CN116908422B - Recycled concrete shrinkage prediction method based on relative humidity - Google Patents
Recycled concrete shrinkage prediction method based on relative humidity Download PDFInfo
- Publication number
- CN116908422B CN116908422B CN202310789018.3A CN202310789018A CN116908422B CN 116908422 B CN116908422 B CN 116908422B CN 202310789018 A CN202310789018 A CN 202310789018A CN 116908422 B CN116908422 B CN 116908422B
- Authority
- CN
- China
- Prior art keywords
- recycled
- concrete
- aggregate
- recycled concrete
- water
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
- 238000000034 method Methods 0.000 title claims abstract description 78
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 94
- 239000004568 cement Substances 0.000 claims abstract description 67
- 238000009792 diffusion process Methods 0.000 claims abstract description 33
- 230000000694 effects Effects 0.000 claims abstract description 31
- 238000002156 mixing Methods 0.000 claims abstract description 26
- 238000010521 absorption reaction Methods 0.000 claims abstract description 24
- 239000011148 porous material Substances 0.000 claims abstract description 14
- 238000004891 communication Methods 0.000 claims abstract description 12
- 238000006703 hydration reaction Methods 0.000 claims abstract description 9
- 238000004364 calculation method Methods 0.000 claims description 34
- 238000012360 testing method Methods 0.000 claims description 26
- 239000011159 matrix material Substances 0.000 claims description 25
- 238000001035 drying Methods 0.000 claims description 18
- 238000006467 substitution reaction Methods 0.000 claims description 17
- 238000007791 dehumidification Methods 0.000 claims description 9
- 229920006395 saturated elastomer Polymers 0.000 claims description 9
- 230000001174 ascending effect Effects 0.000 claims description 8
- 230000008569 process Effects 0.000 claims description 7
- 238000012937 correction Methods 0.000 claims description 6
- 230000000704 physical effect Effects 0.000 claims description 5
- 238000003795 desorption Methods 0.000 claims description 3
- 230000036571 hydration Effects 0.000 claims description 3
- 239000007788 liquid Substances 0.000 claims description 3
- 239000000463 material Substances 0.000 claims description 3
- 238000011002 quantification Methods 0.000 claims description 3
- 230000007246 mechanism Effects 0.000 abstract description 4
- 238000012423 maintenance Methods 0.000 abstract description 3
- 238000005259 measurement Methods 0.000 description 8
- 238000012821 model calculation Methods 0.000 description 8
- 238000001816 cooling Methods 0.000 description 4
- 238000011161 development Methods 0.000 description 4
- 101100001674 Emericella variicolor andI gene Proteins 0.000 description 2
- 230000007774 longterm Effects 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 239000004570 mortar (masonry) Substances 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- 230000002411 adverse Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 229920001971 elastomer Polymers 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000005499 meniscus Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 239000013589 supplement Substances 0.000 description 1
- 230000001502 supplementing effect Effects 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 238000012795 verification Methods 0.000 description 1
Abstract
The invention provides a recycled concrete shrinkage prediction method based on relative humidity, which belongs to the technical field of concrete and comprises the steps of determining basic parameters of recycled aggregate and recycled concrete, calculating equivalent water-cement ratio of the recycled concrete, calculating hydration reaction, calculating humidity diffusion, calculating water release of the recycled aggregate, correcting relative humidity, calculating bulk modulus under standard curing conditions, quantifying distribution of the bulk modulus along with depth, calculating one-dimensional free shrinkage, calculating deformation coordination and the like. The model establishes a recycled concrete shrinkage prediction method based on a shrinkage mechanism, considers the influence of the recycled aggregate content, the water absorption rate, the water content and a mixing method on the equivalent water-cement ratio of the recycled concrete, and simultaneously considers the internal maintenance effect and the 'pore communication' effect of the recycled aggregate. The method can accurately predict the shrinkage distribution condition of the recycled concrete in a closed environment or a dry environment.
Description
Technical Field
The invention belongs to the technical field of concrete, and particularly relates to a relative humidity-based regenerated concrete shrinkage prediction method.
Background
The waste concrete is crushed and screened to prepare recycled aggregate, and the recycled aggregate can replace natural aggregate to mix concrete, which is called recycled concrete. Because of the existence of a large amount of residual cement paste on the surface of the recycled aggregate, the mechanical properties of the recycled concrete are changed, for example, the recycled aggregate increases the drying shrinkage of the concrete by 20-160%, reduces the autogenous shrinkage of the concrete by 20-70%, and the shrinkage of the concrete member with simultaneous drying shrinkage and autogenous shrinkage is more complex in cross section distribution. In order to further clarify the long-term deformation and shrinkage cracking of the recycled concrete structural member, it is highly desirable to propose a shrinkage prediction method of recycled concrete.
Essentially, the main driving force for shrinkage deformation of concrete is the decrease in relative humidity inside it. In particular, autogenous shrinkage and drying shrinkage may be due to loss of relative humidity from self-drying or exposure to a dry environment. And recycled aggregate has significant impact on concrete: (1) The internal curing effect of the recycled aggregate reduces the relative humidity loss in the concrete capillary, specifically, the residual mortar of the recycled aggregate can absorb a large amount of water in the concrete stirring process and gradually release the water in the concrete curing process to supplement the water loss in the concrete capillary; (2) The high porosity, large pore size and multiple cracks of the residual mortar accelerate the loss of moisture to the dry environment, known as the "pore communication" effect; (3) The water content of recycled aggregate affects the microstructure of the Interfacial Transition Zone (ITZ) in recycled concrete, for example, recycled aggregate in a dry state absorbs water and reduces the effective water-cement ratio of the concrete, contributing to denser microstructure of the ITZ, and conversely, pre-saturated recycled aggregate can have an adverse effect. Therefore, there is a need to build a relative humidity based model for predicting shrinkage of recycled concrete.
