When building any concrete structure, mitigating water ingress through the concrete is a critical factor in the overall integrity of the project.
The most common mechanisms that deteriorate concrete all involve water. Water can be directly harmful if the concrete becomes saturated, especially if the water freezes. The freezing water expands causing internal pressure, leading to cracks and scaling that leaves the concrete even more vulnerable to the ingress of water and chemicals. Water can also act as a carrier of harmful chemicals such as chlorides that corrode steel reinforcement, leading to internal stress and cracking. Once the integrity of the concrete is compromised, corrosion can spread quickly and undetected throughout the core of the structure.
As concrete technology advances to mitigate these destructive mechanisms, Permeability Reducing Admixtures (PRAs), are increasingly being used to provide an additional level of protection from within. PRAs are chemical admixtures used to protect concrete from the damaging effects of water and water borne chemicals. These particular admixture types are distinct tools for making durable concrete and with proper selection and use, PRAs (often referred to as “integral systems”) have been used to replace surface-applied sealers, water repellents and membranes.
PRAs provide integral protection against water and chemicals throughout the full depth of a concrete element, and can eliminate the labor needed to apply surface protective systems. Further to these advantages, PRAs are not prone to damage such as punctures and abrasions, and are easier and faster to install overall.
The selection of an appropriate PRA depends on the service conditions, and how water is expected to enter the concrete. A document from The American Concrete lnstitute (ACI), ACI 212.3R-10 Report on Chemical Admixtures for Concrete, subdivides PRAs into two categories based their performance properties:
Altogether, PRAs bring many short and long term benefits to concrete construction. These include cost efficiency and time savings during construction, while also providing quality, lasting protection against water damage, resulting in more durable structures.
By Jeff Bowman, B.Sc., Kryton International Inc. Photos courtesy Kryton International Inc.
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A comprehensive new educational document has been published by ACI. ACI’s Educational Bulletin, E4-12 – Chemical Admixtures, describes the basic types and uses of these admixtures, and works as a valuable introduction to this complex topic. E4-12 is a free resource and can be found on ACI’s website www.concrete.org
Source: concrete homes + low-rise construction (p. 28)
