Long-term performance of magnesium phosphate cement concrete prepared in the winter

Previous studies have established the strength development of magnesium ammonium phosphate cement (MAPC) concrete and magnesium potassium phosphate cement (MKPC) concrete at sub-zero temperatures. However, the long-term performance of these magnesium phosphate cement (MPC) concrete, prepared at low temperatures and exposed to complex environmental effects of cold regions, remains underexplored. This study monitored the mechanical properties and durability of MAPC concrete at different ages for 520 d, which fully demonstrated the feasibility of MAPC concrete for winter construction in cold regions. At the age of 520 d, MAPC concrete had a compressive strength of over 65 MPa and excellent resistance to chloride ion penetration with a measured charge of 129.1 C, and could endure more than 250 rapid freeze-thaw cycles. In contrast, MKPC concrete exhibited significant disadvantages in terms of freeze-thaw resistance during natural freeze-thaw cycles. No expansive substances or damage were found in MKPC concrete that was prepared at low temperatures and subsequently experienced temperature increases along with accelerated hydration. The relatively poor freeze-thaw resistance of MKPC concrete could be attributed to a combination of factors including larger capillary size and volume, reduced air content, greater air-void spacing factor, wider and weaker interface zone between cement mortar and coarse aggregate.