| dc.description.abstract | Due to the continuous upgrading of the service rate of the urban sewerage system in Taiwan area, the sewage sludge production is expected to increase simultaneously. Thus, the sludge incineration has become one of the alternatives for sewage sludge disposal. Although incineration can obtain optimum volume reduction and stabilization for sewage sludge, the sewage sludge ash (SSA) still needs to be reused in order to minimize the land demand for final disposal and the environmental impact. Among those reusing technologies, to apply SSA into cement mortar has been proved to be technically and economically feasible by previous research works. However, the total properties of SSA, and its roles in mortar, and the corresponding modification technologies for SSA mortars, have seldom been discussed in the literatures.
For above reasons, this study selected the sewage sludge of the Ming-Shen Community WWTP and the Pa-Li WWTP to be investigated. The samples of sewage sludge were incinerated in a modular incinerator and the SSA was obtained. The physical properties, chemical compositions, crystalline constituents, and pozzolanic properties of SSA were analyzed. The SSA samples were further applied into mortar to replace partial cement or aggregate. Meanwhile, the workability and compressive strength of SSA mortar were tested. In addition, three potential modifications for SSA mortar, including the high-temperature calcination of SSA, the extended grinding to increase SSA fineness, the application of chemical admixtures, including super-plasticizers and activators, were also investigated and evaluated in this study.
According to the test results, the SSA was essentially the burnt residue of raw sludge and contained fine particles with porous irregular morphology and great amounts of pore volume and surface area. The major chemical compositions of SSA included SiO2, Al2O3, and Fe2O3, and its crystalline constituent was primarily quartz. In addition, SSA exhibited certain pozzolanic activity. When SSA was reused to replace mortar aggregate, the SSA mortar exhibited poor workability and compressive strength. In contrast, when SSA was reused to replace 5-20% mortar cement, the compressive strength at age of 28 days of the hardened SSA mortar could achieve 60-80% of that of control mortar. This result revealed that to reuse SSA in replacing mortar cement has higher potential than in replacing mortar aggregate. Regarding the modification of SSA mortar, this study found that to calcined SSA at 1,000-1,200oC and followed by water quenching, could greatly improve the pozzolanic activity of SSA and the workability of SSA mortars. In addition, the extended grinding of SSA was found to increase 5% of the strength activity index of SSA with per increment of 100 m2/kg of the Blaine fineness. Finally, due to the water-reducing effect provided by the super-plasticizers, and the hydration acceleration effect provided by the activators, to apply the chemical admixtures could improve the workability and compressive strength development at early ages of SSA mortars respectively.
Based on above results, the SSA is a useful material in respect of its physical, chemical, and mineral properties, and can be reused as a pozzolanic material to replace partial cement of mortar. This study has also revealed the roles and mechanisms of SSA, and the effective modification technologies for SSA mortars. These findings are helpful in elevating the potential and value of the application of SSA in cement mortar. | en_US |