AbstractHigh-strength concrete (HSC) has been widely used in civil engineering. HSC is a kind of multiphase composite material with large dispersion. In order to improve the safety of structure or component design, it is of great significance to study the variability of HSC mechanical properties and its variation with time. This paper carries out experimental research on the time-varying properties of C80 fly ash HSC under standard curing conditions, and analyzes the influence of curing time and fly ash content on the mean value and variation coefficient of compressive strength. Based on the compressible packing model (CPM), a compressive strength calculation model of fly ash HSC is established. Because the aggregate distribution characteristics have great influence on strength, the maximum paste thickness is analyzed based on the random aggregate model, a computational model for compressive strength of fly ash HSC considering the randomness of maximum paste thickness is presented further. The results show that the compressive strength values predicted by the proposed model have the same variation rule with predictive values of models in codes containing different fly ash content at different age, and the predictive values of models in codes are all in the prediction range of the proposed model with a 95% guarantee rate. This proposed model not only has a good calculation accuracy, but also has a certain prediction confidence interval, which provides a certain theoretical basis for the random prediction of the compressive strength of high-strength concrete.

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