Self-healing concrete using fly ash, macro synthetic fibres and recycled aggregates

The development of cracks in concrete can reduce its durability and service life, causing its steel rebar to be exposed to harmful substances from the external environment, eventually leading to strength loss of concrete and high repair costs. Self-healing technique can eradicate the crack spontaneously, likely replacing or decreasing maintenance and repair costs. Self-healing concrete using low calcium Fly Ash with recycled Aggregate (RCA) and macro synthetic fibers is a novel approach to increase durability and serviceability, decreasing repair and maintenance costs. This research intends to create self-healing concrete using different volumes of Fly Ash with partially replaced RCA and macro synthetic fibers and to study the autogenous behavior of Fly Ash. Various volumes of Fly Ash 35%,45%, and 60%, respectively, were used. In addition, the coarse Aggregate was partially replaced with RCA. The results show that replacing RCA with natural Aggregate and using Fly Ash significantly decreased the strength of concrete. Thus, to increase the mechanical properties of concrete macro synthetic fibers were used at two percentages 5% and 1%, respectively. After that, concrete samples were cracked after 28 days of curing, and after 5 weeks, they were cured for autogenous self-healing. The results showed that using Fly Ash from 45-50% gave the optimum healing to cracks in 5 weeks and the use of macro synthetic fibers at 0.5% caused the best improvement in mechanical properties of concrete with good workability.