Al Mafraq Hospital extension ... biggest Mideast project to use Rheocrete.
BASF sets Rheocrete record in Abu Dhabi
01 March 2012
LEADING chemical company BASF has helped inhibit corrosion at a new Abu Dhabi hospital building by supplying an admixture that aims to protect the structure from the effects of ground water and chlorides.
To date, more than 380,000 litres of the corrosion inhibitor Rheocrete 222+ has been supplied for the construction of the Al Mafraq Hospital extension, making it the biggest-ever project using this product in the Middle East.
The additional building will triple the hospital’s capacity to 690 beds. Before work on the extension could begin, contractors had to deal with the challenge of protecting the new building from the corrosive effects of ground water and chlorides. BASF Construction Chemicals says its Rheocrete 222+, a combined waterproofer and organic corrosion inhibitor, met the stringent requirements.
David Bowerman of BASF Construction Chemicals’ Admixture Systems says: “A building is only as good as the foundations it is built on. Ground water and chlorides corrode the steel in reinforced concrete structures, weakening it. Unless precautions are taken at the design stage, such structures are likely to require extensive repair to keep them in service. However, the effectiveness of corrosion inhibiting admixtures can vary, so selecting the right product is vital.
“For the Al Mafraq Hospital project, the specifications were stringent given the purpose of the structure and the design life that the contractors needed to achieve.”
Among other requirements, consultants specified that the corrosion inhibitor selected for use in the project had to be environment-friendly, capable of slowing down chloride penetration through the capillary pores of the concrete, as well as able to form a protective corrosion-resistant film around the steel reinforcement. It had to be compatible with other concrete mix ingredients, would not affect the slump or temperature development of the concrete in the plastic state, or the strength development of hardened concrete or concrete-steel bond strength. Further, it needed to be capable of protecting the steel reinforcement where concrete has cracked. Finally, it had to have an established track record in the region and environment.
Rheocrete 222+ fully met these requirements, he says. “Corrosion inhibiting admixtures do not prevent corrosion; they can only delay it. While single-action solutions are dosed into the concrete mix and adsorb onto the rebar, forming a protective film on the surface of the bars, dual-action solutions like Rheocrete 222+ not only form a protective film on the rebar but reduce permeability of the concrete and reduce the rate of chloride penetration,” Bowerman explains.
Rheocrete 222+ has a unique formulation, combining an organic corrosion inhibitor with a hydrophobic pore-blocking waterproofer. The inhibiting action is anodic, reducing the dissolution of iron, and cathodic, acting as a barrier to oxygen.
“The admixture is dosed into the concrete mix and migrates through the concrete to form a protective film on the surface of the rebar. It has no effect on fresh concrete: it does not affect initial slump or workability retention, while also leaving the setting time unaffected. In addition, water absorption is reduced due to the inclusion of pore-blocking chemicals in the formulation, resulting in a stronger mix,” Bowerman continues.
Readymix Abu Dhabi, supplier of concrete to the project, is a confident user of BASF’s products, having made extensive use of its admixtures on numerous projects with consistently good results. “For them, and us, a key challenge has been ensuring consultants and clients understand and support the use of a corrosion inhibiting product with dual capabilities, rather than cheaper products which offer less protection and affect the strength and workability of the mix – which in turn affects placement and other factors and in the long term compromises the soundness and longevity of the structure,” notes Bowerman.
The Rheocrete 222+ admixture was subjected to ASTM G109 testing as well as life-cycle analysis using the ACI Life 365 corrosion modelling programme. It also proved compatible with the superplasticiser used in the mix, namely BASF’s Rheobuild 857AD, a high-range, water-reducing superplasticiser for concretes containing ground granulated blastfurnace slag (GGBS) and silica fume. Approximately 500,000 litres of Rheocrete 222+ and 700,000 litres of Rheobuild 857 AD will be supplied to the project for use in the substructure of the building.
Bowerman continues: “We’ve supplied more than 380,000 litres of product to the project in 2011, so it’s probably the biggest ever project using this product in the Middle East. This is a prestigious project and will serve as an excellent job reference for us. The consistent performance and reliability of our products have enabled us to establish a strong relationship with the consultant on this project and strengthened our association with Readymix Abu Dhabi.”
Fouad Yazbeck of Readymix Abu Dhabi says: “Rheocrete 222+ was a natural selection for Readymix Abu Dhabi in our design of the concrete mixes. As a single product combining both capabilities, namely corrosion inhibition and pore blocking, it saved us the logistics of having to dose two separate admixtures into the mix along with our main superplasticiser.
“Furthermore, compatibility with the existing superplasticiser was not a concern for the consultant as both were supplied by BASF. And BASF’s high levels of technical support played an important part in securing the order – they provided all required documents, from test reports to clarification letters in a timely manner. In addition, supply and after-sales service were spotless.”
BASF, whose portfolio includes chemicals, plastics and performance products, has provided innovative solutions to projects around the Gulf region. Among such projects, it has helped ensure the success of a pioneering project in Kuwait – the Sabah Al-Ahmad Sea City project, which is unusual in that instead of reclaiming land from the sea, it brings water inland to create an ecologically rich marine waterway city.
“The city is a commercial and residential development that will, on completion, house more than 100,000 people,” says Ian Williams, project director at La’ala Al Kuwait Real Estate Company, the developer.
“It’s built on land that was mostly classified ‘Sabkha’ – a salt bog. What La’ala Al Kuwait Real Estate Company proposes is to transform this land into a sustainable, ecologically rich environment by expanding the two existing intertidal creeks into inland lagoons, building self-sustaining islands on these waterways to create wildlife habitats, and planting mangrove to protect the new ecosystem,” he explains.
However, according to him, the biggest challenge was to ensure sea tides could flush the system, oxygenating the water to ensure survival of the ecosystem and prevent pollution.
“The unique engineering solution the developer and designers came up with was a series of six massive tidally powered gates that allow for the tide circulation around the development. These gates were built into specially designed culverts that provide the main passage of the sea water to the lagoons,” Williams says.
However, the project presented a number of challenges, requiring effective solutions. He explains: “All six of the 10-tonne 50 sq m culvert gates were supported by hinges fixed with 25-mm Macalloy tension bars. To ensure these huge tensile loads were evenly distributed back to the concrete structure, a strong and durable non-shrink grout had to be used. BASF had an answer for us.
“Durability was also a key factor, given the extreme saline conditions of the local waters. In addition to the use of galvanised reinforcement, the developer, consultants and owners decided to coat the almost permanently submerged culverts with a protective membrane. BASF Construction Chemicals proposed the use of a complete protection system from its range of advanced solutions.”
“Masterflow 400 solvent-free non-shrink epoxy resin grout was used to grout behind the gate hinges,” Dr Christian Geierhaas, marketing head of BASF Construction Chemicals, explains. “This grout was chosen for its flowability and durability, and its ability to take on the dynamic loads which will be exerted by the Macalloy tension bars.”
Masterseal SP 120 PF, a newly-developed amine cured pitch-free epoxy was used to coat the semi-submerged roofs, walls, and walkways of all the culverts to protect against chloride ion attack.
“We are pleased that BASF was able to participate in the construction of the Sabah Al-Ahmad Sea City and to be associated with the development. BASF as a company is strongly driven by the philosophy of eco-friendly construction and we appreciate and fully support what they are trying to achieve,” Geierhaas concludes.
- TMC set to boost health tourism
- Leister helps seal hospital against leaks
- BASF sets Rheocrete record in Abu Dhabi
