# Effects of aircraft operating fluids and environmental thermal fatigue on fly ash and steel slag based cementitious composites

## TL;DR

This study examines how fly ash and steel slag in concrete resist damage from thermal fatigue and aircraft fluid exposure.

## Contribution

The paper introduces the combined use of fly ash and steel slag to mitigate environmental damage in cementitious composites.

## Key findings

- High-volume fly ash reduces portlandite, improving resistance to environmental stress.
- Steel slag aggregates enhance matrix interlocking but initially weaken flexural strength when exposed to aircraft fluids.
- Hybrid fibres improve flexural strength and reduce cracking in the composite.

## Abstract

This paper investigates the performance of concrete incorporating high-volume fly ash (HVFA) and steel slag aggregates against the detrimental effects of combined cycles of environmental thermal fatigue and exposure to leaked aircraft fluids. A total of 128 cubes and 90 prisms were cast for five mixes and exposed to 60, 120, 180, 240 and 300 combined cycles. The results demonstrate the positive effect of utilization of HVFA which reduces the total amount of portlandite available in the system. The SS aggregates demonstrate a strong interlocking with the surrounding matrix and supply the necessary portlandite for continued pozzolanic reaction. However, their reaction with aircraft fluids causes significant degradation to flexural strength initially, which is redeemed by pozzolanic reaction at a later stage. Hybrid basalt and polypropylene fibres were successful in enhancing the flexural strength and reducing the cracking. The mercury intrusion porosimetry revealed a reduction in pore volume because of HVFA. Scanning electron microscopy and differential scanning calorimetry were also employed to uncover the underlying mechanisms of damage and assess the performance of the cementitious composite.