Cement-based material with spider silk-like microstructure and preparation method of cement-based material

Abstract

The invention provides a cement-based material with a spider silk-like microstructure and a preparation method of the cement-based material, and belongs to the technical field of cement-based materials and preparation of the cement-based materials. The cement-based material comprises the following raw materials: double-component cement, reinforced fibers, mineral whiskers and an additive, the two-component cement comprises silicate cement and sulphoaluminate cement. The expansion effect generated by the hydration reaction of anhydrous calcium sulphoaluminate in the double-component cement not only counteracts the partial shrinkage effect generated by the hydration of Portland cement clinker minerals, but also extrudes the reinforced fibers, so that the binding force between the fibers and a cement matrix is increased. Besides, a secondary frame formed by the generated ettringite raphioid crystals and the added mineral whiskers is combined with a main body frame of the reinforced fibers to form a spider-screen-frame-imitating toughening structure, so that the strength of the material can be improved, and the toughness of the material is also improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cement-based materials and its preparation, and particularly relates to a cement-based material with a spider silk microstructure and a preparation method thereof. BACKGROUND

[0002] Cement concrete pavement materials applied to road engineering bear the repeated effects of shearing and extrusion of traffic load. Traditional Portland cement concrete materials generally have the defects of large brittleness and insufficient flexural strength, which seriously restrict their application in scenarios with high requirements for toughness, such as road engineering.

[0003] The interface transition layer between the aggregate and the cement paste is the weakest, most irregular pore development and most initial defect dense place in the microstructure of the traditional concrete pavement material. Stress concentration is easily caused after stress, causing crack propagation. Common measures to improve the performance of the interface transition layer include using suitable aggregate, adding mineral fine admixture, reducing the water-binder ratio and optimizing the mixing process, etc., the purpose of which is to reduce the initial pore defects and improve the bonding strength of the aggregate and the cement paste. However, these measures cannot effectively reduce the brittleness of the material.

[0004] In order to improve the toughness of the pavement material, millimeter-centimeter length fibers are introduced into the concrete to consume energy through the fiber pull-out effect and inhibit crack propagation. Due to the addition of fibers, the uniform mixing of the raw materials of the concrete is not conducive, so the amount of fiber added is limited. High-toughness metal fibers such as steel fibers pose a safety risk to vehicle tires, pedestrians and animals, and are not suitable for application in cement concrete pavement materials. Polymer-modified cement concrete has high toughness, but the cost is high, and the polymer is prone to aging, which will reduce the service life of the cement concrete pavement material.

[0005] In order to solve the problem of low fiber content and ineffective improvement of material toughness, the application provides a cement-based material with a spider silk microstructure and a preparation method thereof. SUMMARY

[0006] To solve the above technical problems, the application provides a cement-based material with a spider silk microstructure and a preparation method thereof.

[0007] To achieve the above purpose, the application provides the following technical solutions:

[0008] The application provides a cement-based material with a spider silk microstructure, and the raw materials include two-component cement, mineral whiskers, reinforcing fibers and additives.

[0009] The two-component cement includes Portland cement and sulphoaluminate cement; the mass fraction of the sulphoaluminate cement in the total mass of the two-component cement is 5% to 20%.

[0010] Technical effects: The invention is based on the expansion effect of the anhydrous calcium sulphoaluminate hydration reaction in the dual-component cement, which offsets the shrinkage effect of the silicate cement clinker mineral hydration, and produces extrusion on the reinforcing fibers, increasing the bonding force between the fibers and the cement matrix. Under the induction of the additive, the hydration product ettringite is precipitated in the form of fine needle-shaped crystals, and forms a secondary framework with the mineral whisker, which combines with the main framework of the reinforcing fiber to form a spider silk network structure, which not only improves the strength of the material, but also increases the toughness of the material.

[0011] Further, the silicate cement includes ordinary portland cement, slag portland cement, fly ash portland cement, pozzolanic portland cement, composite portland cement, road portland cement, etc. cement varieties with C3S, β-C2S silicate minerals as the main clinker composition; the sulphoaluminate cement includes sulphoaluminate cement, iron aluminate cement, etc. cement varieties with anhydrous calcium sulphoaluminate (3CaO·3Al2O3·CaSO4) as the main clinker composition.

