Truck and Central Mixing Mechanism in Saudi Arabia: A Critical Evaluation

Abstract

Currently there is a trend of eliminating the truck mixing mechanism of concrete production from major construction contracts in Saudi Arabia. Such a shift is liable to produce far reaching effect on the concrete industry. This paper presents an experimental study of strength and uniformity aspects of the concrete produced by the central and the truck mixing mechanisms in order to make a case for or against the latter. Results indicate that, with adequate control on mixing performance factors such as mixing time and drum speed, the two mechanisms comply with strength and uniformity requirements. However, in spite of adequate quality control at the 95% confidence level, the average compressive strength from the truck mechanism is less than that from the central plant, while the variability of strength of the former tends to be more than that of the later. A procedure is presented for determination of the critical mean strength of a truck mix that matches with that of the central mix produced by a given plant. The paper also suggests improvements in the test procedure to enhance the uniformity of concrete produced by the truck mixing mechanism and exercise control on operator performance so that strength variability can be reduced.