| dc.description.abstract | The goal of this study is to find the optimal conditions of cement making in order to maximize the replacement of cement clay by ash obtaining from waste foundry sand(including Core sand and glass sand), stone sludge, limestone and ferrate as raw materials. A computational model was used to formulate the composition of the raw clinkers. In this study, the hydration characteristics of these eco-cements and the engineering properties of their pastes, including their compressive strength, speciation and degree of hydration, were studied and compared to those of ASTM type I ordinary Portland cement (OPC). The amount of free CaO less than 1% and LOI all met the criteria of all eco-cement. The heavy metal leaching concentrations for different clinkers complied with the Taiwan Environmental Protection Agency’s regulatory thresholds. The study demonstrates the feasibility and safety to apply waste foundry sand and stone sludge as a cement replacement material. Results indicate that the major components of OPC such as C3S, C2S, C3A, and C4AF were found in the all ECO clinkers. The FEC series pastes had a retard of initial setting time and final setting time to those of the OPC. Nevertheless, the REC series pastes had shorten of initial setting time and final setting time to those of the OPC. The compressive strength of the FEC series pastes was less than the OPC cured at the first 28 d and the strength an apparently development from 28 to 90 d. For the REC series pastes were greater than that of the OPC paste cured at the first 28 d. However, from 28 to 90 d, the compressive strength could cause an insignificant development. The XRD analyses of the hydrates of the OPC and the two series of eco-cement pastes were Ca(OH)2 and C-S-H gels. In the REC eco-cement pastes, the hydration products showed Mg(OH)2 Brucite. The FTIR analysis for eco-cement pastes cured for 90 d have three wavenumbers. The first wavenumber is located at about 990 - 970 cm-1, and was mainly due to the Si-O bond of calcium silicate hydrates (CSH). The second wavenumber can be observed at about 1424 – 1436 cm-1 and represents the C-O bond of the calcium carbonate (CaCO3). The third wavenumber is located at about 3650 - 3640 cm-1 and represents the decomposition of calcium hydroxide (Ca(OH)2).
The 29Si MAS/NMR spectra of the hydrated samples of the OPC and the eco-cement pastes, the results show the increased intensity of signals from Q1 and Q2 silicone sites in the hydrated pastes. The degree of hydration and the average length of the linear polysilicate anions of OPC pastes, as well as the eco-cement pastes increased with time, up to 90 days. | en_US |