[0012] Further, the volume content of the reinforcing fiber in the cement-based material with a spider silk microstructure is 0-2%, and is not 0; the reinforcing fiber is a millimeter-centimeter length (such as 12mm, 18mm) polyvinyl alcohol (PVA) fiber, polyester (PE) fiber, polypropylene (PP) fiber, etc. synthetic organic fiber with high tensile strength and length-diameter ratio of more than 200, and cellulose (CF) fiber, etc. natural fiber. The fiber is dispersed in the cement matrix to form the main framework of the spider silk network structure, which connects the aggregate and the cement matrix, and when the material is pulled, the energy is consumed through the pull-out effect of the fiber, and the propagation of the initial crack in the interfacial transition layer between the aggregate and the cement matrix is inhibited.

[0013] Further, the mineral whisker has an addition amount of 0-10% (which can be 0) of the mass of the dual-component cement; the mineral whisker includes xonotlite (length 2-10μm, width 0.1-0.6μm) and / or potassium hexatitanate (length 10-100μm, width 0.1-1.5μm). The mineral whisker not only links the cement hydration product, unhydrated cement and admixture particles together, but also induces cement hydration and crystallization, and precipitates crystals on the surface of the whisker.

[0014] In this invention, reinforcing fibers distributed in the cement matrix interweave and arrange with one or more high aspect ratio phases to form a spider silk-like toughening structure, thereby improving the strength and flexural toughness of the cement-based material. The high aspect ratio phases include mineral whiskers such as hard silicate (2-10 μm in length, 0.1-0.6 μm in width) and / or potassium hexatitanate (10-100 μm in length, 0.1-1.5 μm in width), and artificially synthesized mineral whiskers, as well as acicular hydration products such as ettringite (3-10 μm in length, 0.1-0.3 μm in width) and aragonite, generated through in-situ hydration reactions in the cement composition. These crystals are micron-sized and dispersed in the cement matrix, forming the secondary framework of the spider silk-like toughening structure.

[0015] Further, the additive includes one or more of lightly calcined MgO, magnesium carbonate trihydrate, and nano-SiO2, with an addition amount of 0-5% of the total mass of the two-component cement, and the addition amount of the mineral whiskers is not simultaneously 0 with the addition amount of the additive. The needle-like crystals generated by the in-situ reaction include hydration products such as ettringite (3-10 μm in length and 0.1-0.3 μm in width) and aragonite, which are phases promoted by the cement and additives in the cement reaction system. Tettringite crystals are generated in large quantities in the slurry during the initial stage of cement hydration. Without the action of additives, they easily form coarse and short columnar crystals, but when special additives are contained, they can form slender and long needle-like crystals.

[0016] Furthermore, the water-cement ratio of the cement-based material with the spider silk-like microstructure is 0.32-0.38.

[0017] This invention also proposes a method for preparing the aforementioned cement-based material with a spider silk-like microstructure, comprising the following steps:

[0018] (1) Silicate cement, sulfoaluminate cement, mineral whiskers and additives are premixed in proportion to obtain composite powder;

[0019] (2) Weigh the reinforcing fiber and mixing water, soak the reinforcing fiber in the mixing water and then filter it to separate the wet fiber and mixing water;

[0020] (3) Put coarse and fine aggregates into a mixer, spray with some mixing water to obtain a moist aggregate mixture, then add the composite powder, and add the remaining mixing water, wet fiber and water-reducing agent while stirring to obtain a mixture;

[0021] (4) The mixture is poured into a mold, demolded and cured to obtain the cement-based material with spider silk-like microstructure.

[0022] In the preparation method of this invention, the main framework of the spiderweb-like toughening structure connects the aggregate and the cement matrix, inhibiting the propagation of initial cracks existing in the transition layer at the interface between the aggregate and the cement matrix. Mineral whiskers induce cement hydration and crystallization, linking the hydration products with unhydrated particles. The secondary framework, composed of needle-like crystals generated by the hydration of anhydrous calcium sulfoaluminate and mineral whiskers, combines with the main framework of the reinforcing fibers to form the spiderweb-like toughening structure, which not only improves the strength of the material but also increases its toughness.

[0023] Furthermore, in step (2), the soaking time for the reinforcing fiber is 30 minutes.

[0024] Furthermore, in step (3), the portion of the mixing water used for spraying the aggregate accounts for 50% of the total weight of the mixing water.

