Nanomodified ultra-high toughness concrete and method for preparing the same

Abstract

The application provides a kind of nano-modified ultra-high toughness concrete and its preparation method, provide a kind of nano-modified ultra-high toughness concrete, by mass fraction, including the following preparation raw materials: fine aggregate 100~140 parts, water 8~18 parts, water reducing agent 2~4 parts;Cementitious material: silica fume 10~20 parts, superfine fly ash silicate aluminate fine substance 10~30 parts, cement 50~80 parts;Wherein, water-binder ratio is 0.16;And steel fiber volume content 1.2~2.5%, the content of nano-silica is 0.5~2%.The application is limited by the composition of ternary cementitious system and the content of nano-silica;Obtain the working performance and mechanical properties of ultra-high toughness concrete that have been greatly improved;The nano-modified ultra-high toughness concrete preparation method of the application has the characteristics of low cost, convenient operation, wide application scene, suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of concrete, more particularly, to a nano-modified ultra-high toughness concrete and a preparation method thereof. BACKGROUND

[0002] In recent years, with the increasing design requirements of bridges and the increasingly complex use environment, the design of the orthotropic steel bridge deck panel composite system is facing severe challenges. The design of the steel-ultra-high toughness concrete (STC) light composite bridge deck structure can improve the overall stiffness of the bridge deck system and effectively address problems such as fatigue cracking of the steel bridge deck panel and pavement disease. The STC layer is composed of cement, quartz sand, mineral admixtures, steel fibers, water reducing agents and other raw materials, and has high strength, high toughness and excellent durability after hardening, which can adapt to local stress concentration and large deformation of the steel bridge deck panel, and has broad application prospects in the future bridge engineering field. At present, a large number of studies have been conducted in the field of the influence of nano materials on the modification of binary or ternary cementitious systems, mainly involving nano SiO2, nano TiO2, carbon nanotubes CNT, etc. Among them, Xu Peng et al. summarized and analyzed the characteristics, incorporation method and dosage of nano materials such as nano SiO2, nano TiO2, carbon nanotubes CNT and graphene oxide GO, and proposed the concept of multifunctional synergistic development of nano-modified cement-based materials. Wu et al. studied the reinforcing mechanism of nano SiO2 and nano CaCO3 on UHPC, and found that the mechanical strength of UHPC first increases and then decreases with the increase of the dosage of nano SiO2 and nano CaCO3, and the optimal dosage is 1% and 3.2%, respectively. However, there is a lack of research on the modification of ultra-high toughness concrete by nano SiO2.

[0003] A preparation method of nano-silica and steel fiber reinforced concrete is disclosed in the prior art, which comprises the following steps: weighing aggregate, cement, water reducing agent, fly ash, water, nano SiO2 and steel fiber; taking an appropriate amount of nano SiO2 and water reducing agent, adding them into water, stirring uniformly, and reserving; after wetting the mixer, adding coarse aggregate and fine aggregate, stirring, then adding cement and fly ash, stirring, then uniformly incorporating steel fiber along the rotation direction of the mixer impeller, after stirring, adding the mixture of nano material, water reducing agent and part of water, stirring, adding the remaining water, and stirring to obtain the nano-silica and steel fiber reinforced concrete. Although the modification of concrete by nano SiO2 is involved, the modified ultra-high toughness concrete obtained by the above preparation method containing nano SiO2 needs to be steam cured to meet the performance standards; however, steam curing has the disadvantages of complex process, high economic cost, time-consuming and labor-intensive.

[0004] Therefore, there is an urgent need for an ultra-high toughness concrete that can meet the performance standards only through natural curing. SUMMARY

[0005] In view of the above problems, the purpose of the present application is to provide a nano-modified ultra-high toughness concrete and a preparation method thereof, so as to solve at least one of the above technical problems.

[0006] According to one aspect of the present application, a nano-modified ultra-high toughness concrete is provided,

[0007] The preparation raw materials include fine aggregate, water, water reducing agent, cementitious material, steel fiber and nano-silica; wherein the cement-aggregate ratio is 1.0, and the water-cement ratio is 0.16;

[0008] The volume content of the steel fiber is 1.2-2.5%, and the mass content of the nano-silica is 0.5-2%.

[0009] The cementitious material includes cement 50-80%, silica fume 10-20%, ultra-fine fly ash silicate 20-25%, and viscosity reducer 5-10% by weight percentage.

[0010] Further, preferably,

[0011] It also includes basalt fibers treated with a dispersible wetting agent, and the volume content of the basalt fibers is 0.3-0.5%.

[0012] Further, preferably,

[0013] The dispersible wetting agent is water-soluble epoxy emulsion, KH550 and cation.

[0014] Further, preferably,

[0015] The fine aggregate is a mixture of 10-20 mesh quartz sand and 70-140 mesh quartz sand in a ratio of 3:2.

[0016] Further, preferably,

[0017] The content of the nano-silica is 1-2%.

[0018] Further, preferably,

[0019] The particle size of the nano-silica is 20-50 nm.

[0020] The present application also protects a nano-modified ultra-high toughness concrete preparation method for preparing the above-mentioned nano-modified ultra-high toughness concrete; the method comprises:

[0021] The fine aggregate, cementitious material and dispersedly pretreated nano-silica solution are added to the concrete mixer and stirred uniformly;

[0022] The water and water reducing agent are added and stirred uniformly;

[0023] The steel fibers are evenly scattered to obtain the nano-modified ultra-high toughness concrete.

