CN104119010B - High-strength underwater concrete additive of a kind of retardation setting type high workability and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of building materials, and in particular relates to a slow-setting high-fluidity and high-strength underwater concrete additive. The additive can effectively improve the strength and dispersion resistance of concrete, and has the advantages of simple preparation process, low production cost and the like. It is characterized in that it includes metakaolin and compound modifier. The mass ratio of metakaolin to the composite modifier is 50:1-15:1, wherein the composite modifier is composed of polyacrylamide, high-efficiency water reducer and organic water-soluble polysaccharides in order of 70% by mass. It is formulated by mixing %-85%, 10%-20% and 5%-15%, and the sum of the percentages of each component is 100%. As an admixture of underwater concrete, the admixture can improve the working performance, anti-dispersion performance and delay setting time of underwater concrete, and significantly improve the strength of underwater concrete at various ages, especially the early strength. At the same time, it can effectively improve the volume stability of underwater concrete.

Description

A retarding high-fluidity high-strength underwater concrete additive and preparation method thereof

technical field

The invention belongs to the technical field of building materials, and in particular relates to a slow-setting high-fluidity high-strength underwater concrete additive and a preparation method thereof.

Background technique

Along with the development and progress of human society and civilization, as the land resources available for development become less and less, the tentacles of the development of human civilization will extend to the ocean, so the 21st century will be the century of ocean development. Concrete water The next construction will be more and more. The underwater concrete structure is very complex. Therefore, in addition to the strength of concrete, simple construction technology, reasonable economy, good durability and no pollution to the environment are also required. Concrete is still one of the most important and most used construction materials in underwater engineering, and the performance of underwater concrete will directly affect the quality of underwater engineering. Therefore, underwater non-dispersible concrete has increasingly become the research focus of many scholars and engineers. As anti-dispersant has decisive significance to the performance of underwater non-dispersible concrete, the development of additives for underwater non-dispersible concrete has become the main direction of research.

Metakaolin is a kind of aluminosilicate-rich inorganic mineral, which is formed by dehydration after calcining kaolin at an appropriate temperature (500-1000°C). It has strong pozzolanic activity and has been used as an active external admixture in cement concrete and mortar and other cement products. Based on the reactivity of metakaolin, concrete materials with high density, high strength, excellent durability and corrosion resistance can be prepared, which has become a research hotspot in the material field.

However, a single concrete material system obviously cannot meet the above requirements. However, there are single-mixed cellulose and polypropylene viscosifying substances in the relevant patents to prepare underwater concrete, but the resulting concrete has low strength, and the water-to-land strength ratio is only 65%-70% (7d) and 70%-75 % (28d), and the slump loss of concrete is large, so it is not suitable for long-distance transportation and construction. Looking at the research and application results of underwater non-dispersible concrete in the past, the performance of the prepared underwater non-dispersible concrete has limitations, and the strength level of the poured underwater concrete is generally low (below C30), and the water Frost resistance, Cl ^- permeability resistance and other durability of non-dispersible concrete are also lack of research. Therefore, how to realize the excellent working performance, self-leveling, early strength, and good volume stability of underwater concrete needs further research and application in practical engineering.

Contents of the invention

The object of the present invention is to provide a retarded high-fluidity high-strength underwater concrete additive with excellent working performance, retarded, self-leveling, early strength and good volume stability. It can more effectively stimulate the pozzolanic activity of metakaolin in cement-based materials, especially in terms of early strength, and at the same time has a small loss of fluidity, and has a better effect on improving the durability of concrete.

In order to achieve the above object, technical scheme of the present invention is:

A retarding high-fluidity and high-strength underwater concrete additive, characterized in that the additive includes metakaolin and a composite modifier, and the mass ratio of the metakaolin to the composite modifier is 50:1-15:1 , the composite modifier is prepared by mixing polyacrylamide, high-efficiency water reducer and organic water-soluble polysaccharides in the order of 70%-85%, 10%-20% and 5%-15% by mass percentage , the sum of the mass percentages of each component is 100%.

