CN116283002A - Concrete modifier, preparation method thereof and concrete - Google Patents

Abstract

The application discloses a concrete modifier, a preparation method thereof and concrete, wherein the concrete modifier comprises the following components in parts by weight: 50-60 parts of plant fiber, 20-40 parts of polypropylene fiber, 5-10 parts of silica fume and 5-10 parts of metakaolin. The concrete modifier prepared by the method is environment-friendly, has better compatibility with concrete, greatly improves the tensile strength of the concrete, is doped with a small amount of the modifier in the preparation process of the concrete, can remarkably improve the folding resistance and the tensile strength of the concrete, and can keep longer service life under various environmental climates.

Description

Concrete modifier, preparation method thereof and concrete

Technical Field

The application relates to the field of concrete modifiers, in particular to a concrete modifier, a preparation method thereof and concrete.

Background

Concrete is widely used in modern engineering construction due to its low cost, sturdiness and durability, and strong plasticity. However, the concrete is a non-uniform brittle material, the tensile strength of the material is far lower than the compressive strength, but as a common building material, the concrete needs to meet different impact loads, has better tensile strength, and otherwise, potential safety hazards are easily caused. Plant fibers are therefore often incorporated into concrete to increase the tensile strength of the concrete; however, most of the concrete materials have nonpolar and hydrophobic properties, while most of the plant fibers are hydrophilic materials, so that the compatibility of the plant fibers and the concrete is poor.

Disclosure of Invention

In order to solve the problem that plant fibers have poor compatibility with concrete so as to influence the tensile strength of the concrete, the application provides a concrete modifier, a preparation method thereof and the concrete.

In the first aspect, the concrete modifier comprises the following components in parts by weight:

50-60 parts of plant fiber, 20-40 parts of polypropylene fiber, 5-10 parts of silica fume and 5-10 parts of metakaolin.

By adopting the technical scheme, the plant fiber is used as a recyclable material with low price and rich sources, is used as a main physical supporting structure in plants, has higher strength and rigidity, and can well improve the splitting tensile property of concrete. The polypropylene fiber is an artificial synthetic fiber with high tensile strength, good flexibility and low cost, and can improve the splitting performance and the fracture resistance of concrete. When the polypropylene fiber and the plant fiber are mixed for use, the polypropylene fiber improves the performances of chemical resistance, dimensional stability and the like of the plant fiber, and improves the durability of the concrete; the plant fiber can improve the ductility and toughness of the polypropylene fiber, and the composite material formed by the plant fiber and the polypropylene fiber has a synergistic effect in improving the tensile strength and the fracture resistance of concrete. The silica fume and metakaolin can react with hydration product calcium hydroxide in the concrete for secondary hydration, so that the alkalinity of the concrete is reduced, and the phenomenon that the plant fibers are embrittled and lose effect due to the fact that the calcium hydroxide gradually migrates to the internal pores of the plant fibers is reduced; and the interfacial binding force between the plant fiber and the concrete, between the plant fiber and the polypropylene fiber and between the polypropylene fiber and the concrete can be improved, the compatibility between the concrete modifier and the concrete can be improved, and the modifying effect of the concrete modifier can be further exerted.

Preferably, the plant fiber comprises hemp fiber and bamboo fiber, and the weight ratio of the hemp fiber to the bamboo fiber is (9-11): 1.

By adopting the technical scheme, the fibrilia has good mechanical property, ductility and corrosion resistance, the tensile strength and the fracture resistance of concrete can be better improved, the fibrilia has larger surface roughness, and the bonding performance between the fibrilia and the concrete and the polypropylene fiber is relatively better. The bamboo fiber has a large number of hollow structures among the fibers, and has good ductility and toughness. The bamboo fiber and fibrilia can synergistically improve the flexural performance and tensile strength of the concrete.

Preferably, the weight ratio of the plant fiber, the silica fume and the metakaolin is (6-10) 1:1.

