Reinforced concrete, of itself, is a durable and stable construction combination. However, there are environmental elements which very often prematurely age concrete structures, and contribute to corrosion of the reinforcing steel.
Contamination is carried by moisture
These elements typically invade the concrete via its porosity network or ‘matrix’. Contaminants such as carbon dioxide, sulphates and chlorides penetrate into the concrete, setting up conditions for deterioration and premature ageing. Logically, the more porous or permeable the concrete, the higher the rate at which contaminants can penetrate. Conversely, less porous concrete – i.e. more impermeable – will be less receptive to contaminant ingress.
“The permeability of the concrete … has of course a major influence on the rate of chloride penetration.” – Kyosti Tuutti 1
Strength and Durability
Of course, the concrete industry is well aware of the connection between concrete strength and concrete durability. Generally, higher-strength concrete decreases the permeability as well as increasing the compressive strength. It will, however, still let moisture into the concrete matrix over time. To help offset this the use of fly ash and other admixtures is helpful. A hydrogel additive, as part of the mix design, creates an impermeable concrete, thereby extending the life of new structures. This approach provides for much higher and certain durability.
“In order to increase concrete durability, we use higher density concrete mix to reduce permeability and therefore the risk of corrosion of the reinforcement.” – Alexis Borderon 2
How to help existing structures?
In the case of existing concrete, it is greatly beneficial to improve the concrete’s impermeability wherever possible, to help extend the structure’s service life. This is especially urgent if the concrete is already showing signs of early ageing – microcracks or surface deterioration. Increasing the impermeability of existing concrete will significantly improve the remaining length of its service life.
It is possible to apply a catalytic penetrating hydrogel treatment to existing concrete, which penetrates into the porosity, utilizing the free limes and internal moisture, sealing the matrix against the ingress of further contaminants. The concrete is effectively sealed and densified, so that it becomes a solid-state, and the rebar zone is protected. By doing this, the durability of the structure will be significantly improved.
This is assuming, of course, that the structure is not already showing major signs of deterioration. Specific issues such as exposed reinforcing steel, major spalling and so on, must be assessed and remediated according to industry standards.
If you are responsible for the maintenance of an existing concrete structure, talk to Markham about options for extending its service life.
The friendly Markham team is familiar with a broad spectrum of structure types and can tailor a customized approach based on your specific needs and structural environment. Why not get in touch today?
1 “Assessment of Service Life for Concrete Structures”, Kyosti Tuutti (Lund University, 1997)
2 “Crack Depth vs Concrete Cover”, Alexis Borderon (American Concrete Institute – LinkedIn Group Discussion, 2014)