Prediction method of rheological properties of recycled concrete based on coarse aggregate composition

Abstract

The present invention relates to a method for predicting the rheological properties of recycled concrete based on coarse aggregate, comprising the following steps: a , specific surface area of ​​coarse aggregate s a The rheological test data of freshly mixed recycled concrete under the conditions of β and coarse aggregate-mortar mass ratio are used to correct the rheological equation of recycled concrete based on H-B and Bingham rheological equations. Based on the corrected rheological equation, it is used to predict the rheological properties of freshly mixed recycled concrete. This method takes into account the shear-thinning thixotropy of recycled concrete, and uses the replacement rate of recycled coarse aggregate and the specific surface area of ​​coarse aggregate to construct a segmented rheological equation of recycled concrete under the coupling of multiple factors. The corrected rheological equation accurately characterizes the shear stress-shear rate rheological law of freshly mixed recycled concrete, and can accurately predict the rheological performance parameters of recycled concrete. The error between the theoretical prediction results and the experimental results is within ±5%.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete rheological property evaluation, and in particular relates to a method for predicting the rheological properties of recycled concrete based on coarse aggregate composition. Background Art

[0002] Good rheology is the key to ensure the quality of concrete and successful pumping. Concrete with good rheology is easy to pump, has good fluidity and cohesion, and has relatively good strength and durability after final solidification. Concrete with poor rheology is prone to coarse aggregate deposition, blocking the pumping pipeline and having an adverse effect on the structure. It is well known that recycled concrete can make full use of construction waste and industrial waste such as waste concrete, fly ash and slag, and is a green building material that saves energy and reduces emissions. How to improve the rheological properties of recycled concrete by adjusting the replacement rate of recycled coarse aggregate, the mass ratio of coarse aggregate to mortar, and the grading of coarse aggregate particles is one of the hot issues currently concerned by the academic and engineering communities.

[0003] Early rheological properties research mainly focused on the fluidity and cohesion of concrete, and most of them were empirical rheological parameters. Qualitative indicators based on visual inspection are difficult to accurately evaluate the rheological properties and pumpability of fresh concrete. At present, the research on the rheological properties of fresh concrete mainly focuses on qualitative indicators such as slump and expansion, while quantitative analysis is relatively rare. The rheological equations are mostly the relationship between shear stress and shear rate under different natural coarse aggregate gradations; and the recycled coarse aggregate produces new damage and cracks during secondary crushing, which makes the rheological properties of recycled concrete very different from those of ordinary concrete; the constitutive model of natural aggregate is not completely applicable to recycled aggregate. In addition, for recycled aggregates, in addition to the above-mentioned slump and expansion parameters, parameters such as the replacement rate of recycled coarse aggregate, the material ratio of coarse aggregate and mortar, and the particle gradation of coarse aggregate have a greater impact on the rheological properties of recycled concrete. However, there are few studies on this aspect, and no research has been seen on the influence of the coupling of these factors on the rheological properties of recycled concrete. Having good rheological properties is the key to the pumping of recycled concrete. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the purpose of the present invention is to provide a method for predicting the rheological properties of recycled concrete based on coarse aggregate composition.

[0005] The technical solution of the present invention is: a method for predicting the rheological properties of recycled concrete based on coarse aggregate, comprising the following steps:

[0006] According to different recycled coarse aggregate replacement rate r a The rheological test data of fresh recycled concrete under the conditions of coarse aggregate specific surface area Sa and coarse aggregate-mortar mass ratio β are used to correct the rheological equation of recycled concrete based on HB and Bingham rheological equations.

[0007] Based on the modified rheological equation, it is used to predict the rheological properties of fresh recycled concrete.

[0008] Wherein, the specific surface area of ​​the coarse aggregate is s a It is the ratio of the surface area of ​​all coarse aggregate in recycled concrete to the total mass of coarse aggregate.

[0009] The coarse aggregate-mortar mass ratio β coarse aggregate-mortar mass ratio is the ratio of the total mass of natural and recycled coarse aggregate to the total mass of sand, cement, fly ash, slag and water in each cubic meter of freshly mixed recycled concrete.

[0010] Preferably, the modified rheological equation is: Where τ is the surface shear stress, τ0 is the yield stress, is the shear rate, n is the power of the shear rate, K is the consistency coefficient, Pa·sn, η0 is the plastic viscosity at the moment of rheological flow, Pa·s,

[0011] When the shear rate increases When , the n value is obtained by fitting, and the K value is calculated by regression analysis;

[0012] When the shear rate increases When n = 1.000, K = 0, it is equivalent to the Bingham rheological equation:

[0013] Furthermore, when When n=1.065, K<0, the consistency coefficient calculation formula obtained by regression analysis is: K=-26.14τ 0 +1843.76.

[0014] Further, the η 0 =η-0.5 n-1 K = η - 0.956K.

