Until now, the use of untreated polyester fibres in concrete has been delayed because these fibres are not alkali-resistant. To understand the fundamental mecanisms of degradation of such fibres in a cementitious matrix, some physico-chemical experimental techniques (SEM - EDAX - I.R. Spectrometry) associated with flexural tests were used. The degradation of polyester is caused by a saponification reaction and the toughness of the fibre-reinforced composite is quickly reduced.
To prevent such a damage and develop tougher composites, the authors modified the cementitious matrix. Adding burnt clays (kaolin and montmorillonite) to OPC enabled the polyester fibre to withstand the alkaline attack.