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In this investigation, four types of sands as alternatives to river sand, namely, crushed sand (CS), marine sand, fine recycled concrete aggregate (FRCA), and fine reclaimed asphalt pavement (FRAP), were studied for their potential for cement-concrete pavement applications. Initially, the physicochemical and morphological characteristics of these sands were understood and later linked to the hydration kinetics and the behavior of cement-mortar systems in both the fresh and hardened states. Due to their evenly graded particle size distribution, CS and FRCA exhibited higher packing densities despite having more gradient angularity, whereas the interlocking capacity of FRAP was found to be affected by the agglomerated particles. Morphology, fineness modulus, and chemical composition of the sands were observed to be the dominating parameters affecting the hydration kinetics and thus the performance of the mortar mixes. Improving these parameters, especially the grain size distribution, could help in enhancing the potential of these sands for pavement applications. [ABSTRACT FROM AUTHOR]

Due to a shortage of river sand for concrete production, manufactured sand (MS) made from crushed rock has gradually become a substitute. It inherently contains some fines content, which has significant effects on the performance of concrete. To study the effects of the MS type and fines content on the workability, cohesiveness, and strength, concrete mixes made with granite MS or limestone MS and different fines contents at various water/binder ratios were tested. Moreover, the packing density, water film thickness (WFT), paste film thickness (PFT), and microstructures of the concrete mixes produced were examined to investigate if their changes were the root causes of the effects of the MS used. It was found that the use of granite MS attained higher workability and strength but lower cohesiveness, which apparently were caused by the higher packing density and larger WFT and PFT. Also, regardless of the MS type, a fines content of about 10% was the optimum for highest packing density and best concurrent workability-cohesiveness-strength performance. Correlation analysis revealed that the MS and fines content exerted their influences on the workability and cohesiveness through the WFT and PFT, and on the strength through the packing density and microstructure. [ABSTRACT FROM AUTHOR]

Aggregate particle size distributions, shape characteristics, proportions and compaction level collectively influence packing density and, in turn, concrete properties. However, the available packing density prediction models either do not account for aggregate shape characteristics or if they do, the calculations are complicated and applicable only for well-graded aggregate systems. Hence, there is a need for the development of a simple and systematic model to predict aggregate packing density. The Aggregate Image Measurement System (AIMS) was used to obtain the shape parameters of aggregates. Aggregate shape indices were developed to correlate binary (gap-graded) aggregates. A new simple and structured RNP (Ramakanta Nabodyuti Prakash) model is presented in this paper for the estimation of packing density of binary coarse aggregate combinations with the use of shape parameters. The model was developed using a discrete element method (DEM) simulation in EDEM and validated using the experimental results. In the final section of the study, the compressive strength of engineered gap-graded concrete was also evaluated to test the applicability of the model. [ABSTRACT FROM AUTHOR]

Supplementary cementitious materials (SCMs) have become a part of cementitious composites in the manufacturing of cement for improved performance and sustainability. Composite cement is one such type of cement in which ordinary Portland cement (OPC) is partially replaced with fly ash and granulated blast furnace slag (GBFS). In this study, the replacement levels of fly ash and GBFS are optimized to 20% and 30%, respectively, with a 50% OPC content. Apart from the superior properties of these binding materials, a better packing of aggregate comes in handy for improved properties. In this study, the modified Taufer model (MTM) and J. D. Dewar (JDD) model of proportioning the fine aggregates are adopted for improved packing density to obtain better mixes, and a comparison is made with proportions recommended by Indian standard (IS) 383 and IS 650. The packing density obtained in proportioning fine aggregates using the MTM, JDD, IS 650:2008, and IS 383:2016 methods are 0.6814, 0.6737, 0.6238, and 0.6008, respectively. The aggregate sizes recommended based on particle packing models (PPM) particularly, the MTM method tends to improve the packing by reducing the voids content. A direct influence of such effective packing can be observed from the microstructure studies conducted on different samples. MTM samples evidenced better packing compared to other methods of proportioning the mixes. The compound phase changes and development of microstructure were examined using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), a back scattered electron (BSE), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Also, the quantification of portlandite and calcium carbonate available in the samples was determined using thermogravimetric analysis (TGA) and differential thermal analysis (DTA) for different proportions. At 28 days, the specimens cast using MTM showed 11.11% and 15.5% higher compressive strength than the specimens prepared using IS 650:2008 and IS 383:2016, respectively. At every stage of curing, MTM mixes exhibited superior compressive strength. [ABSTRACT FROM AUTHOR]

Studies on the characterization and performance of residual sugarcane bagasse ash (SCBA) obtained from high-temperature cogeneration boilers in concrete are highly limited. This study investigated the pretreatment process and optimization of SCBA collected from high-temperature boilers by various physicochemical methods. The effect of recalcination and grinding on the physical and mineralogical properties of SCBA were also examined. The percentage replacement of cement with SCBA was optimized using packing density and flow. The performance of optimized binder with combinations of cement and SCBA was validated through compressive strength of mortar specimens. From the results, it was observed that SCBA from high-temperature boilers can be used as a supplementary cementitious material with minimal processing efforts, and a 15% level of replacement is suggested as the optimum level for SCBA-blended cement. Based on the investigation, a framework with a step-by-step procedure including pretreatment and optimization methods is suggested for the use of SCBA. [ABSTRACT FROM AUTHOR]

In theory, the addition of fly ash microsphere (FAM), which is finer than cement, and condensed silica fume (CSF), which is even finer, to successively fill the voids between cement grains can increase the packing density of the cementitious materials and reduce the volume of voids to be filled with water. This would release more water to increase the flowability at same water/cementitious materials (W/CM) ratio or allow the W/CM ratio to be lowered to increase the strength at same flowability requirement. This study was aimed to evaluate the effects of FAM and CSF on the packing density of cementitious materials and the water film thickness (WFT) in cement paste and investigate the effects of the WFT on the flowability, cohesiveness, adhesiveness, and strength of cement paste. The results showed that adding FAM and CSF can significantly increase the packing density and WFT and thereby greatly improve the overall performance of cement paste. [ABSTRACT FROM AUTHOR]