CN109626886B - Steel fiber self-compacting concrete mix proportion design method based on mortar rheological property - Google Patents

Steel fiber self-compacting concrete mix proportion design method based on mortar rheological property Download PDF

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CN109626886B
CN109626886B CN201910142217.9A CN201910142217A CN109626886B CN 109626886 B CN109626886 B CN 109626886B CN 201910142217 A CN201910142217 A CN 201910142217A CN 109626886 B CN109626886 B CN 109626886B
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mortar
concrete
steel fiber
self
compacting concrete
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CN109626886A (en
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何小兵
刘亚
彭勇军
韩少华
刘旭东
陈利
申强
李洁
蒋远辉
贾秋炳
姜帆
周超
刘树鑫
沈武福
张旭升
张韬
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Chongqing Jiaotong University
Second Engineering Co Ltd of China Railway 18th Bureau Group Co Ltd
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Second Engineering Co Ltd of China Railway 18th Bureau Group 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
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D11/00—Control of flow ratio
    • 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
    • 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
    • C04B2201/00—Mortars, concrete or artificial stone characterised by specific physical values
    • C04B2201/50—Mortars, concrete or artificial stone characterised by specific physical values for the mechanical strength

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Abstract

The invention discloses a steel fiber self-compacting concrete mix proportion design method based on mortar rheological characteristics, which comprises the steps of establishing a steel fiber concrete expansion SF prediction model; determining a water-cement ratio and a cementing material ratio according to the concrete strength grade requirement, and determining a self-compacting concrete mortar mixing ratio; testing the yield stress and the plastic viscosity of the mortar by adopting a rotating ball method, substituting the actually measured yield stress of the mortar into a steel fiber concrete expansion SF test model to predict the expansion degree of the steel fiber concrete and the like; the design accuracy is higher, is closer to the reality, can well accomplish the optimization and the performance control to the component at the material selection in-process, and overall design step and thinking are clear, easy and simple to handle reasonable, have avoided the blindness among the prior art operation, have reduced because of trial adjustment repeatedly brings time, manpower, material and energy waste, therefore have better maneuverability and practicality.

Description

Steel fiber self-compacting concrete mix proportion design method based on mortar rheological property
Technical Field
The invention relates to the technical field of constructional engineering concrete, in particular to a design method of a steel fiber self-compacting concrete mixing proportion based on the rheological property of mortar.
Background
The steel fiber self-compacting concrete is a composite material, has very high mobility, relies on self gravity to fill the template space under the condition of not vibrating, and the steel fiber self-compacting concrete after hardening can utilize the reinforcing and toughening effects of the steel fiber to improve the strength of the concrete, so the steel fiber self-compacting concrete has excellent workability and toughness. At present, a design method for the mix proportion of the steel fiber self-compacting concrete is not specified clearly, in the prior art, the research on the design method for the mix proportion of the steel fiber self-compacting concrete is relatively less, and the design method for the mix proportion of the steel fiber self-compacting concrete is characterized in that a coarse aggregate method is replaced by directly doping the steel fiber, the steel fiber with the same volume or the same specific surface area on the basis of the self-compacting concrete. The method can meet the steel fiber with certain parameters, but the replacement of the coarse aggregate can change the mechanical property of the concrete.
Disclosure of Invention
In view of the above, the invention aims to provide a steel fiber self-compacting concrete mix proportion design method based on mortar rheological characteristics, which can better complete component optimization and performance control in the material selection process, has clear overall design steps and thought, is simple, convenient and reasonable to operate, avoids blindness in operation in the prior art, reduces waste of time, labor, materials and energy caused by repeated trial adjustment, and has better operability and practicability.
