Aluminosilicate minerals have become an important resource for an emerging sustainable material for construction known as geopolymer. Geopolymer, an alkali-activated material, is becoming an attractive alternative to Portland cement because of its lower carbon footprint and embodied energy. However, the synthesis process requires typically a two-part system for alkali activation wherein the solid geopolymer precursor is mixed with aqueous alkali solutions. These alkali activators are corrosive and may be difficult to handle in the field-scale application. In this study, a one-part geopolymer in which coal fly ash was mixed with solid alkali activators such as sodium hydroxide and sodium silicate to form a powdery cementitious binder was developed. This binder mixed with soil only requires water to form the soil-fly ash (SO-CFA) geopolymer cement, which can be used as stabilized soil for backfill/foundation. This geopolymer product was then evaluated for chemical stability by immersing the material with 5% by weight of sulfuric acid solution for 28 days. Indication suggests that the geopolymer exhibited high resistance against acid attack with an observed increase of unconfined compressive strength even when the immersion time in acidic solution was increased to 56 days. The mineralogical phase, microstructure, and morphology of the material were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), respectively. Results not only confirmed the formation of gypsum due to acid attack but also indicated the dissolution of anorthite and albite that may have caused the microstructure to be composed of sodium aluminosilicate hydrate (N–A–S–H) and calcium (alumino) silicate hydrate (C(–A)–S–H) with poly(ferro-sialate-siloxo) and poly(ferro-sialate-disiloxo) networks. A column leaching test with deionized water was also performed on the soil-fly ash geopolymer to study the leachability of metals in the material. Results showed that arsenic exhibits higher mobility in the geopolymer as compared to that of cadmium, chromium, and lead.

Geopolymer cement has been popularly studied nowadays compared to ordinary Portland cement because it demonstrated superior environmental advantages due to its lower carbon emissions and waste material utilization. This paper focuses on the formulation of geopolymer cement from nickel–laterite mine waste (NMW) and coal fly ash (CFA) as geopolymer precursors, and sodium hydroxide (SH), and sodium silicate (SS) as alkali activators. Different mix formulations of raw materials are prepared to produce a geopolymer based on an I-optimal design and obtained different compressive strengths. A mixed formulation of 50% NMW and 50% CFA, SH-to-SS ratio of 0.5, and an activator-to-precursor ratio of 0.429 yielded the highest 28 d unconfined compressive strength (UCS) of 22.10 ± 5.40 MPa. Furthermore, using an optimized formulation of 50.12% NMW, SH-to-SS ratio of 0.516, and an activator-to-precursor ratio of 0.428, a UCS value of 36.30 ± 3.60 MPa was obtained. The result implies that the synthesized geopolymer material can be potentially used for concrete structures and pavers, pedestrian pavers, light traffic pavers, and plain concrete.

A sustainable solution for crack maintenance in geopolymers is necessary if they are to be the future of modern green construction. This study aims to develop self-healing biogeopolymers that could potentially rival bioconcrete. First, a suitable healing agent was selected from Bacillus subtilis, Bacillus sphaericus, and Bacillus megaterium by directly adding their spores in the geopolymers and subsequently exposing them to a precipitation medium for 14 days. Scanning electron microscope with energy-dispersive X-ray (SEM-EDX) analysis revealed the formation of mineral phases for B. subtilis and B. sphaericus. Next, the effect of biochar-immobilization and co-culturing (B. sphaericus and B. thuringiensis) on the healing efficiencies of the geopolymers were tested and optimized by measuring their ultrasonic pulse velocities weekly over a 28-day healing period. The results show that using co-cultured bacteria significantly improved the observed efficiencies, while biochar-immobilization had a weak effect, but yielded an optimum response between 0.3–0.4 g/mL. The maximum crack width sealed was 0.65 mm. Through SEM-EDX and FTIR analyses, the precipitates in the cracks were identified to be mainly CaCO₃. With that, there is potential in developing self-healing biogeopolymers using biochar-immobilized spores of bacterial cultures.

A novel approach one-part geopolymer was employed to investigate the feasibility of enhancing the strength of in-situ soil for possible structural fill application in the construction industry. Geopolymer precursors such as fly ash and volcanic ash were utilized in this study for soil stabilization. The traditional geopolymer synthesis uses soluble alkali activators unlike in the case of ordinary Portland cement where only water is added to start the hydration process. This kind of synthesis is an impediment to geopolymer soil stabilizer commercial viability. Hence, solid alkali activators such as sodium silicate (SS), sodium hydroxide (SH), and sodium aluminate (SA) were explored. The influence of amount of fly ash (15% and 25%), addition of volcanic ash (0% and 12.5%), and ratio of alkali activator SS:SH:SA (50:50:0, 33:33:33, 50:20:30) were investigated. Samples cured for 28 days were tested for unconfined compressive strength (UCS). To evaluate the durability, sample yielding highest UCS was subjected to sulfuric acid resistance test for 28 days. Analytical techniques such as X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscope/energy-dispersive X-ray spectroscopy (SEM/EDX) were performed to examine the elemental composition, mineralogical properties, and microstructure of the precursors and the geopolymer stabilized soil.

Geopolymer cement has been popularly studied nowadays compared to ordinary Portland cement because it demonstrated superior environmental advantages due to its lower carbon emissions and waste material utilization. This paper focuses on the formulation of geopolymer cement from nickel-laterite mine waste (NMW) and coal fly ash (CFA) as geopolymer precursors, and sodium hydroxide (SH) and sodium silicate (SS) as alkali activators. Different mix formulations of raw materials are synthesized to produce a geopolymer based from an I-optimal design and obtained different compressive strengths. A mixed formulation of 50% NMW and 50% CFA, SH-to-SS ratio of 0.5, and an activator-to-precursor ratio of 0.429 yielded the highest 28-day unconfined compressive strength (UCS) of 22.10 ± 5.40 MPa. Furthermore, using an optimized formulation of 50.12% NMW, SH-to-SS ratio of 0.516, and an activator-to-precursor ratio of 0.428, a UCS value of 36.30 ± 3.60 MPa was obtained. The result implies that the synthesized geopolymer material can be potentially used for concrete structures and pavers, pedestrian pavers, light traffic pavers, and plain concrete.