USE OF FLY ASH AND DENSE GRADED AGGREGATES TO CONSTRUCT DURABLE CONCRETE PAVEMENTS

摘要

In the regions lying in the upper northern hemisphere concrete highway pavements fail because of poor durability rather than lack of strength. The pavements fail because of excessive range of temperatures, e.g., about -35°Cto 38°C that cause freezing and thawing. Other environmental effects such as moisture / precipitation, and the increased use of deicing chemicals are also responsible for the failure of pavements. It is shown in this paper that using fly ash as a replacement of Portland cement and changing the grading of aggregates produce concrete that is more economical and durable. A total of eight concrete mixes were cast, four of them using aggregates as per current specifications and another four mixes using dense graded aggregates, and fly ash contents of 30, 35, 40, and 45% replacement for Portland cement respectively. All mixes had an air content of 6% and 25 to 37 mm slump for the freshly mixed concrete. In this study various ASTM and AASHTO standard tests such as slump, unit weight and yield of concrete, and air content were conducted on the freshly mixed concrete. Compressive and flexural strength; density, absorption, and air voids; electrical indication of concrete's ability to resist chloride ion penetration; resistance of concrete to rapid freezing and thawing; and microscopical determination of parameters of the air-void system were conducted on the hardened concrete. The beneficial effects of using dense graded aggregates and fly ash is shown on the durability of concrete highway pavements.