Evaluation of the effect of concrete compositional changes and the use of ethyl-alcohol and biodegradable-oil-based release agents on the final surface appearance of self-compacting concrete precast elements

his paper investigates bughole minimization techniques in self-compacting concrete in a precast concrete plant in Brazil. Specifically, the objective of this study was to improve the final surface appearance of self-compacting concrete precast elements with respect to the presence of bugholes. Bugholes are imperfections that appear on a concrete surface after demoulding. The experimental study was based on the modification of concrete composition and the use of two types of release agents. In particular, ethyl-alcohol and biodegradable-oil-based admixtures were applied on laminated plywood formwork. By using a specific image analysis method, the concrete surface was analyzed using digital images taken from concrete board plates with dimensions of 1.00 x 0.30 x 0.08 m. The results indicate that a reduction in the concrete shear stress ratio contributed to reduce the percentage of bugholes, whereas no significant difference in the concrete surface appearance was observed as a function of the investigated release agents. (C) 2013 Elsevier Ltd. All rights reserved.