| dc.description.abstract | In this study, waste sludges were used as raw cement materials or pozzolans to produce the cementitious materials. The usage of marble sludge, sewage sludge, drinking water treatment plant sludge, and basic oxygen furnace sludge as replacements for the raw cement materials was feasible. The results were also found that marble sludge could replace up to 50% of the limestone and other materials could serve as entire substitutions for the traditional raw materials in cement production. The major components of Portland cement were all found in eco-cement (EC) clinkers. The compressive strength (Sc) and microstructural evaluations conducted at 28 days revealed the hydration reaction and usefulness of EC. It was observed that the Sc data correlated linearly with the pore volume (Pv) data at 28 days. The proposed model equation could be represented as Sc = 178−461Pv (correlation coefficient, R2 = 0.96).
Waste materials with pozzolanic characteristics, such as sewage sludge ash (SSA), coal combustion fly ash (FA), and granulated blast furnace slag (GBS), were reused partially as cement replacements for making blended cement mortars. The results revealed that with dual replacement of cement by SSA and GBS and triple replacement by SSA, FA, and GBS at 50% of total cement replacement, the Sc of the blended cement mortars at 56 days was 93.7% and 92.9% of the control cement mortar, respectively. GBS had the highest strength activity index value and could produce large amounts of CaO to enhance the pozzolanic activity of SSA/FA, and form calcium silicate hydrate gels to fill the capillary pores of the cement mortar. In the cement mortar with modified SSA and GBS at 70% of total cement replacement, the Sc at 56 days was 92.4% of the control mortar. These results confirm the assumption that modifying the content of calcium in SSA further increased its pozzolanic reaction.
Due to the fact that EC was used waste sludges in the kiln feed, there was no real reduction in emissions and energy consumption in calcination, and the ignition loss was greater than ordinary cement. Therefore, the impact score generated by the EC was higher than ordinary and blended cement at the equal amount as a result of excluding the environmental benefit of reusing the waste sludges that have the need for final disposal. Incidentally, blended cement could effectively reduce the total environment impact score and the score was 52.7% of that of ordinary cement. Results from life cycle assessment (LCA) methods also indicated that cement manufacturing in Taiwan was high-resource-consumption and energy-depletion industry. However, Eco-indicator 95 method excluded the impact assessment of consumption of energy and resource, but the impact of mineral extraction was taken into consideration by IMPACT 2002+ method. Consequently, IMPACT 2002+ should be a more applicable LCA method for the cement industry because the manufacture of cement always consumes a massive amount of raw material and energy for mineral extraction.
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