Compressive and Flexural Properties of Ultra-Fine Coal Gangue-Based Geopolymer Gels and Microscopic Mechanism Analysis

Abstract

Geopolymer gel that possesses advantageous features of fast setting, high strength, and good durability is increasingly used in civil engineering, including rapid retrofit projects, roadway, and other construction projects. Furthermore, geopolymer gel is also a green and economical material as it derives from solid wastes. In this study, activators with different sodium silicate modulus and alkali content were used to activate ultrafine coal gangue and slag powder to prepare coal-gangue-based geopolymers with high strength. To study the influence of slag powder content, sodium silicate modulus, and alkali activator content on strength, a two-stage design was adopted. In the first stage, the orthogonal test with three factors and four levels (10–40% slag, 0.4–1.0 modulus, 16–22%) was used to obtain the influence of each factor on the strength and select the design range of the specimen mix ratio with higher strength. In the second stage, based on the orthogonal experiment, the scope was narrowed to continue to find the optimal excitation scheme and the relationship between the influencing factors and strength. Further, mineral compositional, microstructural, functional group and elemental analyses were performed using X-ray diffraction technique, IR infrared diffraction, electron microscope observation and energy spectrum analysis to elucidate the mechanisms of the strength development. The results show that the factors affecting the geopolymer’s strength were in the order of slag content > alkali content > modulus. The optimum dosage of alkali activator was 18–20%, and the sodium silicate modulus was 0.6–0.8, and the compressive and flexural strength could reach above 40 MPa and 5.9 MPa, respectively. The compressive strength and modulus were in a parabolic relationship. Three types of cementing gels (N-A-S-H, C-A-S-H, and C-N-A-S-H) that were characterized with dense structure and high strength were identified from coal gangue and slag powder after alkali excitation.

Analytical Review of the Current State of Technology, Structure Formation, and Properties of Variatropic Centrifugally Compacted Concrete

“…It is noted that the gel transition time decreases with increasing amounts of calcium sulfoaluminate and gypsum additions [91] Prescription (supplement use) coal gangue and slag powder…”

“…The macrostructure of concrete produced through the utilization of centrifugal compaction technology exhibits irregularities. In accordance with conventional categorization, it can be divided into the following three layers: internal, middle, and external [91]. The study in [69] is devoted to the investigation of the dependence of the processes of formation of cement gel and methods of the compaction of cement systems.…”

Activation Mechanism of Coal Gangue and Its Impact on the Properties of Geopolymers: A Review

“…The analysis showed that the optimal concentration of mixed activator was 18-20%. The optimal modulus is 0.6-0.8 [64,104]. Guo et al [98] proposed that the modulus of Na 2 SiO 3 affects the polymerization reaction.…”

A Study on the Cement Gel Formation Process during the Creation of Nanomodified High-Performance Concrete Based on Nanosilica

“…Slag nanomodification of cement composites has already established itself as a promising and effective solution for improving the micro- and macrostructure of various characteristics of concretes, mortars, products, and structures composed of them [ 6 , 7 , 8 , 9 , 10 , 11 ]. At the same time, much attention is being paid to the parameters of slag grinding; its activation, including alkaline; its use in combination with other finely dispersed additives, for example, fly ash and nanosilica; as well as the processes of hydration and structure formation of Portland slag cement [ 9 ].…”