[0015] Furthermore, the plastic viscosity η and yield stress τ 0 By different recycled coarse aggregate replacement rate r a , coarse aggregate-mortar mass ratio β and coarse aggregate specific surface area s a The rheological parameters were calculated using the formula obtained by fitting.

[0016] Furthermore, using the formula

[0017] η=8.12r a +32.82β-3.86×10 3 (s a -0.154) 2 -9.66;

[0018] τ 0 =113.38r a +413.72β-8.50×10 4 (s a -0.152) 2 -85.67;

[0019] The plastic viscosity η and yield stress τ of concrete are calculated respectively 0 .

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention studies the influence of coarse aggregate composition on the rheological properties of fresh recycled concrete, explores the influence of recycled coarse aggregate replacement rate, coarse aggregate-mortar mass ratio, and coarse aggregate grading on the rheological properties of concrete, and then selects appropriate parameters. Considering the shear thinning thixotropy of recycled concrete, the recycled coarse aggregate replacement rate and the coarse aggregate specific surface area are used to construct a segmented rheological equation of recycled concrete under the coupling of multiple factors. The modified rheological equation accurately characterizes the shear stress-shear rate rheological law of fresh recycled concrete, and can accurately predict the rheological performance parameters of recycled concrete. The error between the theoretical prediction result and the test result is within ±5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The test results of plastic viscosity and yield stress of recycled concrete under different influencing factors are shown;

[0023] Figure 2 The test results of plastic viscosity and yield stress of fresh recycled concrete with different specific surface areas and equivalent particle sizes are shown in Figure 2.

[0024] Figure 3 The torque-speed curve of fresh recycled concrete mixture under different influencing factors;

[0025] Figure 4 Comparison of rheological equations before and after correction;

[0026] Figure 5 The predicted results of the modified formula are compared with the measured results. DETAILED DESCRIPTION

[0027] In order to have a further understanding of the present invention, the present invention is further described below in conjunction with embodiments and drawings.

[0028] Example

[0029] 1. Experimental plan

[0030] In this embodiment, the rheological test of recycled concrete was performed using a German Schleibinger eBV-T rheological tester that supports self-setting of time-speed programs.

[0031] 2. Analysis of the influence of various factors on the rheological parameters of recycled concrete

[0032] According to the rheometer test results, the plastic viscosity and yield stress data of each sample were calculated, and the following can be obtained: Figure 1 The line graph and three-phase diagram of the influence of recycled coarse aggregate replacement rate, coarse aggregate-mortar mass ratio and coarse aggregate gradation on the plastic viscosity and yield stress of fresh recycled concrete are shown. It can be seen that the recycled coarse aggregate replacement rate, coarse aggregate-mortar mass ratio and coarse aggregate gradation have an impact on the plastic viscosity and yield stress of fresh recycled concrete.

[0033] Considering that the gradation of coarse aggregate is difficult to quantify when establishing the rheological equation, the specific surface area s a The plastic viscosity and yield stress of recycled concrete are quantitatively described by the equivalent particle size d. The equivalent particle size d is the average particle size of individual particles that make the mass of coarse aggregate in recycled concrete equal, which is calculated by the sieve residue curve. a It is the ratio of the surface area of ​​all coarse aggregates in recycled concrete to the total mass of coarse aggregates, obtained through experimental measurement or theoretical calculation. a The calculation results of plastic viscosity and yield stress corresponding to the equivalent particle size d are as follows: Figure 2 As shown. It can be seen that as the specific surface area of ​​coarse aggregate increases, the plastic viscosity and yield stress of recycled concrete approximately increase first and then decrease. However, the regularity between the equivalent particle size d and the plastic viscosity and yield stress of recycled concrete is not obvious. This shows that the equivalent particle size d cannot accurately describe the change law of plastic viscosity and yield stress. Therefore, this study only uses the specific surface area parameter s of coarse aggregate. a Construct rheological equation of recycled concrete.

[0034] 3 Correction and verification of rheological equation of recycled concrete

[0035] 3.1 Selection of rheological equation considering thixotropy

[0036] Based on the results of Part 2, the thixotropic curves of freshly mixed mixtures under different recycled coarse aggregate replacement rates, coarse aggregate-mortar mass ratios and coarse aggregate specific surface areas were analyzed, and it was found that all freshly mixed mixtures showed different degrees of shear thinning ( Figure 3 ), the shear stress-shear rate should be described by a piecewise nonlinear mathematical formula. Therefore, considering the shear rate The rheological equation of fresh recycled concrete was corrected based on the HB and Bingham rheological equations according to the different rules during rising and falling.

[0037] HB rheological equation:

[0038] Bingham rheological equation:

[0039] Modified RAC rheological equation:

[0040] Where n is the power of shear rate, K is the consistency coefficient, Pa·s n . η 0 is the plastic viscosity at the moment of rheological flow, Pa·s. τ 0 is the yield stress. τ is the surface shear stress.

