  This study examines the effect of partially replacing cement with blue
gumwood ash (BGWA) in stabilizing laterite soil to be used as a potential road
base material. Initially, Ordinary Portland Cement was introduced to the soil
at varying contents from 0 to 12% in steps of 3% by weight of the soil sample.
Each wet sample of the soil was subjected to the Californian bearing ratio
(CBR) and unconfined compressive strength (UCS) tests in determining the
optimal soil-cement mix. Results show that CBR and UCS values increased as
cement content increased, and a 6% cement content corresponding to a UCS value
of 2.88 MPa at 7 days of curing met the specifications of the Overseas Road
Note 31 to be used in the construction of road bases. The second treatment
involved partially replacing the 6% cement content with BGWA in decreasing
steps of 1%. Peak CBR value of 348% at 2% BGWA content (>160% recommended by
Kenya road design manual) and UCS value of 2.99 MPa at 7 days of curing were
obtained. Thus, BGWA can partially replace cement in stabilizing laterite soil
for use in the construction of road bases as per the Overseas Road Note 31
specifications.

Physics and Society