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Concrete is the material of choice for most building foundations and other subsurface construction. However, concrete is porous, and water can seep through openings, cracks, and pores. To prevent that from happening and protect the concrete, there are several ways to waterproof a concrete structure, most of which involve the application of some type of membrane over the concrete. However, one proven choice is based on chemically treating the concrete to make it permanently waterproof using crystalline concrete technology. This course will explore what this technology is and delve into its very successful use in both new and existing construction as well as how it can be used to address special design conditions, such as elevator pits and cisterns.
All photos courtesy of XYPEX Chemical Corporation
The design team for the new Amos Rex Museum in Helsinki, Finland, considered many solutions for waterproofing the underground art galleries and storage areas. It ultimately chose crystalline concrete admixture to protect against the high water table because of its proven track record in similar high-profile projects worldwide.
Crystalline Concrete Technology
The technology behind crystalline concrete has been around for more than 50 years but is not necessarily all that well understood by design and construction professionals. The following is meant to clarify the science, chemistry, and practical applications behind it.
Crystalline Technology: What It Is and How It Works
Crystalline technology takes advantage of the natural and porous characteristics of concrete. With water as the catalyst, specific chemicals are used that react with the natural by-products of cement hydration (calcium hydroxide, mineral salts, mineral oxides, and un-hydrated and partially hydrated cement particles).
This reaction forms a nonsoluble crystal that grows to form a web-like crystalline structure within the interconnected pores and other voids in concrete. In this way, the crystalline structure becomes a permanent, integral part of the concrete itself. Because it is nonsoluble, it fills the voids, cracks, capillaries, pores, and other openings to make the concrete impermeable, thus preventing the ingress of water and other liquids even under strong hydrostatic pressure. That means it also protects against liquid-borne chemicals that can deteriorate concrete or corrode steel reinforcing, even in harsh, aggressive environments.
When the cement particles used in concrete hydrate, the reaction between water and the cement causes it to become a hard, solid, rocklike mass. The reaction also generates chemical by-products that lie dormant in the concrete. Crystalline technology adds another set of chemicals to the mixture. When these two groups, the by-products of cement hydration and the crystalline chemicals, are brought together in the presence of moisture, a chemical reaction occurs that produces a new nonsoluble structure in the capillaries, micro cracks, and shrinkage cracks that are characteristically found in the concrete. By means of the crystalline reaction, the porosity of the concrete is plugged and the ability of water (and/or or water-borne elements) to penetrate the substrate is prevented.
Crystalline technology products are manufactured in the form of a dry powder compound consisting of portland cement, very fine treated silica sand, and selected chemicals. It is the chemicals that react with the by-products of cement hydration to produce the nonsoluble crystalline formation.
Crystalline Technology: What It Does
There are essentially two things that are achieved by using crystalline products with concrete. The first is waterproofing. Scanning electron microscope images have provided a close-up view of how newly formed crystalline structures bridge and seal the capillary tracts and cracks in concrete. These images show clearly how the diffusion of liquids into the concrete are stopped, thus creating a permanent, waterproof concrete condition.
Crystalline waterproofing also offers protection against things that could otherwise work to deteriorate the concrete, including sulfate and acid attacks; chloride diffusion, which can damage reinforcing steel; carbonation; and alkali reactions. This occurs because virtually all of these issues are associated with water penetration into the concrete, which carries these harmful substances. By sealing against the water, and by being impervious to these other chemicals too, the crystalline formation protects and preserves the concrete and the steel reinforcing, thus helping to assure the long-term durability and life of concrete structures.
There are three types of products with specific formulations for different concrete applications, all designed achieve the same results. For newly poured concrete, an admixture is available that is added to the concrete mix and releases its crystalline effects as the concrete is poured and cured. For existing concrete or for joints and seams in concrete structures, there are slurry-type coating products that are designed to be applied to the surface of the concrete. These create an integral waterproofing effect directly on the existing substrate. Finally, for concrete slabs, there is a dry-shake product that can be spread across the top of the slab as it is finished to integrate the waterproofing chemistry. These different options can be incorporated into a structure as it is being constructed or later on in the life cycle as a maintenance material to correct water problems and further enhance durability. Perhaps the most significant point about the use of any of these crystalline concrete products is the fact that they are permanent and become integral to the concrete due to their chemical reactions. Other types of waterproofing are applied and subject to separation from the concrete or deterioration over time, requiring some repair and replacement.
