مقاله انگلیسی رایگان در مورد خواص مکانیکی بتن بازیافتی با مصالح آجر خاک رسی – الزویر 2018

Concrete, owing to its availability, easy preparation and fabrication, is the most popular construction material. Today, concrete is the second most used material after water, with nearly three tonnes used annually for each person on earth. Due to the vast amount of concrete being produced and the huge amount of demolition waste from old concrete structures, the reuse of concrete waste by the construction industry is becoming increasingly important. This is motivated not only by the environmental protection, but also by the conservation of natural aggregate resources, the shortage of waste disposal land, and the increasing cost of waste treatment prior to disposal. In Chinait is estimated that there are approximately 15.5 million tonnes of construction waste produced annually [1], the majority of which is the concrete and bricks. Research work on the use of recycled materials is mainly focussed on the use of recycled concrete aggregate (RCA) and its influence on the properties of the fresh and hardened recycled concrete [2- 11]. RCA is different from virgin aggregate only due to the adhered old cement and/or mortar that is attached to the natural aggregate present at the core. The volume fraction of adhered mortar in a RCA decreases with the increase in the nominal size of RCA [12]. It was reported that for RCA with sizes of 4–8 mm, 8–16 mm and 16–32 mm, the volume fraction of mortar is about 60%, 40% and 35%, respectively [13]. Although it has been a long history to use RCA as granular material in pavement design, extensive research on the performance of RCA in structural applications is only very recent [14]. The use of RCA in high performance concrete has not been widely accepted, primarily due to the reduction in both mechanical and durability properties found in recycled aggregate concretes [15]. The statistical analysis showed that RCA derived from crushed concrete consists of 65-80 vol.% of natural coarse and fine aggregates and 20-35 vol.% of old cement paste [16]. It was reported that the mortar in RCA contributes to a lowered relative density and higher water absorption than virgin aggregate [17-19]. The higher portion of attached mortar and weaker interface between aggregate and mortar in RCA lead to lower concrete quality such as low compressive strength and poor durability. It was also reported that the use of RCA leads concrete to have higher shrinkage and creep strains [20]. It was suggested that a good RCA should meet certain criteria in order to be suitable for use in reinforced concrete [21]. These include an aggregate relative density of 2.3 or higher, a maximum mortar content of 50%, and a maximum water absorption of 3%. Some practice codes restrict the use of RCA with water absorption capacity greater than 7-10% to be used in structural concrete.