This paper describes a review of the state-of-the-art research carried on the fresh and hardened properties of Alkali Activated Binders and Concretes. Though, many research have been carried out in the recent times on alkali activated binders, few key parameters still remain unattended, that restricts the commercial application of AAMs to the general construction activities. Fresh properties, mechanical strength and durability performance of Alkali activated concrete with various Alumino silicates as base materials is mentioned. An essential parameter of Alkali activated concrete is the concentration of alkaline solution on which various properties like mechanical strength, setting time and durability depends. Influence of wide range of concentrations from 6 to 16 M on these properties are studied and reported in this paper. This paper mainly concentrates on properties of readily available base materials such as Fly ash and Slag and the means to improve their performance through the use of various industrial and agro-based byproducts as additives. Problems pertaining to practical applicability of AAMs to general construction activities are also highlighted.

India ranks among the foremost global producers and consumers of cement, and the cement industry contributes significantly to carbon emissions. Alkali-activated materials have gained significant attention as a sustainable alternative to Portland cement, offering the potential to mitigate carbon dioxide emissions and promote effective recycling of waste materials. Fly ash (FA) and Ground granulated blast furnace slag (GGBS) are preferred raw materials for Alkali-activated concrete (AAC) owing to their effective repurposing of waste, widespread accessibility, advantageous chemical composition, and performance attributes. This review provides a comprehensive analysis of the current state-of-the-art on the durability aspects of fly ash/slag-based AAC. The paper explores the unique characteristics of FA/GGBS-based AAC, emphasizing their potential to enhance the durability of concrete structures. Insights into the material behaviour under various environmental exposures, including aggressive chemical environments and freeze–thaw cycles, are presented. Furthermore, the article addresses both the obstacles and prospects associated with implementing fly ash/slag-based AAC as a potential construction material suitable for large-scale infrastructure projects. This overview is designed to direct future research efforts and provide practitioners with insights into the potential of FA/GGBS-based AAC for ensuring the prolonged durability of concrete structures.

This paper discusses the properties of dried sewage sludge (SS) and its influence on the microstructure development of HVFA concrete when used as a partial replacement of binder material. A detailed characterization of dried sludge samples collected from a sewage treatment plant is carried out using XRF, XRD, TGA, and FTIR techniques. HVFA concrete mix is designed for 50 MPa with 50% fly ash of the total binder content. Sludge is ground to a particle size of 150 µ and 75 µ and replaced at levels of 5%, 10%, and 15% of the total binder content. The strength activity index of the dried sludge sample is acceptable as per standards. Taking concrete mixes with HVFA as a reference, the fresh properties of binder paste and concrete with sewage sludge have been studied. Mechanical properties that define the applicability to various infrastructure projects are reported for all the studied mixes. EI, CI, COST per unit compressive strength for all mixes are also determined to comment on the environmental impact of the use of SS in concrete. The compressive strength of concrete specimens decreases with the increase in replacement level of SS. However, in comparison with OPC concrete, 75 µm SS at 5% replacement level concrete mechanical strength is within the acceptable limit for M50 concrete mix. The addition of SS as a binder to the concrete has a lower environmental impact, embodied energy, CO₂emission, and cost per unit strength. But more than 10% replacement level resulted in reducing CS, FS, and STS by 11.17%, 6.23%, and 6.99%.Graphical abstract

This paper reported on the micro-level properties of alkali-activated pastes cured in ambient conditions. The mechanisms influencing setting time and the microstructure development of fly ash, slag, and metakaolin were studied. The mortar compressive strength of the binders and their ultrasonic pulse velocity (UPV) were tested after 56 days of ambient curing. The micro-level properties of paste cured at ambient conditions for seven days were determined to understand the phases developed. NASH gel was observed to delay setting and possessed lower compressive strength, while CASH gel was set early and possessed high compressive strength. The micro-characterisation of the alkali-activated binder system developed with fly ash and metakaolin showed the presence of NASH gel. The alkali-activated binder system developed with GGBS contained multiple gels, such as N, C-ASH, and CSH. The molecular structures of CSH, CASH, NASH, and N, C-ASH are also presented and were obtained using high score plus software.

Although alkali-activated concrete (AAC) has gained significant attention as a sustainable alternative to traditional Portland cement-based concrete due to its reduced carbon emissions and improved durability, optimizing AAC mix design still remains a challenging task as it involves complex interactions between various factors, constituent materials, and their proportions. This study presents the performance based multi-response optimization of alkali-activated concrete mix using Taguchi-integrated Grey Relational Analysis aiming for improved workability, mechanical and permeability properties. This study employs Taguchi’s L₉ orthogonal array to reduce the experimental trials, thereby saving time and resources. The Grey Relational Analysis optimizes factors like binder ratio, solution to binder (Al/b) ratio, and molarity of NaOH and Na₂SiO₃/NaOH ratio, encompassing alkali-activated concrete’s fresh, mechanical, and durability characteristics with structural grade properties. The results show that binder ratio (FA:GGBS) of 90:10, Al/b ratio of 0.45, 10 M NaOH solution with Na₂SiO₃/NaOH ratio of 1 has produced the optimum alkali-activated concrete mix of structural (M40) grade.