Evaluation of interfacial strength between hydrating cement paste and epoxy coating

Abstract

The objective of this work is to determine the interfacial strength between cement paste and epoxy, coated at the different instant of time during the hydration. The factors influencing the magnitude of interfacial adhesive strength were also studied. To pursue this, the interfacial adhesive strength between cement paste and epoxy coated at different days of hydration was determined by performing macro-mechanical experiments such as slant shear and pull-off adhesion test. The various instant of hydration when epoxy was coated are 2, 7, 14, 21, and 28 days from the point of initiation of hydration. The possible influencing factors considered were water-cement ratio, curing time, and thickness of the coating. Results of macro-mechanical tests show that the average interfacial adhesive strength between cement paste and the epoxy coating was in the same range, irrespective of the instant of coating. Although the higher surface energy and work of adhesion should result in a higher interfacial strength for epoxy coated on 2nd day, the measured value of interfacial strength, however, did not show such. One of the possible reasons why interfacial strength of epoxy coated on the 2nd day is similar to 28th day coating in spite of higher surface energy and work of adhesion, is the presence of the larger amount of surface water during the earlier days. The effect of this excess water balances out the contributory effect of the physical interactions and mechanical interlocking. From the parametric study, it was observed that the factors considered in the present study play a major role, particularly when coated during the early days of hydration.