A Microwave Transmission Instrument for Rapid Dry Rubber Content Determination in Natural Rubber Latex

We report the design, implementation and testing of an instrument for rapid dry rubber content (DRC) determination in rubber latex. It is composed of rectangular waveguide antennae, microwave generator, power detector, and microcontroller. According to the theory of microwave transmission, the power loss of microwaves passing through latex is related to the DRC. This attenuation is determined by measuring the transmitted microwave intensity with a power detector. The appropriate frequency that gives the best correlation between DRC and attenuation was found to be about 2.36 GHz. The microwave power measurement is processed by the microcontroller using the empirical calibration equation to estimate DRC in rubber latex. The instrument was tested using new latex samples with various DRC, sampled locally in Songkhla province, Thailand, and the DRC estimates by the instrument were compared to the slow but accurate standard oven-drying results. The estimates had an 0.21 % mean error and R ² = 0.9983, indicating good practical performance.     

Performances of SDCM and DCM walls under deep excavation in soft clay: Field tests and 3D simulations

This study presents the results of full-scale tests and three-dimensional finite element analyses of deep cement mixing (DCM) and stiffened deep cement mixing (SDCM) columns under lateral loads and DCM and SDCM walls under deep excavation in soft clay. The DCM walls used in this study comprised one, two and three rows of DCM columns, whereas the SDCM walls consisted of only one row of DCM columns with steel H-beams inserted in either all DCM columns or in alternating DCM columns. The measured and simulated results are presented in terms of profiles of lateral displacement, settlement and bending moment.     

Cytostatic activity of 1,10-phenanthroline derivatives generated by the clip-phen strategy

The cytostatic activities of a series of twelve 1,10-phenanthroline (Phen) derivatives and of their copper complexes were studied on L1210 murine leukemia cells. Large increases in the biological activity were observed for compounds of the 3-Clip-Phen series, in which two Phen moieties were bridged at their C3 positions by an alkoxy linker, the 3-pentyl-Clip-Phen derivative showing an IC(50) value of 130 nM while Phen shows an IC(50) value of 2500 nM under the same conditions. IC(50) values seemed to be modulated not only by the position, the nature, and the length of the linker of Clip-Phen but also by hydrophobicity. Since copper complexes of Phen are chemical nucleases and nucleic acids are thus a potential target for these compounds, the corresponding copper complexes were also studied. Copper complexation of the 3-Clip-Phen ligands did not increase their biological activities. Attempts to vectorize 3-Clip-Phen derivatives with a DNA binder such as spermine or with a cell-penetration peptide failed to increase their biological activity relative to the original 3-Clip-Phen series.     

Fracture of parallel strand lumber (PSL) under impact loading

The behavior of Parallel Strand Lumber (PSL) subjected to impact loading was studied. Eighteen 100 mm ×100 mm×650 mm flexural specimens were tested under both static and impact loading conditions. It was found that the failure modes of PSL were similar under both loading conditions with the specimens failing mostly by a combination of shear and flexural modes. PSL also exhibited stress rate sentitive characteristics; however, the rate sensitivity was affected by the localized damage at the contact surface.

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Résumé Le comportement de composites unidirectionnels à base de bois (PSL) soumis à des tests d'impact a été étudié. Dix-huit éprouvettes de 100×100×650 mm ont été testées en mode statique et en mode impact. Le mode de rupture observé pour chaque type d'essais était similaire: une combinaison d'effets de cisaillement et de flexion. La sensibilité du composite unidirectionnel PSL au taux de déformation a également été vérifiée. Toutefois, cet effet tend à s'amenuiser en raison de l'endommagement localisé aux surfaces de contact.

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Editorial Note Prof. Sidney Mindess is a RILEM Senior Member and a Member of the Board to Editors of the journal Materials and Structures.     

Use of crumb rubber to improve thermal and sound properties of pre-cast concrete panel

In this study, the thermal and sound properties of crumb rubber concrete panel were investigated. The crumb rubber from used tires, produced in a local recycling plant, was used to replace fine aggregate at ratios of 10%, 20% and 30%. Properties such as thermal conductivity, thermal resistivity, heat transfer, conductance value, sound absorption at different frequency and noise reduction were investigated. Results indicated that crumb rubber concrete panel was not only lighter but had higher sound absorption and lower heat transfer properties than the conventional concrete panel.     

