CN115340338A - Polypropylene fiber cement-based material and preparation method thereof - Google Patents

Abstract

The invention discloses a polypropylene fiber cement-based material and a preparation method thereof, wherein the polypropylene fiber cement-based material comprises the following raw materials in parts by weight: 560-670 parts of cement, 450-560 parts of fly ash, 450-550 parts of fine sand, 13-17 parts of polypropylene monofilament fiber, 6-8 parts of a high-efficiency water reducing agent and 290-315 parts of water; the fine sand is river sand or silica sand with the maximum grain size not more than 0.6 mm; the diameter of the polypropylene monofilament fiber is 30 micrometers, and the length of the polypropylene monofilament fiber is 12mm; the polypropylene monofilament fiber has a Y-shaped cross section, and the surface of the polypropylene monofilament fiber is subjected to indentation treatment. The invention can prepare the large-deformation cement-based material with the typical characteristics of multi-crack cracking and deformation hardening.

Description

A kind of polypropylene fiber cement-based material and preparation method thereof

This application is a divisional application for an invention patent with an application date of November 21, 2019, an application number of 201911146587.6, and an invention title of "Formulation and preparation method of a domestic polypropylene fiber cement-based material".

technical field

The invention belongs to the technical field of cement-based composite materials, and in particular relates to a polypropylene fiber cement-based material and a preparation method thereof.

Background technique

The "functionalization" and "composite" of cement-based materials have become an important direction of modern concrete research. Ultra-high toughness synthetic fiber reinforced cement-based materials are one of the emerging functional concrete materials. They are used in the field of road and bridge construction materials. It has great application potential. One of the advantages of this fiber-reinforced cement-based material over conventional concrete materials is its excellent crack control capabilities. Usually cement-based materials are difficult to limit the expansion of initial cracks, and the structure will quickly lose its bearing capacity under continuous load, while ultra-high toughness synthetic fiber-reinforced cement-based materials give full play to the strengthening and toughening effect of synthetic fibers. Greatly limit the continued expansion of the initial crack. When the material needs to follow larger structural deformations, it can limit the propagation of the initial crack by creating multiple harmless shallow cracks near the main crack. Utilizing this multi-slit cracking feature, the ultra-high toughness synthetic fiber reinforced cement-based material can be used as a new type of concrete bridge protective layer material, which can effectively control the crack width under the action of the environment and load, thereby preventing the penetration of harmful media in the environment and Its erosion of internal reinforcement. The material can also be used as an ideal concrete pavement repair material, which can effectively inhibit the generation and expansion of base reflection cracks, and the restraint effect of fibers can control the crack width in a harmless range, thus greatly improving the road structural slab performance and impermeability and durability. The second advantage of ultra-high toughness synthetic fiber-reinforced cement-based materials lies in their unique large deformation capacity. The material can maintain or even increase the load-bearing capacity while following obvious structural deformation under bending or tensile loads, that is, it has deformation hardening. feature. The large deformation capacity of this material has a high degree of fit with steel. On the one hand, it has a deformation ductility close to that of steel. On the other hand, its crack width control characteristics make it a protective structure for steel. There is great application potential in the construction of composite bridges. In addition, ultra-high toughness synthetic fiber reinforced cement-based materials also have broad application prospects in lightweight high-rise buildings, earthquake-resistant concrete, and bridge deck connecting plates.

Therefore, the development and application of ultra-high toughness synthetic fiber-reinforced cement-based materials can provide important functional new materials for the construction or reinforcement of a new generation of concrete facilities in my country, and have far-reaching significance for improving the safety and durability of concrete structures in my country.

At present, domestic research on ultra-high toughness synthetic fiber reinforced cement-based materials is still in the preliminary stage, and there are very few cases of its actual engineering application. One of the reasons is that foreign literature rarely provides guidance on the mix ratio design and preparation process details of this material, and there is no generally recognized technical specification to guide the preparation of this material in China. R&D progress is relatively slow. The second reason is that foreign countries have blocked and monopolized the surface treatment technology of polyvinyl alcohol fibers. At present, domestic and foreign scholars mainly rely on this special polyvinyl alcohol fiber to prepare ultra-high toughness synthetic fiber reinforced cement-based materials. It is difficult to realize the engineering application promotion.

