Keywords: non-destructive test, durability of concrete structures, cover-concrete quality, permeability, water absorption, visual observation, water intentional spraying test.

To realize the construction of a concrete structure with excellent durability, from the viewpoint of concrete quality, it is necessary to provide a simple and cost-effective test method that can be used by practitioners. We have already proposed a water intentional spraying test (WIST), a simple non-destructive test method for coverconcrete quality. Although the WIST has been validated, applicable measurement sites have been limited to vertical members such as concrete walls. In this study, we have described a new measurement procedure and evaluation index for applying WIST to horizontal members such as concrete slabs. In the proposed method, a small amount of water is sprayed on the surface of the horizontal member. Immediately after the water spray, the gloss increases on the concrete surface where there are remains of water, and it gradually disappears due to water absorption. The presence or absence and disappearance of gloss is visually confirmed. The value of the gloss retention time after watering obtained visually is reduced for low quality concrete. In particular, the reduction of the gloss retention time due to early demolding is remarkable. The gloss retention time on the underside surface of the specimen had a variation coefficient of approximately 30% depending on the shape of the specimen. This study suggests that the weight change of the specimen increases in proportion to the height-to-depth ratio of the specimen. This is considered to be one of the causes for the error in the measurement result of the cover-concrete quality due to the scale and position of the measurement member. When applying non-destructive evaluation of cover-concrete quality to structures, it is necessary to assume that the coefficient of variation of measured values reaches approximately 30%. In the case where the gloss may disappear in several seconds, the coefficient of variation increased, however, the author confirmed the possibility of evaluating the cover-concrete quality using the gloss retention time. In this study, the author has proposed a simple non-destructive test method for cover-concrete quality that used the gloss retention time rT as an evaluation index. In the evaluation of the cover-concrete quality based on the rT, differences in dimensions and shapes of concrete members affect measured value of rT. However, the fluctuations of these measured values don’t hinder the classification of concrete of extremely poor quality. Quality assessment using rT contribute to the construction of highly durable structures and the reduction of maintenance costs.

download the full-text of this paper (PDF, 6 pages, 267 Kb)

go to the previous paper
go to the next paper
return to the table of contents
return to the volume description