Rehabilitation by cracking and seating of concrete pavement optimized by FWD analysis

Abstract

One of the main roads to the town of Copenhagen was constructed in 1942 during the Second World War as a 4 lane concrete pavement. The slabs are constructed directly on the clay subgrade using a 50 mm slag material levelling layer. The pavement has, despite of a traffic load of about 150,000 10t ESAL per direction per year, functioned until today, but over the last 10 years in a very poor condition. The preliminary investigations revealed that several of the concrete slab corners were badly supported, that the soil below the concrete had surface E moduli of down to 35 MPa, while the clay material had CBR values of down to 19 %. A preliminary design with estimated E values of 6,000 MPa for the cracked and seated concrete layer resulted in a designed asphalt overlay with a thickness of 170 mm for 6.0 mill. 10t ESAL equivalent to a design period of approx. 40 years. In the Spring of 1999 a small test section was selected. The concrete pavement was cracked and seated
and FWD measurements were carried out. The measurements resulted in design E values of the cracked
and seated concrete slabs of 1,600 MPa. The redesign resulted in an asphalt overlay thickness of 200
mm for 4.8 mill. 10t ESAL equivalent to a design period of approx. 32 years. After construction of the asphalt layer, the FWD measurements on the asphalt surface revealed that the E values of the cracked and seated concrete layer had changed to 7,000 MPa over the cracks. These results were later confirmed partly by measurements carried out one year later during the second half of the rehabilitation of the old concrete pavement, partly by measurements carried out two years after the construction.