An Appraissal of the Performance of Geosta as a Stabilising Agent for Deltaic Laterite in Sub-Base Construction

This study was prompted by the massive and unprecedented failure experienced within a very short time after construction of “Ada-George Road” which had deltaic lateritic sub-base stabilised with undisclosed but most probably uncontrolled (scientifically) proportions of cement and geosta (a relatively new chemical stabiliser). Samples of the deltaic laterite were taken from two of the borrow-pits within Port Harcourt metropolis from which materials were quarried for the construction of the sub-base. The results showed that although geosta addition to deltaic laterite mixed with cement gives considerable improvement on the strength of the resulting mixture, this stabilisation is only effective at very low geosta content not exceeding 2% depending on the optimum geosta content (OGC) which in turn is a function of the percentage of fines of the soil. But the Ada George road project appeared to be politically rather than scientifically motivated. Consequently, the OGC must have been grossly exceeded in the construction of this geosta stabilised sub-base. As a result, the as-built CBR must have been much lower than expected hence the massive failure that resulted. Even for 2% geosta content, this composite stabilisation was also found to be most effective at 4% cement content.