Avaliação das características físicas e mecânicas de blocos leves de concreto álcali-ativado

Abstract

The need to reduce the environmental impact of construction has encouraged the development of alternative materials to Portland cement, including alkali-activated materials (AAM). In this context, this study investigated the technical and scientific feasibility of producing lightweight sealing blocks using alkali-activated cement combined with expanded polystyrene (EPS) as lightweight aggregate. The first experimental stage was the physical-chemical characterization of the fly ash used as the main precursor, followed by the formulation of the paste activated with hydroxide and sodium silicate. The second stage consisted of producing concrete by partially replacing natural sand with EPS in three different mix designs. The alkali-activated paste was characterized in the fresh state using the Kantro mini-slump test, the Ford cup flow value and the bulk density. In the hardened state, the compressive strength was determined and the formation of agglomerating gels and pore volume were analyzed using Scanning Electron Microscopy (SEM). The workability of the concrete was assessed using the cone trunk slump test. Cylindrical specimens (10 x 20 cm) and two-hole concrete blocks (10 cm x 24 cm x 24 cm) were molded for compressive strength analysis. The results showed that the cement paste was moderately workable, with an average spread of 123.6 mm and high viscosity, resulting in a flow time of 184 seconds. The apparent density of the paste was 1.6738 g/cm³, reflecting its compactness and the homogeneous distribution of the components. Microstructural analysis revealed the presence of unreacted fly ash particles and a porous structure. The lightweight concretes were highly workable, with average slum p values of 24.90 cm. In the hardened state, the concrete blocks had compressive strengths ranging from 2.2 MPa to 4.0 MPa, demonstrating their viability for non-structural applications such as internal sealing. Partially replacing sand with EPS significantly reduced the density of the blocks, an interesting result for reducing the loads on foundations and potentially improving thermal and acoustic insulation, although it caused a proportional reduction in mechanical strength. The results confirm that the use of EPS as a lightweight aggregate, combined with alkali-activated cement, represents a viable and environmentally sustainable technical solution for the construction industry, helping to reduce the carbon footprint and reuse industrial waste.