Expertise confirms enormous load-bearing capacity of HMV ash

The Altenwerder Container Terminal (CTA), one of the most modern terminals in the world, has been in operation in the Port of Hamburg since 2001 as part of the port expansion. Due to the high stress caused by heavy loads, a very high load-bearing capacity of the ground is required there. The independent HeidenLabor from Roggentin has thoroughly examined the asphalt surfaces of the CTA and has now published an expert opinion. The bearing capacity of the installed domestic waste incineration ash (HMV ash for short; called HMVA or HMV ash in the report) was also examined. HeidenLabor comes to the conclusion that the construction method has proven itself. “The deformation resistance of the HMVA base layer is good even under the highest loads”, the study concludes.

The CTA has an asphalt surface pavement with an unbound base layer of HMV ash. In the 1st construction phase, 300,000 tonnes of HMV ash were used, in the 2nd another 110,000 tonnes. The HMV ash was placed on the approx. 80 ha container handling area (except in the area of the tracks) as a base layer below the bituminous surface course.

The aim of the survey was to determine whether the construction method used was suitable for port fortifications. The investigations extended to the four-lane road west of the stacking blocks, via which all truck traffic leaving the terminal is routed, and to a section of the water-side quay handling areas used by Automated Guided Vehicles (AGV), because it can be assumed that these are subject to increased stress.

First, a visual condition assessment was carried out. While no significant or systematic damage could be detected on the western tracks in front of the stacking blocks, some material fatigue phenomena in the form of cracks were observed on the eastern tracks. In the AGV area, due to the lane-moving, guided traffic, a medium to pronounced rutting was found, as expected, in some areas. There were no cracks in the asphalt pavement.

In order to get to the bottom of the observations, drill cores were taken and measurements carried out with the Falling Weight Deflectometer (FWD). Different structure thicknesses were determined: In the area with hardly visible damage, the structure consists of approx. 16 cm asphalt, approx. 49.5 cm HMVA base layer, including rinsing sand. In the area with material fatigue it is approx. 15 cm asphalt, approx. 36 cm HMVA base layer, including rinsing sand. Accordingly, it is primarily the different structure thicknesses that explain the visually recorded differences.

In the area of the AGV sites, the ruts were analysed in particular. The average layer thickness before the first stacking block is 7.3 cm (asphalt surface course) plus 8.9 cm (asphalt base course). In the expert evaluation, the criteria load-bearing capacity, strength, frost resistance and chemical transformation were examined. Soil samples were taken to answer the questions and analysed in the laboratory.

With the help of back-calculated deflection data from the FWD measurement on the road, the E-modules of the individual layers could be determined. They are between 4000 and 5000 MPa for asphalt and between 200 and 800 MPa for HMV ash base course. The rut formation in the area of the AGV surface could be assigned to the individual layers on the basis of the asphalt strips removed and the additional track depth measurements.

HeidenLabor comes to the conclusion “that the coating thicknesses and the material data correspond to the assumptions. The design is economical and the condition corresponds approximately to the predicted values. With the help of the data obtained, it will be possible in future to make a much more reliable prognosis of the condition or to measure the layer thicknesses for construction methods with HMVA base layer on highly stressed surfaces.”. According to HeidenLabor, the CTA experience with construction methods can be used for further construction measures. Dipl.-Ing. Lars Strehse, deputy head of container technology and head of construction technology at HHLA Container-Terminal GmbH, is also satisfied: “The load-bearing capacity of the ash has fully met our expectations. We are satisfied that we have opted for this building material”.

By paving HMV ash on the Altenwerder Container Terminal site, this building material has demonstrated its suitability as a base course even under particularly high loads. The ash was able to meet the high load-bearing capacity requirements of 180 MN/m2, which are necessary due to the heavy container traffic, without any problems. Since the technical equivalence to ballast base layers could be confirmed, it is conceivable to use HMV ash as an unbound base layer under heavily trafficked roads. Here, too, HMV ash could play off its cost advantage by ensuring a high load-bearing capacity.