Effect of reinforcement on plastic shrinkage and settlement of self-consolidating concrete as repair material

The experimental investigation on plastic shrinkage and plastic settlement for different self-consolidating concrete (SCC) mixtures as repairing materials is presented. The concrete mixtures were placed on the surface of the concrete substrate slabs at different restraint degrees. Four different types of repairing materials such as plain SCC, SCC with silica fume (SF), SCC with latex and SF, and SCC with latex, SF and fiber were evaluated. The slabs included both reinforcement and without reinforcing bars. The tests involved measurement of concrete bleeding and evaporation rates, steel bar strains and crack characteristics. The results indicated that bleeding rate is not the only controlling factor, but restraint condition, configuration of steel bars and the concrete strain capacity are also affect plastic shrinkage and settlement behaviors significantly. Latex and fiber were found to be effective in reduction of cracks and concrete strains. Cracks did not develop on the surface of concrete containing latex and fiber. The results showed that if a slab is reinforced by one single bar (in each direction of the slab), at relatively large diameter as used in this study, it would not improve the plastic shrinkage behavior, although it causes plastic settlement cracking.     

Influence of thermal and chemical pretreatment on structural stability of granular sludge for high-rate hydrogen production in an UASB bioreactor

Fermentation of organic waste materials presents an alternate route instead of photosynthetic and chemical routes for hydrogen production. Low yield of biohydrogen production is the major challenge in the fermentative hydrogen-producing technology. Improvement of fermentation process by various sludge pretreatment methods is one of the ways that have been applied to boost hydrogen productivity. This study sheds new light on the impact of thermal and chemical pretreatments on the hydrogen-producing granular sludge morphology and strength as well as up-flow anaerobic sludge blanket (UASB) reactor performance treating palm oil mill effluent (POME). Thermal pretreatment showed devastating effects on the morphological and structural characteristics of the granules. However, the chemically pretreated granules remained structurally stable and relatively undamaged. The thermal pretreatment increased the cumulative hydrogen production by 40% and 76% over chemical pretreatment and control test (untreated), respectively.     

Hydrogen generation from the ball milled composites of sodium and lithium borohydride (NaBH4/LiBH4) and magnesium hydroxide (Mg(OH)2) without and with the nanometric nickel (Ni) additive

The composites of (NaBH₄+2Mg(OH)₂) and (LiBH₄+2Mg(OH)₂) without and with nanometric Ni (n-Ni) added as a potential catalyst were synthesized by high energy ball milling. The ball milled NaBH₄-based composite desorbs hydrogen in one exothermic reaction in contrast to its LiBH₄-based counterpart which dehydrogenates in two reactions: an exothermic and endothermic. The NaBH₄-based composite starts desorbing hydrogen at 240 °C. Its ball milled LiBH₄-based counterpart starts desorbing at 200 °C. The latter initially desorbs hydrogen rapidly but then the rate of desorption suddenly decelerates. The estimated apparent activation energy for the NaBH₄-based composite without and with n-Ni is equal to 152 ± 2.2 and 157 ± 0.9 kJ/mol, respectively. In contrast, the apparent activation energy for the initial rapid dehydrogenation for the LiBH₄-based composite is very low being equal to 47 ± 2 and 38 ± 9 kJ/mol for the composite without and with the n-Ni additive, respectively. XRD phase studies after volumetric isothermal dehydrogenation tests show the presence of NaBO₂ and MgO for the NaBH₄-based composite. For the LiBH₄-based composite phases such as MgO, Li₃BO₃, MgB₂, MgB₆ are the products of the first exothermic reaction which has a theoretical H₂ capacity of 8.1 wt.%. However, for reasons which are not quite clear, the first reaction never goes to full completion even at 300 °C desorbing ∼4.5 wt.% H₂ at this temperature. The products of the second endothermic reaction for the LiBH₄-based composite are MgO, MgB₆, B and LiMgBO₃ and the reaction has a theoretical H₂ capacity of 2.26 wt.%. The effect of the addition of 5 wt.% nanometric Ni on the dehydrogenation behavior of both the NaBH₄-and LiBH₄-based composites is rather negligible. The n-Ni additive may not be the optimal catalyst for these hydride composite systems although more tests are required since only one n-Ni content was examined.     

Performance of stop-and-wait protocols over high-delay links

The performance of stop-and-wait protocols over links with high propagation delay such as satellite links is discussed. Primary focus is placed on situations where a large block size is employed to compensate for the loss of throughput caused by the large propagation delay. Possible loss in data intergrity due to undetected errors is investigated. The results show that in most environments, acceptably high throughput can be obtained without sacrificing data integrity.     

Investigation on the photocatalytic behaviors of europium carbonate and oxide nanoparticles prepared based on statistically optimized carbonation and calcination routes

This study is focused on evaluating the photocatalytic properties of the europium carbonate and oxide nanoparticles synthesized via optimizing the direct precipitation and decomposition of the precipitate as a precursor into europium oxide by thermal decomposition. The emphasis was directed towards determining the optimal reaction conditions. To this end, the Taguchi method was used to determine the best parameters for the reaction. The carbonate product at this stage, was used in a further step where it underwent a one-step calcinations treatment leading to its decomposition into europium oxide nanoparticles. The nanoparticles were next characterized using X-ray diffraction, SEM, FT-IR and thermal analysis techniques. Then, the photocatalytic behaviors of the europium carbonate and oxide nanoparticles for the photocatalytic degradation of methyl orange under ultraviolet light was investigated and the results exhibited efficient degradation of the target in the presence of both nanoparticles as photocatalysts.     

SOCIAL ATTITUDES AND TRAFFIC NOISE: A Study in Riyadh,Saudi Arabia

ABSTRACT: The authors monitored road traffic noise and surveyed public attitudes in Riyadh, the most rapidly developing urban area in the Kingdom of Saudi Arabia. The specific aims of their study were to measure the levels of traffic noise along heavily traveled arterial roadways, to determine the attitudes of individuals exposed to traffic noise, and to determine the degree of association between noise and social attitudes. The feasibility of implementing a traffic noise control policy, based on the findings of the study, is discussed.