The Construction Specifier – November 2009
Understanding Crystalline Concrete Technology
CONCRETE IS POROUS. WITHOUT WATERPROOFING, IT ABSORBS MOISTURE THAT CAN CAUSE CRACKS, AS WELL AS CONTAMINANTS AND CHEMICALS THAT LEAD TO DETERIORATION. TO PROTECT CONCRETE AND ENSURE IT HAS A LONG, SERVICEABLE LIFE, WATERPROOFING IS ESSENTIAL.
According to ASTM International, concrete waterproofing involves using a material that prevents water passage and resists hydrostatic pressure. The capacity to resist this pressure differentiates ‘waterproof’ from ‘dampproof’, as the latter offers no hydrostatic resistance.
There are many choices and approaches to make concrete truly waterproof. It call be achieved from:
• the positive (i.e. wet/exterior) side;
• the negative (i.e. dry/interior) side; or
• within the concrete itself, via integral chemical additive systems.
The most widely used positive-side waterproofing type is sheet membrane technology. Membranes have been used for decades but, despite advancenlents, their failures and limitations can be costly.
Since the 1980s, many construction projects have employed crystalline admixtures, which are integral waterproofing systems. These integral systems block water passage from any direction by working from the inside out; this makes the concrete itself the water barrier.
It can be difficult to keep up with advancements in both membrane and integral waterproofing as the admixture technologies. However, improvements in integral waterproofing make it a highly effective and valuable system for use in place of the more common membranes.
Sheet membrane systems
Positive-side waterproofing can be achieved using various membrane technologies.
Historically, hot-applied sheet systems—known as built-up bituminous membranes—were used for below-grade concrete waterproofing. These sheets were made from alternating layers of bitumen and felt. When heated, traditional bitumen—both coal tar pitch and asphalt—releases volatile organic compounds (VOCs) and potentially carcinogenic fumes.
Since the early 1990s, the bitumen system’s popularity has fallen due to an increasing number of bans on its use by governmental and regulatory agencies. Another drawback of sheet membranes is their field fabrication requires intensive labor and carefully supervised installation.
Substantial steps have been taken by product manufacturers to replace these membranes. Polymer-modified bitumens have evolved from the original bituminous sheet systems, offering a safer, cold-applied alternative. Material developments, such as thermoplastic and thermosetting polymers, have opened the door for a new series of radically different sheet membranes. Despite such progress, disadvantages persist.
Installation can be challenging as membranes require sealing, lapping, and finishing of seams at the corners, edges, and between sheets.
Additionally, sheet membranes must be applied to a smooth finish without voids, honeycombs, or protrusions. Protection board installation is also required as the membrane can puncture and tear during backfilling.
Sheet membranes pose various other limitations. They are challenging to use in vertical applications and difficult, if not impossible, for blind wall applications. In cases where they can be employed, they may be inaccessible for repairs after installation.
Performance and durability can also be issues. Performance depends on surface adhesion and proper seam lapping. Materials are strongest on the first day after the installation; at that point, they deteriorate over time.
However, hot-applied sheet membranes have been the industry norm for many years—they still hold the majority of the market share and remain popular for waterproof roofing systems. Their continued use is due to impact resistance, toughness, and overall durability compared to other membrane options.
The newest phase in bituminous sheet waterproofing is polymer-modified bitumen (i.e. rubberized asphalt). This cold-applied sheet membrane is composed of polymer materials compounded with asphalt and attached to a polyethylene sheet. The polymer is integrated with the asphalt to create a more viscous and less temperature-sensitive elastic material compared to asphalt on its own. These sheets are self-adhering and eliminate harmful toxins typically associated with asphalt adhesion. They also increase tensile strength, resistance to acidic soils, resilience, self-healing, and bondability.
• poor ultraviolet (UV) radiation resistance;
• use of solvent-based primer and adhesives; and
• need for an installation temperature greater than –4 C (25 F).
