Setting Times of Portland Cement Blended with Locust Bean Pod and Eggshell Ashes
Olubajo Olumide Olu,
Osha Odey Ade,
Abubakar Jibril
Issue:
Volume 8, Issue 5, September 2020
Pages:
103-111
Received:
2 September 2020
Accepted:
18 September 2020
Published:
28 September 2020
Abstract: This paper investigates the potentials of replacing cement with Locust beans pod ash (LBPA) and Eggshell ash (ESA) on the setting time properties of cement blends such as consistency and initial and final setting times. It also covers a comparative analysis on consistency and setting time results of the cement blends and control. The consistency and setting times of control and twenty-eight (28) cement blends were conducted via Vicat apparatus and Toniest machine respectively according to ASTM standards. The locust bean pod and eggshell powder were calcined at 850°C and 500°C for 1 hour respectively to obtain the LBPA and ESA. Results indicated a variation in the water consistencies of cement blended with either/both ashes at various LBPA/LBPA-ESA ratios as cement replacement was increased from 0-10 wt.%. The increase in the water consistencies could be attributed to the diminution of C3S in cement, the unburnt carbon present in the ashes coupled with the porous nature of LBPA and narrower particle size distributions of the cement blends. Whereas, the decrease in the water consistency could be linked with wider particle size distribution. The initial setting times of LBPA cement blends experienced a series of retardations and acceleration while the final setting time experienced a series of accelerations and elongations as the cement replacement was increased. On the other hand, as the cement replacement level was increased, the initial and final setting time of ESA cement blends experienced a retardation followed by accelerations and a series of accelerations and retardations respectively. Similarly, the replacement of ESA with LBPA at various cement replacement led to a variation in both setting times (series of accelerations and retardations) of cement blends. The retardation in the setting times could be linked to the diminution of clinker content or formation of magnesium hydroxide Mg(OH)2, the presence of unburnt carbon in ashes and narrower particle size distribution of the cement blends while the acceleration of the setting times are related to interaction between tricalcium aluminate and limestone to favor ettringite at the expense of monosulfate and a wider particle size distribution of the cement blends. Most of the setting time results for cement blends except 7.5 and 10 wt.% LBPA cement blends were higher than control and all the cement blends were found to fall within standards for various applications.
Abstract: This paper investigates the potentials of replacing cement with Locust beans pod ash (LBPA) and Eggshell ash (ESA) on the setting time properties of cement blends such as consistency and initial and final setting times. It also covers a comparative analysis on consistency and setting time results of the cement blends and control. The consistency an...
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Simulating the Effects of Poisoning on the Rate of the Oxidation of Ammonia over a V2O5/TiO2 Monolithic Diesel SCR Catalyst Using a Multichannel Model
Clas Ulf Ingemar Odenbrand
Issue:
Volume 8, Issue 5, September 2020
Pages:
112-124
Received:
2 September 2020
Accepted:
19 September 2020
Published:
30 October 2020
Abstract: The background to this study is the need to find out if some reactions of O2 oxidation of ammonia oxidation are important in the Selective Catalytic Reduction (SCR) of NO by NH3. The objective of the study was to shed light on the influence of poisoning on these reactions over a diesel SCR catalyst by compounds in the exhaust gases. The method used was to experimentally determine the amounts of products formed at several temperatures and compared them to simulated values. About 700 ppm NH3 was oxidized by 2% O2 in helium yielding N2, N2O, and NO at increasing temperatures. Comparisons are given for a 4.56% vanadia on titania fresh catalyst and the ones used for 890 and 2299 h. The kinetics was simulated using a multichannel model of the monolithic catalyst. The experimental values of the products were nicely fitted by the kinetic model where all three ammonia oxidation reaction rates were of the first order in the concentration of ammonia. The fit was somewhat better for the non-isothermal case than the isothermal one. The deactivation reduces the activation energies for the formation of all products. Effects of flow and concentration maldistribution are shown to be present but are quite small. The temperature increase is 1.30 K for the most active catalyst at the highest temperature (733 K). The use of the multichannel model shows that quite considerable deviations in inlet ammonia concentrations are obtained over the catalyst cross section. This means that the catalyst is not used to its full potential.
Abstract: The background to this study is the need to find out if some reactions of O2 oxidation of ammonia oxidation are important in the Selective Catalytic Reduction (SCR) of NO by NH3. The objective of the study was to shed light on the influence of poisoning on these reactions over a diesel SCR catalyst by compounds in the exhaust gases. The method used...
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