Compared with the traditional natural concrete prediction model, the model considers the influence of recycled aggregate on the cement ratio of concrete, the internal curing effect of the recycled aggregate, the pore communication effect and the like. The recycled concrete shrinkage prediction model provides a calculation basis for the long-term performance of the recycled concrete member, and further promotes academic research and engineering application of the recycled concrete.
Disclosure of Invention
In view of the above, in order to solve the technical problems mentioned in the background art, the present invention provides a method for predicting shrinkage of recycled concrete based on relative humidity, namely, firstly, a model for predicting relative humidity of recycled concrete is provided, and based on the relationship between relative humidity and shrinkage deformation, a model for predicting shrinkage deformation of recycled concrete is further provided. The physical properties of the recycled aggregate are different, so that the influence of the recycled aggregate content, the water absorption, the water content and the mixing method on the equivalent water-cement ratio of the recycled concrete is considered in the model, and the residual cement paste on the surface of the recycled aggregate has the characteristics of high porosity, large aperture and multiple cracks, so that the internal maintenance effect and the 'pore communication' effect of the recycled aggregate are respectively considered in the relative humidity prediction model. Based on relative humidity, a Kelvin-Laplace formula is adopted to calculate one-dimensional free shrinkage of different parts of the recycled concrete, and finally deformation coordination calculation is carried out on the free shrinkage prediction result to obtain a real shrinkage distribution result of the recycled concrete.
In order to achieve the above purpose, the present invention adopts the following technical scheme: the regenerated concrete shrinkage prediction method based on relative humidity specifically comprises the following steps:
(1) Basic performance parameters of the recycled aggregate and the recycled concrete are determined: the water absorption rate, the water content and the matrix water-cement ratio of the regenerated coarse/fine aggregate; density, mixing ratio, mixing method, elastic modulus and poisson ratio of each component of the recycled concrete; boundary conditions and ambient temperature and humidity;
(2) Calculating the equivalent water-cement ratio of the recycled concrete: calculating the equivalent water-cement ratio of the recycled concrete according to the physical properties of the recycled aggregate and the recycled concrete mixing mode;
(3) And (3) performing hydration reaction calculation in the recycled concrete: bring the equivalent water-cement ratio into -Najjar humidity model calculation;
(4) And (3) performing humidity diffusion calculation in the recycled concrete: determining the saturation diffusion coefficient of the recycled concrete by considering the equivalent water-cement ratio and the pore communication effect, and based on the boundary conditions of different humidities -Najjar humidity model calculation;
(5) And (3) performing regenerated aggregate release water calculation: adopting an isothermal dehumidification line of the recycled aggregate to consider an internal curing effect, determining the saturation of the recycled aggregate according to the humidity increment, and further calculating the water release amount and the humidity increment of the recycled aggregate;
(6) Relative humidity correction was performed: correcting the saw-tooth trend which possibly appears in the calculation result, so that the relative humidity does not have an ascending trend;
(7) Bulk modulus of recycled concrete under standard curing conditions: calculating according to the elastic modulus and poisson ratio of the recycled concrete under standard curing conditions to obtain the mass modulus of the recycled concrete;
(8) Quantification of the distribution of the bulk modulus of recycled concrete with depth: the influence of the drying environment on the elastic modulus of the recycled concrete needs to be tested, and when no clear test result is found, the influence depth of the drying environment on the elastic modulus of the recycled concrete is assumed to be 10cm, and the influence factors are linearly distributed along the depth direction;
(9) Calculating the one-dimensional free shrinkage of the recycled concrete: obtaining the volume shrinkage of each layer of the recycled concrete according to the volume modulus and the relative humidity of the recycled concrete, and further obtaining one-dimensional free shrinkage;
(10) And carrying out deformation coordination calculation on the one-dimensional free shrinkage prediction result of each layer to obtain the real shrinkage distribution condition of the recycled concrete.
Further, in the step (2), the influence of the recycled aggregate content, the water absorption, the water content and the mixing method on the equivalent water-cement ratio of the recycled concrete is considered, and the formula is adopted
Calculating;
Wherein w/c equ is the equivalent water-cement ratio of the recycled concrete, and M w and M c are the mass of water and cementing material in the mixing ratio respectively; m CRA and M FRA are the mass of recycled coarse aggregate and recycled fine aggregate, respectively; k CRA and k FRA are the water absorption correction coefficients of the recycled coarse aggregate and the recycled fine aggregate respectively, and are related to the coverage rate of residual cement paste, and generally 0.85-1.0; m CRA and m FRA are respectively the initial water contents of the recycled coarse aggregate and the recycled fine aggregate, and the values are multiples of the water content or the water absorption according to the configuration method; w CRA and w FRA are the water absorption rates of the recycled coarse aggregate and the recycled fine aggregate, respectively.
Further, in the step (4), considering the influence of the pore communication effect of the recycled concrete on the diffusion of the humidity inside the concrete, the method specifically comprises the following steps:
(1) The humidity diffusion calculation of natural concrete is as follows Najjar nonlinear diffusion modelCalculating;
Where h is the relative humidity, h s is the relative humidity affected by cement hydration, t is the age of the concrete, k is the inverse slope of the desorption isotherm, c p is the water diffusivity, related to the saturation diffusion coefficient c 1, c 1 for natural concrete is recorded as According toCalculating;
(2) Based on the equivalent water-cement ratio w/c equ of the recycled concrete and the substitution rate of the recycled coarse/fine aggregate, the saturated diffusion coefficient of the recycled concrete is calculated according to the formula
Calculating;
In the method, in the process of the invention, And/>Is the saturation diffusion coefficient of the recycled coarse aggregate and the natural concrete with the same cement ratio, r RA1 is the larger value of the substitution rate of the recycled coarse aggregate and the substitution rate of the recycled fine aggregate, and r RA2 is the smaller value of the substitution rate of the recycled coarse aggregate and the substitution rate of the recycled fine aggregate.