[0024] Further, preferably,

[0025] Also included is a thin layer ramming method during the casting forming process, including,

[0026] The obtained nano-modified ultra-high toughness concrete is poured from one end of the mold;

[0027] According to the preset thickness of each layer, the pouring and smoothing are performed along the long edge direction of the mold; wherein the thickness of each layer is 0.8-1.2 cm.

[0028] Further, preferably,

[0029] The mixing amount of the nano-silicon dioxide of the nano-modified ultra-high toughness concrete is 2%.

[0030] Further, preferably,

[0031] The steel fiber is a micro-wire copper-plated steel fiber, with a length of 14 mm and an equivalent diameter of 0.22 mm.

[0032] The nano-modified ultra-high toughness concrete preparation method according to the application is used for steel bridge deck paving; by limiting the composition of the ternary cementitious system and the mixing amount of nano-silicon dioxide; the working performance and mechanical properties of the ultra-high toughness concrete are greatly improved; the bridge deck paving nano-modified ultra-high toughness concrete disclosed in the application is a cement-based composite material with better comprehensive performance, which is obtained by nano-SiO2 modification, basalt fiber complex mixing, and molding process optimization. Unlike the STC specified in the existing standard specification, which requires steam curing, the mechanical properties and working performance of the application under natural curing conditions can still meet the design and construction requirements; the nano-modified ultra-high toughness concrete of the application can also achieve the mechanical property standard by using natural curing; the nano-modified ultra-high toughness concrete preparation method of the application has the characteristics of low cost, convenient operation, wide application scene, and is suitable for industrial production.

[0033] To achieve the above and related objects, one or more aspects of the application include features that will be explained in detail below and particularly pointed out in the claims. The following description and the accompanying drawings explain certain illustrative aspects of the application in detail. However, these aspects indicate only some of the various ways in which the principles of the application can be employed. In addition, the application is intended to include all such aspects and their equivalents. BRIEF DESCRIPTION OF DRAWINGS

[0034] Other objects and results of the application will become more fully apparent and easily understood with reference to the following description, taken in connection with the accompanying drawings, wherein:

[0035] Figure 1 A flow chart of the preparation method of the nano-modified ultra-high toughness concrete according to the application is shown; and

[0036] Figure 2 A physical comparison chart of the nano-modified ultra-high toughness concrete under various conditions is shown;

[0037] Figure 3 CT images of ZB-4 nano-modified ultra-high toughness concrete under thin-layer ramming and conventional pouring are shown.

[0038] The same reference numbers in all the drawings indicate similar or corresponding features or functions. DETAILED DESCRIPTION

[0039] In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It can be evident, however, that embodiments can be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing one or more embodiments.

[0040] Silica fume reacts with calcium hydroxide generated by cement hydration to generate C-S-H gel with single chemical composition. The secondary pozzolanic reaction occurs at an early age when silica fume is incorporated, which consumes the amount of CH in the paste and generates more C-S-H gel; the reason for the increase in strength is due to the pozzolanic effect, filling effect, etc. of silica fume. Silica fume can be filled in the paste capillary pores, increase the compactness, refine the pore structure, and have a micro-aggregate effect. At the same time, in the mortar or concrete, silica fume can also improve the paste-aggregate interface zone.

[0041] The application mainly compares and analyzes the working performance and basic mechanical properties of the concrete under various conditions under different nano-SiO2 dosages, and compares and analyzes the flexural strength under the thin-layer ramming and conventional pouring forming processes, and obtains the ultra-high toughness concrete with greatly improved working performance and mechanical properties.

[0042] For the prior art, quartz sand and polycarboxylic acid water reducing agent are mixed by microwave treatment, the quartz sand is dissociated to form nano SiO2 under the action of microwave and acid, and the dispersibility of the prepared nano SiO2 is prepared; the dispersion of the nano material in the application adopts a combination of physical and chemical methods. The physical method is to disperse the nano material at high speed by a mechanical stirrer. The rotating speed of the stirrer blade is 38000 rpm, the maximum capacity is 2.2 L, and the stirring temperature is 40 degrees Celsius. The chemical method is to add a surfactant, that is, to add sodium hexametaphosphate in the mixed solution when dispersing the nano material. The application is to make up for the disadvantage of natural curing strength, and to improve the comprehensive performance of STC by means of complex fiber, nano enhancement, and optimization of forming process; and then realizes the nano modified ultra-high toughness concrete ratio under natural curing, and cooperates with the special preparation process of thin layer ramming, which can achieve the technical effect of the strength required by the specification.

[0043] The specific embodiments of the application will be described in detail below with reference to the accompanying drawings.

