Polypropylene-fibre-reinforced mortar mixes: Optimization to control plastic shrinkage

Volume changes which occur as a newly cast mortar is exposed to drying conditions will result in tensile stresses and lead to cracking of the mortar and concrete at early ages. Because of the growing interest in predicting the tensile shrinkage stresses that give rise to cracking in concrete, and the increasing use of polypropylene-fibre-reinforced cementitious materials, this research has been carried out to investigate how mix proportions influence the plastic shrinkage of polypropylene-fibre-reinforced mortars. This paper describes an experimental approach to the problem, which was intended to investigate the optimization of polypropylene-fibre-reinforced mortar mixes in order to minimize plastic shrinkage. The method selected is based on factorial design of experiments in which the parameters considered are the cement/sand and water/cement ratios and the polypropylene fibre content The test results indicate that polypropylene fibres added to mortars reduce the plastic shrinkage. As a first result, a mathematical equation which allows prediction of the plastic shrinkage as a function of the mix design is given. (C) 1997 Elsevier Science Limited.