The elongation of polypropylene fiber can reach more than 4 times that of polyvinyl alcohol fiber. It is widely used in concrete engineering in my country, with many manufacturers, mature processing technology, low production cost and no pollution products. It is more suitable for engineering than polyvinyl alcohol fiber. promotional reality. However, the strength of polypropylene fiber is lower than that of polyvinyl alcohol fiber, and the bond with cement matrix is also weak. It is not easy to make the material achieve the characteristics of deformation hardening when it is used to prepare ultra-high toughness synthetic fiber reinforced concrete materials.

Contents of the invention

The object of the present invention is to provide a polypropylene fiber cement-based material and a preparation method thereof. The polypropylene fiber cement-based material provided by the present invention has the characteristics of multi-slit cracking and deformation hardening.

To achieve the above object, the present invention provides the following technical solutions:

The invention provides a polypropylene fiber cement-based material, which consists of the following raw materials in parts by weight: 560-670 parts of cement, 450-560 parts of fly ash, 450-550 parts of fine sand, polypropylene monofilament fiber 13-17 parts, 6-8 parts of superplasticizer, 290-315 parts of water;

The fine sand is river sand or silica sand with a maximum particle size of no more than 0.6mm;

The polypropylene monofilament fiber has a diameter of 30 μm and a length of 12 mm;

The polypropylene monofilament fiber has a Y-shaped cross-section, and the surface is processed by indentation.

Preferably, the cement is ordinary 42.5 grade Portland cement.

Preferably, the fly ash is the national standard first grade or second grade fly ash.

Preferably, the high-efficiency water reducer is polycarboxylic acid or naphthalene-based high-efficiency water reducer.

The present invention also provides a preparation method of the polypropylene fiber cement-based material described in the above technical solution, the steps are:

Mix the cement and fly ash weighed according to the metering ratio, and then stir slowly for 30 seconds, add some water to make the water-binder ratio 0.25, and then stir rapidly for 2 minutes to make the slurry fully viscous;

Add the polypropylene monofilament fiber weighed according to the metering ratio three times into the clean slurry under slow stirring. During this process, add part of high-efficiency water reducer to improve the instantaneous fluidity of the mixture, and then stir rapidly for 5 minutes to make the polypropylene monofilament Fully dispersed fibers;

The fine sand weighed according to the metering ratio, the remaining water and the remaining high-efficiency water reducer are sequentially added to the mixture, and after rapid stirring for 5 minutes, pouring is carried out to obtain the polypropylene fiber cement-based material.

Preferably, after the pouring and molding is completed, it also includes demolding the obtained molded product and putting it into a standard curing room for health preservation;

The time for the health preservation is 90d.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The present invention provides a polypropylene fiber cement-based material, which rationally optimizes the mix ratio, controls the size parameters of fine sand and polypropylene monofilament fiber, and can maximize the toughening effect of polypropylene fiber in the mixture , to achieve the purpose of using domestic raw material polypropylene fiber to produce ultra-high toughness synthetic fiber reinforced concrete. Compared with imported polyvinyl alcohol fiber, the present invention uses domestic polypropylene fiber to prepare large deformation cement-based material, which greatly reduces the cost and expands the With the source of raw materials, it has the potential for promotion and application.

(2) The present invention provides a method for preparing polypropylene fiber cement-based materials. For the first time, it proposes the idea of dividing the mixing water into two stages. Promote the full dispersion of polypropylene fibers during stirring, so there is no need to extend the stirring time excessively, and arrange the mixing of adding fine sand in the last step, avoiding the situation where the fluidity of the mixture drops sharply when adding fine sand first and adding fibers, and can also It effectively prevents the problem of local fiber clustering, and solves the problem of difficult mixing of ultra-high toughness synthetic fiber reinforced concrete materials, so that after the fibers are fully dispersed in the clean slurry, some water remains and the high-efficiency water reducer is added in the last step, so that When mixing with fine sand, more free water can be released in the mixture, ensuring that the mixture has good workability throughout the mixing process.

