Adek Percometer
Percostation
Percostation - a Tool for Monitoring Moisture and Bearing Capacity in Road Construction, and Optimising the Use of Load Restrictions
Currently, transport corridors are needed year-round for deliveries to industry and trade. Long breaks in traffic connections are not tolerated, and the costs of a short delay or minor load restriction multiply throughout the stream of production; in Finland the costs of one day of load restrictions have been calculated to amount to approximately € 600.000. On the other hand, as the budget for road maintenance has been reduced, the road owner has an increasing need to protect roads with low bearing capacity e.g. with load restrictions.
One way to better manage the dilemma is to monitor the behaviour of the road structure during sensitive seasons, and to optimise the use of load restriction. During the last 10 years the deformation properties of road aggregates and their relation to electrical properties have been studied intensively in Finland and the USA. The results of these studies show a clear connection between high dielectric values and the susceptibility to permanent deformation. Electrical conductivity has also been found to provide valuable information concerning pore water in a material.
This provides a basis for effective monitoring systems for seasonal changes in the bearing capacity of roads, which enables the imposing of load restrictions based on real-time measurements instead of visual estimation.
Equipment
Roadscanners has developed, in cooperation with the Estonian Adek Ltd, the Percostation; a system for the monitoring critical bearing capacity. The system consists of sensors installed in a problematic road section, at different depths in the road structure and subgrade soil; a data collecting unit installed roadside; and data transfer and analysing systems, which transfer the measurement results via gsm network or telephone cable to the pc screen of the road authority, for use in load restriction planning.
Technically, the Percostation deviates from the Percometer in so far, as it enables measurements of dielectric value, electrical conductivity, and temperature from eight channels. The measurement interval can be set to a minimum of 60 seconds (four channels). The measurement results are stored in the memory of the data-collection unit, where they can be read through a modem connection. The memory of the collection unit is sufficient enough to store 360 measurements at once. The settings of the data-collection unit can also be modified through the modem connection.
The Percostation operates on 12 V of electricity. A sufficient energy supply can be provided by a 260 Ah accu, which is recharged by a solar panel. Without recharging, 260 Ah provides sufficient energy to power the Percostation for approximately 1,5 months.
In operation, Percostation software connects to the measurement station(s), reads the last measurements from its memory and transfers them to a mainframe database where they are stored in files for each individual station. Each file also stores information on the structure, materials, and calculated critical tensions, dielectric values, and electrical conductivity values for the road structure being monitored. Based on this information, the Percostation software can warn the operator when conditions in different layers of the road structure and subgrade are approaching a critical state. The operator can use this information when deciding to impose or lift load restrictions, and for determining the maximum allowed axle weights and/or number of axles.