Further, in the step (5), the influence of the internal curing effect of the recycled concrete on the internal humidity of the concrete is considered, and the method specifically comprises the following steps:
(1) Determining isothermal dehumidification line of recycled aggregate according to matrix water-cement ratio of recycled aggregate, wherein the expression form is
Wherein S is the saturation of the recycled aggregate; m 1、m2 and h * are parameters related to the water-cement ratio of the recycled aggregate matrix;
(2) Quantifying the internal curing effect of recycled aggregate: assuming that the initial water storage amount of the recycled aggregate is close to the saturated water content, the water release amount is according to the formula
Calculating;
Wherein m 1-CRA、m2-CRA and Is a parameter related to the water-cement ratio of the recycled coarse aggregate matrix, m 1-FRA、m2-FRA andIs a parameter related to the water-cement ratio of the recycled fine aggregate matrix.
Further, in the step (6), the saw-tooth trend possibly occurring in the relative humidity calculation result is corrected according to the formula dh < 0, so that the relative humidity does not have an ascending trend.
Further, the recycled concrete mass modulus in step (7) is in accordance withCalculating;
Where K is the mass modulus of the recycled concrete, E c is the elastic modulus of the recycled concrete, and v is the Poisson's ratio of the recycled concrete.
Further, the influence of the dry environment on the elastic modulus of the recycled concrete in the step (8) is determined by a test, and the influence factor of the dry environment on the elastic modulus of the recycled concrete is assumed to be according to the following condition without clear test resultsCalculating;
Wherein, beta E is the influence factor of the dry environment on the elastic modulus of the recycled concrete, beta E0 is the influence factor of the dry environment on the elastic modulus of the recycled concrete at the exposed surface, the influence factor is related to the concrete curing time and the internal curing effect of the recycled aggregate, 0.6-1.0 is taken, and x is the distance from the calculated point to the exposed surface of the recycled concrete.
Further, the recycled concrete in the step (9) is freely shrunk in one dimension according to the formula
Calculating;
Wherein epsilon 1 is the one-dimensional free shrinkage of the recycled concrete; ρ l is the liquid water density; r is a universal gas constant; t represents absolute temperature, M is the molar mass of water, and K s is the bulk modulus of natural aggregate.
Further, in the step (10), deformation coordination calculation is performed on the one-dimensional free shrinkage prediction result of each layer to obtain the actual shrinkage distribution condition of the recycled concrete, and the method specifically comprises the following steps:
(1) Carrying out simplified solution on a recycled concrete test piece with the thickness smaller than 200mm according to a formula of r e＝ri =0 (10), wherein r e and r i are respectively an external load matrix and a concrete internal force matrix;
(2) And calculating the thick recycled concrete test piece with complicated conditions by adopting a layered cooling method by using ABAQUS finite element software.
The invention provides a recycled concrete shrinkage prediction method based on relative humidity, wherein the influence of the recycled aggregate content, the water absorption rate, the water content and a mixing method on the equivalent water-cement ratio of the recycled concrete is considered in a model, and the internal maintenance effect and the 'pore communication' effect of the recycled aggregate are also considered. On the basis of relative humidity, calculating the free shrinkage of different parts of the recycled concrete, and finally, performing deformation coordination calculation on the free shrinkage prediction result to obtain the real shrinkage distribution condition. In combination, the prediction method has the following advantages:
(1) The shrinkage prediction method of the recycled concrete is established from the shrinkage mechanism. The shrinkage mechanism of concrete is: due to self-drying or environmental drying in the concrete, the moisture in the capillary pores is reduced, i.e. the relative humidity is reduced, the radius of the capillary meniscus is reduced, the capillary tension is reduced, negative pressure is generated, and the macroscopic manifestation is that the volume of the concrete is reduced. Unlike the past empirical model, the method for predicting shrinkage of the recycled concrete is developed on the basis of a shrinkage mechanism from the relative humidity.
(2) The influence of the physical properties of the recycled aggregate and the mixing method on the equivalent water-cement ratio of the recycled concrete is fully considered. The waste concrete has wide sources and large quality difference, the produced recycled aggregate is different, and the mixing modes such as an air dry method, an additional water method, a saturation and dry method and the like have different influences on the initial water content of the recycled aggregate.
(3) The 'pore communication' effect of the recycled aggregate is considered, and a recycled concrete humidity transfer model is established. According to the equivalent water cement ratio of the recycled concrete, the moisture transmission coefficient of the natural concrete can be calculated, and the method for calculating the humidity diffusion coefficient of the recycled concrete is further provided by combining the substitution rate of the recycled coarse/fine aggregate, wherein the coupling influence of the substitution rate of the recycled coarse/fine aggregate on the humidity diffusion coefficient is considered.
(4) And the internal curing effect of the recycled aggregate is considered, and a recycled concrete water supplementing model is established. The isothermal dehumidification line of the recycled aggregate is introduced to describe the relation between the relative humidity and the saturation of the recycled aggregate, and the water release amount of the recycled aggregate can be calculated in real time based on the increment of the relative humidity of the concrete on the assumption that the recycled concrete is in a saturated state initially; since the release of water from recycled aggregate may lead to an increase in relative humidity, recycled aggregate again absorbs water, for which a simplified calculation was performed.
