Synergistic Effects of Fly Ash and Ground-Granulated Blast-Furnace Slag on Mechanical Performance, Microstructural Evolution, and Chloride Ingress Resistance of High-Durability Concrete for Aggressive Marine Environments

Author(s): Venkataraman K., Sridhar P.

Affiliation: Department of Civil and Environmental Engineering, Indian Institute of Technology Madras, Chennai, India

Page No: 16-22

Volume issue & Publishing Year: Volume 3, Issue 7, 2026/07/02

Journal: International Journal of Modern Engineering and Management | IJMEM

ISSN NO: 3048-8230

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Abstract:

Industrial by-products with latent hydraulic and pozzolanic reactivity offer a dual dividend for the concrete industry: reduction of clinker-associated carbon emissions and enhancement of long-term durability performance. Fly ash (FA), the aluminosilicate residue collected from the electrostatic precipitators of coal-fired power stations, and Ground-Granulated Blast-Furnace Slag (GGBS), the glassy granulated by-product of iron smelting, are the two highest-volume supplementary cementitious materials (SCMs) consumed globally, yet their binary and ternary combinations under Indian coastal exposure conditions remain incompletely characterised. This study evaluates M30 grade concrete incorporating FA (20%, 30%, 40% cement replacement by mass), GGBS (30%, 50% replacement), and a ternary blend (20%FA + 30%GGBS) across seven mix designs. Fresh properties (slump, Vebe time, setting time), hardened mechanical properties (compressive strength at 7, 28, 56, and 90 days; flexural strength; split tensile strength), and durability indices (water absorption, rapid chloride permeability test per ASTM C1202, accelerated carbonation depth at 28 days, and sulfate expansion at 180 days) are reported. Reinforced beam specimens (150×230×1500 mm) provide structural load-deflection data, and Mercury Intrusion Porosimetry (MIP) with Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) spectroscopy characterise microstructural development at 28 and 90 days. The ternary blend (20%FA + 30%GGBS) achieves 90-day compressive strength of 47.3 MPa, chloride permeability of 284 C (ASTM C1202 "Very Low"), sulfate expansion of 0.021% (well within IS 4031 limits), and embodied CO₂ of 294 kg/m³ — a 28% reduction from the OPC control. SEM confirms elimination of large portlandite crystals and densification of the interfacial transition zone (ITZ), while EDX reveals elevated Al/Ca ratios in GGBS-modified pastes, consistent with formation of hydrotalcite-type phases beneficial for chloride binding.

Keywords:

fly ash, GGBS, ground-granulated blast-furnace slag, supplementary cementitious materials, M30 concrete, chloride permeability, durability, marine exposure, SEM, ITZ, carbonation, sulfate resistance, embodied carbon

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