[0025] Compared with the prior art, the present invention has the following advantages and technical effects:

[0026] The cement-based material with a spider-silk-like microstructure of this invention uses two-component cement. The expansion effect produced by the hydration reaction of anhydrous calcium sulfoaluminate not only offsets part of the shrinkage effect caused by the hydration of silicate cement clinker minerals, but also compresses the reinforcing fibers, increasing the bonding force between the fibers and the cement matrix. Furthermore, the secondary framework formed by the generated ettringite needle-like crystals and the added mineral whiskers, combined with the main framework of the reinforcing fibers, forms a spider-silk-like mesh-like toughening structure, which not only improves the strength of the material but also increases its toughness. Attached Figure Description

[0027] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0028] Figure 1 A schematic diagram of the load-deflection curve for calculating bending toughness;

[0029] Figure 2 The images show the load-deflection curves of the samples obtained from the bending toughness tests of the materials in Examples 1-3 and Comparative Examples 1-3 of this invention. Among them, sample 1# is Comparative Example 1, sample 2# is Comparative Example 2, sample 3# is Comparative Example 3, sample 4# is Example 1, sample 5# is Example 2, and sample 6# is Example 3.

[0030] Figure 3 This is a diagram showing the distribution of fibers in the cement matrix in the cement-based material prepared in Example 3;

[0031] Figure 4 SEM image of the distribution of mineral whiskers (hard silicate whiskers) in the cement-based material prepared in Example 3;

[0032] Figure 5 SEM image of raw material hard silicate whiskers;

[0033] Figure 6 This is a low-magnification SEM image of the morphology of cement hydration products in Example 3.

[0034] Figure 7 This is a high-magnification SEM image of the morphology of cement hydration products in Example 3. Detailed Implementation

[0035] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0036] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0037] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0038] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0039] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0040] This invention provides a cement-based material with a spider-silk-like microstructure. The cement matrix is ​​composed of silicate cement, sulfoaluminate cement, and fine mineral admixtures, all hydrated together. A spider-silk-like mesh-like toughening structure is distributed within the cement matrix. This mesh-like toughening structure is formed by the interweaving and arrangement of reinforcing fibers and a high aspect ratio phase within the material. The reinforcing fibers are introduced externally, while the high aspect ratio phase can be externally added mineral whiskers or generated in situ through an additive-induced reaction in the cement. The reinforcing fibers dispersed within the cement matrix form the main framework of the spider-silk-like mesh-like toughening structure, connecting the aggregate and the cement matrix. When the material is under tension, the pull-out effect of the fibers dissipates energy, inhibiting the propagation of initial cracks in the transition layer at the aggregate-cement matrix interface. The high aspect ratio phase, with micrometer-scale lengths, is dispersed within the cement matrix, linking cement hydration products, unhydrated cement, and admixture particles together to form the secondary framework of the spider-silk-like mesh-like toughening structure.

[0041] Specifically, the cement-based material with a spider silk-like microstructure proposed in this embodiment of the invention comprises two-component cement, mineral whiskers, reinforcing fibers, and additives.

[0042] Two-component cement includes silicate cement and sulfoaluminate cement; based on the total mass of two-component cement as 100%, the mass proportion of sulfoaluminate cement is 5% to 20%.

[0043] In a preferred embodiment of the present invention, the two-component cement comprises silicate cement and sulfoaluminate cement in a mass ratio of (80:20) to (95:5).

[0044] More specifically, in a preferred embodiment of the present invention, the raw materials of the cement-based material with a spider silk-like microstructure include two-component cement, mineral whiskers, reinforcing fibers, additives, fly ash, slag, coarse aggregate, fine aggregate, water-reducing agent, and mixing water.

[0045] In a preferred embodiment of the present invention, the coarse aggregate used is limestone crushed stone with a particle size of 5-20 mm, the fine aggregate is river sand with a fineness modulus of 2.5, and the water-reducing agent is polycarboxylate water-reducing agent.

[0046] In a preferred embodiment of the present invention, silicate cement includes ordinary silicate cement, slag silicate cement, fly ash silicate cement, pozzolanic silicate cement, composite silicate cement, road silicate cement, etc., cement varieties composed mainly of C3S and β-C2S silicate minerals as clinker; sulfoaluminate cement includes sulfoaluminate cement, ferroaluminate cement, etc., cement varieties composed mainly of anhydrous calcium sulfoaluminate (3CaO·3Al2O3·CaSO4). More specifically, the silicate cement used is PO 42.5 ordinary silicate cement, and the sulfoaluminate cement used is SAC 42.5 rapid-hardening sulfoaluminate cement.

[0047] In a preferred embodiment of the present invention, the volumetric content of the reinforcing fiber in the cement-based material with a spider silk-like microstructure is 0-2%, and not 0; the reinforcing fiber is a synthetic organic fiber with high tensile strength and an aspect ratio of 200 or higher, such as polyvinyl alcohol (PVA) fiber, polyester (PE) fiber, or polypropylene (PP) fiber, and natural fibers such as cellulose (CF) fiber, with a length in the millimeter-centimeter range (e.g., 12mm, 18mm). More specifically, the reinforcing fiber used is PVA fiber, and the preferred volumetric content is 1%.

