium oxide in the expansive agent is a key factor affecting the performance of the expansive agent. Therefore, the calcination activity of limestone directly or indirectly determines the expansion performance. Overburning or raw burning of limestone will affect the expansion performance of the expansive agent. At the same time, the early strength development of concrete is often fast, brittle, and has poor stress relaxation ability, which is easy to cause the uncoordinated development of concrete strength, the serious lack of shrinkage compensation ability, and cannot effectively prevent concrete cracking.

[0004] Patent CN103496867B discloses a calcium sulfoaluminate or calcium sulfoaluminate-calcium oxide concrete expansion agent and its preparation method and application. The raw material formula intentionally replaces limestone with not less than 20wt% so that it can be industrially produced on a rotary kiln, which confirms that the increase in carbonate rate is conducive to the preparation of the expansion agent. However, due to the high activity of quicklime itself, it is very easy to react with air to generate a large amount of calcium sulfate and calcium carbonate during storage. Its essence is not much different from directly calcined limestone. At the same time, quicklime as a raw material needs to be crushed and ground, which increases energy consumption. At the same time, new surfaces will be continuously peeled off during the whole process, which easily causes quicklime to react with air.

[0005] The precalciner of the new dry kiln optimizes the combustion, heat exchange and carbonate decomposition process, improves the decomposition efficiency of carbonates, and the generated free calcium oxide and Al and S elements in the kiln better generate anhydrous calcium sulfoaluminate with good activity, reducing the generation of invalid mineral C2AS. The materials are heated evenly, the temperature is precisely controlled, and it has good production continuity. However, the sintering temperature range of the expansion agent is narrow, the liquid phase volume is large, and the firing process is difficult to control, which easily leads to blockage problems in production, making it difficult to carry out continuous industrial production in the new dry kiln. Summary of the invention

[0006] The purpose of the present invention is to provide a method for calcining a concrete expansion agent using a new dry kiln to solve the problem that CSA expansion agent clinker cannot be smoothly and continuously produced in the new dry kiln; at the same time, it solves the technical problems in the prior art that the concrete expansion agent has poor mineral activity, long hydration time, poor comprehensive effect on the mechanical properties and expansion rate restriction of cement mortar, easy destruction of the structure of concrete, and affects the durability of concrete.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A method for calcining a concrete expansion agent using a novel dry kiln comprises the following steps:

[0009] S1. crushing limestone, bauxite and anhydrite respectively;

[0010] S2, weighing crushed limestone, bauxite, and anhydrite in mass percentages of 60-90wt%, 1-6wt%, and 8-35wt%, respectively, and mixing and grinding to obtain a powdery raw material;

[0011] S3, the mixed raw material is pre-decomposed in a preheater, and then put into a rotary kiln for calcination, and after cooling, the expansion agent clinker is obtained, and the clinker is ground to obtain the concrete expansion agent.

[0012] Furthermore, the calcination temperature of the rotary kiln of the new dry process kiln is 1300-1500°C, and the calcination time is 20-40 minutes, that is, the entire calcination process from the powdery material entering the preheater and precalciner of the new dry process kiln to exiting the kiln and entering the grate cooler is maintained at 20-40 minutes.

[0013] Furthermore, the decomposition furnace temperature of the novel dry process kiln is 840-860°C.

[0014] The temperature of the decomposition furnace is the temperature of the pre-decomposition furnace, and the normal process temperature of the decomposition furnace is 880-900°C. Since the raw material itself has many flux minerals and a large amount of liquid phase, the problem of melting and crusting is prone to occur when the normal process temperature is used; and if the temperature of the decomposition furnace is controlled too low, the decomposition rate of carbonate will be low, and the free calcium oxide generated will be too little, which is not conducive to the formation of clinker minerals in the rotary kiln. For this reason, the present invention selects 840-860°C, optimizes the combustion, heat exchange and carbonate decomposition process, controls the decomposition efficiency of carbonate, and solves the problems of material blockage and ring formation in the kiln during production.

[0015] Furthermore, the specific surface area of ​​the concrete expansion agent is 200 to 300 m 2 / kg.

[0016] Furthermore, the powdery material is a powder having a sieve residue fineness of ≤22% obtained by evenly passing through a 0.08 mm square hole sieve.

[0017] Furthermore, the content of CaO in the limestone is ≥52wt%, and the content of SiO2 is ≤2.5wt%.

[0018] Furthermore, the content of Al2O3 in the bauxite is ≥60wt%.

[0019] Furthermore, the content of SO3 in the anhydrite is ≥37wt%.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention does not require additional equipment modification costs, and uses the new dry kiln in the existing cement plant to calcine the concrete expansion agent, and the raw materials used are all conventional raw materials for cement clinker. The present invention fully utilizes the advantages of the pre-decomposition furnace of the new dry kiln, and by lowering the decomposition furnace temperature and controlling it at 840-860°C, it optimizes the combustion, heat exchange and carbonate decomposition processes, controls the carbonate decomposition efficiency, solves the problems of material blockage and ring formation in the kiln during production, and enables the expansion agent clinker to be industrially and continuously produced.

