The aim of this study is to assess the strength controlling parameters of a sandy soil (Botucatu residual soil (BRS))
treated with industrial by-products (basaltic powdered rock (PR) or coal fly ash (FA)) and lime, as well as to show
that the porosity/volumetric lime content (/Lv) plays a fundamental role in the assessment of the target strength.
The controlling parameters evaluated were addition of industrial wastes, quantity of lime, porosity and /Lv: The
unconfined compressive strength (qu) increased non-linearly with the amount of lime and decreased with porosity
for all studied mixtures. Similar equations were found relating qu to /(Lv)0:12 for BRS–lime, BRS-PR–lime and BRSFA–
lime mixtures. Tests of potential reactivity of siliceous materials with alkalis on the materials studied indicated
that the higher amount of dissolved silica in the alkaline environment of the FA, when compared with the BRS and
the PR, was responsible for increasing the number of reactions with the lime and consequently increasing the
strength for BRS (25% FA)–lime mixtures, when compared to BRS–lime and BRS (25% PR)–lime blends.

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