Durability properties of low-carbon concrete incorporating alternative supplementary cementitious materials and manufactured aggregate

Abstract

The demand for concrete has been overwhelming nowadays due to globally booming economy and population, which induces environmental and social issues including the increase in anthropogenic CO2 emission from cement production and natural sand rarefaction by excessive exploitations. A new supplementary cementitious material (SCM) known as a combination of flash calcined clay and limestone has been promoted as promising alternatives to fulfil the development of sustainable concrete. Ferronickel slag sand is also a potential option to replace natural sand in concrete. However, performance in terms of durability is always a concern for the industry delaying the widespread adoption of new low-carbon concrete. This study aims to investigate the durability performance of concrete containing flash calcined clay, limestone as binder replacement (LC3 concrete) and ferronickel slag as natural fine aggregate replacement (FNS concrete). The influence of flash calcined clay, limestone and ferronickel slag on the deterioration of concrete structure including alkali-silica reaction (ASR), reinforcement corrosion in initial and propagation phases were evaluated. The variation of mechanical, physical and durability properties of LC3 concrete with various amounts of calcined clay and limestone and FNS concrete with fly ash as SCM was investigated. The performance of both LC3 and FNS concretes in the initial phase of reinforcement corrosion relating to carbonation and chloride diffusion resistance was investigated through accelerated and natural test protocols. The propagation stage of rebar corrosion of LC3 concrete was monitored and the electrochemical testing methods developed for Ordinary Portland Cement (OPC) concrete were validated for LC3 concrete. The mitigation effect on ASR expansion of flash calcined clay and limestone was systematically evaluated using the accelerated mortar bar test, scanning electron microscopy (SEM) analysis and model reactant experiments. The expansion due to ASR of FNS concrete which is the major concern to adopt manufactured sand into concrete industry was monitored and evaluated by using concrete prism test (CPT) and SEM. Results show that the use of flash calcined clay, limestone and ferronickel slag sand in concrete not only allows to produce low-carbon concretes but also to enhance the durability performance, except for carbonation penetration in LC3 concrete.