(5) Considering the influence of the drying environment on the elastic modulus of the recycled concrete, the influence depth and the distribution form of the drying environment on the elastic modulus of the recycled concrete can be assumed when no clear test result exists, the volume modulus of each layer of the recycled concrete is calculated by adopting a layering method, one-dimensional free shrinkage is calculated, and finally deformation coordination calculation is carried out, so that the real shrinkage distribution situation is obtained. The method can accurately predict the shrinkage distribution condition of the recycled concrete in a closed environment or a dry environment.
Drawings
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present application more apparent, the technical solutions in the embodiments of the present application will be clearly and completely described in the following in conjunction with the embodiments of the present application, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
In the drawings:
FIG. 1 is a computational flow chart of a method for predicting shrinkage of recycled concrete based on relative humidity according to the present invention;
FIG. 2 is a design drawing of a test verification test piece for a relative humidity-based recycled concrete shrinkage prediction method according to the present invention; wherein, the rubber plug is 1-, the PVC hose is 2-, the relative humidity measuring point is 3-, the strain gauge is 4-contracted, the exposed surface is 5-and the sealing surface is 6-;
FIG. 3 is a graph showing the comparison between the relative humidity distribution prediction result and the experimental and actual measurement result of the recycled coarse aggregate concrete by the relative humidity-based recycled concrete shrinkage prediction method;
FIG. 4 is a graph showing the comparison between the shrinkage distribution prediction result of recycled coarse aggregate concrete and the experimental and actual measurement result of the relative humidity-based recycled concrete shrinkage prediction method;
FIG. 5 is a graph showing the comparison between the relative humidity distribution prediction result and the experimental and actual measurement result of the recycled fine aggregate concrete by the relative humidity-based recycled concrete shrinkage prediction method;
Fig. 6 is a graph showing the comparison between the shrinkage distribution prediction result and the experimental and actual measurement result of the recycled fine aggregate concrete according to the relative humidity-based recycled concrete shrinkage prediction method.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. It should be noted that, in the case of no conflict, embodiments of the present invention and features of the embodiments may be combined with each other, and the described embodiments are only some embodiments of the present invention, not all embodiments.
Referring to fig. 1-6, the embodiment is described, which is a method for predicting shrinkage of recycled concrete based on relative humidity, specifically comprising the steps of:
(1) Basic performance parameters of the recycled aggregate and the recycled concrete are determined: the water absorption rate, the water content and the matrix water-cement ratio of the regenerated coarse/fine aggregate; density, mixing ratio, mixing method, elastic modulus and poisson ratio of each component of the recycled concrete; boundary conditions and ambient temperature and humidity;
(2) Calculating the equivalent water-cement ratio of the recycled concrete: calculating the equivalent water-cement ratio of the recycled concrete according to the physical properties of the recycled aggregate and the recycled concrete mixing mode;
(3) And (3) performing hydration reaction calculation in the recycled concrete: bring the equivalent water-cement ratio into -Najjar humidity model calculation;
(4) And (3) performing humidity diffusion calculation in the recycled concrete: determining the saturation diffusion coefficient of the recycled concrete by considering the equivalent water-cement ratio and the pore communication effect, and based on the boundary conditions of different humidities -Najjar humidity model calculation;
(5) And (3) performing regenerated aggregate release water calculation: adopting an isothermal dehumidification line of the recycled aggregate to consider an internal curing effect, determining the saturation of the recycled aggregate according to the humidity increment, and further calculating the water release amount and the humidity increment of the recycled aggregate;
(6) Relative humidity correction was performed: correcting the saw-tooth trend which possibly appears in the calculation result, so that the relative humidity does not have an ascending trend;
(7) Bulk modulus of recycled concrete under standard curing conditions: calculating according to the elastic modulus and poisson ratio of the recycled concrete under standard curing conditions to obtain the mass modulus of the recycled concrete;
(8) Quantification of the distribution of the bulk modulus of recycled concrete with depth: the influence of the drying environment on the elastic modulus of the recycled concrete needs to be tested, and when no clear test result is found, the influence depth of the drying environment on the elastic modulus of the recycled concrete is assumed to be 10cm, and the influence factors are linearly distributed along the depth direction;
(9) Calculating the one-dimensional free shrinkage of the recycled concrete: obtaining the volume shrinkage of each layer of the recycled concrete according to the volume modulus and the relative humidity of the recycled concrete, and further obtaining one-dimensional free shrinkage;
(10) And carrying out deformation coordination calculation on the one-dimensional free shrinkage prediction result of each layer to obtain the real shrinkage distribution condition of the recycled concrete.
In the step (2), the influence of the content of the recycled aggregate, the water absorption, the water content and the mixing method on the equivalent water-cement ratio of the recycled concrete is considered, and the formula is adopted
Calculating;
Wherein w/c equ is the equivalent water-cement ratio of the recycled concrete, and M w and M c are the mass of water and cementing material in the mixing ratio respectively; m CRA and M FRA are the mass of recycled coarse aggregate and recycled fine aggregate, respectively; k CRA and k FRA are the water absorption correction coefficients of the recycled coarse aggregate and the recycled fine aggregate respectively, and are related to the coverage rate of residual cement paste, and generally 0.85-1.0; m CRA and m FRA are respectively the initial water contents of the recycled coarse aggregate and the recycled fine aggregate, and the values are multiples of the water content or the water absorption according to the configuration method; w CRA and w FRA are the water absorption rates of the recycled coarse aggregate and the recycled fine aggregate, respectively.