By adopting the technical scheme, the weight ratio of the silica fume to the metakaolin is optimized, so that the concrete modified by the concrete modifier has better tensile strength, and excessive gelatinous substances are reduced in the hydration process of the concrete, thereby affecting the fluidity of the cement and the contractility of the concrete, and further affecting the fracture resistance and the splitting tensile property of the concrete.

Preferably, the hemp fiber is modified sisal fiber, and the modified sisal fiber is obtained by performing carboxymethylation, nano silicon dioxide deposition and heat treatment on the sisal fiber.

By adopting the technical scheme, sisal fibers are selected, compared with other hemp fibers, the sisal fibers have higher cellulose content, fewer impurities and better tensile strength and elasticity, and when the sisal fibers are used together with polypropylene fibers, the modification effect of the concrete modifier can be further improved. The pectin in the sisal fibers is removed by carboxymethyl modified sisal fibers, so that the length-diameter ratio of the fibers is improved, and the tensile strength of the sisal fibers is improved; hydroxyl groups on the surface of sisal fibers are reduced greatly, carboxyl groups are introduced, so that positive charges are carried on the surface of sisal fibers, electrostatic attractive force is generated between the sisal fibers and cement particles, and the active carboxyl groups can be chemically bonded with cement base materials, so that the compatibility between the concrete modifier and cement is further improved; the formed carboxylic acid groups can also reduce the influence of calcium hydroxide crystals on interface binding force in the hydration process, and further improve the durability and tensile strength of the concrete.

In addition, more surface ravines formed on the surface of the sisal fiber after carboxymethylation modification and active carboxyl groups introduced on the surface are utilized to deposit nano silicon dioxide on the surface of the sisal fiber. On one hand, the surface roughness, specific surface area and hydrophobicity of the sisal fibers are improved, and the compatibility of the sisal fibers with polypropylene fibers and concrete is improved; on the other hand, the nano silicon dioxide is used as a rigid particle to repair the surface ravines of the sisal hemp fiber, so that the bending resistance and the tensile strength of the sisal hemp fiber are improved. In addition, the nano silicon dioxide can form a synergistic effect with silica fume and metakaolin, so that chemical damage of alkalizing substances in the concrete to plant fibers is reduced, and the modifying effect of the concrete modifier is further affected.

Further, the sisal fiber deposited by the nano silicon dioxide is subjected to heat treatment, so that moisture and volatile substances in the sisal fiber are volatilized, the looseness of cellulose is improved, and the ductility of the sisal fiber is further improved; meanwhile, hemicellulose and lignin are cracked to form micromolecular organic matters, the hydroxyl groups on the surfaces are further reduced due to dehydration reaction, and the internal structure of the fiber is crosslinked to form new chemical bonds, so that the hydrophobicity of the sisal fiber is improved, the free energy on the surface is reduced, the polarity on the surface is reduced, and the compatibility with concrete and polypropylene fibers is improved; reduces the water absorption and swelling property of the sisal fibers and enhances the erosion resistance of the sisal fibers to concrete alkalization. The surface impurities of the nano silicon dioxide are removed, the pore structure of the surface of the nano silicon dioxide is exposed, and the specific surface area and the hydrophobic property of the modified sisal fiber are improved.

Preferably, the raw materials of the modified sisal fibers comprise the following components in parts by weight: 10 parts of sisal fibers, 60-105 parts of sodium chloroacetate, 0.2-0.3 part of catalyst, 1-3 parts of tetraethoxysilane and 0.2-0.4 part of ammonia water.

By adopting the technical scheme, the modified sisal fiber has better tensile property and substrate compatibility by adopting the raw material components with the preferable weight parts.

Preferably, 4-dimethylaminopyridine is used as the catalyst.

By using 4-diaminopyridine as a catalyst, the substitution degree of carboxymethyl in sisal fiber can be increased, and the carboxymethylation effect can be further improved.

