Influence of Particle Packing Theories on Strength and Microstructure Properties of Composite Cement–Based Mortars

Abstract

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.