In the step (4), the influence of the pore communication effect of the recycled concrete on the diffusion of the humidity in the concrete is considered, and the method specifically comprises the following steps of:
(1) The humidity diffusion calculation of natural concrete is as follows Najjar nonlinear diffusion modelCalculating;
Where h is the relative humidity, h s is the relative humidity affected by cement hydration, t is the age of the concrete, k is the inverse slope of the desorption isotherm, c p is the water diffusivity, related to the saturation diffusion coefficient c 1, c 1 for natural concrete is recorded as According toCalculating;
(2) Based on the equivalent water-cement ratio w/c equ of the recycled concrete and the substitution rate of the recycled coarse/fine aggregate, the saturated diffusion coefficient of the recycled concrete is calculated according to the formula
Calculating;
In the method, in the process of the invention, And/>Is the saturation diffusion coefficient of the recycled coarse aggregate and the natural concrete with the same cement ratio, r RA1 is the larger value of the substitution rate of the recycled coarse aggregate and the substitution rate of the recycled fine aggregate, and r RA2 is the smaller value of the substitution rate of the recycled coarse aggregate and the substitution rate of the recycled fine aggregate.
In the step (5), the influence of the internal curing effect of the recycled concrete on the internal humidity of the concrete is considered, and the method specifically comprises the following steps:
(1) Determining isothermal dehumidification line of recycled aggregate according to matrix water-cement ratio of recycled aggregate, wherein the expression form is
Wherein S is the saturation of the recycled aggregate; m 1、m2 and h * are parameters related to the water-cement ratio of the recycled aggregate matrix;
(2) Quantifying the internal curing effect of recycled aggregate: assuming that the initial water storage amount of the recycled aggregate is close to the saturated water content, the water release amount is according to the formula
Calculating;
Wherein m 1-CRA、m2-CRA and Is a parameter related to the water-cement ratio of the recycled coarse aggregate matrix, m 1-FRA、m2-FRA andIs a parameter related to the water-cement ratio of the recycled fine aggregate matrix.
And (6) correcting the saw-tooth trend which possibly appears in the relative humidity calculation result according to the formula dh less than or equal to 0 so that the relative humidity does not have an ascending trend.
Further, the recycled concrete mass modulus in step (7) is in accordance withCalculating;
Where K is the mass modulus of the recycled concrete, E c is the elastic modulus of the recycled concrete, and v is the Poisson's ratio of the recycled concrete.
The influence of the drying environment on the elastic modulus of the recycled concrete in the step (8) needs to be tested, and the influence factor of the drying environment on the elastic modulus of the recycled concrete is assumed to be according to the following condition without clear test resultsCalculating;
Wherein, beta E is the influence factor of the dry environment on the elastic modulus of the recycled concrete, beta E0 is the influence factor of the dry environment on the elastic modulus of the recycled concrete at the exposed surface, the influence factor is related to the concrete curing time and the internal curing effect of the recycled aggregate, 0.6-1.0 is taken, and x is the distance from the calculated point to the exposed surface of the recycled concrete.
The recycled concrete in the step (9) is freely contracted in one dimension according to the formula
Calculating;
Wherein epsilon 1 is the one-dimensional free shrinkage of the recycled concrete; ρ l is the liquid water density; r is a universal gas constant; t represents absolute temperature, M is the molar mass of water, and K s is the bulk modulus of natural aggregate.
In the step (10), deformation coordination calculation is carried out on the one-dimensional free shrinkage prediction result of each layer to obtain the actual shrinkage distribution condition of the recycled concrete, and the method specifically comprises the following steps:
(1) Carrying out simplified solution on a recycled concrete test piece with the thickness smaller than 200mm according to a formula of r e＝ri =0 (10), wherein r e and r i are respectively an external load matrix and a concrete internal force matrix;
(2) And calculating the thick recycled concrete test piece with complicated conditions by adopting a layered cooling method by using ABAQUS finite element software.
Specific example 1: recycled concrete test blocks with side lengths of 250mm multiplied by 250mm are manufactured according to the recycled coarse aggregate concrete mix ratio in table 1, the test blocks are sealed on five sides after die stripping, and are exposed to a constant temperature and humidity environment with relative humidity of 60% and temperature of 20 ℃, and different measuring points are arranged inside the test blocks for monitoring the development of relative humidity and shrinkage strain, as shown in fig. 2. In the embodiment, a pretreatment mode of saturation and dry method is adopted for the recycled coarse aggregate, namely, the recycled coarse aggregate is in a saturated state when concrete is stirred, and the water content is equal to the water absorption rate. The water absorption of the regenerated coarse aggregate is measured to be 4.3%, and the matrix water-cement ratio is measured to be 0.35. Under standard curing conditions, the 28-day elastic modulus of the recycled concrete is 27.66GPa, and the Poisson ratio is 0.192.