The invention relates to a steel fiber self-compacting concrete mix proportion design method based on mortar rheological characteristics, which comprises the following steps:
a. establishing a steel fiber concrete expansion SF prediction model, wherein the model comprises the following steps:
Figure BDA0001978911020000011
where ξ is less than or equal to 1, which represents the reduction coefficient; a. b and c are constants and represent the fitting and superposing relationship value between the rheology and the working performance; l and D represent the length and diameter of the steel fiber, respectively; a represents an influence factor of steel fiber; tau ismRepresents the yield stress of the mortar; phi represents the volume mixing amount of the steel fiber;
b. determining a water-cement ratio and a cementing material ratio according to the concrete strength grade requirement, and determining a self-compacting concrete mortar mixing ratio;
c. testing the yield stress and the plastic viscosity of the mortar by adopting a rotating ball method, and substituting the actually measured yield stress of the mortar into a steel fiber concrete expansion SF test model to predict the expansion of the steel fiber concrete;
d. comparing the predicted expansion degree and mortar plastic viscosity of the steel fiber concrete with a set threshold range of the expansion degree of the steel fiber self-compacting concrete and the minimum plastic viscosity required by the mortar, if the predicted expansion degree of the steel fiber concrete is within the set threshold range of the expansion degree of the steel fiber self-compacting concrete and the mortar plastic viscosity meets the requirement, entering the next step, if the predicted expansion degree of the steel fiber concrete is out of the set threshold range of the expansion degree of the steel fiber self-compacting concrete, readjusting the mixing ratio to prepare pure mortar, and returning to the step b until the predicted expansion degree of the concrete is within the set threshold range of the expansion degree of the steel fiber self-compacting concrete;
further, in the step a, the value range of xi is 0.9-1;
further, the minimum plastic viscosity of the mortar meets the requirement of the formula:
Figure BDA0001978911020000021
in the formula: rho is the density of the aggregate, g is the gravitational acceleration, delta rho is the density difference between the aggregate and the slurry, and X is the maximum mortar film thickness of the coarse aggregate;
further, in the step b, the mixing ratio of the self-compacting concrete mortar is obtained by the following steps:
b1establishing a concrete expansion SF1 prediction model, wherein the model is as follows:
SF 1＝(l×Tm-m)×τpure mortar+ n, wherein l, m and n are respectively the relation values obtained by arranging the fitting relation between the screened mortar yield stress and the pure mortar yield stress and the fitting relation between the screened mortar yield stress and the concrete expansion degree, TmThickness of mortar film,. tauPure mortarThe value of the yield stress of the pure mortar is obtained;
b2preparing pure mortar according to a certain mixing proportion, testing the yield stress and the plastic viscosity of the pure mortar by adopting a rotating ball method, and substituting the actually measured yield stress of the pure mortar and the drawn thickness of the mortar film (the thickness of the mortar film wrapped on the surface of the pure mortar film is calculated by utilizing the specific surface area of the coarse aggregate) into a concrete expansion prediction model to predict the expansion degree of the concrete;
b3comparing the predicted concrete expansion degree and the plastic viscosity of the pure mortar with the set threshold range of the self-compacting concrete expansion degree and the minimum plastic viscosity required by the pure mortar, if the predicted concrete expansion degree is within the set threshold range of the self-compacting concrete expansion degree and the plastic viscosity of the pure mortar meets the requirements, entering the next step, if the predicted concrete expansion degree is out of the set threshold range of the self-compacting concrete expansion degree, readjusting the mixing ratio to prepare the pure mortar, and returning to the step f until the predicted concrete expansion degree is within the set threshold range of the self-compacting concrete expansion degree;
b4calculating the total mortar consumption V under the unit volume of the coarse aggregate consumption according to the coarse aggregate gradation by utilizing the mixing proportion of the pure mortar with the concrete expansion degree within the set self-compacting concrete expansion degree threshold rangem1Wherein the thickness of the mortar film is Tm≥2.1mm；
b5Converting the total amount of the unit volume coarse aggregate and the mortar into the mixing ratio of the self-compacting concrete;
