Dolomitic aerated concrete and preparation method thereof

Abstract

The dolomite aerated concrete is prepared from the following raw materials in parts by weight: 25 to 35 parts of cement, 50 to 60 parts of dolomite powder, 15 to 20 parts of quartz powder, 0.2 to 0.5 part of sodium sulfate, 30 to 40 parts of water, 0.05 to 0.1 part of water reducing agent and 0.08 to 0.12 part of foaming agent. According to the invention, the dolomitic industrial solid waste can be applied to the aerated concrete in a high mixing amount, and good mechanical properties, thermal insulation properties, shrinkage properties and the like are considered on the premise of greatly reducing the use amount of a high-silicon material; and the related maintenance method is short in preparation period and suitable for popularization and application.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials, and particularly relates to dolomite aerated concrete and a preparation method thereof. Background Art

[0002] At present, the siliceous raw materials of autoclaved aerated concrete are mainly high-silica sand (river sand, river sand, etc.) and fly ash, and the strength comes from the hydrated calcium silicate, tobermorite, ettringite, etc. generated by the hydration reaction between calcium materials (cement, lime) and siliceous materials during the curing process. However, with the increasing scarcity of high-silica sand, it has become a development trend in the industry to use other materials with wide distribution, high reserves and low prices to partially or completely replace high-silica sand to prepare autoclaved aerated concrete.

[0003] At present, many autoclave aeration plants have adopted industrial high-silica solid waste to replace part of the high-silica sand, and have achieved certain results. However, there are still some more significant problems. Impurities will be introduced into the raw materials during the processing, which is not conducive to production quality control.

[0004] Dolomite deposits are rich in resources, and the proven reserves can meet the needs of economic construction. However, the magnesium content in dolomite is relatively high. Considering that a high magnesium content may cause poor volume stability in building materials, the current use of dolomite raw materials in the field of building materials is very limited. For example, the quality standards for ordinary silicate cement and lime products have strict restrictions on magnesium content, and there is little research on the use of dolomite materials to prepare autoclaved aerated concrete. Summary of the invention

[0005] The main purpose of the present invention is to provide a dolomite aerated concrete and a preparation method thereof in view of the problems and shortcomings of the prior art, which significantly reduces the amount of high-silicon materials used while taking into account good mechanical properties, thermal insulation properties and shrinkage properties; and the maintenance method involved has a short preparation cycle and is suitable for promotion and application.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A dolomite aerated concrete, the raw materials and their weight proportions thereof include: 25-35 parts of cement, 50-60 parts of dolomite powder, 15-20 parts of quartz powder, 0.2-0.5 parts of sodium sulfate, 30-40 parts of water, 0.05-0.1 parts of water reducing agent, and 0.08-0.12 parts of foaming agent.

[0008] In the above scheme, the cement is ordinary Portland cement, above grade 42.5.

[0009] In the above scheme, the dolomite powder has a CaMg(CO3)2 content of 65-95wt%, a SiO2 content of 0-35wt%, a CaCO3 content of 0-10wt%, and a clay mineral content of 0-10wt%; the fineness requirement is 5-15% of the 80μm sieve residue.

[0010] In the above scheme, the SiO2 content of the quartz powder is 85-100%, and the clay mineral content is 0-5%; the fineness requirement is 5-10wt% of the residue on an 80μm sieve.

[0011] In the above scheme, the effective component of the sodium sulfate is more than 95%.

[0012] In the above scheme, the water reducing agent is a polycarboxylic acid high-efficiency water reducing agent, and the water reduction rate is 35-45%.

[0013] In the above scheme, the foaming agent is preferably a physical foaming agent with a pH value of 6 to 8. After being diluted 45 to 60 times with water, the foam produced by the foaming machine has a water secretion of less than 40 ml, a sedimentation distance of less than 10 mm, and a density of 30 to 50 kg / m 3 ; Specifically, protein foaming agents etc. may be selected.

[0014] The above-mentioned method for preparing dolomite aerated concrete comprises the following steps:

[0015] 1) Cement, dolomite powder, quartz powder, sodium sulfate, water reducer and water are measured according to the proportion, stirred to obtain a slurry;

[0016] 2) Measure the physical foaming agent according to the ratio, dilute it with water (extra water, not included in the formula) (45 to 60 times), and then use a foaming machine to make foam;

[0017] 3) mixing the clean slurry with the foam and stirring to obtain a finished slurry;

[0018] 4) Pour the obtained finished slurry into a mold frame to stop gasification and harden, demould, and cut to obtain an aerated concrete body, and autoclave curing to obtain a dolomite aerated concrete product.

