Uso combinado de fibras de PVA e PP em matriz com fíler calcário e metacaulim: efeito nas propriedades de compósitos cimentícios engenheirados

Abstract

Engineered Cementitious Composites (ECC) are fiber-reinforced materials characterized by high ductility and strain-hardening behavior. The typical formulation of these composites employs fly ash as a partial cement replacement and 2% polyvinyl alcohol (PVA) fibers. However, the irregular availability of fly ash in some regions, combined with the high cost of PVA fibers, has driven the search for more viable and sustainable alternatives. In this context, this work aimed to investigate the impact of fully replacing fly ash with a combination of metakaolin and limestone filler in the ECC matrix, as well as to evaluate the effect of hybridizing PVA and polypropylene (PP) fibers on the composite's properties. The experimental program was developed in two stages: (1) formulation of matrices with full replacement of fly ash by metakaolin and limestone filler in proportions (1M1C and 1M2C), determining the superplasticizer content by mini-slump test; and (2) study of the hybridization of PVA and PP fibers at volumetric substitution levels of 0%, 25%, 50%, 75%, and 100% in two distinct matrices. The results showed that the matrix containing metakaolin and limestone filler (1M2C) exhibited workability and mechanical strength similar to the reference matrix (M45), making it a viable alternative. Fiber hybridization significantly affected the composite's behavior. The mixture with 1.5% PVA and 0.5% PP (1.5A_0.5P) offered the best balance between strength and ductility. Increasing the PP content reduced workability and flexural strength but increased deformation capacity. Microstructural analysis confirmed distinct failure mechanisms: rupture of PVA fibers and pull-out of PP fibers. The combined use of metakaolin and limestone filler proved viable for replacing fly ash in ECC production. Fiber hybridization allows the adjustment of ECC properties to meet specific application requirements.