In the above scheme, the metakaolin is prepared by grinding kaolin and calcining at a temperature of 500-1000° C. for 0.5-6.0 hours and then cooling, wherein the mass percentage of SiO ₂ and Al ₂ O ₃ in metakaolin is and ≥50wt%, specific surface area ≥2300m ² /kg.

In the above solution, the polyacrylamide is anionic, has a solid content ≥ 95.0%, a molecular weight of 10-20 million, an effective pH range of 7-14, and is a white solid.

In the above scheme, the high-efficiency water reducer is a powdered polycarboxylate water reducer.

In the above scheme, the organic water-soluble polysaccharide substance is sucrose, sodium gluconate or glucose, with a content of ≥99.0%, and is a white powder solid.

The preparation method of the retarded high-fluidity and high-strength underwater concrete additive is characterized in that: put the dried metakaolin into a ball mill, add a composite modifier, and grind for 30-120 minutes to obtain the described Retarding type high fluidity high strength underwater concrete additive. When in use, the prepared additive is 3%-15% in mass fraction to replace cement to obtain the underwater concrete cementitious material.

In the technical scheme of the present invention, during the modification process of modified metakaolin, under mechanical action of metakaolin, the composite modifier is adsorbed on the surface of metakaolin through physical action and chemical action, and enters the interstices of agglomerated metakaolin particles, which has two Two remarkable functions: one is to fully disperse the agglomerated metakaolin, and the other is to modify the surface of metakaolin particles.

The advantages of the present invention are:

1) The present invention can significantly improve the early strength of concrete poured underwater. The dosage of the modified metakaolin-based underwater concrete additive in ordinary mortar is 3wt%-15wt%, which can significantly improve the 7d strength of the mortar by more than 20%, and the 28d strength The growth rate can still be maintained at more than 15%, while the 7-day water-land intensity ratio remains at 70%-85%, and the 28-day water-land intensity ratio remains at 80-90%. This is metakaolin as a concrete mineral admixture, which can significantly improve the early strength and later durability of concrete due to its pozzolanic activity and micro-filling effect.

2) Modified metakaolin-based underwater concrete additive utilizes the joint action of metakaolin and polyacrylamide to improve the anti-dispersion performance of concrete. Metakaolin has a high specific surface area and fineness. After being added, it improves the water retention performance of the concrete mixture, increases the coagulation performance of the concrete, and can be used together with polyacrylamide in the cement slurry to change the coarse component system of the mixture. The potential on the surface of the particles reduces the repulsion between the particles, increases the attraction between the particles, and makes the multi-phase coarse dispersion aggregate together to thicken. The addition of water-soluble organic polymer polyacrylamide, due to the structure of the polymer molecular chain and the role of molecular branching, can be entangled to form a network structure, so that the cement particles can be fully agglomerated and the concrete can be thickened or flocculated. , to further improve the anti-dispersion ability of concrete. Polycarboxylate superplasticizer can significantly increase the working performance of concrete, and the setting time of concrete can be adjusted through organic water-soluble polysaccharides. Polycarboxylate superplasticizer and sucrose form a diffuse electric double layer on the surface of cement particles, which changes its electrokinetic potential, releases the bound water in the space grid structure formed during the cement hydration process, and increases the fluidity of cement concrete. The increase of the amplitude improves the electrostatic discharge and three-dimensional discharge ability of cement, thus delaying the hydration process of cement in the underwater non-dispersible mortar and reducing the loss of fluidity over time. After adding the modified metakaolin-based additive, the water-land strength ratio of the concrete is 70%-85% in 7 days, and the water-land strength ratio is 80-90% in 28 days. Good fluidity, better filling and self-compacting properties. It has good slump and expansion, and the slump loss is small over time after 1 hour of static rest.

