CN115028419A - Design method for self-compacting concrete mix proportion - Google Patents

Design method for self-compacting concrete mix proportion Download PDF

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CN115028419A
CN115028419A CN202210971058.5A CN202210971058A CN115028419A CN 115028419 A CN115028419 A CN 115028419A CN 202210971058 A CN202210971058 A CN 202210971058A CN 115028419 A CN115028419 A CN 115028419A
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water
cement
fly ash
self
dosage
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CN115028419B (en
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赵云
刘晓敏
周俊龙
张倩
李一康
许云龙
葛隆博
宋子文
路景皓
王海龙
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China Construction Sixth Engineering Division Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
    • C04B28/04—Portland cements
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00034—Physico-chemical characteristics of the mixtures
    • C04B2111/00198—Characterisation or quantities of the compositions or their ingredients expressed as mathematical formulae or equations
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies
    • Y02W30/91—Use of waste materials as fillers for mortars or concrete

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Abstract

A design method of a self-compacting concrete mix proportion comprises the following steps of (1) determining the working performance and the compressive strength grade requirement of the self-compacting concrete according to engineering requirements; (2) determining the proportion of coarse and fine aggregates based on an aggregate stacking theory; (3) selecting the thickness of the mortar film, and calculating the volume ratio of the coarse aggregate; (4) calculating the specific dosage of coarse and fine aggregates; (5) determining the ratio of the fly ash to the cement; (6) calculating the water-to-glue ratio; (7) determining the specific dosage of cement, fly ash and water in the net slurry; (8) determining the dosage of the water reducing agent; (9) the method has the advantages that the actual dosage of the mixing water is determined according to the water content of the aggregate and the dosage of the water reducing agent, the design steps are clear, the operation is easy to follow, the trial-mix times can be effectively reduced, the use of the fly ash can effectively reduce the preparation cost, meanwhile, according to different engineering requirements, the self-compacting concrete meeting different working performance and compressive strength requirements is prepared by adjusting the thickness of the mortar film and the water-cement ratio, and the method has good practicability.

Description

Design method for self-compacting concrete mix proportion
Technical Field
The invention relates to the field of civil engineering materials, in particular to a design method of a self-compacting concrete mixing proportion.
Background
The self-compacting concrete is concrete which can flow and fill all corners of a template by self gravity without vibrating, has good uniformity and does not generate segregation and bleeding. Owing to the good working performance of the self-compacting concrete, the self-compacting concrete is not only suitable for pouring structures with complex template shapes and densely distributed reinforcing steel bars, but also beneficial to reducing the construction time and the construction noise, and increasingly replaces the common concrete in different engineering applications. And the self-compacting concrete has more strict control and requirements on the dosage and specification of raw materials compared with the preparation of common concrete due to the unique working performance of the self-compacting concrete. Although researchers at home and abroad propose a series of design methods for the mix proportion of the self-compacting concrete, the methods still have some defects, for example, many design parameters in the domestic regulation JGT/T283-2012 'technical specification for the application of the self-compacting concrete' are based on experience values, and the difference of raw materials in different regions is likely to cause that the prepared self-compacting concrete is difficult to meet the expected requirement; some methods have higher requirements on test instruments, are not suitable for engineering sites and have limited application range; the dosage of the water reducing agent and the dosage of the mineral admixture are directly given by some methods, and the methods have certain blindness, so that the workload brought by trial preparation is greatly increased, and the prepared self-compacting concrete is difficult to meet the expected requirements; the other patents directly give the amount of each material of the self-compacting concrete, describe little the preparation process and preparation method, and have poor robustness to the raw materials, for example, Chinese patent (publication No. CN 112209683A) discloses a self-compacting concrete C120 premixed dry concrete and its preparation method, comprising, by weight, 480-550 parts of Portland cement, 40-55 parts of coarse aggregate, 70-80 parts of steel fiber, 550 parts of fine aggregate, 11-15 parts of admixture, and 190 parts of mineral admixture. Therefore, it is necessary to provide a design method of self-compacting concrete mix proportion which can adjust the working performance and strength of the concrete according to the engineering requirements.
