Abstract
M.Tech. (Civil Engineering)
The production of dry wastewater sludge from treatment works is in a rise throughout the world. The impact on environmental management makes the dumping of dry wastewater sludge a serious concern for wastewater processing managers. Some solutions to this problem include the use of this by-product in the agricultural industry and construction field, however due to its level of hazardousness; more restrictions are placed on the disposal methods as it is environmentally unsustainable to dispose wastewater sludge.
This dissertation presents a study that investigated the effect of dry wastewater sludge on the strength and durability of concrete when utilized as sand replacement. The sludge was assessed on its microbiological class, stability class and pollution class as per the “Guidelines for the Utilization and Disposal of Wastewater Sludge Volume 1 of 5” by Snyman and Herselman, (2006). The sludge was further characterized on its chemical composition through X-Ray Fluorescence (XRF analysis) and crystalline phases’ X-Ray Diffraction (XRD analysis). Four wastewater sludge percentages at 0% 1%, 3% and 5% replacement by sand mass against fixed water-cement ratios of 0.667, 0.694 and 0.800 were selected for this investigation. Durability tests (Oxygen Permeability Index, Sorptivity and Chloride conductivity) and splitting tensile performances were evaluated at 28 and 90 days.
The results showed a notable reduction on the mechanical performance of concrete with certain sludge percentage replacement. The compressive and splitting tensile strength failures of 0% and 1% were comparable at 0.67 W/C, though the 3% and 5% replacement on 0.69 and 0.8 showed notable failures. Good results of OPI were recorded at W/C of 0.67 and 0.69 (specifically at 28 days for 0%, 1% and 3% only). The Sorptivity results were poor in almost all the mixes except the 0% at a W/C of 0.67. The Chloride conductivity was excellent at all the three W/C ratios, due to high organic content.
In conclusion, the research established that the dry wastewater sludge concrete does have useful factors in the concrete industry; however more research is required toward the evaluation of the durability of dry wastewater sludge concrete and the performance of reinforced concrete sludge, with the inclusion of modifiers, admixtures or extenders to balance the high organic matter content.