Preferably, the modified sisal fiber is prepared by the following method:

carboxymethylation: dissolving sodium chloroacetate and a catalyst in isopropanol to obtain a sodium chloroacetate solution, immersing sisal fibers in a sodium hydroxide solution with the concentration of 2-4mol/L for alkali treatment for 1-3 hours, taking out, immersing in the sodium chloroacetate solution again, mixing for 4-6 hours, washing with acid liquor to be neutral, and drying to obtain carboxymethylated sisal fibers;

depositing nano silicon dioxide: dissolving ethyl orthosilicate in absolute ethyl alcohol to obtain ethyl orthosilicate solution, immersing sisal fiber in the ethyl orthosilicate solution, mixing and stirring for 20-40min, then adding ammonia water, mixing and stirring for 3-5h for the second time, washing and drying to obtain nano silicon dioxide-sisal fiber;

and (3) heat treatment: heating nanometer silicon dioxide-sisal fiber in 120-280 deg.C closed environment for 10-15min, taking out, and oven drying at 50-70 deg.C for 1-2 hr to obtain modified sisal fiber.

Typically, but not by way of limitation, the acid solution may be a conventional solution such as dilute sulfuric acid and dilute hydrochloric acid.

By adopting the technical scheme, parameters in the sisal fiber modification method are optimized, and the sisal fibers are modified in an economic and effective mode, so that the performance of the sisal fibers is improved, and meanwhile, the cost is reduced.

Preferably, the heat treatment step is as follows: heating nanometer silicon dioxide-sisal fiber in a sealed environment at 150-230deg.C for 10-15min, taking out, and oven drying at 50-70deg.C for 1-2 hr to obtain modified sisal fiber.

By adopting the technical scheme, the temperature adopted by the heat treatment is further optimized, the pyrolysis degree of sisal fibers is optimized, the plant fibers obtain better substrate compatibility, and the compatibility and the tensile strength of the concrete modifier are further improved.

In a second aspect, a method for preparing a concrete modifier, comprising the steps of:

and (3) placing polypropylene fibers, plant fibers, silica fume and metakaolin into an internal mixer, banburying for 2-4min at 160-200 ℃, cooling, drying, and performing injection molding to obtain the concrete modifier.

The components of the concrete are mixed together in an banburying mode, so that the uniformity of the components of the concrete modifier is improved, and the dispersibility of the concrete modifier in the concrete is improved, so that the modifying effect of the concrete modifier is improved.

In a third aspect, a concrete, wherein 0.5kg of said concrete modifier is added per cubic meter of concrete.

The concrete modifier has a good modification effect, and the tensile strength and the fracture resistance of concrete can be obviously improved by only doping a small amount of the concrete modifier.

In summary, the application has the following beneficial effects:

1. the composite material is formed by plant fibers and polypropylene fibers, and the concrete modifier is formed by matching silica fume and metakaolin, so that the concrete modifier has good compatibility with concrete, the tensile property of the concrete can be remarkably improved, and the concrete modifier has the advantages of environmental protection and the like.

2. The sisal fibers are modified in the modes of carboxymethylation, nano silicon dioxide deposition and heat treatment in sequence, so that the compatibility and interfacial binding force of the concrete modifier and concrete are remarkably improved, and the modifying effect of the concrete modifier on the concrete is further improved.

Detailed Description

The present application is described in further detail below with reference to examples.

Preparation of modified sisal fibers

Preparation example 1-1, a modified sisal fiber, was prepared by the following steps:

carboxymethylation: 83g of sodium chloroacetate and 0.25g of 4-dimethylaminopyridine are dissolved in 500mL of isopropanol to obtain sodium chloroacetate solution, 10g of sisal fiber is immersed in 500mL of 3mol/L sodium hydroxide solution for standing for 2 hours, taken out, immersed in sodium chloroacetate solution again, mixed and stirred for 5 hours, washed to be neutral by 1mol/L dilute hydrochloric acid solution, and dried to obtain carboxymethylated sisal fiber;

depositing nano silicon dioxide: dissolving 2g of ethyl orthosilicate in 100mL of absolute ethyl alcohol to obtain an ethyl orthosilicate solution, immersing the carboxymethylated sisal fibers in the ethyl orthosilicate solution, mixing and stirring for 30min, then adding 0.3g of ammonia water, mixing and stirring for 4h for the second time, washing and drying to obtain nano silicon dioxide-sisal fibers;

and (3) heat treatment: heating nanometer silicon dioxide-sisal fiber in 190 deg.C closed environment for 13min, taking out, and oven drying at 60 deg.C for 1.5 hr to obtain modified sisal fiber.

