Reactivity of reclaimed concrete aggregate produced from concrete affected by alkali-silica reaction

This paper presents results from a research program that focused on studying the reactivity of reclaimed concrete aggregate (RCA) produced from concrete affected by alkali-silica reaction (ASR). The results showed that RCA produced from ASR-affected concrete causes significant expansion when used in new concrete. The expansion was similar to that produced in concrete containing the reactive aggregate used originally in the old concrete. It is believed that crushing the old concrete exposed fresh faces of the reactive aggregate which causes renewed reaction and expansion in the new concrete. The alkalis contributed from the RCA are also believed to contribute to the expansion. The amount of supplementary cementing materials required to mitigate the expansion in new concrete containing ASR-affected RCA was higher than those normally needed in concrete containing the virgin reactive aggregate. The results showed a good agreement between the 14-day expansion of accelerated mortar bars and the expansion of concrete prisms.     

Speech coding using Best Tree Encoding (BTE) technique based on LPC and trigonometric features

Over the past several years there has been considerable attention focused on coding and enhancement of speech signals. This interest is progressed towards the development of new techniques capable of producing good quality speech at the output. Speech coding is a process of converting human speech into efficient encoded representations that can be decoded to produce a close approximation of the original signal. This paper deals with the problem of speech coding. It proposes novel approach called Best Tree Encoding (BTE) to encode the wavelet packet Best Tree Structure into a vector of four elements. This research is introducing BTE for solving another problem for speech compression and syntheses. Tree node data coefficients are encoded using LPC Filters and trigonometric features. The encoded vector consists of 4 elements from BTE analysis as well as LPC and trigonometric vector for each leaf node. The quality of the reproduced speech is evaluated for both understanding and quality. The quality of speech signal is measured on the basis of signal to noise ratio, log likelihood ratio, and spectral distortion.     

Effect of processing on flavor precursor amino acids and volatiles of sesame paste (tehina)

The content of flavor precursor free amino acids in dehulled sesame seeds, subjected to roasting (R), steaming (S), roasting plus steaming (RS) and microwaving (M), was determined and compared with those of the raw (RW) seeds. R, RS, and S had major effects in reducing the content of free amino acids from 2360 μg/g to 582, 795 and 884 μg/g, respectively; M had no effect on the content of free amino acids. Meanwhile, flavor volatiles of the raw and processed seeds were compared by means of a dynamic headspace analyzer/gas chromatograph-mass spectrometer. Volatiles of RW seeds contained 85 compounds, whereas under the analytical conditions employed, seeds subjected to R, RS, S, and M had 117, 97, 93 and 87 compounds, respectively. Among volatiles identified in the RW seeds were 36 hydrocarbons, 8 aldehydes, 4 ketones, 8 alcohols, 2 acids, 2 esters, and 1 pyrazine. The only pyrazine identified in the RW seeds was 2,5-dimethylpyrazine. Pyrazines, generally recognized as contributors to the roasted aroma of foods, were more numerous (10 in R, 6 in RS, 2 in S, and 2 in M) and prevalent (8.71% in R, 2.97% in RS, 2.04% in S, 0.53% in M, and 0.25% in RW) in the volatiles of processed sesame seeds. The chemical nature of pyrazines also depended on the process employed. Multivariant analysis indicated a highly negative correlation between the loss of free amino acids and production of volatile flavor compounds in the R and RS samples, while the M sample remained unchanged. Furthermore, both R and RS seeds contained dimethyl sulfide and dimethyl disulfide, whereas no sulfur-containing compounds were present in other samples. Of the processed seeds, the flavors of R and RS samples were considered as acceptable, and the flavor intensity of the former was deemed stronger than that of the latter by the experimenters.     

Mineralogical and chemical assessment of concrete damaged by the oxidation of sulfide-bearing aggregates: Importance of thaumasite formation on reaction mechanisms

Damages in concrete containing sulfide-bearing aggregates were recently observed in the Trois-Rivières area (Quebec, Canada), characterized by rapid deterioration within 3 to 5 years after construction. A petrographic examination of concrete core samples was carried out using a combination of tools including: stereomicroscopic evaluation, polarized light microscopy, scanning electron microscopy, X-ray diffraction and electron microprobe analysis.The aggregate used to produce concrete was an intrusive igneous rock with different metamorphism degrees and various proportions of sulfide minerals. In the rock, sulfide minerals were often surrounded by a thin layer of carbonate minerals (siderite). Secondary reaction products observed in the damaged concrete include “rust” mineral forms (e.g. ferric oxyhydroxides such as goethite, limonite (FeO (OH) nH₂O) and ferrihydrite), gypsum, ettringite and thaumasite. In the presence of water and oxygen, pyrrhotite oxidizes to form iron oxyhydroxides and sulphuric acid. The acid then reacts with the phases of the cement paste/aggregate and provokes the formation of sulfate minerals. Understanding both mechanisms, oxidation and internal sulfate attack, is important to be able to duplicate the damaging reaction in laboratory conditions, thus allowing the development of a performance test for evaluating the potential for deleterious expansion in concrete associated with sulfide-bearing aggregates.     

