Strength and durability properties of alkali activated slag and fly ash-based geopolymer concrete

摘要

The research focuses on the strength and durability properties of alkali activated slag (AAS) and fly ash based geopolymer concrete. Although there are numerous studies that have assessed the suitability of AAS and fly ash based geopolymer as the binder in concrete, the main focus of these studies has been the strength properties and durability in terms of chemical attack. Only limited research has been conducted on the chloride penetration and carbonation of these concretes – the main causes of degradation of concrete structures in practice. This study provides new insight into the strength development and the durability performance in terms of chloride and carbonation resistance. The effect of sodium oxide dosage and activator modulus on the compressive strength of mortar specimens was explored and the results used to design suitable AAS and geopolymer concrete mixes. Concrete testing has included measurements of workability, compressive strength, water sorptivity, depth of carbonation, rapid chloride permeability, and chloride ponding. Microstructure studies were conducted, using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDAX), to investigate the effect of different mix formulation on the microstructure, porosity and micro cracks. The study of variables affecting the strength demonstrated that both the sodium oxide dosage and the activator modulus are suitable variables for designing AAS and geopolymer concrete mixes. It is concluded that AAS and fly ash based geopolymer concretes can exhibit comparable strength to OPC and slag-blended OPC concretes. However, with regards to the durability properties such as water sorptivity, chloride and carbonation resistance; the AAS concrete was found to not perform well as a result of surface cracking dominating these characteristics. The fly ash based geopolymer concrete performed better in water sorptivity and chloride penetration tests than the OPC concrete, the slag-blended OPC concrete, and the AAS concrete. It was found that the fly ash based geopolymer concretes exhibited high charge and high conductivity in the accelerated chloride diffusion tests. However it was concluded that this is a reflection of the concentration and composition of the free ions present rather than the ability to resist the diffusion of chloride ions.