مقاله انگلیسی رایگان در مورد ارزیابی تاثیر نانو سیلیکا در ساختار خاکستر بادی بتن غلطکی – الزویر 2018

The construction industry has been advancing since the development of RCC causing a significant change in the method of placement, compaction and consolidation of mass concrete which was a slower process for the traditional or conventional concrete method (Mehta and Monteiro 2006). Roller compacted concrete is an extremely dry mix concrete of zero slump consistency in its fresh state, that is conveyed, placed and compacted using rock fill and earth equipment similar to those used for pavement construction (ACI 207.5R-11 2011). The durability, strength development and rate of hydration of RCC mix depend on the selection of constituent materials. Type I (ordinary Portland cement) and Type II (moderate sulfate resistance cement) are more economically used in RCC due to its lower heat of hydration and longer setting times. Pozzolan such as fly ash or slag are commonly used as supplementary cementitious materials and mineral fillers in RCC; they provide a degree of lubrication during placing and fill the voids between aggregates and paste. Class F fly ash improves workability, increases placement time, and may be used to replace up to 50 % by volume in RCC (Fuhrman 2000). However use of fly ash delay setting times in concrete, reduces early strength development, reduces durability at an early age and reduces the resistance to freezing and thawing (Huang, Lin et al. 2013). In order to utilize the advantages of using fly ash in concrete, it should either be used when an early strength development is not required, or where early setting times is to be avoided such as in roller compacted concrete, where delay in setting time is needed to allow for placing and proper compaction of the concrete. A concrete containing 50% or more fly ash by weight of cement is regarded as a high volume fly ash concrete (Mehta and Monteiro 2006). In order to use fly ash efficiently in RCC, one of the ways of solving the problems associated with fly ash is introducing Nanomaterials such as Nano silica to the concrete containing fly ash (Singh, Karade et al. 2013). The nondestructive testing (NDT) method can be used to evaluate the strength and quality of RCC pavement. The American Society for Nondestructive Testing (NDT) defines nondestructive evaluation as examining an object with technology that does not cause any harm to the object’s future function (Shull 2016). To assess the compressive strength of concrete structures, the most commonly used NDT methods are ultrasonic pulse velocity (UPV) and rebound hammer (RH) test (Al-Mufti and Fried 2012). In RH test, the surface hardness is measured in terms of rebound number (RN) using the Schmidt hammer. It consists of a spring-loaded steel hammer mass which slides along the bar, when released it strikes and makes and makes an impact with the help of a steel plunger on the concrete surface. After impact, the mass rebounds back from the steel plunger.