CN105254196A - Cement concrete modifying agent resistant to sulfate erosion and preparation method thereof - Google Patents

Abstract

The invention discloses an anti-sulfate erosion modifier for cement concrete and a preparation method thereof. It is prepared by mixing metakaolin, roasted hydrotalcite, fly ash and limestone powder, wherein the content of metakaolin is 50-70%. The dosage of roasted hydrotalcite is 15%~30%, the dosage of fly ash is 10~20%, and the dosage of limestone powder is 0~10%. When metakaolin is mixed into cement concrete, metakaolin reacts with calcium hydroxide in cement hydration products to generate a large amount of calcium silicate hydrate and calcium aluminate hydrate, which fill the pores inside the concrete and delay the The transmission of harmful sulfate ions inside the concrete improves the sulfate attack resistance of cement concrete. The invention can remarkably improve the sulfate corrosion resistance and compressive strength of concrete at a lower dosage without affecting the working performance of the concrete.

Description

A kind of cement concrete sulfate corrosion resistance modifier and preparation method thereof

technical field

The invention relates to the technical field of building materials, in particular to a cement concrete sulfate erosion-resistant modifier and a preparation method thereof.

Background technique

In recent years, the durability of cement concrete has been paid more and more attention, and the erosion damage caused by sulfate is one of the important factors affecting the durability of concrete. In my country, Northwest China, South China and coastal areas, there are a lot of saline soil and sulfate soil. At the same time, sea water, acid rain and industrial wastewater have also brought a lot of sulfate ions that are harmful to concrete. Abroad, Germany, Japan, Canada, the United States and other countries also have the phenomenon of sulfate corrosion of concrete structures, which has brought serious economic losses. Based on this, the concrete erosion damage caused by sulfate needs to be solved urgently.

Sulfate attack of concrete is a physical and chemical process that destroys concrete between sulfate ions and minerals in cement hydration products. The reason is expansion cracking caused by the expansion reaction of sulfate ions inside the concrete, and Decrease in concrete strength caused by dissolution of Ca(OH)2 and C-S-H gel in hydration products. Common sulfates include Na2SO4, MgSO4, (NH4)2SO4, K2SO4, etc.

The degree of sulfate attack damage mainly depends on the content of cement tricalcium aluminate in concrete, the amount of cement and the compactness of concrete. At present, the methods to improve the sulfate corrosion resistance of concrete mainly focus on the use of mineral admixtures to improve the compactness of concrete and delay the transmission of sulfate ions in concrete. At the same time, the incorporation of mineral admixtures reduces the amount of cement in concrete and further improves the sulfate attack resistance of concrete. However, the use of a large number of mineral admixtures has adverse effects on the mechanical properties and carbonation resistance of concrete. At present, there is still a lack of an efficient sulfate corrosion resistance modifier to improve the sulfate corrosion resistance of concrete.

Metakaolin is a mineral admixture that has been widely studied in concrete applications. It is formed by removing water and hydroxyl groups from kaolin. With the increase of calcination temperature, the layered structure of kaolin is destroyed, forming a poor crystallinity. The transition phase is metakaolin. As a mineral admixture, metakaolin has been widely used in concrete. Its filling effect and pozzolanic effect can promote its hydration in cement-based materials, improve the early strength and later strength of concrete, and enhance its impermeability and volume stability. Intercalated hydrotalcite is a new type of functional material with a layered structure. Its main feature is that the main structure of the layer is a positively charged structural unit, and the interlayer is an exchangeable anion. When heated to 450-550°C, the interlayer anions are detached and the laminate structure is destroyed, but in the presence of anions and water, the intercalated hydrotalcite can absorb anions to rebuild the laminate structure. Therefore, the calcined intercalated hydrotalcite has the function of adsorbing anions. Fly ash and limestone powder are both commonly used mineral admixtures to improve the durability of concrete. The above-mentioned admixtures all have the effect of improving the sulfate corrosion resistance of concrete, but their comprehensive effects still need to be studied.

Contents of the invention

The technical problem to be solved by the present invention is to provide a cement concrete sulfate corrosion resistance modifier and its preparation method. The invention solves the technical problem of how to improve the sulfate corrosion resistance of cement concrete and comprehensively improve the durability of concrete.

