Supplying drinking water in Brunei is not an easy task. Located on the north coast of the island of Borneo in Southeast Asia, Brunei has adequate water sources but the development of the water supply system has been affected by distance and local conditions.
Even as recent as 1996, a small proportion of residents living in remote inland areas of Brunei were unable to gain access to a potable water supply. Part of Brunei’s water supply is transported some 80km from its rainfall regions to city reservoirs and rapid population growth in Brunei since the 1960’s has led to demand occasionally exceeding available resources.
Everyone in Brunei now has access to good quality drinking water, including those living in rural areas, and Bruneians now use about 450 litres each per day, making Brunei one of the highest water users per capita in the world.
In the 1990’s, the Bukit Barun Water Treatment Works (WTW) was constructed to cater for the increasing water demand in the Brunei-Muara district. The Bukit Barun WTW can supply nearly 80% of the water to the Brunei-Muara district and is now capable of supplying 430 million litres of water daily.
For several years, the Water Services Department in Brunei has concentrated on improving the production capacity and robustness of the water supply system. Under a National Development Plan, several dams and service reservoirs have been constructed in the area and the distribution pipe network system is in the process of being upgraded. The pipes were previously asbestos cement and polyvinyl chloride (PVC) based, but had deteriorated over the years and are being replaced with 1,200 mild steel pipes with a polyurethane external protective coating and an epoxy internal protective coating.
Part of the improvement works involves a £14m extension of Bukit Barun WTW which is due for final completion in September of this year. This extension will increase the WTW’s capacity to 490 million litres of water daily in order to meet increasing water consumption demand. As part of the repair and waterproofing side of the contract, over 5 tons of materials produced by UK manufacturer Flexcrete Technologies Limited have been supplied by Flexcrete’s distributor in Brunei, Rigoh Sdn Bhd. The main contractor for the repair and waterproofing works is Ley Choon EWC Sdn Bhd and the Consulting Engineers are Jurusay Perunding.
A total of four concrete clarifier tanks have been newly constructed and Flexcrete materials were specified in order to underpin and assure the design life of the structures, and provide a solution to non-conformance with specification. Part of the face of the cast concrete wall in the clarifier tank was found to be defective when the shuttering was removed and the requirement was for a concrete reinstatement system that would increase the effective cover to the steel reinforcement. The vertical concrete tank walls are 3m in height and the lamella plate clarifiers are made from stainless steel.
After the surface profile of the concrete was levelled with Monolevel 844SP, an engineering grade pore filler and thin screed that is approved under Regulation 31(4)(a) for use in contact with drinking water, a tropical climate grade of Cementitious Coating 851 was applied over the entire area. A highly advanced, two component, waterborne cementitious modified polymer coating, Cementitious Coating 851 provides an effective barrier against the effects of aggressive acid gases, moisture and chlorides, and also has greatly enhanced chemical resistance. It forms a hard, highly alkaline coating for the protection and structural waterproofing of concrete, resisting positive and negative pressure under a 100 metre head. It is also approved under Regulation 31(4)(a) and is CE marked in accordance with BS EN 1504 Part 2, the pan European standard for concrete repair, as well as carrying British Board of Agrément (BBA) certification.
A 2mm coating of Cementitious Coating 851 provides equivalent cover to 100mm of good quality concrete and being cement based, it chemically reacts with the substrate to form an integral part and will have a design life to match that of the concrete to which it is applied. As it is water-based, it exhibits minimal hazard during application and is non-toxic when cured.
Cemprotec 2000-S, an elastomeric, waterproof reinforcing tape, was also applied between the filter inlet channel and the clarified water channel. WRAS approved, Cemprotec 2000-S provides an impermeable, highly flexible seal over live cracks and joints. This was an ideal product as the requirement was for a solution that could accommodate the expansion movement and at the same time, remain watertight.
In addition, Flexcrete products were used for application to the pre-chlorine flash mixing chamber, in order to protect the concrete structure from chlorine and lime attack. Chlorination is used at Bukit Barun WTW for the oxidation and disinfection of the potable water source. In the pre-chlorination stage, chlorine is added in the flash mixer almost immediately after it enters the WTW and the mixer ensures quick, uniform dispersion of the chlorine. This process removes tastes and odours, whilst controlling biological growth throughout the water treatment system.
Such is the chloride resistance of Cementitious Coating 851 that Flexcrete has received official confirmation it will resist chloride penetration for at least 26 years. In 1988, a 2mm thick film of Cementitious Coating 851 was applied to a concrete slice and sealed in a chloride ion diffusion cell in the laboratory at the VINCI Construction Technology Centre and it is still going strong some 26 years later. The chemical resistance of Flexcrete products was another important consideration, as during the water treatment process at Bukit Barun, lime is added to the water to adjust the pH level of the raw water and reduce the CO² concentration.