Properties of epoxy polymer concrete matrix: Effect of resin-to-filler ratio and determination of optimal mix for composite railway sleepers

The lack of knowledge of the behaviour of an epoxy polymer matrix has become a challenging issue for the design of a serviceable, durable and economic matrix. This study investigated the effect of the resin-to-filler ratio on the thermal, physical, mechanical and durability properties of polymer matrices composed with epoxy resin and light weight filler materials. This ratio was considered the experimental variable on which the properties of a polymer matrix are primarily dependent. The control mix was composed of 100% resin to which an amount of filler material of up to 60% of its volume was added in increment of 10%. No mix with more than 60% filler (that is, one containing 40% resin) was considered because it would not be a workable mix when prepared. A matrix’s fundamental properties, including its generation of heat during mixing and glass transition temperature (thermal), density and porosity (physical), flexural and compressive behaviour (mechanical) and the effect of ultraviolet radiation (durability) were investigated. The results showed that, although adding a filler to the resin could improve the matrices thermal and durability properties as well as reduces its cost, there was a consequent decrease in its physical and mechanical properties. In maintaining a good balance among thermal, physical, mechanical and durability properties and cost, it was observed that mixes containing fillers from 30% to 50% could meet the requirements for coating of composite railway sleepers. Therefore, to select the most suitable one from the range of acceptable mixes an Analytic Hierarchy Process (AHP) was applied. The results from AHP showed that the 30% filler mix was the optimal one when priority was to obtain mechanical properties. However, if the cost of the matrix was considered the most important criterion for selecting the optimal mix, the mix containing 50% filler was the best choice. If durability was the priority, it was suggested that either a 30% or 50% filler mix be used depending on the relative importance of the mechanical properties and cost factors.