Effects of water content, magnesia-to-phosphate molar ratio and age on pore structure, strength and permeability of magnesium potassium phosphate cement paste

Abstract In this study, the pore structure of magnesium potassium phosphate cement paste is investigated using mercury intrusion porosimetry. Several mix proportions, obtained by changing the magnesia-to-phosphate molar ratio ( M / P ) and the water-to-cement mass ratio ( W / C ) of the material, are involved. It is found that lower W / C and longer material age make the porosity lower and the pore structure finer. When the W / C is kept constant, both porosity and critical pore diameter are not monotonic functions of M / P , but the M / P of 6 gives the lowest porosity and the smallest critical pore diameter. Also, the M / P of 6 shows the highest compressive strength and the lowest intrinsic permeability. Based on the experimental results, empirical models describing the relations between the properties and pore structure parameters (porosity ϕ and critical pore diameter d c ) of MKPC paste are developed. The compressive strength is inversely proportional to ϕ , and the intrinsic permeability is directly proportional to d c 2 ϕ .