Microstructural Characterization of the Interfacial Transition Zone in Self-Compacting Concrete Using Multi-Scale Techniques

IJEP 45(13): 1157-1166 : Vol. 45 Issue 13 (Conference 2025)

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Rama Krishna Rao Annavarapu1, Pitta Sundara Kumar1*, Srinivasa Reddy Vempada2 and Kosaraju Satyanarayana3

1. Vignan’s Foundation for Science, Technology and Research (Deemed to be University), Department of Civil Engineering, Guntur – 522 213, Andhra Pradesh, India
2. KG Reddy College of Engineering and Technology, Department of Civil Engineering, Hyderabad – 501 504, Telangana, India
3. Gokaraju Rangaraju Institute of Engineering and Technology, Department of Mechanical Engineering, Hyderabad – 500 118, Telangana, India

Abstract

This study provides a detailed investigation of the interfacial transition zone (ITZ) in M30 grade self-compacting concrete (SCC), focusing on its impact on strength, durability and failure mechanisms. The results show that adding supplementary cementitious materials (SCMs) to the highly flowable and cohesive SCC creates a denser, more refined ITZ than in conventional concrete. A variety of advanced characterization techniques—including micro-CT, mercury intrusion porosimetry (MIP), nanoindentation, scanning electron microscopy (SEM) and backscattered electron imaging (BSE)—were used to examine the microstructural features of the ITZ. Findings reveal increased microstructural uniformity, decreased porosity and a significant reduction in ITZ thickness to about 10–20 mm. Nanoindentation results also showed improvements in hardness and elastic modulus within the ITZ, indicating a stronger interfacial bond. Moreover, XRD and EDX analyses confirmed a lower Ca/Si ratio and reduced calcium hydroxide content, supporting the occurrence of pozzolanic reactions. Overall, these findings demonstrate that SCMs like flyash and silica fume significantly improve ITZ performance. The uniqueness of this research lies in its combined use of multiple characterization methods, enabling a comprehensive understanding of ITZ development in SCC and offering valuable insights for optimizing mixture design and long-term durability assessments.

Keywords

Interfacial transition zone, Self-compacting concrete, Microstructural characterization, Supplementary cementitious materials, Multi-scale analysis

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