Early age plastic shrinkage cracks can reduce the durability of concrete slabs by creating entry surfaces for environmental attack, in particular in hot and windy environments. The elimination of such cracks is essential for durable and sustainable concrete solutions.This paper investigates parametrically the effect of manufactured steel fibres (MSF) and recycled tyre steel fibres (RTSF) on restraining plastic shrinkage and micro cracks at different dosages (10, 20, and 30 kg/m 3 ). The environmental conditions, evaporation rate and water bleeding during the plastic shrinkage tests carried out in a specially designed chamber were controlled and measured according to ASTM C1579, 2006. Various environmental conditions were examined and their impact was assessed on compressive strength and crack potential. A digital image analysis technique was used to measure length, width, and area of the crack on the exposed surface to gain additional insights into crack behaviour.The results show a slight early age (one-day) increase in compressive strength for the cubes inside the chamber that were exposed to the various environmental conditions, mostly as a result of higher temperatures. Through the use of the crack reduction ratio (CRR), both RTSF and MSF are shown to be successful in controlling plastic shrinkage and micro cracks, with the RTSF being superior due to the fact that they are better distributed in the concrete volume. RTSF 30 kg/m 3 was most effective in preventing crack development in most environments or restraining cracks in extremely harsh environments. The adoption of these results will lead to more sustainable concrete slabs in the harsher environmental conditions created by climate change.
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