Hydration and Mechanical Property of the Coral Powder-Fly Ash-Portland Cement Ternary System

Abstract Many concrete materials are required during ongoing construction in islands and reefs. Using local material is one of the effective methods to solve the shortage of raw materials and save energy. It is proved that coral powder (CP) can be used to replace portland cement (PC) partially and cast concrete, but the excessive use of CP will lead to the loss of strength. In order to ensure the strength of the cement-based materials and utilize more CP, fly ash (FA) is introduced into the whole system in this study, aiming to improve the later strength by the pozzolanic reaction of FA. The hydration behavior and hydration products for the CP-FA-PC ternary system are investigated by using a hydration calorimeter and the X-ray diffraction technique. The mechanical properties of this ternary system with time are evaluated by measuring the compressive strength of PC mortar mixed with CP and FA. The obtained results show that the reaction of CP is a very slow and long-term process. CP reacts with hydrated calcium aluminate more easily than with tricalcium aluminate. The loss of strength of cement mortar made with CP can be mitigated by the addition of FA, especially at a later curing age. At 180 days, the compressive strength of the cement mortar with 15 % CP and 25 % FA can reach 52.5 MPa; thus, 40 % PC is saved, and carbon emission is largely reduced.