Development of High Performance Very High Volume Fly Ash Concrete with Addition of Lime and Microstructure Study

High volume fly ash concrete (HVFAC) is a feasible solution not only for reducing greenhouse gas emissions produced by cement but also minimizes the waste deposited by dumping fly ash in many parts of the world. Low strength development is a major drawback of high volume fly ash system and it worsens with cement replacements more than 65%. Development of very high volume fly ash concrete (VHVFAC) without compromising the early strength properties is a challenging question in the concrete industry. This study reports the development of very high volume fly ash concrete with 80% replacement of cement by class F fly ash using the addition of lime without compromising the properties. In this paper, lime additions of 5%, 12%, 20% and 32% were investigated to find out an optimum lime addition for the 80% fly ash in concrete. The developed concrete was tested for workability and compressive strength. Microstructure analysis was carried out at the concrete age of three months to one year using scanning electron microscopy (SEM) and energy dispersive Analysis of X-ray (EDAX). Compressive strength tests were conducted at 7, 28 and 56 days for all the specimens and up to two years for few specimens. The compressive strength tests displayed encouraging early strengths which are comparable and even exceeding results of high volume fly ash concrete with 50% to 70% replacements in the past. Compressive strength results beyond 90 days were competing with that of Ordinary Portland Cement concrete in general. Microstructure studies have guided to reach the optimum lime addition for the 80% fly ash. Mix design, workability and compressive strengths of the very VHVFAC are satisfying the high performance concrete (HPC) criteria.