Sampling Concrete from a Revolving Drum Truck Mixer

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Journal of Testing and Evaluation


Acceptance testing of ready-mixed concrete occurs after the product has been delivered to the consumer in the field. The testing process commences with the collection of a relatively small but representative sample of the fresh concrete. ASTM C172/C172M, Standard Practice for Sampling Freshly Mixed Concrete, states that two or more portions of material should be collected at regularly spaced intervals during discharge of the middle portion of the batch. There is concern within the industry that field technicians are opting to obtain only one portion of concrete from the material initially discharged from a truck. A study undertaken at Valparaiso University investigated the first issue of collecting only one portion of concrete. The primary objective of this research was to determine if the measured properties for a single portion sample taken from the middle of a batch differ statistically from that for a two-portion sample also taken from the middle of the batch. Concrete was sampled 46 times across 11 different construction sites with fresh properties and 28-day compressive strength measured in each case. Construction projects were selected to provide a range of concrete mixture specifications, site conditions, and target property values. Findings indicate that it is not necessary to collect a sample of two or more portions from a revolving drum truck mixer. Rather, a single portion sample of concrete is sufficient for acceptance testing purposes.