Research Report: Testing Concrete for Deep Foundations-PDF

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The 2018 Deep Foundations Institute report evaluates laboratory tests for assessing fresh and hardened properties of concrete used in deep foundations. Six mixtures from different producers were reproduced and tested; admixture dosages were sometimes adjusted to match field slump flow, so laboratory mixes were not always exact replicas.<br /><br />Testing covered workability and rheology, stability, bleeding, forced water loss, setting time, strength, and thixotropic behavior. Laboratory results were also compared with field data.<br /><br />Key findings include:<br /><br />- Slump flow generally correlated with dynamic yield stress, and laboratory and field measurements showed similar workability-retention trends. Laboratory slump flow was usually retained slightly better.<br />- Plastic viscosity changed little over time. Its relationship with slump-flow speed depended on the timing measure used.<br />- ICAR rheometer and portable-vane tests distinguished mixtures’ thixotropic build-up. Delayed slump-flow and L-box tests did not provide reliable indicators.<br />- All mixtures met the study’s static-stability benchmark of no more than 15% column segregation. Laboratory bleeding results broadly matched field results, while laboratory Bauer filter-press water loss was consistently higher.<br />- Some results require caution: one mixture’s rheology data were unreliable, calorimetry data were questionable, and differences in mixing, materials, water, and test procedures limited direct lab–field comparisons.<br /><br />The report recommends selecting one suitable method—such as dynamic yield stress, slump flow, or L-box—to assess filling ability and its change over time. It recommends a static-yield-stress test using either a rheometer or portable vane to monitor structural build-up. Stability should be evaluated separately, though the report could not determine whether segregation, bleeding, and forced-bleeding tests are all necessary.

Keywords

deep foundations

concrete testing

fresh properties

hardened properties

slump flow

rheology

thixotropic behavior

bleeding

segregation

laboratory field comparison