The present invention is realized through the following technical solutions:

A kind of cement concrete anti-sulfate erosion modifier, prepared from metakaolin, roasted hydrotalcite, fly ash, limestone powder, wherein the content of metakaolin is 50~70%, and the content of roasted hydrotalcite is 15%~ 30%, the amount of fly ash is 10~20%, the amount of limestone powder is 0~10%, the above is the mass percentage.

According to the above scheme, the metakaolin is obtained by the following method: (1) put a large piece of kaolin into a ball mill for 20-40 minutes of grinding to obtain kaolin powder; (2) calcining the kaolin powder at 500-800°C 1 to 5 hours, rapidly cooled to room temperature, and ground in a ball mill for 20 to 40 minutes to obtain metakaolin.

According to the above scheme, the calcined hydrotalcite is obtained by the following method: the magnesium aluminum carbonate hydrotalcite is calcined at a temperature of 300°C-750°C for 0.5-6h and then rapidly cooled, and the Al ₂ O ₃ and MgO contents of the calcined hydrotalcite Between 50wt% and 60wt%, the mass average particle size of the particles is less than 10 μm.

According to the above scheme, the fly ash is the fly ash captured in the flue gas after coal combustion in a thermal power plant, and its 45 μm square hole sieve residue is not more than 12%, and the water demand ratio is not more than 95%.

According to the above solution, the limestone powder is finely ground limestone powder, and its specific surface area is not greater than 400m ² /kg.

Above-mentioned a kind of cement concrete anti-sulphate attack modifier and preparation method thereof, comprises the steps:

(1) Ingredients: The content of metakaolin is 40-60%, the content of roasted hydrotalcite is 10%-30%, the content of fly ash is 10-20%, and the content of limestone powder is 0-10%.

(2) After mixing hydrotalcite, fly ash, and limestone powder, mix the mixture with metakaolin, and mix well to obtain a cement concrete sulfate erosion-resistant modifier.

Compared with the prior art, the present invention has the following obvious advantages:

1. In the present invention, metakaolin and calcined hydrotalcite are compounded, and fly ash and limestone powder are used as admixtures to modify the sulfate erosion resistance of cement concrete. Among them, metakaolin is obtained by calcination of bulk kaolin. During the calcination process, the OH- in the structure is removed, and the crystal structure is destroyed, so it has high pozzolanic activity. When metakaolin is mixed into cement concrete, metakaolin reacts with calcium hydroxide in cement hydration products to generate a large amount of calcium silicate hydrate and calcium aluminate hydrate, which fill the pores inside the concrete and delay the The transmission of harmful sulfate ions inside the concrete improves the sulfate attack resistance of cement concrete.

2. The roasted hydrotalcite used in the present invention is obtained by rapid cooling after the magnesium aluminum carbonate hydrotalcite is roasted at a temperature of 300°C-750°C for 0.5-6h, and the calcined hydrotalcite is destroyed in a layered structure at a high temperature. In the presence of anions and water, it will reconstitute with anions to form a layered structure. When calcined hydrotalcite is mixed into cement concrete, the anions first react with calcined hydrotalcite after entering the concrete, thus consuming harmful sulfate ions invaded from the outside, delaying the sulfate reaction inside cement concrete, thereby improving the cement concrete. Sulfate attack resistance.

Three, used fly ash and limestone powder among the present invention, specific surface area is bigger than cement particle, can play significant filling effect in cement concrete, increases the compactness of cement concrete, has delayed the sulfate ion inside concrete transmission. The pozzolanic effect of fly ash in the later stage of cement hydration can enhance the compactness of cement concrete in the later stage, and at the same time, it can improve the poor fluidity caused by the large water demand of metakaolin and roasted hydrotalcite, and improve the working performance of cement concrete mixture.

4. The present invention uses calcined hydrotalcite to improve the sulfate erosion resistance of cement concrete, which changes the previous thinking of only relying on improving the compactness of cement concrete and changing the chemical composition of cement. The invention utilizes calcined hydrotalcite to absorb the sulfate ions invaded from the outside and inside the concrete, and significantly delays the reaction between the sulfate ions and cement hydration products. The curing anion effect of calcined hydrotalcite is superimposed with the optimized pore structure effect of metakaolin, fly ash, and limestone powder, which greatly improves the sulfate attack resistance of cement concrete.

