BASF Construction Chemicals has played a vital role on the Dubai Light Rail (DURL) system with the supply of an adhesive which would bond the precast viaduct segments of the mostly-elevated 50 km-long Red Line.

The product that met the requirements of the project was the Segmental Adhesive Concresive 1441, an epoxy resin-based bonding system, which was subjected to a battery of tests before final selection.
“This is the first project of its type in the Gulf – in the light rail arena and using segmental bridge technology,” says Julian Pritchard, construction systems manager, BASF Construction Chemicals UAE, referring to the Dubai metro, which on completion in 2010 will be the single largest, driverless rail system in the world. “BASF Construction Chemicals’ win against intensive international competition is a considerable coup for the company and is a direct result of our ability to deliver a unique solution that meets the exact requirements of the client, offers significant value-add and complies with world class standards.”
DURL is being designed and built by a consortium that includes Mitsubishi Heavy Industries, Obayashi Corporation, Kajima Corporation and Yapi Markezi of Turkey. The project will be delivered in two phases, the 18 km of Green Line being constructed mainly underground is scheduled to be completed in March 2010, while the Red Line is marked for completion in September 2009.
The Red Line’s viaduct spans are being constructed with a minimum of eight precast viaduct deck segments, each of which is 10 m wide and 4 m in length. While the 50-tonne blocks (post-tensioned segments erected by launching gantries) would stay together due to gravitation, an adhesive was required to additionally bond the two segments.
“It took more than simply matching the standards of competitive solutions to secure this supply contract,” explains Pritchard. “All proposed supplier products needed to comply to FIP (Federation De la Precontrainte) standards which, in the case of the BASF Construction Chemicals adhesive, included standards for bond strength, open time and pot life. The product needed to exceed compressive strength of 75 MPa at 7 days, have mixed density not less than 1.8 with minimum open time of 60 minutes at maximum application temperature.”
He adds: “Segmental Adhesive Concresive 1441 thus had to go through a full range of testing and the physical properties of the product had to be demonstrated to the client and the engineers. It took six months from the time the product was proposed to obtain a SONO (statement of no objection) approval from the client.”
“The adhesive we developed possessed much greater tensile properties than the concrete in which it was adhering to and achieved high early compressive strength,” says R Venkatesh, area manager for BASF Construction Chemicals’ Dubai and Northern Emirates construction systems division. “It was approved to European FIP standards after fast-track testing in Dubai and India. This matched the performance level of competitive products. What secured the order, however, was the offering of product in pack sizes that matched the recommended usage rate per segment, and in both winter (10 to 30 deg C) and a summer grades (30 to 55 deg C), offering the least wastage. In addition, BASF’s ability to manufacture in Dubai was reflected in both the price and in the superior level of technical service offered to the contractor.”

Application
The Red Line’s viaduct deck segments are assembled and bonded together with the epoxy based adhesive to form a complete viaduct span bridging two supporting piers. Together, the 11,400 precast concrete segments, each weighing 50 tonne, will consume approximately 450 tonnes of the adhesive to form the bridge deck upon which the trains will travel. The segmental adhesive is applied at a thickness of 500 microns on either side of the precast elements, creating a seal and preventing any water ingress between the elements.
BASF Construction Chemicals provided on-site guidance and field service to the construction team and offered regular testing and frequent mock-ups. In addition, a QA/QC team set up by the subcontractor was trained by BASF’s technical staff to support site activities and the testing regime.
“BASF Construction Chemicals has been recommended for future projects with the client, the Roads and Transport Authority (RTA), based on its success with this product and its dedicated efforts to support the project,” Pritchard adds.
Meanwhile, BASF has also been involved with rehabilitation of a port in Tanzania’s Dar Es Salaam, where it provided the solution for repairing the badly corroded reinforced concrete piles supporting the wharf.
“The harbour was in dire need of attention,” explains Graham Dean, business development manager for BASF Construction Chemicals in Sub Saharan Africa and Indian Ocean Islands. “It needed to be dredged to increase access, and repairs and refurbishment of key facilities were critical to increase safety and productivity in terms of servicing ships. A primary area of concern was the weakening of the wharf due to the corrosion of the reinforcing within the supporting concrete piles.”
He continues: “In marine environments concrete structures are exposed to the aggressive corrosive properties of chloride contaminated salt water. This is especially so in tidal areas where the continuous wetting and drying subject the concrete structures to numerous stresses. Initially the entry of chlorides is through the micro cracks and the capillary pores of the concrete. With the onset of corrosion, or rusting concrete structures quickly deteriorate, ultimately putting the structural integrity of structures into doubt. BASF Construction Chemicals has specialised systems that are designed to help resolve this issue. We put the specification in place in conjunction with our South African office for Noremco, the Tanzanian arm of Veidekke ASA, one of Norway’s largest and best known contractors to carrying out an application.”
The proposal included the use of Concresive ZR, a zinc-rich primer for coating the steel. Concresive ZR is a single component, solvent borne zinc-rich epoxy primer, providing active galvanic protection to steel. It is recommended for use where chloride induced attack on steel and concrete is involved. It acts as a passivating layer to steel. Then, pre-bagged known performance cementitious repair materials were either directly poured in place or trowled on. The principle repair materials used were Emaco S 88 CT, a fibre reinforced structural repair mortar with low permeability; and MasterFlow 928 T, a non-shrink cementitious flowable grout.
Commenting on the properties of the two repair materials, Dean says: “Emaco S 88 CT possesses excellent bond characteristics to steel reinforcement and to concrete. It is shrinkage compensated, which reduces the risk of cracking; has low permeability; and is extremely durable. It is recommended for protection of concrete subject to attack from water containing chlorides and sulphates, etc., and for repairs in marine environments
“At the same time, Masterflow 928 T is a non-shrink grout of predictable performance. It possesses high bond strength to steel and concrete and delivers early strength development even at fluid consistency. It is impermeable and also has good fatigue and impact resistance.”
The contract for the project was won by Noremco. BASF brought in technical trainers from Dubai to train the application team, as well as to conduct supervisory visits. Says Dean: “The solution was so successful that we finished the task nine months before the due date, giving Noremco the leverage to do a negotiated tender for subsequent phases of the project.”