Continuous quality control of high performance concretes for road – within the framework of site supervision – using a new field tested BASIC-MC programme

Introduction and statement 'of problems: This paper closes the gap in concrete highway engineering technology by evaluating complex compactionphenomena and by deriving mathematical relationships between the concrete-technological, dynamic (thixotropic- plasticized) and physical parameters. It is based on the latest experience, e.g., including the construction of the concrete pavements of the A 23 Federal Motorway, Elmshorn - Itzehoe section (1981), in Germany. Solution of probl-ems: In the process of compaction by the vibrating beam of the concrete placing and finishing machine, i.e., during the thixotropic~plasticized state of the road concrete, so-called dynamic parameters exercise their influence on the concrete. These are, for example, the vibration amplitude (A), acceleration (bg), frequency (no)' centrifugal force (Zp)' damp1ng of the vibrating beam (Wb),damping of the concrete mass (Wb'), natural frquency[n(t)], etc. Such parameters are superimposed upon the concrete technological factors (consistency, grading, water-cement ratio, concrete mix composition,etc.), and together they determine the physical properties of the road concrete (compressive and flexural strength, wear resistance, i.e., resistance to attrition, resistance to frost and de-icing salts as a function of the entrained air content, durability of the concrete, etc.). In order to obtain an optimum result, it is necessary to achieve a properly interadjusted and verifiable superposition of these various sets of influencing factors. The derived relationships between the above-mentioned factors , or parameters, affecting the "final produe t", i. e., the road cancre te produced, are so complex and the calculations so laborious that a new permanent quality monitoring procedure in the form of a loop had to be developed. A permanent solution to meet this requirement is feasible only by the use of a microcomputer program on the construction site. Conclusion: With the aid of a new BASIC-MC program the optimum speed of advance of the concrete placing and finishing machine is continuously calculated and can, if necessary, be immediately corrected during the construction of the highway pavement. The inputs for the MC program are the test data which, under the specifications, have to be determined by on-site measurements anyway. With this procedure the desired physical properties of the concrete are achieved with a high degree of constancy and of effectiveness in utilizing the quality potential. Thie means more particularly: taking due account of the above-mentioned relationships, the program calculates the optimum operation speed of the machine from the measured value for entrained air, water-cement ratio, consistency and cement strength class; at the same time, all the required and anticipated concrete strength values are verified.