[0044] The nano modified ultra-high toughness concrete material described in the application is a cement-silica fume-ultrafine fly ash silicate fine substance-viscosity reducer multi-element cementitious system concrete material. In each cubic meter of concrete, the total mass of cementitious materials is 1066 kg, the proportion of cementitious materials and aggregates, i.e. the glue-bone ratio, is 1.0, the proportion of water and cementitious materials, i.e. the water-cement ratio, is 0.16, the dosage of polycarboxylic acid water reducing agent accounts for 2% to 3% of the mass of cementitious materials, the dosage of steel fiber accounts for 1.2% to 2.5% of the total volume of concrete materials, the dosage of basalt fiber accounts for 0.3% to 0.5% of the total volume of concrete materials, and the dosage of nano silicon dioxide accounts for 0.5% to 2% of the mass of cementitious materials. The cementitious materials are recorded as follows in terms of weight percentage: cement is 50% to 80%, silica fume is 10% to 20%, ultrafine fly ash silicate fine substance is 20% to 25%, and viscosity reducer is 5% to 10%. The ultrafine fly ash silicate fine substance with a SiO2 content of 56.5% has the characteristics of small particle size, spherical shape, and ball bearing effect. In addition, the viscosity reducer has a flow degree of 105% and a viscosity ratio of 55%, and the 7d and 28d activity indexes are 75% and 90% respectively. In order to solve the problem of too low flow degree caused by low water-cement ratio, the above-mentioned ultrafine fly ash silicate fine substance and viscosity reducer are used to improve the flowability of concrete.

[0045] Example 1

[0046] Figure 1 A flow chart of the preparation method of the nano modified ultra-high toughness concrete according to the application is shown.

[0047] As Figure 1As shown, S110, the fine aggregate, cementitious material and dispersed pre-processed nano-silica solution are added into a concrete mixer and stirred evenly.

[0048] The nano-modified ultra-high toughness concrete comprises, by mass fraction, the following preparation raw materials:

[0049] The fine aggregate is 100-140 parts, water is 8-18 parts, and water reducing agent is 2-4 parts; the cementitious material comprises silica fume 10-20 parts, superfine fly ash silicate 10-30 parts, and cement 50-80 parts; wherein the water-binder ratio is less than 0.2; and the nano-silica content is 0.5-2%.

[0050] The incorporation of the silica fume, which is a superfine active mineral admixture, enables good micro-powder filling effect, and reduces the pore size and porosity and optimizes the internal pore structure of the system through chemical reaction.

[0051] The fine aggregate is 10-20 mesh quartz sand and 70-140 mesh quartz sand in a mixing ratio of 3:2. The nano-silica content is 1-2%. The particle size of the nano-silica is 20-50 nm. By removing coarse aggregate and limiting the maximum particle size of the fine aggregate to be no more than 300 μm, the uniformity of the aggregate is improved. And by optimizing the grading of the fine aggregate, the most compact packing is achieved as much as possible to improve the density of the system.

[0052] S120, water and water reducing agent are added and stirred evenly.

[0053] The water reducing agent is STC special polycarboxylic acid high-efficiency water reducing agent, and the water-reducing rate can reach more than 35%; the mixing water is laboratory ordinary tap water.

[0054] S130, uniformly sprinkle steel fibers to obtain the nano-modified ultra-high toughness concrete.

[0055] The steel fiber volume content is 1.2-2.5% (externally added). The length of the steel fiber is 13 mm, the equivalent diameter is 0.2 mm, and the length-diameter ratio is 65. Specifically, the fiber has the effects of strengthening, toughening and crack resistance on the concrete. The concrete without the incorporation of steel fibers shows explosive damage and greater brittleness than ordinary concrete when subjected to compression test. The effect of the fiber depends on the volume content of the fiber and the fiber spacing. The finer the fiber and the higher the fiber content, the better the effect of strengthening the matrix. Therefore, when the fiber volume fraction is the same, the ultra-fine fiber has a much better effect of strengthening, toughening and crack resistance on the ultra-high toughness concrete than the ordinary steel fiber on the ordinary concrete, thereby doubling the flexural strength.

[0056] By limiting the composition of ternary cementitious system and the dosage of nano-silica, the working performance and mechanical performance of the super high toughness concrete are greatly improved.

[0057] Preparation Example 1

[0058] S110, the fine aggregate, cementitious material and dispersed nano-silica solution after pretreatment are added into the concrete mixer and stirred uniformly; it should be noted that the nano-material is dispersed by high-speed stirring to avoid agglomeration;

[0059] The nano-modified super high toughness concrete comprises the following preparation raw materials in mass fraction:

[0060] 10-20 mesh quartz sand 640 parts, 70-140 mesh quartz sand 427 parts; water 171 parts, water reducing agent 22 parts;

[0061] The ternary cementitious system comprises silica fume 107 parts, superfine fly ash silicate 107 parts and cement 853 parts; the dosage of nano-silica is 0.5%. The physical performance index of the cement is shown in Table 1. The physical performance index of the nano-silica is shown in Table 2.

[0062] Table 1 Physical performance index of cement

[0063]

[0064] Table 2 Physical performance index of nano-SiO2

[0065]

[0066]

[0067] S120, water and water reducing agent are added and stirred uniformly to ensure the fluidity of the concrete.

[0068] The water reducing agent is STC special polycarboxylic acid high efficiency water reducing agent, and the water reducing rate can reach more than 35%; the mixing water is laboratory ordinary tap water.

[0069] S130, uniformly sprinkle the steel fiber, and obtain the ZB-1 nano-modified super high toughness concrete after stirring uniformly.

[0070] The steel fiber is 117.75 parts by mass. The physical performance index of the steel fiber is shown in Table 3.

[0071] Table 3 Physical performance parameters of steel fiber

[0072]

[0073] The working performance test is conducted on the obtained ZB-1 nano-modified ultra-high toughness concrete, and after the test is completed, the mixture is placed in a mold and covered with a film to keep water. After two days, the mold is removed. The test piece after the mold is removed is placed in a natural curing environment, that is, a room temperature environment of about 20 DEG C, and a layer of plastic film is covered on the surface of the test piece, and before reaching the test age, it is supplemented with watering conservation. After curing for 7d and 28d, the mechanical property test is carried out.