[0048] In a preferred embodiment of the present invention, the amount of mineral whiskers added is 0-10% (or can be 0%) of the mass of the two-component cement; the mineral whiskers include calcareous silica (2-10 μm in length, 0.1-0.6 μm in width) and / or potassium hexatitanate (10-100 μm in length, 0.1-1.5 μm in width). More specifically, the mineral whiskers used are calcareous silica (2-10 μm in length, 0.1-0.6 μm in width), and the amount added is 5% of the mass of the two-component cement.

[0049] In a preferred embodiment of the present invention, the additive includes one or more of light-burned MgO, magnesium carbonate trihydrate, and nano-SiO2. More specifically, the additive used is light-burned MgO, and the amount added is 5% of the total mass of the two-component cement.

[0050] In a preferred embodiment of the present invention, the water-cement ratio of the cement-based material with a spider silk-like microstructure is 0.36, where the water-cement ratio is the mass ratio of mixing water to cementitious materials (two-component cement, fly ash, and slag).

[0051] For example, 1m 3 The cement-based material with a spider silk-like microstructure includes the following raw materials in appropriate proportions:

[0052] Two-component cement 336kg / m 3 48 kg / m³ of fly ash 3 Slag 96kg / m 3 PVA fiber 13kg / m 3 (At this point, the fiber volume fraction is 1.0%), 172.5 kg / m³ 3 Mixing water (water-cement ratio of 0.36), coarse aggregate 1030 kg / m³ 3 Fine aggregate 750kg / m 3 Water-reducing agent 15kg / m 3 ;or

[0053] Two-component cement 336kg / m 3 48 kg / m³ of fly ash 3 Slag 96kg / m 3 PVA fiber 13kg / m3 (At this point, the fiber volume fraction is 1.0%), 172.5 kg / m³ 3 Mixing water (water-cement ratio of 0.36), coarse aggregate 1030 kg / m³ 3 Fine aggregate 750kg / m 3 Water-reducing agent 15kg / m 3 And lightly calcined MgO 16.8kg / m 3 (5% of the mass of two-component cement); or

[0054] Two-component cement 336kg / m 3 48 kg / m³ of fly ash 3 Slag 96kg / m 3 PVA fiber 13kg / m 3 (At this point, the fiber volume fraction is 1.0%), 172.5 kg / m³ 3 Mixing water (water-cement ratio of 0.36), coarse aggregate 1030 kg / m³ 3 Fine aggregate 750kg / m 3 Water-reducing agent 15kg / m 3 And hard calcium silicate 16.8kg / m 3 (5% of the mass of two-component cement).

[0055] This invention also proposes a method for preparing a cement-based material with a spider silk-like microstructure, comprising the following steps:

[0056] (1) Silicate cement, sulfoaluminate cement, mineral whiskers and additives are premixed in proportion to obtain composite powder;

[0057] (2) Weigh the reinforcing fiber and mixing water, soak the reinforcing fiber in the mixing water and then filter it to separate the wet fiber and mixing water;

[0058] (3) Put coarse and fine aggregates into a mixer, spray with some mixing water to get a moist aggregate mixture, then add composite powder, and add the remaining mixing water, wet fiber and water-reducing agent while stirring to get a mixture.

[0059] (4) The mixture is poured into a mold, demolded and cured to obtain a cement-based material with a spider silk-like microstructure.

[0060] In step (2) of the preferred embodiment of the present invention, the soaking time of the reinforcing fiber is 30 min.

[0061] In step (3) of the preferred embodiment of the present invention, the mixing water used for spraying the aggregate accounts for 50% of the total weight of the mixing water.

[0062] All raw materials used in the embodiments of this invention were purchased commercially.

[0063] The technical solution of the present invention will be further illustrated by the following embodiments.

[0064] Example 1

[0065] A method for preparing a cement-based material with a spider silk-like microstructure includes the following steps:

[0066] (1) PO 42.5 ordinary Portland cement and SAC 42.5 rapid-hardening sulfoaluminate cement are blended at a mass ratio of 80:20, and then mixed with fly ash and slag at a concentration of 336 kg / m³. 3 48kg / m 3 96kg / m 3 The proportions are mixed to obtain composite powder;

[0067] (2) Weigh out 13kg / m 3 PVA fiber (fiber volume fraction 1.0%) and 172.5 kg / m 3 Mixing water (water-to-binder ratio 0.36): PVA fibers were soaked in the mixing water for 30 minutes and then filtered out to separate the wet fibers from the mixing water.

