Abstract: The paper examines the mechanism of pozzolan-soil reactions, using a recent study on the chemical stabilization of a Class A-2-7 (3) lateritic soil, with corn cob ash (CCA) as case study. The objectives are to establish a nexus between cation exchange capacity of the soil, the alkaline forming compounds in CCA and percentage CCA addition to soil beyond which no more improvement in strength properties can be achieved; and to propose feasible chemical reactions to explain the chemical stabilization of the lateritic soil with CCA alone. The lateritic soil, as well as CCA of pozzolanic quality Class C were separately analysed for their metallic oxide composition using the X-Ray Fluorescence technique. The cation exchange capacity (CEC) of the soil and the CCA were computed theoretically using the percentage composition of the base cations Ca2+, Mg2+ K+ and Na2+ as 1.48 meq/100 g and 61.67 meq/100 g respectively, thus indicating a ratio of 0.024 or 2.4%. This figure, taken as the theoretical amount required to just fill up the exchangeable sites of the clay molecules, compares well with the laboratory observation of 1.5% for the optimum level of CCA addition to lateritic soil. The paper went on to present chemical reaction equations between the alkaline earth metals in the CCA and the silica in the lateritic soil to form silicates, thereby proposing an extension of the theory of mechanism of soil stabilization to cover chemical stabilization with pozzolanic ash only. The paper concluded by recommending further research on the molecular structure of soils stabilized with pozzolanic waste ash alone, with a view to confirming the chemical equations advanced in the study.
Abstract: The chemical and physical characteristics of rainwater
harvested from a typical rooftop were progressively studied. The
samples of rainwater collected were analyzed for pH, major ion
concentrations, TDS, turbidity, conductivity. All the Physicochemical
constituents fell within the WHO guideline limits at some points as
rainfall progresses except the pH. All the components of rainwater
quality measured during the study showed higher concentrations
during the early stages of rainfall and reduce as time progresses.
There was a downward trend in terms of pH as rain progressed, with
18% of the samples recording pH below the WHO limit of 6.5-8.0. It
was observed that iron concentration was above the WHO threshold
value of 0.3 mg/l on occasions of heavy rains. The results revealed
that most of physicochemical characteristics of rainwater samples
were generally below the WHO threshold, as such, the rainwater
characteristics showed satisfactory conditions in terms of
physicochemical constituents.