[0074] Preparation Example 2

[0075] S110, the fine aggregate, the cementitious material and the dispersed pre-processed nano-silica solution are added to the concrete mixer and stirred uniformly; it should be noted that the nano-material is dispersed by high-speed stirring to avoid agglomeration;

[0076] The nano-modified ultra-high toughness concrete comprises, by mass fraction, the following preparation raw materials:

[0077] 10-20 mesh quartz sand 640 parts, 70-140 mesh quartz sand 427 parts; water 171 parts, water reducing agent 22 parts;

[0078] Ternary cementitious system: silica fume 213 parts, superfine fly ash silicate 320 parts, cement 533 parts; the dosage of nano-silica is 1%. The physical performance index of the cement and the physical performance index of the nano-silica are the same as those of Preparation Example 1.

[0079] S120, water and water reducing agent are added and stirred uniformly to ensure the fluidity of the concrete.

[0080] The water reducing agent is STC special polycarboxylic acid high-efficiency water reducing agent, and the water reducing rate can reach more than 35%; the mixing water is laboratory ordinary tap water.

[0081] S130, uniformly sprinkle the steel fiber, and after stirring uniformly, obtain ZB-2 nano-modified ultra-high toughness concrete.

[0082] The steel fiber is 235.5 parts by mass. The physical performance index of the steel fiber is the same as that of Preparation Example 1.

[0083] The working performance test is conducted on the obtained ZB-2 nano-modified ultra-high toughness concrete, and after the test is completed, the mixture is placed in a mold and covered with a film to keep water. After two days, the mold is removed. The test piece after the mold is removed is placed in a natural curing environment, that is, a room temperature environment of about 20 DEG C, and a layer of plastic film is covered on the surface of the test piece, and before reaching the test age, it is supplemented with watering conservation. After curing for 7d and 28d, the mechanical property test is carried out.

[0084] Preparation Example 3

[0085] S110, the fine aggregate, cementitious material and dispersed pre-processed nano-silica solution are added into a concrete mixer and stirred uniformly; it should be noted that the nano-material is dispersed by high-speed stirring to avoid agglomeration;

[0086] The nano-modified ultra-high toughness concrete comprises, by mass fraction, the following preparation raw materials:

[0087] 10-20 mesh quartz sand 640 parts, 70-140 mesh quartz sand 427 parts; water 171 parts, water reducing agent 43 parts;

[0088] Ternary cementitious system: silica fume 160 parts, superfine fly ash silicate 160 parts, cement 747 parts; the dosage of nano-silica is 1.5%. The physical performance index of the cement and the physical performance index of the nano-silica are the same as those in Preparation Example 1.

[0089] S120, add water and water reducing agent and stir uniformly to ensure the fluidity of the concrete.

[0090] The water reducing agent is STC special polycarboxylic acid high efficiency water reducing agent, and the water reducing rate can reach more than 35%; the mixing water is laboratory ordinary tap water.

[0091] S130, uniformly sprinkle steel fibers, and obtain ZB-3 nano-modified ultra-high toughness concrete after stirring uniformly.

[0092] The steel fiber is 196.25 parts by mass. The physical performance index of the steel fiber is the same as that in Preparation Example 1.

[0093] The working performance of the obtained ZB-3 nano-modified ultra-high toughness concrete is tested, and after the test is completed, the mixture is placed in a mold and covered with a film to keep water. After two days, the mold is removed. The test piece after demolding is placed in a natural curing environment, i.e. a room temperature environment of about 20℃, and a layer of plastic film is covered on the surface of the test piece, and water is sprayed for maintenance before reaching the test age. After curing for 7d and 28d, the mechanical property test is carried out.

[0094] Preparation Example 4

[0095] S110, the fine aggregate, cementitious material and dispersed pre-processed nano-silica solution are added into a concrete mixer and stirred uniformly; it should be noted that the nano-material is dispersed by high-speed stirring to avoid agglomeration;

[0096] The nano-modified ultra-high toughness concrete comprises, by mass fraction, the following preparation raw materials:

[0097] 10-20 mesh quartz sand 640 parts, 70-140 mesh quartz sand 427 parts; water 171 parts, water reducing agent 43 parts;

[0098] Ternary cementitious system: silica fume 160 parts, superfine fly ash silico-aluminate fine 160 parts, cement 747 parts; the dosage of nano-silica is 2.0%. Among them, the physical performance index of cement, the physical performance index of nano-silica are the same as preparation example 1.

[0099] S120, add water and water reducing agent and stir uniformly to ensure the liquidity of the concrete.

[0100] The water reducing agent is STC special polycarboxylic acid high efficiency water reducing agent, and the water reducing rate can reach more than 35%; the mixing water is laboratory ordinary tap water.

[0101] S130, uniformly sprinkle steel fibers, and obtain ZB-4 nano modified ultra-high toughness concrete after uniform stirring.

[0102] Among them, the steel fiber is 196.25 parts by mass. The physical performance index of steel fiber is the same as preparation example 1.

