Characterization of plastic shrinkage cracking in fiber reinforced concrete using image analysis and a modified Weibull function

Abstract

Numerous strategies have been advocated to reduce the potential for plastic shrinkage cracking in concrete through mixture proportioning, curing methods, or the use of fiber reinforcement. The effectiveness of each approach must be adequately quantified to determine whether the additional initial cost of each strategy is justified. The majority of current research to characterize plastic shrinkage cracking in concrete relies on manual crack observation and measurement that is typically only performed at select locations. These manual measurements of crack width may provide only limited information and may be subject to operator bias. This paper describes a systematic methodology that uses a semi-automated image analysis approach to accurately quantify the salient features of the plastic shrinkage crack patterns.A restrained slab specimen with a stress riser was used to amplify the potential for plastic shrinkage cracking. The specimens described in this paper were exposed to an accelerated drying environment for the first 6 hours after casting. At an age of 24 hours, the crack was assessed using a series of thirteen gray level images that were acquired along the crack path. Crack contours were extracted from these images using gray level intensity thresholding to create binary images. Subtracting the binary image from a uniformly spaced grid enabled the crack width to be determined at numerous locations. This image analysis technique permits the crack widths to be assessed rapidly at numerous locations without operator bias. The measured crack widths were statistically analyzed using a modified Weibull distribution function. This enabled the crack width distribution to be fully described using only two or three parameters. It is anticipated that this approach can be used to better quantify the effects of short randomly distributed fiber reinforcement on plastic shrinkage crack formation. RESUMF~

Characterisation of bending cracks in R/FRC using image analysis

“…This method is very straight forward and is especially attractive considering the matrix nature of the pixel arrangement within an image. However, as stated by Qi et al [24], when the direction of the crack changes, due to such factors as the presence of aggregates or fibres, and becomes nearly horizontal, the crack width, locally, would be greatly overestimated. In fact, as soon as the direction of the crack deviates from the global direction of propagation, the crack width measured perpendicularly to the global or local directions of propagation differs, a difference that rapidly increases as the angle of deviation increases.…”

“…For instance, Qi et al [24] used image analysis to measure the crack width of plastic shrinkage cracks formed along a stress raiser on slab specimens. They adopted an approach in which the crack width was determined to be the length of the segments resulting from subtracting a certain grid mask, consisting of equally spaced lines in the perpendicular direction of the stress raiser, from the binary image of the cracks.…”

“…[23,24]. This technique was used in this study to investigate the effect of adding fibre reinforcement at low dosages (<1% vol.)…”

Use of a New Approach (Design of Experiments Method) to Study Different Procedures to Avoid Plastic Shrinkage Cracking of Concrete in Hot Climates

“…Husain and Nijad (2001) have also reported that there is no long-term benefit, in terms of compressive strength, from using curing compounds. The inclusion of polypropylene fibers was also found to eliminate plastic shrinkage cracking in concrete specimens subjected to simulated hot weather (Al-Tayyib et al 1988;Banthia et al 1996;Qi et al 2003). …”

“…Another technique uses a small plate to measure free plastic shrinkage, with no embedment (Almusallam et al 1998;Al-Amoudi et al 2006;Bella et al 2009). A specific mold with embedding at the bottom has also been used (Qi et al 2003;Sivakumar & Santhanam 2007). These methods do not simulate stress fields that are produced in reality, as stated by Banthia (Banthia et al1996;, who has developed a method to produce realistic shrinkage conditions.…”