[0068] (3) Mix coarse aggregate and fine aggregate at 1030 kg / m³ respectively. 3 750kg / m 3 The amount of additive is added to the concrete mixer, and half of the mixing water is sprayed on to obtain a moistened aggregate mixture. Then, the obtained composite powder is added, and while mixing, the remaining mixing water, wet fiber, and water-reducing agent (15 kg / m³) are added. 3 ), to obtain the mixture;

[0069] (4) The mixture is poured into a 100×100×400mm mold, demolded after 24 hours, and cured in a concrete curing room for 28 days to obtain a cement-based material with a spider silk-like microstructure.

[0070] Example 2

[0071] Same as Example 1, except that PO 42.5 ordinary Portland cement and SAC 42.5 rapid-hardening sulfoaluminate cement are blended at a mass ratio of 95:5, and 5% (16.8 kg / m³) of the total mass of the two-component cement is added. 3 Lightly calcined MgO was used as a crystallization-inducing additive, and other conditions were the same as in Example 1. The specific preparation method was as follows:

[0072] A method for preparing a cement-based material with a spider silk-like microstructure includes the following steps:

[0073] (1) PO 42.5 ordinary Portland cement and SAC 42.5 rapid-hardening sulfoaluminate cement were blended at a mass ratio of 95:5, and then mixed with fly ash, slag, and lightly calcined MgO at a concentration of 336 kg / m³. 3 48kg / m 3 96kg / m 3 16.8kg / m 3 The proportions are mixed to obtain composite powder;

[0074] (2) Weigh out 13kg / m 3 PVA fiber (fiber volume fraction 1.0%) and 172.5 kg / m 3 Mixing water (water-to-binder ratio 0.36): PVA fibers were soaked in the mixing water for 30 minutes and then filtered out to separate the wet fibers from the mixing water.

[0075] (3) Mix coarse aggregate and fine aggregate at 1030 kg / m³ respectively. 3 750kg / m 3 The amount of additive is added to the concrete mixer, and half of the mixing water is sprayed on to obtain a moistened aggregate mixture. Then, the obtained composite powder is added, and while mixing, the remaining mixing water, wet fiber, and water-reducing agent (15 kg / m³) are added. 3 ), to obtain the mixture;

[0076] (4) The mixture is poured into a 100×100×400mm mold, demolded after 24 hours, and cured in a concrete curing room for 28 days to obtain a cement-based material with a spider silk-like microstructure.

[0077] Example 3

[0078] Same as Example 1, except that PO 42.5 ordinary Portland cement and SAC 42.5 rapid-hardening sulfoaluminate cement are blended at a mass ratio of 90:10, and the fiber is replaced from a single PVA fiber to two types of fibers: PVA fiber and PP fiber, with the former added at an amount of 9.75 kg / m³. 3 The latter is 3.25 kg / m 3 The total amount remains unchanged, and 5% (16.8 kg / m³) of the total mass of the two-component cement is added. 3 The hard silicate calcium silicate whiskers were prepared under the same conditions as in Example 1, and the specific preparation method was as follows:

[0079] A method for preparing a cement-based material with a spider silk-like microstructure includes the following steps:

[0080] (1) PO 42.5 ordinary Portland cement and SAC 42.5 rapid-hardening sulfoaluminate cement are compounded at a mass ratio of 90:10, and then mixed with fly ash, slag, and hard silicate whiskers at a concentration of 336 kg / m³. 348kg / m 3 96kg / m 3 16.8kg / m 3 The proportions are mixed to obtain composite powder;

[0081] (2) Weigh out 13kg / m 3 PVA fiber (fiber volume fraction 1.0%) and 172.5 kg / m 3 Mixing water (water-to-binder ratio 0.36): PVA fibers were soaked in the mixing water for 30 minutes and then filtered out to separate the wet fibers from the mixing water.

[0082] (3) Mix coarse aggregate and fine aggregate at 1030 kg / m³ respectively. 3 750kg / m 3 The amount of additive is added to the concrete mixer, and half of the mixing water is sprayed on to obtain a moistened aggregate mixture. Then, the obtained composite powder is added, and while mixing, the remaining mixing water, wet fiber, and water-reducing agent (15 kg / m³) are added. 3 ), to obtain the mixture;

[0083] (4) The mixture is poured into a 100×100×400mm mold, demolded after 24 hours, and cured in a concrete curing room for 28 days to obtain a cement-based material with a spider silk-like microstructure.

