Title:
Contribution of fibers to Crack Reduction of Cement Composites During the Initial and Final Setting Period
Author(s):
P. Balaguru
Publication:
Materials Journal
Volume:
91
Issue:
3
Appears on pages(s):
280-288
Keywords:
cements; cracking (fracturing); crack width and spacing; fibers; mix proportioning; setting (hardening); shrinkage; synthetic fibers; Materials Research
DOI:
10.14359/4334
Date:
5/1/1994
Abstract:
The contribution of steel, synthetic, and cellulose fibers to the shrinkage-crack reduction potential of cement composites during the initial and final setting periods and its evaluation are presented. The primary variables of the investigation were fiber type, matrix composition, and test methods. Fiber type consisted of steel and nonmetallic (synthetic and cellulose) fibers with lengths varying from a fraction of an inch to 2.4 in. (mm to 60 mm). For steel fibers, three fiber lengths of 1.2, 2.0, and 2.4 in. (30, 50, and 60 mm) were investigated at volume contents of 75 and 100 lb/yd 3 (45 and 60 kg/m 3). The nonmetallic fibers were made of cellulose, nylon, polyethylene, polypropylene, or polyester. Cellulose and polyethylene fibers were in pulp form (microfibers) with lengths in the order of a few millimeters and diameters in microns. Polypropylene fibers were evaluated both in pulp form and in relatively longer lengths of 0.75 in. (19 mm). The longer polypropylene fibers were fibrillated. Nylon and polyester fibers were made of single filaments with lengths varying from 0.75 to 2.0 in. (19 to 50 mm). The matrix consisted of cement mortar with various cement-sand ratios, concrete containing coarse aggregates, and lightweight concrete. Regarding test methods, the primary variables were specimen thickness and plan dimensions of the test panels. The results indicate that both steel and synthetic fibers make a definite contribution to shrinkage-crack reduction during the initial and final setting periods. The microfibers (pulp form) are more effective in rich cement mortars, whereas the longer fibers [0.75 in. (19 mm)] are more effective in lean mortars and concrete. None of the test methods available in the published literature are suitable for standardization in their present form. The primary drawbacks are attempting to induce cracks in plain matrixes under normal conditions in terms of temperature, humidity, and wind velocity, and possible errors that could occur in the measurement of crack area.