Alkali-activated binders (AAB) are a suitable and sustainable alternative to ordinary Portland cement (OPC), with reductions in natural resource usage and environmental emissions in regions where the necessary industrial residues are available. Despite its potential, the lack of mix design methods still limits its applications. This paper proposes a systematic parametric validation for AAB mix design applied to pastes and concretes, valorizing steel slag as precursors. The composed binders are based on coal fly ash (FA) and Basic Oxygen Furnace (BOF) steel slag. These precursors were activated with sodium silicate (Na₂SiO₃) and sodium hydroxide (NaOH) alkaline solutions. A parametric investigation was performed on the mix design parameters, sweeping the (i) alkali content from 6% to 10%, (ii) silica modulus (SiO₂/Na₂O) from 0.75 to 1.75, and (iii) ash-to-slag ratios in the proportions of 75:25 and 50:50, using parametric intervals retrieved from the literature. These variations were analyzed using response surface methodology (RSM) to develop a mechanical model of the compressive strength of the hardened paste. Flowability, yield stress, and setting time were evaluated. Statistical analyses, ANOVA and the Duncan test, validated the model and identified interactions between variables. The concrete formulation design was based on aggregates packing analysis with different paste contents (from 32% up to 38.4%), aiming at self-compacting concrete (SCC) with slump flow class 1 (SF1). The influence of the curing condition was evaluated, varying with ambient and thermal conditions, at 25 °C and 65 °C, respectively, for the initial 24 h. The results showed that lower silica modulus (0.75) achieved the highest compressive strength at 80.1 MPa (28 d) for pastes compressive strength, densifying the composite matrix. The concrete application of the binder achieved SF1 fluidity, with 575 mm spread, 64.1 MPa of compressive strength, and 26.2 GPa of Young’s modulus in thermal cure conditions. These findings demonstrate the potential for developing sustainable high-performance materials based on parametric design of AAB formulations and mix design.

There is a growing demand for sustainable solutions in civil engineering concerning the carbon footprint of cementitious composites. Alkali-Activated Binders (AAB) are materials with great potential to replace ordinary Portland cement (OPC), with similar strength levels and lower environmental impact. Despite their improved environmental performance, their durability remains a gap in the literature, influenced by aspects of mechanical behavior, physical properties, and microstructure. This paper aims to assess the impact of steel slag aggregates and curing temperature of a proposed AAB based concrete formulation by characterizing fresh state, mechanical behavior, and microstructure. The proposed AAB is composed of fly ash (FA) and basic oxygen furnace (BOF) steel slag (SS) as precursors, sodium silicate and sodium hydroxide solution as activators, in total replacement of OPC, using baosteel slag short flow (BSSF) SS as aggregate in comparison with natural aggregate. The concrete formulation was designed to achieve a high-performance concrete (HPC) and a self-compacting concrete (SCC) behavior. Mechanical characterization encompassed hardened (compressive strength and Young’s modulus), fresh state (J-ring, slump flow, and T50), and durability tests (scanning electronic microscopy, water penetration under pressure, and chloride ion penetration). The compressive strength (64.1 ± 3.6 MPa) achieves the requirements of HPC, while the fresh state results fulfill the SCC requirements as well, with a spread diameter from 550 mm to 650 mm (SF-1 class). However, the flow time ranges from 3.5 s to 13.8 s. There was evidence of high chloride penetrability, affected by the lower electrical resistance inherent to the material. Otherwise, there was a low water penetration under pressure (3.5 cm), which indicates a well-consolidated microstructure with low connected porosity. Therefore, the durability assessment demonstrated a divergence in the results. These results indicate that the current durability tests of cementitious materials are not feasible for AAB, requiring adapted procedures for AAB composite characterization.

RESUMO O presente trabalho apresenta a análise de um elemento não convencional para sistema vedação de edificações: o bloco de concreto prensado com a incorporação de PET reciclado. Para tanto foi realizada uma análise experimental realizando-se a substituição, em volume, do agregado miúdo (pó de pedra) por PET triturado, nos teores de 15%, 30% e 45%. Foram determinados características geométricas, índices físicos e características mecânicas dos blocos produzidos. Os resultados obtidos permitem concluir que os blocos que apresentaram os melhores resultados foram os com 15% de PET, uma vez que a sua resistência à compressão apresentou valor maior que a dos demais, destacando ainda uma menor absorção, resultantes possivelmente do maior grau de empacotamento e melhor homogeneidade do compósito obtido.

Resumo Os geopolímeros figuram como uma alternativa potencial aos ligantes de cimento Portland em algumas aplicações. Contudo, existem muitas lacunas de pesquisa a serem preenchidas dentro dessa temática. Assim, este estudo teve como objetivo investigar as propriedades reológicas e mecânicas de pastas geopoliméricas à base de cinza volante Classe F ativadas por uma solução de NaOH e Na2SiO3, com relações ativador/precursor de 0,5, 0,6 e 0,7, em massa. Além disso, foram realizadas análises microestruturais e químicas. As propriedades reológicas foram determinadas a partir de ensaios de fluxo com taxas de cisalhamento variando de 0 s-1 a 100 s-1 a 25 ºC. A análise mecânica foi realizada a partir de ensaios de resistência à compressão simples nas pastas endurecidas. Os resultados de resistência à compressão simples indicaram melhores valores para menores relações de ativador/precursor. Nos ensaios de fluxo, o material comportou-se como um fluido pseudoplástico e, com o aumento da relação ativador/precursor, houve redução dos valores de viscosidade aparente. Assim, avaliando-se os resultados mecânicos e reológicos, percebeu-se que a pasta que apresentou melhores propriedades foi a de relação ativador/precursor 0,6.