Concrete – June 2009
“Integral systems block the passage of water from both the positive and negative sides by working from within the concrete.”
Concrete by its very nature is porous. Any water absorbed into unprotected concrete can cause reinforcing steel corrosion and concrete spalling – Idevastating long-term effects to both the durability and structural integrity of a structure. The answer to designers, engineers and contractors perpetual headache is simple: keep the water out of the concrete. The solution is not as complicated as some may fear.
Gary Penk, Kryton International
There are three options. Concrete can be waterproofed from the positive (wet/exterior) side, negative (dry/ interior) side or from within the concrete itself (integral systems).
The oldest and most widely used method is positive-side waterproofing using sheet membranes but its failures and limitations are common and costly.
Integral systems block the passage of water from both the positive and negative sides by working from within the concrete. This technology, which dates back to the early 1900s, has undergone many improvements and developments over the last 30 years. It is now a highly effective, time-saving and cost-saving technology to use in place of traditional membrane systems.
Integral crystalline waterproofing is most often a dry powder mix of Portland cement, fine silica sand and a specific (and usually proprietary) blend of chemicals. It is either an admixture added to ready-mixed concrete at the time of batching for in-situ pours or sprayed concrete applications, or a surface-applied mixture used for existing structures. Surface-applied crystalline waterproofing formulas are brushed or sprayed onto existing structures as a slurry coating or spread over and trowelled into freshly poured concrete slabs as a dry-shake treatment.
When the blend of chemicals comes into contact with water, as it inevitably does, long narrow crystals grow within the concrete. These block the movement of water by filling the natural pores, capillaries and hairline cracks in concrete. Instead of forming a barrier on the positive or negative side of your concrete, they turn the concrete itself into a water harrier.
The advantages of this solution:
- Permanent solution – becomes a part of the concrete so it won’t wear away, crack, tear or peel – even against high hydrostatic pressure.
- Perfect for blind-wall applications – can be added to the concrete or applied to the negative side of the structure (against water pressure). There is no need to save room outside the structure for membrane application.
- Protects reinforcing steel – adds to the longevity of concrete structures by preventing the penetration of waterborne contaminants and chloride-laden liquids that cause the corrosion of reinforcing steel.
- Saves weeks on construction schedule – can be applied to green concrete or added directly to the concrete. No need to wait for membrane application and backfilling can begin right away.
Two types of integral crystalline waterproofing
Close-up of Krystol grout, part of the Krystol KWS system being installed at five blocks high.Most integral waterproofing systems are compounds that either increase the density of the concrete or increase its ability to repel water. As these systems work to repel water, they are ‘hydrophobic’. Although hydrophobic systems may perform satisfactorily for damp-proofing, they can’t reliably resist liquid under hydrostatic pressure and have limited to no ability to reactivate and self-seal f u t w cracks and leaks. In contrast, hydrophilic systems actually use available water to grow crystals within the concrete – effectively shutting off pathways for moisture that can damage concrete.
Hydrophilic technology, such as Kryton International’s Krystol Waterproofing System, has distinct advantages over other crystalline products:
- penetrates deeper into concrete – many inches over time
- self-seals hairline cracks – minimum 0.5mm
- reactivates in the presence of moisture – even years later
- effective against hydrostatic pressure – up to 140m of head pressure
- impervious to physical damage and deterioration.
Kryton’s Krystol line includes Krystol Internal Membrane (KIM), an admixture for new concrete. It also includes Krystol T1 and T2 surface-applied slurry system for existing concrete and Krystol Broadcast dry-shake system for concrete flatwork. Krystol systems have also been developed for repairing cracks, holes and water-proofing concrete construction joints, tie-holes and pipe penetrations.
KIM has received an Agrément Certificate from the British Board of Agrément stating that KIM provides watertight concrete, enhances concrete durability, improves protection against corrosion of reinforcing steel and is safe for use in potable water applications such as reservoirs, culverts and other similar structures. It was approved by the British Drinking Water Inspectorate to ensure the product does not contain or produce toxic materials that would make water unsafe for human consumption.
Many traditional waterproofing methods use petroleum- based membranes or coatings on the concrete surface that require adhesives with highly volatile organic compounds. Oil from membranes can leach out and contaminate ground water. Vapour from the compounds can cause respiratory problems and contribute to ‘sick building syndrome’. However, hydrophilic and hydrophobic crystalline waterproofing is environmentally friendly. Crystalline waterproofing is a non-toxic, non-flammable, odourless product, and crystalline-treated concrete can also be recycled, unlike membrane-coated concrete.
London City Hall
Located on the south bank of the River Thames and next to Tower Bridge, London City Hall is a state-of-the-art building with a series of underground concrete tunnels and transformers room that were constructed using conventional membrane waterproofing systems. Leaks soon occurred through the concrete to allow room for service pipes, also leaked due to the high water pressure of the River Thames. In 2001, before City Hall opened, the Krystol concrete waterproofing system was chosen for repairing cracks, joints and holes in concrete. It was applied from the inside against the water pressure to eliminate water entry. The drilled holes for the service pipes were filled with Krystol Bari-cote, followed by a slurry application of Krystol T1 and T2 to stop all water from entering the service rooms. By the time City Hall opened in 2002, the building was watertight.
Manchester contractor Westshield chose KIM for its latest private residential development at Bowdon near Altrincham. The team needed a product that would be suitable for a below-grade structure that was to be built using the Amvic ICF (insulating concrete formwork) wall system and specifications outlined by the purchaser.
KIM was chosen to treat the concrete for the lift pit, car lift, ground floor slab (split pour), walls of the basement and the attached ground floor level swimming pool retaining structure. In total, around 170 cu m of KIM treated concrete was placed in conjunction with approximately 200m of Krystol Waterstop System.
Using Kryton in the basement meant that Westshield did not have to over-excavate the site in order to apply an external tanking membrane – they could take advantage of all the space available to them. In addition, once the ground floor was in place, they could backfill with confidence that their structure was 100% waterproof. Completion on the home is expected before the end of 2009.