Page 405 - Handbook of Thermal Analysis of Construction Materials

Section 7.0 - Magnesia Phosphate Cement Binders 383

with a decrease in the polyphosphate content. At 28 days, there is a small
increase in the compressive strength at higher polyphosphate contents. For
polyphosphate contents < 58%, the compressive strength exceeds 8 MPa
after 2 hours at ambient temperature and, at 7 days, at least 75% of the 28
day strength was achieved. The setting time increases as the polyphosphate
content increases.

Figure 9. Compressive strength vs polyphosphate content of the ammonium phosphate
solution used for several phosphate cement concretes. [66]

The effect of water content (of mortars containing silica sand) on
elastic modulus, flexural strength, and compressive strength is evident in
Figs. 10 and 11. [63] The net effect is a decrease in modulus with water
content at each test age. Decreases of 80% in flexural strength and
compressive strength occurred at a water content of 12% at 7 days. It was
concluded that the crystal structure and morphology of the binder was
highly sensitive to the water content. It was confirmed that an increase in
the quantity of ammonium phosphate hexahydrate, MgNH PO •6H O,
4
2
4
occurred with an increase in water content from 5 to 8%. Reaction products