Laboratory evaluation of magnesium phosphate cement paste and mortar for rapid repair of cement concrete pavement

• Pretreatment of borax and magnesium phosphate cement.
• Combination of borax, fly ash and aluminate cement as retarders.
• Replacement of monohydrogen phosphate cement to balance between setting time and strength.
• Enhancement of water resistance and toughness by crumb rubber.
• Enhancement of strength and toughness by silica sol.

This study investigated the various aspects of magnesium phosphate cement (MPC) paste and mortar, both of which were made after pulverization of potassium dihydrogen phosphate and borax. Borax and fly ash could remarkably delay MPC paste setting time but not long enough to accommodate the operational needs in some occasions. On the other hand, high dosage of aluminate cement could result in significant increase in setting time, but it reduced strength as well. The result showed that the substitution of monohydrogen phosphate for potassium dihydrogen phosphate in MPC paste could strike a balance between strength and extended setting time. Blending MPC paste with 5% crumb rubber not only significantly improved water resistance but also reduced brittleness as indicated by a decreased compressive–flexural strength ratio. Laboratory testing results of MPC mortars were presented regarding fluidity, dry shrinkage, bonding strength and abrasion resistance. The results demonstrated that the MPC mortar exhibited a much lower dry shrinkage of 25.6 millionths than that of 200–1000 millionths in common concrete pavement, a desirable bonding strength (of 4.1 MPa) with the old pavement substrate, and a favorable abrasion resistance (with a mass loss of 2.45 kg per square meter). The field application case of the MPC patching material indicated desirable both for construction and quick opening to the traffic.