[0103] The working performance test is carried out on the obtained ZB-4 nano modified ultra-high toughness concrete, and after the test is completed, the mixture is put into the mold and covered with film to keep water. After two days, the mold is removed. The test piece after the mold is removed is placed in a natural curing environment, i.e. a room temperature environment of about 20℃, and a layer of plastic film is covered on the surface of the test piece, and water conservation is supplemented before the test age is reached. After curing for 7d and 28d, the mechanical property test is carried out.

[0104] Preparation example 5

[0105] S110, add fine aggregate, cementitious material and dispersed pretreated nano-silica solution into the concrete mixer and stir uniformly; it should be noted that the nano material is dispersed by high speed stirring to avoid agglomeration;

[0106] The nano modified ultra-high toughness concrete comprises, by mass fraction, the following preparation raw materials:

[0107] 10-20 mesh quartz sand 640 parts, 70-140 mesh quartz sand 427 parts; water 171 parts, water reducing agent 43 parts;

[0108] Ternary cementitious system: silica fume 160 parts, superfine fly ash silico-aluminate fine 160 parts, cement 747 parts; the dosage of nano-silica is 2.5%. Among them, the physical performance index of cement, the physical performance index of nano-silica are the same as preparation example 1.

[0109] S120, add water and water reducing agent and stir uniformly to ensure the liquidity of the concrete.

[0110] The water reducing agent is STC special polycarboxylic acid high efficiency water reducing agent, and the water reducing rate can reach more than 35%; the mixing water is laboratory ordinary tap water.

[0111] S130, uniformly scatter steel fibers, and obtain ZB-5 nano-modified ultra-high toughness concrete after stirring uniformly.

[0112] The steel fiber is 196.25 parts by mass. The physical performance index of the steel fiber is the same as that of Preparation Example 1.

[0113] The working performance of the obtained ZB-5 nano-modified ultra-high toughness concrete is tested, and after the test is completed, the mixture is placed in a mold and covered with a film to retain water. After two days, the mold is removed. The test piece after the mold is removed is placed in a natural curing environment, i.e. a room temperature environment of about 20°C indoors, and a layer of plastic film is covered on the surface of the test piece, and water conservation is supplemented before the test age is reached. After curing for 7d and 28d, the mechanical property test is carried out.

[0114] Preparation Example 6

[0115] S110, the fine aggregate, the cementitious material and the dispersed pre-treated nano-silica solution are added to the concrete mixer and stirred uniformly; it should be noted that the nano-material is dispersed by high-speed stirring to avoid agglomeration;

[0116] The nano-modified ultra-high toughness concrete comprises, by mass fraction, the following preparation raw materials:

[0117] 10-20 mesh quartz sand 640 parts, 70-140 mesh quartz sand 427 parts; water 171 parts, water reducing agent 32 parts;

[0118] The ternary cementitious system: silica fume 107 parts, superfine fly ash silicate 107 parts, cement 853 parts; the dosage of nano-silica is 2%. The physical performance index of the cement and the physical performance index of the nano-silica are the same as those of Preparation Example 1.

[0119] S120, add water and water reducing agent and stir uniformly to ensure the fluidity of the concrete.

[0120] The water reducing agent is STC special polycarboxylic acid high efficiency water reducing agent, and the water reducing rate can reach more than 35%; the mixing water is laboratory ordinary tap water.

[0121] S130, uniformly scatter steel fibers and basalt fibers treated with a dispersible impregnating agent, and obtain ZB-6 nano-modified ultra-high toughness concrete after stirring uniformly.

[0122] The steel fiber is 172.7 parts by mass.

[0123] The basalt fiber is 8 parts.

[0124] The physical properties of the basalt fiber are shown in Table 4; the surface impregnating agent composition of the basalt fiber is shown in Table 5.

[0125] Table 4 Physical properties of basalt fibers

[0126]

[0127] Table 5 Composition of basalt fiber surface wetting agent

[0128]

[0129] The working performance of the obtained ZB-6 nano-modified ultra-high toughness concrete is tested, and after the test is completed, the mixture is placed in a mold and covered with a film to retain water. After two days, the mold is removed. The test piece after the mold is removed is placed in a natural curing environment, i.e. a room temperature environment of about 20°C, and a layer of plastic film is covered on the surface of the test piece, and water is sprayed for curing before reaching the test age. After curing for 7d and 28d, the mechanical property test is carried out.

[0130] Preparation Example 7

[0131] S110, the fine aggregate, the cementitious material and the dispersed pre-processed nano-silica solution are added into the concrete mixer and stirred uniformly; it should be noted that the nano-material is dispersed by high-speed stirring to avoid agglomeration;

[0132] The nano-modified ultra-high toughness concrete comprises, by mass fraction, the following preparation raw materials:

[0133] 10-20 mesh quartz sand 640 parts, 70-140 mesh quartz sand 427 parts; water 171 parts, water reducing agent 32 parts;

[0134] Ternary cementitious system: silica fume 213 parts, superfine fly ash silicate 160 parts, cement 693 parts; the dosage of nano-silica is 2%. Among them, the physical performance index of cement and the physical performance index of nano-silica are the same as those in Preparation Example 1.

[0135] S120, add water and water reducing agent and stir uniformly to ensure the fluidity of the concrete.

[0136] The water reducing agent is STC special polycarboxylic acid high-efficiency water reducing agent, and the water reducing rate can reach more than 35%; the mixing water is laboratory ordinary tap water.

[0137] S130, uniformly sprinkle the steel fiber and the dispersed basalt fiber treated by the wetting agent, and stir uniformly to obtain ZB-7 nano-modified ultra-high toughness concrete.