Preparation examples 1-2, a modified sisal fiber, were prepared by the following steps:

carboxymethylation: dissolving 105g of sodium chloroacetate and 0.3g of 4-dimethylaminopyridine in 500mL of isopropanol to obtain sodium chloroacetate solution, immersing 10g of sisal fiber in 500mL of 3mol/L sodium hydroxide solution, standing for 1h, taking out, immersing in sodium chloroacetate solution again, mixing and stirring for 4h, washing to be neutral by using 1mol/L dilute hydrochloric acid solution, and drying to obtain carboxymethylated sisal fiber;

depositing nano silicon dioxide: dissolving 3g of ethyl orthosilicate in 100mL of absolute ethyl alcohol to obtain an ethyl orthosilicate solution, immersing the carboxymethylated sisal fibers in the ethyl orthosilicate solution, mixing and stirring for 20min, then adding 0.4g of ammonia water, mixing and stirring for 5h for the second time, washing and drying to obtain nano silicon dioxide-sisal fibers;

and (3) heat treatment: heating nanometer silicon dioxide-sisal fiber in 230 deg.C closed environment for 10min, taking out, and oven drying at 60deg.C for 2 hr to obtain modified sisal fiber.

Preparation examples 1-3, a modified sisal fiber, were prepared by the following steps:

carboxymethylation: dissolving 60g of sodium chloroacetate and 0.2g of 4-dimethylaminopyridine in 500mL of isopropanol to obtain sodium chloroacetate solution, immersing 10g of sisal fiber in 500mL of 3mol/L sodium hydroxide solution, standing for 3h, taking out, immersing in sodium chloroacetate solution again, mixing and stirring for 6h, washing to be neutral by using 1mol/L dilute hydrochloric acid solution, and drying to obtain carboxymethylated sisal fiber;

depositing nano silicon dioxide: dissolving 1g of ethyl orthosilicate in 100mL of absolute ethyl alcohol to obtain an ethyl orthosilicate solution, immersing the carboxymethylated sisal fibers in the ethyl orthosilicate solution, mixing and stirring for 20min, then adding 0.2g of ammonia water, mixing and stirring for 5h for the second time, washing and drying to obtain nano silicon dioxide-sisal fibers;

and (3) heat treatment: heating nanometer silicon dioxide-sisal fiber in a sealed environment at 150deg.C for 15min, taking out, and oven drying at 60deg.C for 1 hr to obtain modified sisal fiber.

Preparation examples 1-4, a modified sisal fiber, was different from preparation example 1-1 in that the temperature of the closed environment was 280℃in the heat treatment stage.

Preparation examples 1-5, a modified sisal fiber, were different from preparation example 1-1 in that the temperature of the closed environment was 120℃in the heat treatment stage.

Preparation examples 1-6, a modified sisal fiber, were prepared by the following steps:

depositing nano silicon dioxide: dissolving 2g of ethyl orthosilicate in 100mL of absolute ethyl alcohol to obtain ethyl orthosilicate solution, immersing sisal fibers in the ethyl orthosilicate solution, mixing and stirring for 30min, then adding 0.3g of ammonia water, mixing and stirring for 4h for the second time, washing and drying to obtain nano silicon dioxide-sisal fibers;

and (3) heat treatment: heating nanometer silicon dioxide-sisal fiber in 190 deg.C closed environment for 13min, taking out, and oven drying at 60deg.C for 1.5 hr to obtain modified sisal fiber (i.e. sisal fiber is not subjected to carboxymethylation treatment).

