In order to control the reaction rate of magnesium potassium phosphate cement (MKPC) and to obtain a hardened material with good mechanical properties and prolonged setting time, sodium chloride was added as a set retarder. In addition to that, and for an economical construction material, this work focused on the combined effect of sodium chloride and magnesia characteristics in order to obtain the less calcined magnesia that gives with sodium chloride the desired material. The results showed

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... at sodium chloride can reduce the reaction heat release and delay the setting time. The addition of NaCl in MPKC pastes prepared with magnesia calcined at 800°C and 900°C has a little influence on the retarding of the reaction and the enhancement of the compressive strength. However, the significant retarding effect was obtained using magnesia calcined at temperatures higher than 1000°C. The testing results demonstrate that the best correlation between higher compressive strength and an adequate setting time was obtained using magnesia calcined at 1100°C. For this sort of magnesia, the compressive strength development was investigated and the possible retarding mechanism was discussed.