Water absorption and frost heaving of recycled aggregates

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.