[0019] In the above scheme, the stirring treatment step in step 1) includes: firstly stirring slowly at a speed of 90 to 120 r / min for 2 to 4 minutes, and then stirring rapidly at a speed of 900 to 1200 r / min for 1 to 2 minutes; the stirring treatment step in step 3) includes: firstly stirring slowly at a speed of 60 to 90 r / min for 2 to 4 minutes, and then stirring rapidly at a speed of 120 to 250 r / min for 1 to 2 minutes.

[0020] In the above scheme, the temperature used in the static gas hardening step is 45-55° C., the relative humidity is not less than 80%, and the static time is 3-4 hours.

[0021] In the above scheme, during the autoclave curing process, vacuum is firstly performed, the vacuum degree is -0.04 to -0.06 MPa, saturated water vapor is then filled in to raise the temperature to the target curing temperature (150 to 180°C), constant temperature curing is performed, and finally the air is exhausted and the temperature is lowered to obtain the autoclaved aerated concrete product.

[0022] Furthermore, the saturated water vapor has a temperature of 150-200° C. and a pressure of 0.5-1.4 MPa.

[0023] In the above scheme, during the aeration process, the temperature in the kettle is first raised to 130-150°C at a rate of 1-1.5°C / min and kept for 3-4 hours, and then raised to 150-180°C at a rate of 2-3°C / min and kept for 3-4 hours. After the curing is completed, the air is exhausted and the temperature is lowered to end the curing.

[0024] Furthermore, in the cooling step, the temperature is firstly lowered to 80-100°C at a rate of 1.5-2.5°C / min, and then the kettle is opened.

[0025] The dolomite aerated concrete prepared according to the above scheme has a compressive strength of more than 4.0MPa and a bulk density of 620-650kg / m 3 ; Drying shrinkage is 0.19~0.21mm / m, and thermal conductivity is less than 0.13W / (m·K).

[0026] The performance optimization mechanism of aerated concrete of the present invention includes:

[0027] 1) The present invention is directed to a system with dolomite powder, cement and quartz powder as main raw materials, and autoclaving curing is divided into two stages. The main reaction process of the first stage (130-150° C.) is as follows: cement first reacts to generate hydration products such as calcium silicate hydrate and calcium hydroxide; then dolomite powder reacts with calcium hydroxide to generate minerals such as calcium carbonate and magnesium hydroxide; in addition, the addition of sodium sulfate increases the alkalinity in the liquid phase and promotes the reaction process of dolomite; the main reaction process of the second stage (150-180° C.) is as follows: magnesium hydroxide, a dolomite reaction product, reacts with quartz powder to generate magnesium silicate hydrate; calcium silicate hydrate crystallizes to generate tobermorite; dolomite powder is no longer merely an inert filler in autoclaved aerated concrete, but has reaction activity, generates different reaction products in the first stage and the second stage, and promotes the improvement of the strength of the finished product.

[0028] 2) The dolomite reaction product, magnesium hydroxide, is partially dissolved in the calcium silicate hydrate crystals, making the crystals coarser and thicker, and can also promote the formation of CSH gel and the crystallization of tobermorite. The improvement of the morphology of the hydration product and the promotion of the formation of the hydration product by magnesium hydroxide are beneficial to improving the mechanical properties of the obtained aerated concrete;

[0029] 3) The first stage of the autoclave curing of the present invention can generate a large amount of magnesium hydroxide with loose structure and strong expansion. However, since the quartz powder basically does not participate in the reaction at this stage, the capillary porosity is relatively large, which can effectively solve the problem of poor volume stability caused by the enrichment of magnesium hydroxide at this stage; further combined with the second stage of the autoclave curing, the magnesium hydroxide further reacts with quartz to form hydrated magnesium silicate, which can effectively increase the amount of hydration products while reducing the weak points of strength, and promote the strength development of aerated concrete.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1) The present invention adopts dolomite powder to replace siliceous materials in large quantities, and combines the staged autoclave curing process, so that the dolomite reaction product magnesium hydroxide is formed in the first stage and further generates hydrated magnesium silicate in the second stage, thereby solving the negative impact of the dolomite reaction product magnesium hydroxide on the performance of aerated concrete and providing a new technical solution for the resource utilization of dolomite powder.