In addition, the emission of the fly ash in China reaches hundreds of millions of tons every year, and if the emission of the fly ash is not controlled and treated, atmospheric pollution is caused and harm is caused to human health. A large number of researches show that the fluidity of the self-compacting concrete can be improved and the shrinkage of the concrete can be reduced by adopting a proper amount of fly ash to replace cement. Therefore, the optimal ratio of the fly ash to the cement is determined, and a design method of the mixing proportion of the high-performance fly ash type self-compacting concrete is provided, which is favorable for further expanding the application range of the self-compacting concrete.
Disclosure of Invention
On the basis of the theoretical technology of the existing concrete mixing proportion method, the working performance and the compressive strength of the self-compacting concrete are adjusted by changing the thickness of the mortar film, and the overall performance of the self-compacting concrete is improved as much as possible by optimizing the proportion of the aggregate framework and optimizing the components of the clean mortar, so that the self-compacting concrete mixing proportion design method capable of meeting different engineering requirements is provided.
The technical scheme adopted by the invention is as follows:
a design method for the mix proportion of self-compacting concrete comprises the following steps:
(1) determining the working performance and compressive strength grade requirements of the self-compacting concrete according to engineering requirements;
(2) selecting the mass proportion of various coarse aggregates and fine aggregates, uniformly mixing the coarse aggregates and the fine aggregates according to the selected proportion, filling the cylindrical measuring container with the mixed aggregates for three times, carrying out inserting tamping compaction on the mixed aggregates after each filling, and calculating the mixed aggregatesAccording to the principle of maximum density and minimum porosity, the proportion between coarse aggregate and fine aggregate is determinedr；
(3) Dividing the self-compacting concrete into a particle framework consisting of coarse aggregates and mortar consisting of fine aggregates, a cementing material, water and a water reducing agent, enabling coarse aggregate particles of each grade to be equivalent to a standard sphere, enabling the thickness of the mortar film wrapping the coarse aggregates to be half of the average distance between the coarse aggregates, preparing the concrete by adopting an absolute volume method, and then preparing the self-compacting concrete with the volume of 1m 3 Its volume can be calculated according to equation 1:
in the case of the formula 1,
Figure 944742DEST_PATH_IMAGE001
；
in the formula:V ca is the absolute volume of the coarse aggregate particles, m 3 ；V ca,sur Volume of mortar for coating coarse aggregate particles, m 3 ；V ca,void Volume of mortar for filling voids between coarse aggregate particles, m 3 。
Calculating the volume of the mortar wrapping the spherical coarse aggregate particles by adopting a formula 2:
in the formula 2, the first and second groups,
Figure 297226DEST_PATH_IMAGE002
；
in the formula:tthe thickness of the mortar film for wrapping the coarse aggregate is mm;S ca is the sum of the surface areas of the coarse aggregates of the various fractions, mm 2 。
The coarse aggregate is continuously graded, and the particle size of each fraction of coarse aggregate is determined by a screening method, so that the sum of the surface areas of each fraction of coarse aggregateS ca Can be calculated according to equation 3:
in the formula 3, the first and second phases,
Figure 426725DEST_PATH_IMAGE003
；
in the formula:S ca,i is the sum of the surface areas of the i-th fraction coarse aggregates, mm 2 ；
Figure 802342DEST_PATH_IMAGE004
Is the equivalent particle size of the ith fraction coarse aggregate particles, mm;N ca,i the number of particles of the ith fraction coarse aggregate.
Calculating the equivalent particle size of the ith fraction coarse aggregate particles according to formula 4:
in the case of the formula 4,
Figure 409910DEST_PATH_IMAGE005
；
in the formula:D ca,i+1 andD ca,i indicates the adjacent mesh size, mm; .
Calculating the particle number of the ith fraction coarse aggregate according to formula 5:
in the case of the formula 5,
Figure 882480DEST_PATH_IMAGE006
；
in the formula:m ca is the total mass of the coarse aggregate particles in kg/m 3 ；k ca,i The mass fraction of the i-th grade coarse aggregate particles obtained by a screening method is expressed by decimal fraction;m ca,i the mass of a single particle in the i-th grade coarse aggregate is kg/m 3 ；ρ ca Apparent density of coarse aggregate particles, kg/m 3 。
The voids between the coarse aggregate particles are calculated according to equation 6:
in the case of the formula 6,
Figure 668033DEST_PATH_IMAGE007
；
in the formula:ρ ′ ca is the bulk density of coarse aggregate particles, kg/m 3 。
Equation 7 is obtained from equations 1 to 6, and the volume of the coarse aggregate is calculated according to equation 7:
in the formula 7, the first and second groups,
Figure 593264DEST_PATH_IMAGE008
；
as can be seen from equation 7, when the coarse aggregate gradation is determined, the volume of the coarse aggregateV ca The thickness of the mortar film is taken as an independent variable function, and the thickness of the mortar film can be adjustedtThe value of (A) changes the working performance of the self-compacting concrete to adapt to different engineering requirements.
