عنوان مقاله [English]
High quality precast hydraulic dry concrete curbs may affect the properties of concrete materials consisting of aggregates, cement, water-cement ratio, production method, technical principles during construction, production, and environmental conditions. To achieve high-quality pre-cast pressed concrete curbs, this study investigate various cement types, quantity of cement as well as water to cement ratio, which have not been studied before.Usually, the hydraulic pressing is based on a six-mould hydraulic press, with up to 400 ton of pressing force. This process consists of filling a mould with a wet mix concrete, and then applying excessive water pressure nest is then expelled and compaction is complete. Moreover, immediately after pressing, curb is strong enough to be handled and is removed from the press, and then stacked near the machine within a dry atmosphere of the building for an overnight curing.The present study investigates freeze-thaw resistance of dry concrete curb. For this purpose, 27 concrete mixes are designed and casted by dry pressing method for concrete curb that is uses low water- to- cement ratios. Mixes were constructed by different cement strength grades (352-2, 425-1, and 525-1 based on which the 28-day strength of cement mortar in $Kg/cm^2$ for water to cement ratio is 0.485.), cement quantity, various water to cement ratios, and cement to fine aggregate ratios.The results show that the types of cement can significantly affect compressive
strength, flexural strength, and durability of dry pressed concrete curb. In all cycles of freezing and thawing of specimens, compressive strength is shown to be lower with constant water to cement ratio, and with the increase of the amount of cement, the flexible strength increases. The mix design of row 25 with cement strength grade 525, cement quantity of 400, and water to cement ratio of 0.27 is the most optimal mix design selection.