Elemental mapping by micro X-ray fluorescence to assess binder distribution of improved soils

This paper explores micro X-ray fluorescence (µXRF) as a novel technique in geotechnical engineering to investigate the binder distribution in a cement-improved clay. The technique scans a 2D surface of a specimen providing continuous heatmaps of an element of interest such as calcium, a major component in cement. A soft and sensitive natural clay was improved with cement using different mixing times ranging between 30 s and 10 min. The subsequent µXRF tests revealed a poor binder distribution with considerable binder accumulations for short mixing times. Longer mixing times, however, resulted in a well distributed binder. The unconfined compressive strength after around four weeks of curing ranged from 100 to 200 kPa for the shortest mixing times to 400–450 kPa for the longest mixing time as a direct result of the varying binder distributions. The paper demonstrates that the µXRF technique can be a useful technique to characterise the binder distribution in improved soils.