[0138] Among them, the steel fiber is 157 parts by mass.

[0139] The basalt fiber is 13.2 parts;

[0140] The physical properties of the basalt fibers and the surface sizing agent composition of the basalt fibers are the same as those in Preparation Example 6.

[0141] The working performance of the obtained ZB-7 nano-modified ultra-high toughness concrete is tested, and after the test is completed, the mixture is placed in a mold for film water retention. After two days, the mold is removed. The test piece after the mold is removed is placed in a natural curing environment, i.e. a room temperature environment of about 20°C, and a layer of plastic film is covered on the surface of the test piece, and water conservation is supplemented before the test age is reached. The mechanical property test is carried out after curing for 7d and 28d.

[0142] Preparation Example 8

[0143] S110, the fine aggregate, the cementitious material and the dispersed pre-processed nano-silica solution are added to the concrete mixer and stirred uniformly; it should be noted that the nano-material is dispersed by high-speed stirring to avoid agglomeration;

[0144] The nano-modified ultra-high toughness concrete comprises, by mass fraction, the following preparation raw materials:

[0145] 10-20 mesh quartz sand 640 parts, 70-140 mesh quartz sand 427 parts; water 171 parts, water reducing agent 32 parts;

[0146] Ternary cementitious system: silica fume 160 parts, superfine fly ash silicate 160 parts, cement 747 parts; the dosage of nano-silica is 2%. The physical performance index of the cement and the physical performance index of the nano-silica are the same as those in Preparation Example 1.

[0147] S120, water and water reducing agent are added and stirred uniformly to ensure the fluidity of the concrete.

[0148] The water reducing agent is STC special polycarboxylic acid high-efficiency water reducing agent, and the water reducing rate can reach more than 35%; the mixing water is laboratory ordinary tap water.

[0149] S130, uniformly sprinkle the steel fiber and the dispersed basalt fiber treated by the sizing agent, and stir uniformly to obtain ZB-8 nano-modified ultra-high toughness concrete.

[0150] The steel fiber is 164.8 parts by mass.

[0151] The basalt fiber is 10.57 parts;

[0152] The physical properties of the basalt fibers and the surface sizing agent composition of the basalt fibers are the same as those in Preparation Example 6.

[0153] The working performance test is carried out on the obtained ZB-8 nano-modified ultra-high toughness concrete, and after the test is completed, the mixture is placed in a mold and covered with a film to keep water. After two days, the mold is removed. The test piece after the mold is removed is placed in a natural curing environment, that is, a room temperature environment of about 20 DEG C, and a layer of plastic film is covered on the surface of the test piece, and before reaching the test age, it is supplemented with watering conservation. After curing for 7d and 28d, the mechanical property test is carried out.

[0154] Comparative example 1

[0155] S110, the fine aggregate, the cementitious material and the dispersed pre-processed nano-silicon dioxide solution are added to the concrete mixer and stirred uniformly; it should be noted that the nano-material is dispersed by high-speed stirring to avoid agglomeration;

[0156] The nano-modified ultra-high toughness concrete comprises, by mass fraction, the following preparation raw materials:

[0157] 10-20 mesh quartz sand 640 parts, 70-140 mesh quartz sand 427 parts; water 171 parts, water reducing agent 32 parts;

[0158] Ternary cementitious system: silica fume 213 parts, superfine fly ash silicate 160 parts, cement 693 parts; the dosage of nano-silicon dioxide is 0%. The physical performance index of the cement and the physical performance index of the nano-silicon dioxide are the same as those of preparation example 1.

[0159] S120, water and water reducing agent are added and stirred uniformly to ensure the fluidity of the concrete.

[0160] The water reducing agent is STC special polycarboxylic acid high efficiency water reducing agent, and the water reducing rate can reach more than 35%; the mixing water is laboratory ordinary tap water.

[0161] S130, uniformly sprinkle the steel fiber, and after stirring uniformly, obtain DB-1 nano-modified ultra-high toughness concrete.

[0162] The steel fiber is 196.25 parts by mass. The physical performance index of the steel fiber is the same as that of preparation example 1.

[0163] The working performance test is carried out on the obtained DB-1 nano-modified ultra-high toughness concrete, and after the test is completed, the mixture is placed in a mold and covered with a film to keep water. After two days, the mold is removed. The test piece after the mold is removed is placed in a natural curing environment, that is, a room temperature environment of about 20 DEG C, and a layer of plastic film is covered on the surface of the test piece, and before reaching the test age, it is supplemented with watering conservation. After curing for 7d and 28d, the mechanical property test is carried out.

[0164] Comparative example 2

[0165] S110, the fine aggregate, cementitious material and dispersed pre-processed nano-silica solution are added into a concrete mixer for uniform stirring; it should be noted that the nano-material is dispersed by high-speed stirring to avoid agglomeration;

[0166] The nano-modified ultra-high toughness concrete comprises, by mass fraction, the following preparation raw materials:

[0167] 10-20 mesh quartz sand 640 parts, 70-140 mesh quartz sand 427 parts; water 171 parts, water reducing agent 32 parts;

[0168] The ternary cementitious system comprises: silica fume 213 parts, superfine fly ash silico-aluminate fine substance 160 parts, and cement 693 parts; the dosage of nano-silica is 3%. The physical performance indicators of the cement and the physical performance indicators of the nano-silica are the same as those in Preparation Example 1.

