Since the crystalline waterproofing coating system has a unique chemical diffusing characteristic, proper surface preparation of the concrete is critical to the performance of the treatment. Concrete surfaces need to have an open pore texture to allow the transfer of the reactive crystalline chemicals from the coating into the concrete substrate. The surface also needs to be clean and free of form oil, laitance, and other foreign matter to ensure proper adhesion of the coating.
Crystalline waterproofing admixture
When used as an admixture the same chemical reactions take place, but cost is lowered by eliminating the labour associated with the application of a surface treatment. Additionally, the use of crystalline waterproofing as an admixture moves labour offsite, eliminating scheduling and delays.
Since the admixture is added to the concrete mix at the batch plant or a ready-mix truck, it ensures the crystalline formation occurs uniformly throughout the structure rather than penetrating from the surface as would be the case with a surface application. In addition to waterproofing, crystalline admixture can reduce shrinkage cracking as well as increase compressive strengths. This may be because the water is taken up into the crystalline structure, leading to a longer, internal moist cure that is beneficial for shrinkage reduction and compressive strength development. For most mix designs, the dosage rate is two to three per cent based on the Portland cement content.
While crystalline waterproofing admixture is compatible with super plasticizers, air-entraining agents, water reducers, fly ash, pozzolans, and other ingredients used to improve the performance of modern concrete mixes, it is best to check with the manufacturer to ensure there is no incompatibility with other elements of the concrete mix, particularly concrete set retarders.
Negative-side waterproofing
Where existing underground structures are experiencing water seepage because of failed exterior membrane or coating systems, the problem can be remedied by the application of crystalline waterproofing on the negative side (inside) of the structure. Under these conditions, surface coatings—depending on the adhesion—blister and peel when moisture seeping through the concrete from the exterior dissolves soluble minerals and deposits them under the coating in the form of efflorescence. Since crystalline waterproofing penetrates into the concrete and plugs the pores beneath the surface, it stops water seepage in the concrete before it reaches the inside surface. This does not depend on its adhesion to the surface and will not blister and peel off like surface barriers.
Vapour transmission through basement floors and walls is also a common problem leading to unpleasant damp, musty odours. Testing in Japan and Europe has shown the application of crystalline technology can reduce vapour flows as much as 50 per cent by reducing the size of the capillary tracts in the concrete as well as making some of them discontinuous, which, in most cases, provide a drier, more pleasant atmosphere.
Crystalline waterproofing materials also have the ability to self-heal micro-cracks (<30 μm [1181 μin]) in the concrete substrate as well as macro-cracks up to 0.4 mm (16 mils) in width. The rate of self-healing is dependent on the size and nature of the crack (static or moving) and the hydrostatic pressure the crack may be subjected to. Self-healing can be evident in only a few days or as long as a few months depending on the ambient conditions.
Real-world examples
Several examples of how crystalline waterproofing technology products were used in real world construction applications situations are illustrated by the following projects.
May Bank Headquarters
The triple tower development designed as a new headquarter building for May Bank in Kuala Lumpur, Malaysia, involved diaphragm wall construction incorporating a nine-level underground parking garage. A crystalline technology admix (dosed at 3 kg/m3 [0.19 lb/cf]) was selected for the project to assist with controlling hydration heat, reduce shrinkage cracking, give the slab the capacity to ‘self-heal,’ and waterproof the concrete as well as increase its strength and durability.
The basement slab required approximately 24,000 m3 (847,552 cf) of crystalline admix-dosed mass concrete. Commencing on September 26, 1997, the initial pour of approximately 13,200 m3 (466,154 cf) was conducted over a 60-hour period; it was then and remains today the third largest continuous pour conducted in the world and the largest in Southeast Asia.
Valdez Marine Terminal
Two coats of crystalline waterproofing were applied to the ballast water purifying facility’s tanks at the Valdez Marine Terminal located at the end of the Trans Alaskan Pipeline System, Prince William Sound, Alaska. More than 25,000 m2 (250,000 sf) of coating materials was applied to the two final water purifying tanks. The ballast water treatment system sends oily water through multiple processes to strip it of any hydrocarbons before it is released into the ecologically sensitive waters of Prince William Sound.
Columbia College
Columbia College is British Columbia’s oldest university transfer college. The main campus is housed in a five-storey, 6782-m2 (73,000-sf) building just east of Vancouver’s downtown core at 438 Terminal Avenue. The building has a one-level, below-grade parking garage falling just above the sea level from the nearby False Creek Inlet. Due to the local climate and high-water table, the structure was subject to ongoing groundwater and below-grade hydrostatic pressure.
To waterproof the foundation slab, walls, and elevator pit, without the uncertainty and extra labour of membranes or coatings, the designers chose a crystalline admixture to add to the 500 m3 (17,657 cf) of ready-mix concrete required for the project. The crystalline admix was introduced at a two per cent dosage (based on the total weight of cementitious ingredients).
Crystalline waterproofing patching material and coating products were used in combination with a polyvinyl chloride (PVC) waterstop to permanently seal the joints where exterior walls landed on the slab. Additionally, crystalline waterproofing admix was also used as a modified grout to ensure a well-consolidated wall/slab interface. Once completed, all walls and joints in the foundation structure were dry and free of leaks.
Other applications
Crystalline waterproofing admix is also used by precast concrete producers to add value and enhance the performance of concrete pipes, manholes, septic tanks, and architectural panels. Apart from waterproofing these products, crystalline technology enhances chemical resistance and reduces shrinkage cracking, thus prolonging service life. Since it is sold in powder form, crystalline waterproofing can also be included in the mix design for bagged cement products such as shotcrete, mortar mixes, and stuccos.
Conclusion
Although concrete may appear to be a simple product to manufacture, it requires a highly engineered approach. In today’s design and construction environment, where more stringent requirements, such as longer life cycles, more durable concrete, and value-engineering concepts are expected, careful consideration must be paid to not only the basic requirements, such as the water/cement ratio and materials, but also to more sophisticated chemical admixtures. With its ability to reduce the porosity and permeability of conventional concrete, crystalline waterproofing technology is a valuable addition to building sciences.
A protective layer of crystalline waterproofing is applied to the Valdez Marine Terminal water purifying tanks in Prince William Sound, Alaska.
David Ross is the technical services director for Xypex Chemical Corp. of Vancouver, a manufacturer of crystalline waterproofing materials. He can be reached at dave@xypex.com.
