Use of paraffin impregnated lightweight aggregates to improve thermal properties of concrete panels

In this study, the effect of aggregates impregnated with phase change material (paraffin type) on properties of concrete is investigated. The experimental series consists of two stages. The first stage is to investigate the techniques used to impregnate phase changed material (paraffin type) into lightweight aggregates and the properties of aggregates with paraffin inside (PLA). Two impregnation techniques are introduced, (1) heat only and (2) heat and pressure (autoclaving). Using the obtained results, the aggregate with the highest level of impregnation in the shortest time is selected to use in the concrete production process of the next stage. In the second stage, the properties of concrete mixed with non-paraffin and paraffin impregnated lightweight aggregates (PLA) at different proportions are investigated. The experimental series include density and absorption, compressive strength, thermal storage (and insulation) and sound transmission loss. Results in aggregate level show the increase in specific gravity and the decrease in absorption with paraffin inserted into aggregates. In concrete form, the density, compressive strength and sound insulation are found to increase with the PLA replacement ratio. The sound transmission loss, on the other hand, becomes less efficient with increasing PLA replacement ratio.     

Comparative flexural performance of compacted cement-fiber-sand

This research investigates the influence of seven different fiber types on the flexural performance of compacted cement-fiber-sand (CCFS) with four fiber fractions (0.5, 1, 1.5 and 2% by volume). The seven types of fibers are 12?mm polypropylene, 19?mm polypropylene, 40?mm polypropylene, 55?mm polypropylene, 33?mm steel, 50?mm steel and 58?mm polyolefin fibers. The overall CCFS performance was divided into seven sub design performance indicators: (1) peak strength; (2) peak strength ratio; (3) residual strength ratio; (4) ductility index; (5) toughness; (6) equivalent flexural strength ratio; and (7) maximum crack width. The interaction mechanism of the fiber/cement-sand interface was investigated by scanning electron microscopy. Finally, the effectiveness of each fiber type was compared and rated in terms of the overall performance. The results show that the 50?mm steel fiber provided the best overall sub performance, resulting in an excellent overall flexural performance; in comparison, the 12?mm polypropylene fiber exhibited very poor performance. However, the 19?mm polypropylene and 33?mm steel fiber specimens provided very good and good overall performances, respectively. The nature of the fiber surface and the fiber length affects the overall performance of CCFS. The surface of the steel fibers, compared to the other synthetic fiber types, is more hydrophilic and is more compacted in a cemented-sand matrix without separation of the interfacial zone, providing the best overall flexural performance.     

The shear fracture of concrete under impact loading using end confined beams

An investigation of the shear fracture of plain and steel fibre reinforced concrete (SFRC) under impact loading was carried out on both unconfined and confined beams. It was found that confinement played a significant role on the behaviour and properties of both plain and SFRC beams.A shear mode of failure could be obtained with increasing end confinement stresses. End confined concrete beams were stronger and tougher than unconfined ones, as indicated by the increase in both peak load and fracture energy. However, they were found to be less stress rate sensitive than unconfined concrete beams. This was due to the change in the failure mode from flexure to shear with sufficient end confinement. Using end confinement appears to be a promising method for the study of shear fracture in concrete.     

Effect of loading rate on damage of concrete

In this study, damage mechanics theory was used directly to determine the damage of concrete subjected to both static and impact compressive loadings. Two approaches based on the variations of (1) elastic modulus (E) and (2) strain rate (ε), were used. Results from both approaches indicated that the damage to concrete at peak load depended mainly on the rate of loading, as it increased with increasing loading rate. The specimens subjected to impact loading were found to suffer higher damage than those subjected to static loading, as seen by the larger value of D at peak load (0.8-0.9 for concrete subjected to impact loading and 0.65 for concrete subjected to static loading). Beyond the peak, the strain energy was sufficient to cause the damage to increase to one (D=1) without any further applied load.