Scanning electron microscope images of crystalline formation in a concrete pore show its ability to fill and plug the voids that are inherent in concrete.
Crystalline Technology in New Construction
The waterproofing goal in new construction is usually to address water penetration on the “positive side.” This is typically the exterior side of the concrete where it meets the soil or weather and is subject to water exposure. Of course, to do so means that there needs to be access to the exterior side, which is usually only possible during construction.
Traditional Waterproofing
A typical waterproofing practice is to use a membrane over the exterior face of the concrete with three types being common. The first is a loose-laid sheet membrane such as a heavy PVC sheet used under concrete floor slabs. The membrane itself is typically very waterproof, but there can be a real issue in the overlapping seams, which can still seep water between the overlaps and migrate into the concrete. A second approach, primarily for walls, is to use a fully adhered sheet waterproofing that is meant to be attached while the concrete is still wet or curing. The success of this approach can be very dependent on the skilled labor installing it and the weather conditions during installation. While the adhered nature means that seam concerns may be lessened compared with loose laid, that is only true as long as the membrane does not separate over time or get damaged during backfill operations. A third alternative is to use a bentonite-based system for waterproofing. Bentonite is a natural mineral that swells when it becomes wet and provides water stopping capability. It is typically more costly than a membrane and may endure backfilling a bit better, but it too has limitations. In particular, it does not work when subjected to salt water (i.e., any water with a high chloride content).
In addition, to the use of membranes, it is also common practice to incorporate a drainage system around a foundation. Placing a continuous drain tile along the perimeter that runs to daylight or another dispersion point helps collect water running down the face of the concrete and channel it away. The drain tile is usually covered with gravel and a filter fabric to keep things running smoothly.
Crystalline technology was used on the foundation-capping beam, escalator and other pits, as well as pool and spa on the 52nd floor.
Concrete is the material of choice for most building foundations and other subsurface construction. However, concrete is porous, and water can seep through openings, cracks, and pores. To prevent that from happening and protect the concrete, there are several ways to waterproof a concrete structure, most of which involve the application of some type of membrane over the concrete. However, one proven choice is based on chemically treating the concrete to make it permanently waterproof using crystalline concrete technology. This course will explore what this technology is and delve into its very successful use in both new and existing construction as well as how it can be used to address special design conditions, such as elevator pits and cisterns.
All photos courtesy of XYPEX Chemical Corporation
The design team for the new Amos Rex Museum in Helsinki, Finland, considered many solutions for waterproofing the underground art galleries and storage areas. It ultimately chose crystalline concrete admixture to protect against the high water table because of its proven track record in similar high-profile projects worldwide.
Crystalline Concrete Technology
The technology behind crystalline concrete has been around for more than 50 years but is not necessarily all that well understood by design and construction professionals. The following is meant to clarify the science, chemistry, and practical applications behind it.
Crystalline Technology: What It Is and How It Works
Crystalline technology takes advantage of the natural and porous characteristics of concrete. With water as the catalyst, specific chemicals are used that react with the natural by-products of cement hydration (calcium hydroxide, mineral salts, mineral oxides, and un-hydrated and partially hydrated cement particles).
This reaction forms a nonsoluble crystal that grows to form a web-like crystalline structure within the interconnected pores and other voids in concrete. In this way, the crystalline structure becomes a permanent, integral part of the concrete itself. Because it is nonsoluble, it fills the voids, cracks, capillaries, pores, and other openings to make the concrete impermeable, thus preventing the ingress of water and other liquids even under strong hydrostatic pressure. That means it also protects against liquid-borne chemicals that can deteriorate concrete or corrode steel reinforcing, even in harsh, aggressive environments.
