Effect of curing temperature on creep behavior of fly ash concrete

• We examined the creep of concretes cured under temperatures of 20 °C, 50 °C and 90 °C.
• The influence of temperature was analyzed by a variety of microscopic analysis.
• The main factor of effecting creep is quantity and microstructure of C–S–H gel.
• The hydration products have a trend of crystallize under curing temperature of 90 °C.

To investigate the effect of curing temperature on creep behavior of fly ash concrete, the specific creep of concretes, with the water-binder ratio of 0.33 and different fly ash replacements of 20% and 40%, cured under temperatures of 20 °C, 50 °C and 90 °C was examined. All concrete specimens were loaded at 33% of their compressive strength to measure the creep, when they had an equivalent cubic strength of (48.0 ± 2.0) MPa. Based on the amount of non-evaporable water, the porosity and pore size distribution of hardened cement pastes, the scanning electron microscope (SEM) morphology of hydration products and X-ray diffraction (XRD) analysis, the influence of curing temperature on creep of fly ash concrete was analyzed. The results show that when concretes were loaded with the same stress level, the main factor influencing creep of fly ash concrete was the quantity and microstructure of C–S–H gel. Compared with the concrete with 20% fly ash dosage under the curing temperature of 20 °C, the concrete cured under the temperature of 50 °C produced more hydration products, with a slight decrease of Ca(OH)2, and the specific creep of which is close to the reference concrete. At the curing temperature of 90 °C, concrete also produced more C–S–H gel, with a great decrease of Ca(OH)2, and the total specific creep after 360 days is 87.1% of the reference concrete. The hydration products had a trend of crystallizing under temperature of 90 °C and fly ash concrete produced a few hydration products of Tobermorite which could reduce the creep evidently. The concrete with 40% fly ash dosage under the cuing temperature of 50 °C also produced more hydration products, but the specific creep of which increases significantly and is 119.5% of the reference concrete.