[0084] Comparative Example 1

[0085] Same as Example 1, except that the addition of SAC 42.5 rapid-hardening sulfoaluminate cement is omitted, that is, PO 42.5 ordinary Portland cement and SAC 42.5 rapid-hardening sulfoaluminate cement are mixed at a mass ratio of 100:0, and the amount of water-reducing agent is reduced to 9.6 kg / m³. 3 And without adding fiber, the other conditions are the same as in Example 1.

[0086] Comparative Example 2

[0087] Same as Example 1, except that PO 42.5 ordinary Portland cement and SAC 42.5 rapid hardening sulfoaluminate cement are compounded at a mass ratio of 90:10, and no fiber is added. Other conditions are the same as in Example 1.

[0088] Comparative Example 3

[0089] Same as Example 1, except that the addition of SAC 42.5 rapid-hardening sulfoaluminate cement is omitted, i.e., PO 42.5 ordinary Portland cement and SAC 42.5 rapid-hardening sulfoaluminate cement are mixed at a mass ratio of 100:0, and the fiber is replaced from a single PVA fiber to two types of fibers, PVA fiber and PP fiber, with the former added at a rate of 9.75 kg / m³. 3 The latter is 3.25 kg / m3 The total volumetric doping remains unchanged.

[0090] Comparative Example 4

[0091] Similar to Comparative Example 1, the only difference is that PO 42.5 ordinary Portland cement and SAC 42.5 rapid-hardening sulfoaluminate cement were blended at a mass ratio of 90:10, and 5% (16.8 kg / m³) of the total mass of the two-component cement was added. 3 It contains hard silicate calcium silicate whiskers, without the addition of fibers.

[0092] Performance testing

[0093] Toughness tests were performed on the cement-based materials prepared in the examples and comparative examples, and the flexural toughness values ​​or equivalent flexural toughness values ​​were used for characterization.

[0094] The flexural toughness test was conducted according to the relevant provisions of the "Standard for Test Methods of Fiber Reinforced Concrete" CECS13-2009, and the load-deflection curves of the samples were obtained. The results are shown in [Figure Number]. Figure 1 Specifically, in this invention, the concrete specimen samples are 100×100×400mm in size, and the mid-span deflection δ is determined according to CECS13 and ASTM C1609. k Take L / 150, where L is the span between the test beam supports, and take the value of L as 300 mm, to obtain δ. k The value is 2.0 mm. The mid-span deflection is calculated as δ. k Area under the load-deflection curve Ω k ( Figure 1 The shaded area represents the bending toughness value. To facilitate comparison of the bending toughness of specimens of different sizes, Ω is... k Value divided by specimen cross section bH 2 The value is used to obtain the equivalent bending toughness value W. e k The value is calculated using the formula (1).

[0095]

[0096] In the formula: W e k —Equivalent bending toughness (kJ / m) 3 );

[0097] Ω k — Bending toughness (J), which is the mid-span deflection of δ k The area under the load-deflection curve (N·mm);

[0098] bH 2 —The cross-sectional parameters of the specimen, where b and H are the width and height (mm) respectively. In this invention, the values ​​of b and H are both 100mm.

[0099] The samples were subjected to a four-point bending toughness test on a testing machine with a span L of 300 mm and a loading rate of 0.1 mm / s. The load and mid-span deflection values ​​of the samples were obtained. Load-deflection curves obtained from the actual bending toughness tests of the materials in Examples 1-3 and Comparative Examples 1-3 are shown. Sample #1 is Comparative Example 1, Sample #2 is Comparative Example 2, Sample #3 is Comparative Example 3, Sample #4 is Example 1, Sample #5 is Example 2, and Sample #6 is Example 3. The fracture deflection and ultimate load values ​​obtained from the curves are listed in Table 1. The bending tensile strength of the samples was calculated based on the four-point bending test. Figure 1 The bending toughness value and the equivalent bending toughness value are calculated using formula (1).