[0022] 2. The present invention makes full use of the advantages of the new dry kiln, so that the material is heated more evenly and calcined more fully. The fired expansion agent clinker has uniform size, stable free calcium oxide content and activity, denser structure, more stable activity of free calcium oxide and anhydrous calcium sulphoaluminate, and better comprehensive effect on the mechanical properties of cement mortar and the restriction of expansion rate. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] Example 1

[0025] As a preferred embodiment of the present invention, a method for calcining a concrete expansion agent using a novel dry kiln is disclosed in this embodiment, comprising the following steps:

[0026] S1. crushing limestone, bauxite and anhydrite respectively;

[0027] S2, weighing the crushed limestone, bauxite and anhydrite in mass percentages of 82wt%, 2wt% and 16wt%, mixing and grinding, and evenly passing through a 0.08mm square hole sieve to obtain a raw material with a sieve residue fineness of ≤22%;

[0028] S3. The mixed raw material is pre-decomposed in a preheater and then calcined in a rotary kiln at a temperature of 1450°C for 20 minutes. The decomposition furnace temperature of the new dry kiln is 850°C. After cooling, the expansion agent clinker is obtained, and the clinker is ground to obtain a concrete expansion agent.

[0029] In this embodiment, the specific surface area of ​​the concrete expansion agent is 250m 2 / kg.

[0030] In this embodiment, the content of CaO in the limestone is 53wt%, and the content of SiO2 is 1.3wt%.

[0031] In this embodiment, the content of Al2O3 in bauxite is 65.1wt%.

[0032] In this embodiment, the content of SO3 in the anhydrite is 38.3wt%.

[0033] Example 2

[0034] As a preferred embodiment of the present invention, a method for calcining a concrete expansion agent using a novel dry kiln is disclosed in this embodiment, comprising the following steps:

[0035] S1. crushing limestone, bauxite and anhydrite respectively;

[0036] S2, weighing the crushed limestone, bauxite and anhydrite in mass percentages of 68wt%, 2wt% and 30wt%, mixing and grinding, and evenly passing through a 0.08mm square hole sieve to obtain a raw material with a sieve residue fineness of ≤22%;

[0037] S3. The mixed raw material is pre-decomposed in a preheater and then calcined in a rotary kiln at a temperature of 1450°C for 30 minutes. The decomposition furnace temperature of the new dry kiln is 860°C. After cooling, the expansion agent clinker is obtained, and the clinker is ground to obtain a concrete expansion agent.

[0038] In this embodiment, the specific surface area of ​​the concrete expansion agent is 250m 2 / kg.

[0039] In this embodiment, the content of CaO in the limestone is 53wt%, and the content of SiO2 is 1.3wt%.

[0040] In this embodiment, the content of Al2O3 in bauxite is 65.1wt%.

[0041] In this embodiment, the content of SO3 in the anhydrite is 38.3wt%.

[0042] Example 3

[0043] As a preferred embodiment of the present invention, a method for calcining a concrete expansion agent using a novel dry kiln is disclosed in this embodiment, comprising the following steps:

[0044] S1. crushing limestone, bauxite and anhydrite respectively;

[0045] S2, weighing the crushed limestone, bauxite and anhydrite in mass percentages of 60wt%, 5wt% and 35wt%, mixing and grinding, and evenly passing through a 0.08mm square hole sieve to obtain a raw material with a sieve residue fineness of ≤22%;

[0046] S3. The mixed raw material is pre-decomposed in a preheater and then calcined in a rotary kiln at a temperature of 1350°C for 40 minutes. The decomposition furnace temperature of the new dry kiln is 840°C. After cooling, the expansion agent clinker is obtained, and the clinker is ground to obtain a concrete expansion agent.

[0047] In this embodiment, the specific surface area of ​​the concrete expansion agent is 250m 2 / kg.

[0048] In this embodiment, the content of CaO in the limestone is 53wt%, and the content of SiO2 is 1.3wt%.

[0049] In this embodiment, the content of Al2O3 in bauxite is 65.1wt%.

[0050] In this embodiment, the content of SO3 in the anhydrite is 38.3wt%.

[0051] Example 4

[0052] As a preferred embodiment of the present invention, a method for calcining a concrete expansion agent using a novel dry kiln is disclosed in this embodiment, comprising the following steps:

[0053] S1. crushing limestone, bauxite and anhydrite respectively;

[0054] S2, weighing the crushed limestone, bauxite and anhydrite in mass percentages of 90wt%, 2wt% and 8wt%, mixing and grinding, and evenly passing through a 0.08mm square hole sieve to obtain a raw material with a sieve residue fineness of ≤22%;

[0055] S3. The mixed raw material is pre-decomposed in a preheater and then calcined in a rotary kiln. The calcination temperature is 1500°C and the calcination time is 20 minutes. The decomposition furnace temperature of the new dry kiln is 855°C. After cooling, the expansion agent clinker is obtained, and the clinker is ground to obtain a concrete expansion agent.

[0056] In this embodiment, the specific surface area of ​​the concrete expansion agent is 250m 2 / kg.

