Effects of hydrostatic pressure on the integrity of concrete

The effect of simulated sea dumping conditions on some physical properties of concrete are described. From measurements of ultrasound transit time and diametral compression strength it has been shown that some degradation occurs during pressurisation/depressurisation treatment. Optical examination of polished cross-sections have shown that the major feature of the degradation is the formation of voidage at the cement matrix/aggregate particle interface. The extent of this voidage appears to be related to the hardness of the aggregate particles; hard aggregates cause a larger voidage region than softer aggregates. It is believed that the voidage results from the partial non-recovery of the cement matrix during depressurisation. No other matrix cracking was observed and the mass transport properties of the concrete were unaffected. It is inferred from the evidence that less degradation occurs when the concrete is open to the ingress of sea-water than when it is pressurised in air for any given pressurisation/depressurisation schedule and that the most damaging treatment is rapid depressurisation. (author)