[0041] According to the revised RAC rheological scheme, the rheological data of the freshly mixed mixture obtained by the test were fitted. After fitting, the specific results are as follows:

[0042] Rising section: n = 1.065, K < 0, and the calculation formula (4) of the rising section consistency coefficient is obtained through regression analysis.

[0043] K=-26.14τ 0 +1843.76 (4)

[0044] Descending section: Since there is no influence of viscosity, n = 1.000, K = 0, and equation (3) is transformed into equation (2).

[0045] Consistency coefficient K and yield stress τ 0 Both describe the overall resistance of the fluid to shear, and there is a correlation between the two. The data range is 0~0.5rev / sec. According to formula (2) and formula (3), we have:

[0046] η 0 =η-0.5 n-1 K=η-0.956K (5)

[0047] The Pearson correlation coefficient was above 0.96.

[0048] 3.2 Correction of rheological equation of recycled concrete

[0049] According to the variation law of rheological properties of recycled concrete in Part 2, the replacement rate of recycled coarse aggregate r a , coarse aggregate-mortar mass ratio β, and specific surface area s a The plastic viscosity η and yield stress τ of recycled concrete are obtained by fitting the rheological properties parameters of recycled concrete obtained by experimental calculation. 0 It can be calculated as follows:

[0050] η=8.12r a +32.82β-3.86×10 3 (s a -0.154) 2 -9.66 (6)

[0051] τ 0 =113.38r a +413.72β-8.50×10 4 (s a -0.152) 2 -85.67 (7)

[0052] Where r a is the replacement rate of recycled coarse aggregate, ranging from 0 to 1; s a is the specific surface area of ​​coarse aggregate, m 2 / kg, η and τ 0 Same as r a ,β,s a The Pearson correlation coefficients were all above 0.92.

[0053] In summary, the rheological equation of the shear stress-shear rate curve of recycled concrete under different recycled coarse aggregate replacement rates, coarse aggregate-mortar mass ratios and particle gradings is proposed, as shown in equation (8).

[0054]

[0055] In the formula They are the shear rate and shear rate growth rate, that is, the first and second derivatives of the shear strain γ with respect to time t, and the dimensions are all in the international system of units.

[0056] 3.3 Verification of rheological equation of recycled concrete

[0057] In order to verify the proposed rheological equation of recycled concrete, the representative R30 group test data were selected and compared with the existing HB rheological equation and the improved Bingham rheological equation. Figure 4 shown.

[0058] from Figure 4 It can be seen that in the rising section where the shear rate increases, the modified rheological equation of recycled concrete is closer to the test results than the HB equation and the improved Bingham equation, and has higher accuracy. In the falling section where the shear rate decreases, the modified rheological equation of recycled concrete is transformed into the Bingham equation, and the modified equation has almost the same accuracy as the HB equation and the improved Bingham equation. Considering the correlation between the rising and falling sections of the rheological equation of recycled concrete, the proposed rheological equation (8) can accurately reflect the rheological properties of recycled concrete, and has higher accuracy than other equations.

[0059] In addition, 64 sets of recycled concrete plastic viscosity and yield stress test data samples were selected to verify the rheological equation of recycled concrete. The results are as follows: Figure 5 As shown, the error between the theoretical prediction results and the experimental results is within ±5%.

[0060] comprehensive Figure 4 and Figure 5 It can be seen that the modified rheological equation (8) proposed in the present invention can better predict the rheological properties of recycled concrete with high prediction accuracy.

[0061] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0062] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for predicting the rheological properties of recycled concrete based on coarse aggregate composition, characterized in that: The following steps are involved: According to different recycled coarse aggregate replacement rate r a , coarse aggregate-mortar mass ratio β and coarse aggregate specific surface area s a Based on the rheological test data of recycled concrete under the above conditions, the rheological equation of recycled concrete is corrected based on the HB and Bingham rheological equations; Based on the modified rheological equation, it is used to predict the rheological properties of fresh recycled concrete; Wherein, the modified rheological equation is: , In the formula, τ is the surface shear stress, τ 0 is the yield stress, is the shear rate, n is the power of the shear rate, K is the consistency coefficient, Pa·s n ; η0 is the plastic viscosity at the moment of rheological flow, Pa·s, When the shear rate increases When ≥0, n = 1.065, K < 0, the consistency coefficient calculation formula obtained by regression analysis is: ; When the shear rate increases When <0, n = 1.000, K = 0, ; The data range is 0~0.5rev / sec; , plastic viscosity η and yield stress τ0 are affected by different recycled coarse aggregate replacement rates r a , coarse aggregate-mortar mass ratio β and coarse aggregate specific surface area s a The formula obtained by fitting the rheological parameters under the condition of flow is: ； ； The rheological properties of the freshly mixed recycled concrete are determined by various interrelated rheological equations, as shown in the following formula: .

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