Preparation examples 1-7, a modified sisal fiber, were prepared by the following steps:

carboxymethylation: 83g of sodium chloroacetate and 0.25g of 4-dimethylaminopyridine are dissolved in 500mL of isopropanol to obtain sodium chloroacetate solution, 10g of sisal fiber is immersed in 500mL of 3mol/L sodium hydroxide solution for standing for 2 hours, taken out, immersed in sodium chloroacetate solution again, mixed and stirred for 5 hours, washed to be neutral by 1mol/L dilute hydrochloric acid solution, and dried to obtain carboxymethylated sisal fiber;

and (3) heat treatment: heating carboxymethylated sisal fiber in 190 deg.c closed environment for 13min, taking out, and stoving at 60 deg.c for 1.5 hr to obtain modified sisal fiber (without depositing nanometer silica).

Preparation examples 1-8, a modified sisal fiber, were prepared by the following steps:

carboxymethylation: 83g of sodium chloroacetate and 0.25g of 4-dimethylaminopyridine are dissolved in 500mL of isopropanol to obtain sodium chloroacetate solution, 10g of sisal fiber is immersed in 500mL of 3mol/L sodium hydroxide solution for standing for 2 hours, taken out, immersed in sodium chloroacetate solution again, mixed and stirred for 5 hours, washed to be neutral by 1mol/L dilute hydrochloric acid solution, and dried to obtain carboxymethylated sisal fiber;

depositing nano silicon dioxide: 2g of ethyl orthosilicate is dissolved in 100mL of absolute ethyl alcohol to obtain an ethyl orthosilicate solution, the carboxymethylated sisal fibers are immersed in the ethyl orthosilicate solution, mixed and stirred for 30min, then 0.3g of ammonia water is added, mixed and stirred for 4h for the second time, and the modified sisal fibers are obtained after washing and drying (i.e. without a heat treatment step).

Preparation examples 1-9, a modified sisal fiber, were prepared by the following steps:

and (3) heat treatment: heating sisal fiber in 190 deg.c closed environment for 13min, taking out, stoving at 60 deg.c for 1.5 hr to obtain modified sisal fiber (i.e. heat treatment step).

Examples

Example 1, a concrete modifier, was prepared using the following steps:

55g of plant fiber, 30g of polypropylene fiber, 7.5g of silica fume and 7.5g of metakaolin are taken and put into an internal mixer for banburying for 3 minutes at 180 ℃, and after cooling and drying, the concrete modifier is obtained by injection molding.

Wherein the plant fiber is formed by mixing 50g of modified sisal fiber and 5g of bamboo fiber, and the modified sisal fiber is derived from preparation example 1-1. The rotation speed of the internal mixer is 50r/min, and the drying condition is that the temperature is 60 ℃ and the drying time is 20h.

Example 2, a concrete modifier, was prepared using the following steps:

60g of plant fiber, 20g of polypropylene fiber, 10g of silica fume and 10g of metakaolin are taken and put into an internal mixer for banburying for 4 minutes at 160 ℃, and after cooling and drying, the concrete modifier is obtained by injection molding.

Wherein the plant fiber is formed by mixing 55g of modified sisal fiber and 5g of bamboo fiber, and the modified sisal fiber is derived from preparation examples 1-3. The rotation speed of the internal mixer is 50r/min, and the drying condition is that the temperature is 60 ℃ and the drying time is 20h.

Example 3, a concrete modifier, was prepared using the following steps:

50g of plant fiber, 40g of polypropylene fiber, 5g of silica fume and 5g of metakaolin are taken and put into an internal mixer for banburying for 2 minutes at 180 ℃, and after cooling and drying, the concrete modifier is obtained by injection molding.

Wherein the plant fiber is formed by mixing 45g of modified sisal fiber and 5g of bamboo fiber, and the modified sisal fiber is derived from preparation examples 1-3. The rotation speed of the internal mixer is 50r/min, and the drying condition is that the temperature is 60 ℃ and the drying time is 20h.

