TOWARDS CARBON-NEUTRAL CEMENT: MULTISCALE STRUCTURAL, CHEMICAL, AND PERFORMANCE EVOLUTION OF ULTRA-HIGH GGBS BLENDED SYSTEMS FOR NEXT-GENERATION LOW-CARBON CONCRETE

Abstract

The urgent global emphasis on decarbonizing the construction industry has intensified the search for low-carbon alternatives to traditional Portland cement, which remains one of the largest contributors to anthropogenic CO₂ emissions. Ground granulated blast-furnace slag (GGBS) has emerged as a highly effective supplementary cementitious material (SCM) capable of significantly lowering clinker demand while enhancing long-term durability. This study provides a comprehensive multiscale investigation into the structural, chemical, and performance evolution of ultra-high GGBS blended systems, defined as cementitious formulations incorporating 60–85% slag replacement. The research aims to elucidate the underlying hydration mechanisms, microstructural transformations, and engineering performance characteristics that govern the feasibility of deploying such high-volume slag blends for next-generation low-carbon concrete. Advanced characterization techniques, including SEM, XRD, TGA, FTIR, and MIP, were employed to analyze the hydration process and microstructural development across different curing ages. The results reveal a distinct shift from clinker-dominated hydration to slag-driven pozzolanic reactivity, leading to progressive formation of secondary C–S–H gels with lower Ca/Si ratios. These gels contribute to refined pore structures, reduced permeability, and enhanced long-term densification. Chemical analyses further confirm substantial portlandite consumption and the evolution of aluminosilicate hydrates, which improve resistance against sulfate attack, chloride penetration, and alkali–silica reactivity. Although early-age hydration is slower due to reduced clinker availability, mechanical performance significantly improves after extended curing, with optimized mixes achieving strengths comparable to or exceeding conventional OPC systems. Performance assessments demonstrate that the adoption of appropriate activators, curing protocols, and particle size optimization can effectively mitigate limitations such as delayed setting, low early strength, and reactivity variability. The study identifies key technical challenges such as sensitivity to temperature, dependence on alkaline activation, and industrial-scale variability in slag quality that must be addressed to ensure reliable field application. Nonetheless, the long-term performance benefits, including enhanced durability, reduced thermal cracking potential, and lower embodied carbon, firmly position ultra-high GGBS blends as a viable pathway toward carbon-neutral cement technologies. Overall, the findings provide critical scientific insights and practical guidance for the development of ultra-high slag blended cements. By establishing strong correlations between microstructural evolution, chemical transformation, and macro-scale performance, this work contributes to advancing sustainable cement innovation and supports global strategies aimed at reducing the environmental footprint of concrete construction.