Cool concrete from CEMEX
CEMEX UK have developed a new ready-mixed concrete mix which is being used in the UK for the first time for the construction of the foundations of new Terminal 2 building at Heathrow Airport.
The new mix design, developed in close collaboration with Laing O’Rourke as part of its joint venture with Ferrovial Agroman for BAA, incorporates high levels of pulverized fuel ash (pfa) combined with high-range water-reducing admixtures to reduce heat generation in the concrete, thereby minimizing thermal gradients in the structure and reducing the risk of early age thermal cracking.
The innovative concrete mix was developed at CEMEX’s UK National Technical Centre in Southam, Warwickshire, over a two-month period as part of the £7 million contract secured by the company for the supply of more than 100,000 cubic metres of ready-mixed concrete for use in the construction of Terminal 2.
The new mix incorporates CEM II/B-V factory blended cement from CEMEX’s new flagship cement plant in Tilbury, Essex, in combination with pfa and limestone aggregates to produce the low-heat concrete.
CEMEX UK’s technical director, Steve Crompton, explained the development: ‘A traditional concrete mix could easily generate peak concrete temperatures in excess of 700°C, potentially leading to issues with early age thermal cracking.
‘Given the substantial pours this contract involves, it was a key challenge to minimize the heat generation in the concrete while still meeting the strength and durability requirements for the structure.
‘Following rigorous investigations and testing, we arrived at this new mix design, which incorporates a unique combination of CEM II/B-V with pulverized fuel ash combined with state-of-the-art admixtures manufactured at our own admixture factory in Rugby.
‘The result is an easy-to-place, low-heat concrete. The mix performed even better than expected with the peak temperature recorded on the first pour reaching just 53°C despite being placed on one the warmest days of the year so far.’