Oil spills and leaks are frequently occurrences in Civil Engineering projects, particularly in structures that have to deal with storage, transportation, and processing of oil products. Oil contamination could occur as a result of a car accident, oil-containing equipment failure, or deliberate actions from others. This paper will analyze the effects of oil contamination on concrete, outline the tools for a forensic investigation of the material, and provide several repair and remediation methods.
Effects of Oil Contamination on Concrete
Different research vary in their accounts of how much oil contamination affects a concrete element. Błaszczyński (1996) states that the effects of crude oil and its products are classified by the majority of the sources available as either non-harmful or mildly-harmful. Diab (2011) disagrees, saying that the oil spillage underneath machineries is the primary reason for the deterioration of reinforced concrete platforms. The accounts on the precise effects of oil spilled onto concrete platforms or contaminating the mix during production vary: some researchers found that in some cases the effects can be even beneficial – oil-contaminated concrete can be more resistant to freezing and thawing effects (Diab, 2011). At the same time, contamination of the mix with 5% or more oil makes concrete lose up to 50% of its compressive strength (Diab, 2011). Błaszczyński’s (1996) account of the long-term effects of oil contamination on the durability of concrete states that, in general, an oil-contaminated concrete behaves like a new material, with reduced stress-strain parameters.
Forensic Investigation of Contaminated Concrete Elements
Visual examination of concrete may reveal places of contamination due to the fact that most oils tend to get into the pores of the material and are increasingly hard to be removed (Francois et al., 2017). This method, however, will not completely examine the extent of damage beside the fact that oil contamination had already occurred. There are several methods for inspecting the oil contamination based on the age of the element. If the contamination happens during the construction of the concrete element obtaining a sample cube during construction, which is normally done to control the compressive strength of the material. If there has been a contamination of the mix with oil, compressive strength be reduced.
For structures that have already been built and become contaminated, the standard procedure involves the drilling and extracting of concrete cores to use for testing (Francois et al., 2017). This destructive method is used to show the depth of corrosion and its effects on concrete strength. A non-destructive evaluation method that could be used on-site is the Ultrasonic Pulse Velocity (UPV) method, which can detect various damages in a structural component (Francois et al., 2017). Since oil penetration may result in compressive strength reduction, the concrete element becomes more susceptible to damage. However, it does not provide exact compressive strength parameters and can be affected by rebar, voids, and cracks.
Repair and Remediation Methods
Repair and remediation methods depend on the depth of the contamination and the length of exposure. The standard protocol for spillage contaminations includes cleaning and sealing the contaminated elements to prevent floor failures (Francois et al., 2017). Chemical solutions are used on the mechanically-prepared concrete surfaces and cleaned under high pressure and temperature. This is done to bind the hydrocarbons with water and remove them with vacuum suction. In the cases where contamination has gone too deep, an entire surface layer may have to be removed (Francois et al., 2017). Should the contamination had happened during the creation of the mix, it may be the grounds for removal and replacement of the entire structure.
Conclusions
Though oil spillage was considered harmless to concrete before, new evidence shows detrimental effects of oil contamination on hard concrete and concrete mixes. When introduced to a concrete mix results in a concrete mix reduction. In some instances, the addition of oil may improve resistance to freezing and thawing. Test methods include visual examination, sample cube tests, concrete core examination, and the UPV method. Restoration methods include chemical cleaning under high temperature and pressure or full replacement of the contaminated area.
References
Błaszczyński, T. Z. (1996). Concrete in contact with crude oil products. Statyba, 2(6), 13-17.
Diab, H. (2011). Effect of mineral oil on reinforced concrete structures Part I. Deterioration of compressive strength. JES. Journal of Engineering Sciences, 39(6), 1321-1333.
François, R., Laurens, S., & Deby, F. (2018). Corrosion and its consequences for reinforced concrete structures. Elsevier.