Alkali-activated materials (AAM) are currently the subject of increasing interest and research, mainly due to the possibility of reducing the carbon dioxide (CO 2 ) emissions in their production when compared to Portland cement (PC) and still achieve superior performance in many aspects when compared to traditional PC-based products. However, the use of sodium silicate (SS) as an alkaline activator in AAM is controversial when the aim is to reduce the environmental impact, as the production of the first also releases significant amount of CO 2 per ton of activator produced. Therefore, a demand has emerged for alternative silica-rich materials that could effectively reduce the demand for SS without compromising the mechanical behavior of the matrices and consequently the performance of fiber reinforced AAM. This paper investigates the gradual replacement (0-18% wt.) of metakaolin (MK) with silica fume (SF) in PVA-reinforced AAM, allowing the reduction of SS in the activator, also containing NaOH. Matrices with different composition were studied, i.e., with [SiO 2 ]/[Al 2 O 3 ] molar ratios of 3.0 and 3.8. All formulations were reinforced with 2% vol. of PVA fibers. The mechanical properties investigated were compressive strength, modulus of elasticity, flexural strength, and toughness. Apparent dry density, water absorption, and porosity of the composites were also assessed to give an indication of their durability. Single fiber pullout, fracture toughness, and direct tensile tests were also carried out in order to understand the deformation capability of the composites. Results indicated that the employment of SF may effectively reduce the demand for SS in the alkaline activators, in order to produce alkali-activated composites with lower environmental impact (reduced CO 2 emissions). Adjustments in the formulations may improve toughness in flexion in 170% with 30 wt.% reduction of SS in the activator, as well as improvements in deformation capability in tension. The development of strain-hardening MK-based AAM, however, has some challenging aspects that are also discussed.

Alkali-activated materials (AAM) compared to Portland cement (PC) may significantly reduce the carbon dioxide emissions, as well as the consumption of non-renewable natural resources in civil engineering applications. Further environmental advantages are possible if natural aggregates used for mortars and concretes are replaced with residues and wastes from industrial or mining activities. This paper compares the performance of PC with AAM as binders in cementitious wall panels for external cladding in hot and humid climate. Three different cementitious matrices are proposed, consisting of either 100% Portland cement (PC), 100% alkali-activated metakaolin (MK) or 80/20 alkali-activated Metakaolin/Blastfurnace slag (80/20 MK/BFS). Mortars were produced with the addition of tailing from iron-ore mining activities in the state of Minas Gerais, Brazil, at an aggregate to binder ratio of 1.0 for all matrices. The thermal property determined for the three mortars was Thermal Conductivity using a heat flow meter (HFM) apparatus according to ISO 8301 (1999); their apparent density was also measured. After that, one-story house building simulation was carried out using the Energy Plus Software. The main room annual operative temperature provided by different panels used as cladding was compared to the adaptive comfort range established on ASHRAE Standard 55/2013 for a Brazilian and Portuguese hot and humid climate. According to the Climate Zone Definitions of ANSI/ASHRAE Standard 169/2006, Belo Horizonte (Brazil) and Funchal (Portugal) were selected as a sample of 2A zone that presents a hot and humid climate. Partial results of this research were presented in this paper. Results show that building simulations can effectively contribute to validate the selection of materials in the production of sustainable wall panels that provide suitable thermal conditions to the users in hot and humid climate.

High-performance cementitious composites have been developed to overcome the brittleness of mortars and concretes, thus improving the deformation and toughness of these materials under flexion and tension. Poli Vinyl Alcohol (PVA) fibres are employed in the production of such “Engineered Cementitious Composites” - ECC; the PVA fibres have a loadcarrying capacity after the first crack (matrix failure), which changes the mechanical behaviour of the composites from brittle to ductile and significantly increases the ultimate strength. This deflection or strain-hardening behaviour is accompanied by a multiple cracking of the composites, which results from the design of a proper formulation, with correct amount of PVA fibres (usually 2% vol. fraction) and employment of a very fine sand (passing 0.6 mm). Recent developments in the area of ECC comprise the replacement of Portland cement (PC) matrices with alkali-activated materials (AAM). The idea is to produce composites with similar performance but with improved chemical durability and lower environmental impact. A more sustainable solution would consider the replacement of the fine sand with mine tailings in the production of ECC-AAM. Some tailings from the iron-ore mining activities in Brazil are significantly finer than those aggregates used for PC mortars and concretes; therefore, they cannot be employed in traditional PC-based materials. Nevertheless, those fine materials could replace the fine natural aggregate used in the production of ECC. This paper investigates the replacement of a natural quartz sand with an iron-rich mine tailing in PVA-reinforced AAM. Four composites were studied from a combination of two different matrices and 2 different aggregates. The matrices were obtained from the alkaline activation of metakaolin (MK) with sodium silicate (Na2SiO3) and sodium hydroxide (NaOH); silica fume (SF) was used to adjust their composition: SiO2 / Al2O3 molar ratio equal to 3.0 or 3.8. The aggregates used were either natural quartz (passing 0.6 mm) or tailings produced during the mining activities of iron ore in the state of Minas Gerais, Brazil. The mine tailing studied is much finer than the natural sand (passing 0.3 mm) but it was used as received in the production of ECC-AAM. The aggregate to binder ratio was kept constant (equal to 1.0 in mass) irrespective of the type of aggregate. All mortars were reinforced with 2% vol. of PVA fibres; extra water was added to the mixes to maintain the same consistency for the composites. The mechanical properties investigated are compressive strength, flexural strength and toughness. The apparent dry density of the mortars was also assessed. The preliminary results presented in this paper indicate that iron-rich tailings may be effectively used in the production of ECC-AAM; however, durability tests are still necessary.