Effect of Water on Strength Development of Cold Setting Epoxy Resins

Abstract

The bond strength development of epoxy resins was investigated by means of the shear and tensile bond strength methods. All the experiments were conducted in a low temperature laboratory controlled, at 4°C, 70per cent R. H.Firstly, the shear bond strength method of JIS K 6801 using birch timber of edge grain was applied. The moisture content of the adherent was of 6 kinds ranging from 10 to 106per cent, and the hardening time was of 4 kinds ranging from 1 to 8 days. The results were: (1) Water does not have so much deteriorating effect on the bond strength development of epoxy resins as on that of a polyvinyl acetate emulsion adhesive or an urea resin adhesive, (2) with epoxy resins a greater strength development is obtained at a smaller moisture content of wood, and (3) the usable range of moisture content of wood is under 32per cent with epoxy resin No. 1 and under 10per cent with epoxy resin No. 3, while epoxy resin No. 2 is not suitable for the purpose of adhesion of wood.Secondly, the tensile bond strength method using cement mortar briquette of ASTM C 190 was applied. The water content was of 5 kinds ranging from 3.2 to 8.0per cent, and the hardening time was of 3 kinds ranging from 1 to 4 days. The results were: (1) Water does not have so much deteriorating effect on the bond strength development of epoxy resins as on that of polyvinyl acetate solution adhesive, (2) with epoxy resins a greater strength development is obtained at a smaller water content of cement mortar, and (3) in case of the adhesion of finishing materials, the usable range of water content of cement mortar is under 8.0per cent with epoxy resins No. 1 or No. 2, while in case of the adhesion of structural materials, the usable range of water content of cement mortar is under 7.3per cent with No. 1 and under 3.2per cent with No. 2.