3) The present invention can improve the volume stability and durability of concrete. After metakaolin is added to ordinary concrete, due to the pozzolanic effect and micro-filling effect of metakaolin, the compactness of concrete can be greatly improved, thereby effectively reducing concrete volume shrinkage and Improves the durability of concrete. However, the addition of modified metakaolin improves the working performance of underwater concrete and increases the active reaction rate of metakaolin, which is more conducive to reducing the volume shrinkage of concrete and improving the durability of concrete. Therefore, modified metakaolin can significantly improve the volume stability of concrete and improve the durability of concrete.

Description of drawings

Fig. 1 is the drying shrinkage diagram of the reference sample, the metakaolin sample and the mortar specimen of Example 1.

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

A retarding type high-fluidity high-strength underwater concrete additive, which is obtained by grinding metakaolin and a composite modifier in a ball mill for 30 minutes, wherein the mass ratio of metakaolin to the composite modifier is 15:1, the described The composite modifying agent is prepared by mixing polyacrylamide, polycarboxylate water reducer and sucrose in the order of 80%, 15% and 5% by mass.

Taking the mortar specimen as the object of investigation, metakaolin was used to replace the cementitious material with 6%, 8%, and 12% respectively, and 1% water reducing agent was added to prepare the mortar. River sand (passed through a 2.36mm sieve) and the retarded high-fluidity high-strength underwater concrete additive of Example 1 were added at 6%, 8%, and 12% respectively, and the water-cement ratio was 0.45.

According to GB/T2429-2005 "Cement Mortar Fluidity Measurement Method" test the fluidity of the mixture of the reference sample, metakaolin sample and the additive of Example 1; according to GB/T17671-1999 "Cement Mortar Strength Test Method" , test the 7 days and 28 days compressive strength of reference sample and embodiment 1 with universal pressure testing machine. Dispersion resistance refers to China National Petroleum Corporation enterprise standard underwater non-dispersive concrete construction technical specification Q/CNPC92-2003.

Table 1 Properties of mortar specimens

Table 1 shows that the fluidity of the mortar test piece in Example 1 is significantly improved compared to the metakaolin and the reference sample with the same amount. This shows that the slow-setting high-fluidity high-strength underwater concrete additive in Example 1 has a greater effect on improving the work performance, and can realize self-leveling of the mortar. Compared with the reference sample, the additive of Example 1 and metakaolin can reach more than 30MPa at 7d due to the viscosifying effect of metakaolin and the promoting effect on strength, while the water and land strength of 7d and 28d all show obvious growth, and the resistance The dispersion performance has also been further improved, meeting the requirements of Q/CNPC92-2003 against dispersion performance. This also shows that the present invention has a strong promoting effect on the early strength, and the 28d strength shows that it has no influence on the later strength development, and also makes the test piece have a higher anti-dispersion performance.

The dosage of the additive in Example 1 is selected to be 8%, and the clean slurry is used as the object of investigation, referring to the measurement method of cement setting time in GB/T1346-2001 "Cement Standard Consistency Water Consumption, Setting Time, Stability Test Method", respectively Determination of the initial and final setting times of the reference sample (Huaxin P.O42.5 cement), the metakaolin sample and the additive of Example 1 (amount of 8% to replace cement by equal mass).

The additive of table 2 embodiment 1 is on the influence of coagulation time

Table 2 shows that the incorporation of metakaolin shortens the initial and final setting times of the slurry accordingly. However, the addition of the additive in Example 1 greatly delayed the setting time of the gelled material, wherein the initial setting time was delayed by about 8 hours compared with the reference sample. It shows that the present invention has stronger retarding effect on concrete, and meets the requirement of Q/CNPC92-2003 on setting time.

The dosage of the additive in Example 1 is selected to be 8%, and the drying shrinkage test is carried out with reference to the JCJ/T70-2009 standard. Cured under the condition of humidity greater than 90% RH. After demoulding, place them in an environment with a temperature of 20°C and a relative humidity of 60% RH for curing, and then measure their lengths at 3d, 5d, 7d, 14d, and 28d, as shown in Figure 1.

