Title:
Shrinkage Cracking in Polyolefin Fiber-Reinforced Concrete
Author(s):
N. Banthia and C. Yan
Publication:
Materials Journal
Volume:
97
Issue:
4
Appears on pages(s):
432-437
Keywords:
crack; fiber-reinforced concrete; shrinkage.
DOI:
10.14359/7406
Date:
7/1/2000
Abstract:
The effectiveness of fibers in controlling plastic shrinkage and thermal cracking in cement-based materials is well recognized. For any cement-based composite, however, the type of fiber and its dimensions are the two most important factors controlling such cracking. In this investigation, four types of polyolefin fibers (Types 19/15, 25/15, 25/38, and 50/63, where in l/d, l is the length of the fiber and d is the equivalent diameter; Type 19/15, for example is 19 mm long and 0.15 mm in equivalent diameter) were investigated. A newly developed technique was employed for this purpose. In this technique, fiber-reinforced concrete to be tested is laid on top of a fully hardened base concrete that provides the bottom restraint and this results in cracking in the freshly placed overlay. Cracking in the overlay is then monitored as a function of time. It was noted that while the polyolefin fibers are generally effective in reducing the amount and size of the shrinkage cracking, the dimensions of the fiber have a decisive influence on the results. For example, crack widths that exceeded 1 mm in plain concrete specimens were reduced to less than 0.40 mm with 0.7% by volume of the 50/63 fiber, but were completely eliminated at the same volume fraction of Type 19/15 fiber. For a fiber, the specific fiber surface (a parameter defined as the fiber surface area in a unit volume of the composite) appears to be of critical importance. Along with a description of the test procedure, analysis scheme, and the results, this study also provides recommendations for future work.