CN103274653A - High-flexibility and low-shrinkage fiber reinforced cement-based composite material - Google Patents

Abstract

The invention belongs to the technical field of building materials, in particular to a fiber-reinforced cement-based composite material with high toughness and low drying shrinkage. The composite material is made of cement, fly ash, silica fume, gypsum, expansion agent, water reducer, shrinkage reducer, defoamer, thickener, fine sand, fiber and water, among which cement, fly ash, Silica fume, gypsum, expansion agent, water reducer, shrinkage reducer, defoamer, thickener, fine sand and fiber account for 77% to 85% of the total mass, and water accounts for 15% to 23% by mass . The fiber-reinforced cement-based composite material of the invention has the performance characteristics of low drying shrinkage, high toughness, small crack width, fast setting and early strength, high compressive strength, and good synergy with other materials.

Description

A high toughness and low dry shrinkage fiber reinforced cement-based composite material

technical field

The invention belongs to the technical field of building materials, in particular to a fiber-reinforced cement-based composite material with high toughness and low drying shrinkage.

Background technique

Concrete is a typical brittle material. After the load reaches the peak load, its bearing capacity drops sharply, and the deformation occurs concentratedly at the initial crack. Therefore, cracks appear in ordinary concrete structures after the stress exceeds the tensile strength of the concrete. To balance the deformation required by mechanical and environmental loads, the crack width will expand to a macroscopically visible level. Cracking not only reduces the load-bearing capacity of the structure, but also allows moisture and harmful chemicals to penetrate the protective layer and directly contact the steel reinforcement, which eventually leads to a reduction in the durability of the structure.

To solve the long-term durability of concrete, while improving the anti-permeability of the concrete material in a non-cracked state, it is also necessary to control the crack width of the structure after cracking in a complex environment. In the Journal of JSCE, Volume 10, No. 2, 1993, an academic paper titled "Frommicromechanics to structural engineering-the design of cementitious composites for civil engineering application" published by Victor C.Li was published, which explained a High-toughness fiber-reinforced cement-based composites designed through mesomechanics. The material's macro ultimate tensile strain can reach 3% to 5%, and its mechanism is that multiple microcracks are formed during the tensile process of the material (the width of a single crack is about 80μm, and the crack spacing is about 10mm). The characteristic of the macroscopic tensile stress-strain relationship is that the tensile stress does not decrease with the increase of the tensile strain, which is commonly referred to as the phenomenon of strain hardening. The formation of multiple micro-cracks during the stretching process increases the macroscopic tensile strain of the material by more than a hundred times. Due to the bridging effect of the fibers between the cracks, the overall force transmission performance of the material is not weakened by the formation of fine cracks. Due to the excellent stress-strain performance and crack width control function, the future application of this material in civil engineering has attracted widespread attention from scholars at home and abroad.

High-ductility fiber-reinforced cement-based composites have major defects, that is, the base material shrinks too much on drying (drying shrinkage reaches 1500-2000 microstrain in 28 days). Although the crack width is controlled after cracking, the risk of cracking increases due to the excessive drying shrinkage of the material, and the synergistic workability with other materials is significantly deteriorated (the 28-day drying shrinkage strain of ordinary concrete is usually 400-800 microstrain).

Contents of the invention

Aiming at the deficiencies of the prior art, the invention provides a fiber-reinforced cement-based composite material with high toughness and low drying shrinkage.

A fiber-reinforced cement-based composite material with high toughness and low drying shrinkage, the composite material is composed of cement, fly ash, silica fume, gypsum, expansion agent, water reducer, shrinkage reducer, defoamer, thickener, fine sand, Fiber and water are mixed, and the total mass percentage of cement, fly ash, silica fume, gypsum, expansion agent, water reducing agent, shrinkage reducing agent, defoamer, thickener, fine sand and fiber is 77% ~85%, water accounts for 15%~23% by mass.

