Author: Lorella Angelini, Angelini Consulting Services, LLC
There are many ways to design concrete mixes. Different types of ingredients and dosages can be used in various combinations so as to respond to construction and specification requirements. However all concrete mixes share one basic, common denominator: they should not develop cracks, even under stress conditions.
Not only are cracks aesthetically unpleasant, they are also very detrimental since they provide a way of entry for contaminants, such as chlorides and sulphates, into concrete. Once it penetrates into the cracks, water alone can cause concrete spalling by freeze-thaw cycles.
Between the technologies for permanently sealing cracks in concrete, epoxy resins are widely used, especially for structural cracks. Epoxies have great adhesion to concrete, high compressive and tensile strength, volume stability, and are available in a variety of formulations for different types of applications. For example, wall cracks can be sealed by injecting epoxies at low or high pressure, preferably moving from the bottom to the top of the wall. Other types of epoxies with low or ultra-low viscosity can be used to seal cracks in concrete decks or pavements. In this case the material is fed into the cracks by gravity. This application method is also used with HMWM (High Molecular Weight Methacrylate) or MMA (Methyl Methacrylate) resins that have a level of viscosity so low that can be compared to water.
In the future these proven technologies may have to confront with a new, experimental method to seal concrete cracks that is based on the use of natural bacteria. By introducing bacteria into concrete cracks, simply using a garden sprayer, long, thin cracks can be sealed in a relatively short time with the limestone compound produced by the bacteria, when these organisms come in contact with water. More information about the sealing mechanism is reported in the links. The Netherlands and the UK appear to be on the leading edge of this exciting development program.
Epoxy injection:
http://www.concretenetwork.com/concrete/crack_injection/basicsteps.html
http://www.concreteconstruction.net/repair/epoxy-injection-for-cracked-concrete_o.aspx
https://www.concrete.org/store/productdetail.aspx?ItemID=503707&Format=DOWNLOAD
Gravity fed epoxies:
http://docslide.us/documents/crack-repair-by-gravity-feed-with-resin.html
Gravity-fed MMA:
http://trrjournalonline.trb.org/doi/10.3141/2202-10
Bacteria-healed cracks: