Experimental investigation on characteristics of bughole generation based on a visualization test for various concretes

This study focuses on fundamental properties of bugholes generated from concreting. Bughole, a surface imperfection of concrete, occurs randomly and remains on hardened concrete surface. Bugholes are often observed on concrete having a negative angle, such as sidewall of tunnel lining concrete. The bughole problem may be significantly related to appearance (surface quality) of tunnel lining concrete rather than strength and durability. The authors reported characteristics and a reducing method of bugholes in our previous study. The previous investigation focused on a concrete mixture used in tunnel lining. To understand the properties of bugholes, various concretes should be tested as well as the tunnel lining concrete. The present study uses a transparent acryl form to observe bugholes generated from fresh concrete, and employs a steel form to examine bugholes on hardened concrete. The remarkable observations are (1) quantity of bugholes gradually decreases in accordance with higher slump and lower water-cement ratio; (2) unfilled-concrete (void) contributes to increase of large bugholes (2 mm or greater); (3) quantity of bugholes (2-5 mm) are related to unit weight of each components except for coarse aggregate. © 2017 The Society of Materials Science, Japan.