Avaliação do uso de blendas de cinza volante e metacaulinita nas propriedades físicas, mecânicas e desgaste por erosão de compósitos cimentícios do tipo strain hardening

Abstract

The erosion process has a significant influence on the loss of lifespan and destruction of buildings. The use of fiber reinforced cementitious composites, as concrete repair can improve superficial wear strength. With the aim of analyzing the impact of fly ash and metakaolin blends on the performance of PVA fiber-reinforced cementitious composites, six mixtures with blend of fly ash (FA) and metakaolin (MC) were produced. The mixtures had 0% FA + 50% MC (MC50), 10%FA + 40% MC (MC40CV10), 20% FA + 30% MC (MC30CV20), 30% FA + 20% MC (MC20CV30), 40% FA + 10% MC (MC10CV40), and 50% FA + 0% MC (CV50). In all mixtures, the cement content relative to the cementitious material (by mass) was fixed at 50%. Additionally, two others mixtures (CV1 and CV2) were produced, with only fly ash as supplementary cementitious material, and different water-to-cementitious material ratios. In CV1 and CV2 mixtures, the fly ash to cementitious material ratio was 55%. The results of the experimental tests on the composite matrix indicate that the mixture with 50%metakaolin (MC50%) and 10% fly ash and 40% metakaolin (MC40CV10), showed highest compression strength and toughness, highlighting its greater capacity to absorb energy before fracturing. The results of the composites tests also demonstrated that the MC40CV10 mixture exhibited higher density, compression strength, and modulus of elasticity. On the other hand, the CV50 mixture, although maintaining significant compression strength, showed higher strain and deflection capacity under bending and direct tension. It is worth noting that all composites exhibited strain-hardening behavior when subjected to direct tension, with strain capacities between 1.5% and 2.9% and tensile strengths between 3.6 MPa and 5.6 MPa. Under bending loads, the composites also showed high deflection capacities (between 10.8 mm and 26.9 mm) and flexural strengths between 7.8 and 9 MPa. Under erosion wear, the CV50, MC10CV40, and MC50 composites exhibited the lowest erosion wear after 72 hours of testing. However, initial wear, after 12 hours of testing, was lower on the MC50 and MC40CV10 mixtures, which also showed more elevated surface hardness. In addition, 2.5 cm thick repair layer was not sufficient, because the wear reached the concrete surface at distinct points, after 48 hours of testing. The results also indicate that reducing the water content in composite was beneficial to reduce porosity, increasing compressive strength and erosive wear strength.