One of the chief by-products of modern wastewater treatment could be used to create more sustainable and resilient forms of concrete.
A new study from the Universiti Teknologi MARA in Selangor, Malaysia has investigated the use of dried and incinerated sludge as a partial replacement for Portland cement in the production of concrete.
The study replaced the Ordinary Portland Cement (OPC) used in concrete mixes with domestic waste sludge powder (DWSP) to varying degrees in order to assess its impact on the performance of the final product.
The sludge powder was produced by first producing wet sludge cakes and drying them in the open for as long as week in order to remove moisture.
The cakes were then burnt in a ferrocement furnace for a period of 72 hours and ground into a fine powder by an LA abrasion machine for inclusion in the concrete production process.
The results of the study indicate that the DWSP holds considerable promise as a partial replacement for cement, producing concrete whose average water absorption values were still within a range of just three to five per cent.
For Grade 40 concrete, the incorporation of DWSP actually made the product less permeable than the OPC control concrete, with highly enhanced resistance to the penetration of the chloride ions that result in the corrosion of steel reinforcement.
The presence of DWSP in Grade 50 concrete, however, had the opposite effect, conferring the product with higher degrees of permeability.
Should methods be developed for improving the performance of concrete that employs domestic waste sludge powder as a replacement ingredient, it could dramatically improve the sustainability of both concrete production and the wastewater treatment process.
The handling of dry sludge in urban areas is a major dilemma in many parts of the world as a result of environmental restrictions on its disposal as well as the copious amounts of the material produced by high-density population zones.
Most jurisdictions prohibit the burial of dry sludge in the earth or its usage as a fertiliser due to the high amounts of heavy metal it contains, while in urban areas it use for landfill is limited the space restrictions.