Example 4, a concrete modifier, differs from example 1 in that the modified sisal fibers are derived from preparation examples 1-4.

Example 5, a concrete modifier, differs from example 1 in that the modified sisal fibers are derived from preparation examples 1-5.

Example 6, a concrete modifier, differs from example 1 in that the modified sisal fibers are derived from preparation examples 1-6.

Example 7, a concrete modifier, differs from example 1 in that the modified sisal fibers are derived from preparation examples 1-7.

Example 8, a concrete modifier, differs from example 1 in that the modified sisal fibers are derived from preparation examples 1-8.

Example 9, a concrete modifier, differs from example 1 in that the modified sisal fibers are derived from preparation examples 1-9.

Example 10, a concrete modifier, differs from example 1 in that the bamboo fibers are replaced with an equivalent amount of modified sisal fibers.

Example 11, a concrete modifier, differs from example 1 in that the plant fiber was obtained by mixing 25g of modified sisal fiber and 20g of bamboo fiber.

Comparative example

Comparative example 1, a concrete modifier, differs from example 1 in that the polypropylene fibers are replaced with equal amounts of vegetable fibers, the weight ratio of modified sisal fibers to bamboo fibers in the vegetable fibers being 10:1.

Comparative example 2, a concrete modifier, differs from example 1 in that the silica fume and metakaolin are replaced with equal amounts of vegetable fibers, the weight ratio of modified sisal fibers to bamboo fibers in the vegetable fibers being 10:1.

Comparative example 3, a concrete modifier, comprising the following components in parts by weight: 16 parts of chitosan, 15 parts of sodium 4-isopropylbenzene sulfonate, 12 parts of 2-mercaptobenzothiazole, 6 parts of methyl dihydrojasmonate, 11 parts of p-nitrosodimethylaniline and 7 parts of isooctyl acetate.

The method comprises the following steps: (1) Adding p-nitrosodimethylaniline, chitosan and methyl dihydrojasmonate into a reaction kettle, adding 20 parts of 85% ethanol solution, protecting with nitrogen, and stirring at-70 ℃ for reaction for 2 hours; (2) Mixing 2-mercaptobenzothiazole with isooctyl acetate, adding 75% ethanol solution 2 times of the mixture by weight, and uniformly mixing; obtaining a first mixed solution; (3) Dropwise adding the mixed solution into the reaction kettle in the step (1), wherein the dropwise adding speed is 100 drops/min; (4) Heating the reaction kettle to-5 ℃, adding 4-sodium isopropylbenzene sulfonate, and stirring for reacting for 1h; (5) And continuously heating the obtained product to 80 ℃, stirring and reacting for 1h, and preserving heat for 20min to obtain the product.

Performance test

Concrete modifiers of examples 1 to 11 and comparative examples 1 to 3 were prepared by adding 0.5kg of the concrete modifier per cubic meter of concrete, and then each sample of the concrete was tested, and each sample was tested 6 times in parallel, and the results were averaged, and the results are shown in table 1.

Test 1: tensile strength, refer to GB/T50081-2002 standard for test method of mechanical properties of ordinary concrete, and curing age is 28d.

Test 2: flexural strength, refer to GB/T50081-2002 standard for test methods of mechanical Properties of ordinary concrete, and curing age is 28d.

Table 1: test results of tensile Strength and flexural Strength of examples 1-11, comparative examples 1-3

Group of	Tensile Strength/MPa	Flexural Strength/MPa	Destruction morphology
				Example 1	46	64	Ductile failure
Example 2	44	62	Ductile failure
				Example 3	45	62	Ductile failure
Example 4	37	52	Ductile failure
				Example 5	35	49	Ductile failure
Example 6	33	44	Ductile failure
				Example 7	39	54	Ductile failure
Example 8	34	48	Ductile failure
				Example 9	26	39	Brittle fracture
Example 10	40	58	Ductile failure
				Example 11	37	56	Ductile failure
Comparative example 1	30	41	Ductile failure
				Comparative example 2	32	45	Brittle fracture
Comparative example 3	22	35	Brittle fracture

