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The effect of powdery industrial solid wastes on the optimal proportion of pastes and self-compacting concrete (SCC) is investigated in this study. There were nine groups of powdery industrial solid wastes designed, including cement, fly ash (FA), limestone powder (LP), granulated blast furnace slag (GBFS), and modified phosphogypsum (MPG). The powder materials have different properties, such as zeta potential, density, and specific surface area. The paste rheological threshold theory was used to calculate the self-compacting paste (SCP) zone and the optimal proportion. To assess the effect of powder properties on the optimal mix proportion, a model was proposed. The linear regression method was used to obtain quantitative relationships between the optimal proportion and powder characteristics, which can benefit in the SCC optimization process. A new powder combination was designed, and the optimal water-to-powder ratio by volume (VW/VP) and the dosage of superplasticizer by mass (SP%) can be calculated using the powder combination's physical and chemical properties. The search area was narrowed, and the SCP zone was obtained, where a good SCC was achieved, validating the powder effect model's effectiveness. [ABSTRACT FROM AUTHOR]

The multiscale rheological threshold theory can guide the mix design of self-compacting concrete (SCC) from a trans-scale view. Through the paste thresholds calculated by the mini-slump flow test results, the workability of SCC can be predicted. However, this method shows insufficient prediction accuracy when handling multiplexed powder. In the existing threshold calculation formula, the characteristics of powder materials were described through empirical values, without considering the specific properties of various powders. This paper focuses on the application of the multiscale rheological threshold theory to multiplexed powder SCCs. Through the research on the characteristics of powder materials, especially D50 and Span, the effect of the powder properties on paste thresholds was carried out. The prediction accuracies were confirmed by four sets of self-compacting mixtures at paste and concrete scales and were verified with another set of tests. There are a total of 45 paste and 45 SCC test results with multiplexed powders, including cement, fly ash, and limestone powder. The predicting accuracies are expressed as the relative accuracy ε and the accuracy index ε′, calculated by the comparison of self-compacting zones at paste and SCC scales. The calculation results showed that ε and ε′ of the modified method increased. This modified method can be efficient for the mix design of SCC containing multiplexed powders. [ABSTRACT FROM AUTHOR]

The use of fly ash (FA) limestone and powder (LP) in combination with cement in concrete has several practical, ecological, and economic advantages by reducing carbon dioxide emissions, reducing the excessive consumption of natural resources, and contributing to a cleaner production of self-compacting concrete (SCC). A mix design method for SCC based on paste rheological threshold theory can guide the SCC mix design by paste tests. This method can be visualized by the self-compacting paste zone (SCP zone), a plane area where all the mix points meet the paste threshold theory, and SCC zone, a plane area consisting of all the mix points satisfying the criteria of qualified SCC. In the case of cement SCC, the SCP zone coheres with the SCC zone. However, in the case of the addition of FA or LP with different granulometry and shape characteristics from cement, experimental results indicate that the SCP zone is separated from the SCC zone. This work quantitatively studied the influence of FA and LP on the movement of the SCP zone by introducing the improved powder equivalence model. The improved model was obtained by powder equivalence coefficients calculated through the mortar test results with or without FA or LP, instead of SCC tests in the former method. The equivalence coefficients by volume of FA and LP are 0.55 and 0.79, respectively, which means that 1.82 unit volume of FA or 1.27 unit volume of LP is equivalent to one unit volume of cement. The improved powder equivalence model was verified by the successful preparation of SCC incorporating FA or LP simply and effectively. The equivalent SCP zone cohered better with the SCC zone than the former SCP zone, which could guide the quick mix design of SCC without SCC premix tests. [ABSTRACT FROM AUTHOR]

