Paper by VAR DER HERBERG from ISCR 5th 1986 Aachen Germany
1. Introduction Since 1962 no cement concrete had been used in the governmental road sy~tem as a paving material. After 1975 the need to use this material again was felt more and more. Somewhere about 1982, during the decision making period regardi~g the type of pavement to be chosen for the section De Lutte - De Poppe in highway RW 1 (E8) near the West German border, the need arose to set the (sum of the) costs of construction and maintenance of asphalt concrete against cement concrete in a responsible way. About the same time it turned out that, cement concrete - in view of the bearing capacity of the subsoil - could be a real alternative to a number of Rijkswaterstaat road projects. In order to develop an adequate weighing model on this subject a working group was set up. Meanwhilè, this working group has prepared a report. This report is the basis of this contribution. 2. Purpose and restrictions In the first instance the working group restrained itself to the business economic costs of construction, maintenance and the corresponding Rijkswaterstaat efforts. The method developed is meant to give decision makers an instrument to have these costs - which form an important weighing factor - quantified in a responsible way and include them in the total decision making process. It should be considered, however, that other things can play a more or less important role, as economy in a wider perspective, political, market strategic and financial factors. 3. Range of applications The method c. q. the model developed can be used in the following stages of a project: 3.1. (pre)design stage: decision concerning the type of pavement, to be prepared by the Department 3.2. tender stage: decision which type of pavement will be constructed. Therefore, the construction costs as expected in the calculation method will be substituted by eligible price offers. 4. Basis of the calculation method The calculation method is based on the so-called "discounted cash flow". This method appeared to be most useful for the weighing of costs at such projects. For, the method anables all the costs (negative cash flow) coming up during the life of constructions to be projected by means of a certain interest percentage (discount rate) at a certain time (moment to decide). Due to this fact a direct comparison between the costs of various constructions is possible. 5. Maintenance forecasts To attain a good illustration and a practical handling of the (theoretical) calculation method, the working group has prepared a number of maintenance forecasts. It is important to mention that these forecasts are rather conditioned and may therefore not be considered generally applicable. The "completion" of the matter in the model will therefore have to be done per situation per project. The maintenance forecasts mentioned before can be used for the preparation of calculation examples to improve the understanding of how to deal wi th the model. 6. Finally The method developed can be considered a first step in the direction of a more systematic input and weighing of the economic aspects in the decision making at Rijkswaterstaat (road) projects.