Fig. 1 illustrates: when the dosage of the additive in the embodiment 1 is 8%, relative to the metakaolin, the additive in the embodiment 1 obviously reduces the drying shrinkage of the mortar specimen. It shows that the present invention is more conducive to the volume stability of mortar.

Example 2

A retarding type high-fluidity and high-strength underwater concrete additive, which is ground in a ball mill for 120 minutes by metakaolin and a composite modifier, wherein the mass ratio of metakaolin to the composite modifier is 20:1, and the composite The modifying agent is prepared by mixing polyacrylamide, polycarboxylate water reducer and sucrose in the order of 75%, 20% and 5% by mass.

Taking the concrete specimen as the object of investigation, the additives in Example 2 are used to replace the cementitious material in an equivalent amount of 10% to configure the concrete. Slump and expansion; according to GB/T50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete", test the benchmark sample and the additives of Example 2 with a universal pressure testing machine for 7 days and 28 days compressive strength; concrete anti-dispersion test According to Q/CNPC92-2003. The cement loss was 1.1%, the pH was 11.2, and the suspended matter content was 132mg/L. The water-land strength ratio was 72% at 7 days, and 83% at 28 days; the expansion degree of the underwater non-dispersible concrete was 452mm, and the slump lost 9.2% over time in 1 hour.

Example 3

A retarding type high-fluidity high-strength underwater concrete additive, which is obtained by grinding metakaolin and a composite modifier for 90 minutes in a ball mill, wherein the mass ratio of metakaolin to the composite modifier is 30:1, the described The composite modifier is prepared by mixing polyacrylamide, polycarboxylate water reducer and sucrose in the order of 70%, 25% and 5% by mass.

Taking the concrete specimen as the object of investigation, the metakaolin-based additive was used to replace the cementitious material in an equivalent amount of 12% to configure the concrete, and the slump and Expansion; in accordance with GB/T50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete", use a universal pressure testing machine to test the 7-day and 28-day compressive strength of the benchmark sample and the example; the concrete dispersion resistance test is in accordance with Q/CNPC92-2003 conduct. The loss of cement is 1.0%, the pH is 10.8, and the content of suspended matter is 132mg/L. The water-land strength ratio was 82% at 7 days, and 88% at 28 days; the expansion degree of the underwater non-dispersible concrete was 512mm, and the slump lost 9.4% over time in 1 hour.

Claims (5)

1. the high-strength underwater concrete additive of retardation setting type high workability, it is characterized in that, described additive comprises metakaolin and composite modifier, the mass ratio of described metakaolin and composite modifier is 50:1-15:1, described composite modifier is by polyacrylamide, high efficiency water reducing agent and organic water soluble polysaccharose substance are followed successively by 70%-85% according to mass percent, 10%-20% and 5%-15% mixed preparing forms, the mass percent sum of each component is 100%, described metakaolin is kaolin behind at 500-1000 DEG C temperature lower calcination 0.5-6.0 hour of grinding, and cooling is obtained, wherein, SiO in metakaolin ₂with Al ₂o ₃mass percentage sum>=50wt%, specific surface area>=2300m ²/ kg, described polyacrylamide is anionic, solid content>=95.0%, and molecular weight is 1000-2000 ten thousand, and the scope of effective pH value is 7-14.

2. the high-strength underwater concrete additive of retardation setting type high workability according to claim 1, is characterized in that: described high efficiency water reducing agent is Powdered polycarboxylate water-reducer.

3. the high-strength underwater concrete additive of retardation setting type high workability according to claim 1, is characterized in that: described organic water soluble polysaccharose substance is sucrose, Sunmorl N 60S or glucose.

4. the preparation method of the high-strength underwater concrete additive of retardation setting type high workability according to claim 1, it is characterized in that: the metakaolin through drying is put into ball mill, add composite modifier, milling time is 30-120min, obtains the high-strength underwater concrete additive of described retardation setting type high workability.

5. the application of the high-strength underwater concrete additive of retardation setting type high workability in concrete as claimed in claim 1, it is characterized in that, the volume scope of described additive is 8-12%.