Investigating the Properties of Base Layer Containing Recycled Portland cement And Asphalt Concrete

Enormous amounts of waste materials generated from the demolition of buildings and pavements have created problems for the environment. In this research, various percentages of base material made of natural aggregate have been replaced with recycled concrete and asphalt that has been crushed and graded, and some physical and engineering properties have been studied. Physical properties such as density and water absorption, cleanliness, hardness and resistance to abrasion and performance properties including compaction characteristics, load-bearing capacity (CBR) and hydraulic conductivity have been evaluated. The results show that, in terms of the criteria specified in specifications for base materials, the mixtures containing recycled aggregates are weaker; however, but most of them satisfy the requirements of specification to be used as highway pavement base layer. In terms of load-bearing capacity defined by CBR, all the mixtures containing recycled concrete aggregates satisfy the minimum requirement of 80% for CBR, but some of the mixtures containing recycled asphalt concrete aggregate do not satisfy the CBR requirement. The results of permeability test show that the permeability increases with increasing recycled asphalt replacement, and decreases with increasing recycled concrete replacement. In addition, highest increase of permeability is obtained by replacing the fine fraction of natural aggregate with recycled asphalt, and the lowest permeability is obtained by replacing the fine fraction of natural aggregate with recycled concrete aggregate (11 times lower than the control mixture). Crease in permeability (an increase of about 5 times) and fine-grained concrete placement caused the largest decrease in permeability.