The negative environmental impacts associated with the usage of Portland cement (PC) in concrete induced intensive research into finding sustainable alternative concrete mixes to obtain “green concrete”. Since the principal aim of developing such mixes is to reduce the environmental impact, it is imperative to conduct a comprehensive life cycle assessment (LCA). This paper examines three different types of sustainable concrete mixes, viz., alkali-activated concrete (AAC) with natural coarse aggregates, AAC with recycled coarse aggregates (RCA), and bacterial concrete (BC). A detailed environmental impact assessment of AAC with natural coarse aggregates, AAC with RCA, and BC is performed through a cradle-to-gate LCA using openLCA v.1.10.3 and compared versus PC concrete (PCC) of equivalent strength. The results show that transportation and sodium silicate in AAC mixes and PC in BC mixes contribute the most to the environmental impact. The global warming potential (GWP) of PCC is 1.4–2 times higher than other mixes. Bacterial concrete without nutrients had the lowest environmental impact of all the evaluated mixes on all damage categories, both at the midpoint (except GWP) and endpoint assessment levels. AAC and BC mixes are more expensive than PCC by 98.8–159.1% and 21.8–54.3%, respectively.

The drying shrinkage of alkali-activated concrete (AAC) is a very complex process, and it warrants long-term testing. The present study was focused on the development of drying shrinkage prediction models for ambient-cured AAC. AAC with four distinct precursor combinations for experimental validation and investigation of the influence of mix proportions were used. The applied fly ash (FA) to ground granulated blast-furnace slag (GGBFS) ratio was varied as 100:0, 70:30, 60:40, and 50:50. Drying shrinkage strains were determined for hardened paste, mortar, and concrete specimens. The observed drying shrinkage behavior was correlated with the mineralogical, chemical, and morphological characteristics of corresponding paste specimens of alkali-activated binder (AAB). These characteristics were evaluated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), respectively. The results showed that the drying shrinkage of hardened AAB paste and AAB mortar increases by 26%–32% and 13%–28% with GGBFS content, respectively. The qualitative and quantitative microstructural analysis suggested that this behavior could be ascribed to the formation of a calcium aluminosilicate hydrate matrix. Moreover, FA-based AAC exhibited maximum shrinkage, probably due to its comparatively high overall porosity with the addition of both coarse and fine aggregates. Using the experimental data, stepwise linear and multivariate nonlinear regression models were developed by modifying existing portland cement concrete (PCC) models to predict the drying shrinkage strains of AAC. Recommended linear and nonlinear regression models were selected based on the least deviation from the experimental value. The modified GL2000 model was found to be the best fit for shrinkage predictions in AAC because of its simplicity and comparable precision to experimental findings.

Alkali-activated binders (AABs) offer the opportunity to upcycle a variety of residues into products that can have added value. Although AABs are reported to have a superior high-temperature performance, their thermal behavior is heavily governed by their microstructure. The present study, therefore, evaluates the effect of varying fly ash:slag ratios, activator modulus (Ms), and high temperatures on the microstructure of AAB using X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy coupled with energy-dispersive spectroscopy. Furthermore, the mechanical properties of alkali-activated concrete (AAC) are investigated through compressive, bond, flexural, and split tensile strengths. A life cycle assessment of AAC is performed using the ReCiPe 2016 methodology. The results from microstructural experiments show the formation of new crystalline phases and decomposition of reaction products on high temperature exposure, and they correlate well with the observed mechanical performance. The 28-days compressive strength with slag content is enhanced by 151.8–339.7%. AAC with a fly ash:slag ratio of 70:30 and Ms of 1.4 is proposed as optimal from the obtained results. The results reveal that the biggest impact on climate change comes from transport (45.5–48.2%) and sodium silicate (26.7–35.6%).