A Comparative Study of Metakaolin/Slag-Based Geopolymer Mortars Incorporating Natural and Recycled Sands

Abstract

Great efforts are being made to minimize the negative impact of the Portland cement industry on the environment by using industrial by-products during the manufacture of clinker or by the partial replacement of cement during the preparation of concrete. However, the carbon footprint remains relatively high in addition to the large consumption of natural resources such as sand and other aggregates. A solution to these problems is to completely replace Portland cement with a new generation of mineral binders, commonly known as geopolymers, which have properties similar to those of Portland cement. These binders can be obtained by the alkali-activation of siliceous or aluminosilicate materials. This study aims to develop pozzolanic type binders at room temperature (20°C) from the alkali-activation of aluminosilicate materials based on metakaolin and blast furnace slag at different percentages. Different activators were employed, including solid (NaOH) and liquid (Na2SiO3.nH2O). The optimal mixtures were used for making mortars based on natural sand (NS) and concrete recycled sand (CRS). A comparative experimental study of the physical, mechanical, and microstructural characteristics of the two types of mortars was conducted. Cement mixtures with a high amount of slag and an association of sodium hydroxide and sodium silicate gave the best physico-mechanical properties. A drop in the compressive strength of mortars prepared with CRS was observed after 365 days, but it was still higher than those with NS. The obtained results show the possibility of designing an eco-friendly CRS-based geopolymer mortar that is more resistant than NS-based mortar with a homogeneous and integrated microstructure. Doi: 10.28991/CEJ-2022-08-08-07 Full Text: PDF

Recycled Concrete Aggregates: A Promising and Sustainable Option for the Construction Industry

“…In this study, RCA was used as the recycled aggregate (Figure 1). The use of RCA instead of NA has a positive impact on the environment and economy [14,28]. After this analysis, the physical and mechanical properties of the recycled aggregate were determined in accordance with EN 12620 [13].…”

“…Zega et al (2010) studied the effect of different types of coarse aggregates and water-to-cement (w/c) ratios on the properties of recycled aggregates [30]. The grading of the recycled aggregate did not depend on the w/c ratio of the concrete from which the recycled aggregate was derived nor on the shape and texture of the parent concrete aggregate [28,29]. In a concrete system, the use of RCA with a surface containing adhered mortar layers creates two types of interfacial transition zones (ITZs): an old ITZ zone and a new one, as shown in Figure 3.…”

“…The unit weight or density of typical concrete is approximately 2400 kg per cubic meter. According to EN 206, normal-weight concrete is defined as concrete under oven-dry conditions with a density greater than 2000 kg/m 3 but not exceeding 2600 kg/m 3 [28]. In this study, the fresh densities of all the mixtures were determined in accordance with EN 12350-6 [36].…”

Assessment of Fly Ash-Rice Straw Ash-Laterite Soil Based Geopolymer Mortar Durability

“…Fly ash is one of the by-products of coal combustion in a steam power plant (PLTU) [7][8][9]. The use of geopolymer fly ash and rice straw ash as material binders has also been developed in order to provide environmentally friendly products, bearing in mind that the cement factory, in addition to producing cement, also produces quite large carbon dioxide emissions into the atmosphere [10,11]. Fly ash is rich in silica and alumina.…”

Influential and Intellectual Structure of Geopolymer Concrete: A Bibliometric Review

“…The introduction of geopolymers into the construction process could lead to a 73% reduction in greenhouse gas emissions and a 43% decrease in energy consumption [1,9]. This alternative, deemed a green building material, circumvents the need for cement [10], and GPC possesses the potential to supersede conventional concrete due to its lower CO2 emissions.…”