Summary: | 碩士 === 國立臺灣師範大學 === 化學研究所 === 90 === Epcat, a waste catalyst from oil crackers, composed mainly alumina and silica, is expected to have pozzolanic activity.
In this study, pastes and mortars with Epcat were prepared and cured, and their compressive strengths after 3, 7 and 28 curing days were measured. The water/binder (W/B) ratios were 0.2, 0.25 and 0.3, and the replacement levels of cement by Epcat were 0, 5, 10 and 15 wt %. Proper amount of superplasticizer was added into each mix to ensure similar workability. The results indicate that the presence of Epcat would increase the compressive strength of mortars substantially, but increase the compressive strength of the related pastes only slightly. Compared to the the control motor cure at 3-28 days, mixes with 5-15% Epcat increase the compressive strength by amounts ranging from 13 to 41 %. In contrast, pastes with 5-15% Epcat only increase 1.4 to 14.3% in strengths over the plain paste at 3-28 days.
As the W/B ratio decreases or the catalyst content increases, the strength enhancement effect becomes more significant. The improvement in the mechanical properties of mortars is not only due to the increase in the hydrated cement paste itself, but also due to improved bonds between the cement paste and aggregate.
On the other hand, the pozzolanic property of Epcat was studied by using differential scanning calorimeter (DSC). Experimentally, cement pastes (water/binder ratio=0.3) incorporated with 0 ~ 30 wt% Epcat were prepared and cured for 1 ~ 28 days before DSC measurements. The cement hydrated products such as calcium hydroxide, C-S-H gel, and ettringite, were identified from the DSC diagrams of cement pastes. The results show that cement pastes with Epcat present produce more C-S-H and less CH than those without, indicating that the catalyst does accelerate the cement hydration by initiating the pozzolanic reaction with CH. Besides, the effect becomes more prominent when more Epcat was added in cement pastes or the curing time is longer.
Finally, we replace part of silica fume by Epcat in the composition of reactive powder concrete (RPC). When the replacement of silica fume is up to 67%, the compressive strength of the resulting RPC cured at 3, 7 and 28 days are 72, 100 and 115 MPa, respectively. These strength values are 14~30% higher than that of the control. The increase on the compressive strength is due to higher pozzolanic reactivity of Epcat relative to silica fume.
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