Thermal-cured alkali-activated binders (AABs) are a potential replacement for traditional portland cement (PC) in concrete, primarily for precast applications. To avoid this energy-intensive regime and encourage wider application, this study investigates the development of ambient-cured AABs by adding graphene oxide (GO) nanoparticles. The mechanical strength and durability characteristics are determined for alkali-activated slag (AAS) mortar specimens prepared using 4, 6, and 8 molar (4, 6, and 8 M) concentrations of sodium hydroxide in the alkaline activator. The different percentages of GO by weight of slag are 0.0, 0.03, 0.06, and 0.09%. The mechanical parameters considered are compressive, flexural, and splitting tensile strengths. The durability parameters investigated are the rapid chloride permeability test (RCPT), sorptivity, and acid resistance. The performance of ambient-cured AAS mortar specimens containing GO is compared with thermal cured AAS mortar specimens (without any GO inclusions) and the control cement mortar (PC) to evaluate the effect of GO on the mortar characteristics. The strength of AAS mortar is observed to be higher both with and without GO inclusions for the molarity of sodium hydroxide greater than 4 M. The mixture containing 0.06% GO with a 4 M activator is found to exhibit optimal mechanical and durability characteristics. Mineralogical, chemical, and microstructural investigations confirm that the addition of GO to the ambient-cured AAS accelerates the rate of hydration, even at a lower concentration of the activator (4 M) due to its high specific surface area and consequent formation of a greater number of nucleation sites. Hence, ambient-cured AAS mortar prepared using 4 M sodium hydroxide and 0.06% GO is recommended for practical use.

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%).

The application of nanomaterials in alkali-activated composites is gaining popularity over the decade. The thermally cured alkali-activated concrete is a potential replacement for traditional Portland cement-based concrete in precast industries. The present study is focused on the strength and durability performance of graphene oxide (GO) based ambient-cured alkali-activated slag (AAS) mortar at different percentages of replacement of slag. The performance of ambient temperature cured ASS with different percentages of GO is compared with the thermally cured alkali-activated mortar at the activator fluid concentration of 8 molar and conventional cement mortar. The compressive and flexural strengths of ambient-cured alkali-activated slag mortar increased by 22% and 15% respectively, compared to the other mixes up to 0.06% GO addition. This is due to accelerated alkali activation of slag owing to the higher specific surface and amorphicity of these nanoparticles, as confirmed by microanalyses. Additionally, the resistance to chloride-ion penetration is also enhanced due to this GO addition, making this a viable option for usage in aggressive environments.

The global annual production of 4.1 billion tons of portland cement (PC) causes significant carbon dioxide emissions and depletion of natural limestone reserves. Alkali-activated binder (AAB) is a possible sustainable solution to this problem. AAB is produced by the reaction between an aluminosilicate-rich precursor (such as low calcium fly ash, blast furnace slag, and metakaolin obtained as industrial waste and by-products) and an alkaline activator composed of sodium silicate and sodium hydroxide. AAB is a potential substitute for PC to lower the carbon footprint and prevent industrial waste disposal into utilizable land. The present formulation of AAB needs thermal curing, which is energy-intensive for plant and field productions. In-situ thermal curing at 60–80 °C is impracticable and limits AAB usage to precast members only. This study focuses on developing AAB mixtures cured at ambient temperature and characterizing their mineralogical, chemical, and mechanical properties for varying precursor proportions (fly ash to slag ratios) and activator modulus, Ms, calculated as (sodium silicate: sodium hydroxide). Using these proportions, the compressive strength and bond strength of alkali-activated concrete (AAC) cured under ambient conditions are evaluated at room temperature and under the influence of high exposure temperatures up to 900 °C. AAC prepared using 70% fly ash, 30% slag, and Ms of 1.4 with ambient curing is proposed as optimal from this study.

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.

