CN1868957A - Disruption inhibiting material of concrete sulphate crystal - Google Patents

Abstract

The invention belongs to the technical field of building materials, and in particular relates to a concrete sulfate crystal destruction inhibiting material. It is composed of air-entraining agent, water reducing agent and active admixture, wherein the water reducing agent is lignin sulfonate, β-methyl naphthalene sulfonate polycondensate, melamine formaldehyde polycondensate or polycarboxylate reducing One or more of the water preparations; the air-entraining agent is triterpenoid saponin surfactant, sodium salt compound of rosin resin, fatty acid salt compound, sulfonated hydrocarbon or alkyl-phenylmethylsulfonic acid One or more of salt compounds; the active admixture is one or more of fly ash, slag powder, silica fume or coal gangue powder. When the invention is mixed into concrete, the expansion ratio caused by sulfate crystallization of concrete can be significantly reduced, the spalling amount and strength loss of concrete caused by salt crystallization can be greatly reduced, and the ability of concrete to resist damage by sulfate crystallization is significantly improved. The production process of the invention is simple, the price is cheap, and it is also easy to popularize and apply.

Description

Sulfate Crystal Destruction Inhibition Materials for Concrete

technical field

The invention belongs to the technical field of building materials, and in particular relates to a concrete sulfate crystal destruction inhibiting material.

Background technique

Sulfate corrosion is one of the most important forms that affect the durability of concrete. In railways, highways, mines and hydropower projects, it has been found that groundwater has the problem of sulfate corrosion of concrete buildings, and some have seriously endangered the safe operation of buildings. For example, in some civil air defense projects in Qinghai Province, some tunnel projects on the Chengdu-Kunming Railway, and highway projects in the Qinghai Salt Lake area, the concrete buildings completely collapsed in less than a year in the salt lake brine and saline soil. The concrete corrodes faster. Concrete sulfate attack has attracted the attention of academia and engineering, but compared with the research on other durability of concrete, such as frost resistance, carbonation, steel corrosion, and alkali-aggregate reaction, the research on concrete sulfate attack is relatively weak However, some phenomena that appear in the research process and in actual engineering are still difficult to explain with persuasive viewpoints. Due to different research methods and testing methods, researchers have not reached a consensus on many issues of sulfate erosion damage, and some even have the opposite. Some engineering units do not have enough understanding of the mechanism of sulfate attack. When dealing with and repairing concrete buildings suffering from sulfate attack, the expected results cannot be achieved due to improper material design.

It is generally accepted that ettringite and gypsum expansion are the most important causes of sulfate failure in concrete. Sulfate attack can be summarized into the following damage forms: 1. Expansion damage caused by ettringite. When the cations in the sulfate solution are soluble ions (such as Na ⁺ , K ⁺ ), the sulfate reacts with C ₃ A to form ettringite. The formation of ettringite is considered to increase the volume by 2.5 times, resulting in expansion stress. resulting in cracking of concrete. In fact, the salt crystallization caused by Na ₂ SO ₄ , Ca ₂ SO ₄ or MgSO ₄ is also an important cause of concrete sulfate erosion damage, and this problem is more prominent in the western saline-alkali area and tidal area. In the natural use environment, it is a common phenomenon that salt crystallization causes surface erosion of porous materials such as concrete and stone, among which the damage caused by Na ₂ SO ₄ is the most common and serious.

Dry-wet cycles in fresh water cause little change in the length of the specimen, but dry-wet cycles in sulfate solution will cause the expansion rate of the specimen to gradually increase, and the higher the salt concentration, the faster the increase rate. Our research shows that C40 ordinary concrete soaked in 10% Na ₂ SO ₄ solution for 180 days, the loss of compressive strength is small or even increased, and after 14 dry-wet cycles in Na ₂ SO ₄ solution, the compressive strength The strength loss is 60%, the flexural strength loss is 35%, and the concrete has been completely destroyed after 18 cycles.

In addition, the solubility of Na ₂ SO ₄ is greatly affected by temperature. When the temperature is lowered, it is easy to crystallize as Na ₂ SO ₄ ·10H ₂ O, which will cause larger volume expansion and salt crystallization pressure. As the concentration of Na ₂ SO ₄ increases, the temperature at which the salt solution begins to expand in volume also increases, that is, it is easier to reach supersaturation and crystallize, and the salt crystal expansion rate also increases significantly.

For the prevention and control measures of sulfate erosion, most of them adopt methods such as controlling the content of C ₃ A and C ₃ S and adding active admixtures to prevent sulfate erosion caused by ettringite and gypsum; China's cement standards stipulate that sulfate resistance C ₃ A content of cement should be less than 5%, C ₃ A + C ₄ AF < 22%, C ₃ S < 50%, and C ₃ A of advanced sulfate-resistant cement < 3.5%. The newly promulgated industry standards for the durability of concrete structures by the Ministry of Construction and the Ministry of Railways use ordinary silicate cement, medium sulfate-resistant cement and high-sulfate-resistant cement _C The A content is controlled below 8%, 5% and 3% respectively. In the case of high environmental impact, more than 20% of fly ash or slag powder must be added. However, for the sulfate attack caused by salt crystallization, the content of C ₃ A is not the decisive factor. Studies have shown that the corrosion resistance of sulfate-resistant cement concrete is not better than that of ordinary cement concrete in the harsh environment of alternating dry and wet conditions.

