Properties of controlled low-strength materials incorporating cement kiln dust and slag

This research evaluated the potential use of cement kiln dust (CKD) together with slag to replace the use of cement in the production of controlled low-strength material (CLSM). The low strength requirements of CLSM compared to conventional concrete enable the use of industrial by-products for the production of CLSM. In this study, the workability-related fresh properties of CLSM mixtures were observed through slump flow diameter, V-funnel flow time and filling capacity. Setting times, temperature rise, air content and unit weight of CLSM mixtures were also determined as part of fresh properties. The hardened properties that were monitored for 28 days included the unconfined compressive strength. The test results presented herein show that a combination of less than 50 kg/m³ slag and up to 300 kg/m³ CKD provides a good mix that satisfies the requirements of a CLSM with similar or better properties to that of CKD-based CLSM mix containing Portland cement. Suitable CLSM mixtures with reasonable fresh and hardened properties could also be developed by using CKD alone. However, reduced strength in such CLSM mixtures may limit their field application. The slag significantly assisted in increasing compressive strength of CKD-based CLSM mixtures. A CLSM mix containing a combination of slag and CKD was shown to have excellent characteristics for flowable backfill and excavatable base material. Therefore, producing CKD/slag based CLSM through the use of co-generated products from the cement and iron manufacturing processes can provide leadership for the construction industry in the transition for sustainable development.     

Performance Evaluation of Cost-Effective Multicast–Unicast Key Management Method

Group key management is one of the key security issues in multicast networks. The main challenge is to provide a secure group key management method which avoids high key update cost in terms of the number of transmitted keys. In order to achieve low key update cost for group key management, most of the existing methods increase their encryption/decryption cycles which requires a strong cryptographic function. In this paper, a cost-effective key management method is proposed to address the problem of high key update cost without increasing the encryption/decryption cycles. We evaluated our proposed method with existing tree-based methods by using Markov chain and Poisson Arrival Process. Results indicate the efficiency of our proposed method in reducing the key update cost significantly compared to the existing tree-based key management methods.     

Antifungal activity of Lactobacillus fermentum Te007, Pediococcus pentosaceus Te010, Lactobacillus pentosus G004, and L. paracasi D5 on selected foods

In the search for new preservatives from natural resources to replace or to reduce the use of chemical preservatives 4 strains of lactic acid bacteria (LAB) were selected to be evaluated for their antifungal activity on selected foods. The supernatants of the selected strains delayed the growth of fungi for 23 to 40 d at 4 °C and 5 to 6 d at 20 and 30 °C in tomato puree, 19 to 29 d at 4 °C and 6 to 12 d at 20 and 30 °C in processed cheese, and 27 to 30 d at 4 °C and 12 to 24 d at 20 and 30 °C in commercial bread. The shelf life of bread with added LAB cells or their supernatants were longer than normal bread. This study demonstrates that Lactobacillus fermentum Te007, Pediococcus pentosaceus Te010, L. pentosus G004, and L. paracasi D5 either the cells or their supernatants could be used as biopreservative in bakery products and other processed foods. PRACTICAL APPLICATION: The heat stability nature of the antifungal compounds produced by the LAB isolates offers a promising application of L. fermentum Te007, P. pentosaceus Te010, L. pentosus G004, and L. paracasi D5 as biopreservative in bakery products or other processed foods to replace or reduce the use of chemical preservatives.     

Improvement in the measurement of spectrophotometric data in the m-hydroxydiphenyl pectin determination methods

In the pectin analysis of foods by visible spectrophotometry using the m-hydroxydiphenyl (MHDP) as the chromogenic reagent, the evolution of the absorbance at 520 nm of the MHDP/5FF chromophore with respect to the elapsed time from the beginning of the reaction for different d-galacturonic acid concentrations was studied.It was observed that after 45 min, the stability of the readings predicted by the different methods was not reached. This evolution depended on the d-galacturonic acid concentration. The need to analyse the samples in sequence was noted, in such a way that after the addition of MHDP, a protocol was established so that the spectrophotometric data measurements taken at the highest absorbance have high reproducibility.     

Numerical investigation of the first bifurcation for the flow in a rotor–stator cavity of radial aspect ratio 10

The nature of transition to unsteadiness of rotor–stator disk flows of large radial aspect ratio is investigated by means of several numerical tools which consist in computing the base flow even when unstable, performing linearized or non-linear time integrations starting from initial conditions of different amplitudes and computing the spectrum of the Jacobian using the ARPACK library. From these numerical experiments we conclude that, in a cavity of radial aspect ratio 10, the transition to unsteadiness occurs through a subcritical Hopf bifurcation. In addition these calculations show the existence of a large amplitude chaotic branch for values of the Reynolds number far below the linear stability threshold, and onto which the solutions are attracted for large subcritical values due to the strong non-normality of the Jacobian of the evolution operator.     