[0032] 2) During the autoclaving process, dolomite powder reacts to produce a large amount of calcium carbonate. Due to its high strength and lack of gel pores, it can effectively inhibit the shrinkage problem caused by capillary tension during the water loss of capillaries and gel pores, which is beneficial to reducing the drying shrinkage value of aerated concrete.

[0033] 3) The dolomite reaction product, magnesium hydroxide, can promote the formation of CSH gel and the crystallization of tobermorite. Compared with conventional autoclaved aerated concrete, it is beneficial to shorten the curing time and reduce the curing temperature, thereby promoting the improvement of product production efficiency and reducing the use of steam. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below in conjunction with the embodiments to facilitate a clearer understanding of the present invention, but they do not limit the present invention.

[0035] In the following examples and comparative examples, the cement used is P·O42.5 ordinary Portland cement. The dolomite powder has a CaMg(CO3)2 content of 81%, a SiO2 content of 6%, a CaCO3 content of 7%, a clay mineral content of 4%, and a fineness of 80μm with a sieve residue of 8%. The quartz powder has a SiO2 content of 94%, a clay mineral content of 4%, and a fineness of 80μm with a sieve residue of 6%. The effective ingredient of sodium sulfate is 97%. The water reduction rate of the polycarboxylic acid water reducer is 40%. The physical foaming agent uses the HTW-1 plant protein composite foaming agent provided by Henan Huatai New Materials Technology Co., Ltd., with a pH value of 6.5. After dilution 50 times, the foam has a water secretion of 25ml, a sedimentation distance of 6mm, and a density of 43kg / m 3 The high-temperature saturated steam used in the autoclave curing process has a temperature of 200°C and a pressure of 1.4MPa.

[0036] Example 1

[0037] A method for preparing dolomite aerated concrete comprises the following steps:

[0038] (1) Take 30 parts of cement, 55 parts of dolomite powder, 15 parts of quartz powder, 0.3 parts of sodium sulfate, 35 parts of water, and 0.08 parts of water reducer, stir slowly at a speed of 90 r / min for 4 min, and then stir quickly at a speed of 1200 r / min for 1 min to obtain a slurry;

[0039] (2) Take 0.1 part of the foaming agent, dilute it 50 times with water and use a foaming machine to make foam;

[0040] (3) Mixing the clean slurry with the foam, stirring slowly at a speed of 60 r / min for 4 min, and then stirring quickly at a speed of 120 r / min for 1 min to obtain a finished slurry;

[0041] (4) pouring the obtained finished slurry into a mold frame and letting it stand for gasification and hardening. The temperature of the standing room is 50° C. and the relative humidity is 85%. After standing for 3.5 hours, the slurry is demoulded and cut to obtain an aerated concrete body;

[0042] (5) The aerated concrete body is autoclaved and cured to obtain a finished product; during the curing process, the vacuum is first evacuated to -0.05 MPa, and then saturated water vapor (temperature 200°C, pressure 1.4 MPa) is filled in. The temperature is first raised to 140°C at a rate of 1.2°C / min and kept at that temperature for 3 h, and then raised to 160°C at a rate of 2.5°C / min and kept at that temperature for 3 h. The air is exhausted and the temperature is lowered to 100°C at a rate of 2.0°C / min. After the autoclave is opened, the aerated concrete product is obtained.

[0043] Example 2

[0044] A method for preparing dolomite aerated concrete, the preparation method is substantially the same as that of Example 1, except that: during the curing process, the mixture is first evacuated to -0.05 MPa, then filled with saturated water vapor (temperature 200°C, pressure 1.4 MPa), heated to 140°C at a rate of 1.2°C / min and kept warm for 4 hours, then heated to 180°C at a rate of 2.5°C / min and kept warm for 4 hours, and exhausted and cooled after the curing, and the temperature is reduced to 100°C at a rate of 2.0°C / min, and the finished aerated concrete product is obtained after the kettle is opened.

[0045] Example 3

[0046] A method for preparing dolomite aerated concrete, the preparation method of which is roughly the same as that of Example 1, except that: 35 parts of cement, 50 parts of dolomite powder, 15 parts of quartz powder, 0.3 parts of sodium sulfate, 35 parts of water, and 0.08 parts of a water reducer are taken, first slowly stirred at a speed of 90 r / min for 4 minutes, and then quickly stirred at a speed of 1200 r / min for 1 minute to obtain a clean slurry.

