Department of Architecture and Civil Engineering

Effects of compositional variables on durability and performance of alkali activated binders

At a glance

Funding body: BRE Trust
Principal investigator: Kevin Paine
Co-investigators: Pete Walker and Keith Quillin (BRE)
Researcher: Kofi Abora
Dates: 2008-2011

Abstract

Concrete is the most used material within the construction industry and as this is likely to continue; CO2 emission is likely to increase due to the energy intensive process associated with the production of cement, the primary component of concrete. In addition to the energy use, CO2 is generated from the calcination of the calcium carbonate.

Over recent years, concrete producers and precast manufactures have become increasingly concerned with the sustainability aspect of their products. This has led to the utilisation of blended cements and research into the development of novel cements.

One type of these novel cements is based on alkali activated binders which consist of industrial waste ash which can provide alternatives to clinker based cement providing the added benefit of recycling as well as reducing CO2 emission.

However before alkali activated technology can be used as a viable construction material, the long term durability of the concrete in line with the effect of compositional variability of the mixes has to be clearly understood.

One such area of concern due to the high pH alkali solution required for the activation of the binders is alkali silica reaction (ASR) and the focus of this research. Various authors conclude that ASR occurrence with Portland cement (PC) is more damaging when compared to alkali activated systems (AAS), however no evidence that ASR is not susceptible in AAS. Therefore long term data are required to study the effect of exposing AAS using different degree of reactive aggregates to ASR conditions.

To determine and validate the possible occurrence of ASR within the specimens, the research will also focus on:
1. determing the alkali levels within the concrete over time using atomic absorption spectrometry. This will provide a basic understanding of the alkali threshhold over time.

2. identification of ASR gel within the concrete specimen. This is essential to provide conclusive evidence of ASR occurrence as visual observation of the expansion and cracking does not imply the occurrence of ASR.

Publications

ABORA K., QUILLIN K., PAINE K. A. AND DUNSTER A., 2009. Effect of mix design on consistence and setting time of alkali activated concrete. Proceedings of the 11th International Conference on Non-conventional Materials and Technologies, 2009, Bath, UK.

DUNSTER A, ABORA K. AND QUILLIN K., 2010. Alkaline ash binders for precast concrete products: Reduced environmental impacts in manufacture and use. Building Research Establishment IP 9/10, 2010.

The cement industry has sought to improve energy efficiency and reduce CO2 emissions, but further substantial reductions may require a step change in the basic technology of cement manufacture, implying the introduction of new types of cement. Of the available options, alkali activated ash, clay and slag binders in which suitably processed industrial wastes and clays are mixed with a high pH activator, are attracting a lot of attention. Much of the research work carried out on alkali activated binders has focussed on assessing their properties in pastes and mortars. However, studies of the properties of concretes made using alkali activated binders have been very limited. In particular very little information is available relating to long term performance and durability and their dependence on composition.