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Concrete Durability – A Waterproofing Admixtures Technology Update

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:

• PRAN  (Permeability  Reducing  Admixture   for   Non-Hydrostatic Conditions) admixtures are intended for applications that  are not subject to hydrostatic water pressure and are sometimes called damproofing admixtures. Most PRANs’ contain  water repellant chemicals that shed water and reduce water absorption into the concrete.
• PRAH  (Permeability  Reducing  Admixture  for  Hydro­ static Conditions) are primarily intended for use in concrete that  is exposed to water under  pressure and  are sometimes called waterproofing admixtures. They are able to withstand the high hydrostatic pressure for applications such as base­ments, tunnels and water containment structures.

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)