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The bulk of the paper deals with a comparison of the flexural performance of 102-mm (4-in.)-square standard molded specimens with corresponding specimens of the same size produced either by sawing the bottom (tension) surface of a 102 by 152-mm (4 by 6-in.) cross section or by sawing the bottom and sides of a 152 by 152 mm (6 by 6-in.) cross section. The performance of plain concrete is discussed in terms of its flexural strength under third-point loading [ASTM Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading) (C 78)]. The conclusion is that sawing need not adversely affect the measured strength when done carefully with proper equipment. The performance of fiber-reinforced concrete is discussed in terms of changes in first-crack strength and toughness parameters defined according to ASTM Test Method for Flexural Toughness and First-Crack Strength of Fiber-Reinforced Concrete (Using Beam with Third Point Loading) (C 1018). The majority of the results deal with changes in those parameters that are associated with differences in fiber alignment between the molded and sawed specimens. The results of two other small studies involving differences in fiber alignment are also included. In the first, alignment is varied by inserting steel plates in the freshly mixed concrete during consolidation, and in the second by using the same length of fiber in 102-mm (4-in.) and 152-mm (6-in.) cross sections. The conclusion is that preferential fiber alignment by the mold surfaces can increase first-crack strength and toughness indices. To avoid undue influence of fiber alignment in small specimens on flexural test data determined in accordance with Method C 1018, the ratio of minimum specimen cross section to fiber length should not be less than 3.0, except perhaps when strict compliance with this criterion means using specimens larger than 152 mm (6 in.) square.
Professor of Civil Engineering, University of Calgary, Alberta,
Stock #: CCA10098J