When the cement particles used in concrete hydrate, the reaction between water and the cement causes it to become a hard, solid, rocklike mass. The reaction also generates chemical by-products that lie dormant in the concrete. Crystalline technology adds another set of chemicals to the mixture. When these two groups, the by-products of cement hydration and the crystalline chemicals, are brought together in the presence of moisture, a chemical reaction occurs that produces a new nonsoluble structure in the capillaries, micro cracks, and shrinkage cracks that are characteristically found in the concrete. By means of the crystalline reaction, the porosity of the concrete is plugged and the ability of water (and/or or water-borne elements) to penetrate the substrate is prevented.
Crystalline technology products are manufactured in the form of a dry powder compound consisting of portland cement, very fine treated silica sand, and selected chemicals. It is the chemicals that react with the by-products of cement hydration to produce the nonsoluble crystalline formation.
Crystalline Technology: What It Does
There are essentially two things that are achieved by using crystalline products with concrete. The first is waterproofing. Scanning electron microscope images have provided a close-up view of how newly formed crystalline structures bridge and seal the capillary tracts and cracks in concrete. These images show clearly how the diffusion of liquids into the concrete are stopped, thus creating a permanent, waterproof concrete condition.
Crystalline waterproofing also offers protection against things that could otherwise work to deteriorate the concrete, including sulfate and acid attacks; chloride diffusion, which can damage reinforcing steel; carbonation; and alkali reactions. This occurs because virtually all of these issues are associated with water penetration into the concrete, which carries these harmful substances. By sealing against the water, and by being impervious to these other chemicals too, the crystalline formation protects and preserves the concrete and the steel reinforcing, thus helping to assure the long-term durability and life of concrete structures.
There are three types of products with specific formulations for different concrete applications, all designed achieve the same results. For newly poured concrete, an admixture is available that is added to the concrete mix and releases its crystalline effects as the concrete is poured and cured. For existing concrete or for joints and seams in concrete structures, there are slurry-type coating products that are designed to be applied to the surface of the concrete. These create an integral waterproofing effect directly on the existing substrate. Finally, for concrete slabs, there is a dry-shake product that can be spread across the top of the slab as it is finished to integrate the waterproofing chemistry. These different options can be incorporated into a structure as it is being constructed or later on in the life cycle as a maintenance material to correct water problems and further enhance durability. Perhaps the most significant point about the use of any of these crystalline concrete products is the fact that they are permanent and become integral to the concrete due to their chemical reactions. Other types of waterproofing are applied and subject to separation from the concrete or deterioration over time, requiring some repair and replacement.
Scanning electron microscope images of crystalline formation in a concrete pore show its ability to fill and plug the voids that are inherent in concrete.
Crystalline Technology in New Construction
The waterproofing goal in new construction is usually to address water penetration on the “positive side.” This is typically the exterior side of the concrete where it meets the soil or weather and is subject to water exposure. Of course, to do so means that there needs to be access to the exterior side, which is usually only possible during construction.
Traditional Waterproofing
A typical waterproofing practice is to use a membrane over the exterior face of the concrete with three types being common. The first is a loose-laid sheet membrane such as a heavy PVC sheet used under concrete floor slabs. The membrane itself is typically very waterproof, but there can be a real issue in the overlapping seams, which can still seep water between the overlaps and migrate into the concrete. A second approach, primarily for walls, is to use a fully adhered sheet waterproofing that is meant to be attached while the concrete is still wet or curing. The success of this approach can be very dependent on the skilled labor installing it and the weather conditions during installation. While the adhered nature means that seam concerns may be lessened compared with loose laid, that is only true as long as the membrane does not separate over time or get damaged during backfill operations. A third alternative is to use a bentonite-based system for waterproofing. Bentonite is a natural mineral that swells when it becomes wet and provides water stopping capability. It is typically more costly than a membrane and may endure backfilling a bit better, but it too has limitations. In particular, it does not work when subjected to salt water (i.e., any water with a high chloride content).