The use of gamma irradiation to induce the miscibility between urea‐formaldehyde and vinyl acetate versatic ester copolymer latex blend

The objective of this research was to investigate the miscibility behavior of urea‐formaldehyde (UF) resin and vinyl acetate versatic ester copolymer latex (VAcVe) blends. Blend of various compositions of UF resin as thermoset polymer and VAcVe as thermoplastic polymer were prepared. This study shows how the addition of VAcVe latex can alter the behavior of UF resin toward hardness, press‐ability, and inhibition of cracks occurred in the UF resin films and moulds. After that, these blends (UF/VAcVe) were irradiated with gamma rays in different doses. Physical properties such as solubility percent, water absorption behavior in water, and effect of dilute acid and dilute alkali were studied. Thermogravimetric analysis shows that VAcVe is more stable against thermal decomposition than UF resin over the entire temperature range studied. Also, the thermal stability of polymer blends (UF/VAcVe) increases with increasing the ratio of VAcVe component in the blend. The influence of addition of VAcVe on compressive strength was studied. The results showed an improvement with a decrease in compressive strength due to the flexibility, this improvement is related to the amount of VAcVe. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of pore size on the tensile behavior of open-cell Ti foams: Experimental results

Open-cell Ti foams having an average pore size of 50 and 150 µm, respectively have been subjected to room temperature tensile tests to explore their tensile properties. Since extensometry is difficult in foams due to problems such as localized surface deformation and attachment of clip gauges, the foams' mechanical properties have been measured in this work accurately by the help of a camera which records the resulting dimensional changes during the loading. The camera acts as a non-contact extensometer and thus it helps in avoiding any small amounts of pre-deformation that might be caused by the attachment of conventional extensometer to the sample's surface prior to testing. Ti foam samples of smaller pores were found to experience higher strength and elongation than those with larger ones. The cell walls in both foam samples failed suddenly in the 45° maximum shear plane direction.     

Drinking Water Treatment Options for Eliminating Freshwater Algae

A massive mixed algal growth may have many adverse effects on the water quality and causes acute problems, especially in different treatment steps for the production of drinking water. The effectiveness of drinking water treatment options for eliminating the nuisance created by River Nile water algae was the main objective of this study. The algal removal rate increased when using oxidants combined with alum-potassium permanganate; this was the most effective treatment combination for algal removal. When natural flocculant seeds of Moringa oleifera were used, the algal removal rate increased by more than 18% than that obtained by a chemical coagulant.     

Corrosion and Corrosion Inhibition of Steel Pipelines in Montmorillonitic Soil Filling Material

Silicon - Buried steel pipelines pass through different soils therefore; it could be subjected to dissimilar soil corrosion. A possible way to overcome this problem is using one kind of soil as...     

THERMODYNAMICS OF COBALT(II) EXTRACTION BYTHENOYLTRIFLOUROACETONE AND DIBENZO-18-CROWN-6 IN NITROBENZENE-TOLUENE MIXTURES

Cobalt (II) was extracted by thenoyltrifluoroacetone (HTTA) and its mixture with dibenzo-18-crown-6(Dbl8C6) at different temperatures in nitrobenzene (Nb); toluene (Tol) or their mixtures, from perchlorate aqueous media of constant ionic strength (o.l;H⁺,NaClO₄) buffered with acetic acid-sodium acetate solutions. Slop analysis of the experimental results indicated that the stoichiometry of the chelate and the adduct extracted are Co(TTA)₂and Co(TTA)₂?Dbl8C6, under all the experimental conditions investigated. The extraction constants of the chelate (k₂o)’ tne mixed species (k_2land the formation constant of the adduct ( B_2lwere evaluated for the different diluents used at the different temperatures. It was found that log k_2oand log_2lincrease by increasing the dielectric constant (€ ) of the diluent whereby log B_2ldecreases by increasing €. These results were expressed in terms of linear free energy relationships. From the effect of the temperature on the different constants evaluated; the thermodynamic constants of the systems were calculated and discussed in terms of the nonspecific effect of the diluents used and the dehydration of the extracted chelate to form the adduct.     

SYNERGIC EXTRACTION OF COBALT(II) BY STRUCTURALLY RELATED CROWN ETHERS AND THENOYLTRIFLUOROACETONE

ABSTRACT

Cobalt (II) was extracted from perchlorate aqueous media by thenoyltrifluoroacetone (HTTA)alone and mixed with 12-Crown-4 (12C4) 15-Crown-5 (15C5) 18-Crown-6 (18C6)dibenzo-18-Crown-6 (Dbl8C6)dicyclohexyl-18-Crown-6 (Dchl8C6) or dicyclohexyl-24-Crown-8 (Dch24C8), in chloroform. The extraction constant of the chelate (K20) the extraction constant of the mixed species (K21), the synergic factor (S.F.) and the formation constant of the extracted adducts (β₂₁) were evaluated. The adduct stoichiometry was found to have the general formula Co(TTA)₂CE, irrespective of the crown ether (CE) used. It was found that no specific cavity size is required for the adduct formation. The synergic values K₂₁, S.F., and β₂₁as related to the crown ether took the order Dch24C8 > 18C6 > Dchl8C6 > 15C5 > Dbl8C6 > 12C4, which could be explained in terms of the crown ether basicity rather than the correspondence between the cavity size of the crown ether and the cobalt(II) crystal radii. The sequence 18C6 > Dchl8C6 > Dbl8C6 was interpreted in terms of the withdrawing ability of Dch and Db as substitutes in reducing the basic character of the adjacent crown ether oxygen donors.