Portland cement (PC) concrete is one of the most popular construction materials with significant embodied carbon. It is anticipated that India's planned infrastructural development will increase PC production to 800 million tons per annum over the next decade. In addition to global warming, waste disposal is another major concern for environmental sustainability. Building-derived materials (BDMs) generated from construction and demolition activities, and industrial wastes like fly ash (FA) accumulate rapidly due to India's infrastructural development. This research investigates an alkali-activated binder (AAB) concrete made of FA, ground granulated blast furnace slag (SG) binders, and BDM aggregates to reduce the use of PC and reuse the waste. For this study, four AAB mixes with FA:SG ratios of 100:0, 70:30, 60:40, and 50:50 with five different aggregate replacement percentages (0, 25, 50, 75, and 100% BDM) are studied. Crushed BDM is obtained from the demolition of matured M35-grade concrete specimens. Physical, mineralogical, and morphological characteristics of crushed BDM are determined to evaluate their utility as aggregates. Compressive strength results show that the mix with FA: SG of 70:30 and 100% BDM is optimal and recommended for practical use for structural members.

Owing to their lower carbon footprint and efficient performance compared to portland cement (PC), alkali-activated binders (AAB) show promising potential as an alternative to PC. The present paper investigates the high-temperature performance of AAB concrete through compressive and bond strength tests. Four different AAB concrete mixes with varying proportions of fly ash: slag (100:0, 70:30, 60:40, and 50:50) cured under ambient conditions are exposed to elevated temperatures. The mechanical performance of AAB concrete is corroborated with microstructural changes. The results show that AAB concrete with fly ash: slag ratio of 70:30 exhibits the best mechanical performance after exposure to elevated temperatures. This behaviour is attributed to the growth of new crystalline phases of akermanite and gehlenite as observed from the X-ray diffraction patterns. This study shows that there is an optimum proportion of slag content beyond which the mechanical performance of AAB concrete significantly deteriorates when exposed to elevated temperatures. The failure pattern of AAB concrete during the bond strength test varies with the precursor proportion and the exposure condition.

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.

This study is aimed at development and testing of concrete made using alkali-activated binders (AAB) and cured at ambient temperatures. Standard test specimens are prepared for evaluating compressive strength, flexural strength, and splitting tensile strength. Numerical models of AAB test specimen are developed in ABAQUS and are calibrated using the experimental results. The numerical models are used for reliability analysis of AAB concrete test specimen using Monte Carlo simulations. The performance functions for AAB concrete for failure in compression, flexure, and splitting tension are derived. The results of the reliability analysis elucidate that the trends in the AAB concrete failure are similar to that of Portland cement (PC) concrete failure, with flexural loading being the governing failure mode. These results instigate a further exploration of AAB concrete as a viable alternative of PC concrete.

The compressive strength of alkali-activated binder (AAB) concrete is governed by several factors like type, chemical composition and proportion of raw materials, and curing regime. Empirical prediction of such a relationship entails the utilisation of robust and intelligent algorithms. Random Forest (RF) is an advanced ensemble algorithm with advantages of effective generalisation ability, strong resistance to overfitting, and importance analysis. Several approaches to improve the prediction accuracy of RF are available in the literature. The present study aims to compare the accuracy of RF and its different configurations to predict the compressive strength of ambient-cured AAB concrete. Five different RF packages, RF, regularised RF, cforest, ranger, and random forest-SRC, are used in the present study. Three attribute evaluators from the feature selection module: classifier attribute evaluator, correlation attribute evaluator, and reliefF are investigated to find the relative importance of the input parameters. A total of 364 data sets with seven input parameters (fly ash, slag, sodium silicate (SS), sodium hydroxide (SH), fine aggregate, coarse aggregate, the molarity of SH) are used to evaluate the compressive strength of AAB concrete. The results show that the ranger algorithm with reliefF feature selection developed using the selected database exhibits the most accurate prediction based on MAE and RMSE values. It is also observed that the molarity of SH is the most critical factor affecting the compressive strength of ambient-cured AAB concrete.