[0169] S120, water and water reducing agent are added and stirred uniformly to ensure the fluidity of the concrete.

[0170] The water reducing agent is STC special polycarboxylic acid high-efficiency water reducing agent, and the water reducing rate can reach more than 35%; the mixing water is laboratory ordinary tap water.

[0171] S130, uniformly sprinkle steel fibers, and obtain DB-2 nano-modified ultra-high toughness concrete after uniform stirring.

[0172] The steel fiber is 196.25 parts by mass. The physical performance indicators of the steel fiber are the same as those in Preparation Example 1.

[0173] The working performance of the obtained DB-2 nano-modified ultra-high toughness concrete is tested, and after the test is completed, the mixture is placed in a mold and covered with a film to retain water. After two days, the mold is removed. The test piece after the mold is removed is placed in a natural curing environment, i.e. a room temperature environment of about 20℃ indoors, and a layer of plastic film is covered on the surface of the test piece, and water conservation is supplemented before the test period is reached. The mechanical property test is carried out after curing for 7d and 28d.

[0174] Test Example 1

[0175] The ZB-1 nano-modified ultra-high toughness concrete, ZB-2 nano-modified ultra-high toughness concrete, ZB-3 nano-modified ultra-high toughness concrete, ZB-4 nano-modified ultra-high toughness concrete, ZB-5 nano-modified ultra-high toughness concrete, ZB-6 nano-modified ultra-high toughness concrete, ZB-7 nano-modified ultra-high toughness concrete, ZB-8 nano-modified ultra-high toughness concrete, and DB-1 nano-modified ultra-high toughness concrete, DB-2 nano-modified ultra-high toughness concrete obtained are respectively poured according to the thin layer ramming and the conventional one-time pouring process to obtain the bending resistance test piece, and the bending resistance strength performance test is carried out after curing for 7d and 28d.

[0176] Thin layer ramming refers to pouring new mixed concrete from one end of the mold, and pouring and smoothing along the flow direction (long side direction of the mold) at about 1 cm thick per layer; and one-time pouring refers to pouring new mixed concrete into the test mold at one time, only smoothing and scraping the excess slurry at the top layer, and using a non-magnetic vibration table for 30s vibration.

[0177] According to GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixture", the slump and spread of the mixture are tested to test the workability of the concrete mixture; the mechanical properties of the concrete mixture are tested according to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", and the compressive strength, splitting tensile strength and flexural strength of the concrete test piece are tested, wherein the specimen size for compressive strength test and splitting tensile strength test is a cube with a side length of 100 mm, and the specimen size for flexural strength test is 100 mm x 100 mm x 400 mm.

[0178] The test results of the slump, spread, splitting tensile strength and compressive strength of each test piece are shown in Table 6.

[0179] Table 6: Slump, spread, splitting tensile strength and compressive strength of flexural test piece

[0180]

[0181] As can be seen from Table 6, with the increase of the amount of nano-SiO2, the workability of STC decreases significantly, and the compressive strength and splitting tensile strength both increase first and then decrease. This is because the nano-silica has small particle size and large specific surface area, and when it is added to concrete, it can improve the pore structure of the cement slurry and generate more dense hydration products inside the structure, thereby improving the mechanical strength and durability of the material. However, with the further increase of the content of nano-materials, the fluidity of the concrete becomes worse, and the fiber distribution is more affected by the fluidity, resulting in a decrease in the flexural strength of the concrete.

[0182] Based on the experimental results, by limiting the composition of the ternary cementitious system and the amount of nano-silica (nano-SiO2 content of 0.5%-2%), an ultra-high toughness concrete with greatly improved workability and mechanical properties is obtained. Among them, when the amount of nano-SiO2 is 2%, the effect is best, and the 28d flexural strength of ZB-4 is increased by about 21% compared with DB-1 in thin layer ramming.

[0183] In addition, compared with conventional pouring, the flexural strength of STC in thin layer ramming is improved. For example, the 28d flexural strength of ZB-1 in thin layer ramming process is increased by about 23% compared with conventional pouring process.

[0184] The multi-scale toughening of the complex fiber can make the fiber play its own role at different stress levels during the fracture process of the concrete, achieve the purpose of step-by-step crack resistance, and further improve the toughness of the STC. The basalt fiber treated by the dispersible wetting agent has a hydrophobic surface and better dispersibility. The appropriate replacement of a part of the steel fiber mixed into the super-toughness concrete can improve the working performance and anti-shrinkage performance of the STC, and the comprehensive performance is improved better. It can be seen from Table 6 that the complex fiber can increase the spread of the nano-modified super-toughness concrete specimen by about 10% and reduce the strength by about 5%. The fluidity of the specimen is improved without reducing the strength.

[0185] Figure 2 In the comparison diagram of the thin layer ramming process and the conventional process forming specimen, the left side is the specimen formed by the thin layer ramming method, and the right side is the specimen formed by the conventional process. It can be seen from Figure 2 that the surface of the specimen after the thin layer ramming is smoother, and the hole defects are smaller, while the surface of the specimen formed by the conventional process is rough, and the defects are more. In addition, the DB-1 group specimen and the DB-2 group specimen with the nano-SiO2 content not between 0.5% and 2.5% have gradually larger holes and more defects, and the comparison of the two forming processes is obvious.

