Fibrillated polyalkene films in cement.

A review is made of existing theories for predicting the tensile stress-strain behaviour and the mechanisms of fibre-matrix stress transfer for fibre reinforced cements. The applicability of the inherent assumptions in the theories to practical fibre cements and polyalkene cements in particular is discussed. A description is given of the structure, mechanical properties and production techniques of fibrillated polyalkene films in order that their properties may be related to those of the composites. Five types of fibrillated polyalkene film and a monofilament were incorporated in a high strength cement based matrix. The general composite tensile behaviour was examined with particular reference to the "first cracking" strain of the composite and the fibre-matrix stress transfer mechanisms. The films were mainly opened to four times their unopened width but two composites were made with unopened film to increase the axial alignment of the fibrils. The majority of testing was after 28 days water curing with two composites also being cured for 1 year. Composites were monitored for load,strain and acoustic emission measurements. A small number pull out tests were performed on narrow unfibrillated strips of film. It is shown that the general behaviour of the composite complies with existing theoretical predictions. However, a new model is proposed for predicting the "first cracking" strain of the matrix. The fundamental mechanism of fibre-matrix stress transfer is attributed to misfit resulting from the non-uniform cross section of the individual fibrils. The implications of this work are assessed and a tentative film specification is proposed for the production of improved composites.