Cementitious Materials with low additions of waste GRP dust: effect on fresh and hardened properties

The viability of improving some durability aspects of cementitious materials through the addition of low dosages of very fine Glass Reinforced Plastic by-product is investigated. Replacing up to10% of sand volume with GRP dust delays the setting time of cement paste, but the delay can be partially recovered by adopting a previously thermal treated GRP dust. GRP dust increases workability deformability and total porosity, though with a smaller average radius, of cementitious materials and it significantly reduces the mechanical performance, when wet curing conditions are adopted. The risk of cracking induced by restrained shrinkage, capillary water absorption and resistance to efflorescence are better with waste GRP dust addition, especially when combined with silane. This decrease could involve enhanced durability of GRP mortars when used as supporting role.