Department of Architecture and Civil Engineering

Strength properties of lime mortared brickwork

At a glance

Funding body: EPRSC
Principal investigator: Pete Walker
Co-investigators: Dina D'Ayala
Researcher: Zhaoxia Zhou (PhD student)
Academic partners: University of Bradford, University of Bristol
Industry partners: Lime Technology; Brick Development Association; Castle Cement; Lhoist UK; Ibstock Bricks; Buro Happold; Network Rail
Dates: 2006-2009

Abstract

Masonry construction, including both clay bricks and concrete blockwork, relies on 10 mm mortar joints to bond the units together. In the UK around 50 million m2 (wall area) of fired clay bricks and 60 million m2 of concrete blocks are produced every year, requiring around 1.5 billion litres of mortar. The functions of mortar in masonry construction are to provide an even bed between units, bond units together to provide flexural strength and seal joints against rain penetration.

Increasingly the construction industry is realising that hydraulic lime mortars fulfil these requirements extremely well. One significant benefit of lime mortars, in comparison with more widely used cement mortars, is a 40% reduction in carbon dioxide emissions, a significant greenhouse gas. The work is developing low-energy high-performance mortars using a novel quicklime drying technique for the aggregates, the inclusion of admixtures with the mix and the extension of the binder phase to include pozzolanas and alternative low energy cements.

This project is investigating and developing the use of quicklime addition to the fine aggregate as the means to dry the sand. The approach relies upon both the chemical combination of water to yield calcium hydroxide and the associated heat production. However, the amount of quicklime required will vary with sand moisture content and desired mortar mix. As the mortar mix designs become leaner (lower strength), increased quantities of quicklime will be required to dry the sand. The leanest mixes will require significant quantities of quicklime with an associated reduction in the hydraulic lime component. This will limit the potential engineering properties of the mortar unless modifications are made to its composition.

The study is investigating possible modifications, including the use of admixtures such as water reducers, pozzolanas, as well as more energetic hydraulic binders such as Roman cement. Current editions of the structural design codes for masonry do not include design data for lime mortared masonry. In combination with the development of low-energy mortars, the proposed work will seek to address this lack of data.

The research methodology comprises experimental investigation of dry mix low-energy mortars, including the study of efficiency of lime slaking to dry wet sand during the mixing process, micro-structural analysis of mortars, and investigation of low energy mortared masonry properties. Experimental studies are supported by numerical analysis of masonry properties and comparative life cycle analysis of masonry.

Research of sand drying and mortar properties is undertaken at the Universities of Bradford and Bristol, whilst experimental and numerical investigation of masonry properties and life cycle analysis are completed at the University of Bath.