h. r. darvishvand

One of the current approaches for concrete retrofitting is called fiber reinforced polymer (FRP) wrapping. In this study, concrete retrofitting means compressive strength and seismic parameters improvement (such as failure strain, energy absorption, and ductility). Cost analysis may raise issues of concern regarding the economic value of this kind of retrofitting and for this reason, economic analysis was conducted based on experimental works. In this regard, 21 samples were prepared for three compressive strengths of concrete (20, 35, and 50MPa) and warped with different layers of carbon and glass fiber reinforced polymers (0, 1, 3, and 5 layers). Samples were subjected to stress-strain tests and concrete properties were estimated. The results showed that carbon and glass fibers, respectively, are more effective in improving the compressive strength and seismic parameters of concrete. But, the economic analysis indicated that glass fiber is more cost-benefit than carbon fiber in improving the concrete properties, especially for one layer of FRP. The economic analysis was not able to specify the application of FRP for which concrete samples are more economical, and for this reason, statistical analysis was used to respond to this vague and achieve a comprehensive assessment. The analysis indicated that the use of FRP is more cost-benefit for lower concrete strength.

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 9.5, 12.5, 19 and 25 mm for water to cement ratio were 0.35, 0.42, 0.54 and 0.76. In this investigation, the total of 32 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.