High-Quality Concrete with Recycled Aggregates

New laboratory and field investigations showed that it is possible to achieve durable concrete by using recycled aggregate above 4 mm from old pavements with cracks but no frost- or concrete structure deterioration. The concrete compressive and tensile strengths were slightly higher and the cracking sensitivity was slightly lower for higher recycled aggregate contents. This is due to the rough surface of the crushed recycled aggregate and its better bond to the new hardened cement paste as well as the local reduction of the water/cement ratio in the bond area due to the porosity of the old hardened cement paste. Concrete mixes with recycled aggregate above 4 mm had a high freeze-thaw and de-icing salt resistance. High recycled aggregate contents cause higher shrinkage and swelling due to the higher content of old hardened cement paste. An efficient and durable drainage is necessary to avoid high warping of concrete slabs.