Abstract
Geopolymers are created by mixing a source of aluminosilicates, which can be natural or by-products from other industries, with an alkaline solution. These materials based on by-products from other industries have proven to be a less polluting alternative for concrete production than ordinary Portland cement (OPC). Geopolymers offer many advantages over OPC, such as excellent mechanical strength, increased durability, thermal resistance, and excellent stability in acidic and alkaline environments. Within these properties, mechanical strength, more specifically compressive strength, is the most important property for analyzing geopolymers as a construction material. For this reason, this study compiled information on the different variables that affect the compressive strength of geopolymers, such as Si/Al ratio, curing temperature and time, type and concentration of alkaline activator, water content, and the effect of impurities. From the information collected, it can be mentioned that geopolymers with Si/Al ratios between 1.5 and 2.0 obtained the highest compressive strengths for the different cases. On the other hand, high moderate temperatures (between 80 and 90 °C) induced higher compressive strengths in geopolymers, because the temperature favors the geopolymerization process. Moreover, longer curing times helped to obtain higher compressive strengths for all the cases analyzed. Furthermore, it was found that the most common practice is the use of sodium hydroxide combined with sodium silicate to obtain geopolymers with good mechanical strength, where the optimum SS/NaOH ratio depends on the source of aluminosilicates to be used. Generally speaking, it was observed that higher water contents lead to a decrease in compressive strength. The presence of calcium was found to be favorable in controlled proportions as it increases the compressive strength of geopolymers, on the other hand, impurities such as heavy metals have a negative effect on the compressive strength of geopolymers.
Highlights
The results showed that Si/Al ratio is the most important parameter followed by Al/Na, H2 O/Na2 O
Tian et al indicates that this may be due to the fact that the alkaline activator (NaOH) did not have time to react completely and was exposed to the evaporated water when it was above 100 ◦ C (consider that for the formation of the geopolymer, it was mixed for 13 min, 6 h of curing at 100 ◦ C and later it was left to age at ambient conditions for different periods (3, 7 or 28 days) prior to the tests carried out on the geopolymer)
Tian et al [197] studied the effect of replacing part of the alkaline activator (NaOH) with calcium oxide (CaO) produced industrially to form a geopolymer based on copper tailings from China with the same composition of their work when varying the temperature cured [81] and fly ash
Summary
Hengels Castillo 1,2, * , Humberto Collado 1,2 , Thomas Droguett 3,4 , Sebastián Sánchez 3,5 , Mario Vesely 1 , Pamela Garrido 3 and Sergio Palma 2. Complex Fluids Laboratory, Department of Metallurgical Engineering and Materials, Universidad Técnica. Escuela de Ingeniería Química, Pontificia Universidad Católica de Valparaíso, Valparaíso 2340025, Chile
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