(4) Calculating the single-component dosage kg of the coarse aggregate according to the volume of the coarse aggregate determined in the step (3) and a formula 8:
in the case of the formula 8,
Figure 4522DEST_PATH_IMAGE009
；
according to the coarse and fine aggregate proportion determined in the step (2)rCalculating the single dosage kg of the fine aggregate according to the formula 9:
in the formula 9, the first and second groups,
Figure 331598DEST_PATH_IMAGE010
；
(5) because the proper amount of fly ash is added, the fluidity of the self-compacting concrete can be improved, the using amount of cement can be reduced, and the cost for preparing the self-compacting concrete can be reduced, therefore, the fly ash is used for replacing part of the cement. In order to optimize the using amount of the fly ash, the clean slurry without the fly ash is taken as a reference group, the fly ash with different using amounts is used for replacing cement, the clean slurry under different replacing rates of the fly ash is prepared, and the expansion degree of each group of clean slurry is measured by using truncated cone circular dies with the diameters of the bottom and the top of 100mm and 70mm respectively and the height of 50 mm. And determining the ratio of the fly ash to the cement according to the principle of maximum net slurry expansion.
(6) Calculating the water-cement ratio corresponding to the compressive strength preparation value according to a formula 10 given by the domestic specification JGT/T283 and 2012 'technical specification for self-compacting concrete application':
in the formula 10, the process is described,
Figure 553632DEST_PATH_IMAGE011
；
in the formula:f cu,0 the preparation value of the compressive strength of the cube is MPa;
Figure 170688DEST_PATH_IMAGE012
the mass ratio of water to the cementing material is;f ce the measured compressive strength of the cement is 28d, and is MPa;𝛼the mineral admixture replaces the cement in mass ratio;
Figure 933108DEST_PATH_IMAGE013
is the gel coefficient of the fly ash, when𝛼When the content is less than or equal to 0.3,
Figure 52373DEST_PATH_IMAGE013
take 0.4. According to the regulation of the relationship between the formulated value of the compressive strength and the target value in JGJ 55-2011 'design rule of the mix proportion of common concrete', the relationship between the formulated value of the compressive strength and the target value is determined by adopting a formula 11:
in the formula 11, the first and second groups,
Figure 507625DEST_PATH_IMAGE014
；
in the formula:f cu,d the target value of the compressive strength is MPa;𝜎the standard deviation of compressive strength is MPa.
(7) Calculate the net pulp volume according to equation 12:
in the formula 12, the process is described,
Figure 594399DEST_PATH_IMAGE015
；
in the formula:V paste is the volume of the paste, m 3 ；V mortar Is the mortar volume, m 3 ；V fa Volume of fine aggregate, m 3 ；ρ fa Is the apparent density of fine aggregate, kg/m 3 。
The net slurry consists of water, cement, fly ash and air, and therefore, the volume composition of the net slurry is expressed according to equation 13:
in the formula 13, the first and second groups,
Figure 98193DEST_PATH_IMAGE016
；
in the formula:V c volume of cement, m 3 ；V fl Is the volume of fly ash, m 3 ；V w Volume of water, m 3 ；V a Volume of air, m 3 ；m cm Is the mass of the cementing material (cement and fly ash), kg;ρ c is the apparent density of cement, kg/m 3 ；ρ fl Is the apparent density of the fly ash in kg/m 3 ；ρ w Is the density of water, kg/m 3 . It should be noted that, when the volume of air is not measured, the volume of air isV a The yield was taken to be 2%.