[0100] Table 1 Key mix proportion parameters and flexural toughness of 28-day samples

[0101]

[0102]

[0103] Figure 2 Sample #1 is the concrete sample from Comparative Example 1. Only PO 42.5 ordinary Portland cement was used; no sulfoaluminate cement, crystallization-inducing additives, or fibers were added. This concrete sample rapidly fractured into a brittle state after reaching the ultimate flexural tensile load, with the load dropping to zero. The fracture deflection was only 0.16 mm, the flexural toughness was only 1.4 J, and the equivalent flexural toughness was 1.4 kJ / m. 3 It is evident that, although the flexural tensile strength of the sample can exceed 5.0 MPa without the addition of fiber, sulfoaluminate cement, and crystallization-inducing additives, the flexural toughness is very poor, and the sample rapidly fractures and fails when it reaches the ultimate load.

[0104] Sample #2 is the concrete sample from Comparative Example 2. It was a blend of PO 42.5 cement and SAC 42.5 rapid-hardening sulfoaluminate cement at a mass ratio of 90:10, without any crystallization-inducing additives or fibers. This concrete sample's load-deflection curve reached the ultimate flexural tensile load, and it rapidly fractured, with the load dropping to 0. The fracture deflection value increased slightly to 0.36 mm, the flexural toughness value was 2.7 J, and the equivalent flexural toughness value was 2.7 kJ / m. 3 The strength increased slightly. It is evident that, without fiber but with sulfoaluminate cement, although the flexural tensile strength of the sample reached 5.84 MPa, the flexural toughness did not significantly improve, and the sample still rapidly fractured to the ultimate load. This indicates that the presence or absence of fiber is a key factor affecting the flexural toughness of the material, and fiber plays a dominant role in improving the toughness of the sample.

[0105] Sample #3 is the concrete sample from Comparative Example 3. Only PO 42.5 ordinary Portland cement was used; no SAC 42.5 sulfoaluminate cement or crystallization-inducing additives were added. However, PVA fibers (0.75% by volume) and PP fibers (0.25% by volume) were added. After reaching the ultimate flexural tensile load, the load of this concrete sample rapidly decreased, but did not drop to zero. Its flexural toughness value was 8.6 J, and its equivalent flexural toughness value was 8.6 kJ / m. 3 After reaching the ultimate flexural tensile load, the load of the concrete sample rapidly decreased, but did not drop to zero. This indicates that the addition of fibers improves the flexural toughness of the sample, preventing brittle fracture, but the bond between the fibers and the cement matrix is ​​not strong. Therefore, the fibers need a better bond with the cement matrix to demonstrate their effective toughening effect. The dominant role of fibers in improving material toughness requires auxiliary components. Based on the results of the examples, the addition of sulfoaluminate cement is indispensable; sulfoaluminate cement is a crucial auxiliary component. The expansion during the hydration process of sulfoaluminate cement compresses the fibers, increasing the bond strength between the fibers and the cement matrix. Furthermore, its hydration product, ettringite, if precipitated as slender needle-like crystals, or under the action of crystallization-inducing additives, forms a secondary framework for the toughening structure together with high aspect ratio mineral whiskers.

[0106] Sample #4 is the concrete sample from Example 1, made by blending PO 42.5 cement and SAC 42.5 cement at a mass ratio of 20:80, without adding crystallization-inducing additives, but containing 1.0% PVA fiber by volume. After reaching the ultimate flexural tensile load, the load on this concrete sample only decreased slowly. Its flexural toughness value reached 32.5 J, with an equivalent flexural toughness value of 32.5 kJ / m. 3 .

[0107] Sample #5 is the concrete sample from Example 2, composed of PO 42.5 ordinary Portland cement and SAC 42.5 sulfoaluminate cement in a mass ratio of 95:5. It contains 5% lightly calcined MgO as a crystallization inducing additive, and 1.0% PVA fiber by volume. After reaching the ultimate flexural tensile load, the load of this concrete sample rapidly decreases to 9.24 kN, then decreases slowly. Its flexural toughness value is 20.5 J, and its equivalent flexural toughness value is 20.5 kJ / m. 3 .

[0108] Sample #6 is the concrete sample from Example 3, composed of PO 42.5 ordinary Portland cement and SAC 42.5 sulfoaluminate cement in a mass ratio of 90:10. It also contains 5% (by mass) of hard silicate calcium silicate whiskers, and 0.75% (by volume) of PVA fiber and 0.25% (by volume) of PP fiber. After reaching the ultimate flexural tensile load, the load of this concrete sample decreased to some extent. Its flexural toughness value is 17.7 J, and its equivalent flexural toughness value is 17.7 kJ / m. 3 .

