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Phenols are common contaminants of brownfield sites where coal carbonation (manufacture of town gas, coking plants and tar works) occurred. Phenol (C6H5OH) is reported to be detrimental to strength development of concrete.
A BRE study (see reference below) concluded that a small reduction in strength development could occur at concentrations of 0.1% (1000mg/l) compared to a control but this reduction may be accounted for within the normal variations of concrete strength. Higher concentrations of phenol showed a clear pattern of reduced strength development over the 2 year test period. For instance in comparison to specimens cured in tap water, specimens cured in 0.2% and 2.5% phenol solutions showed a strength development of only 87% and 81% respectively at 2 years.
Concentrations normally encountered on site are up to 2000mg/l. Soil samples from gasworks were found to be around 100 mg/l, although some as high as 500mg/l, and a coking plant of a steel works up to 1400mg/l.
The test programme was limited to a concrete of Portland cement content of 310kg/m3 with a w/c ratio of 0.6.
Acknowledgement: Concrete Society
Other references:M A Smith, The effect of phenol on concrete, Magazine of Concrete Research, Vol. 37, No. 133, Dec 1985