From equation 13 to equation 14, the mass of the cement can be calculated:
in the case of the formula 14,
Figure 134282DEST_PATH_IMAGE017
；
further, the mass of cement, fly ash and water are calculated according to the formulas 15-17:
in accordance with the formula 15, the data rate,
Figure 947386DEST_PATH_IMAGE018
；
in the formula 16, the process is described,
Figure 334505DEST_PATH_IMAGE019
；
in the formula 17, the process is described,
Figure 376410DEST_PATH_IMAGE020
；
in the formula:m c kg is the mass of cement;m fl the mass of the fly ash is kg;m w is the mass of water.
(8) The dosage of the water reducing agent has important influence on the working performance of the self-compacting concrete, and the proper dosage of the water reducing agent can effectively improve the fluidity of the self-compacting concrete and reduce the water consumption. However, when the water reducing agent is used excessively, the fresh concrete is easy to bleed and separate, and conversely, when the dosage of the water reducing agent is too small, the fresh concrete is difficult to meet the requirement of self-compaction. Therefore, it is very critical to determine the proper amount of water reducing agent. Similar to the process of determining the ratio of the fly ash to the cement, preparing clean slurry under the determined water-cement ratio, determining the expansion degree of the clean slurry under different water reducer dosages by using a truncated cone circular mold, determining the dosage of the water reducer by analyzing the change rule of the expansion degree and the flow time of the clean slurry and observing the flow state of the clean slurry, selecting the dosage of the water reducer with larger expansion degree and shorter flow time of the clean slurry to prepare the self-compacting concrete, determining the mass ratio of the water reducer to the cementing material at the moment, and calculating the dosage of the water reducer according to a formula 18:
in the formula 18, the process is described,
Figure 719536DEST_PATH_IMAGE021
；
in the formula:m sp the dosage of the water reducing agent is kg.
(9) In general, water reducers used in concrete mixing plants are all liquid types, and aggregates contain a certain amount of moisture, so the actual mixing water amount for preparing self-compacting concrete is calculated according to equation 19:
in the formula 19, the process is described,
Figure 516590DEST_PATH_IMAGE022
；
in the formula:m wm the actual added water amount, kg, for preparing the self-compacting concrete;𝛾 sp is the solid content in the water reducing agent,%;𝛾 ca water content of the coarse aggregate,%;𝛾 fa the water content of the fine aggregate is percent.
(10) And (4) trial preparation is carried out according to the concrete mixing proportion calculated in the steps (2) to (9) until the prepared self-compacting concrete meets the expected working performance and strength requirements. If the initial trial fitting does not meet the expected requirement, the adjustment strategy is as follows: the working performance of the self-compacting concrete is controlled by adjusting the dosage of the water reducing agent and the thickness of the mortar film, and the compressive strength of the self-compacting concrete is controlled by adjusting the water-cement ratio and the dosage of the cementing material.
The invention has the beneficial effects that: the invention has clear design steps, easy operation, and can effectively reduce trial-mix times, effectively reduce the preparation cost by using the fly ash, and simultaneously prepare the self-compacting concrete meeting different working performance and compressive strength requirements by adjusting the thickness of the mortar film and the water-cement ratio according to different engineering requirements, thereby having good practicability.
Drawings
FIG. 1 is a graph showing the change in density and porosity of coarse and fine aggregates mixed at different ratios according to the present invention.
FIG. 2 is a graph showing the expansion change law of the net slurry of the present invention at different substitution rates of fly ash.
FIG. 3 is a graph showing the variation of the net slurry spread and the time taken for the net slurry to stop flowing under different water reducing agent dosages.
Detailed Description
To further illustrate the practice of the present invention, the following is a mix design process for C50 self-compacting concrete.
The cement is P.O 42.5 grade ordinary portland cement, and the fly ash is second grade fly ash.
The basic properties of the cements used were tested according to the specification GB 175-2007 Universal Portland Cement, and the results are shown in Table 1.
TABLE 1
Figure 63109DEST_PATH_IMAGE023
Common water-washed river sand with fineness modulus of 2.74 is used as fine aggregate, the particle size distribution range is 0-4.75mm, and the apparent density is 2612 kg/m 3 Bulk density of 1590 kg/m 3 The water content is 1.1 percent, and the mud content is less than 2 percent; the coarse aggregate is continuous graded crushed stone with particle size distribution range of 4.75-16 mm and apparent densityρ ca 2708kg/m 3 Bulk density ofρ ′ ca 1560kg/m 3 The water content was 0.5%.The particle composition of the fine aggregate and the coarse aggregate is shown in Table 2.
