Design revolution and leaps of imagination are not a prerequisite to sustainable construction. In the case of concrete, pushing the envelope of existing materials and a close watch on workmanship is playing a part, says David Ball.
Figures released by the Sustainable Concrete Forum in its Concrete Industry Sustainability Performance Report (5th report)* make encouraging reading.
By 2010, the industry was sourcing a quarter of its energy from waste-derived material rather than fossil, ahead of 2012 targets. Recycled and secondary materials now account for 28% of the GB aggregates market – the highest market share in Europe and more than three times the European average. The concrete industry is also a net user of waste, using 63 times more waste than it sends to landfill.
This article originally appeared in Construction News, available online here
In reducing embodied CO2 and demand on primary materials, concrete has been able to flex and reformulate itself. As statistics show, it has permitted the replacement of traditional cement and aggregate content with a greater proportion of recycled/secondary materials and by-products from other industries – while still fulfilling all usual design functions.
When it comes to hypercritical applications, however, such as tall buildings or below ground structures under significant hydrostatic pressure, sustainability can be side-lined by structural or waterproofing concerns.
Project teams typically respond to the more onerous strength and durability criteria by increasing overall concrete strengths and, therefore, the cement content in the concrete design. But this comes at unnecessary cost to sustainability, carbon footprint and construction budget when proven, low carbon formulations are possible.
A higher proportion blended concrete mix, enhanced with a waterproofing admixture, will reduce cement content while equally meeting, if not exceeding, required water-resistance and required integrity, strength and durability.
In many respects, the waterproofing admixture has come of age in the drive for sustainable construction. As a constituent of the concrete mix, it makes waterproofing integral to the concrete, doing away with external membranes, protection boards and temporary works. Depending on the make, waterproofing admixtures can also materially influence important characteristics of the slab, providing a number of opportunities to reduce concrete’s carbon footprint.
Admixtures can alter the microstructure of concrete, reducing the open pore structure volumetrically, and, with some formulations, by order of magnitude. As well as inhibiting the ingress of moisture, sulphates and other chemicals, this altered structure improves compressive strength, durability and potentially crack reduction, among others.
Admixtures offer another serious opportunity to reduce concrete’s carbon impact – by reducing the amount of steel reinforcement required.
The improved crack reduction from using a suitable admixture and binder means concrete does not need to be designed to BS EN 1992 Part 3, which stipulates 0.2mm maximum crack width allowance, rather than the 0.3mm of BS EN 1992 Part 1. This allows the use of a third less steel – significant in terms of the lowered carbon footprint and construction cost.
A lighter reinforcement solution relies all the more on good workmanship – careful pouring, placement and curing – to achieve dimensional stability and structural integrity. Some admixture specialists, like PUDLO, provide this supervision – a vital element of reassurance in making more sustainable choices.
For the first time, the Sustainable Concrete Forum report reflects UK average reinforcement content in its figures, increasing CO2 emissions indicators by between 9% and 10%. While reinforcement steel producers have committed to reducing their embodied energy and carbon impact, building designers could also make a difference by identifying opportunities to reduce reinforcement.
Project teams are urged to involve concrete technical specialists at the earliest stage. This will ensure that materials, design and installation are rigorously planned and supervised to minimise the carbon impact (and cost) of their choices.
David Ball, Chairman of the David Ball Group
The article was published in Construction News www.cnplus.co.uk