The specific mass percentages of the cement, fly ash, silica fume, gypsum, expansion agent, water reducing agent, shrinkage reducing agent, defoamer, thickener, fine sand and fiber are as follows:

Cement 20%～26%;

Fly ash 6.6%～8.7%;

Silica fume 1.7%～2.2%;

Gypsum 1.7%～2.2%;

Expansion agent 3.3%～4.3%;

Water reducing agent 0.3%～0.7%;

Shrinkage reducing agent 0.7%～0.9%;

Defoamer 0.06%～0.08%;

Thickener 0.010%～0.014%;

Fine sand 33%～48%;

Fiber 0.8% ~ 1.0%.

The cement is sulphoaluminate cement with a strength grade of 42.5.

The fly ash is a first-class low-calcium fly ash.

The amorphous SiO ₂ content of the silicon powder is greater than 90%.

The gypsum is high-strength building gypsum powder.

The expansion agent is a commercially available sulphoaluminate concrete expansion agent; the shrinkage reducer is a commercially available concrete shrinkage reducer; the defoamer is a commercially available concrete defoamer; the thickener is a commercially available concrete water retention agent thickener.

The thickener is methyl cellulose ether or hydroxypropyl methyl cellulose ether.

The water reducer is a polycarboxylate water reducer or a naphthalene-sulfamate composite water reducer.

The fine sand is 100-200 mesh quartz sand.

The fiber is a polyvinyl alcohol fiber, the fiber length is 12 mm, and the fiber diameter is 39 μm.

The beneficial effects of the present invention are:

The fiber-reinforced cement-based composite material of the present invention has the performance characteristics of low drying shrinkage, high toughness, small crack width, fast setting and early strength, and also has high compressive strength and good synergy with other materials, specifically:

1. Low drying shrinkage

In order to achieve low drying shrinkage of high-toughness fiber-reinforced cement-based materials, an expansion agent is added to the raw materials. The mechanism is: during the early hardening process of cement, the added expansion agent reacts with the hydration product of cement to form calcium vanadium stone with micro-expansion performance, which makes the substrate (mortar) of high-toughness material expand moderately and compensates for various types of shrinkage out of shape.

The test shows that the shrinkage value of the cement-based composite material after material compensation treatment is reduced from 1500 microstrain to 200 microstrain, which is 87% lower than that of the traditional high-toughness fiber-reinforced cement-based composite material. And the shrinkage value is lower than that of ordinary concrete, which means that the high-toughness and low-shrinkage fiber-reinforced cement-based composite material will not crack in the structure of ordinary concrete without cracking, which greatly reduces the cracking risk of traditional high-toughness fiber-reinforced cement-based materials.

2. High toughness

In order to achieve high toughness of materials, the properties of fiber, substrate (mortar) and fiber-substrate interface must be rationally designed by mesomechanics. The elastic modulus of the polyvinyl alcohol fiber selected in the present invention is equivalent to that of the base material, the strength is high, and the bonding performance with the base material is good. By adjusting the water-binder ratio to achieve a good match between the properties of the substrate (strength, fracture toughness, etc.) and the fiber. In addition to low drying shrinkage, the cement-based material designed in this way can also achieve high toughness and fine crack width.

The macroscopic ultimate tensile strain of the material can reach 3%-5%, and its mechanism is that multiple microcracks are formed during the tensile process of the material (the width of a single crack is about 80μm, and the crack spacing is about 10mm). The characteristic of the macroscopic tensile stress-strain relationship is that the tensile stress does not decrease with the increase of the tensile strain, which is commonly referred to as the phenomenon of strain hardening. The formation of multiple micro-cracks during the stretching process increases the macroscopic tensile strain of the material by more than a hundred times. Due to the bridging effect of the fibers between the cracks, the overall force transmission performance of the material is not weakened by the formation of fine cracks.

3. Good compression performance

As a structural engineering material, the high-toughness and low-shrinkage fiber-reinforced cement-based composite material of the present invention should not only have the characteristics of high toughness and low shrinkage, but also have good compression resistance. Due to the selection of cement mortar as the base material of the material and the bridging effect of the fiber on the original crack and the extended crack, the material can obtain good compressive performance. By adjusting the water-binder ratio, the 28d compressive strength of the material can reach 20-30MPa, and the corresponding ultimate compressive strain can reach more than 0.3%.

