Concrete, the world’s most widely used building material, is inexpensive, readily available, versatile, and strong. However, it is also a hard sponge and vulnerable to water penetration. Water and dissolved materials (such as chlorides and sulfates) are absorbed into concrete through capillary absorption, resulting in concrete degradation, rusting of steel reinforcement, water infiltration into interior spaces, and increased interior humidity levels. Water can damage sensitive interior spaces and installed flooring systems, and result in costly and disruptive maintenance and repairs, and even litigation. As such, solutions are required to protect concrete and concrete structures.
Architects, engineers, and builders around the world are increasingly turning to hydrophobic admixtures to help solve these challenges when building with concrete. Hydrophobic admixtures are used to enhance concrete durability (including protecting steel rebar from corrosion), minimize concrete maintenance requirements, waterproof structures, and protect flooring from moisture vapor-related failure. In the process, owners and builders save time and money with reduced risk in both design and construction.
CONCRETE DEGRADATION
Moisture migration into concrete is the leading cause of concrete degradation worldwide. Most degradation processes encountered by concrete require water, dissolved chemicals, and the presence of oxygen. Dissolved salts (chlorides) or other deleterious chemicals (i.e., sulfates) can be rapidly transported to the steel reinforcement imbedded in the concrete through the capillary network. The resulting initiation of corrosion causes rebar to expand, breaking up the concrete it is embedded in. Additionally, in cases where water has permeated through a concrete substrate, it may damage building interiors. In each case, the presence of water is detrimental.
There are two primary water transport mechanisms in concrete: capillary absorption (or sorptivity) and permeability.
Capillary absorption: As mix water required for concrete placement leaves concrete, it leaves behind a porous capillary structure. Capillary absorption is the movement of water through the small pores in concrete in the absence of an externally applied hydraulic head, and is the result of surface interactions between the water and the pore wall. Capillary absorption is the primary transport mechanism for water in concrete structures. Capillary absorption is so powerful and rapid that it requires no pressure to function and creates far more damage potential than any of the other transport mechanisms. In often repeated studies and experiments, even extremely dense concrete mixes with high compressive strengths, low water cement ratios, and excellent pressure permeability readings rapidly transport water through capillary absorption. To ensure durable concrete it is absolutely essential to adequately address capillary absorption as the designer’s primary duty.
Permeability: Permeability is the movement of water due to a pressure gradient, such as when concrete is under hydrostatic pressure. Performance under hydrostatic pressure is a simple function of concrete density, or cementitious content. Concrete’s naturally dense matrix, (of even moderate quality mixes) provides an extremely difficult environment to push water through even under high pressure. The water pressure gradient encountered by a concrete structure is rapidly diminished by the resistance created by its relatively dense matrix. Concrete neutralizes the pressure gradient within the concrete very quickly and then capillary action once again becomes the primary transport mechanism and moves the water further into the structure.
THE TECHNOLOGY
Hydrophobic admixtures react with metallic ions including calcium in cement to form polymers that repel water. When added to concrete, these polymer formations throughout the concrete matrix block water ingress and reduce moisture vapor transport. Capillary transport is effectively shut down and water and chlorides are not able to reach steel reinforcement. In addition, some hydrophobic admixtures react with the steel itself during concrete mixing, creating a passivating layer of protection on the surface of steel rebar.
Hydrophobic admixtures have also been shown to protect concrete against sulfate degradation by reducing sulfate penetration and resulting concrete expansion. In water- or wastewater-treatment applications, or in environments with sulfate-rich soils, sulfates can lead to rapid concrete failure.
Hydrophobic admixtures may be liquid or powder-based solutions, and are typically mixed directly into concrete mixes. Hydrophobic admixtures generally do not negatively impact other concrete properties. However, it is important to check with your chosen provider of hydrophobic admixtures to ensure that the admixtures can meet your specific concrete design requirements.
HYDROPHOBIC ADMIXTURES
Hydrophobic admixtures are used in a broad range of applications and building types throughout the world. Here are a few examples of uses.
Maximizing concrete durability: As water and dissolved salts reach steel reinforcement, corrosion begins, ultimately resulting in cracking of the surrounding concrete and concrete failure. Some hydrophobic admixtures have been shown to inhibit corrosion and enhance the life of concrete. Using integral admixtures in the concrete can also eliminate the need to use topical coatings, which often need to be reapplied periodically to protect the concrete surface.
Waterproofing, membrane-replacement: Leaks in concrete structures can result in damaged interiors and equipment, costly downtime, and litigation. Warranted waterproofing solutions, which may include a service component offered by the hydrophobic admixture supplier, provide peace of mind that water will not jeopardize your project and can save money.
Protecting flooring from moisture: Moisture trapped between concrete subfloors and flooring is causing widespread problems in the healthcare, education, and office industries. As moisture vapor becomes trapped, either after moving through the concrete slab or after being absorbed from the top surface of the slab. Hydrophobic admixtures reduce moisture vapor transmission through the concrete slab and reduce absorption of water introduced to the top of the slab in the form of liquid water or humidity. By protecting the slab itself, and inspecting joints and penetrations in the slab as well as the installation of the vapor barrier, hydrophobic solution providers are able to offer a performance warranty against moisture-related flooring failure. ■
For More Information:
Hycrete, Inc. is the leading provider of hydrophobic admixtures for concrete waterproofing and corrosion protection. For more information, visit www.hycrete.com.
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Modern Contractor Solutions, October 2013
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