Traditional asphalt and concrete pavements generally suffer from severe rutting and cracking due to heavy loading and hot and dry weather which prevail in most of the Middle East countries, so that the roller-compacted concrete pavements (RCCPs) frequently is used as a substitute. It was found that RCCP mechanical properties depend on fine content considerably. A comprehensive laboratory investigation was carried out to evaluate the workability, strength and durability properties of roller compacted concrete pavements (RCCP) containing high-volume and low-volume non-plastic aggregates Fractions Finer Than 75 µm (FFT75). Firstly concrete mixtures were made with 0%, 5%, 7.5%, 10%, 18% and 25% non-plastic Natural Filler (NF) in order to determine an optimum percent of usage, then concrete mixtures were made with 2.5%, 7.5%, 10% and 15% non-plastic finer than sieve #200, in order to examine the possibility of using unwashed aggregate. Also, in this paper the image analysis was performed on FFT75 to investigate the relation between these very fine materials, rheological and mechanical properties of RCCP. Material <75 µm was analyzed using a scanning optical microscope. In addition the variables affecting the mix proportion of RCCP such as cement content, and the effect of Super Plasticizer (SP) have been evaluated and discussed. Results showed that it is feasible to use unwashed aggregates in RCCP mixes but a few limitations should be carefully considered. Also natural filler caused to improve the mechanical properties of RCC. In sequence, one of the major findings was that the main factor that controlled most of hardened properties is achieving sufficient compaction and unlike conventional concrete increasing cement content may not result in strength increase. Based on the results obtained, the optimum aggregates proportion and W/C ratio have been found in order to make RCC for pavement applications that meet all specified limits in the ACI 325.10 state-of-the-art report and ACI 211.3R-97. The image analysis results justified that FFT75 materials have considerable characters that affect the fresh and harden concrete properties. Finally the optimum percentage of Superplasticizer was determined and because of its effects on the workability and strength properties it can be used in mixtures with unwashed aggregates to solve their mechanical problems.
Abstract