Authors:
Mohammed K. Abed, Isam M. Ali, Mohammed Salah Nasr, Ahmed Samir Naje, Anishbhai Vahora, Abul Hasan

Addresses:
Department of Civil Techniques, Al-Furat Al-Awsat Technical University, Kufa, Al-Najaf, Iraq. College of Engineering, University of Babylon, Hillah, Babylon, Iraq. Department of Water Resources Engineering Management, College of Engineering, Al-Qasim Green University, Al-Qasim, Babylon, Iraq. Department of Engineering, Brask Inc. – IEE, Sulphur, Louisiana, United States of America. Department of Mechanical Engineering Technology, Augusta Tech Drive, Augusta Technical College, Augusta, Georgia, United States of America.

Abstract:

This research investigates the overall mechanical and thermal performance of reactive powder concrete (RPC) subjected to elevated temperatures of 250°C, 400°C, and 600°C for soaking periods of 30 and 60 minutes. Two mixture designs were evaluated: a conventional reference matrix (Mix R) with a low water-binding ratio of 18%, and a fibre-reinforced composite containing 0.2% volume fraction of polypropylene (PP) fibres (Mix RF). Each mixture was hyperthermally stable at 250°C, with internal autoclaving favouring secondary pozzolanic reactions. Compressive losses were 2.50% for Mix R and 3.49% for Mix RF at 28 days. At 400°C, portlandite and calcium-silicate hydrate (C-S-H) gel dehydrated, decreasing compressive strength by 14.5% and 17.1%, respectively. This effect intensified after 60 minutes of soaking. The traditional matrix (Mix R) at 600°C had destructive, explosive thermal spalling and premature failure due to asymmetric internal vapour flow trapped in its ultradense microstructure. However, adding 0.2% PP fibres to Mix RF melted them, creating a continuous network of interconnected microcapillary channels that efficiently facilitated internal hydrostatic vapour flow, maintaining structural integrity and providing a controlled, progressive thermal degradation pathway for internal vapour-stress relief. By providing micro-channels for internal vapour pressure relief, 0.2% polypropylene fibres prevent explosive thermal spalling in Reactive Powder Concrete (RPC) at 600°C. The AI model also accurately predicted residual compressive strength (R2 = 0.999), suggesting that fibre dose is the most important element with a 50.2% relative contribution. 

Keywords: Reactive Powder Concrete (RPC); Thermal Degradation; Elevated Temperature; Thermal Spalling; Hyperthermal Stability; Compressive Strength; Microcapillary Channels.

Received on: 23/06/2025, Revised on: 08/10/2025, Accepted on: 19/10/2025, Published on: 05/06/2026

DOI: 10.69888/FTSSM.2026.000757

FMDB Transactions on Sustainable Structures and Materials, 2026 Vol. 2 No. 1, Pages: 52-69

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