Description of drawings

Fig. 1 is the load-deflection curve in the loading process of embodiment 1 of the present invention;

Fig. 2 is the load-deflection curve during the loading process of Example 2 of the present invention.

Detailed ways

The principles and features of the present invention are described below, and the examples given are only used to explain the present invention, and are not intended to limit the scope of the present invention. The present invention is described more specifically by way of examples in the following paragraphs, and the advantages and characteristics of the present invention will be more apparent from the following description and claims.

Example 1

Take 670g cement and 450g fly ash and dry mix for 30s, add 280g water and stir quickly for 2min. Turn the mixer to slow speed, divide 13g fiber into the clean slurry in three times, then add 4g water reducing agent, and stir rapidly for 5 minutes. Set the mixer to slow speed, add 500g of fine sand to the mixture, then add 4g of water reducing agent and 20g of water, and stir rapidly for 5 minutes.

The mixed mixture is poured into a 15mm×100mm×400mm test mold for molding, demolded after 24 hours and put into a standard curing room for health preservation.

Cement: 42.5 grade ordinary Portland cement produced by a factory in Changchun is used.

Fly ash: First-class fly ash produced by a factory in Henan is used.

Sand grains: Ultra-fine river sand with a maximum grain size of 0.3 mm is used.

Fiber: Polypropylene monofilament fiber produced by a factory in Hubei, with a diameter of 38 μm and a length of 12 mm.

Water reducer: HD-14 naphthalene series high-efficiency water reducer produced by a factory in Shenyang is used.

Stir according to the above steps, and the fluidity of the mixture is good during the whole process. After curing the prepared specimens for 90 days, a four-point bending test of thin plates was carried out with reference to "Test Methods for Properties of Glass Fiber Reinforced Cement" (GB/T 1523-2008), and the bending strength and The corresponding deflection is shown in Table 1;

The performance test result of the polypropylene fiber cement base material that table 1 embodiment 1 obtains

Bending strength (MPa) Mid-span deflection (mm) First crack strength 5.84 0.682 Ultimate strength 10.18 8.368

During the test, 8 cracks appeared in the pure bending section of the bottom surface of the specimen, showing a multi-slit cracking phenomenon. The test results showed that when the specimen reached the initial crack strength, the mid-span deflection was 0.682mm. As the loading continues, the bending deformation increases significantly. When the ultimate strength is reached, the mid-span deflection has reached 8.368mm, and the bending strength is 74% higher than the initial cracking strength, which is a typical deformation hardening phenomenon.

Figure 1 shows the load-deflection curve during the loading process. It can be seen that at the end of the straight line segment of the curve, the cement matrix reaches its first crack strength. After that, the bearing capacity of the specimen continued to increase until it reached the ultimate strength, which was a deformation hardening process. After that, the specimen can continue to follow the significant deflection deformation, and the high level of load-bearing capacity is still maintained in the process.

In summary, the polypropylene fiber cement-based material specimen prepared according to the steps of the present invention has the typical characteristics of multi-slit cracking and deformation hardening.

Example 2

Take 560g of cement and 560g of fly ash and dry mix for 30s, add 280g of water and stir quickly for 2min. Turn the mixer to slow speed, divide 15g fiber into the clean slurry in three times, then add 4g water reducer, and stir rapidly for 5 minutes. Set the mixer to slow speed, add 500g of fine sand to the mixture, then add 4g of water reducer and 10g of water, and stir rapidly for 5 minutes.

The mixed mixture is poured into a 15mm×100mm×400mm test mold for molding, demolded after 24 hours and put into a standard curing room for health preservation.

Cement: 42.5 grade ordinary Portland cement produced by a factory in Changchun is used.

Fly ash: First-class fly ash produced by a factory in Henan is used.

Sand grains: Ultra-fine river sand with a maximum grain size of 0.6 mm is used.