TABLE 2
Figure 236602DEST_PATH_IMAGE024
The admixture is high-efficiency polycarboxylate superplasticizer mother liquor, the solid content is 20%, and the admixture is diluted by 2 times for use.
The mixing water is daily drinking water.
Example (b): the concrete implementation steps of the embodiment, which are designed by taking the mixing proportion of the C50 self-compacting concrete as an example, are as follows:
(1) determining the working performance and compressive strength grade requirements of self-compacting concrete
And setting the target compressive strength to 50MPa after 28d, and preparing self-compacting concrete with different working performance grades by adjusting the thickness of the mortar film.
(2) Determining the ratio between coarse and fine aggregates
Five kinds of coarse and fine aggregates with different proportions are selected, and the density and the porosity of the mixed aggregates are measured, and are shown in figure 1. As can be seen from fig. 1, as the volume fraction of the fine aggregate gradually increases, the density of the mixed aggregate continues to increase, and the porosity correspondingly decreases until the mass fraction of the fine aggregate increases to 50%, the density of the aggregate reaches its maximum value, and the increase in the volume fraction of the fine aggregate increases the porosity and decreases the density of the aggregate, and in order to obtain a more dense skeleton, the volume fractions of the fine aggregate and the coarse aggregate in the total amount of the aggregate are selected to be 50% and 50%, respectively.
(3) Calculating the volume ratio of the coarse aggregate
Firstly, according to formula 4 in the technical scheme
Figure 434234DEST_PATH_IMAGE025
Wherein:D ca,i+1 andD ca,i indicates the adjacent mesh size, mm; the coarse aggregate gradation calculates the equivalent particle size and mass fraction of the coarse aggregate particles at each level, and the calculation results are shown in table 3.
TABLE 3
Figure 402190DEST_PATH_IMAGE026
In order to achieve different self-compaction performance grades, three mortar film thicknesses with different thicknesses are selected, wherein the mortar film thicknesses are respectively 2.1mm, 2.5mm and 2.9mm according to a formula 7
Figure 436005DEST_PATH_IMAGE008
And the volume of the coarse aggregate corresponding to the thickness of the three mortar films is respectively 0.32m 3 ，0.30 m 3 ，0.28 m 3 。
Taking the mortar film with the thickness of 2.1mm as an example, the process of calculating the volume of the coarse aggregate according to the formula 7 is as follows:
Figure 68980DEST_PATH_IMAGE027
taking the mortar film with the thickness of 2.5mm as an example, the volume of the coarse aggregate is calculated according to the formula 7 as follows:V ca =1/[2708/1530+6×2.5×（36.3/14.53+39.9/11.2+32.4/6.72+1.4/3.35）×0.01]≈0.30m 3 。
taking the mortar film with the thickness of 2.9mm as an example, the volume of the coarse aggregate is calculated according to the formula 7 as follows:V ca =1/[2708/1530+6×2.9×（36.3/14.53+39.9/11.2+32.4/6.72+1.4/3.35）×0.01]≈0.28m 3 。
(4) calculating the specific dosage of coarse aggregate and fine aggregate
According to the formula 8, the process is,
Figure 199748DEST_PATH_IMAGE009
the single use amounts of the coarse aggregates corresponding to the three mortar film thicknesses (2.1 mm, 2.5mm and 2.9 mm) can be calculated to be 867kg, 812kg and 758kg respectively, and further, the single use amounts of the fine aggregates corresponding to the three mortar film thicknesses can be calculated to be 867kg, 812kg and 758kg respectively according to the formula 9.
(5) Determining the ratio of fly ash to cement
According to the step (5) in the invention content, two water-cement ratios with large difference are selected, the water-cement ratios are set to be 0.25 and 0.45, five different fly ash dosages are adopted to replace cement, the water reducer dosages are 1.6% of the weight of the cementing material, the extension degree of each group of net slurry under two different water-cement ratios is measured by using a truncated cone circular die, and the change rule of the extension degree of the net slurry under different fly ash substitution rates is shown in figure 2. It can be found that under two different water-cement ratios, the expansion degree of the net slurry shows a change rule of increasing firstly and then decreasing with the increase of the coal ash substitution rate, and when the coal ash substitution rate is in a range of 20-30%, the net slurry has better flowing property, so that 25% of coal ash is used for replacing cement, namely the ratio of the coal ash for replacing the cement is 25%.