further, step b4In the method, coarse aggregate gradation and actually measured apparent density rho are utilizedsdAnd measured bulk density ρpdCalculating the stacking space V of the coarse aggregate per unit volume according to the formula 1v1Calculating the surface area A of the coarse aggregate per unit volume according to the formula 2c1：
In the formula 1, the first and second groups,
Figure BDA0001978911020000031
in the formula 2, the first and second groups,
Figure BDA0001978911020000032
in the formula: kiThe aggregate with the i-th grade particle size accounts for the mass fraction of the total aggregate;
Figure BDA0001978911020000033
for simplifying the particle size of the i-th-grade coarse aggregate, the calculation formula is as follows:
Figure BDA0001978911020000034
wherein Di+1、Di-1Indicates the size of the adjacent mesh;
further, step b4In (b), the stacking space V of coarse aggregate per unit volume is utilizedv1Surface area Ac1Calculating the volume V of the mortar required for wrapping the unit absolute volume of the coarse aggregate by the formula 3e1Calculating the total volume V of the mortar required under the unit volume of the coarse aggregate by the formula 4m1：
Formula 3, Ve1＝Tm·Ac1；
Formula 4, Vm1＝Ve1+Vv1；
Further, step b5In the method, the total volume V of the mortar required under the dosage of coarse aggregate per unit volume is utilizedm1Calculating the self-compaction per unit volume by equation 5Volume V of coarse aggregate in concretegCalculating the volume V of mortar in the self-compacting concrete of unit volume by formula 6m：
In the case of the formula 5,
Figure BDA0001978911020000041
in the case of the formula 6,
Figure BDA0001978911020000042
the invention has the beneficial effects that: the steel fiber self-compacting concrete mix proportion design method based on the rheological property of the mortar has higher design accuracy, is closer to reality, can better complete the optimization and the performance control of components in the material selection process, has clear overall design steps and thought and simple and reasonable operation, avoids the blindness in the operation of the prior art, reduces the waste of time, labor, materials and energy caused by repeated trial adjustment, and has better operability and practicability.
Detailed Description
The invention relates to a steel fiber self-compacting concrete mix proportion design method based on mortar rheological characteristics, which comprises the following steps:
a. establishing a steel fiber concrete expansion SF prediction model, wherein the model comprises the following steps:
Figure BDA0001978911020000043
wherein xi is less than or equal to 1, the reduction coefficient is represented, the difference between a theoretical calculated value and an actual value of the steel fiber self-compacting concrete is reflected and is related to the length-diameter ratio of the steel fiber, the larger the length-diameter ratio is, the smaller the reduction coefficient is, and the preferable value range is 0.9-1; a. b and c are constants and represent the relation value of fitting superposition between the rheology and the working performance: optimization can be performed according to a large number of test accumulations, and the change of data does not affect the essence of the invention:
Figure BDA0001978911020000044
τSFM＝A×φ+τm
wherein L, D-represents the length and diameter of the steel fiber; a-represents an influence factor of steel fibers;
Figure BDA0001978911020000051
YSFsteel fiber concrete expansion; tau isSFSCCScreening out the yield shear stress of the steel fiber mortar; tau isSFMSteel fiber mortar yield stress; tau ismMortar yield stress; phi represents the doping amount of the steel fiber; . Tau ismRepresents the yield stress of the mortar; b. determining the water-cement ratio and the cementitious material ratio according to the concrete strength grade requirement, and determining the mixing ratio of the self-compacting concrete mortar:
the self-compacting concrete mortar mixing proportion is obtained by the following steps:
b1building a concrete expansion SF1 calculation model, wherein the model is as follows:
SF 1＝(l×Tm-m)×τpure mortar+ n, wherein l, m and n are respectively the relation values obtained by arranging the fitting relation between the screened mortar yield stress and the pure mortar yield stress and the fitting relation between the screened mortar yield stress and the concrete expansion degree, TmThickness of mortar film,. tauPure mortarThe value of the yield stress of the pure mortar is obtained;