Detailed ways

The present invention provides a high-toughness and low-shrinkage fiber-reinforced cement-based composite material. The present invention will be further described in conjunction with specific implementation methods below.

Example 1

A fiber-reinforced cement-based composite material with high toughness and low dry shrinkage, which is composed of cement, fly ash, silica fume, gypsum, expansion agent, water reducer, shrinkage reducer, defoamer, thickener, fine sand, fiber and It is mixed with water, of which cement, fly ash, silica fume, gypsum, expansion agent, water reducing agent, shrinkage reducing agent, defoamer, thickener, fine sand and fiber account for 80.5% of the total mass percentage, and water accounts for The mass percentage is 19.5%.

The cement is rapid-hardening sulfoaluminate cement with a strength grade of 42.5; the fly ash is a low-calcium fly ash of the first grade; the silica fume is micro-silica fume produced by Gansu Sanyuan Silicon Material Co., Ltd.; the gypsum is high-strength building gypsum powder; The expansion agent is a commercially available ZY composite concrete expansion agent; the water reducer is a polycarboxylate high-efficiency water reducer; the shrinkage reducer is a commercially available concrete shrinkage reducer; the defoamer is Lumiten EL type defoamer produced by Shanghai BASF Applied Chemical Co., Ltd. The thickener is a commercially available concrete water-retaining thickener, and its component is hydroxypropyl methylcellulose ether; the fine sand is 100-200 mesh quartz sand; the fiber is polyvinyl alcohol fiber produced by Japan Kuraray Company. The mass percent of above-mentioned each component is as follows:

Rapid hardening sulfoaluminate cement 26%; fly ash 8.7%; silica fume 2.2%; gypsum powder 2.2%; expansion agent 4.3%; polycarboxylate superplasticizer 0.4%; %; water-retaining thickener 0.01%; 100-200 mesh quartz sand 35%; polyvinyl alcohol fiber 1%.

The preparation of the above-mentioned high-toughness and low-shrinkage fiber-reinforced cement-based composite material: cement, fly ash, silica fume, gypsum, expansion agent, water-reducing agent, shrinkage-reducing agent, defoamer, thickener, fine sand, Fiber and water are mixed and stirred to obtain the product.

The test results of the various performances of the products obtained in this embodiment are listed in Table 1. Among them, the test blocks used in the mechanical test were put into the standard curing room for water curing (temperature 20±2°C) after demoulding for 24 hours, and the tensile and compressive tests were carried out on the mechanical testing machine after 28 days; the dry shrinkage test was carried out with cement The rubber sand dilatation measuring instrument is used, and the test block is placed under standard test conditions for 24 hours, and then the mold is removed, and then its shrinkage value at each age is measured.

Table 1 Example 1 High toughness and low drying shrinkage fiber reinforced cement-based composite material test results table (28 days)

Tensile strength/MPa 4.84 Ultimate tensile strain/% 1.49 Compressive strength/MPa 27.54 Ultimate compressive strain/% 0.55 Shrinkage value/με 109

Example 2

A fiber-reinforced cement-based composite material with high toughness and low dry shrinkage, which is composed of cement, fly ash, silica fume, gypsum, expansion agent, water reducer, shrinkage reducer, defoamer, thickener, fine sand, fiber and It is mixed with water, of which cement, fly ash, silica fume, gypsum, expansion agent, water reducing agent, shrinkage reducing agent, defoamer, thickener, fine sand and fiber account for 79% by mass, and water accounts for 79% by mass The percentage is 21%.

The cement is rapid-hardening sulfoaluminate cement with a strength grade of 42.5; the fly ash is a low-calcium fly ash of the first grade; the silica fume is micro-silica fume produced by Gansu Sanyuan Silicon Material Co., Ltd.; the gypsum is high-strength building gypsum powder; The expansion agent is a commercially available ZY composite concrete expansion agent; the water reducer is a naphthalene-sulfamate composite high-efficiency water reducer; the shrinkage reducer is a commercially available concrete shrinkage reducer; the defoamer is produced by Shanghai BASF Applied Chemical Co., Ltd. Lumiten EL type defoamer; the thickener is a commercially available concrete water-retaining thickener, and its component is hydroxypropyl methyl cellulose ether; the fine sand is 100-200 mesh quartz sand; the fiber is polyester produced by Japan Kuraray Company Vinyl fibers. The mass percent of above-mentioned each component is as follows:

Rapid hardening sulfoaluminate cement 25.5%; fly ash 8.55%; silica fume 2.2%; gypsum powder 2.2%; expansion agent 4.2%; polycarboxylate superplasticizer 0.4%; %; water-retaining thickener 0.02%; 100-200 mesh quartz sand 34%; polyvinyl alcohol fiber 1%.