As can be seen from the combination of examples 1 to 5 and table 1, the sisal fibers are better modified in the heat treatment step at the temperature of 150 to 230 ℃ in the closed environment, and the prepared concrete modifier is more remarkable in improvement of the concrete performance because of the following reasons: when the temperature is less than or equal to 150 ℃, the sisal fiber only loses internal moisture and a small part of volatile substances, and the internal structure and components are not changed, so that the performances of the sisal fiber, such as surface polarity, hydrophobicity and the like, are not greatly changed, and the surface nano silicon dioxide and the fiber are not subjected to stronger crosslinking, so that the bonding fastness of the nano silicon dioxide and polypropylene can not be improved; and when the temperature is higher than or equal to 280 ℃, the carbonization degree of the sisal fibers is too high, so that the sisal fibers lose toughness and ductility. When the temperature is 150-230 ℃, lignin and hemicellulose in the sisal fibers are partially decomposed, new cross-links are formed between the fibers and between nano silicon dioxide and the fibers, the hydrophobicity and the surface polarity of the sisal fibers are improved, the compatibility of the modified sisal fibers and polypropylene fibers is good, the prepared concrete modifier is good in compatibility with concrete, the tensile strength and the flexural strength of the concrete can be remarkably improved, the concrete is converted from brittle failure to ductile failure, and the safety performance of the concrete is improved.

By combining the embodiment 1 and the embodiment 6-7 and combining the table 1, it can be seen that the prepared concrete modifier has better compatibility with concrete by adopting carboxymethylation, depositing nano silicon dioxide and thermally treated modified sisal fiber, can obviously improve the flexural property and tensile strength of the concrete, but one or two steps are omitted, so that the modification effect of the concrete modifier can be influenced, and the roughness of the sisal fiber and the surface charge quantity can be influenced if the carboxymethylation modification is not carried out, so that the compatibility of the sisal fiber with other substances is further influenced; in addition, the deposition effect of the nano silicon dioxide is also affected, the nano silicon dioxide belongs to nano particles, and if the fiber coating surface has no carboxyl groups and the hydroxyl groups of the nano silicon dioxide are combined to form chemical bonds, the agglomeration effect is easy to generate, and the modification effect of the concrete modifier is affected; furthermore, the combination of carboxymethylation and heat treatment can further reduce the number of hydroxyl groups on the surface of the fiber, reduce calcium hydroxide particles formed in an interface bonding area and improve the interface bonding force. If the nano silicon dioxide is not deposited, the nano silicon dioxide has better mechanical property, can reduce the surface free energy of the fiber surface, improve the hydrophobicity of the fiber, can fill the gaps and the pores of the fiber, reduce the formation of calcium hydroxide crystals in the fiber, and improve the folding resistance and the compatibility of the sisal fiber; meanwhile, the sisal fiber after depositing the nano silicon dioxide can be crosslinked with the nano silicon dioxide in the process of forming new crosslinking among fiber structures in the heat treatment process, so that the agglomeration phenomenon of the nano silicon dioxide is reduced, the nano silicon dioxide is uniformly dispersed in all the ravines and pores of the fiber to form a large number of micro stress areas, and when the sisal fiber is stretched, a large number of micro deformations occur, so that the concrete has better bending resistance and tensile strength. If only heat treatment is used, the ductility and tensile strength of sisal fibers are reduced, and the modifying effect of the concrete modifier is affected.

In combination with example 1 and examples 10-11 and with Table 1, it can be seen that the compatibility between the modified sisal fibers and the bamboo fibers is due to the fact that the fibers in the bamboo fibers have larger gaps, and have better ductility and tensile strength, while the fibers in the modified sisal fibers are more slender and elastic, and the plant fibers obtained by combining the modified sisal fibers and the bamboo fibers can provide stronger bending resistance and tensile strength.