• Fly ash and limestone powder were incorporated into SCC to improve its workability. • A modified model was used to predict the paste rheological thresholds of fresh SCC. • Powder parameters were introduced into paste rheological threshold formulas. • Powder volume fractions were considered in paste rheological threshold formulas. • The modified model was verified based on SCCs with different powder compositions. Self-compacting concrete (SCC) containing composite powders has many advantages, such as its abilities to reduce the heat of hydration, optimise the particle packing, and maintain the workability better than pure cement SCC. The rheology of the paste is important for understanding the flow behaviors of SCC. This study investigates the effects of fly ash (FA) and limestone powder (LP) on the rheological thresholds of SCC pastes. By introducing a powder fitting coefficient, intrinsic viscosity, and volume fractions, the original rheological model is improved. Both models are used to predict the paste yield stress threshold and paste plastic viscosity threshold of fresh SCC. After calibrating the fitting coefficient and intrinsic viscosity of the FA and LP, the modified model can accurately predict the self-compacting paste (SCP) zone, where SCC can be obtained by mixing paste with sand and gravel. The absolute and relative accuracies of the modified model are far greater than those of the original model, except for the case of C + 30%FA, for which the modified model is superior to the original model in terms of the location of the SCP zone. SCC experiments with different coarse aggregate contents, sand properties, and powder compositions are conducted to verify the modified model, and indicate that the powder fitting coefficient and intrinsic viscosity remain constant. [ABSTRACT FROM AUTHOR]

• Limestone powder (LP) or fly ash (FA) or both were used to replace cement. • The addition of LP or FA or both increase the flowability of paste and SCC. • Different roles in paste and SCC make SCP zone not accurately matching SCC zone. • A powder equivalence model were applied to process the zone mismatch. This work studied a mix design method of self-compacting concrete (SCC) containing limestone powder (LP) or fly ash (FA) or both. The addition of LP or FA or both was shown to reduce the water/powder volumetric ratio (Vw/Vp) and the superplasticizer/powder mass ratio (SP%) and increase the SCC flowability. The reason for these phenomena is that powders such as LP and FA have ball bearing effect, filler effect and adsorption effect, which play a larger role in paste than in SCC owning to the relative percentage of LP or FA or both decreasing after adding aggregates. The different role limit the applicability of the paste rheological threshold theory, which results in the self-compacting paste (SCP) zone not accurately matching the SCC zone. A powder equivalence model was proposed to solve the influence of the above three effects on this zone mismatch. LP and FA can be converted to equivalent cement through equivalence coefficients based on the SCC flowability. The equivalence coefficients of LP by volume and by mass are 0.75 and 0.6, respectively. The equivalence coefficients of FA by volume and by mass are 0.50 and 0.38, respectively. Based on the equivalence coefficients from the experiments, LP and FA were mutually used in SCCs with the coefficients unchanged. The result shows that the equivalent SCP zone for the addition of LP and FA coincide partly with the SCC zone. [ABSTRACT FROM AUTHOR]

• We investigated mix design method of self-compacting concrete with fly ash content. • We considered paste rheological threshold theory & material packing characteristics. • The basic water demand experiments were used to obtain the packing density. • Results show that accuracies of the improved method are higher than initial method. This study investigated an enhanced mix design method of self-compacting concrete (SCC) with fly ash (FA) content based on paste rheological threshold theory and material packing characteristics. Seven SCC mixes with FA replacement levels of 0%, 10%, 20%, 30%, and 40% by volume were conducted to investigate the effect of FA on the rheological properties of SCC. A basic water demand experiment of mortar was designed to obtain the packing density of mortar. Furthermore, the equivalent packing density was defined and calibrate to quantify and represent the effect of FA. The yield stress and plastic viscosity threshold formula were modified based on the equivalent packing density. And the bilinear interpolation method was used to analyze the paste and SCC results. Besides, twenty seven SCC series with different water to cement ratio, FA replacement levels were conducted to verify the applicability of the enhanced method. The results show that, the relative accuracies of the improved method are higher than 83%, whereas those of the initial method are no greater than 60%. [ABSTRACT FROM AUTHOR]