Fiber: Polypropylene monofilament fiber produced by a factory in Beijing, with a diameter of 30 μm, a length of 12 mm, a Y-shaped cross-section, and an indentation treatment on the surface.

Water reducer: CQJ-JSS02 polycarboxylate high-efficiency water reducer produced by a factory in Shanghai is used.

Stir according to the above steps, and the fluidity of the mixture is good during the whole process. After curing the prepared specimens for 90 days, a four-point bending test of thin plates was carried out with reference to "Test Methods for Properties of Glass Fiber Reinforced Cement" (GB/T 1523-2008), and the bending strength and The corresponding deflection is shown in Table 2;

The performance test result of the polypropylene fiber cement-based material that table 2 embodiment 2 obtains

Bending strength (MPa) Mid-span deflection (mm) First crack strength 8.01 0.794 Ultimate strength 11.68 11.296

In the test, there were 10 cracks in the pure bending section of the bottom surface of the specimen, showing a multi-slit cracking phenomenon. The test results showed that when the specimen reached the initial crack strength, the mid-span deflection was 0.794mm. As the loading continues, the bending deformation increases significantly. When the ultimate strength is reached, the mid-span deflection has reached 11.296mm, and the bending strength is 45% higher than the initial cracking strength, which is a typical deformation hardening phenomenon.

Figure 2 is the load-deflection curve during the loading process. It can be seen that after the cement matrix reaches its initial crack strength, the bearing capacity of the specimen continues to increase until it reaches the ultimate strength, which is a deformation hardening process. After that, the specimen can continue to follow the significant deflection deformation, and the high level of load-bearing capacity is still maintained in the process.

In summary, the polypropylene fiber cement-based material specimen prepared according to the steps of the present invention has the typical characteristics of multi-slit cracking and deformation hardening.

Finally, it should be noted that: the above is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, it still The technical solutions recorded in the foregoing embodiments may be modified, or some technical features thereof may be equivalently replaced. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (6)

1. The polypropylene fiber cement-based material is characterized by comprising the following raw materials in parts by weight: 560-670 parts of cement, 450-560 parts of fly ash, 450-550 parts of fine sand, 13-17 parts of polypropylene monofilament fiber, 6-8 parts of a high-efficiency water reducing agent and 290-315 parts of water;

the fine sand is river sand or silica sand with the maximum grain size not more than 0.6 mm;

the diameter of the polypropylene monofilament fiber is 30 micrometers, and the length of the polypropylene monofilament fiber is 12mm;

the polypropylene monofilament fiber has a Y-shaped cross section, and the surface of the polypropylene monofilament fiber is subjected to indentation treatment.

2. The polypropylene fiber cement-based material according to claim 1, wherein the cement is ordinary grade 42.5 portland cement.

3. The polypropylene fiber cement-based material of claim 1, wherein the fly ash is a national standard primary or secondary fly ash.

4. The polypropylene fiber cement-based material of claim 1, wherein the high efficiency water reducer is a polycarboxylic acid or naphthalene based high efficiency water reducer.

5. A method of producing a polypropylene fibre cement-based material as claimed in any one of claims 1 to 4, characterised by the steps of:

mixing cement and fly ash weighed according to a metering ratio, slowly stirring for 30s, adding partial water to enable the water-to-gel ratio to be 0.25, and quickly stirring for 2min to enable the pure slurry to be fully viscous;

adding the polypropylene monofilament fibers weighed according to the metering ratio into the clear slurry in slow stirring for three times, adding part of the high-efficiency water reducing agent in the process to improve the instantaneous fluidity of the mixture, and then stirring quickly for 5min to fully disperse the polypropylene monofilament fibers;

and sequentially adding the fine sand, the rest water and the rest high-efficiency water reducing agent which are weighed according to the metering ratio into the mixture, quickly stirring for 5min, and pouring and forming to obtain the polypropylene fiber cement-based material.

6. The preparation method according to claim 5, characterized in that after the pouring molding, the obtained molded product is demolded and placed in a standard curing room for curing;

the curing time is 90 days.

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