SUSTAINABLE CONCRETE CONSTRUCTION IN THE MIDDLE EAST

Christopher Stanley*, Technical Director, Unibeton Ready Mix, Abu Dhabi, United Arab Emirates

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33rd Conference on OUR WORLD IN CONCRETE & STRUCTURES: 25 – 27 August 2008, Singapore

SUSTAINABLE CONCRETE CONSTRUCTION IN THE MIDDLE EAST

Christopher Stanley*, Technical Director, Unibeton Ready Mix, Abu Dhabi, United Arab Emirates

Abstract

Ninety miles (140km) from Dubai, on the coast of the Arabian Gulf, Abu Dhabi, the

capital of the United Arab Emirates, is listed by Fortune money magazine as the

richest city in the world. Appearances can be deceptive, because Abu Dhabi is a

quieter more conservative city; but all that is about to change. Abu Dhabi is set to

achieve a growth rate in the next ten years even in excess of Dubai, whilst hopefully

gaining experience from the environmental problems generated by Dubai’s rapid

expansion in order to build a more sustainable environment. The town is focusing on

Green, energy saving construction & the largest Ready Mixed Concrete Company in

the Gulf is leading the field, with the promotion of Green sustainable concrete. [In this

context green is taken to mean environmentally friendly concrete with low carbon

dioxide emissions, not concrete in its plastic state.] This uses materials that represent a

75% saving on carbon dioxide emission against the more traditional type of

conventional concrete made from Ordinary Portland cement. It is a considerable

advance, bearing in mind that more than a million cubic metres of concrete are poured

in a month in what must be the world’s greatest construction frenzy, where it is

estimated that over 25% of the world’s Tower Cranes are currently in use. Both Abu

Dhabi & Dubai are constructing some impressive structures, ranging from a 1.2km

high tower, man made islands in the shape of palm trees jutting out into the Arabian

Gulf, and an amazing assortment of buildings and structures including bridges & an

elevated monorail transportation system. However one of the more interesting

developments known as Masdar is just about to start. This development is setting its

sights on a zero carbon footprint. It is a 6 square kilometre development which will

use in excess of 4.2 million cubic metres of concrete. Environmental responsibility in

the Construction Industry is taken very seriously and Green building codes are in the

course of production by the Government Authorities.

Introduction The major constituent in concrete is Portland cement is calcium carbonate in the form of limestone, marble, or chalk. What is not generally appreciated is that during the cement manufacturing process a considerable amount of carbon dioxide is driven off when the ingredients are heated to around 1200 degC in a rotary kiln. It is estimated that about 900kg of carbon dioxide are given off for every 1000kg of cement that is produced. In addition the aggregate production consumes electrical energy in the crushing & sieving & further transportation costs for fuel add to the production of carbon dioxide.

Figure 1. Increase in cement consumption – percent 2000 – 2007 based on

statistics prepared by D Cooney

Figure 2. Cement consumption per capita 2005. Based on statistics prepared by D Cooney

Concrete is the world’s most important construction material whose use is increasing year by year. We cannot do without it and therefore it is important to find economical ways of optimizing its use by carrying out concrete construction in a manner which can help to reduce carbon dioxide emission into the atmosphere. This can be achieved in a number of ways. The obvious alternative is to use partial cement replacements in the mix. These include ground granulated slag & pulverized fuel ash together with small additions of silica fume. Other energy saving methods include a greater use of self compacting concrete; and also high strength concrete, which enables the use of thinner sections in buildings & structures with the corresponding benefits in the economical use of materials. The addition of various types of fibres into the mix & the replacement or the reduction in the quantity of steel reinforcement (which generates three times as much carbon dioxide in its manufacture as does cement), also helps with the reduction of carbon dioxide emissions. Currently there are no economically viable replacements for steel reinforcement but optimization in the design together with the use of high strength concrete is beneficial. The greatest focus on green concrete is with the use of partial cement replacements such as PFA & slag. In addition rice husk ash has been considered but it needs to be produced by controlled burning techniques & is currently seldom used in the Middle East. Apart from the savings in carbon dioxide emission, slag & PFA help to control the temperature rise in concrete & the peak temperature reached, which is very important where the ambient temperature is often over 55degC. Typical additions of slag replacement of cement in Abu Dhabi are about 50% & PFA is between 25-30%, but 40% is being considered for some projects. Clearly with either of these materials emphasis on curing after placing is essential in order to benefit from the pozzolanic properties of strength development & reduction in permeability.

With such high outputs of concrete, potential shortages of materials is always cause for concern, especially cement & water. This is another advantage of reducing the cement content in concrete mixes.

Compressive Strength of Concrete Mixes with Partial Cement Replacements ( 350kg/m3 cement content)

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Figures 2 & 3. Typical strength development curves for concrete mixes with partial cement replacements based on trials carried out in Dubai.

Compressive Strength of Concrete Mixes with Partial Cement Replacements ( 450kg/m3 cement content)

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High rise & high performance Currently the world’s tallest concrete buildings are under construction in Dubai. The Burj Dubai, commenced construction in 2005. It is now about 800m high and nearing completion. Another, the Al Burj, which

will be 1.2km high, is just coming out of the ground. There are plans for even taller structures presently under consideration.

