Investigation and Optimisation of the Rheological Properties of Magnesium Potassium Phosphate Cement with Response Surface Methodology

Magnesium phosphate cement (MPC) is a promising alternative cement. However, the rheological property of this new binder is still to be explored. In this study, Response Surface Methodology (RSM) was adopted with Central Composite Design (CCD) to establish mathematical models describing the rheological characteristics of MPC in terms of initial mini slump (Y(1)), mini-slump loss (Y(2)), yield stress (Y(3)) and plastic viscosity (Y(4)), as a function of three independent variables, namely, water-to-solid ratio (W/S ratio, X(1)), MgO to MKP ratio (M/P ratio, X(2)) and borax dosage (X(3)). The results show that the M/P ratio and borax dosage could significantly affect the yield stress and mini-slump loss of MPC, while the W/S ratio was the significant coefficient influencing plastic viscosity and initial mini slump. The numerical optimised values of X(1), X(2) and X(3) were 0.280, 7.528 and 0.170, respectively, and an MPC paste with desirable rheological characteristics (Y(1) 161.858 mm, Y(2) 11.282, Y(3) 0.680 Pa, Y(4) 0.263 Pa·s) with the highest desirability of 0.867 can be obtained.