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

• Pore structure of MKPC paste is investigated using mercury intrusion porosimetry.
• An optimum magnesia-to-phosphate molar ratio exists and gives the best properties.
• Compressive strength of MKPC paste is inversely proportional to its porosity.
• Permeability of MKPC paste is directly proportional to a permeability determiner.

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 dc) of MKPC paste are developed. The compressive strength is inversely proportional to ϕ  , and the intrinsic permeability is directly proportional to dc2ϕ.

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