TABLE 1 mixing ratio of recycled coarse aggregate concrete (unit: kg/m 3) in example 1
By using the relative humidity-based recycled concrete shrinkage prediction method, basic parameters of recycled aggregate and recycled concrete are measured by adopting a test to calculate, and the calculation process is as follows:
(1) Basic performance parameters of the recycled aggregate and the recycled concrete are determined: the water absorption rate, the water content and the matrix water-cement ratio of the regenerated coarse aggregate are respectively 4.3%, 4.3% and 0.35; the densities of water, cement, recycled coarse aggregate and natural fine aggregate in the recycled concrete are 1000kg/m 3、3150kg/m3、2583kg/m3、2580kg/m3 respectively, and the mixing method is a saturation surface dry method, the 28-day elastic modulus of the recycled concrete is 27.66GPa, and the Poisson ratio is 0.192 according to the proportion shown in Table 1; the boundary condition is that one side is open after concrete is poured for one day, and the temperature and the humidity of the environment are respectively 20 ℃ and 60% relative humidity;
(2) Calculating the equivalent water-cement ratio of the recycled concrete:
(3) Calculating hydration reaction in the recycled concrete, and bringing the equivalent water-cement ratio into -Najjar humidity model calculation;
(4) And (3) calculating the humidity diffusion in the recycled concrete, and the saturation diffusion coefficient of the recycled concrete:
Bringing boundary conditions and saturation diffusion coefficients into -Najjar humidity model calculation;
(5) The regenerated aggregate release water is calculated, and the isothermal dehumidification line parameters of the regenerated aggregate can be valued according to the matrix water-cement ratio and the table 2. Determining the water release amount of the recycled aggregate according to the humidity increment:
TABLE 2 isothermal dewetting line parameters for recycled aggregates
Solving forThe Najjar humidity model can obtain the relative humidity increment of different depths;
(6) Correcting the relative humidity, namely correcting the possible zigzag trend of the calculated result according to the formula dh less than or equal to 0, so that the relative humidity does not have an ascending trend, and finally obtaining a relative humidity development curve;
(7) Bulk modulus of recycled concrete under standard curing conditions: and calculating according to the elastic modulus and poisson ratio of the recycled concrete under standard curing conditions to obtain the mass modulus of the recycled concrete:
(8) Influence factor distribution of dry environment on the elastic modulus of recycled concrete:
(9) Calculating the one-dimensional free shrinkage of each layer of recycled concrete:
(10) And calculating by means of ABAQUS software through a layered cooling method, and performing deformation coordination calculation on the one-dimensional free shrinkage prediction result of each layer to obtain the real shrinkage distribution condition of the recycled concrete.
The relative humidity and test actual measurement result pair calculated by the prediction method is shown in the figure 3, and the shrinkage strain and test actual measurement result pair calculated by the prediction method is shown in the figure 4, so that the result shows that the relative humidity and shrinkage deformation prediction method in the recycled concrete is accurate.
Specific example 2: according to the mix ratio of the recycled fine aggregate concrete in table 3, a recycled concrete test block with the side length of 250mm×250mm was prepared, the test block was sealed on five sides after the removal of the mold, and was exposed to a constant temperature and humidity environment with the relative humidity of 60% and the temperature of 20 ℃, and different measuring points were set inside the test block to monitor the development of the relative humidity and shrinkage strain, as shown in fig. 2. In the embodiment, a mixing mode of a 70% additional water method is adopted for the recycled fine aggregate, namely, the recycled fine aggregate is in an air-dried state when concrete is mixed, and part of water is added into mixing water to compensate the water absorption capacity of the recycled fine aggregate. The water absorption and the water content of the regenerated fine aggregate were found to be 8.49% and 4.07%, respectively, and the matrix water cement ratio was found to be 0.6. Under standard curing conditions, the 28-day elastic modulus of the recycled concrete is 26.06GPa, and the Poisson ratio is 0.239.
TABLE 3 mixing ratio (unit: kg/m 3) of recycled fine aggregate concrete in example 2
By using the relative humidity-based recycled concrete shrinkage prediction method, basic parameters of recycled aggregate and recycled concrete are measured by adopting a test to calculate, and the calculation process is as follows:
(1) Basic performance parameters of the recycled aggregate and the recycled concrete are determined: the water absorption rate, the water content and the matrix water-cement ratio of the regenerated fine aggregate are 8.49%, 4.07% and 0.6 respectively; the densities of water, cement, natural coarse aggregate and recycled fine aggregate in the recycled concrete are 1000kg/m 3、3150kg/m3、2732kg/m3、2359kg/m3 respectively, the mixing method is a 70% additional water method, the 28-day elastic modulus of the recycled concrete is 26.06GPa, and the Poisson ratio is 0.239; the boundary condition is that one side is open after concrete is poured for one day, and the temperature and the humidity of the environment are respectively 20 ℃ and 60% relative humidity;
(2) Calculating the equivalent water-cement ratio of the recycled concrete:
(3) Calculating hydration reaction in the recycled concrete, and bringing the equivalent water-cement ratio into -Najjar humidity model calculation;
(4) And (3) calculating the humidity diffusion in the recycled concrete, and the saturation diffusion coefficient of the recycled concrete:
Bringing boundary conditions and saturation diffusion coefficients into -Najjar humidity model calculation;
(5) The regenerated aggregate water release calculation is carried out, the isothermal dehumidification line parameters of the regenerated aggregate can be obtained according to the matrix water-cement ratio and the table 2, and the regenerated aggregate water release amount is determined according to the humidity increment:
Solving for The Najjar humidity model can obtain the relative humidity increment of different depths;
(6) And correcting the relative humidity, namely correcting the possible zigzag trend of the calculated result according to the formula dh less than or equal to 0, so that the relative humidity does not have an ascending trend, and finally obtaining a relative humidity development curve.
(7) Bulk modulus of recycled concrete under standard curing conditions: and calculating according to the elastic modulus and poisson ratio of the recycled concrete under standard curing conditions to obtain the mass modulus of the recycled concrete:
(8) Influence factor distribution of dry environment on the elastic modulus of recycled concrete:
(9) Calculating the one-dimensional free shrinkage of each layer of recycled concrete:
(10) And calculating by means of ABAQUS software through a layered cooling method, and performing deformation coordination calculation on the one-dimensional free shrinkage prediction result of each layer to obtain the real shrinkage distribution condition of the recycled concrete.
