| dc.description.abstract | This study investigated the pozzolanic reactions and engineering properties of slag blended cements (SBC). In this work, SBCs were prepared by blending slag, which was generated from the melting of municipal solid waste incinerator fly ash (referred to as MSWFS), with five types of cements, respectively. Major cement constituents such as C3S (i.e., 3CaO.SiO2) and C3A (i.e., 3CaOAl2O3) were also used alternatively in replacement of cement for contrast. The experiments were divided into three parts: (1) characterization of the slag prepared by melting the MSW incinerator fly ash at 1400℃ for 30 min; (2) assessment of the pozzolanic reaction in the SBC pastes incorporating C3S and C3A with blend ratio ranged from 10% to 40% at various curing ages; and (3) evaluation of the effects of slag on pozzolanic reaction in the SBC pastes for five cements at various curing ages, focusing on their compressive strength, hydration heat behavior, hydration degree, crystalline speciation, and variation of microstructure.
The results showed that lower hydration heat of C3S and C3A samples with the incorporation of MSWFS was observed, possibly due to the partial replacement of the mineral constituents by the slag with less activity. In general, the incorporation of slag into C3S and C2S, respectively, decreased the initial hydration reaction whereas increased the pozzolanic reaction at later stage by consuming CH to form CSH and CAH. This was evidenced by the DTA results, which showed a delayed transformation of C3A from C4AH13 to C3AH6. Moreover, hydration degree and the average length of C-S-H, (i.e., the number of Si of linear poly silicate anions in C-S-H gel, Psi) as determined by applying nuclear magnetic resonance (NMR) techniques also indicated a delayed initial hydration and an enhanced later pozzolanic reaction. In the C3S-slag paste, the Psi value increased with increasing curing age as compared with that of the C3S paste. The results of x-ray powder diffractometer (XRPD) revealed that the pozzolanic reaction in C3S-slag paste was mainly affected by the Si2+ and Al3+ released by the slag. On the other hand, the incorporation of slag delayed the initial hydration of C3A in C3A-slag paste, and decreased the formation of ettrigite (AFt) and monosulfoaluminate (AFm) in C3A-gypsum-slag paste.
The early unconfined compressive strength (UCS) of SBC pastes for five types of cement were found to decreased with increasing slag blend ratio, whereas the later strength increased. In addition, the UCS for all types of SBC pastes tested with slag blend ratio<20% outperformed that of their pastes without slag. Moreover, the results of mercury intrusion porosimetry (MIP) analysis indicated that the total and the capillarity pore volume decreased with increasing ages, whereas the gel pore volume increased, showing the later pozzolanic nature of the pulverized fly ash slag. | en_US |