S.A Haj Seiyed Taghia - Department of civil Engineering, Qazvin Branch, Islamic Azad University, Qazvin, Iran
H.R. Darvishvand - Department of civil Engineering, Qazvin Branch, Islamic Azad University, Qazvin, Iran
M. Ebrahimi - Engineering Technology Department, South Carolina State University, SC, USA

Three parameters, size, shape of aggregate, and water to cement ratio, play important role on concrete behavior. To study the effect of these parameters, two types of aggregates were used, rounded (river) and sharped corners (broken). The maximum sizes of aggregates were chosen to be ۹.۵, ۱۲.۵, ۱۹ and ۲۵ mm for water to cement ratio were ۰.۳۵, ۰.۴۲, ۰.۵۴ and ۰.۷۶. In this investigation, the total of ۳۲ mixed designs were made. The stress-strain tests were performed on the entire samples, and the results were compared with the Popovics model. To further evaluate the analysis, three criteria, correlation coefficient, variation coefficient, and percentage of change in energy absorption were demonstarted. Analysis showed that there is significant differences between the Popovics model and our experimental results. The Modified Popovics model was introduced for better understanding the concrete behavior in compression. The proposed model covered a wide range of the parameters concerned in this investigation. The Modified Popovics model was comapred with several models such as the Popovics, Hognestad, Thorenfeldt, and Tsai and the results showed that modified approach has a better clarification for behavior of concrete in compression. Moreover, the results indicated that these models were more accurate for prediction of concrete behavior with rounded aggregates in comparison to sharped aggregates.

Aggregate, water to cement ratio, Stress-Strain Test, Correlation coefficient, Variation Coefficient, Percentage of Change in Energy Absorption