The relative humidity and test actual measurement result pair calculated by the prediction method is shown in fig. 5, and the shrinkage strain and test actual measurement result pair calculated by the prediction method is shown in fig. 6, so that the result shows that the relative humidity and shrinkage deformation prediction method in the recycled concrete is accurate.
The embodiments of the invention disclosed above are intended only to help illustrate the invention. The examples are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best understand and utilize the invention.
Claims (6)
1. A relative humidity-based recycled concrete shrinkage prediction method is characterized by comprising the following steps of: the method specifically comprises the following steps:
(1) Basic performance parameters of the recycled aggregate and the recycled concrete are determined: the water absorption rate, the water content and the matrix water-cement ratio of the regenerated coarse/fine aggregate; density, mixing ratio, mixing method, elastic modulus and poisson ratio of each component of the recycled concrete; boundary conditions and ambient temperature and humidity;
(2) Calculating the equivalent water-cement ratio of the recycled concrete: calculating the equivalent water-cement ratio of the recycled concrete according to the physical properties of the recycled aggregate and the recycled concrete mixing mode;
(3) And (3) performing hydration reaction calculation in the recycled concrete: carrying out calculation by taking the equivalent water-cement ratio into a Ba ž ant-Najjar humidity model;
(4) And (3) performing humidity diffusion calculation in the recycled concrete: determining the saturation diffusion coefficient of the recycled concrete by considering the equivalent water-cement ratio and the pore communication effect, and calculating based on a Ba ž ant-Najjar humidity model under different humidity boundary conditions;
(5) And (3) performing regenerated aggregate release water calculation: adopting an isothermal dehumidification line of the recycled aggregate to consider an internal curing effect, determining the saturation of the recycled aggregate according to the humidity increment, and further calculating the water release amount and the humidity increment of the recycled aggregate;
(6) Relative humidity correction was performed: correcting the saw-tooth trend which possibly appears in the calculation result, so that the relative humidity does not have an ascending trend;
(7) Bulk modulus of recycled concrete under standard curing conditions: calculating according to the elastic modulus and poisson ratio of the recycled concrete under standard curing conditions to obtain the mass modulus of the recycled concrete;
(8) Quantification of the distribution of the bulk modulus of recycled concrete with depth: the influence of the drying environment on the elastic modulus of the recycled concrete needs to be tested, and when no clear test result is found, the influence depth of the drying environment on the elastic modulus of the recycled concrete is assumed to be 10cm, and the influence factors are linearly distributed along the depth direction;
(9) Calculating the one-dimensional free shrinkage of the recycled concrete: obtaining the volume shrinkage of each layer of the recycled concrete according to the volume modulus and the relative humidity of the recycled concrete, and further obtaining one-dimensional free shrinkage;
(10) Carrying out deformation coordination calculation on the one-dimensional free shrinkage prediction result of each layer to obtain the real shrinkage distribution condition of the recycled concrete;
in the step (2), the influence of the content of the recycled aggregate, the water absorption, the water content and the mixing method on the equivalent water-cement ratio of the recycled concrete is considered, and the formula is adopted
(1) Calculating;
Wherein w/c equ is the equivalent water-cement ratio of the recycled concrete, and M w and M c are the mass of water and cementing material in the mixing ratio respectively; m CRA and M FRA are the mass of recycled coarse aggregate and recycled fine aggregate, respectively; k CRA and k FRA are respectively the water absorption correction coefficients of the recycled coarse aggregate and the recycled fine aggregate, and are related to the coverage rate of the residual cement paste, and 0.85-1.0 is taken; m CRA and m FRA are respectively the initial water contents of the recycled coarse aggregate and the recycled fine aggregate, and the values are multiples of the water content or the water absorption according to the configuration method; w CRA and w FRA are the water absorption rates of the recycled coarse aggregate and the recycled fine aggregate, respectively;
in the step (4), the influence of the pore communication effect of the recycled concrete on the diffusion of the humidity in the concrete is considered, and the method specifically comprises the following steps of:
(1) The humidity diffusion calculation of natural concrete is based on Ba ž ant-Najjar nonlinear diffusion model (2) Calculating;
Where h is the relative humidity, h s is the relative humidity affected by cement hydration, t is the age of the concrete, k is the inverse slope of the desorption isotherm, c p is the water diffusivity, related to the saturation diffusion coefficient c 1, c 1 for natural concrete is recorded as According to(3) Calculating;
(2) Based on the equivalent water-cement ratio w/c equ of the recycled concrete and the substitution rate of the recycled coarse/fine aggregate, the saturated diffusion coefficient of the recycled concrete is calculated according to the formula
(4) Calculating;
In the method, in the process of the invention, And/>Is the saturation diffusion coefficient of the recycled coarse aggregate and the natural concrete with the same cement ratio, r RA1 is the larger value of the substitution rate of the recycled coarse aggregate and the substitution rate of the recycled fine aggregate, and r RA2 is the smaller value of the substitution rate of the recycled coarse aggregate and the substitution rate of the recycled fine aggregate.
2. The relative humidity-based recycled concrete shrinkage prediction method of claim 1, wherein: in the step (5), the influence of the internal curing effect of the recycled concrete on the internal humidity of the concrete is considered, and the method specifically comprises the following steps:
(1) Determining isothermal dehumidification line of recycled aggregate according to matrix water-cement ratio of recycled aggregate, wherein the expression form is （5）；
Wherein S is the saturation of the recycled aggregate; m 1、m2 and h * are parameters related to the water-cement ratio of the recycled aggregate matrix;
(2) Quantifying the internal curing effect of recycled aggregate: assuming that the initial water storage amount of the recycled aggregate is close to the saturated water content, the water release amount is according to the formula
(6) Calculating;
Wherein m 1-CRA、m2-CRA and Is a parameter related to the water-cement ratio of the recycled coarse aggregate matrix, m 1-FRA、m2-FRA and/>Is a parameter related to the water-cement ratio of the recycled fine aggregate matrix.
