A sample holder system for high-precision and reliable resistivity measurements of laboratory lime-cement samples

Lime-cement mixing is a method used for ground improvement of clay soils. Before mixing at a field site, laboratory samples are prepared and tested to decide the amount of lime-cement binder needed to reach the desired material strength. Strength measurements are not possible before a sample hardens, and the test process to predict final strength takes 30 days. Resistivity measurements are possible immediately after sample preparation. If a correlation can be made between lime-cement resistivity and strength, resistivity measurements could provide a useful early indication of sample strength development. Laboratory resistivity measurements have shown a correlation between resistivity and material strength in cement-based mixtures, but lime-cement mixtures have not been thoroughly investigated. Conventional four-electrode soil box sample holders are not well suited to resistivity measurements of laboratory-prepared lime-cement samples, since the rectangular shape makes packing and removal of the material impractical. The method is also inherently destructive due to spike electrodes that penetrate the sample, which would bias strength measurements. Non-intrusive two-electrode methods can be used but they introduce measurement uncertainties. Additionally, the hydration of lime-cement is an exothermic reaction. To quantify the effect of temperature variations on measured resistivity, sample temperature measurements are needed. We present a new sample holder design with non-intrusive sensors that enables temperature compensated 4-electrode resistivity measurements of laboratory-prepared lime-cement samples. Sensors are integrated into 3D-printed lids that comply with standard geotechnical sample cylinder dimensions for ease-of-use with a high repeatability (<0.2% coefficient of variation).