Abstract
For the purpose of developing the early strength of concrete, accelerated curings such as steam and autoclave curings are widely applied to the manufacture of precast concrete products. The uses of polymer-modified mortar and concrete are also expected for precast products. The study of hardener-free epoxy-modified mortars using bisphenol F epoxy resin with low viscosity has not been examined in detail. It has a merit in workability than that of the epoxy-modified mortars using bisphenol A epoxy resin with high viscosity. The purpose of this study is to clarify the mechanism of the strength development through dry curing of steam cured and combined steam/heat cured hardener-free epoxy-modified mortars. As a result, the flexural, compressive and tensile strengths of accelerated-cured hardener-free epoxy-modified mortars are improved with an increase in the polymer-cement ratio, and are considerably larger than that of unmodified mortar. The strengths of initial steam cured hardener-free epoxy-modified mortars are somewhat inferior to that of initial combined steam/heat cured hardener-free epoxy-modified mortars. However, the extent of the strength improvement with additional dry curing period is marked in steam cured mortars rather than combined steam/heat cured mortars. Accordingly, it is judged that initial steam cured hardener-free epoxy-modified mortar is suitable for precast concrete products, in consideration of long-term strength development and economic perspective. From a practical point of view, the optimal accelerated curing for the epoxy-modified mortars is recommended as follows: 1-d moist [$20^{\circ}C$, 90%(RH)]+1-d steam($90^{\circ}C$)+1-d heat($100^{\circ}C$) curing.
