Free and restrained plastic shrinkage of cementitious materials made of engineered kraft pulp fibres

Abstract

Early age cracks caused by plastic shrinkage of cementitious materials is a major problem in concrete structures. These cracks allow ingress of water, chlorides, and other deleterious materials and minerals into the material, causing early deterioration and damage to structures. Recently, two low-cost special Kraft pulp fibres have been designed and developed for reinforcement in cementitious materials. These fibres have never been used in any previous cementitious materials. Softwood fibres are engineered by extreme refinement followed by specific modification to produce these two special fibres. The modifications are done to create numerous tiny fibrils on the surface of the fibres to help increase the bond between the fibres and the cement matrix. These fibres are called mechanically modified fibre and chemically treated fibre and they are not commercially available. The expectation is that these fibres would be successful in eliminating cracks and reducing the strain induced by plastic shrinkage in cementitious materials. Hence, this study undertook both restrained and free plastic shrinkage tests on various fibre-reinforced composites made of these two engineered fibres. Furthermore, the effect of fibre type and fibre content on compressive strength was determined. The study found that these two engineered pulp fibres are highly effective in controlling both cracks and strains induced by plastic shrinkage.