Concrete Technology Today – vol.3 July 2009
There are two common causes of reinforcement corrosion and both are associated with a lowered pH level of concrete. In the first, chloride ions cause a localised breakdown of the passive film on the steel. The second common cause involves a general breakdown of the passive film through carbonation, which happens when the concrete’s pH is neutralised predominantly through a reaction with atmospheric carbon dioxide.
Steel is particularly at risk of corrosion in environments that are repeatedly exposed to salt from marine water, salt spray or de-icing salt. The salt’s chloride ions work their way into concrete through pores or cracks. When a concentration of the chloride ions reaches the steel, theydestroy the protective film and corrode the steel.
Carbonation is a natural process that begins when concrete is poured. Carbon dioxide from the air reacts with the lime present in all cement paste, which produces calcium carbonate. The calcium carbonate lowers the pH level of the concrete. While it begins at the surface of the concrete, carbonation moves its way deeper into the pores of the concrete. If the concrete is cracked, the carbon dioxide from the air will penetrate the concrete more quickly, resulting in a lower pH level and greater chance of steel degradation.
Kryton International has developed a crystalline waterproofing system that transforms porous concrete into an impermeable barrier. While Kryton is not the only company to provide integral waterproofing products, it is responsible for creating the world’s first integral crystalline concrete waterproofing admixture and has been developing and improving its technology for over 35 years.
Kryton’s Krystol™ Concrete Waterproofing System includes the company’s flagship product, Krystol Internal Membrane (KIM®). KIM is a chemical admixture in a dry powdered form that creates waterproof concrete and protects against steel reinforcement corrosion. When combined with water and concrete, Krystol reacts with un-hydrated cement particles to form millions of needle-like crystals. These crystals grow and fill the naturally occurring pores and voids in concrete, permanently blocking water flow. If cracks form due to settling or shrinkage, incoming water triggers the crystallisation process again, even years after the concrete has set. More crystals grow, filling the new cracks and ensuring the waterproof barrier is maintained and protected.
KK Times Square is located in the heart of Kota Kinabalu, Sabah. It is a popular tourist destination near Borneo. Sprawling 23 acres, it is dubbed the area’s largest urban commercial project. KK Times Square was designed to accommodate the city’s expanding commercial activities, offering shopping, dining, entertainment, office spaces and leisure activities for residents and tourists.
The commercial hub is being built in two phases, the first of which was completed in 2007. Phase One is an ultra-modern, eight-acre development with 12 distinct buildings. The buildings, rising five-, six- and eight-storeys, have a total floor space of more than 645,000 sq ft.
In light of the project’s proximity to Sutera Harbour in the South China Sea, the project called for a waterproofing system that could withstand constant hydrostatic pressure, protect against the corrosion of steel reinforcements and withstand the uncompromising heat and humidity of Sabah for many years. The project team also recognised they were tackling a massive development. Meeting deadlines, affordability and ease of application were critical. They needed a waterproofing system that would last, minimising future repair costsand headache for tenants and their patrons.
After reviewing several waterproofing options, the project team selected the Krystol Concrete Waterproofing System. More than 100,000 kgs of KIM in 15,000 cu m of concrete was used in the basement slabs and elevator pits of KK Times Square Phase One. Additionally, the team used in excess of 25,000 kgs of Krystol T1 and T2 on the elevated car ramps, pedestrian walkways, drainage areas and rooftops. Finally, the team also used the Krystol Waterstop System to protect 2400 m of joints in the retaining walls and basement slab-to-slab areas.
With proven success under the project team’s belt, they moved forward with plans to use Kryton’s products in Phase Two. Phase Two will be a 15-acre development showcasing a five-star hotel, shopping complexes, exhibition facilities, restaurants, cineplexes, two prime office towers and condominiums. Kryton will waterproof another 15,000 cu m of concrete for this phase. When complete, KK Times Square will be completely waterproofed with Kryton’s Krystol Waterproofing System, protecting against the threat of steel reinforcement corrosion from the South China Sea and creating a strong, durable concrete structure.