Strength and Microstructure Characteristics of Metakaolin-Based Geopolymer Mortars with High Water-to-Binder Ratios

Abstract

Geopolymers and other alkali-activated materials were investigated in detail as alternatives to ordinary Portland cement because of their reduced CO2 emissions, high (radionuclide) binding capacities, and low permeabilities. The last two properties make them potential materials for the immobilization of several types of chemical waste. In this context, the direct immobilization of liquid waste streams would be a useful application. This study aimed to develop geopolymers with high water-to-binder ratios, but with good mechanical strengths, while elucidating the parameters that dictate the strengths. Three potential metakaolin geopolymer recipes were cast and cured for 28 days, after which their strengths, mineralogy, and microstructures were determined. The results show that it is possible to attain acceptable mechanical strengths at water-to-binder ratios that vary from 0.75 to 0.95, which is a significant increase from the ratio of 0.55 that is commonly used in the literature. It was found that the most important parameter that governs the mechanical strength is the dilution of the activating solution, which is represented by the H2O/Na2O ratio, while the microstructure was found to benefit from a high SiO2/Al2O3 ratio.

Effect of Slag on the Strength and Shrinkage Properties of Metakaolin-Based Geopolymers

“…The shrinkage testing and theoretical research are more complex than investigating the mechanical properties of metakaolin-based geopolymers. Numerous studies have found that the mixture ratio (alkali activator content [17,18], slag content [18], fly ash content [19], and water-binder ratio [20]), curing method [17,21], and additives) significantly influences the volume stability of metakaolin-based geopolymers [22]. Fu et al [23] reported that metakaolin can coarsen the pore structure of hardened slag, thereby reducing autogenous and drying shrinkage.…”

Solidification Experiment of Lithium-Slag and Fine-Tailings Based Geopolymers

“…Its main raw material can be aluminosilicate minerals occurring in nature, or it can be made from solid industrial waste with a high aluminum-silicon content [2][3][4]. Studies have shown that blast furnace slag [5], zeolite [6], metakaolin [7], fly ash [8], red mud [9], and other synthetic geopolymers have many advantages, such as high strength, low toxicity substance leaching rates, good durability, etc. Such synthetic geopolymers are widely used in industrial applications such as brick-making and road construction.…”