(6) Determining the preparation strength and water-cement ratio of self-compacting concrete
The target strength of the concrete is 50MPa according to the step (1) in the example 1, and the formulated strength of the self-compacting concrete can be calculated according to the specification JGJ 55-2011 'design rule for common concrete mixing ratio':
Figure 276288DEST_PATH_IMAGE028
，𝜎standard deviation of compressive strength, MPa.
Calculating the water-to-gel ratio corresponding to the compression strength preparation value according to the formula 10:
Figure 46667DEST_PATH_IMAGE029
。
(7) determining concrete dosage of cement, fly ash and water in the clean slurry
The volume of the net slurry is calculated according to the formula 12, and the net slurry volumes corresponding to the film thicknesses (2.1 mm, 2.5mm and 2.9 mm) of the three kinds of mortar are respectively 0.35m 3 、0.39m 3 And 0.43m 3 。
Taking the mortar film with the thickness of 2.1mm as an example, the process of calculating the net slurry volume according to the formula 12 is
Figure 296382DEST_PATH_IMAGE030
；
Taking the mortar film with the thickness of 2.5mm as an example, the net slurry volume is calculated according to the formula 12V paste =1-0.39-894/2612≈0.27m 3 ；
Taking the mortar film with the thickness of 2.9mm as an example, the net slurry volume is calculated according to the formula 12V paste =1-0.43-894/2612≈0.23m 3 ；
The single use amount of the cementing materials is calculated according to the formula 14, and the single use amounts of the cementing materials corresponding to the film thicknesses (2.1 mm, 2.5mm and 2.9 mm) of the three types of mortar are 495kg, 555kg and 615kg respectively.
Taking the mortar film with the thickness of 2.1mm as an example, the process of calculating the net slurry volume according to the formula 14 is
Figure 219339DEST_PATH_IMAGE031
Volume of air thereinV a 2% of the apparent density of the fly ashρ fl 2300 kg/m 3 ；
Calculating the single use amount of cement, fly ash and water under different mortar film thicknesses according to formulas 15 to 17, wherein the single use amount of cement, fly ash and water is 371kg, 124kg and 158kg respectively when the mortar film thickness is 2.1 mm; when the thickness of the mortar film is 2.5mm, the single dosage of the cement, the fly ash and the water is 416kg, 139kg and 178kg respectively; when the mortar film thickness was 2.9mm, the amounts of cement, fly ash and water used were 461kg, 154kg and 197kg, respectively. Taking the mortar film with the thickness of 2.1mm as an example, the process of calculating the single dosage of the cement, the fly ash and the water according to the formula 15 to the formula 17 is as follows:
cement:
Figure 529098DEST_PATH_IMAGE032
fly ash:
Figure 786773DEST_PATH_IMAGE033
water:
Figure 840179DEST_PATH_IMAGE034
。
(8) determination of the amount of Water-reducing agent
According to the step (8) in the invention, the water-to-gel ratio is selected to be 0.32, and the extension degree of each group of net slurry under different water reducing agent doses is measured by using a truncated cone circular mold. FIG. 3 shows the net slurry spread and the time taken for the net slurry flow to stop for different water reducing agent dosages. Although the net paste spread continued to increase with increasing water reducer dosage, it was found during the test that bleeding and segregation occurred in the net paste when the water reducer dosage was 2.6% of the cement dosage. On the other hand, with the increase of the dosage of the water reducing agent, the flow time of the net slurry is obviously reduced, however, when the dosage of the water reducing agent reaches 2.4 percent of the cementing material, the flow time tends to be stable, and the flow time of the net slurry is positively correlated with the viscosity of the net slurry, so that the net slurry with short flow time is selected to be beneficial to reducing the viscosity of the self-compacting concrete. Comprehensively considering the effect of the dosage of the water reducing agent on improving the fluidity and viscosity of the net slurry, and selecting the dosage of the water reducing agent to be 2.4 percent of the weight of the cementing material. The dosage of the water reducing agent is calculated according to the formula 18, and the dosages of the water reducing agent corresponding to the film thicknesses (2.1 mm, 2.5mm and 2.9 mm) of the three mortars are 11.88kg, 13.32kg and 14.76kg respectively.