Under the environmental conditions of on-site use, because the surface of the concrete structure will suffer from frequent dry-wet cycles, the salt solution will continue to crystallize and accumulate inside the concrete, and eventually cause salt crystallization pressure damage. Therefore, in some areas with high salt concentration and frequent dry-wet cycles, the salt crystallization damage of concrete is more serious than that in the laboratory. In fact, the sulfate erosion damage of many projects in the actual use environment of concrete is mainly caused by sulfate crystallization damage.

Contents of the invention

The object of the present invention is to propose a material for inhibiting the destruction of concrete sulfate crystallization.

The concrete sulfate crystal destruction inhibition material proposed by the present invention is composed of an air-entraining agent, a water reducing agent and an active admixture, and the weight ratio of its components is:

Component % by weight

Water reducing agent 1.9-98%

Air-entraining agent 0.1-20%

Active admixture 0-98%

The total amount thereof satisfies 100%.

Wherein, the water reducer is one or more of lignosulfonate, β-methylnaphthalenesulfonate polycondensate, melamine formaldehyde polycondensate or polycarboxylate water reducer; The agent is one or more of triterpene saponin surfactants, sodium salt compounds of rosin resins, fatty acid salt compounds, sulfonated hydrocarbons or alkyl-phenylmethyl sulfonate compounds; The active admixture is one or more of fly ash, slag powder, silica fume or coal gangue powder.

The preferred composition ratio of the present invention is as follows:

Component % by weight

Water reducing agent 5-98%

Air-entraining agent 0.1-5%

Active admixture 1.9-92%

The total amount thereof satisfies 100%.

The mixing amount of the present invention in concrete is 1-20% of the weight of the concrete cementitious material. The preferred mixing amount of the present invention in concrete is 1-10% of the weight of the concrete cementitious material.

In the present invention, after the air-entraining agent is added to the concrete, a large number of tiny air bubbles can be introduced into the cement paste, which acts as a "buffer valve" for volume expansion, and can effectively reduce and delay the volumetric expansion caused by sulfate erosion. swell. Adding water reducer to concrete can reduce the water-cement ratio of concrete and can compensate for the loss of compressive strength caused by air-entrained concrete. Adding active admixtures can refine the pore structure of concrete, increase the compactness, reduce the content of C ₃ A and CH in concrete that are susceptible to sulfate attack, and improve the structure of the transition zone between slurry and aggregate in concrete.

In the present invention, the water reducing agent and the air-entraining agent should meet the quality requirements of the national standard GB8076-1997 "Concrete Admixtures" for the water reducing agent and the air-entraining agent. The grade of fly ash is Class I and Class II fly ash, the water demand ratio of fly ash is less than 105%, and the loss on ignition is less than 5%. The specific surface area of the mineral powder is greater than 350m ² /kg, the loss on ignition of the silica fume is less than 5%, and the SiO ₂ content is greater than 80%. Coal gangue powder is made of spontaneously combusted coal gangue or natural coal gangue after calcined and ground, with a specific surface area greater than 300m ² /kg.

The preparation method of the present invention is as follows:

For powdery materials, add each component material into the mixer in proportion, stir for 3-5 minutes, and mix to obtain the desired product. For liquid materials, add each component material into the disperser, stir for 8-12 minutes, weigh and pack, and obtain the desired product.

After the invention is mixed into the concrete, the space generated by the introduced air bubbles can accommodate more salt crystals, that is, the introduced tiny air bubbles can effectively buffer the expansion caused by sulfate crystallization. The expansion rate and peeling amount caused by salt crystallization pressure are significantly reduced, the strength loss is greatly reduced, and the ability of concrete to resist sulfate crystallization damage is significantly improved. The invention has high value for improving the durability of concrete, especially for improving the service life of concrete in western saline-alkali areas and coastal tidal areas. The material has simple production process, low price and is easy to popularize and apply.

The invention can effectively inhibit the damage caused by the sulfate crystallization of concrete, and is effective in preventing and controlling the sulfate erosion of concrete, especially in environments with high sulfate concentration and frequent dry-wet cycles (such as western saline-alkali land, road surface, tidal zone, etc.) The improvement of sex has important practical significance.

Detailed ways

The present invention is further illustrated below by way of examples.

Example 1

Melamine formaldehyde condensate 73% (weight percentage, the same below)

Lignosulfonate 25%

Modified rosin thermal polymer 2%

Total 100%

The above-mentioned materials are all liquid, put the above-mentioned materials into a disperser, stir for 10 minutes, weigh and pack, and obtain the desired product. The obtained product is mixed into concrete, and its mixing amount in the concrete is 1% by weight of the concrete cementitious material. The air content, expansion rate, spalling amount, compressive strength loss, and flexural strength loss properties of the concrete mixture are shown in Table 1.