Careful installation practices must also be followed. Sheets can debond if:
• they are not promptly covered after installation;
• the top edges are not sealed;
• primer is incorrectly applied; or
• tie-holes are not flush with the concrete surface.
These waterproofing membranes are currently employed in all applications where hot-applied sheet systems were previously used; they can be utilized to waterproof all three areas of concrete construction, including structural slabs, slabs-on-ground, and foundation walls.
Thermoplastic polymers have led to the manufacturing of thermoplastic membranes. These membranes are composed of polyvinyl chloride (PVC), chlorinated polyurethane, or chlorosulfonated polyethylene, with glass fiber-reinforced PVC being the most popular membrane type.
Improvements in integral admixture waterproofing technologies make it a highly effective and valuable system for use in place of the more common membranes.
Thermoplastic materials soften when heated and harden when cooled, so sheets can be attached with solvent-based adhesives or by heat-welding at the seams—a significant advantage over field-fabricated seams. Thermoplastic membranes also effectively resist chemicals and hydrostatic pressure.
• physical properties that change by thermal cycling;
• deterioration of PVC when in contact with hydrocarbons;
• use of solvent-based primer and adhesives; and
• inability to place asphalt-based protection boards directly on PVC membranes.
These waterproofing membranes are commonly used as liners in water and sewerage containment applications. They are fully adhered to the substrate in horizontal and vertical applications, but can also be loosely laid over a framed slab.
Thermoplastic membranes can be employed to waterproof all components, including structural slabs, slabs-onground, and foundation walls. The concrete must be a ‘floor quality’ steel trowel finish, however, in order to ensure good adhesion.
Thermosetting membranes technology (i.e. vulcanized rubber) is more resistant to heat, solvents, general chemical attack, and creep than thermoplastic membranes are, due to the vulcanization of butyl, ethylene propylene diene monomer (EPDM), or neoprene rubber.
However, as thermosetting materials harden permanently when heated, these sheets can only be attached using solvent-based adhesives on the seams.
Further, as seams between sheets are field-fabricated, they never attain the base material’s tensile strength.
Sheets are also difficult to install on vertical surfaces, as they tend to stretch due to a low elastic modulus and lack of reinforcement. Additionally, their non-breathability may cause disbonding or blistering if negative vapor drive is present. Other disadvantages include:
• use of solvent-based primers and adhesives; and
• the restriction of elastomeric (movement) properties by fully adhered systems.
These waterproofing membranes are used in similar applications as thermosetting membranes, but only require a ‘smooth’ concrete finish.
Clay systems (bentonite)
This positive-side waterproofing method has been employed for more than 75 years, but its popularity has recently increased. As impure clay swells to block water, bentonite is versatile and comes in various forms, from prefabricated panels to trowelable mixtures.
Clay systems are excellent for waterproofing, but need sufficient hydration for success—in some applications, this can be difficult and unreliable. First, high hydrostatic pressure is required for complete hydration of the clay Molecules. Hydration must occur immediately after installation and backfilling; it must also take place in an adequately confined area to avoid lifting or cracking the concrete slab.
Bentonite can self-heal, is non-toxic, and is relatively easy to install, but is rarely minimal in places where leaking risk must be minimal and humidity control is necessary. These conditions are essential because bentonite materials are weather-sensitive and not resistant to soil chemicals (e.g. brines, acids, or alkalines), which ultimately decreases their ability to thoroughly waterproof structures.
Bentonite systems cannot be installed during rainfall, while groundwater level is fluctuating, or in areas with constant wetting and drying cycles because the clay will deteriorate. Installation is also not advised in places with free flowing water that would wash away clay. Once installed, bentonite is difficult to remove. This attribute limits options for future repair or replacement.
Bentonite sheets are most beneficial for blindside wall applications as they can be nailed directly to the foundation walls. Bentonite can also be used in other applications, especially now with the variety of forms in which it is supplied.