b2preparing pure mortar according to a certain mixing proportion, testing the yield stress and the plastic viscosity of the pure mortar by adopting a rotating ball method, and substituting the actually measured yield stress of the pure mortar and the drawn thickness of the mortar film (the thickness of the mortar film wrapped on the surface of the pure mortar film is calculated by utilizing the specific surface area of the coarse aggregate) into a concrete expansion prediction model to predict the expansion degree of the concrete; designing the pure mortar mixing proportion according to the concrete strength requirement and combining with experience, preparing corresponding pure mortar, testing the yield stress and plastic viscosity of the pure mortar through a rotary rheometer, substituting the yield stress of the pure mortar obtained through testing into a model to predict the concrete expansion degree, (when the maximum settling distance of coarse aggregate is one mortar film thickness, the minimum plastic viscosity required by the pure mortar controls the anti-segregation performance of the self-compacting concrete, namely, the prevention of segregationThreshold value of segregation of freshly mixed concrete mix) the minimum plastic viscosity requirement of the mortar is utilized, and the reduction relationship between the screened mortar and the pure mortar is considered, and the minimum plastic viscosity required by the pure mortar is calculated:
in the formula 1, the first and second groups,
Figure BDA0001978911020000052
in the formula: etaminMinimum plastic viscosity required for pure mortar; beta is the coefficient of plastic viscosity reduction of pure mortar relative to screened mortar, and is recommended to be 0.79; dmaxThe maximum particle size of the coarse aggregate; rhopdIs the apparent density of the coarse aggregate; rhomDensity of pure mortar;
b3comparing the predicted concrete expansion degree and the pure mortar plastic viscosity with the set self-compacting concrete expansion degree threshold range and the pure mortar minimum plastic viscosity, if the predicted concrete expansion degree is within the set self-compacting concrete expansion degree threshold range and the pure mortar plastic viscosity meets the requirements, entering the next step, if the predicted concrete expansion degree is outside the set self-compacting concrete expansion degree threshold range or the pure mortar plastic viscosity is less than the threshold value, readjusting the mixing ratio to prepare the pure mortar, and returning to the step b2Until the predicted concrete expansion degree is within the set threshold range of the self-compacting concrete expansion degree; if the predicted expansion degree meets the specified requirement of the expansion degree of the self-compacting concrete (namely: the threshold value of the expansion degree of the self-compacting concrete) and the plastic viscosity of the pure mortar is greater than the threshold value, carrying out the next mortar total calculation; otherwise, the mixing proportion of the mortar is readjusted to carry out the test of the rheological parameters of the mortar until the requirements are met;
b4calculating the total mortar consumption V by using the pure mortar mixing ratio of the concrete expansion degree within the set self-compacting concrete expansion degree threshold rangem1Wherein the mortar film thickness T is setmNot less than 2.1 mm; the method specifically comprises the following steps:
calculating a stacking gap V of coarse aggregate per unit volume by using coarse aggregate gradation through the formula 1v1Calculating the surface area A of the coarse aggregate per unit volume by the formula 2c1：
In the formula 1, the first and second groups,
Figure BDA0001978911020000061
in the formula 2, the first and second groups,
Figure BDA0001978911020000062
in the formula: kiI mass fraction% of the aggregate with the first-grade particle size in the total aggregate;
Figure BDA0001978911020000063
for simplifying the particle size of the i-th-grade coarse aggregate, the calculation formula is as follows:
Figure BDA0001978911020000064
wherein Di+1、Di-1Indicating adjacent mesh sizes.
Utilizing the specific surface area A of the stacking voids per unit volume of coarse aggregatec1Calculating the volume V of the mortar required for wrapping the unit absolute volume of the coarse aggregate by the formula 3e1Calculating the total volume V of the mortar required under the unit volume of the coarse aggregate by the formula 4m1：
Formula 3, Ve1＝Tm·Ac1，
Formula 4, Vm1＝Ve1+Vv1。
b5Calculating the mixing ratio of various raw materials in the self-compacting concrete with unit volume according to the total consumption of the mortar; the method specifically comprises the following steps: the total volume V of the mortar required by the dosage of coarse aggregate per unit volumem1Calculating the volume V of coarse aggregate in the self-compacting concrete of unit volume by formula 5gCalculating and calculating the volume V of the mortar in the self-compacting concrete of unit volume through a formula 6m：
In the case of the formula 5,
Figure BDA0001978911020000071
and converting the total amount of the single-volume coarse aggregate and the mortar into the mixing ratio of the self-compacting concrete according to the mixing ratio of the pure mortar.