In addition, to the use of membranes, it is also common practice to incorporate a drainage system around a foundation. Placing a continuous drain tile along the perimeter that runs to daylight or another dispersion point helps collect water running down the face of the concrete and channel it away. The drain tile is usually covered with gravel and a filter fabric to keep things running smoothly.
Crystalline technology was used on the foundation-capping beam, escalator and other pits, as well as pool and spa on the 52nd floor.
Crystalline Waterproofing
Instead of using a separate membrane, crystalline technology provides concrete waterproofing for new construction by using any or all of the available application methods. A crystalline admixture can be added directly into the concrete mix at the batching plant (preferred) or on-site (for small batches) for most concrete elements. In addition, a slurry mixture can be used to cover joints and seams or untreated concrete and be applied by brush or spray methods. For new concrete slabs or decks, a dry-shake formulation can be troweled into the fresh concrete prior to finishing.
All of these methods provide a continuous waterproof surface across the concrete without any seams. As such, crystalline waterproofing eliminates the need for separate membranes. (Note that a drain tile system along the base of a wall around the perimeter is still recommended). This usually provides significant cost savings compared to the installation of a membrane of any type. Further, it is notably more cost-effective to use integral products (admixture and dry shake) during new concrete construction than an applied coating after the wall is completed.
Some of the characteristics of new construction using crystalline concrete include the following:
- Resistance to extreme hydrostatic pressure: The pressure of water on a concrete wall is what drives many water leaks. Crystalline concrete will resist this effectively whether applied on the positive (exterior) side or the negative (interior) surface of the concrete.
- Integral application: The crystalline treatment becomes a fully integral part of the concrete substrate. It does not require sealing, lapping, and finishing of seams as with membranes. It cannot puncture, tear, or come apart at the seams
- Chemical resistance: Aggressive chemicals found in many subsurface and concrete construction locations are not a problem for crystalline applications since most do not affect the crystalline structures.
- Crack sealing: All concrete will develop some cracking as it cures. Crystalline admixtures can fill and seal static hairline cracks up to 0.4 millimeter wide.
- Human safety: Crystalline applications are nontoxic and contain zero volatile organic compounds (VOCs).
- Cost: It is routinely less costly to incorporate crystalline technology for waterproofing when compared to most other methods.
- Permanence: As noted, the crystalline admixture becomes a permanent part of the concrete that will remain in place for the full lifespan of that concrete.
- Abrasion resistance: Some formulations are available that provide greater resistance to abrasion where required.
- Construction scheduling: As an admixture, crystalline waterproofing is added to the concrete at the time of batching and therefore is not subject to climatic restraints. Further, it does not require protection during backfilling or during placement of steel, wire mesh, or other materials. All of this increases the flexibility in time scheduling and helps projects meet or even beat construction deadlines.
Due to this significant list of properties, crystalline concrete has been used successfully in new construction for commercial buildings, industrial settings, institutional facilities (hospitals, schools, higher education, etc.), multifamily housing, and even high-end single-family homes. All have received the waterproofing and other protective benefits of this technology applied during new construction and realized over the full life of the building.
Using Crystalline Technology in Existing Buildings
Water leaks often happen in concrete walls in existing buildings, particularly below grade. Of course, that means, the “positive side” (exterior) of the concrete is likely buried and not readily accessible. Hence, “negative-side” (interior) waterproofing is typically undertaken on the inside face of the concrete. Although water may still penetrate the exterior surface of the concrete, with this approach, it will be prevented from reaching the inside surface without impacting the interior of the building or any spaces/functions/materials found there. Of course, protection against concrete deterioration is not achieved as with positive-side treatment, but water penetration stops at the interior side of the concrete so the inner surface is protected. The degree of protection and the effectiveness of the interior coating will depend on the product used. Some are simply painted applications that may hold up for a while but are not guaranteed for more than a few years.
A crystalline waterproofing system was used on the negative-side interior walls of this below-grade parking structure. A fountain complex is located above this garage, which introduces water into the surrounding subgrade.
