Compressive strength development and durability properties of high-calcium fly ash incorporated concrete in extremely cold weather

Abstract

This research paper takes into account of three mineralogically different high calcium fly ashes (HCFA) consisted of anhydrite, generated in power plants in Ulaanbaatar, Mongolia. The purpose of this research is to understand how the morphology and mineralogy of HCFA influence the fresh and hardened properties of concrete; how pre-curing condition influences the long term strength development in different seasons; and to investigate the durability of HCFA concrete in extreme outdoor exposure conditions and freezing and thawing environment. Compressive strength development of fly ash concretes up to 540 days in extremely cold weather, strength dependence on pre-curing condition, freezing and thawing durability and the influence of ash mineralogy on durability were investigated. As a part of the investigation, the concrete specimens were kept outdoor at sub-zero temperature for more than four months. This paper concludes that strength approximately equal to that of the control can be obtained at early ages by 20 wt% replacement of total cementitious content by fly ash. When a comparison is made with equal mixtures, but equal pre-curing, winter concrete can only be achieved approximately 80% strength of autumn concrete after 3 months and then no considerable improvement happens even at one year. When a comparison is made with equal mixtures, but different pre-curing, the specimens exposed to the outdoor a day after placement show a permanent strength loss of 24%, with compare to the specimens cured in water at 20 °C for 28 days before exposing to the outdoor in winter. Durability factors of all fly ash incorporated concretes determined by freezing and thawing test were in the range of 78–91 at 300 cycles, satisfying the threshold in which concrete is likely to perform well.