The preparation of the above-mentioned high-toughness and low-shrinkage fiber-reinforced cement-based composite material: cement, fly ash, silica fume, gypsum, expansion agent, water-reducing agent, shrinkage-reducing agent, defoamer, thickener, fine sand, Fiber and water are mixed and stirred to obtain the product.

The test results of the various performances of the product obtained in this embodiment are listed in Table 2. Among them, the test blocks used in the mechanical test were put into the standard curing room for water curing (temperature 20±2°C) after demoulding for 24 hours, and the tensile and compressive tests were carried out on the mechanical testing machine after 28 days; the dry shrinkage test was carried out with cement The rubber sand dilatation measuring instrument is used, and the test block is placed under standard test conditions for 24 hours, and then the mold is removed, and then its shrinkage value at each age is measured.

Table 2 Example 2 High toughness and low drying shrinkage fiber reinforced cement-based composite material test results (28 days)

Tensile strength/MPa 4.03 Ultimate tensile strain/% 1.24 Compressive strength/MPa 20.94 Ultimate compressive strain/% 0.45 Shrinkage value/με 202

Claims (10)

1. A fiber-reinforced cement-based composite material with high toughness and low dry shrinkage, characterized in that: the composite material is composed of cement, fly ash, silicon powder, gypsum, expansion agent, water reducing agent, shrinkage reducing agent, defoamer, Thickener, fine sand, fiber and water, of which cement, fly ash, silica fume, gypsum, expansion agent, water reducer, shrinkage reducer, defoamer, thickener, fine sand and fiber account for The total mass percentage is 77%-85%, and water accounts for 15%-23% by mass. The specific mass percentages of the cement, fly ash, silica fume, gypsum, expansion agent, water reducing agent, shrinkage reducing agent, defoamer, thickener, fine sand and fiber are as follows: Cement 20%～26%; Fly ash 6.6%～8.7%; Silica fume 1.7%～2.2%; Gypsum 1.7%～2.2%; Expansion agent 3.3%～4.3%; Water reducing agent 0.3%～0.7%; Shrinkage reducing agent 0.7%～0.9%; Defoamer 0.06%～0.08%; Thickener 0.010%～0.014%; Fine sand 33%～48%; Fiber 0.8% ~ 1.0%. 2. The composite material according to claim 1, characterized in that the cement is sulphoaluminate cement with a strength grade of 42.5. 3. The composite material according to claim 1, characterized in that: the fly ash is a first-grade low-calcium fly ash. 4. The composite material according to claim 1, characterized in that: the amorphous SiO ₂ content of the silicon powder is greater than 90%. 5. The composite material according to claim 1, characterized in that: the gypsum is high-strength building gypsum powder. 6. The composite material according to claim 1, characterized in that: the expansion agent is a commercially available sulphoaluminate concrete expansion agent; the shrinkage reducer is a commercially available concrete shrinkage reducer; the defoamer is a commercially available commercially available concrete defoamer; the thickener is a commercially available concrete water-retaining thickener. 7. The composite material according to claim 6, characterized in that: the thickener is methyl cellulose ether or hydroxypropyl methyl cellulose ether. 8. The composite material according to claim 1, wherein the water reducer is a polycarboxylate water reducer or a naphthalene-sulfamate composite water reducer. 9. The composite material according to claim 1, characterized in that: the fine sand is 100-200 mesh quartz sand. 10. The composite material according to claim 1, characterized in that: the fibers are polyvinyl alcohol fibers, the fiber length is 12 mm, and the fiber diameter is 39 μm.