3. The relative humidity-based recycled concrete shrinkage prediction method of claim 1, wherein: in the step (6), according to the formulaAnd correcting the saw-tooth trend possibly occurring in the relative humidity calculation result so that the relative humidity does not have an ascending trend.
4. The relative humidity-based recycled concrete shrinkage prediction method of claim 1, wherein: the volume modulus of the recycled concrete in the step (7) is according to(7) Calculating;
Where K is the mass modulus of the recycled concrete, E c is the elastic modulus of the recycled concrete, and v is the Poisson's ratio of the recycled concrete.
5. The method for predicting shrinkage of recycled concrete based on relative humidity according to claim 4, wherein: the influence of the drying environment on the elastic modulus of the recycled concrete in the step (8) needs to be tested, and the influence factor of the drying environment on the elastic modulus of the recycled concrete is assumed to be according to the following condition without clear test results(8) Calculating;
Wherein, beta E is the influence factor of the dry environment on the elastic modulus of the recycled concrete, beta E0 is the influence factor of the dry environment on the elastic modulus of the recycled concrete at the exposed surface, the influence factor is related to the concrete curing time and the internal curing effect of the recycled aggregate, 0.6-1.0 is taken, and x is the distance from the calculated point to the exposed surface of the recycled concrete.
6. The relative humidity-based recycled concrete shrinkage prediction method of claim 5, wherein: the recycled concrete in the step (9) is freely contracted in one dimension according to the formula(9) Calculating;
Wherein epsilon 1 is the one-dimensional free shrinkage of the recycled concrete; ρ l is the liquid water density; r is a universal gas constant; t represents absolute temperature, M is the molar mass of water, and K s is the bulk modulus of natural aggregate.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310789018.3A CN116908422B (en) | 2023-06-30 | Recycled concrete shrinkage prediction method based on relative humidity |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310789018.3A CN116908422B (en) | 2023-06-30 | Recycled concrete shrinkage prediction method based on relative humidity |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN116908422A CN116908422A (en) | 2023-10-20 |
| CN116908422B true CN116908422B (en) | 2024-06-25 |
Family
ID=
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2012166964A (en) * | 2011-02-10 | 2012-09-06 | Ube Industries Ltd | Dry shrinkage reducing method and manufacturing method of concrete |
| CN108229093A (en) * | 2018-01-23 | 2018-06-29 | 广西大学 | The construction method of saturation regeneration concrete chloride diffusion coefficient multi-scale prediction model |
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2012166964A (en) * | 2011-02-10 | 2012-09-06 | Ube Industries Ltd | Dry shrinkage reducing method and manufacturing method of concrete |
| CN108229093A (en) * | 2018-01-23 | 2018-06-29 | 广西大学 | The construction method of saturation regeneration concrete chloride diffusion coefficient multi-scale prediction model |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| Nilsson | Hygroscopic moisture in concrete-drying, measurements & related material properties | |
| CN110621634A (en) | Sustainable building material and preparation method and application thereof | |
| Hajibabaee et al. | Mechanisms of dimensional instability caused by differential drying in wet cured cement paste | |
| CN106007539A (en) | Cement-based material internal curing agent, and preparation method and application thereof | |
| Pichelin et al. | Sustainability, transfer and containment properties of concrete subject to delayed ettringite formation (DEF) | |
| CN112414902A (en) | Method for evaluating chloride ion transmission in concrete by considering chemical damage effect of sulfate | |
| CN116908422B (en) | Recycled concrete shrinkage prediction method based on relative humidity | |
| Babaahmadi et al. | Physical and mechanical properties of cementitious specimens exposed to an electrochemically derived accelerated leaching of calcium | |
| Tajudin et al. | Relationship of physical parameters in Pb-contaminated by stabilization/solidification method | |
| CN111239253A (en) | Detection method and application of aggregate elastic modulus | |
| Di Bella et al. | Application of microstructurally-designed mortars for studying early-age properties: Microstructure and mechanical properties | |
| Yang et al. | Effect of saturation degree on chloride transport in mortars under two conditions: diffusion and continuous immersion | |
| Jin et al. | Multiscale model for the scale effect of tensile strength of hardened cement paste based on pore size distribution | |
| CN116908422A (en) | Recycled concrete shrinkage prediction method based on relative humidity | |
| CN116908423B (en) | Prediction method for relative humidity distribution in recycled concrete | |
| CN111505046B (en) | Prediction method of concrete early-age thermal expansion coefficient multi-scale model | |
| Ambad et al. | Impact of controlled permeable formwork liner against chloride penetration on the concrete structures | |
| CN116908423A (en) | Prediction method for relative humidity distribution in recycled concrete | |
| Jones | Examining the freezing and thawing behavior of concretes with improved performance through internal curing and other methods | |
| CN112147054B (en) | Rapid test method for matrix communication porosity of semi-flexible pavement | |
| Weber et al. | Manipulating the water content and microstructure of high performance concrete using autogeneous curing | |
| CN107816936A (en) | It is a kind of to obtain the method that the deformation of concrete for hydraulic structure bulking is hardened under non-standard temperature | |
| Asamoto et al. | Length Change and Water Uptake Characteristics of Synthesized Calcium Silicate Hydrates | |
| Soufi et al. | Investigation of the protection efficiency of repair mortar against chloride corrosion in repaired zones of reinforced concrete | |
| CN111462839B (en) | Multiscale prediction method for thermal expansion coefficient of hardened cement mortar |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant |