Prediction of optimal ranges of mix ratio of self-compacting mortars (SCMs) based on response surface method (RSM)

The influences of constituents on the rheological and mechanical properties of self-compacting mortars and efficient mix proportion optimization are two key issues in the design of self-compacting mortars (SCMs). Due to the lack of specifications of the mix design, a wider range of variable optimization can provide great feasibility to meet wider requirements of rheological and hardening properties of SCMs. In this study, response surface methodology (RSM) was adopted to systematically investigate on the independent and interactive effects of fly ash (FA), silica fume (SF), sand-binder ratio (s/b) and water-binder ratio (w/b) on the rheological and mechanical properties of SCMs. A total of 30 SCMs mixes were formulated by using the Central Composite Design (CCD) method to determine the contents of the four variables at 5 levels, e.g., FA range from 0 to 30%, SF ranged from 0 to 16%, sand-binder ratio varied from 1.0 to 1.4 and water-binder ratio from 0.34 to 0.38. The results showed that these four variables and their partial interactions have significant influences on the rheological and mechanical properties of SCMs, especially SF and sand-to-binder ratio. The prediction of the optimal range of variables in multi-response optimization was developed and validated. The result showed that the contents of FA, SF, s/b, w/b ranging in 10–20%, 6–10%, 1.1–1.2, 0.35–0.36 respectively leaded a better workability and greater compressive strength of SCMs.