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• Residual alkali activity of RCAs with initial AAR damage is evaluated. • RCA with a certain level of AAR can improve the strength of SCRAC. • AAR product filled and reinforced the adhering mortar in RCA. • Compressive strength of SCRAC is predicted by a model considering filling effects. The use of recycled concrete aggregate (RCA) is an effective approach to achieve environmental sustainability. However, the presence of defects due to previous alkali–aggregate reactions (AARs) has caused reluctance toward its use in constructions. This study investigated the application and influence of RCAs with different degrees of initial AAR damage on the mechanical behavior and porosity of self-compacting recycled aggregate concrete (SCRAC). Concrete cubic specimens with different degrees of AAR were produced by soaking the raw materials in a high-alkaline solution. In order to obtain RCAs with different initial AAR durations of 7, 28, 60, and 210 days. The specimens were then crushed using a jaw crusher. The residual reactivity of the RCA produced from concrete affected by the AAR was detected using the accelerated mortar bar test. The rheological properties of the SCRAC with different RCAs were tested. Compressive strength, flexural strength, mercury intrusion porosimetry, and scanning electron microscopy tests were conducted to analyze the effects of RCAs with different degrees of initial AAR damage on the mechanical properties and porosity of the SCRAC. The results show that the RCA can maximally strengthen the compressive strength of the SCRAC after 60 days of alkali immersion at a replacement rate of 30 %. Furthermore, a prediction model considering the filling effect for calculating the influence of RCAs with initial AAR damage on the compressive strength of the SCRAC was proposed. For practical engineering applications, the AAR can strengthen RCAs and improve the utilization rate of RCA, which is beneficial for the sustainable development of the environment. [ABSTRACT FROM AUTHOR]

This paper presents a new numerical method to optimize the mix proportion of self-compacting concrete (SCC) at paste level based on a paste rheological threshold theory that the SCC formulated paste must satisfy the criteria to ensure SCC with good flowability and segregation resistance. A total of 12 mini-slump flow tests were initially conducted, and relevant rheological characteristics were derived. The correlation between mixture variables and rheological characteristics was determined using a bilinear interpolation method. A self-compacting area at paste level was defined by choosing the mixture whose rheological characteristics satisfied the criteria. The economical mixture was obtained from the area, and an iteration process was introduced to ensure that the rheological characteristics of this mixture satisfied the criteria. Finally, an optimized SCC mixture from an economical aspect was achieved, and the robustness of the mixture was also analyzed. [ABSTRACT FROM AUTHOR]

This work studies the effect of fine aggregate characteristics on the thresholds of self-compacting paste rheological properties. Fine aggregate characteristics consist of gradation and content. The specific surface area (SSA) was used to quantitatively describe the gradation of fine aggregate. The most lenient criteria for qualified mortar were formulated from the view of yield stress and plastic viscosity. Mortar experiments were conducted by separately changing the SSA and sand ratio. For each combination, a series of mortar and corresponding paste experiments were performed by adjusting the water-cement ratio and the superplasticizer dosage to obtain paste rheological thresholds. Experimental verification tests on self-compacting concrete (SCC) was conducted. This method can be easily implemented with wide scope of sand gradation and content. Using this method, the aim of predicting the SCC workability from the rheological characteristics of paste was achieved. [ABSTRACT FROM AUTHOR]

Hydraulic concrete structures in cold regions are vulnerable to freeze-thaw damage. This paper proposes a multi-scale simulation analysis approach to investigate the mechanical properties and frost resistance of Low-heat Portland (LHP) cement, Moderate-heat Portland (MHP) cement, and Ordinary Portland cement (OPC) concrete. The hydration heat, hydration degree, pore size distribution, and compressive strength of LHP, MHP, and OPC concrete at different curing ages, as well as the ice amount, expansion strain, and mechanical properties under different freeze-thaw cycles are calculated and compared. Due to the lower early-hydrated C 3 S content of LHP and the higher later-hydrated C 2 S content, the porosity of LHP after 90d curing is lower than that of MHP and OPC, resulting in better mechanical properties and frost resistance. On this basis, the evolution model proposed in this paper can quantitative analysis the frost resistance of cement paste based on different content of C 3 S and C 2 S, which provided a feasible method for predicting the frost resistance of hydraulic concrete structures in cold regions. • Multi-component hydration numerical simulation establishing microstructure difference. • Freeze-thaw damage is calculated by meso-scale frost pressure model. • Weibull distribution and durability factor is adopted to predict frost resistance. • LHP perform better mechanical properties and frost resistance than MHP and OPC. [ABSTRACT FROM AUTHOR]

