Study was recently conducted at Kingston University to assess the suitability of using recycled concrete aggregate (RCA) and reclaimed asphalt pavement (RAP) in unbound subbase mixtures. The results showed that the use of 100% recycled aggregates increased the optimum moisture content and decreased the maximum dry density of the subbase materials in comparison with natural aggregates. Moreover, the replacement of RCA by reclaimed asphalt pavement by 50% decreased the optimum moisture content and increased the maximum dry density in proportion to 100% RCA. The effects of physical properties on 0% air void and compaction curve were discussed for each type of subbase. The CBR values of the subbase materials prepared with 100%RCA is lower than subbase mixture with 100% natural aggregates. The CBR further decreased for replaced subbase with RAP so that 50%RCA+50%RAP is not suitable for unbound subbase from the point of CBR view. In each mix the trend of CBR value was investigated in terms of water content. This research found some significant practical points to use in site works. Reference to this paper should be made as follows: Ayan, V.; Limbachiya, M. C.; Omer, J. R.; Azadani, S. M. N. 2014. Compaction assessment of recycled aggregates for use in unbound subbase application, Journal of Civil Engineering and Management 20(2): 169-174. http://dx.

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Water absorption and frost heaving of aggregates have a strong influence on the performance of a highway pavement. This is because several mechanical properties of aggregates change in direct response to water ingress and ground freezing. Recycled aggregates of different types are increasingly being used in pavements; however, their frost heaving and water absorption potential has not been fully investigated and documented. In the present study the opportunity was taken to study the water absorption and freeze–thaw properties of three different aggregates: (i) 100% recycled concrete aggregate, (ii) 100% natural aggregate from limestone rock, and (iii) 50% recycled concrete aggregate + 50% reclaimed asphalt pavement. For different particle size ranges, extensive tests were carried out for each of the above materials ((i)–(iii)) using the pyknometer and wire basket methods as well as simulation in a self-refrigerated unit. The following three kinds of density were measured: (a) over-dry, (b) saturated and surface dry, and (c) apparent particle density. The 100% natural aggregate had the lowest water absorption and highest densities ((a)–(c)) whereas the 100% recycled concrete aggregate had the highest water absorption. In contrast to the above findings, the frost heave potential was found to be much less sensitive to the aggregate type and particle size. Water absorption of recycled concrete aggregate decreased with increasing mean particle size. The measured relationships between density, grading and water absorption led to increased understanding of the behaviour of materials containing different fractions of recycled concrete aggregate and reclaimed asphalt pavement.

Water absorption properties of recycled materials play an important role in pavement performance. The performance of aggregates changes after absorbing water, then it affects highways layers such as base, subbase, capping. This is why these materials must comply requirements of codes and standards. With regard to the increasing trend of application of recycled aggregates in highways layers, this issue needs more investigation. This research is only a part of our large research programm e on three different purposed mixes of unb ound subbase m ixture b elow: 1) 100% Recycled Concrete Aggregate (R CA); 2) 100% Lime Stone (NA); 3) 50% RCA + 50% Reclaimed Asphalt Pavement (R AP). Water absorption for each mix has been performed in different size fraction with pyknometer and wire basket methods. The relationship between density, gra ding and water absorption and its comparison for mixes would be indicating the changes in beha viour of aggregates and future performance of subbase. Laboratory testing showed that 100% Lime Stone had the higher densities than other mixes and water absorption value of 100% RCA was about 40% higher than 50% RCA + 50% RAP in 31.5 mm -4 mm fraction.