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Massive growth in the infrastructure industry and development has led to a phenomenal increase in cement usage. The cement industry emits the greenhouse gas (CO2) and cement production requires more embodied energy. There is an increasing research interest in geopolymers (GP) for developing an alternate binder for civil engineering applications because of its low energy consumption and eco-friendly nature. GP contain alkali-activated material, which is relatively new, and Geopolymer concrete (GPC) has superior mechanical and durability properties compared to ordinary Portland cement (OPC) concrete. The objective of the review article is to make all-encompassing review of long-term (LT) and short-term (ST) properties of GP, their chemistry, reaction mechanism, effect of reaction parameters, fresh properties, stability under elevated temperature exposure, bond between steel and reinforcement and various field implementations. It is concluded that GPC can achieve structural grade strength when different industrial waste materials as precursors are used in its preparation by varying the alkaline concentration, curing method and curing temperature. It is also concluded that GP gives better thermal resistance at elevated temperature exposure up to 1000 °C whereas OPC fails. Various research and development works carried out in India by utilising the locally available industrial waste-based source materials are also discussed. Applications of GP technology in current scenario have also been reviewed. The gap in GP technology pertaining to corrosion, carbonation and leaching effects of GPC need to be focussed in future research.

The study presented in this paper is on the effect of heat treatment on fly ash based geopolymer mortar synthesized from fly ash (Class F –Low lime) using alkaline binary activator solution containing sodium hydroxide (18 M) and sodium silicate solution (MR 2.0), cured at 80oC for 24 h. 7 days aged specimen heated at elevated temperature (200°C, 400°C, 600°C and 800°C) for the sustained period of 2hrs. The TGA/DTA analysis and thermal conductivity measurement as per ASTM C113 were carried out besides the compressive strengths. The thermal stability of the fly ash mortar at elevated temperature was found to be high as reflected in the observed value of f800°C/f30°C being more than 1 and this ratio was raised to about 1.3 with the addition of 2% Zirconium di oxide (ZrO2). No visible cracks were found on the specimens with and without ZrO2 when 800°C was sustained for 4 hrs in smaller specimens of size: 50 mm diameter x 100 mm height and in also bigger size specimens: 22 cm × 11 cm × 7 cm) specimens. TGA/DTA analysis of the geopolymer paste showed that the retention of mass was around 90%. The addition of ZrO2 improved thermal resistance. The micro structure of the matrix found to be intact even at elevated temperature that was evident from the FESEM studies.

The recovery of nitrogen (N) and phosphorous (P) from wastewater and its conversion to value-added products serve two purposes: satisfying the stringent N, P discharge threshold and meeting the demand for P fertilizers. The driving force for N, P recovery from an increased quantity of discharged wastewater is its environmental impact, on one hand, and the price of inorganic fertilizer and its judicious use, on the other. The available technology for N, P recovery is its precipitation and crystallization as struvite from diversified wastewater sources in several reactor models designed for the purpose. In addition, the electrochemical method of precipitation of struvite is also found to be very effective and novel. The use of electrogenic microorganisms is furthermore favorable to disintegrate the organic matter through the catalytic reaction and a simultaneous recovery of nutrients and the production of bioelectricity can be achieved. The advantage of the electrogenic microorganism method is a high percentage of recovery with good efficiency without the addition of any additional chemicals for pH adjustments. This review describes different aspects of chemical and electrochemical precipitation and the use of microbial electrolysis cell and microbial fuel cell in struvite precipitation from different sources. The critical factors influencing the efficiency and quality of the product are the technique adopted and the interacting process factors such as time and pH. The key differences in each process technology are described in detail with their pros and cons. To conclude, a robust process technology for quality struvite production facilitates its widespread use as a fertilizer. [ABSTRACT FROM AUTHOR]