Taking the mortar film with the thickness of 2.1mm as an example, the process of calculating the dosage of the water reducing agent according to the formula 18 is as follows:
Figure 617642DEST_PATH_IMAGE035
。
(9) according to equation 19
Figure 291112DEST_PATH_IMAGE036
And calculating the actual mixing water quantity, wherein the actual mixing water quantity corresponding to the three mortar film thicknesses (2.1 mm, 2.5mm and 2.9 mm) is 133.4kg, 153.0kg and 171.6kg respectively.
Taking the mortar film with the thickness of 2.1mm as an example, the process of calculating the actual mixing water amount according to the formula 19 is
Figure 521236DEST_PATH_IMAGE037
。
(10) The self-compacting concrete mixing ratios under three different mortar film thicknesses determined according to the steps (2) to (9) are shown in table 4, and the three mortar film thicknesses respectively correspond to the self-compacting concretes with three different working performance grades.
TABLE 4
Figure 378334DEST_PATH_IMAGE038
The self-compacting concrete with different mortar film thicknesses is subjected to working performance and compressive strength tests, and the test results are shown in table 5.
TABLE 5
Figure 259571DEST_PATH_IMAGE039
From the results, the C50 self-compacting concrete prepared by the mixing proportion method can not only meet different self-compacting performance grades by changing the thickness of the mortar film, but also better meet the initial design requirement of compressive strength.
It should be noted that the present invention is not limited to the above-mentioned C50 self-compacting concrete preparation examples, and the adjustment modes of changing the concrete performance target, changing the mortar film thickness, changing the aggregate type, changing the aggregate gradation, and changing the mineral admixture type are common variations of the present invention, and are not described in detail herein.
The embodiments of the present invention have been described in detail, but the description is only for the preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made within the scope of the present invention shall fall within the scope of the present invention.

Claims (5)

1. A design method for the mix proportion of self-compacting concrete is characterized by comprising the following steps:
(1) determining the working performance and compressive strength grade requirements of the self-compacting concrete according to engineering requirements;
(2) determining the proportion of coarse and fine aggregates based on an aggregate stacking theory: selecting a plurality of mass proportions of coarse aggregate and fine aggregate, uniformly mixing the coarse aggregate and the fine aggregate according to the selected proportions, and filling the mixed aggregate for three timesA cylindrical measuring container, tamping and compacting the mixed aggregate after each filling, calculating the density and the void ratio of the mixed aggregate, and determining the proportion between the coarse aggregate and the fine aggregate according to the principle of maximum density and minimum void ratior；
(3) Selecting the thickness of the mortar film, calculating the volume ratio of the coarse aggregate,
Figure 164917DEST_PATH_IMAGE001
wherein, in the step (A),V ca is the absolute volume of the coarse aggregate particles;ρ ca is the apparent density of coarse aggregate particles, kg/m 3 ；ρ ′ ca Is the bulk density of coarse aggregate particles, kg/m 3 ；tThe thickness of the mortar film for wrapping the coarse aggregate is mm;k ca,i the mass fraction of the i-th grade coarse aggregate particles obtained by a screening method is expressed by decimal fraction;
Figure 210233DEST_PATH_IMAGE002
is the equivalent particle size of the ith fraction coarse aggregate particles, mm;
(4) calculating the specific dosage of the coarse and fine aggregates according to the optimal proportion of the coarse and fine aggregates and the volume ratio of the coarse and fine aggregates: the single dosage of the coarse aggregate, kg,
Figure 543125DEST_PATH_IMAGE003
wherein, in the step (A),m ca is the total mass of the coarse aggregate particles in kg/m 3 ；ρ ca Apparent density of coarse aggregate particles, kg/m 3 ；V ca Is the volume of the coarse aggregate;
the single dosage of the fine aggregate, kg,
Figure 91918DEST_PATH_IMAGE004
wherein, in the step (A),m fa is the total mass of the fine aggregate particles in kg/m 3 ；
(5) Determining the ratio of the fly ash to replace cement according to the influence rule of the fly ash on the net slurry expansion degree;
(6) calculating the water-cement ratio according to the target value of the concrete compressive strength,
Figure 366911DEST_PATH_IMAGE005
wherein, in the step (A),f cu,0 the preparation value of the compressive strength of the cube is MPa;
Figure 633944DEST_PATH_IMAGE006