Example 2

Fly Ash 50%

Mineral powder 35%

β-methyl naphthalene sulfonate condensation polymer 14.5%

Triterpene saponin air-entraining agent 0.5%

Weight 100%

Add the above-mentioned components into the mixer in proportion, stir for 3-5 minutes, and mix to obtain the desired product, which is bagged and sealed for packaging. The obtained product is mixed into concrete, and the mixing amount in the concrete is 5% of the weight of the concrete cementitious material. The air content, expansion rate, spalling amount, compressive strength loss, and flexural strength loss properties of the concrete mixture are shown in Table 1.

Example 3

Fly Ash 42%

Silica fume 50%

β-methyl naphthalene sulfonate condensation polymer 7.7%

Triterpene saponin air-entraining agent 0.3%

Weight 100%

Add the above-mentioned components into the mixer in proportion, stir for 3-5 minutes, and mix to obtain the desired product, which is bagged and sealed for packaging. The obtained product is mixed into concrete, and its mixing amount in the concrete is 10% of the weight of the concrete cementitious material. The air content, expansion rate, spalling amount, compressive strength loss, and flexural strength loss properties of the concrete mixture are shown in Table 1.

Example 4

Fly Ash 62%

Coal gangue powder 32%

β-methyl naphthalene sulfonate condensation polymer 4.4%

Lignosulfonate 1.5%

Sodium Lauryl Sulfate 0.1%

Total 100%

Add the above-mentioned components into the mixer in proportion, stir for 3-5 minutes, and mix to obtain the desired product, which is bagged and sealed for packaging. The resulting product is mixed into concrete, and its mixing amount in the concrete is 15% of the weight of the concrete cementitious material, and the air content, expansion rate, spalling amount, compressive strength loss, and flexural strength of the concrete mixture See Table 1 for loss performance.

Table 1. Concrete performance comparison before and after using the present invention sample Gas content (%) Expansion rate (×10 ^-4 ) Peeling amount(g/m ² ) Loss of compressive strength (%) Loss of flexural strength (%) benchmark 0.4% 18.75 3570 75.5 56.0 Example 1 3.5% 7.34 1728 60.8 35.3 Example 2 6.2% 3.97 1011 58.3 26.1 Example 3 5.5% 5.31 1370 61.1 28.6 Example 4 4.0 6.55 1531 62.5 31.8

The air content in Table 1 refers to the air content of the concrete mixture; the expansion rate, peeling amount, loss of compressive strength, and loss of flexural strength are the hardened concrete specimens after 28 days of standard curing, in 10% Na ₂ SO ₄ solution The data measured after 18 dry-wet cycles, where the loss of compressive and flexural strength refers to the strength of the concrete specimen after 18 cycles in Na ₂ SO ₄ solution compared with the standard culture specimen after 28 loss rate. As can be seen from Table 1, after using the present invention, the expansion rate and peeling amount of concrete in 10% Na _{SO solution} are significantly reduced, and the loss of compressive strength and flexural strength are greatly reduced, that is, the sulfuric acid resistance of concrete The ability to destroy salt crystals is significantly improved.

Claims (5)

1, a kind of disruption inhibiting material of concrete sulphate crystal is characterized in that being made up of air entrapment agent, water reducer and active admixture, and the weight proportion of its component is:

Weight percentages of components

Water reducer 1.9-98%,

Air entrapment agent 0.1-20%,

Active admixture 0-98%,

Its total amount satisfies 100%;

Wherein, described water reducer is one or more in sulfonated lignin, beta-methylnaphthalene sulfonate polycondensate, melamino-formaldehyde polycondensate or the polycarboxylate dehydragent; Described air entrapment agent is one or more in sodium salt compound, soap compounds, sulfonation hydrocarbon polymer or the alkyl-phenmethyl Sulfonates compound of triterpenoid saponin tensio-active agent, rosin tree lipid; Described active admixture is one or more in flyash, slag micropowder, silicon ash or the colliery powder.

2, disruption inhibiting material of concrete sulphate crystal according to claim 1 is characterized in that being made up of air entrapment agent, water reducer and active admixture, and the weight proportion of its component is:

Weight percentages of components

Water reducer 5-98%

Air entrapment agent 0.1-5%

Active admixture 1.9-92%

Its total amount satisfies 100%.

3, a kind of using method of disruption inhibiting material of concrete sulphate crystal as claimed in claim 1 or 2, it is characterized in that suppressing the incorporation of material in concrete is the 1-20% of concrete gel material weight.

4, the using method of disruption inhibiting material of concrete sulphate crystal according to claim 3, it is characterized in that suppressing the incorporation of material in concrete is the 1-10% of concrete gel material weight.

5, disruption inhibiting material of concrete sulphate crystal according to claim 1 and 2 is characterized in that described flyash grade is I, II level, and the water demand ratio of flyash is less than 105%, and loss on ignition is less than 5%; Described breeze specific surface area is greater than 350m ²/ kg; Described silicon ash loss on ignition is less than 5%, SiO ₂Content is greater than 80%; Described colliery powder specific surface area is greater than 300m ²/ kg.