Epoxy resin without any hardener can harden in the presence of hydroxide ions in cement mortars and concretes at ambient temperature. However, the hardening rate of the Hardener-Free epoxy resin at ambient temperature is slow, and the acceleration of the hardening reaction of the Hardener-Free epoxy resin is requested. Also, wood tar of wood by-product is produced in the process of refining charcoal. But, people do not have any way to use this product. Therefore, wood tar is not used but just destroyed. Then wood tar is known as a kind of material that contains many phenol. Polyamine is often used as a hardener of epoxy resin. Polyamide, acid anhydride, and phenolic are also used as hardener. Wood tar which contains many phenol is expected to harden epoxy resin.
The purpose of this study is to clarify the function of wood tar as a hardener of epoxy resin and physical and durability properties of epoxy-modified mortar using wood tar. The epoxy-modified mortars are prepared with various polymer-binder ratios of 1∼5% and wood tar contents of 5∼20% for epoxy resin, and tested for hardening rate of epoxy resin, semi-adiabatic temperature, XRD analysis, flexural and compressive strengths, tensile strength, adhesion in tension, pore volume, drying shrinkage and freeze-thaw durability.
As a result, the hardening rate of the epoxy-modified mortars with wood tar is improved with a decrease in the polymer-binder ratio, and is considerably larger than that of the epoxy-modified mortar without wood tar. The compressive strength of the epoxy-modified mortar with wood tar is improved by increasing wood tar contents up to 10%. The compressive strength tends to decrease when the contents are over 15%. The flexural and tensile strengths of the epoxy-modified mortar with wood tar are improved with increasing wood tar contents up to 15%. And, irrespective of the polymer-binder ratio, all the strengths of the epoxy-modified mortars with wood tar are markedly improved at a wood tar content of 5%. Regardless of the polymer-binder ratio, the adhesion in tension of the epoxy-modified mortars reaches a maximum at a wood tar content of 5%. The improvement rates of adhesion in tension at polymer-binder ratios of 1, 3, and 5% are 15.38, 17.65 and 12.5% respectively when compared to the epoxy-modified mortars without wood tar. By contrast, the 28-day drying shrinkage of the epoxy-modified mortars with wood tar is smaller than that of the epoxy-modified mortars without wood tar, except for polymer-binder ratio of 5% and wood tar content of 20%. The drying shrinkage of the epoxy-modified mortars becomes remarkedly smaller than that of the unmodified mortars without wood tar and epoxy resin. Consequently, it is expected to strengthen the adhesion by dimensional stability of attached mortar using wood tar and epoxy resin in the initial setting of epoxy resin. In this study, the relative dynamic modulus of elasticity of the epoxy-modified mortars with wood tar is over 80%, therefore, the freeze-thaw durability is found to be superior.
Accordingly, it is judged that wood tar contents of 5~10% for epoxy resin are suitable for a hardener of epoxy-modified mortar. Also the epoxy-modified mortar using wood tar as a hardener can be suggested as a better type of attached mortar of ETHICS in terms of properties of hardening rate, adhesion in tension, drying shrinkage, and freeze-thaw durability.