In combination with example 1, comparative examples 1 to 3 and table 1, it can be seen that polypropylene fiber, silica fume and metakaolin all enhance the modifying effect of the concrete modifier because plant fiber is easily damaged by alkaline crystals formed in concrete, and the compatibility of plant fiber with concrete is poor, polypropylene fiber can protect plant fiber, silica fume and metakaolin can improve the compatibility of plant fiber with concrete, and the synergistic effect between the four can enhance the modifying effect of the concrete modifier. Compared with the common concrete modifier, the concrete modifier has the characteristics of less mixing amount and obvious effect, and the concrete modifier adopted by the application is wide in source, green and environment-friendly, and meets the national call of low carbon and environment protection.

The present embodiment is merely illustrative of the present application and is not intended to be limiting, and those skilled in the art, after having read the present specification, may make modifications to the present embodiment without creative contribution as required, but is protected by patent laws within the scope of the claims of the present application.

Claims (10)

1. The concrete modifier is characterized by comprising the following components in parts by weight:

50-60 parts of plant fiber, 20-40 parts of polypropylene fiber, 5-10 parts of silica fume and 5-10 parts of metakaolin.

2. A concrete modifier according to claim 1, wherein the plant fibers comprise hemp fibers and bamboo fibers in a weight ratio of (9-11): 1.

3. A concrete modifier according to claim 1, wherein the weight ratio of vegetable fibre, silica fume and metakaolin is (6-10): 1:1.

4. The concrete modifier of claim 1, wherein the hemp fiber is modified sisal fiber, and the modified sisal fiber is obtained by performing carboxymethylation, nano silicon dioxide deposition and heat treatment on sisal fiber.

5. The concrete modifier according to claim 4, wherein the raw materials of the modified sisal fibers comprise the following components in parts by weight: 10 parts of sisal fibers, 60-105 parts of sodium chloroacetate, 0.2-0.3 part of catalyst, 1-3 parts of tetraethoxysilane and 0.2-0.4 part of ammonia water.

6. A concrete modifier according to claim 5, wherein said catalyst is 4-dimethylaminopyridine.

7. The concrete modifier of claim 4, wherein the modified sisal fibers are prepared by the following method:

carboxymethylation: dissolving sodium chloroacetate and a catalyst in isopropanol to obtain a sodium chloroacetate solution, immersing sisal fibers in a sodium hydroxide solution with the concentration of 2-4mol/L for alkali treatment for 1-3 hours, taking out, immersing in the sodium chloroacetate solution again, mixing for 4-6 hours, washing with acid liquor to be neutral, and drying to obtain carboxymethylated sisal fibers;

depositing nano silicon dioxide: dissolving ethyl orthosilicate in absolute ethyl alcohol to obtain ethyl orthosilicate solution, immersing carboxymethylated sisal fibers in the ethyl orthosilicate solution, mixing and stirring for 20-40min, adding ammonia water, mixing and stirring for 3-5h for the second time, washing and drying to obtain nano silicon dioxide-sisal fibers;

and (3) heat treatment: heating nanometer silicon dioxide-sisal fiber in 120-280 deg.C closed environment for 10-15min, taking out, and oven drying at 50-70 deg.C for 1-2 hr to obtain modified sisal fiber.

8. A concrete modifier according to claim 7, said heat treatment step being: heating nanometer silicon dioxide-sisal fiber in a sealed environment at 150-230deg.C for 10-15min, taking out, and oven drying at 50-70deg.C for 1-2 hr to obtain modified sisal fiber.

9. The method for preparing a concrete modifier according to claims 1-8, characterized by the following steps:

and (3) placing polypropylene fibers, plant fibers, silica fume and metakaolin into an internal mixer, banburying for 2-4min at 160-200 ℃, cooling, drying, and performing injection molding to obtain the concrete modifier.

10. A concrete according to claim 9, wherein 0.5kg of said concrete modifier is added per cubic meter of concrete.