An orthogonal experimental study on the influence of steam-curing on mechanical properties of foam concrete with fly ash

Abstract

Foam concrete can be widely utilized as precast walls for its low density, excellent heat resistance and sound insulation. The challenge of its application is its low strength due to the porous matrix, which prolongs the demolding time. Steam curing at an early time is a common strategy to improve its early-age strength. Here, an orthogonal experiment (OA16) was adopted to investigate the influence of curing parameters on the properties of foam concrete. Specific compressive strengths (SCS) given as the ratio of the strength and the density at 12 h (12 h) and 28 days (28d) were calculated to evaluate the early-age and long-age strength. The range analysis and the analysis of variance (ANOVA) showed that the optimum steam-curing system that can yield the highest 12 h SCS (1.9 MPa, which meets the demand for demolding) is that preheating temperature of 25 ℃, preheating duration of 4 h, curing temperature of 50 ℃, together with 1.5% early-strength agent Na2SO4. Compared to the normal cured concrete, the addition of mineral power (fly ash by 20%) will successfully increase the early-age strength under steam curing, while XRD, SEM and FTIR analysis all show there are more hydrated products formed after steam curing and the activity of fly ash is activated to form C-S-H gels. However, improving early-age strength too much will lead to a deficiency of later-age strength growth. MIP analysis also exhibited high pore probability in the sample cured under higher steam-curing temperatures. These results can provide experiences for the wide application of foam concrete in precast walls and help improve the efficiency of their template turnover.

Keywords

• Foam concrete
• Orthogonal experiments
• Steam curing
• Early-age strength
• Long-term strength
• Fly ash activity