Use of magnesia sand for optimal design of high performance magnesium potassium phosphate cement mortar

Magnesium potassium phosphate cement (MKPC) mortar as a construction repair material has been studied and applied for several years. In this paper, reactive magnesia sand is employed to replace conventional inert quartz sand as the fine aggregate of MKPC mortar, to adjust the M/P (i.e. MgO-to-KH2PO4) molar ratio of cement paste during mortar formation, as well as to improve the mortar performance though strengthening the bonding capacity of the interfacial transition zone (ITZ) (i.e. the paste to aggregate interface). Experimental results showed that the compressive strength of the MKPC mortar with reactive magnesia sands could achieve a mean value of 36.65 MPa at 12 h, and outperformed about 27.30% than that with inert quartz sand at 28-day. The interfacial transition zone (ITZ) development in the MKPC mortar with magnesia sands was investigated using the on-site X-ray computed tomography (CT). The failure modes of specimens subjected to uniaxial compression were analyzed and visualized by means of image processing technique. In addition, the chemical interaction between the paste and the aggregate was theoretically and experimentally analyzed, explaining well the excellent volume stability of the MKPC mortar with reactive magnesia sands.