Mix design strategy to reduce the poured earth shrinkage

Abstract

The aim of this paper is to find an approach in mix design to reduce the poured earth shrinkage. First, the raw material is analysed and evaluated. Afterwards, three approaches to limit the shrinkage adapted from concrete are presented: The reduction of water in the binder, the optimisation of the packing as well as the optimisation of the paste/aggregate ratio.
As known from literature: the less water is used, the less shrinkage occurs. Therefore, the water amount in the binder is minimised by adding the deflocculant sodium hexametaphosphate (NaHMP). Three pastes are mixed to measure the difference in shrinkage. Every paste contains the same amount of NaHMP, whereas the amount of added water varies.
The second approach is to lessen shrinkage by utilising densely packed aggregates. It is examined, whether rounded or crushed aggregates are better related to shrinkage and how the compacity of different sand/gravel ratios impacts shrinkage.
The sand/gravel ratio that achieves the smallest shrinkage values in the first round of experiments is then fixed for the third stage which is optimising the paste/aggregate ratio. Numerous ratios with different pastes are mixed in order to optimise the shrinkage.