Demand for increasingly tall structures is driving the technological boundaries of concrete and its derivatives. For those in the sector, higher-strength concrete is increasingly in demand as contractors – driven by consultants’ need for taller towers – increase the strength of concrete to unheralded levels. This comes as demand for key raw materials has driven prices even higher over the last four to five months.
This desire for stronger concrete places greater emphasis on the behaviour of the mixture, and whether its flow characteristics enable the foundations to be modelled correctly, says Hamish Cowie, general manager, Soletanche Bachy. While this isn’t necessarily a concern, it represents unchartered territory.
“Because of the extremely high-rise buildings that are under construction and planned, to get the capacity, the concrete strength must be higher. As you increase the strength, the rheology [the behaviour, such as flow characteristics] changes. What is important for us is that it flows, and that it continues to flow and remains fluid during the entire concreting process,” he says.
The emphasis on increasingly tall towers has seen the sector use concrete strengths that are double that of a conventional building. Generally speaking, with a mid-rise building, piles range from 25-35m in length. But with the higher-rise buildings being drawn up, there is talk, Cowie says, of foundations reaching 90-100m. In order to take loads from a tower of this height it is estimated the concrete will be 70-80N in strength. By contrast, a common concrete is 45N.
Developers, however, continue to push the envelope for projects within the region. Last week, the Torch Tower project at Dubai Marina witnessed the largest concrete pour in Dubai at 11,000m
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. The raft for the 74-storey, 345m-high tower took just 27 hours. And according to Bill Mullen, general manager of Dubai Select, which is the developer, some of the sections of the tower will incorporate concrete that will be 100N in strength.
But such a reliance on one product is inevitably placing strain on the industry, with major producer BASF announcing that it is being forced to increase its prices to offset tightening production margins. John Sarkis, general manager – UAE, BASF, believes these trends are an industry-wide concern and has noticed a general upturn in the price of construction chemicals in the region.
“In the long term, we see some movement upwards, even though the cost of admixture in a cubic metre is rarely more than 10% of the total cost of concrete. The ready-mix concrete market in the UAE is very competitive and producers are on relatively small margins so they will definitely want to pass on any added cost to the end users.”
The company announced in April it would be initiating price increases throughout the Middle East on its Pozzolith, Glenium and Rheobuild ranges. This is due to a steady price increase over the last nine months for naphthalene, which has resulted in double digit cost increases for superplasticisers. In addition, ever increasing demands for raw materials and the weakening US dollar against most major currencies has led to higher landed costs for raw materials.
Superplasticisers are one of the major ingredients used in modern concrete and influence many of its properties, especially its workability. They are chemical admixtures, which help maintain adequate workability and plasticity of fresh concrete at low water/cement ratio for a required period of time without affecting the setting and hardening behaviour of concrete. According to PR Landge, president, Chemanol, over the past six years, the company has witnessed a tremendous increase in naphthalene-based superplasticisers, owing to the growth in the construction industry worldwide in general, and Middle East in particular.
“Chemanol’s naphthalene consumption has grown by eight times since 2001. Over the past six years, many other superplasticiser manufacturers have come to the market and added to the pressure on naphthalene availability,” he says.
At the same time that naphthalene consumption is increasing exponentially, manufacture (which stems from distillation of coal tar or separation from C-10 streams coming from petroleum refineries) is decreasing. This has resulted in the current situation, with the industry facing severe availability constraints and pricing issues. Price increases over the past five years have been as high as four times the price of 2001.
“The superplasticiser industry is going through turmoil as it is finding it extremely difficult to pass on the increase in cost of production to its customers and if the situation continues like this, the superplasticisers manufacturers will have no option but to rationalise production,” adds Landge.
These issues have not affected technological advancement, however. According to David Bowerman, admixtures manager, BASF, the company has introduced a Glenium Hyperplasticiser, whereby the water content can be decreased more than with traditional superplasticisers.
The company’s latest development is the Total Performance Control concept. This ensures that ready-mix producers, contractors and engineers achieve a concrete that is the same high quality as originally specified: starting at the batching plant, to the delivery and application into place, and followed by its hardening process.
Rheodynamic concrete, he adds, is the latest generation of self-compacting concrete, which provides a concrete mix with exceptional placing characteristics, accelerated cement hydration for early strength development and high-quality concrete.
“Total Control is the state-of-the-art technology that provides improved short and long-term performances of concrete by controlling the two distinct features essential for high quality concrete: extended workability and low water/cement ratio. A key element is the newly developed Glenium SKY superplasticiser.” BASF is a market leader in the manufacture and supply of polycarboxilic ether-based hyperplasticisers such as Glenium. These admixtures assist in the production of high-strength, high-flow and highly durable concrete and are an important component in the production of rheodynamic or self-compacting concrete.
And this is one of the key issues affecting the industry; to meet the increasing concrete requirements of specifiers and contractors, the company is tailor-making bespoke admixtures utilising in-house polymers. A prime example is for the Burj Dubai, for which a new Glenium SKY had to be developed to meet the various requirements. These were pumpability (600m vertical), workability retention (three hours) and high early strength (12Mpa at 10 hours).
On the subject of the increasing strength demands being witnessed across the region, Bowerman is not concerned about the trend, believing it to be a positive development within the industry. “In layman’s terms, higher strength generally means greater durability. This can only be a positive trend and a benefit to the real estate developers and property owners in this country,” he says.
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