b. Testing the yield stress and the plastic viscosity of the mortar by adopting a rotating ball method, substituting the actually measured yield stress of the mortar into a steel fiber concrete expansion SF1 measurement model to predict the expansion of the steel fiber concrete:
the minimum plastic viscosity formula for a mortar is:
Figure BDA0001978911020000072
in the formula: rho is the density of the aggregate, g/cm3G is the acceleration of gravity, m/S2(ii) a Delta rho is the density difference between aggregate and slurry, g/cm3(ii) a X is the maximum mortar film thickness of the coarse aggregate, cm, and meanwhile, correction is needed according to the plastic viscosity reduction relation between screened mortar and mortar.
Firstly, calculating the thickness of the steel fiber wrapped slurry:
the specific surface area of the steel fiber is different from that of the sand, the specific surface area of the coarser aggregate is smaller, so the steel fiber is considered as the fine aggregate, and the calculation formula is as follows by calculating the over-net slurry thickness of the mortar sand used in the self-compacting concrete:
1. net slurry thickness of sand:
specific surface area A of sand according to gradation of fine aggregatec：
Figure BDA0001978911020000073
In the formula: rhosIs the apparent density of the fine aggregate; kiI mass fraction% of the aggregate with the first-grade particle size in the total aggregate;
Figure BDA0001978911020000074
is the average particle diameter of i-th order particle diameter coarse aggregate, Di+1，Di-1The sizes of two adjacent sieve pores are set;
Figure BDA0001978911020000081
utilize the followingCalculating the thickness T of the net slurry film by using a formula through a specific surface area methodm：
Figure BDA0001978911020000082
In the formula: veM is the net slurry volume used in a unit mortarSandIs the mass of sand used per unit volume of mortar.
2. The specific surface area of the steel fiber is calculated as:
mass m of individual fibresiComprises the following steps: m isi＝π·(R/2)2·l·ρ
Surface area S of individual fibersiComprises the following steps: si＝π·R·l+2×π×(R/2)2
Specific surface area of fiber:
Figure BDA0001978911020000083
in the formula: r is the diameter of the fiber, l is the length of the fiber, and ρ is the density of the fiber.
3. When the volume of the steel fiber in the steel fiber mortar is increased by a percent, the net slurry increase amount is as follows:
mincrement of net pulp＝mSF×ASF×Tm×ρPulp cleaner
In the formula: m isSFIs the mass of the steel fiber with the volume fraction of a%Pulp cleanerIs the net slurry density.
Secondly, regarding the water-gel ratio and the cementing material ratio
The water-gel ratio and the dosage of the cementing material are calculated according to the requirements of the application technical specification of the self-compacting concrete.
1) Preparing corresponding concrete strength according to engineering requirements, and determining a water-cement ratio formula of the concrete as follows:
Figure BDA0001978911020000084
in the formula: m isb-mass of cementitious material per unit of concrete; m isw-is the amount of cementitious material in a unit of concrete;fce-is cement 28d compressive strength (MPa); gamma-is the gelatinization coefficient of the mineral admixture; the fly ash (beta is less than or equal to 0.3) can be 0.4, and the mineral powder (beta is less than or equal to 0.4) can be 0.9.
2) The mass of the cementing material in per cubic meter of self-compacting concrete is as follows:
Figure BDA0001978911020000091
in the formula: va is the volume of air introduced into each cubic of concrete, and for non-air-entraining type self-compacting concrete, Va can be 10-20L. RhowDensity of mixing water per cubic concrete, typically 1000kg/m3。
3) Apparent density of gelled material ρbThe cement admixture is determined according to the relative contents and the respective apparent densities of the mineral admixture and the cement, and the calculation formula is as follows:
Figure BDA0001978911020000092
in the formula: rhom-is the apparent density of the mineral admixture, (kg/m 3); rhoe-is the apparent density of the cement, (kg/m 3); beta-the mass fraction of the mineral admixture in each cubic concrete in the cementitious material (%).