Liquid-applied membranes (LAMs) can be applied with a brush, spray, roller, trowel, or squeegee, and usually contain urethane or polymeric asphalt (hot- or cold-applied) in a solvent base. These membranes are usually applied on the positive side of set concrete and have high elastomeric properties. More recent technologies have also made negative-side applications possible.
Additionally, LAMs require:
• skilled, experienced labor;
• a clean and dry substrate (which can be a construction environment challenge);
• a protection layer before backfilling;
• properly cured concrete to avoid inadequate adhesion and blistering; and
• a sub-slab for horizontal applications.
Liquid-applied membranes can be problematic due to their lack of resistance to UV radiation and inability to withstand foot traffic. The liquids themselves also contain toxic and hazardous VOCs.
Although LAMs work well on projects with multiple plane transitions, intricate geometric shapes, and protrusions, they are typically only used in cases where prefabricated sheets do not work.
Negative-side waterproofing systems are applied to the concrete structure’s dry side, opposite the water pressure. Typically (but not always), negative-side waterproofing systems come in the form of cementitious coatings rather than membranes technologies, because the latter would be at risk of debonding from the external water pressure. Waterproofing coatings are often trowelled onto the concrete, brushed, or sprayed as slurry.
The placement of negative-side waterproofing on the dry, inside surface of a structure is its main advantage. This application offers easier application, leak detection, and maintenance over positive-side waterproofing. It is often used where positive-side waterproofing is not an option, such as inaccessible areas like pits or shafts.
Although cementitious waterproofing offers limited flexibility and no self-sealing ability, it is very durable and typically costs less than alternatives. However, negative-side cementitious waterproofing is rarely used for new construction because it leaves concrete exposed to any corrosive soil chemicals and freeze-thaw cycles.
Positive-side systems act as a physical barrier between the concrete and dirt/ground water. In contrast, negative-side waterproofing takes place on the opposite side of the concrete wall, stopping water from entering the structure without protecting the concrete itself. Concrete can still be penetrated by water and waterborne contaminants, leading to deterioration. Consequently, the use of negative-side waterproofing is predominantly limited to remedial work.
Integral admixture systems are added at the batching plant or onsite, and react chemically within the concrete. Instead of forming a barrier on the positive or negative side of concrete, they turn the concrete itself into a water barrier.
Integral concrete waterproofing systems are categorized in three main ways—as densifiers, water repellents, or crystalline/pore blockers.
Densifiers include pozzolans and supplementary cementing materials (SCMs) such as fly ash, silica fume, metakaolin, and slag. Densifiers react with the calcium hydroxide formed in hydration, creating another by-product that increases concrete density and slows water migration.
Densifiers are typically not characterized as waterproofing materials or repellents. They have no ability to seal cracks and joints. Concrete under hydrostatic pressure requires additional waterproofing methods to protect from damage and deterioration.
SCMs can be used to modify concrete’s properties. They are typically employed as a replacement for a portion of the portland cement and to increase the strength and durability of a concrete structure. When added in the right proportion, they can also reduce the concrete’s overall cost.
Systems that work to repel water are known as ‘hydrophobic.’ These products typically come in liquid form, and include oils, hydrocarbons, stearates, or other long-chain fatty acid derivatives.
Although hydrophobic systems may perform satisfactorily for dampproofing, they are less successful at resisting liquid under hydrostatic pressure. Additionally, these compounds’ performance is highly dependent on the concrete itself. Pre-curing and post-curing stresses cause cracking in any concrete, creating pathways for water passage.
Hydrophobic systems are ineffective at waterproofing such cracks under hydrostatic pressure. These systems are best suited for above-grade applications or non-critical areas with low water tables.
Crystalline-based systems typically come in a dry, powdered form and are hydrophilic in nature. Unlike their hydrophobic counterparts, crystalline systems actually use available water to grow crystals inside concrete, effectively closing off pathways for moisture that can damage concrete. They block water from any direction because the concrete itself becomes the water barrier.
