Effect of recycled PET fibers inclusion on the shrinkage of adobe brick

In recent decades, the importance of sustainability and the use of recyclable materials have led to the development of numerous investigations related to natural materials linked to un-conventional technologies. Earthen materials construction, such as adobe, however, is both an ancient and sustainable technique, since it relies on locally found unfired soil, eliminating or greatly diminishing pollutants emission.  This paper aims to investigate the influence of recycled PET fibers (polyethylene terephthalate) on the shrinkage of adobe bricks. Specimens with dimensions 5 x 5 x 30 cm were used for shrinkage tests. A compressive strength test was also carried out to study the influence of recycled PET (R-PET) fiber on mechanical behaviour. Soil characterization by liquid limit, plastic limit, plasticity index, density and particle size distribution tests were performed. The natural soil was then mixed with other soil, rich in clay, allowing for two different mixes, both suitable for adobe mixes. Finally, R-PET fibers of 32 mm length and 14 μm diameter were added in the mixtures with 0.25% and 0.5% contents in order to verify the effectiveness of R-PET fibers on the shrinkage control of the material. Shrinkage tests showed the R-PET fiber had little influence on the mixture with lower clay content and a greater influence on the mixture with a higher clay content, reaching a reduction in shrinkage of up to 48%. Similar effect was observed regarding to compressive tests. The highest mechanical strength was reached in the specimen made of adobe with higher clay content and 0.5% R-PET fiber.