A study of the property of laterite bricks stabilized with Egg Shell Ash (ESA) and Saw Dust Ash (SDA) in relation to that stabilized with cement was conducted, this was with a view to obtaining an economic replacement for cement. Laterite was stabilized using 0, 2, 4, 8 and 16% (by weight of dry soil) of a mixture of ESA and SDA. The laterite was also stabilized with 5% (by weight of dry soil) of cement to serve as control. For each of these mixes, OMC and MDD of stabilized laterite and compressive strength (qu) of bricks made from stabilized laterite were determined. The results obtained were 47% calcium oxide in ESA, 59.8% silica in SDA, optimum MDD of 1.75 kg/m 3 , OMC of 19.0% for laterite and optimum of 1.2 N/mm 2 for ash stabilized laterite bricks. The optimum results were obtained for ash content of 2 and 4%. The maximum qu obtained for cement stabilized brick was however 2.1 N/mm 2. In conclusion, SDA and ESA can be a substitute for cement in low cost housing.

The results of the undrained shear strength (Su) and stiffness (Vs) of electrochemically stabilised residual tropical laterite soil (RTLS) are presented. Calcium (Ca2+) and phosphate (PO43−) ions from calcium chloride and phosphoric acid, respectively, were injected individually and together into remoulded RTLS by applying 1 and 2 V/cm direct current electrical gradient for 5 d to facilitate cementation within the treated soil. Three different systems were employed using 1·0 M calcium chloride or 0·01 M sodium chloride as the anolyte and 1 M phosphoric acid or 0·01 M sodium chloride as the catholyte. Polarity reversal was also employed in some tests. The efficacy of the treatment was based on the soil Su and stiffness. The injection of Ca2+ led to a reduction in both the Su (90%) and stiffness (8%) of the treated RTLS. The injection of PO43− resulted in improvement in both the soil Su (151%) and stiffness (20%) of the treated RTLS. The study concluded that in stabilising the RTLS, injection of PO43− is effective whereas the injection of Ca2+ is not.

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