In contrast to water repellents, crystalline technologies enable self-sealing. They involve admixtures made up of a blend of cementitious and proprietary chemicals that actually work with the available water in concrete to form insoluble crystals; the needle-like crystals grow until all pores are blocked and no water can penetrate the concrete. These crystalline formulas can allow concrete to self-seal hairline cracks up to 0.5 min (0.02 in.).
Concrete treated with these admixtures contains chemicals that lie dormant within. If a crack forms, any water influx causes more crystals to grow, re-blocking and sealing the passage against water and waterborne contaminants. Whenever new water enters the concrete through changing water levels or new cracks, crystals continue to grow and seal the concrete. The crystals within the concrete are impervious to physical damage and deterioration; there is no danger of punctures, tears, or seam leaks. Consequently, a building’s durability increases when crystalline admixtures are used.
In addition to promoting and enhancing the natural hydration process of cement, these systems are highly versatile, useful, and reliable for a wide range of applications. For example, concrete treated with crystalline admixtures is suitable for complex architectural designs. As architectural protrusions are not waterproofing challenges, any type of concrete structure—vertical, horizontal, or shaped—can be securely waterproofed.
Concrete waterproofed with crystalline admixtures affords other benefits. It contains no VOCs and can be completely recycled when demolition takes place. Membranes do not have to be separated from the concrete, waterborne contaminants are not present in the concrete, and petroleum-based materials are not left behind to leach into soil.
Additionally, crystalline admixtures present a number of installation advantages. Unlike traditional membrane waterproofing, which tends to be labor- intensive and expensive, crystalline technology decreases maintenance costs and is easy to handle—admixtures can be shipped in dissolvable, palpable bags that are thrown into the concrete batch during mixing.
As admixtures are added, they speed up the construction schedule and decrease labor costs by combining steps with concrete placing.
Limitations and considerations
Despite their benefits, design /construction professionals should keep in mind integral waterproofing systems are no substitute for sound construction practices. These systems must be used in conjunction with industry standards and best practices for concrete construction.
As the concrete itself makes up the barrier to water penetration, crystalline waterproofing requires above-average concrete. Substandard construction practices and products that lead to poor consolidation, unplanned cold joints, and improperly cured concrete cannot be tolerated.
Additionally, integral crystalline waterproofing systems should not be employed in applications under constant movement. During the crystallization process, crystals align in a three-dimensional array that breaks when subjected to excessive movement. Areas that require flexibility and face recurring movement would be better serviced with another system. Expansion joints and some suspended slabs and roof decks with excessive cracking may not self-seal at an acceptable rate.
Built-up options are generally the most costly due to the materials involved and the need for highly trained, experienced applicators. The time and space to apply sheet membranes is an indirect cost to this application method.
Integral waterproofing admixtures tend to be less expensive for materials, and labor costs are almost non-existent given the application method. They also allow for a larger building footprint and reduce maintenance and repairs over the long term. (For a cost comparison, see Figure 1.)
Although sheet membranes have been—and continue to be—the industry norm, integral hydrophilic systems should receive their due. Advancements in this technology make it a highly versatile and sophisticated method for waterproofing. It provides an inexpensive way to seamlessly waterproof concrete, creating permanent and durable structures.
Kevin Yuers is vice president of Kryton International and is responsible for product development, technical services, and operations. A veteran of the construction and renovation industries, Yuers has spent most of his career in concrete waterproofing. He has written several articles on the subjects of concrete waterproofing, crystalline-based technology, and concrete coatings and repair systems. He can be contacted via e-mail at firstname.lastname@example.org.
Concrete is a porous material that has the ability to soak up water (and waterborne contaminants). A crystalline integral concrete admixture is a relatively new and advanced technology that can be used in the place of traditional protective membranes. Proprietary chemicals in the material enhance the natural hydration process of cement, blocking the pores with millions of needle-like crystals—the concrete itself becomes the barrier to water penetration.
03 00 00-Concrete
07 10 00-Dampproofing and Waterproofing
07 16 16-Crystalline Waterproofing