Development of high performance very high volume fly ash concrete with 80 replacement of cement by fly ash

摘要

Concrete is one of the most sustainable building materials in terms its production and maintenance compared to other building materials, but the concrete industry is not sustainable because of its huge production and even growing demand worldwide. The main culprit being cement, the main ingredient in concrete, is responsible for world’s 7% greenhouse gas emissions as per the statistics. 1 ton of CO2 produces between 0.7 to 1.0 ton of CO2 worldwide. And, internationally about 4.2 b tons of cement was produced in 2012 as per the statistics and the demand is growing rapidly each year. Though emissions produced by cement is less compared to other major emissions due to human activity, there is a scope to reduce the emissions produced by cement. Supplementary Cementitious Materials (SCMs), are a way to reduce CO2 emissions produced by concrete by replacing the cement. With SCMs, there is opportunity to reduce the emissions up to 70%, with the typical replacement of cement being 15-40% so far for structural purposes and up to 70% for non-structural purposes such as embankments and road pavements. High Volume Fly Ash Concrete (HVFAC), which is defined as FA replacement above 50% partly addresses this issue. But, unlike geopolymer concrete with 100% fly ash, HVFAC does not require heat curing which is an advantage over geopolymer concrete in being accepted by the construction industry. This research is aimed to produce high performance very high volume fly ash concrete (VHVFAC) with 80% replacement of cement without compromising the properties. Low strength development being the drawback in high volume fly ash concrete, above 40% replacements, the challenge addressed in this research is achieving comparable strength development to normal concrete. Using ultra-fine fly ash, adding a small percentage of Silica Fume as a property enhancer and the addition of hydrated lime were three main factors manipulated to achieve this research objective. With this approach, the outcome of the research is a new HVFA with 80% of cement replaced by fly ash. This new concrete mix produced is assessed for all the basic mechanical tests such as compressive strength, flexural strength, split tensile strength, modulus of elasticity and drying shrinkage, a long-term mechanical property. The VHVFAC was also tested for durability properties such as water absorption, carbonation, and tested against aggressive environment such as sulphates and chlorides. Also it was tested for permeability, surface hardness, UPV and resistivity using NDT testing methods. The concrete produced achieved similar mechanical properties and superior durability properties compared to the other HVFA concretes as well as OPC concrete from the literature and satisfied the requirements to be named as ‘high performance concrete’ or “Green” concrete as a sustainable solution for concrete industry.