Five, the concrete mixed with the anti-sulphate erosion modifier of the present invention has no obvious reduction in work performance, and its slump reduction rate is all lower than 15%, and the slump reduction rate after the number 3 modifier is mixed Below 5%; the compressive strength of concrete has increased significantly, among which the 3-day compressive strength has an average increase of more than 67%, the 7-day compressive strength has an average increase of more than 40%, and the 28-day compressive strength has an average increase of more than 20%. The strength loss after cycling is significantly reduced, and the sulfate attack resistance of concrete is significantly improved.

detailed description

In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

Example 1

The invention discloses a sulfate corrosion-resistant modifier for cement concrete, which is prepared from metakaolin, calcined hydrotalcite, fly ash and limestone powder. Metakaolin is calcined at 700°C for 4 hours and then cooled and pulverized. Calcined hydrotalcite is calcined at 500°C for 4 hours and then cooled. The ratio of modifiers used to modify the sulfate attack resistance of cement concrete is shown in Table 1.

Table 1 Proportion of cement concrete anti-sulfate attack modifier

With reference to the provisions of GB/T749-2008 "Test Method for Resistance to Sulfate Erosion of Cement", the present invention uses cement concrete sulfate erosion resistance modifier combined with cement and dihydrate gypsum to prepare cement mortar test blocks, and the experimental water-cement ratio is 0.36 , The size of the test block is 25×25×280 mm. By adding a certain amount of dihydrate gypsum in the cement, the SO ₃ content in the cement reaches 7.0%, so that the excess SO ₄ ^2- directly reacts with the minerals in the cement that affect the sulfate erosion resistance to generate expansion. The invention measures the sulfate erosion resistance of the cement mortar by measuring the influence of different proportioning modifiers on the expansion rate of the mortar test pieces at different ages.

Add the anti-sulfate erosion modifier shown in Table 1 into the cement according to the method of external mixing, the mass percentage is 10%, put the mortar test block in water at 20±1°C for immersion curing, and test and cure for 14 days , 42 days, and 70 days later, the length of the test block, calculate the expansion rate of the cement mortar test piece, and compare it with the blank sample. The calculation results are shown in Table 2.

Table 2 Expansion rate of modified cement mortar specimens

The test results show that the sulfate corrosion resistance modifier used in the present invention can absorb sulfate ions in cement hydration products, and improve the potential sulfate corrosion resistance of cement mortar. Among them, the expansion rate of samples numbered 3, 4, and 5 was significantly reduced, indicating that the modifier in this ratio has a better effect of modifying the resistance to sulfate attack.

Example 2

The invention discloses a sulfate corrosion-resistant modifier for cement concrete, which is prepared from metakaolin, calcined hydrotalcite, fly ash and limestone powder. Metakaolin is calcined at 700°C for 4 hours and then cooled and pulverized. Calcined hydrotalcite is calcined at 500°C for 4 hours and then cooled. According to numbers 3, 4, and 5 in Table 1, prepare cement concrete sulfate corrosion modifiers, and add them to cement concrete in proportions of 0, 5% and 10%, respectively. The cement concrete proportioning ratio is shown in Table 3.

Table 3 concrete mix ratio

According to the method of GB/T50080-2002 "General Concrete Mixture Performance Test Method Standard", the slump of the concrete mixture was tested, and the test results are shown in Table 4.

Table 4 concrete slump

The test results show that the performance of the concrete mixed with the anti-sulphate corrosion modifier is not significantly affected, which meets the requirements of engineering use.

Example 3

The invention discloses a sulfate corrosion-resistant modifier for cement concrete, which is prepared from metakaolin, calcined hydrotalcite, fly ash and limestone powder. Metakaolin is calcined at 700°C for 4 hours and then cooled and pulverized. Calcined hydrotalcite is calcined at 500°C for 4 hours and then cooled. According to No. 3, 4, and 5 in Table 1, prepare cement concrete sulfate corrosion modifiers, and add them to cement concrete in proportions of 5% and 10%, respectively. The proportion of cement concrete is shown in Table 3.

