Potential of salvaged steel fibers for reinforcement of unfired earth blocks

Used tires are dumped in the open air and consequently become a serious environmental concern in Cameroon. To find ways to recycle this waste material, a research project aimed at investigating the mechanical properties of unfired bricks reinforced with salvaged steel fibers from used tires was undertaken at the University of Yaoundé I, Cameroon. Tests of tensile strength were initially carried out using 6% cement to soil ratio to determine the critical fiber length and optimum fiber content. Mechanical properties, namely unconfined compressive strength, flexural strength, and tensile strength tests were evaluated afterwards by means of varying cement to soil ratio together with optimum fiber length and content.Satisfactory results were obtained regarding the bond between recycled steel fibers and soil–cement. Data of tensile strength recorded showed that the critical fiber length and optimum fiber content were respectively 35 mm and 2% by volume. It was also observed that mechanical properties evaluated over time are unaffected by the presence of optimum fiber content despite the random distribution of the latter. Further analysis of experimental results led to the conclusion that steel fibers act like springs by helping the masonry unit absorb a substantial plastic energy and resist large deformation without full disintegration.

► Fibers shorter than critical length induce tensile stress below fiber tensile strength.
► Effect of fibers on the soil matrix is not fully achieved until cracking has occurred.
► Ductility of the block improves in all directions because of fiber distribution.