380,000 litres of admixture used at Al Mafraq
Hospital extension is biggest-ever project in region to use product
The extension of the Al Mafraq Hospital in Abu Dhabi, which comprises the construction of an additional building, will triple its capacity to 690 beds.
Before construction could begin, however, contractors had to deal with the challenge of protecting the new building from the corrosive effects of ground water and chlorides.
BASF Construction Chemicals' Rheocrete 222+, a combined waterproofer and organic corrosion inhibitor, met the stringent requirements.
To date, over 380,000 litres of the admixture has been supplied, making it the biggest ever project using this product in the Middle East.
Says David Bowerman of BASF Construction Chemicals' Admixture Systems: "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 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 others, 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, could 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. Lastly, it needed to have an established track record in the region and environment.
BASF Construction Chemicals' Rheocrete 222+ fully met these requirements. Explains Bowerman: "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."
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.
Says Bowerman: "The admixture is dosed into the concrete mix and migrates through the concrete to form a protective film on the surface of the rebars. It has no effect on fresh concrete.
"it does not affect initial slump or workability retention, 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."
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 Construction Chemicals' Rheobuild 857AD, a high-range, water-reducing superplasticiser for concretes containing GGBS and silica fume.
About 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.
Notes Bowerman: "We supplied over 380,000 litres of product to the project last year, so it is 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."
Says Fouad Yazbeck of Readymix Abu Dhabi: "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. 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 aftersales service were spotless."