CONSIDERATION IN QUALITY VARIATIONS OF PLYWOOD FOR CONCRETE FORMS BY REUSE AND FINISH OF CONCRETE SURFACE USING REUSED PLYWOOD

Abstract

 In recent years, although the form materials and construction methods have been diversified into various kinds, conventional formwork method using plywood for concrete on sheathing plates is the most common construction. The conventional form is temporary structural object until the concrete hardened. Additionally, in order to formwork need economy and rationality, plywood reused as much as possible with the conventional formwork. However, influence of form reuse on the quality of plywood and the finish of concrete surface using those reused plywood, has never been studied.

 The purpose of this study is to clarify the quality variation of plywood by form reuse and the finish of concrete surface using reused plywood. In this paper, on the basis of the experimental results, the influence of reuses on the quality of plywood, such as bending strength, bending Young’s modulus, and surface roughness, were examined. Also, the influence of reuses on the finish of concrete surface, such as surface roughness, glossiness, color unevenness, and water absorption, were examined.

 Experiments in this paper, the influence of up to 10 reuses of two types of plywood uncoated plywood and coated plywood was investigated. Furthermore, as an influence of work of the formwork in construction site, factors of this experiment is included the influence of with or without water immersion of plywood by rainwater and the influence of with or without application of release agent.

 The tendency of the influence by reuse of plywood based on experiment are as follows.

 (1) The bending strength and bending Young’s modulus of plywood decreased with reuse, especially uncoated plywood showed noticeable.

 (2) In case of bending strength and bending Young’s modulus of uncoated plywood, the decreasing tendency with reuse is reduced by applying a release agent.

 (3) Although the surface roughness of unpainted plywood is increased significantly with one reusing, thereafter does not variation so much. In case of coated plywood, the surface roughness of plywood is about the same as unused plywood even at time 10 reuses.

 (4) In case of surface roughness of uncoated plywood, the increasing tendency with reuse becomes noticeable when change in moisture content by rainwater, and the increasing tendency with reuse is reduced by applying a release agent.

 (5) The surface roughness of concrete increased with reuse, especially noticeable in concrete using uncoated plywood.

 (6) In case of surface roughness of concrete using uncoated plywood, the increasing tendency with reuse becomes noticeable when change in moisture content by rainwater, and the increasing tendency with reuse is reduced by applying a release agent.

 (7) Although the glossiness of concrete using coated plywood is decreased linearly until at time around 7 reuses, thereafter does not variation so much. In case of concrete using uncoated plywood, the glossiness of concrete surface is less variation with reuse.

 (8) For both types of plywood, the color unevenness and water absorption of concrete surface is increased with reuse.