Performance and durability of fly ash based geopolymer as concrete repair material

Deterioration of concrete structures made of Ordinary Portland Cement is inevitable, and this requires repair of replacement materials. A good and high adhesive repair material is very important so as to ascertain the safety of the damaged concrete structures. The existing repair materials, especially those that applied Ordinary Portland Cement (OPC), appear to require a certain curing condition, in which prior studies have also revealed a weak link in the bonding strength within the repaired structures. With that, repair and rehabilitation works have emerged to be significant fields, particularly in developing a new repair material. The implementation of geopolymer binder is the subject of interest in the attempt of evaluating and developing new genres of repair materials. In this study, geopolymer that is made from the activation of aluminosilicate source material such as fly ash in alkali medium was prepared and appears to promote higher strength and durability when applied as concrete repair materials. This study incorporated several essential processes that began with sample characterization of raw material. It consisted of chemical composition characterization, microstructure characterization, and phase characterization, which contributed to strength development of the geopolymer. A number of physical and mechanical testing, such as density, setting time, workability, compressive strength, and bonding strength between geopolymer repair material and concrete substrate had been examined in order to evaluate the performance of geopolymer as a repair material in paste and mortar forms. After that, the various surface preparations of substrates were explored to determine the impact of surface roughness on the bonding strength between geopolymer and concrete substrate. Based on the laboratory outcomes, fly ash based geopolymer seemed to possess an exceptional potential for application as repair material. Fly ash, which contains significant amounts of silica (38.4%), alumina (14.5%), iron (19.57%), and calcium (18.4%), emerged as a suitable source material to produce geopolymer repair material as it displayed the desirable strength with cured only at ambient temperature (24 oC ± 2). Determination of the optimum alkali medium at 12 M exhibited optimum compressive strength (57.4 MPa) and optimum bonding strength (10.5 MPa) for fly ash based geopolymer. The result from this experimental study has revealed that the use of geopolymer as repair material is chemically bond to the OPC based concrete substrate. The study of geopolymer with varied binders to the sand ratio at 1:2 revealed the optimum compressive strength and bonding strength at 56.39 MPa and 12 MPa, apart from attaining the desired workability as repair material. This result meets the requirement stipulated by the Malaysian Public and Works Department (PWD) in terms of strength, setting time, and workability. Geopolymer repair material which is based on fly ash shows a good and strong bonding strength through slant shear test as high as 12 MPa and very fast setting make itu suitable for use as concrete repair material.