Paper by HEWITT GHADDOCK MERCER from ISCR 8th 1998 Lisbon Portugal
To ensure the satisfactory performance of rigid pavements, it is necessary to control the air content of the concrete slabs. The aim is to maintain a prescribed quantity of cntraincd air in surface slabs to rcducc frost damage. Also, it is required to minimise the quantity of air, which results from insufficient compaction, to avoid an unacceptable reduction in concrete strength. Consequently, the United Kingdom Specification requires the calculation of the total air voids within the concrete from measurements of the dry density of cores cut from the slab and knowledge of the theoretical maximum dry density of the concrete mix. Hardened concrete with an air content that exceeds the designated limits must be broken out and replaced with new material. Prompt identification of non-compliant material at the time of pavement construction, by measuring the density of plastic concrete, would reduce the amount of any remedial work. This procedure would also reduce the number of cores that are required for the determination of density. Research has therefore been carried out to develop safe working practices with nuclear density gauges by using aluminium sheaths to protect the gauges from contamination with concrete fines. This report describes a successful trial on a public road of a standard gauge and a stratagauge. In general, the concrete complied with the Specification.