Hand-held microprocessor implementation of heretofore large computer simulations

Abstract

Quality control engineers in highway construction must decide when hot asphalt concrete construction can proceed in order to satisfy rigid specifications on the final density of the asphalt mat. To achieve the proper density, the hot asphalt mat must exceed an average temperature of 175°F during the compaction (rolling) process. The field engineer must be able to predict the time-temperature profile of the hot asphalt mat while considering environmental temperatures, solar flux, cloud cover, thermophysical properties of the asphalt and mat, air velocity, etc. Solution can be achieved on large computers using finite difference methods. Field implementation of large computer results has been impractical until recently. Practical implementation is achieved by using a little known finite difference method first proposed by Saul'yev. His method is unconditionally stable and uses very little memory. The Saul'yev method has been programmed for the HP 97 programmable calculator and gives excellent answers which reproduce those achieved on large scale computers. The new work to be reported includes the following: 1. 1. A practical finite difference method implemented on the HP 97 that predicts in 11 min the time-temperature profile for freshly placed asphalt. 2. 2. An heuristic analytical solution that predicts the desired results in less than 5 min. 3. 3. A laboratory tested method to circumvent the need to measure the thermophysical properties of the base material. 4. 4. The use of simulated least squares to infer the thermal conductivity of asphalt concrete and the heat transfer convection coefficient. The inferred results reproduce accurately laboratory measured properties. Computational results will be supported with laboratory measurements. The use of the HP 97 microprocessor (hand-held programmable calculator) has proved to be a very powerful tool for implementing decision rules which will extend the late construction season, improve quality control, speed highway construction and provide cost effective benefits for the public.