The durability of concrete is significantly influenced by its binder composition, especially in the presence of aggressive chemical environment. This paper represents a study on the strength, durability, and corrosion resistance of quaternary blended mortar made with Portland pozzolana cement (PPC), ground granulated blast furnace slag (GGBS) and rice husk ash (RHA) exposed to marine environment. Binary blended concrete mix using GGBS and RHA as partial replacement for cement is already well established. Previous research reports several shortcomings in using binary blended and ternary mix including low initial strength and increasing shrinkage strains with increasing percentages of GGBS, silica fume and RHA as partial substitutes for cement. Hence, this study is focused on overcoming the limitations of binary and ternary blended mixes by implementing a quaternary blended mix using GGBS and RHA to partially replace cement. This quaternary blended cementitious system is optimized based on its mortar compressive strength, determined by varying the percentages of GGBS and RHA as substitute for cement. These optimized quaternary mortar specimens are moist-cured for 28 days and then exposed to an artificially prepared marine environment for 180 days. The optimized quaternary blended mortar specimens show improved mechanical strengths, both compressive and flexural. These specimens also exhibit enhanced resistance to chloride penetration, corrosion, and water absorption compared to the control mix after 28 days of water curing. A quaternary blended mortar mix prepared with 70% PPC, 20% GGBS, and 10% RHA exhibits the maximum mechanical strength, resistance to chloride penetration, and corrosion, mass loss and water absorption upon exposure to marine environment up to a period of 180 days. Mineralogical analyses using X-ray diffraction (XRD), chemical bond analyses using Fourier Transform Infra-Red (FTIR) spectroscopy, and microanalyses using scanning electron microscopy (SEM) in conjunction with energy dispersive X-ray spectroscopy (EDS) are implemented to determine the effects of marine environment exposure on the different mixes. The findings are then used to corroborate the observations from the specimen scale mechanical and chemical characterizations.

Alkali-activated binder (AAB) is gaining popularity as a viable substitute for Portland cement (PC). A reaction between aluminosilicate-rich precursors, generally industrial residue including fly ash and/or slag, and alkaline activators like sodium/potassium silicate and/or hydroxide produces AAB. Previous research on AAB shows their superior mechanical performance compared to PC. However, AAB with a greater proportion of slag tends to exhibit higher shrinkage than PC. Owing to the complex chemistry of AAB, its final performance as a binder depends on several factors like the type and combination of precursors used, chemistry of activators, and curing conditions. The present study, therefore, is an experimental investigation to evaluate the drying shrinkage of AAB paste, mortar and concrete with varying precursor and activator combinations. In this study, the drying shrinkage strains of AAB prepared using two different slag: fly ash ratios of 30:70 and 40:60 are determined for paste, mortar, and concrete specimens. The silicate modulus (silica to sodium oxide ratio or Ms) of the activating solution is varied as 1.0 and 1.4, and the corresponding effect on shrinkage is evaluated. The shrinkage strains were calculated from length changes measured using a length comparator and height gauge. The results from the present study show that optimum proportioning precursors reduce the drying shrinkage of AAB. Explanations were presented for the possible mechanisms which improve the dimensional stability of AAB.

Synthetic activators used in alkali-activated binder are the primary contributors to its adverse environmental effects. Therefore, this study aims to perform a life cycle assessment of alkali-activated mortar (AAM) prepared from industrial waste as precursors and activators. The impact analysis is performed through ReCiPe methodology for six different AAM mixes. Environmental impacts of replacing conventional precursors (fly ash and slag) with waste ceramic powder (WCP) and red mud (RM) and conventional activators (sodium silicate (SS) and sodium hydroxide (SH)) with RM, desulfurization dust, and silica fume are assessed. The efficiency of ReCiPe is compared with recommendations from the International Reference Life Cycle Data System. Sensitivity analysis for SH produced using three different techniques and simplified cost analysis for the mortar mixes is conducted. SS is observed to contribute 50–59% of climate change for mixes with conventional activator combination. WCP as a precursor warrants higher dosage of SS and SH, thereby increasing the environmental impact. Replacing SS with silica fume has the least negative effects on ecosystem quality and human health. AAM prepared with conventional activators shows lower resource depletion due to a lower dosage of activators and the absence of pretreatment of fly ash. ReCiPe can be used to evaluate all the impact categories except freshwater ecotoxicity and human toxicity, for which USEtox is suggested. Sensitivity analysis shows that the membrane cell process of SH production is eco-efficient. Savings of up to 14% are observed by replacing both precursors and activators with industrial residues.