[0109] Figure 2 The results show that the addition of fibers can effectively improve the flexural toughness of the samples. The improvement is particularly significant when PO 42.5 ordinary Portland cement and SAC 42.5 sulfoaluminate cement are combined. The hydration of sulfoaluminate cement generates a large number of needle-like ettringite crystals, which expand in volume and compress the reinforcing fibers, increasing the bonding force between the fibers and the cement matrix. The abundant ettringite and hard silicate whiskers, phases with similar high aspect ratios dispersed in the cement matrix, form a secondary framework. Together with the dispersed fiber framework in the material structure, they constitute a spiderweb-like toughening structure.

[0110] The load-deflection curve of sample 4 was obtained from the test and Figure 2 The curve is similar to curve #2. The fracture deflection and ultimate load values ​​obtained from the curve are listed in Table 1. The calculated tensile strength of the sample is 6.23 MPa, but its bending toughness and equivalent bending toughness are 4.6 J and 4.6 kJ / m, respectively. 3 It is evident that while the flexural strength of the sample improved with the addition of sulfoaluminate cement and additives without the addition of fibers, the flexural toughness did not improve significantly, and the sample still failed rapidly with brittle fracture when it reached the ultimate load. This indicates that the flexural toughness of the sample cannot be improved by using sulfoaluminate cement and additives alone without the addition of fibers.

[0111] The fiber distribution diagram in the cement matrix of the cement-based material prepared in Example 3 is shown in Figure 3. Figure 3 .

[0112] The SEM image of the distribution of mineral whiskers (hard silicate whiskers) in the cement-based material prepared in Example 3 is shown below. Figure 4 SEM images of the hard silicate whiskers used are shown below. Figure 5 It can be seen that the mineral whiskers are interspersed in the cement paste, and their surfaces are covered by cement hydration products.

[0113] Figure 6 This is a low-magnification SEM image of the morphology of cement hydration products in Example 3. Figure 7 The high-magnification SEM image shows that ettringite consists of slender needle-like crystals interspersed within needle-like CSH clusters.

[0114] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A cement-based material with a spider silk-like microstructure, characterized in that, The raw materials include two-component cement, reinforcing fibers, mineral whiskers, and additives; the two-component cement includes silicate cement and sulfoaluminate cement; based on the total mass of the two-component cement as 100%, the mass percentage of sulfoaluminate cement is 5% to 20%.

2. The cement-based material with a spider silk-like microstructure according to claim 1, characterized in that, The volumetric content of the reinforcing fiber in the cement-based material with a spider silk-like microstructure is 0-2%, and not 0.

3. The cement-based material with a spider silk-like microstructure according to claim 2, characterized in that, The reinforcing fiber is selected from one or more of polyvinyl alcohol fiber, polyester fiber, polypropylene fiber and cellulose fiber, and has an aspect ratio greater than 200.

4. The cement-based material with a spider silk-like microstructure according to claim 1, characterized in that, The amount of mineral whiskers added is 0-10% of the mass of the two-component cement, and the amount of additive added is 0-5% of the total mass of the two-component cement, and the amounts of mineral whiskers and additives added are not both 0.

5. The cement-based material with a spider silk-like microstructure according to claim 4, characterized in that, The mineral whiskers include calcareous silica and / or potassium hexatitanate.

6. The cement-based material with a spider silk-like microstructure according to claim 4, characterized in that, The additives include one or more of lightly calcined MgO, magnesium carbonate trihydrate, and nano-SiO2.

7. The cement-based material with a spider silk-like microstructure according to claim 1, characterized in that, The water-cement ratio of the cement-based material with a spider silk-like microstructure is 0.32-0.

38.

8. A method for preparing a cement-based material with a spider silk-like microstructure as described in any one of claims 1-7, characterized in that, Includes the following steps: (1) Silicate cement, sulfoaluminate cement, mineral whiskers and additives are premixed in proportion to obtain composite powder; (2) Weigh the reinforcing fiber and mixing water, soak the reinforcing fiber in the mixing water and then filter it to separate the wet fiber and mixing water; (3) Put coarse and fine aggregates into a mixer, spray with some mixing water to obtain a moist aggregate mixture, then add the composite powder, and add the remaining mixing water, wet fiber and water-reducing agent while stirring to obtain a mixture; (4) The mixture is poured into a mold, demolded and cured to obtain the cement-based material with spider silk-like microstructure.

9. The method for preparing the cement-based material with a spider silk-like microstructure according to claim 8, characterized in that, In step (2), the soaking time for the reinforcing fiber is 30 minutes.

10. The method for preparing the cement-based material with a spider silk-like microstructure according to claim 8, characterized in that, In step (3), the portion of the mixing water used for spraying the aggregate accounts for 50% of the total weight of the mixing water.

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