Effect of strontium and zirconium doped barium cerate on the performance of proton ceramic electrolyser cell for syngas production from carbon dioxide and steam

Syngas has been produced from carbon dioxide (CO₂) and steam using a proton ceramic electrolyser cell. Proton-conducting electrolytes which exhibit high conductivity can suffer from low chemical stability. In this study, to optimize both proton conductivity and chemical stability, barium cerate and doped barium cerate are synthesized using solid state reaction method: BaCeO₃ (BC), Ba_0.6Sr_0.4CeO_3-α (BSC), Ba_0.6Sr_0.4Ce_0.9Y_0.1O_3-α (BSCY), and BaCe_0.6Zr_0.4O_3-α (BCZ). The BC, BSC, and BSCY are calcined at 1100 °C for 2 h and BCZ is calcined at 1300 °C for 12 h, respectively. All samples exhibit 100% perovskite and crystallite sizes equal 37.05, 28.46, 23.65 and 17.46 nm for BC, BSC, BSCY and BCZ, respectively. Proton conductivity during steam electrolysis as well as catalytic activity toward the reverse water gas shift reaction (RWGS) is tested between 400 and 800 °C. The conductivity increases with temperature and the values of activation energy of conduction are 64.69, 100.80, 103.78 and 108.12 kJ mol⁻¹ for BSCY, BC, BSC, and BCZ, respectively. It is found that although BCZ exhibits relatively low conductivity, the material provides the highest CO yield at 550–800 °C, followed by BSCY, BSC, and BC, correlating to the crystallite size and BET surface area of the samples. Catalytic activity toward RWGS of composited Cu and electrolytes is also measured. Additional Cu (60 wt%) significantly increases catalytic activity. The CO yield increases from 3.01% (BCZ) to 43.60% (Cu/BCZ) at 600 °C and CO can be produced at temperature below 400 °C. There is no impurity phase detected in BCZ sample after exposure to CO₂-containing gas mixture (600 °C for 5 h) while CeO₂ phase is detected in BSC and BSCY and both CeO₂ and BaO are observed in BC sample.     

The Potential Source of B. licheniformis Contamination During Whey Protein Concentrate 80 Manufacture

The objective of this study was to determine the possible source of predominant Bacillus licheniformis contamination in a whey protein concentrate (WPC) 80 manufacturing plant. Traditionally, microbial contaminants of WPC were believed to grow on the membrane surfaces of the ultrafiltration plant as this represents the largest surface area in the plant. Changes from hot to cold ultrafiltration have reduced the growth potential for bacteria on the membrane surfaces. Our recent studies of WPCs have shown the predominant microflora B. licheniformis would not grow in the membrane plant because of the low temperature (10 °C) and must be growing elsewhere. Contamination of dairy products is mostly due to bacteria being released from biofilm in the processing plant rather from the farm itself. Three different reconstituted WPC media at 1%, 5%, and 20% were used for biofilm growth and our results showed that B. licheniformis formed the best biofilm at 1% (low solids). Further investigations were done using 3 different media; tryptic soy broth, 1% reconstituted WPC80, and 1% reconstituted WPC80 enriched with lactose and minerals to examine biofilm growth of B. licheniformis on stainless steel. Thirty‐three B. licheniformis isolates varied in their ability to form biofilm on stainless steel with stronger biofilm in the presence of minerals. The source of biofilms of thermo‐resistant bacteria such as B. licheniformis is believed to be before the ultrafiltration zone represented by the 1% WPC with lactose and minerals where the whey protein concentration is about 0.6%.     

Optimisation of digestion method for determination of arsenic in shrimp paste sample using atomic absorption spectrometry

The microwave digestion method was developed and verified for the determination of arsenic in shrimp paste samples. Experimental design for five factors (HNO₃ and H₂O₂ volumes, sample weight, microwave power and digestion time) were used for the optimisation of sample digestion. For this purpose, two level half factorial design, which involves 16 experiments, was adopted. The concentration of arsenic was analysed by graphite furnace atomic absorption spectrometry. Design Expert® 7.0 software was used to interpret all data obtained. The combination of 2 mL HNO₃ and 1 mL H₂O₂ volumes, 0.1 g sample weight, 1400 W power and 5 min digestion time was found to be the optimum parameters required to digest the shrimp paste samples. Tests with spiked samples presented good recoveries with relative standard deviations between 0.32% and 5.35%.     

Cocoa (Theobroma cacao) shell-based activated carbon by CO2 activation in removing of Cationic dye from aqueous solution: Kinetics and equilibrium studies

Cocoa shell (CS) was used as a low-cost precursor for production of activated carbon (AC) and evaluated for its ability to adsorb Methylene Blue (MB) dye. Cocoa shell-based pellets were carbonized at 800 °C and subjected to 850 °C under a flow of CO₂ in different activation times. The cocoa (Theobroma cacao) shell-based activated carbon (CSAC) showed moderate surface area with the average pore size 2.7 nm. CSAC also displays the presence of aliphatic, aromatic hydrocarbons and near absence of C–O, carboxylic acid, and the –COOH functional group. Only the presence of O–H groups was detected. The influences of adsorption time and initial dye concentration on adsorption performance have been measured in a batch system. The results are well described by the Freundlich and Langmuir isotherms. The results from the kinetic study show that MB adsorption follows pseudo-second-order and Boyd models, which indicated the MB adsorption on the CSAC was controlled by film diffusion.