Thermal Performance of Sustainable Concrete at Elevated Temperatures

Abstract

Concrete is a heterogeneous composite material composed primarily of cement, aggregates, and water, often enhanced with supplementary cementitious materials and chemical additives to meet specific strength and durability requirements. The performance of concrete under elevated temperature conditions is highly dependent on its composition, making the behaviour of different concrete types significantly variable during and after thermal exposure. Furthermore, post-fire properties are influenced by several factors, including heating rate, curing duration and method, cooling regime, and mix constituents. This paper presents a comprehensive review of the influence of concrete constituents on the behaviour of concrete subjected to elevated temperatures. The findings indicate that the incorporation of fibers can enhance the residual tensile capacity of concrete; however, it may also increase the susceptibility to spalling due to the development of internal stresses. Supplementary cementitious materials, such as metakaolin and silica fume, are observed to improve strength characteristics, with silica fume demonstrating the most significant enhancement. Additionally, materials such as fly ash and silica fume contribute to reduced permeability, improved workability, and increased compressive strength, particularly at moderate levels around 200 °C. In general, most concrete types exhibit a gradual reduction in strength up to approximately 400 °C, followed by a more pronounced deterioration at higher temperatures. Beyond 800 °C to 1000 °C, significant structural degradation and spalling occur, rendering the material incapable of sustaining load. The review highlights the critical need for further research and the development of design code provisions that explicitly account for the effects of different concrete constituents and emerging sustainable materials under elevated temperature conditions.

Introduction

This study reviews the behavior of different types of concrete under elevated temperatures and fire exposure, highlighting the growing need for fire-resistant construction materials due to increasing fire incidents worldwide. Fires pose serious threats to human life, infrastructure, and economic resources, particularly in rapidly urbanizing regions. Although modern concrete technologies such as fiber-reinforced, self-compacting, and self-healing concrete have improved structural performance, their response to high temperatures remains a significant area of research.

Concrete undergoes complex physical and chemical changes when exposed to heat. At temperatures around 100°C, free water evaporates, causing mass loss, while compounds such as ettringite decompose. Between 450°C and 550°C, portlandite decomposition leads to significant strength reduction. Around 573°C, quartz aggregates experience phase transformation, creating internal stresses and cracking. Above 700°C, the decomposition of calcium silicate hydrate (C-S-H) gel severely weakens the concrete matrix, and at temperatures between 600°C and 1200°C, concrete loses most of its load-bearing capacity.

The performance of concrete under fire depends greatly on its composition, including aggregates, binders, supplementary cementitious materials (SCMs), and fibers. Aggregate type significantly influences thermal stability; calcareous aggregates generally perform better than siliceous aggregates because they avoid quartz phase transformation and retain more residual strength. Materials such as silica fume, metakaolin, fly ash, and slag can improve durability and thermal resistance, while fibers help reduce cracking and spalling.

Normal Strength Concrete (NSC), typically having compressive strengths of 20–55 MPa, is widely used due to its cost-effectiveness and balanced properties. Under moderate temperatures (200–300°C), NSC may temporarily gain strength due to continued hydration and pozzolanic reactions, especially when silica fume is incorporated. However, beyond 400°C, strength decreases significantly because of dehydration, cracking, and mass loss. NSC containing calcareous aggregates demonstrates better fire resistance than mixes with siliceous aggregates. Air-entraining agents can also reduce explosive spalling by relieving internal vapor pressure.

High Strength Concrete (HSC) offers superior mechanical strength and durability because of its dense microstructure and low water-cement ratio. However, this dense structure makes HSC more vulnerable to explosive spalling during fire exposure because trapped vapor generates high internal pressures. Various mitigation techniques, including the use of limestone aggregates, air-entraining admixtures, polypropylene fibers, metakaolin, and ground pumice, improve thermal performance by increasing permeability and reducing internal pressure buildup. Some HSC mixes can retain up to 70–80% of their original strength at temperatures of 500–600°C when properly modified.

The study also emphasizes the importance of cooling conditions after fire exposure. Natural air cooling generally causes less damage than rapid water quenching, which creates thermal shock, increases cracking, and reduces residual strength. Experimental approaches such as stressed, unstressed, and residual testing are used to assess post-fire behavior, with residual testing being the most common due to its practicality.

Conclusion

Overall, the review concludes that concrete fire performance is strongly influenced by material composition, aggregate type, supplementary cementitious materials, fibers, heating rates, and cooling methods. Existing design standards such as ACI and Eurocode do not fully account for these variables, highlighting the need for more comprehensive predictive models and updated guidelines for modern sustainable concrete materials exposed to fire conditions.

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Copyright

Copyright © 2026 Mali Omprakash Dinkar, Prof. Hemant D. Wagh, Dr. D. M. Patel. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.