Scanning the available literature on creep of concrete, it can be observed that the vast majority of the experimental works on creep have been conducted only on concrete specimens. However, it is believed that in order to enhance the current knowledge of creep mechanism of concrete, a studying of the creep response of its mortar and hydrated cement paste is necessary. In consequence, the present paper describes an experimental program that was performed for investigating the basic creep and creep recovery mechanisms of normal- and high-strength concretes having 28 days compressive strengths of about 400 and 800 kgf/cm2, respectively as well as their individual constituents; that are the mortars and the hydrated cement pastes. In this program, the basic creep tests were conducted on cylindrical sealed specimens ( 10 cm in diameter and 18 cm height) of cement paste, mortar and concrete. In the creep tests, the sustained stress can be applied using prestressing steel bar passing through the centroid of the specimen. The creep sustained stress levels were not exceeding 40 percent of the ultimate compressive strength existing at the time of load application and were maintained for about one month, with creep recovery observed for a period of 7 days. All basic creep measurements were performed in a temperature controlled room maintained at a temperature of about 20± 2 oC. The test conditions included ages at loading of 3,7,14 and 28 days. From the obtained results, the contributions of mortar and cement paste on the basic creep of normal- and high-strength concretes were evaluated. Furthermore, based on the data of the present experimental work the simple formula of the double power law was developed in order to predict the basic creep of concrete from the basic creep of its hydrated cement paste. In the proposed formula, the aggregate content as well as its mechanical properties were taken into account. Finally, the proposed formula was tested on creep results and was found to be accurate enough to model the basic creep of normal- and high-strength concretes over time. |