Crystalline Renovations
The preferred choice for negative-side waterproofing is to use crystalline products that are applied from the inside. These are provided in powder form, mixed with water on-site, and applied as a cementitious slurry coat to above-or below-grade concrete. The intent is to cover the entire inner wall surface and thus create the conditions for the crystalline chemistry to diffuse into the substrate and create a continuous water seal. It can be a single coat or the first of a two-coat application where recommended by the product manufacturer.
Like any field applied product, surface preparation is obviously critical. The slurry coat can be applied to wet surfaces, but the existing wall needs to be intact and stable enough to receive the coating. In some cases, removing loose or damaged pieces may be necessary followed by appropriate repairs. Providing water plugging or other measures for large holes may also be called for. All of these steps require the judgement of a design professional and the skills of tradespersons to do the needed work.
The application of crystalline coatings on existing buildings yields all of the same characteristics as when installed on new construction, plus some other notable ones as follows:
- Wet or dry application: Crystalline applications do not require a dry surface for installation. This is particularly helpful in conditions where dryness would be difficult or impossible to achieve.
- Simplified preparation: Compared to some other alternatives, there is no costly surface priming or leveling needed prior to the application
- Durability: The finished treatment, when installed properly, is not subject to deterioration from either the inside or outside as other coatings may be. Hence there is typically no need to plan on replacing it after several years.
- Cost: Crystalline treatments on negative-side surfaces are less costly to apply than most other methods, particularly over the remaining life of the building.
Special Building Conditions
In addition to conventional concrete walls, floor slabs, and other structures, crystalline technology has been found to be particularly useful in building conditions that are more specialized or require more detailed attention. This can include the type of conditions described as follows.
Elevator Pits
Out of necessity, elevator pits are often the lowest points of excavation in a building. That means they breach the waterproofing continuity of the surrounding slab and need to be waterproofed in their own right. Exacerbating the issue is that the shape and geometry of typical elevator pits have more joints and variations, all of which usually offer more opportunities for water leakage. That can be a serious problem since equipment and/or materials in the pit need protection from water for smooth operation and long-term durability.
A common practice in elevator pits is to install a sump with a pump in the hope that any water that does find its way in will end up there and be pumped out. Of course, that does not help in a power outage, and even a sump with a cover will allow moisture to permeate up into the pit. A better solution is to use crystalline concrete in the elevator pit to assure a continuous waterproof enclosure. That way, water and moisture never get into the pit to begin with, equipment is protected, and it does not matter if the power is on or not to keep things dry.
Cisterns/Water Storage
A number of buildings may require bulk-water storage either to store water for fire protection or collect and store “grey water” for reuse in the interest of water conservation. An underground storage tank can be installed for this purpose, but sometimes it is more economical and space efficient to locate such a tank in the lowest level of a building and make it out of concrete. Waterproofing is clearly an important requirement in this case, and given all of the characteristics already described, crystalline concrete is an ideal solution for this circumstance. In fact, it has been used quite successfully not only for storing water in buildings but also all manner of infrastructure and water-processing and storage facilities.
Shotcrete Construction
Shotcrete is a technique where concrete is spray applied under pressure onto a substrate with reinforcing in place or another surface. It is most commonly used in heavy construction projects such as tunnels, highways, etc. but has also been used for foundations where lot-line restrictions do not allow excavation or access on both sides for formwork. Waterproofing such an installation is also problematic since adding membranes can be difficult or complicated. Instead, adding crystalline admixture to the shotcrete mix has been shown to be a very cost-effective and reliable way to provide waterproofing.
Conclusion
Crystalline concrete waterproofing has gained much greater acceptance over the past 10 years and is now being used on larger and more prominent projects across the country and internationally. It is worth considering for any project where concrete is being used and waterproofing is needed.
Peter J. Arsenault, FAIA, NCARB, LEED AP, is a nationally known architect, consultant, presenter, and prolific author of more than 200 continuing education courses. www.pjaarch.com, www.linkedin.com/in/pjaarch