Thirdly, determining yield stress tau of mortarmAnd plastic viscosity etam
Under the condition that the water-cement ratio and the cementing material are determined, the volume fraction of the sand and the mixing amount of the water reducing agent can be adjusted, the volume fraction of the sand is between 0.42 and 0.46 according to the reference standard value, the mixing amount of the water reducing agent is determined according to the yield stress and the plastic viscosity of the prepared mortar, namely the yield stress is as small as possible, the yield stress of the base concrete and the steel fiber self-compacting concrete is also minimum, but the stability of the mortar must be met, and the minimum plastic viscosity of the mortar must meet the following requirements:
Figure BDA0001978911020000093
in the formula: rho is the density of the aggregate, g/cm3, g is the acceleration of gravity, m/S2(ii) a Delta rho is the density difference between aggregate and slurry, g/cm 3; and X is the maximum mortar film thickness of the coarse aggregate in cm.
Meanwhile, the reduction relation between the plastic viscosity of the screened mortar and the plastic viscosity of the pure mortar needs to be considered for correction.
Fourthly, determining the mortar film thickness of the coarse aggregate and a constant c.
According to the self-compacting concrete mixing ratio based on mortar rheology, the value based on a limited data sample is recommended to be 2.5mm-2.9mm, and c is 760. The data relation generated by a large number of data samples is changed, and the essence of the method is not influenced.
Fifthly, determining the influence coefficient A of the steel fiber, the net pulp thickness wrapped by the steel fiber and the length-diameter ratio of the steel fiber
Figure BDA0001978911020000101
And after determining the yield stress of the mortar, determining the thickness of the steel fiber wrapped net slurry according to the relation between the yield stress of the steel fiber mortar and the yield stress of the mortar and the thickness of the sand wrapped net slurry. And determining the influence coefficient A of the steel fibers through a steel fiber mortar rheological test. The aspect ratio of the steel fibers can be measured by the morphology of the steel fibers.
Figure BDA0001978911020000102
Sixthly, relating to constants a and b
In the formula, constants a and b are relationship values of fitting superposition between rheology and working performance, wherein a is-0.011, and b is 0.066, and a large number of data samples bring about data optimization without influencing the essence of the invention.
c. Comparing the predicted expansion degree and mortar plastic viscosity of the steel fiber concrete with a set threshold range of the expansion degree of the steel fiber self-compacting concrete and the minimum plastic viscosity required by the mortar, if the predicted expansion degree of the steel fiber concrete is within the set threshold range of the expansion degree of the steel fiber self-compacting concrete and the mortar plastic viscosity meets the requirement, entering the next step, if the predicted expansion degree of the steel fiber concrete is out of the set threshold range of the expansion degree of the steel fiber self-compacting concrete, readjusting the mixing ratio to prepare pure mortar, and returning to the step b until the predicted expansion degree of the concrete is within the set threshold range of the expansion degree of the steel fiber self-compacting concrete; the steel fiber self-compacting concrete can be regarded as being designed by carrying out secondary mixing proportion on the self-compacting concrete and steel fiber neat paste. For the determination of the mixing ratio of the self-compacting concrete, a mixing ratio design method in the prior art can be adopted, preferably the mixing ratio design method of the self-compacting concrete described in the invention is adopted, and for the steel fiber net slurry, when only the net slurry and the steel fiber are considered, the steel fiber is easy to agglomerate, so the steel fiber mortar is considered. When the mix proportion of the steel fiber mortar is designed, the volume fraction of the sand and the water-cement ratio are kept unchanged. Due to the addition of the steel fibers, the dosage of the cementing material is adjusted, and the rheological parameters of the steel fiber mortar are measured by a rotary rheometer.