[0186] With the change of the dosage of nano-SiO2, the flexural strength also changes. Whether it is thin layer ramming process or conventional process, the best interval of the dosage of nano-SiO2 is 0.5%-2.5%. This is because the incorporation of nano-SiO2 can refine the internal pores of concrete, and at the same time, due to the nucleation effect of nano-particles, the loose C-S-H gel can be changed into a network structure with nano-particles as the core, forming a more dense and higher strength C-S-H gel, so that the matrix strength is significantly improved. But when the dosage exceeds 2.5%, nano-SiO2 is difficult to disperse in the stirring process, causing agglomeration phenomenon and unable to uniformly fill in the internal pores of concrete, but forming a weak zone at the cement stone and interface, thereby reducing the matrix strength. The flexural strength is largely dependent on the distribution of fibers, and the distribution of steel fibers is affected by the fluidity of the paste. When the dosage of nano-SiO2 increases from 0% to 0.5% (not including 0.5%), the fluidity of concrete decreases but changes little, the fiber distribution is less affected by the fluidity of concrete, and due to the activity effect of nano-SiO2, the bonding strength of concrete is increased, so that the flexural strength of concrete under the two forming processes is improved. When the dosage of nano-SiO2 increases to more than 2.5%, the fluidity of concrete becomes worse, and the fiber distribution is more affected by the fluidity, so that the flexural strength of concrete under the conventional process decreases. At this time, the best dosage of nano-SiO2 is 1%, but in the case of artificial smoothing, the continuous improvement of the matrix strength of concrete by nano-SiO2 reduces the pore defects caused by the reduction of fluidity, so that the flexural strength of concrete under the thin layer ramming process continues to increase, and the best dosage of nano-SiO2 is 2%. When the dosage continues to increase beyond 2.5%, the paste is very viscous, and the concrete is difficult to flow, so the influence of the forming process is limited, the fiber distribution is relatively poor, the internal pore defects and weak zones of the specimen increase, and the flexural strength of concrete decreases.

[0187] Test Example 2

[0188] After the ZB-4 nano-modified ultra-high toughness concrete is respectively subjected to thin layer ramming and conventional pouring, CT images are obtained. Among them, Figure 3 a is thin layer ramming; Figure 3 b is conventional pouring. Since the cross section of steel fiber is circular, it appears as a white bright spot after binary processing during CT scanning. When the shape of white bright spot is closer to a circle and more full, it means that the fiber is perpendicular to the direction of CT ray, i.e. parallel to the long axis direction of the specimen, at this time the fiber tends to be distributed in the same direction. By observing Figure 3 It can be seen that the steel fiber tends to be distributed in the same direction in thin layer ramming, and the thin layer ramming method helps to improve the performance of concrete, thereby improving the flexural strength.

[0189] Finally, it should be noted that the above examples are merely intended to illustrate the technical solutions of the present application and not to limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A nano-modified ultra-high toughness concrete, characterized in that, The nano-modified ultra-high toughness concrete is a naturally cured concrete; The raw materials include: fine aggregate, water, water-reducing agent, cementitious material, steel fiber and nano-silica; wherein the binder-aggregate ratio is 1.0 and the water-binder ratio is 0.

16. The volume fraction of steel fiber is 1.2-2.5%, and the mass fraction of nano-silica is 0.5-2%. By weight percentage, the cementitious materials include: 50%~80% cement, 10%~20% silica fume, 20%~25% ultrafine fly ash aluminosilicate fines, and 5%~10% viscosity reducer.

2. The nano-modified ultra-high toughness concrete as described in claim 1, characterized in that, It also includes basalt fibers treated with a dispersible sizing agent, wherein the volume content of the basalt fibers is 0.3~0.5%.

3. The nano-modified ultra-high toughness concrete as described in claim 1, characterized in that, The fine aggregate is a mixture of 10-20 mesh quartz sand and 70-140 mesh quartz sand in a ratio of 3:

2.

4. The nano-modified ultra-high toughness concrete as described in claim 1, characterized in that, The mass content of the nano-silica is 1~2%.

5. The nano-modified ultra-high toughness concrete as described in claim 4, characterized in that, The particle size of the nano-silica is 20~50nm.

6. A method for preparing nano-modified ultra-high toughness concrete, characterized in that, The method for preparing the naturally curing, nano-modified, ultra-high toughness concrete of claim 1 includes: Fine aggregate, cementitious materials, and pre-treated nano-silica solution are added to a concrete mixer and mixed evenly. Add water and water-reducing agent and stir well; Steel fibers are evenly sprinkled in to obtain nano-modified ultra-high toughness concrete.

7. The method for preparing nano-modified ultra-high toughness concrete as described in claim 6, characterized in that, This also includes the use of thin-layer compaction during the casting process, including, The obtained nano-modified ultra-high toughness concrete was poured from one end of the mold. According to the preset thickness of each layer, pour and smooth along the long side of the mold; wherein, the thickness of each layer is 0.8~1.2 cm.

8. The method for preparing nano-modified ultra-high toughness concrete as described in claim 6, characterized in that, It also includes basalt fibers with a density of 2.643 g / cm³. 3 It has a diameter of 17 micrometers.

9. The method for preparing nano-modified ultra-high toughness concrete as described in claim 6, characterized in that, The steel fiber is a microfiber copper-plated steel fiber with a length of 14 mm and an equivalent diameter of 0.22 mm.

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