Abstract: A process was developed for modification of the surface of poly(p-phenylene terephthalamide) fibres so that these fibres function as a reinforcing agent in a cold-molded cementitious composite at levels below 1% by weight. The surface modification treatment involves treatment of the fibres with aqueous alkaline hydroxide between 20.degree. C. and 95.degree. C. for between 20 minutes and 7 hours. The modified fibre is used to replace asbestos in the cementitious composite and it has been found that this improves both the green strength and the flexural strength of the autoclaved material.