Abstract:
Subgrade is the lowest layer of the pavement that must eventually support all the loads that come onto
the pavement structure. Therefore, it is essential to make sure that the layer is stable and has sufficient
shearing strength to withstand the traffic induced stresses without excessive deformation. If the
subgrade soil is poor, sufficient shearing strength, then it must be stabilized to improve its properties.
In this paper Buton Rock Asphalt (BRA) was studied to stabilize the expansive clay subgrade soil of
Semarang-Purwodadi road in North-East Central Java Province of Indonesia. Amount of 2%, 4%, 6%,
and 8% of BRA by weight of soil were added. As comparison or control, natural sand in amount of 5
to 25% in increments of 5% by weight of soil was also added. Laboratory works show that BRA can
improve bearing capacity of soil far higher than the natural sand resulted. By adding 8% by weight of
soil, BRA can improve bearing capacity of those of expansive clay soil, measure by using CBR, from
the value of CBR 1.6% to 5.97% or increase 373%, while 20% of sand only increasing the CBR of
soil become 3.90% or increase 244%. Increasing of CBR by adding BRA is in linear line with the line
equiation y = 51.54x + 2.126. This mean if the percentage of BRA also 20% the CBR value of BRAstabilized
soil is 12.43% and suitable as well as very good for subgrade material.