Plate 1. (left) The Al Burj Tower. Dubai. The pile foundations of this tower have just been cast. When completed this will be the tallest free standing structure in the world with a height of 1.2km. Plate 2. (right) The Burj Dubai Tower Dubai. Nearing completion this tower is about 800 metres high. These use 80Mpa – 100Mpa concrete. Concrete can be a simple material, but mix design submissions are usually accompanied with many sets of test data, often requested by Consultants, the relevance of which is somewhat questionable. The important aspect with all the buildings & structures under construction is to ensure their long term service life with the use of high performance concrete, combined with high quality workmanship. Lack of locally available cement and aggregates means that most concrete in the region is produced from materials that are transported more than 100km from their centres of production. A 40 grade concrete is used for much of the work with typical slumps of about 160mm at the time of discharge. The concrete usually contains workability retention admixtures which have a typical 30mm slump reduction over a period of 120 minutes. Due to high ambient temperatures, flaked ice is used to control the initial concrete placing temperature, which is particularly important where thick sections are being placed. The rapid chloride permeability test is often

specified to measure the susceptibility of the concrete to chloride ingress, and values below 1000 coulombs are regularly obtained with typical values below 700 coulombs. The percentage water absorptions are normally below 1%. In reality the concrete is virtually impermeable, although some project specifications call for the addition of pore blocking admixtures to be included in the mix. Many large pours are carried out at night when the ambient temperatures are lower. During the summer months the ambient temperature often exceeds 55degC and all external construction work stops between the hours of 12pm – 4pm. One of the major problems on construction sites is plastic shrinkage cracking of the concrete, often due to hot drying winds blowing across the site and typically affecting exposed flat slabs. In addition, the width of the cracks can be amplified by the effects of both thermal contraction and early drying shrinkage taking place. Therefore the need for good workmanship and especially the early application of moist curing cannot be over emphasized. Record breaking concrete But where is all this concrete being used? Dubai is currently the largest user of concrete in the Emirates, followed by Abu Dhabi. Only 4% of Dubai’s income comes from oil, unlike its neighbour, which sits on about 10% of the world’s oil reserves. Therefore it concentrates on service industries such as Banking & Tourism for most of its income and the emphasis is on developing the tourist playground of the future. Some projects would almost seem out of context, like a massive ski slope complete with real snow, which is the largest indoor skiing centre in the world.

Plate 3. Dubai World. A giant leisure park more than twice the size of Disneyworld.

But under construction is Dubai World, a massive theme park twice the size of Disneyworld in the USA which will employ about100,000 people. Dubai Mall will be the world’s largest shopping mall with 1000 stores in a 3million square metre area. The Princess Tower at over 100 stories is the largest residential building in the world, adjacent to Dubai Marina. Hyrdopolis, the world’s first underwater hotel, is due for completion next year.

Plate 4. Dubai Mall. The world’s largest shopping mall.

Plate 5. Hydropolis. The world’s first underwater hotel. Due for completion in 2009. Visible from outer space, are three large artificial islands; Palm Island will have 2000 villas and 40 luxury hotels. Trump International hotel is

one of the centerpieces of the island but only 5km away the Burj al Arab hotel, currently the tallest hotel in the world sits on its own island It is the world’s only 7stars hotel, complete with a swimming pool just below roof level, made from waterproof concrete, and its own helicopter pad.

Plate 6. Palm Island. One of the largest artificial island complexes in the world. 2000 luxuryvillas are constructed on the palm leaves. There will also be 40 luxury hotels. World famouscelebrities have already purchased properties on this development which also has a monorailtransportation system.

Plate 7. Some of the luxury villas on Palm Island.

Plate 8. The Burj al Arab Hotel. Currently the tallest hotel in the world sits on its own island off the Dubai waterfront.

Plate 9. The Metro elevated rail system running between Dubai & Jebel Ali.

However with all this record breaking construction, it is important not to loose track of all the more conventional construction work that is taking place both in Abu Dhabi and Dubai, in terms of buildings and structures. This ranges from housing, offices, a museum resembling the Louvre in France, bridges & general infrastructure work. One of the largest pours of self-compacting concrete in the Gulf was the 16,000m3 in a single pour for the base of the 72 floor Landmark Tower in Abu Dhabi. It was followed by an even larger pour of conventional concrete where more than 22,000m3 were placed continually over a period of 35hrs for the base of the Sky Spiral Tower.

Plate 10. Casting the foundation of the Sky Spiral Tower. More than 22,000m3 of concrete were cast in a continuous single pour lasting 35 hours. This was the largest continuous pour in the Gulf.

There are plans for a major development of Saadiyat Island off the coast of Abu Dhabi. This will be a landscaped low rise housing project.

Plate 11. Saadiyat Bridge under construction in Abu Dhabi. Due for completion in 2009. Over 163,000 cubic metres of Ready Mixed Concrete are being used in its construction.

The initial project involves the construction of Saadiyat bridge linking the island with Abu Dhabi. The project involving the placing of 163,000m3 of concrete is due for completion in December 2009. Al Reem Island in Abu Dhabi is a mix of luxury high & low rise development. Two 44 floor tower blocks have already been completed & by 2110 it will almost resemble Manhattan. Conclusion There are so many notable projects in the region that are under construction but it is not possible to address more than a few of them in this short paper. The significant aspect is the concentration on producing Green, ecologically friendly concrete, using advanced production equipment and stringent quality control; and in this respect the United Arab Emirates probably leads the world.