Calculation example:
taking the design of the mixing proportion of the C50 steel fiber self-compacting concrete as an example, the water-cement ratio is determined to be 0.28, the cementing material is ordinary portland cement and fly ash, and the fly ash accounts for 30% of the using amount of the cementing material.
The mixing proportion of the mortar is designed as follows:
the lower limit of plastic viscosity is calculated according to the minimum plastic viscosity requirement of the mortar described in claim 3 (.
TABLE 1 mortar mix design and rheology parameters
Figure BDA0001978911020000111
The base concrete comprises the following components in percentage by weight:
the prediction extension degree is calculated according to (self-compacting concrete mix proportion design method based on the rheological property of mortar)
Figure BDA0001978911020000112
TABLE 2 base concrete mix design
Figure BDA0001978911020000113
The expansion degree meets the requirement of self-compacting concrete. The morphological parameters of the steel fiber are as follows:
TABLE 3 Steel fiber parameters
Figure BDA0001978911020000114
TABLE 4 Steel fiber Unit mass to increase the amount of neat paste
Figure BDA0001978911020000115
Designing the steel fiber concrete mixing proportion:
Figure BDA0001978911020000116
note that: the content of the steel fiber is 0.5 percent of the volume of the matrix concrete as shown in the test number SF-0.5 percent
The results of the expansion prediction are shown in table 5:
YSF＝0.99×(-75.69×φ+753)
TABLE 5 theoretical and actual extension of steel fiber concrete
Figure BDA0001978911020000121
Error (theoretical value-measured value)/theoretical value x 100
Finally, the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all of them should be covered in the claims of the present invention.

Claims (7)

1. A steel fiber self-compacting concrete mix proportion design method based on mortar rheological characteristics is characterized by comprising the following steps: the method comprises the following steps:
a. establishing a steel fiber concrete expansion SF prediction model, wherein the model comprises the following steps:
Figure FDA0001978911010000011
where ξ is less than or equal to 1, which represents the reduction coefficient; a. b and c are constants and represent the fitting and superposing relationship value between the rheology and the working performance; l and D represent the length and diameter of the steel fiber, respectively; a represents an influence factor of steel fiber; tau ismRepresents the yield stress of the mortar; phi represents the volume mixing amount of the steel fiber;
b. determining a water-cement ratio and a cementing material ratio according to the concrete strength grade requirement, and determining a self-compacting concrete mortar mixing ratio;
c. testing the yield stress and the plastic viscosity of the mortar by adopting a rotating ball method, and substituting the actually measured yield stress of the mortar into a steel fiber concrete expansion SF test model to predict the expansion of the steel fiber concrete;
d. and (c) comparing the predicted expansion degree and mortar plastic viscosity of the steel fiber concrete with the set threshold range of the expansion degree of the steel fiber self-compacting concrete and the minimum plastic viscosity required by the mortar, if the predicted expansion degree of the steel fiber concrete is within the set threshold range of the expansion degree of the steel fiber self-compacting concrete and the mortar plastic viscosity meets the requirement, entering the next step, if the predicted expansion degree of the steel fiber concrete is out of the set threshold range of the expansion degree of the steel fiber self-compacting concrete, readjusting the mixing ratio to prepare pure mortar, and returning to the step b until the predicted expansion degree of the concrete is within the set threshold range of the expansion degree of the steel fiber self-compacting concrete.
2. The mortar rheology characteristic-based steel fiber self-compacting concrete mix proportion design method according to claim 1, characterized in that: in the step a, the value range of xi is 0.9-1.
3. The mortar rheology characteristic-based steel fiber self-compacting concrete mix proportion design method according to claim 1, characterized in that: the minimum value of the plastic viscosity of the mortar meets the requirement of a formula:
Figure FDA0001978911010000012
in the formula: rho is the density of the aggregate, g is the gravitational acceleration, delta rho is the density difference between the aggregate and the slurry, and X is the maximum mortar film thickness of the coarse aggregate.
