Characterization methods for polypropylene fibre-reinforced cement mortar composites:Licentiate thesis

An interdisciplinary, horizontal approach was adopted to arrive at a set of physico-chemical and mechanical methods which will provide tools for a general material characterization of polypropylene fibre-reinforced cement mortar composites with relatively low fibre contents (0.3 - 2.5% by volume). Concrete, cement mortar and their constituents as well as polypropylene fibre processing and the main properties of fibres are outlined. Principles of mechanical modelling of fibre concrete and mortar are discussed. A surface chemical approach is also presented. Test methods for studying polypropylene fibre mortar composites are outlined both theoretically and experimentally, especially in regard to frost and fire resistance, mechanical properties and microstructure. For comparison purposes the same mortar composition was used throughout the study. Methods for identification and characterization of fibres are also discussed. Comparative tests were made of the way in which polypropylene fibres with different surface characteristics affect the properties of this mortar. The polypropylene fibres were commercial fibres from film and special fibres from three-layer films the outer layers of which had been modified with functionalized polyolefins. This study shows that we cannot characterize a complex material like fibre concrete solely on the basis of one or two types of mechanical test, or just by considering the effects at the fibre/matrix interface. Many tests must be performed to ensure the functional properties of a fibre concrete product that are relevant to its end use. These include at least strength, durability, fire resistance, permeability, insulation properties, and appearance. Naturally, these property demands should be clearly defined according to the specified end use. Polypropylene fibres in low dosages (0.1 - 1% by volume) improve the cracking behaviour of mortar by reducing crack widths caused by drying shrinkage. Polypropylene fibres in higher dosages (1 - 2% up to 10% by volume) increase the flexural toughness of mortar composite. With tailoring of the fibre surface properties and the utilization of special concrete compositions and production techniques, these fibres provide interesting possibilities for the manufacture of precast fibre concrete elements and products