Proposing a Methodology to Identify the Optimum Mix Design of Autoclaved Aerated Concrete Blocks in the Context of Sri Lanka

Abstract

AbstractIntroduction of Green Building Materials and Products (GBMP) results in a reduction of energy consumption over the lifetime of a building thus leading to a reduction in toxic, environmental pollution as well as ensuring the security of energy and raw resources as appropriate. The building construction industry has widely used fly ash based products as GBMP. Fly ash is a waste material generated from electricity power plants and is used in cement production with special properties such as workability and durability as well as in the production of concrete. However, in Sri Lanka, the industrial usage of fly ash is very low as compared to the high volume generated from the Coal Power Plant located in Norochcholai, Sri Lanka. This very wasteful, fly ash can be effectively used as a fundamental raw material in the manufacturing of Autoclaved Aerated Concrete (AAC) blocks—which are popular as light weight building materials. Using Autoclaved Aerated Concrete in Sri Lanka, facilitates two major aspects: Firstly, unused waste fly ash can be removed from the Norachcholai power plant premises in a sustainable way; Secondly, the Sri Lankan construction industry gains a sustainable building material. Nevertheless, there are certain issues in using fly ash based AAC in construction sites, such as its problem of drying shrinkage in the block which leads to cracks in constructed walls. The AAC manufacturing process is done in accordance with IS: 2185 (Part 3)—1984, but raw material sources are not providing the required qualities according to the code. Although the raw materials are not providing the required qualities for the production process it is a must to use available sources in Sri Lanka. This question can be addressed by optimizing the mixture design for the available materials in Sri Lanka, considering its drying shrinkage and compressive strength, stays within the limits given in BS EN 771-4:2011+A1:2015 Specification masonry units Part 4. Eleven different mixture designs were prepared by varying fly ash, cement and lime, subsequently tested and thereafter, an equation to calculate drying shrinkage and compressive strength was formulated as a function of fly ash cement and lime. Using the results of this research, optimization of the mixture design can be done in the AAC manufacturing plant.KeywordsAutoclaved aerated concreteCompressive strengthDrying shrinkageResponse surface methodology