Title: Accelerated Strength Test Results from Expanded Polystyrene Molds with Emphasis on Initial Concrete Temperature
Author(s): Andre Bisaillon
Publication: Symposium Paper
Appears on pages(s): 201-228
Keywords: accelerated tests; compressive strength; concretes; cylin-ders;
polystyrene; portland cement type 1; quality control; regression
An accelerated-curing method to predict the 28-day strength of concrete, from 2-day self-cured test results was evaluated in the field. All concrete samples were collected at the job-site as a part of normal field control work. The method consists of casting and curing the concrete in expanded polystyrene molds which accelerates the rate of strength gain at early age and of testing the cylinders at 48 hours (24 hours). A total of 37 different mixes and 18,908 cylinders test results from four suppliers using different brands and types of cements and admixtures were studied. Particular attention was given to the influence of initial concrete temperature on thestrength prediction. Under the conditions prevailing during this study, the evaluation of the field test results indicate that with Type I cement, a) the 28-day strength can be predicted with a high degree of confidence, from the 2-day self-cured accelerated concrete strength test, when the relationship has been established with several cement factors or strength levels; ` within standard temperature placing limits of concrete 50 to 9OoF (10 to 32oC), the predicted results are consis-tent with the behaviour of concrete under those conditions; c) the addition of initial concrete temperature as a variable allows a better estimate of the 28-day strength although the improvement is not very significant from a quality control stand point. With Type II cement, prelim-inary test results obtained indicate that the strength prediction is not suitable without modification of the present method. Further studies are required for low heat cements.