[0057] In this embodiment, the content of CaO in the limestone is 53wt%, and the content of SiO2 is 1.3wt%.

[0058] In this embodiment, the content of Al2O3 in bauxite is 65.1wt%.

[0059] In this embodiment, the content of SO3 in the anhydrite is 38.3wt%.

[0060] Comparative Example 1

[0061] In this comparative example, the concrete expansion agent is prepared in the same manner as in Example 1 except that the decomposition furnace temperature of the new dry process kiln is 880°C.

[0062] Comparative Example 2

[0063] In this comparative example, the concrete expansion agent is prepared in the same manner as in Example 1 except that the content of CaO in the limestone is 51wt%, the content of SiO2 is 3.8wt%; the content of Al2O3 in the bauxite is 45.8wt%; and the content of SO3 in the anhydrite is 38.3wt%.

[0064] The concrete expansion agents calcined in Examples 1 to 4 and Comparative Examples 1 to 2 were subjected to a molding mortar limited expansion test according to GB23439-2017 "Standard Method for Concrete Expansion Agents", the cement used was the reference cement specified in GB0876, and the amount of concrete expansion was 5 and 10 wt% of the cement dosage. The results are shown in Table 1 below.

[0065] Table 1 Results of the molding mortar expansion restriction test

[0066]

[0067] As shown in Table 1, the expansion agent prepared by the embodiment has a limited expansion rate significantly better than the comparative example, indicating that the expansion agent prepared by the present invention has good expansion performance. In comparative example 1, due to the high temperature of the decomposition furnace, when the raw material reacts in the pre-decomposition furnace, the decomposition rate of carbonate is very high, and the free calcium content generated is more, and the gypsum decomposition volatilization rate is high, and the liquid phase amount of the clinker is large, resulting in serious molten crusting and material blocking. After 3 days of continuous production, the kiln was forced to stop for artificial circling treatment, affecting industrial continuous production. In comparative example 2, due to the increase in silicon content and the decrease in calcium content in the limestone, the free calcium oxide content generated by the raw material when passing through the preheater is low. After the raw material enters the rotary kiln, it generates anhydrous calcium sulfoaluminate, silicate and other minerals with other minerals, and the remaining free calcium oxide is very low, which affects the expansion performance of the expansion agent. However, the aluminum content in bauxite is reduced, and the aluminum content required for the generation of anhydrous calcium sulfoaluminate minerals is insufficient, and intermediate minerals are generated, and the hydration activity is low. The reduction of anhydrous calcium sulfoaluminate content also affects the performance of the expansion agent.

[0068] In summary, the method provided by the present invention can enable continuous industrial production of expansion agents in a new dry process kiln, and the product also has good expansion performance.

[0069] Finally, it should be noted that the above embodiments are only preferred embodiments of the present invention to illustrate the technical solutions of the present invention, rather than limiting them, and certainly not limiting the patent scope of the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. In other words, any changes or modifications made to the main design concept and spirit of the present invention that have no substantive significance, and the technical problems they solve are still consistent with the present invention, should be included in the protection scope of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention in other related technical fields is also included in the patent protection scope of the present invention.

Claims

1. A method for calcining a concrete expansion agent using a new dry kiln, characterized in that: The following steps are involved: S1. crushing limestone, bauxite and anhydrite respectively; S2, weighing crushed limestone, bauxite, and anhydrite in mass percentages of 60-90wt%, 1-6wt%, and 8-35wt%, respectively, and mixing and grinding to obtain a powdery raw material; S3, the mixed raw material is pre-decomposed in a preheater, and then put into a rotary kiln for calcination, and after cooling, the expansion agent clinker is obtained, and the clinker is ground to obtain the concrete expansion agent.

2. The method of calcining concrete expansion agent using a novel dry kiln according to claim 1, characterized in that: The calcination temperature of the rotary kiln of the novel dry process kiln is 1300-1500° C., and the calcination time is 20-40 minutes.

3. The method of calcining concrete expansion agent using a novel dry kiln according to claim 1, characterized in that: The decomposition furnace temperature of the novel dry process kiln is 840-860°C.

4. The method of calcining concrete expansion agent using a novel dry kiln according to claim 1, characterized in that: The specific surface area of ​​the concrete expansion agent is 200 to 300 m 2 / kg.

5. The method of calcining concrete expansion agent using a novel dry kiln according to claim 1, characterized in that: The powdery material is a powdery material having a sieve residue fineness of ≤22% obtained by evenly passing through a 0.08 mm square hole sieve.

6. The method of calcining concrete expansion agent using a novel dry kiln according to claim 1, characterized in that: The content of CaO in the limestone is ≥52wt%, and the content of SiO2 is ≤2.5wt%.

7. The method of calcining concrete expansion agent using a new dry kiln according to claim 1, characterized in that: The content of Al2O3 in the bauxite is ≥60wt%.

8. The method of calcining concrete expansion agent using a novel dry kiln according to claim 1, characterized in that: The content of SO3 in the anhydrite is ≥37wt%.

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