Among the recent discoveries for alternatives of portland cement (PC) concrete, Alkali-activated binder (AAB) concrete is prolifically being considered as the most eco-friendly and sustainable alternative. The present study evaluates the shrinkage behaviour for three different AAB mixtures containing fly ash and/or slag at different proportions which are activated by sodium hydroxide and sodium silicate. Multiple linear regression models are developed to predict shrinkage strains of ambient-cured AAB concrete as a function of age and percentage of fly ash in the precursor. The aim of this work is to come up with a generalized equation that can predict the shrinkage of various binary blended AAB mixes cured at room temperature. The predicted models are ranked based on RMSE and then compared with the experimental data. The correlations were found to be quite satisfactory (R-2 = 0.937) and can be used to estimate the shrinkage for similar AAB mixtures. It is observed that the proposed model agrees more closely with the experimental results from the present study.

The current scenario of construction industry highlights the need for development of sustainable construction materials that provide properties comparable to portland cement (PC). Alkali-activated binder (AAB) produced by alkaline activation of aluminosilicate-rich industrial wastes, like fly ash and slag is one such potential alternative to PC which substantially reduces the embodied energy of concrete and solves the problem of industrial wastes disposal. However, the practical usage of AAB is limited owing to the complexity in optimizing the mix. The performance of AAB is influenced by several parameters, type and composition of activators, proportion and composition of the precursors, and curing conditions. Previous research on AAB substantiate its high-temperature stability compared to PC. The specimen-level performance of AAB can be well estimated from its microstructural changes. However, there is limited research reported on the mechanism contributing to the enhanced high-temperature stability of blended-AAB. The present study aims to investigate comprehensively the microstructural evolution of fly ash/slag-based AAB when exposed to high-temperatures. Three AAB mixes with varying fly ash: slag ratio (100:0, 70:30 and 50:50) are exposed to four different temperatures (ambient, 538 degrees C, 760 degrees C and 892 degrees C). The microstructural evolution is investigated using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microcopy and energy dispersive spectroscopy. The findings from the present study conclude that considerable changes in the microstructure are evinced only after 760 degrees C. Higher slag content is favorable under ambient conditions, but degrades the performance of AAB at high-temperatures. Incorporation of optimum content of slag promotes the formation of new crystalline phases enhancing the high-temperature performance. (C) 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Recent Advances in Materials & Manufacturing Technologies.

To reduce the CO2 emissions associated with the manufacture of portland cement (PC), an efficient alternative like an alkali-activated binder (AAB) is the requirement of the industry. To promote the use of AAB in construction activities, a practically implementable mix proportion is required. Owing to the several raw ingredients of AAB concrete and their associated uncertainties, partial replacement of PC by AAB may be adopted instead of complete replacement as per industrial requirements. Hence, the present study aims to determine an optimal proportion for partial replacement of PC with AAB and recommend a technique for it based on site conditions. Three modes of partial replacement are followed: combining all the dry ingredients for AAB and PC followed by the addition of the requisite liquids (PAM); combining the PC and the AAB concrete in two horizontal layers (PAH); and two vertical layers (PAV). 28-day old specimens are exposed to 10% v/v solutions of HCl, H2SO4, and HNO3 to evaluate changes in mechanical, physical, and microstructural characteristics through compressive strength, corrosion depth, and microscopy. Based on deterioration in strength and integrity, PAH or PAV can be adopted in absence of acid attack, whereas PAM is recommended in presence of acid attack.

Enormous global CO2 emissions associated with cement production necessitates the use of sustainable cementitious alternatives. Alkali-activated binder (AAB) which utilizes industrial wastes as precursors is a promising substitute for cement. To promote the practical use of AAB concrete, this paper presents an investigation on the mechanical and microstructural properties of ambient-cured AAB concrete. Fly ash/slag ratio is varied and the optimum mix is proposed based on compressive strength test results. Pull-out test is performed to evaluate the bond strength of ambient-cured reinforced AAB concrete. The specimen-level tests are supplemented with results from X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) along with energy-dispersive spectroscopic (EDS) analysis of the AAB paste samples. This is done to corroborate the microstructural characteristics with the mechanical properties at specimen-level. Fly ash: slag ratio of 70:30 is recommended as the optimum proportion considering both strength and economical aspects. Incorporation of slag results in the formation of the additional reaction products, refining the pore structure and enhancing strength. The AAB mix with fly ash: slag ratio of 50:50 exhibits the highest compressive strength and bond strength.