Direct Tensile Strength Testing at 6 Hours of Fiber Reinforced Concrete Mortar Fractions


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Title: Direct Tensile Strength Testing at 6 Hours of Fiber Reinforced Concrete Mortar Fractions

Author(s): P. P. Kraai and G. L. Vondra

Publication: Special Publication

Volume: 155


Appears on pages(s): 153-170

Keywords: cements; comminution; cracking (fracturing); tensile strength; fiber reinforced concretes; mortars (material); polypropylene fibers; shrinkage; Materials Research

Date: 8/1/1995

The prime consideration in minimizing concrete cracks in the field is to maximize the early (six hour) tensile strength development in order to resist the volume reduction due to rapid water loss. This paper describes a test method, which simulates field conditions, for measuring direct tensilestrength soon after initial set at six hours. The prototype direct tensile test described presents an effort to quantify results as a measure of crack resistance. In this investigation, three different types of concrete mortar fractions were evaluated: 1) plain, 2) polypropylene fibers mixed in the batch, and 3) the same fiber bur roughened by intergrinding with cement for better mechanical bond. Results of tensile testing indicate that the process of intergrinding fibers with cement improves the tensile strength of similar mortar reinforced with smooth fibers by 63 percent. Comparing the ground fiber results to a plain (no fiber) mortar mixture shows almost three times higher direct tensile strength. Based on this exploratory work on early tensile strength testing, it appears to be a viable method to arrive at quantifiable values, which will lead to a better understanding of the concrete cracking phenomenon and its control.