According to the method of GB/T50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete", the 3-day, 7-day and 28-day compressive strength of concrete was tested, and the test results are shown in Table 5.

Table 5 concrete compressive strength test results

The test results show that the compressive strength of the concrete mixed with the anti-sulfate corrosion modifier is significantly improved, especially the early strength.

Example 4

The invention discloses a sulfate corrosion-resistant modifier for cement concrete, which is prepared from metakaolin, calcined hydrotalcite, fly ash and limestone powder. Metakaolin is calcined at 700°C for 4 hours and then cooled and pulverized. Calcined hydrotalcite is calcined at 500°C for 4 hours and then cooled. According to No. 3 in Table 1, prepare cement concrete sulfate attack modifier, replace cement and add to cement concrete according to the ratio of 5% and 10%, respectively. The ratio of cement concrete is shown in Table 3.

Refer to the provisions of GBT50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" to carry out the concrete sulfate attack resistance test. The test piece was cured in the natural environment for 28 days. After drying, it was placed in 2mol/L Na ₂ SO ₄ solution for dry-wet cycle experiment. Soak in Na ₂ SO ₄ solution for 48 hours as a dry-wet cycle. The experiment tested its compressive strength after each cycle and compared it with a blank sample. The test results are shown in Table 6.

Table 6 Strength loss of concrete in sulfate environment

The test results show that the strength loss value of the concrete mixed with the sulfate corrosion resistance modifier is significantly reduced after the dry-wet cycle, and the sulfate corrosion resistance of the concrete is significantly improved.

The technical means disclosed in the solutions of the present invention are not limited to the technical means disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be pointed out that for those skilled in the art, some improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also regarded as the protection scope of the present invention.

Claims (7)

1. for a resisting erosion of sulfate properties-correcting agent for cement concrete, it is characterized in that: mixed by metakaolin, calcined hydrotalcite, flyash and limestone powder.

2. as claimed in claim 1 for the resisting erosion of sulfate properties-correcting agent of cement concrete, it is characterized in that: metakaolin volume is 50 ~ 70%, calcined hydrotalcite volume is 15% ~ 30%, and doping quantity of fly ash is 10 ~ 20%, limestone powder volume is 0 ~ 10%, is more than mass percentage.

3. as claimed in claim 1 or 2 for the resisting erosion of sulfate properties-correcting agent of cement concrete, it is characterized in that: its blending means is: after hydrotalcite, flyash, limestone powder are mixed, compound is mixed with metakaolin, after mixing, obtains cement concrete resisting erosion of sulfate properties-correcting agent.

4. as claimed in claim 1 or 2 for the resisting erosion of sulfate properties-correcting agent of cement concrete, it is characterized in that: described metakaolin makes to obtain with the following method: bulk kaolin is put into the grinding that ball mill carries out 20 ~ 40 minutes by (1), obtains kaolin powder; (2) kaolin powder is calcined 1 ~ 5 hour at 500 ~ 800 DEG C, be cooled fast to room temperature, and carry out the grinding of 20 ~ 40 minutes in ball mill, obtain metakaolin.

5. as claimed in claim 1 or 2 for the resisting erosion of sulfate properties-correcting agent of cement concrete, it is characterized in that: described calcined hydrotalcite makes to obtain with the following method: cooling is obtained fast after the roasting temperature 0.5-6h of 300 DEG C-750 DEG C for magnalium carbonate hydrotalcite, the Al of calcined hydrotalcite ₂o ₃with between content of MgO 50wt%-60wt%, the mass median diameter of particle is less than 10 μm.

6. as claimed in claim 1 or 2 for the resisting erosion of sulfate properties-correcting agent of cement concrete, it is characterized in that: described flyash is the flying dust captured in the flue gas after thermal power plant coal burning, its 45 μm of square hole sieves tail over and are not more than 12%, and water demand ratio is not more than 95%.

7., as claimed in claim 1 or 2 for the resisting erosion of sulfate properties-correcting agent of cement concrete, it is characterized in that: described limestone powder be Wingdale levigate after powder, its specific surface area is not more than 400m ²/ kg.