Mechanical Performance, Microstructural Analysis with Metakaolin and Fly Ash as Supplementary Cementitious Materials

Author(s): Suresh R. Kulkarni

Affiliation: Department of Civil and Structural Engineering, Visvesvaraya National Institute of Technology, Nagpur, India

Page No: 66-70

Volume, Issue & Publishing Year: Volume 3, Issue 7, July 2026

Journal: International Journal of Advanced Engineering Application (IJAEA)

ISSN NO: 3048-6807

Abstract:
The growing environmental urgency to decarbonise cement-intensive construction has accelerated interest in high-volume supplementary cementitious material (SCM) blends that simultaneously reduce clinker factor and enhance structural performance. Metakaolin (MK), produced by calcining kaolin clay at 600–800°C, and Fly Ash (FA), the aluminosilicate by-product of coal combustion, are both established SCMs whose individual effects on concrete are well characterised; however, systematic multi-variable data on M30 grade concrete incorporating varying MK and FA replacement levels under Indian temperature and humidity conditions remain limited. This study investigates the fresh, mechanical, and long-term durability properties of M30 concrete mixes incorporating MK at 5%, 10%, 15%, and 20% cement replacement and FA at 5% and 10% replacement, with a control mix for baseline. Properties evaluated include slump, compressive strength at 28, 56, and 90 days, flexural strength, split tensile strength, water absorption, Rapid Chloride Permeability Test (RCPT) charge passed, and CO₂ emissions. Load-deflection response of reinforced beams and Mercury Intrusion Porosimetry (MIP) pore-structure evolution at ages 3–90 days characterise structural performance and microstructural development. M30 + 15% MK achieves 90-day compressive strength of 49.7 MPa — 31.5% above the control — and the lowest RCPT value (680 C, classified "Very Low" per ASTM C1202), accompanied by a 13% CO₂ reduction versus the plain M30 control. SEM analysis confirms dense, well-knit interfacial transition zones in MK-modified specimens, while EDX reveals elevated Si/Ca and Al/Ca ratios consistent with extensive secondary pozzolanic C-S-H and zeolitic product formation.

Keywords: metakaolin, fly ash, supplementary cementitious materials, M30 concrete, compressive strength, chloride permeability, SEM, EDX, pozzolanic reaction, durability

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