Abstract
The modulus of elasticity (E) is an important property of concrete that needs to be quantified when designing complex structures. The methods to best quantify this property are empirical within the laboratory, but outside the laboratory, designers may depend on estimation models. There exists numerous estimation models at the designer’s disposal but the accuracy and reliability of those models have not been comprehensively and comparatively assessed.
The actual E values of 108 specimens, whose properties differed in aggregate type, cement type, concrete strength and curing age, were measured. The actual E values were compared to the predictions made by 23 estimation models. The accuracy of each model was analysed statistically to conclusively determine which of the models was most accurate.
The Noguchi et al (2009) model was found to be the most accurate and consistently so, rendering an overall coefficient of variation of 15.94%. The CEB-FIP (1970) model was found to be the least accurate, resulting with an overall coefficient of variation of 31.81%.
In addition to the primary objective, this study included the analysis of the degree of influence of aggregate percentage content, compressive strength, curing age and concrete density on the actual elastic modulus of concrete. The concrete’s density was found to be a major factor in the resulting E of concrete as the statistics had shown that the correlation was highly significant (P = 2.39 x 10-7 %). Concrete strength on the other hand, a factor that most models use as a primary basis for their estimations, was not as influential as assumed. In fact, the statistical results showed the correlation to have a level of significance of 11.1 %. It was therefore highly recommended that E estimation models should, at least, include the density of concrete as a common parameter more than the inclusion of concrete strength.
Separate to the topic of concrete E, this research also assessed the average strength relationship between concrete cylinders and concrete cubes. The average cylinder-cube strength relationship slightly increases with the increase in curing age indicated by a correlation coefficient of 0.998. The strength of the cylinders were found to be, on average, approximately 85 % of the cube strengths.
M.Tech. (Civil Engineering)