4. The mortar rheology characteristic-based steel fiber self-compacting concrete mix proportion design method according to claim 1, characterized in that: in the step b, the mixing proportion of the self-compacting concrete mortar is obtained by the following steps:
b1establishing a concrete expansion SF1 prediction model, wherein the model is as follows:
SF 1＝(l×Tm-m)×τpure mortar+ n, wherein l, m and n are respectively the relation values obtained by arranging the fitting relation between the screened mortar yield stress and the pure mortar yield stress and the fitting relation between the screened mortar yield stress and the concrete expansion degree, TmThickness of mortar film,. tauPure mortarThe value of the yield stress of the pure mortar is obtained;
b2preparing pure mortar according to a certain mixing proportion, testing the yield stress and the plastic viscosity of the pure mortar by adopting a rotating ball method, and substituting the actually measured yield stress of the pure mortar and the thickness of a planned mortar film into a concrete expansion prediction model to predict the expansion degree of the concrete;
b3comparing the predicted concrete spread and the plastic viscosity of the pure mortar with a set threshold range of self-compacting concrete spread and minimum plastic viscosity required for the pure mortar, e.g.If the predicted concrete expansion degree is within the set self-compacting concrete expansion degree threshold range and the plastic viscosity of the pure mortar meets the requirement, the next step is carried out, if the predicted concrete expansion degree is out of the set self-compacting concrete expansion degree threshold range, the mixing proportion is adjusted again to prepare the pure mortar, and the step b is returned2Until the predicted concrete expansion degree is within the set threshold range of the self-compacting concrete expansion degree;
b4calculating the total mortar consumption V under the unit volume of the coarse aggregate consumption according to the coarse aggregate gradation by utilizing the mixing proportion of the pure mortar with the concrete expansion degree within the set self-compacting concrete expansion degree threshold rangem1Wherein the thickness of the mortar film is Tm≥2.1mm；
b5Converting the total amount of the unit volume coarse aggregate and the mortar into the mixing ratio of the self-compacting concrete.
5. The mortar rheology characteristic-based steel fiber self-compacting concrete mix proportion design method according to claim 4, characterized in that: step b4In the method, coarse aggregate gradation and actually measured apparent density rho are utilizedsdAnd measured bulk density ρpdCalculating the stacking space V of the coarse aggregate per unit volume according to the formula 1v1Calculating the surface area A of the coarse aggregate per unit volume according to the formula 2c1：
In the formula 1, the first and second groups,
Figure FDA0001978911010000031
in the formula 2, the first and second groups,
Figure FDA0001978911010000032
in the formula: kiThe aggregate with the i-th grade particle size accounts for the mass fraction of the total aggregate;
Figure FDA0001978911010000033
for simplifying the particle size of the i-th-grade coarse aggregate, the calculation formula is as follows:
Figure FDA0001978911010000034
wherein Di+1、Di-1Indicating adjacent mesh sizes.
6. The mortar rheology characteristic-based steel fiber self-compacting concrete mix proportion design method according to claim 5, characterized in that: step b4In (b), the stacking space V of coarse aggregate per unit volume is utilizedv1Surface area Ac1Calculating the volume V of the mortar required for wrapping the unit absolute volume of the coarse aggregate by the formula 3e1Calculating the total volume V of the mortar required under the unit volume of the coarse aggregate by the formula 4m1：
Formula 3, Ve1＝Tm·Ac1；
Formula 4, Vm1＝Ve1+Vv1。
7. The mortar rheology characteristic-based steel fiber self-compacting concrete mix proportion design method according to claim 5, characterized in that: step b5In the method, the total volume V of the mortar required under the dosage of coarse aggregate per unit volume is utilizedm1Calculating the volume V of coarse aggregate in the self-compacting concrete of unit volume by formula 5gCalculating the volume V of mortar in the self-compacting concrete of unit volume by formula 6m：
In the case of the formula 5,
Figure FDA0001978911010000035
in the case of the formula 6,
Figure FDA0001978911010000036
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