Enhancing the resistance of cementitious composites to environmental thermal fatigue using high-volume fly ash and steel slag

Daily fluctuations in environmental temperature induce thermal fatigue and cause degradation in concrete structures. This study introduces a novel approach of utilizing high-volume fly ash, steel slag fine aggregates, and basalt-polypropylene fibres to prevent degradation against environmental thermal fatigue (ETF). Five mixes were considered with variations in fine aggregate type, fibre length and volume. The compressive and flexural strengths were analysed after exposure to 60, 120, 180, 240, and 300 ETF cycles between 20 and 60 °C (at constant relative humidity). The residual compressive strength of mix with 100 % river sand and 100 % steel slag as fine aggregates was ∼106 % and ∼112 % respectively after 300 ETF cycles. The developed cementitious composites performed significantly better than the mixes utilized in the existing literature. The mix with 100 % steel slag aggregate even demonstrated a continual rise in compressive strength as opposed to mixes with river sand whose strength declined after 180 or 240 ETF cycles. Flexural strength also improved up to 180 ETF cycles and then started to decline in all mixes. A thorough microstructural analysis was also conducted using scanning electron microscopy, differential scanning calorimetry, and mercury intrusion porosimetry to gain further insights into the underlying mechanism of the newly introduced matrix composition against ETF.