International Journal of Advanced Engineering Application

Microstructural Characterisation of M30 Grade Concrete Incorporating Fly Ash and Ground Granulated Blast-Furnace Slag as Supplementary Cementitious Materials

Author(s):Rajesh Kumar Verma

Affiliation: Department of Civil Engineering, National Institute of Technology Warangal, Warangal, Telangana, India

Page No: 62-66

Volume issue & Publishing Year: Volume 3, Issue 6, 2026/06/10

Journal: International Journal of Advanced Engineering Application (IJAEA)

ISSN NO: 3048-6807

DOI:

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Abstract:
The partial replacement of Ordinary Portland Cement (OPC) with supplementary cementitious materials (SCMs) represents a key strategy for addressing the dual imperatives of structural performance and carbon footprint reduction in the Indian construction industry, where OPC production accounts for approximately 8% of global CO₂ emissions. Fly Ash (FA), the fine particulate residue collected from coal-fired thermal power stations — generated at approximately 220 million tonnes per year in India, with only 67% utilisation — and Ground Granulated Blast-Furnace Slag (GGBS), a latent hydraulic by-product of pig iron smelting in blast furnaces, are both well-established SCMs whose individual effects on concrete properties have been extensively documented. Ternary blends combining FA and GGBS at optimised proportions offer potentially synergistic structural and durability benefits that exceed those achievable through individual binary substitution, but systematic comparative data under central Indian construction material conditions and humidity regimes remain limited. This study investigates the fresh, hardened mechanical, and durability properties of M30 grade concrete incorporating FA (20%, 40% cement replacement by weight), GGBS (30%, 50% replacement), and a ternary blend (20% FA + 30% GGBS) across six mix designs. Properties evaluated include workability (slump, compacting factor), compressive strength at 28 and 90 days, flexural and split tensile strength, water absorption, chloride ion permeability by RCPT (ASTM C1202), and SEM/EDX microstructural analysis at 28 days. Load-deflection responses of reinforced beams (150×200×1200 mm) and Mercury Intrusion Porosimetry (MIP) pore structure evolution at ages 3–90 days provide structural and microstructural development data. The M30 + 20% FA + 30% GGBS ternary blend achieves the highest 90-day compressive strength of 44.8 MPa (23% above control), with chloride permeability of 688 C (RCPT) — a 49% reduction versus control — and embodied CO₂ of 276 kg/m³ (34% reduction). SEM analysis confirms dense interfacial transition zones and markedly reduced calcium hydroxide crystallinity in GGBS-rich specimens. EDX reveals elevated Al/Ca and Si/Ca ratios in the ternary blend consistent with extensive C-S-H and C-A-S-H gel formation. The ternary blend is recommended as the optimal mix design for M30 structural concrete in moderate-to-severe chloride exposure environments.

Keywords: GGBS, supplementary cementitious materials, compressive strength, durability, chloride permeability, SEM, EDX, carbon footprint, ternary blend

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