Measuring lateral pressure of concrete: From casting through hardening

The submission deals with the measurement of lateral pressure applied by concrete mixes on formwork immediately after being poured and through the setting process. Immediately after pouring, concrete may be considered to be a heterogeneous mix of solid soil/colloidal particles and water. Over time this mix transforms into a solid. Two issues have been considered in this submission. The effects of transducer size relative to particle/aggregate size of the concrete mixture and the effect of membrane deflection on the reliability of the measurement of concrete pressure.Testing was carried out on a standard concrete mix with a maximum particle size of 10 mm with deflecting and non-deflecting transducer configurations, 23 and 80 mm in diameter. Response of the sensors was investigated by testing the dry aggregate components of the concrete. Test results demonstrate that the response of a deflecting membrane sensor is dependent upon particle size. The response of the non-deflecting sensors is seen to be unique and independent of particle size.Testing of fresh concrete through the hardening process has shown that deflecting membrane pressure transducers indicate residual lateral pressure long after the concrete solidifies. Non-deflecting pressure transducers indicate reduction in pressure, reaching zero as the concrete sets.

► Measurement of concrete pressure with deflecting membrane sensors results in residual pressure.
► This residual pressure is erroneous, it is a result of the changing rheology of the concrete.
► Lateral pressure registered using the null system is correct despite the changing rheology.
► The measured lateral pressure reaches zero as the concrete hardens.