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Data are presented covering the period 1974 to 1976 inclusive as collected by Manitoba Hydro and by R.M. Hardy and Associates Ltd. The former is a public utility and the latter a consulting engineering group. The Mani-toba Hydro results are from a project in Northern Manitoba utilizing CSA Type 10 (ASTM Type 1) portland cements manufactured in both Manitoba and Ontario. Results from the Hardy group were collected on a number of projects in Southern Alberta - principally sidewalk concrete control work in the City of Calgary and a gas plant near Pincher Creek, Alberta. Results from CSA Types 10 and 50 (ASTM Type I and V) portland cements are presented separately. Regression equations are developed and compared with equations prepared from earlier Western Canadian data.

In recent years there has been an increasing acceptance of accelerated strength tests for routine quality control of concrete and to estimate the 28-day compressive strength. However, very little, or no data, are available as to the use of accelerated strength tests for estimating the potential splitting-tensile strength and modulus of rupture of concrete. This study reports results of an investigation to determine the possibility of using the boiling procedure as an accelerated splitting-tension test. A total of twenty-two concrete mixes were made in the laboratory using limestone and natural sand as coarse and fine aggregates respectively. A total of 176 cylinders, 6 x 12 in. (152 x 305 mm) in size, and 44 prisms, 3.5 x 4 x 16 in. (89 x 102 x 466 mm) in size, were tested. The cylinders were tested in splitting-tension after accelerated- and moist-curing, and the prisms were tested in flexure after moist-curing. The correlations between the splitting-tensile strengths of accelerated-cured specimens and those of moist-cured specimens were statistically significant. The average within-batch variation for the splitting-tensile strength of accelerated-cured specimens was 5.1 per cent; the corresponding value for the strength of the 28-day moist-cured specimens was 5.7 per cent. From the analysis of the test results, it is concluded that the accelerated splitting-tensile test appears to be an adequate means for controlling the quality of pavement concrete. Those contemplating the use of the accelerated test for predicting the later-age splitting-tensile and flexural strengths of concrete are cautioned that they should develop their own correlations to allow for the variations in aggregates and cements.

Research conducted in different parts of the world has led to the development of several pmcedues for accelerated stren th tests for concrete. While these procedures most il y relate to prediction of concrete compressive strength, no such work has been reported on flexural strength of concrete, which is essential In rigid pavement design. Studies reported herein attempt to bridge this gap. Among the different promising procedures for accelerated curing, Akroyd's Modified Boiling Water Method was considered to be the most suitable for field jobs like construction of concrete pavement. The studies were conducted with three different types of coarse aggregate and two ordinary portland cements of varying compound composition. The concrete mixes were designed for three different water-cement ratios 0 The findings confirmed that the correlations between the strengths of 7 or 28 days normally cured specimens and those cured under the stipulated accelerated condition were affected by the type of coarse aggregate and characteristics of cement like fineness and compound composition, but not by the quantity of cement present In the concrete mix. I t could be generally concluded that the Modified Boiling Water Method was capable of predicting the 7 or 28 days standard compressive and f lexur al strengths with reasonably good degree of accuracy.

This study evaluates the field worthiness and accuracy of a chemical technique (Kelly/Vail) for determining water and cement contents of fresh concrete. The results are compared directly to mixture proportions of cement and water and to cement contents obtained by a nuclear cement content gauge method. The study also evaluates the accuracy of estimating 28 day compressive strengths by both accelera-ted curing technique and the Kelly/Vail technique. The study proved the Kelly/Vail system to be field worthy, rapid (less than 15 min.) and simple enough to be operated by technicians or inspectors. Kelly/ Vail water and cement contents when used in conjunction with an air content test can estimate the strength potential of fresh concrete. The Kelly/Vail strength estimates are not as accurate as the accelera-ted curing estimates of 28 day compressive strengths, but the Kelly Vail tests are sufficiently accurate to be meaningful and they are significantly more timely - 15 min. versus 24 hours than accelerated strength tests.

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.