Development of zero cement composite for the protection of concrete sewage pipes from corrosion and fatbergs

The pursuit of environmental friendly alternatives for ordinary Portland cement (OPC) finds increased attention when the latter poses serious durability issues in major infrastructure applications, such as sewage drainage pipes. The presence of large quantities of free lime in OPC concrete used in the manufacturing of sewage pipes, exposes them to (i) concrete corrosion in acidic sewage environment, and (ii) clogging of sewage network due to the formation of calcified fatbergs. There appears to be very limited or no research on the development of an eco-friendly zero cement composite that can protect the concrete sewage pipes from corrosion and can eliminate the free lime that contributes towards the formation of fatbergs. Therefore, to address this research gap, an experimental investigation was undertaken on quaternary blended cement composites containing nano-silica, fly-ash, slag, and hydrated lime. These cement composites were tested for compressive strength to identify their mechanical properties, and an acid attack durability test exposed to 3.5% sulfuric acid solution to identify their corrosion performance in an aggressive acid environment. X-ray diffraction, thermogravimetric and scanning electron microscopic analysis were carried out to ascertain the physicochemical properties of the cement composites. The results show that an eco-friendly zero cement concrete developed with a quaternary blended mix of nano-silica, fly-ash, slag and hydrated lime successfully addresses the mechanical and durability requirements of the concrete sewage pipes. It surpasses ASTM's minimum strength requirement for the sewage pipes, and brings about a significant improvement in withstanding an aggressive acidic environment as evident from the 96% reduction in its mass loss due to concrete corrosion, compared to that of the OPC concrete. Moreover, the high amorphous silica content present in nano silica, slag and fly-ash assists in totally consuming the free lime that interacts with fat, oil and grease to produce fatbergs.