[0047] Comparative Example 1

[0048] A method for preparing dolomite aerated concrete, the preparation method is substantially the same as that of Example 1, except that: during the curing process, the vacuum is first evacuated to -0.05 MPa, saturated water vapor is then introduced to increase the temperature to 160°C at a rate of 1.2°C / min, the temperature is kept at that rate for 6 hours, the exhaust is performed to reduce the temperature to 100°C at a rate of 2.0°C / min, and the aerated concrete product is obtained after the kettle is opened.

[0049] Comparative Example 2

[0050] A method for preparing dolomite aerated concrete, the preparation method of which is roughly the same as that of Example 1, except that: 30 parts of cement, 55 parts of dolomite powder, 15 parts of secondary fly ash, 0.3 parts of sodium sulfate, 35 parts of water, and 0.08 parts of water reducer are taken; the mixture is first slowly stirred at a speed of 90 r / min for 4 minutes, and then quickly stirred at a speed of 1200 r / min for 1 minute to obtain a clean slurry.

[0051] Comparative Example 3

[0052] A method for preparing dolomite aerated concrete, wherein the preparation method is substantially the same as that of Example 1, except that sodium sulfate is not introduced in step 1).

[0053] The autoclaved aerated concrete obtained in Examples 1 to 3 and Comparative Examples 1 to 3 was subjected to performance tests according to standard GB / T 11969-2008. The results are shown in Table 1.

[0054] Table 1 Autoclaved aerated concrete performance test results

[0055]

[0056] The present invention is not limited to the above-mentioned embodiments. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention. The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A dolomite aerated concrete, characterized in that: The raw materials and their weight proportions include: 25-35 parts of cement, 50-60 parts of dolomite powder, 15-20 parts of quartz powder, 0.2-0.5 parts of sodium sulfate, 30-40 parts of water, 0.05-0.1 parts of water reducing agent, and 0.08-0.12 parts of foaming agent.

2. The dolomite aerated concrete according to claim 1, characterized in that: The dolomite powder has a CaMg(CO3)2 content of 65-95wt%, a SiO2 content of 0-35wt%, a CaCO3 content of 0-10wt%, and a clay mineral content of 0-10wt%; and a fineness of 80μm with a sieve residue of 5-15%.

3. The dolomite aerated concrete according to claim 1, characterized in that: The quartz powder has a SiO2 content of 85-100% and a clay mineral content of 0-5%; the fineness requirement is 5-10% of the residue on an 80 μm sieve.

4. The dolomite aerated concrete according to claim 1, characterized in that: The cement is ordinary Portland cement, grade 42.5 or above.

5. The dolomite aerated concrete according to claim 1, characterized in that: The water reducing agent is a polycarboxylic acid high efficiency water reducing agent, and the water reducing rate is 35-45%.

6. The dolomite aerated concrete according to claim 1, characterized in that: The foaming agent is a physical foaming agent.

7. The method for preparing dolomite aerated concrete according to any one of claims 1 to 6, characterized in that: The steps include: 1) Cement, dolomite powder, quartz powder, sodium sulfate, water reducer and water are measured according to the proportion, stirred to obtain a slurry; 2) Measure the physical foaming agent according to the ratio and dilute it with water to make foam; 3) Mixing the clean slurry with the foam and stirring to obtain a finished slurry; 4) Casting the obtained finished slurry, stopping the gas generation and hardening, demoulding to obtain an aerated concrete body, and autoclaving and curing to obtain a dolomite aerated concrete product.

8. The preparation method according to claim 7, characterized in that: The autoclave curing step comprises: firstly, evacuating the air, then filling with saturated water vapor and heating to a target curing temperature, performing constant temperature curing, and finally, exhausting the air and cooling the air.

9. The preparation method according to claim 8, characterized in that: The temperature of the saturated water vapor is 150-200° C., and the pressure is 0.5-1.4 MPa.

10. The preparation method according to claim 8, characterized in that: The heating and constant temperature maintenance steps of filling with saturated water vapor include: firstly, heating the temperature in the kettle to 130-150°C at a rate of 1-1.5°C / min and keeping it warm for 3-4 hours, and then heating the temperature in the kettle to 150-180°C at a rate of 2-3°C / min and keeping it warm for 3-4 hours.

Images