• Improvement of a mix design method for SCC with ternary blends powders is proposed. • Paste rheological threshold theory and packing properties of powders are considered. • Results show that accuracy of this improved method are increased by 78%. • SCC contains FA and LP is suitable for the improved mix design method. This work investigates an improved mix design method based on paste rheological threshold theory for self-compacting concrete (SCC) with ternary blends powder materials. Six batches of SCC and their equivalent paste tests were first performed to test and verify the applicability of the initial mix design method with SCC contains LP (limestone powder) and FA (fly ash). The basic water demand experiments of mortar were used to obtain the packing density of mortar. A total of 21 SCC tests were then conducted to present an improved mix design method. Yield stress and plastic viscosity threshold formulas are modified based on material packing characteristics. The bilinear interpolation method was used to process paste and SCC results. Futhermore, a total of 36 SCC series were conducted to verify the applicability of the improved method. Prediction accuracy formula according to the figure area were introduced to assess the predictive effect of the improved method. Results show that the relative accuracies of the improved method are higher than 78%, while the initial method is no greater than 45%. This improved mix design method is still applicable with SCC contains both LP and FA. [ABSTRACT FROM AUTHOR]

• A new theoretical model was established for SCC. • A coefficient in the plastic viscosity threshold formula was modified. • Bilinear interpolation method was used to determine the SCP and SCC zones. • Prediction accuracies based on figure area were defined. • Proposed method is independent of the type of cement. This work studies the effects of coarse aggregate content on the paste rheological thresholds of fresh self-compacting concrete (SCC). A new mechanical model for highly flowable SCC was established, and a coefficient in the plastic viscosity threshold formula was modified after conducting experimental tests on Wu's model. The threshold of the paste yield stress decreases while the threshold of the paste plastic viscosity increases with the increase of aggregate content. The bilinear interpolation method was used to process the paste and SCC results. Prediction accuracy formulae based on figure area were introduced to assess the predictive effect of the new model. The relative accuracies of the new model are greater than 70%, whereas the relative accuracies of Wu's model are no greater than 45%. At last, Two types of cement were used to conduct the verification experiments and high prediction accuracies were obtained. The results show that the application of this method is independent of the type of cement used. [ABSTRACT FROM AUTHOR]

• Coarse aggregate properties consist of shape, gradation, and content. • Coarse aggregate properties are quantified by equivalent specific surface area. • Equivalent mortar film thickness was used to modify the original model. • The modified model was verified with different coarse aggregate properties. This paper puts forward an enhanced mix design method for self-compacting concrete (SCC) based on paste rheological threshold theory and equivalent mortar film thickness theories. 18 sets of paste and SCC tests were carried out to test the initial mix design method with coarse aggregate contents of 285, 315, and 322 L/m3, the results show that the initial mix design method cannot accurately predict the SCC test results. The equivalent specific surface area of coarse aggregate (SSA eq) was chosen to quantify and represent the particles' shape, gradation, and contents on mortar film thickness, and the equivalent mortar film thickness was proposed to modify the original rheological model. In addition, 36 sets of paste and SCC tests with different coarse aggregate characteristics were prepared to verify the enhanced method. Using prediction accuracy formula to evaluate the enhanced mix design method. Both methods are used to predict the fresh SCC. Results show that the average value of relative accuracies and Intersection-over-Union (IoU) in the enhanced method are, 0.84, 0.79, respectively, whereas in the original method are, 0.60, 0.59, respectively. [ABSTRACT FROM AUTHOR]