عنوان مقاله [English]
Using channels cover to increase the strength of soil walls against permeability, decreasing out wash and other water losses, are the main purposes for improving the water transmitting efficiency. Because the covers are expensive, their application for channels must be taken under great accuracy. Lining by concrete is one of the most common method in water transmission canals. This type of lining/cover has been investigated by many researchers. This study aims to determine the in-situ strength of concrete cover for Qazvin irrigation water transmitting canal. The strength was evaluated by using twist-off method. The method is partially-destructive manner which is fast, cost effective, accurate, simple and applicable for all kinds of horizontal and vertical concrete surfaces. The results of this research show that the covers are 40-year old with in-situ strength of 14-34 MPa. The concrete cover locates under water level and is exposed to wetting and drying, frequent freezing and thawing and permanent corrosion. The concrete cover is also under the sulphide and chloride attacks, strongly. . After twist-off test, The concrete covers with insufficient strength were replaced after twisting-off test.. Hence, the new concrete cover has the ability to resist against physical and chemical damages. To increase the efficiency of transported water, it is recommended that the concrete covers of conveys, to the cement content of designs, the w/c ratio, the aggregate size, the additives (e.g. pozzolan), performing condition and curing, all must be taken in consideration.