Properties and Mechanical Strength Analysis of Concrete Using Fly Ash, Ground Granulated Blast Furnace Slag and Various Superplasticizers

Supplementary cementitious materials (SCMs) have been widely used to replace cement in recent years in order to reduce the burden of cement on the environment. In this study, fly ash (FA) and ground-granulated blast furnace slag (GGBFS) were used as long-term 40%, 50% and 60% replacement cement in order to explore the mechanical strength of different superplasticizers (SPs) under high substitution amounts. The results of the study showed that, in terms of the nature of work, when 60% of cement was replaced with SCM, the initial setting time was increased by 40–70 min. The values of the ratio of the initial to final setting time (I/F ratio) are equivalent when the I/F values of PCE and SNF are at W/B = 0.27 and 0.35, and at the lowest W/B (0.21) in this study, the I/F calculation result was the difference between PCE and MLS. The I/F value is equal, which means that when the W/B is low, PCE and MLS have the same impact on workability, and as W/B increases, the impact of PCE and SNF is similar. In terms of compressive strength, W/B = 0.21. The 1-day curing age of PCE was compared with the 91-day curing age, and it was found that at high volumes of replacement, increasing GGBFS by 10% can increase the strength by 37%. Using the ultrasonic wave velocity as the input value and the compressive strength result as the output value, the MATLAB back propagation neural network prediction model was carried out. The best correlation coefficient R value of MLS was 0.97, and the mean squared error was 2.21, which has good prediction ability.

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