Properties of confined fibre-reinforced concrete under uniaxial compressive impact

The effect of confinement on plain and fibre-reinforced concrete (FRC) prisms subjected to uniaxial compressive impact was studied. It was found that the response of the material changed with the degree of confinement. Confined concrete exhibited more ductile behaviour, with both strength (f_c′) and ultimate strain (ε_ult) increasing with the degree of confinement. However, the elastic modulus (E) of the confined specimens was found to be about the same as or slightly lower than those of unconfined prisms. In addition, the relationship between stress and stress rate (n value) was also determined. It was found that, with confinement, the material became more rate sensitive.     

Impact resistance of laterally confined fibre reinforced concrete plates

The effect of both biaxial and uniaxial lateral confinement on fibre reinforced concrete (FRC) plates under transverse impact loading was investigated. It was found that confinement had a major effect on the failure patterns as well as on the mechanical properties of both plain and fibre reinforced concretes. With different types and degrees of confinement, the failure changed from a flexural mode to a punching shear mode or a combined flexural-shear mode. With confinement, the apparent strength of concrete increased by up to two or three times and the inertial load decreased to a small enough fraction of the measured impact load that it could be ignored in the analysis. The ability of the FRC to absorb energy also increased with increasing confinement.

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Résumé Les effets du confinement bi-axial et uni-axial sur les propriétés de plaques de béton renforcé de fibres ont été examinés en conditions de choc. Il a été trouvé que le confinement a des effects majeurs sur le mode de rupture ainsi que sur les propriété mécaniques du béton normal et celles du béton de fibres. Avec un changement de confinement, le mode de rupture a également changé, passant de la flexion au cisaillement. En raison du confinement, la résistance du béton a doublé voire triplé, et le chargement inertiel a été réduit substantiellement. L'absorption d'énergie a aussi augmenté à cause du confinement.

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Editorial Note Prof. Sidney Mindess is a RILEM Senior Member and a Member of the Board of Editors of Material and Structures. Prof. N. Banthia is a Senior Member. He participates in the work of RILEM TCs 162-TDF (Test and design methods for steel fibre reinforced concrete) and 181-EAS (Early age shrinkage induced stresses and cracking in cementitious systems).     

Preliminary study on bullet resistance of double-layer concrete panel made of rubberized and steel fiber reinforced concrete

In this study, the impact resistance of double-layer concrete panels made of rubberized and steel fiber reinforced concrete subjected to direct fire weapon (11 mm or 0.45 magnum bullet size) is investigated. Concrete panels with dimensions of 400 × 400 × 50 mm are subjected to impact forces from 11 mm-diameter bullets at a distance of 10 m. Three types of concrete panels are tested: single-layer steel fiber reinforced concrete (SFRC), single-layer crumb rubber concrete (CRC), and double-layer CRC/SFRC. For a double-layer CRC/SFRC, the CRC layer of 12.5 mm is added to the front surface by partially replacing part of the SFRC panel. The CRC layer is expected to act as a cushion layer to absorb impact energy from the bullet and to reduce damage to the concrete panel.     

Residual flexural behavior of fiber reinforced concrete after heating

In this study, the effects of fire on the flexural performance and residual strength of plain and fiber reinforced concrete are investigated. Three types of concrete are tested: plain, polypropylene (PFRC) and steel fiber reinforced concrete (SFRC). Prior to the flexural test, the specimens were exposed to fire for 15, 30, 45, and 60 min on a furnace. The burnt specimens were then tested under flexural load to measure their toughness and residual strength. Results indicate the reduction of flexural strength for both plain and FRC after being subjected to fire. For FRC, the effect of fire on the flexural response depends mainly on the fiber type and fire exposure duration. For PFRC, the flexural strength is found to drop significantly for every exposure duration, while toughness is found to increase at short exposure duration and then, drop quickly after long exposure duration due to the fiber evaporation effect. For SFRC, the flexural strength and toughness are found to drop gradually for every exposure duration due to the deterioration of cement paste and reduction in bond strength. SFRC exhibits a more consistent ability to maintain load carrying capacity after long exposure to fire than PFRC.