B. Naga Malleswara Rao

This study investigates the feasibility of incorporating recycled concrete aggregates (RCA) into fly ash-based geopolymer concrete for sustainable pavement applications. The research evaluates RCA’s physical and mechanical properties compared to virgin coarse aggregates (VCA) and assesses the performance of geopolymer concrete mixtures with up to 40% RCA replacement. Aggregate characterization revealed that RCA exhibited higher water absorption (4.39%), crushing value (20.9%), impact value (28.2%), and abrasion value (26.1%) compared to VCA, yet these values remained within acceptable limits for pavement applications. Geopolymer concrete specimens were tested for compressive strength, water absorption, abrasion resistance, and chloride ion permeability. Results indicated that increasing RCA content led to a gradual decrease in compressive strength, from 40.16 MPa to 33.52 MPa, while water absorption increased from 5.2% to 6.8%. Abrasion resistance declined as RCA content rose, and chloride ion penetrability increased from 1687 to 2196 coulombs. However, mixtures with up to 20% RCA replacement met the strength and durability criteria required for pavement construction. This study demonstrates the potential for utilizing RCA in geopolymer concrete pavements, offering a sustainable solution for waste management and resource conservation in the construction industry.

Conventional coarse aggregates, extracted from natural sources, pose environmental challenges such as habitat destruction, resource depletion, and high energy consumption. To mitigate these effects, this study prepared geopolymer aggregates (G.A.) using fly ash–GGBFS and an alkali ac- tivator solution through pelletization. Furthermore, two aggregate drying methods, oven drying, and ambient air drying, are adopted to evaluate their optimal performance through physical and mechanical tests. The results Indicated that oven-dried geopolymer aggregates exhibited optimal behavior in all experimental aspects compared to ambient air-dried aggregates. Specifically, the 80% fly ash–20% GGBFS mixed aggregates demonstrated lower crushing value (20.80%), impact value (24.7%), water absorption (13.67%), and abrasion values (7.01%) than other mixes. No considerable difference was observed in the density and specific gravity of aggregates between the two drying methods. Subsequently, these aggregates were used as a 100% replacement for conventional coarse aggregates in concrete, and the concrete's mechanical properties, such as compressive, split tensile, and flexural strengths, were investigated. Please update the following sentence in place of the highlighted sentence. The mix M3 (i.e., 80% fly ash–20% GGBFS mixed aggregates incorporated concrete) showed superior performance and are considered the opti- mum mix. Specifically, in the compressive strength results, the mix M3 showed a 26.31% and 14.28% strength increase compared to the 100% fly ash aggregates incorporated concrete mix in oven-dried aggregates and ambient-dried aggregates incorporated concrete, respectively. The lin- ear regression equation derived from the experimental results was used to predict the split tensile and flexural strength, showing a good correlation between the experimental and expected results.

The study was carried out with the influence of four Bacillus species, namely Bacillus subtilis (BS), Bacillus licheniformis (BL), Bacillus halodurans (BH), and Bacillus cereus (BC), in order to improve the impermeable nature of concrete. The selected bacterial agents were cultured according to the nutrient broth medium method and prepared with two variable cell concentrations of 108 and 109. In this study, bacteria were used in two different modes, i.e., as an additive to the concrete and as a curing agent. However, all the concrete specimens were cracked with a 65% stress level concentration and then cured in calcium lactate (only for bacteria-induced concrete specimens) and bacterial solution (only for normal concrete specimens) for crack healing. The durability behavior of these concrete specimens was monitored before crack, after crack, and after healing. In this regard, the following durability tests were performed: Rapid Chloride Permeability Test (RCPT), Water absorption test, Open porosity test, and Acid attack test. From the experimental observations, a decline in the passage of coulombs by 1352 C, water absorption by 3.47%, open porosity by 4.61%, and increased resistance against acid attack was found in normal concrete specimens cured under bacterial solution (especially in Bacillus halodurans with cell concentrations of 109) compared to other ones. Based on the analysis of the results, bacterial cultures have enriched the durability of the concrete by filling the voids and cracks with calcite crystals. However, Bacillus halodurans has shown better durability performance in both types of concrete, i.e., bacterial concrete cured in calcium lactate and normal concrete cured in bacterial solutions.

Erosion is a fundamental and complex natural process that is strongly modified by the activities such as land clearance, agriculture, forestry, construction, surface mining and urbanisation. Inventory on soil loss is vital for effective soil conservation planning of a watershed for sustainable development. An alternative sustainable practice is maintaining a tolerable level of erosion. To control erosion, sound land management practices are to be adopted. Modelling spatial distribution of soil erosion under alternate conservation plan options will help to select the option providing the desired benefits. Mathematical and physical based models with continuous simulation used for estimation of soil erosion requires time series data. The information obtained using remote sensing, Geographic Information System (GIS) techniques help the decision makers to prepare soil erosion map accurately in less time and less cost, which help in estimating, analyzing and solving the complex problem of soil erosion. Using the derived Digital Elevation Model (DEM) from the contour map, Slope and aspect maps have been prepared. In the present study Universal Soil Loss Equation (ULSE) is used for the estimation of soil erosion. The various ULSE factor such as, soil erodibility, slope, aspect, rainfall erosivity index factor map has been generated by linking the attribute data and digital soil map data. The developed GIS based ULSE factors are used in the soil erosion modelling under alternate land use conditions and the results are compared.