The market for concrete products is ever-changing

Developments in concrete technology have arrived thick and fast in the past decade, driven by the ever present desire to save time and money, as well as growing awareness about the environmental consequences of construction in general and concrete consumption in particular.

Indeed, the sustainability agenda has influenced many of the innovations that have appeared and are continuing to appear across the industry.

CO2 reduction

Reducing the amount of CO2 used in concrete production is a constant refrain, as is increasing the use of recycled materials. But other drivers for innovation, such as the perennial pressure to get the best return on investment for each building made have also led to sustainability benefits.

Take high-strength concrete. "There's a lot of interest in high strength concrete, particularly in high rise construction as it means smaller columns, thinner slabs and bigger spaces," says Steve Crompton, technical director for Cemex in the UK. "Ten years ago high strength meant C50. Now that's practically normal and demand for C60 is common in urban areas. Demand is also growing from contractors to supply concrete of C80-C100 to get the greatest benefits for high rise structures."

Jasen Gauld, technical services manager at Hanson, agrees. "A requirement for a C70/85 concrete strength grade is not unusual. High strength concrete comes with the added benefits for the contractor of reducing formwork and reducing the time for removal of formwork and propping. Also, from a design perspective, the use of high strength concrete better allows for reductions in concrete cover to reinforcement or provides an increase in durability for the same amount of cover."

The idea that stronger concrete also means you need less of it, a sustainability saving in itself, is shared by Jeremy Greenwood, managing director of Lafarge Readymix. "The concrete is so high spec you need physically less of it. Extensia, for example, can be laid a third less thick per m2. Not only is less concrete used, it also means you don't need steel reinforcement, so you lose the CO2 associated with reinforcements and you save the labour and cost involved in having to place it."

Such developments are worth nothing if they are not available to meet demand, however, and last year rumours circulated suggesting high strength concrete was too rare to be of widespread use.

Design and availability

Not so, says Martin Hardwick, product director at the British Ready-Mix Concrete Association (BRMCA), who recently commissioned a presentation on high strength concrete, looking at both design and availability. "We looked where, geologically, the materials are, where the quarries are and where the plants are and found it to be available from 40%-50% of existing plants in the UK with their existing materials supply.

"There remains a question about instant availability you need more forethought if you want a C120 or C140 product than C60, but we want to set the record straight and remove the misconception that it's just not available."

According to Hardwick, the industry is also starting to enhance existing readymix plants to be able to use non-standard materials at short notice. Gauld says the process is well under way at Hanson. "We have been making sizeable investments across the UK to provide modern batching plants that are conducive to the production of high strength concrete. For example, in London alone there has been a planned programme of modernisation in ready-mixed concrete plants, with nine new plants recently installed."

Strength isn't everything, however, and one of the most significant changes to the concrete market has been the development of the flexibility afforded by self-compacting concrete. Figures from the BRMCA reveal a 10% growth year-on-year in enquiries for self-compacting products and growth in volume terms from near zero in 2000 to a projected 400,000m3 in 2008.

"Contractors across the sector are highlighting that self compacting concrete's long-term benefits can far outweigh initial production and supply costs," the research concludes.

These sentiments are echoed by Greenwood. First come the savings in terms of a reduced build time. "We believe you can save 15% of construction time, but you need the delivery rate to be able to match the pour rate to be able to maximise the savings in terms of time," he says. "It's no good being able to lay 80m3 per hour if it can only be delivered at 20m3 per hour."

There are other benefits as well, however. "A lot of recent innovation has focused on labour saving, in terms of placement and finishing. Agilia basically lays itself. Only one person is needed to lay a 70/80m2 flat floor, and no-one is needed for house foundations. No power floating is necessary to give it a great finish, a better finish than can be achieved with a power float, and you can pour it round tight steel reinforcement. It also avoids the need for vibration, which is both labour and money saving, and then there are the health and safety benefits of not walking around rebar to vibrate the concrete. The gaps in rebar are always a perfect fit for a size nine boot."

Crompton agrees. "There's an eroding skills base, so there's a drive from contractors for products that help with the ease of construction, such as concrete that flows under its own weight and self compacting concrete that doesn't need vibrating and needs fewer skilled workers to place it."

Admixture technology

The technical developments that facilitate such products are many and varied, though the use of admixtures has been crucial. "A lot of concrete developments in recent years have been driven by admixture technology," says Crompton. "Very small doses of these chemicals - two litres per cubic metre, perhaps - can have dramatic effects on strength and fluidity."

The benefits have been widespread, with sustainability improvements once again to the fore. "Twenty years ago you couldn't use high levels of pulverised fuel ash (PFA), an alternative to cement that reduces the CO2 used in the production of concrete, as it slowed down strengthening," he explains. "Now we typically replace up to 30% of cement with PFA and we're looking at up to 70%. It's a similar story with slag. Now, replacement rates of 50% might be typical, and we're looking right up at 85%/90% for very specialist applications.

"This is the specialist end of concrete technology, but the sustainability agenda means we're trying to push the boundaries for more routine work as well. Ten to 15 years ago quality was the issue. Now we're increasingly being asked to look at the sustainability side of things."