the mass ratio of water to the gelled material;f ce the measured compressive strength of the cement is 28d, and is MPa;𝛼the mineral admixture replaces the cement in mass ratio;
Figure 504948DEST_PATH_IMAGE007
is the gel coefficient of the fly ash, when𝛼When the content is less than or equal to 0.3,
Figure 173827DEST_PATH_IMAGE007
take 0.4, an
Figure 619721DEST_PATH_IMAGE008
Wherein, in the step (A),f cu,d the target value of the compressive strength is MPa;𝜎standard deviation of compressive strength, MPa;
(7) determining the concrete dosage of cement, fly ash and water in the clean slurry and the mass of the gel material, namely the mass of the cement and the fly ash according to the water-to-glue ratio and the proportional relation of the components,
Figure 46154DEST_PATH_IMAGE009
(ii) a The mass of the cement is determined by the mass of the cement,
Figure 48745DEST_PATH_IMAGE010
(ii) a The mass of the fly ash,
Figure 759081DEST_PATH_IMAGE011
(ii) a The mass of the water is such that,
Figure 923346DEST_PATH_IMAGE012
wherein, in the process,m cm is the mass of the gel material, namely the mass of the cement and the fly ash, kg;V paste is the net slurry volume;V a volume of air, m 3 ；ρ c Is the apparent density of cement, kg/m 3 ；ρ fl Is the apparent density of the fly ash in kg/m 3 ；ρ w Is the density of water, kg/m 3 ；m c Kg is the mass of cement;m fl the mass of the fly ash is kg;m w kg, mass of water;
(8) determining the dosage of the water reducing agent according to the rule of the influence of the dosage of the water reducing agent on the expansion degree and the flow time of the net slurry, and determining the mass ratio of the water reducing agent to the gel material as𝛽And the metering of the water reducing agent,
Figure 102655DEST_PATH_IMAGE013
wherein, in the step (A),m sp the dosage of the water reducing agent is kg;
(9) determining the actual dosage of mixing water according to the moisture content of the aggregate and the dosage of the water reducing agent,
Figure 836167DEST_PATH_IMAGE014
whereinm wm The actual added water amount, kg, for preparing the self-compacting concrete;𝛾 sp is the solid content in the water reducing agent,%;𝛾 ca water content of the coarse aggregate,%;𝛾 fa water content of fine aggregate,%;
(10) and (3) preparing concrete according to the concrete mixing proportion obtained in the process, and checking whether the working performance and the compressive strength of the concrete meet the requirements or not.
2. The method for designing the mix proportion of the self-compacting concrete according to claim 1, wherein the tamper does not touch the bottom of the container and the top surface of the previous layer of compacted aggregate during the tamping and compacting in the step (2).
3. The method for designing the mix proportion of the self-compacting concrete as recited in claim 1, wherein the fly ash is used to replace a portion of the cement in the step (5), and in order to optimize the amount of the fly ash, the fly ash is used as a reference group, the fly ash is used to replace the cement in different amounts, the slurries with different fly ash replacement rates are prepared, the extension of each group of slurries is measured by using truncated cone circular molds with the diameters of the bottom and the top of 100mm and 70mm, respectively, and the height of 50mm, and then the ratio of the fly ash to the cement is determined according to the principle that the extension of the slurries is the largest.
4. The self-compacting concrete mix proportion design method according to claim 1, wherein the method for determining the water reducing agent amount in the step (8) comprises the following steps: preparing neat paste under the condition of determining the water-gel ratio, determining the expansion degree of the neat paste under different water reducing agent dosages by using a truncated cone circular die, determining the dosage of the water reducing agent by analyzing the change rule of the expansion degree and the flow time of the neat paste and observing the flow state of the neat paste, selecting the dosage of the water reducing agent with larger expansion degree and shorter flow time to prepare self-compacting concrete, and determining the dosage of the water reducing agent according to the mass ratio of the water reducing agent to a cementing material.
5. The method for designing the mix ratio of self-compacting concrete according to claim 1, wherein the adjustment strategy for the step (10) of primarily adapting the mix ratio of concrete without meeting the expected requirement is: the working performance of the self-compacting concrete is controlled by adjusting the dosage of the water reducing agent and the thickness of the mortar film, and the compressive strength of the self-compacting concrete is controlled by adjusting the water-cement ratio and the using amount of the cementing material.
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