The 28 day strength of concrete cylinders cured under standard laboratory conditions can now be reliably predicted at early ages by use of (a) the Modified Boiling Test or (b) the Autogenous Curing Test. The availability of early strength indicators for concrete can be used to great advantage during construction provided these strengths can be related to the strength of the structural elements.To permit an estimate to be made of the strength of in-place concrete on structures appurtenant to the Welland Channel By-pass, the temperature rise of the structural elements was monitored with an automatic 16 point recording potentiometer. The time temperature curve of the in-place concrete was compared to that of 6 in. by 12 in. (150 mm by 300 mm) concrete cylinders taken during casting of the structure and cured autogenously for 48 h, thus permitting an estimate of the in-place concrete strength to be made from the results of the 48 h autogenous strengths.On the basis of the in-place concrete strength estimates, decisions were made regarding the application of post tensioning forces and/or the removal of formwork and supporting shoring.