Abstract
Fly ash is broadly utilized to produce concrete materials. This study presents a strength estimation model and a CO2 reduction design method for concrete with fly ash. First, a hydration-based strength (HBS) model is proposed for the evaluation of strength development at different ages of fly ash composite concrete with different mix proportions. Second, CO2 emissions for 1 MPa strength were evaluated. The analysis results show that, as the fly ash-to-binder ratio (FA/B) increased, the CO2 emissions for 1 MPa strength decreased. For concrete with a low water-to-binder ratio (W/B), the addition of high content of fly ash had an obvious dilution effect, which increased the reaction degree of cement and reduced CO2 emissions for 1 MPa strength. Moreover, the extension of the design age could reduce CO2 emissions for 1 MPa strength. Third, a genetic-algorithm-based optimal design model is proposed to find the individual mass of cement and fly ash of low-CO2 concrete. The analysis results show that, as the water contents increased from 160 to 170 kg/m3, to obtain the same strength, cement mass and fly ash mass increased, while the water/binder ratio and fly ash/binder ratio did not change. This means that the reduction in mixed water is one feasible way to lower CO2 emissions. In summary, the proposed strength–emission integrated analysis method is useful for designing sustainable fly ash composite concrete with the desired strength and low levels of CO2 emissions.
Highlights
Fly ash is an industrial byproduct of coal burning in power plants, and it is broadly utilized to produce concrete materials
To overcome the weaknesses of previous studies, this study presents the integrated analysis of the procedure of hydration–strength–CO2 emissions of fly ash composite concrete
This study presents an integrated analysis of the strength development and CO2 emissions of fly ash composite concrete
Summary
Fly ash is an industrial byproduct of coal burning in power plants, and it is broadly utilized to produce concrete materials. Yang et al [17] proposed an integrated procedure for the design of low-CO2 concrete This procedure can evaluate the CO2 emission of concrete, binder contents for aimed strength, and types and replacement percentages of supplementary cementitious materials for aimed strength and CO2 reduction levels. The rest of this work is structured as follows: Sections 2 and 3 present the strength evaluation model and the CO2 emission model, respectively; Section 4 shows the genetic algorithm-based optimal design of low-CO2 fly ash composite concrete; Section 5 discusses the strength evaluation and CO2 reduction strategy; and Section 6 presents the conclusions. The main limitations of the hydration strength model are that the current model does not consider the effect of aggregate on the development of strength nor does it cover the difference in the reaction rate of the silicate and aluminate phase of fly ash
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