Concrete @ your Fingertips

Influence of hydrocarbon with concrete

It has been asked "do hydrocarbons influence concrete degradation".

Hydrocarbons are typically a compound of hydrogen and carbon, such as those which are the chief components of petroleum and natural gas carbon atoms. Awareness of the risk on brownfield sites should be evaluated; the most common will be associated with industrial sites with fuel tanks e.g.

Filling station:   Petrol & Diesel
Garages, Workshops, Oil Storage & Refineries:   Petrol, Diesel & Oils
Timber yards and Wharves:  Creosote, Diesel, Fuel Oil

Brownfield sites often require concrete to be placed in contact with soils contaminated with hydrocarbons. Hydrocarbons can adversely affect the hydration of fresh concrete if intermixed i.e. they retard concrete strength gain. Results from analysis where a concentration of hydrocarbons was introduced into the mix water indicated the potential loss of 25% in strength.  When hydrocarbons are in contact with hardened concrete, generally, there is no degradation as they are not mixed into the fresh concrete.

If there is concern, a protective membrane can be used to protect the concrete from the contaminated soils or by providing a sacrificial layer of concrete. Improving the paste quality by reducing the water/cement ratio is another option.

One placement method that could be considered to be at a higher risk is Contiguous Flight Auger (CFA) piling. The auger cuts through contaminated soil so that when it is retracted, the void formed is filled with concrete. Although full intermixing is unlikely, the surface of the pile may be contaminated.

Foundations cast against soil should have little contamination although this may be dependent on the mass pressure of concrete against the contaminated soil. Concrete that is formed and then backfilled or precast concrete elements are not going to be affected by hydrocarbons.

Reference:

Effects of hydrocarbon contamination on concrete strength – ICE Publishing Geotechnical Engineering 149 Issue 3 – S.A. Wilson, N.J. Langdon & P. J Walden

Actions of mineral oils  - The Chemistry of Cement and Concrete, 4th ed  - F.M Lea, P.338

Acknowledgement: The Concrete Society

Other references:Concrete Society-ITE