Abdulrahman M. Alhozaimy

Mechanical properties of polypropylene fiber reinforced concrete and the effects of pozzolanic materials

Abstract A comprehensive set of experimental data were generated regarding the effects of collated fibrillated polypropylene fibers at relatively low volume fractions (below 0.3%) on the compressive, flexural and impact properties of concrete materials with different binder compositions. Statistical analysis of results produced reliable conclusions on the mechanical properties of polypropylene fiber reinforced, concrete and also on the interaction of fibers and pozzolanic admixtures in deciding these properties. Polypropylene fibers were observed to have no statistically significant effects on compressive or flexural strength of concrete, while flexural toughness and impact resistance showed an increase in the presence of polypropylene fibers. Positive interactions were also detected between fibers and pozzolans.

Ductility of Concrete Beams Reinforced with FRP Bars and Steel Fibers

A total of 18 concrete beams were tested to study the influence of adding steel fibers (SF) to concrete mix on the ductility of concrete beams reinforced with fiber reinforced plastics bars (FRP beams). The main variables in the study were the type and volume fraction of the steel fiber. The study also investigated the accuracy of an available model, developed originally to predict the flexural strength of concrete beams reinforced with SF and steel bars (SF-steel beams), after modification in estimating the flexural capacity of the fibrous FRP beams (SF-FRP beams). The results indicate that the ductility of FRP beams is less than 50% of that of the respective steel beams. The results also reveal that the ductility of SF-FRP beams is directly related to the fiber content. In addition, the test results show that inclusion of 1% of hooked SF can improve the ductility of FRP beams to be the same as that of the steel beams. Furthermore, comparison between the predicted and measured flexural capacity of SF-FRP beams shows that the modified model can predict the measured results within a reasonable accuracy.

Investigation of effect of fineness dependent volume of fine aggregate on passive layer formation and corresponding corrosion of steel reinforced concrete using electrochemical approach

Abstract This paper aims to determine the effect of the fineness modulus of fine aggregate on the quality and development of passive film and its subsequent effect on the corrosion of reinforced concrete structures. The study uses both electrochemical laboratory controlled experimentation and finite element modelling approach. Corrosion is an electrochemical process that requires an electrolyte for the occurrence of a corrosion reaction. Therefore, it is necessary to calculate the effective corrosion rate with reference to the saturated area of the concrete only when there is corrosion of reinforced concrete structures. Theoretically and numerically, the saturated area depends on the capillary zone porosity, gel zone porosity and degree of saturation in the aggregate free volume of concrete, which is a heterogeneous material. It is thus important to understand the effect of aggregate fineness on the corrosion of steel rebars. Therefore, detailed investigations were conducted using a variety of fine aggregates and combinations thereof. The initiative for this research came from the observation that the interfacial transition zone (ITZ) around the steel bar in concrete does not contain coarse aggregate, but could be surrounded by mortar and not only paste. Hence, the fine aggregate volume may also influence the corrosion rate. Some fine aggregate, which is finer than coarse aggregate, could be present in the vicinity of the steel bar surface, depending on the fineness modulus, which may affect both the development of the passive layer and the corrosion rate. The previous research data in this area were found to be limited. Hence, these factors have been investigated in the present study. Both mortar and concrete prismatic specimens were cast, and the quality of passive layer development and the corrosion severity were compared between specimens to determine the effect of fine aggregate volume with respect to the respective fineness modulus values. The corrosion potential, current and rate values obtained through experimentation showed significant differences in their magnitudes with respect to the variation in the fineness modulus. A directly proportional relation was observed between the fineness modulus of fine aggregate and the corrosion of rebars. Therefore, in the light of the experimental results obtained in this study, a finite element based numerical model incorporating the effect of the fineness modulus of fine aggregate on corrosion of steel rebars in concrete has been developed and successfully verified in this study.

Use of fine ground dune sand as a supplementary cementing material

AbstractThe process of Portland cement production is associated with high consumption of energy and resources. Therefore, there is a need to replace the Portland cement with environmental friendly materials. This study was conducted to determine the feasibility of using ground dune sand as cement replacement materials under different curing conditions. Portland cement was replaced by ground dune sand at five levels of replacement (0–40% by weight). The compressive strength of mortar under standard and autoclave curing conditions and the influence of different autoclave temperatures and durations were investigated. The microstructure of selected mixtures was analyzed by XRD and SEM. Results showed that the compressive strength under the standard curing decreased as the level of replacement increased. However, under autoclave curing compressive strength increased as the content of ground dune sand increased. XRD and SEM revealed the absence of calcium hydroxide and the formation of secondary calcium silicat...

Effect of various activation methods on the reactivity of ground dune sand as partial cement replacement

Dune sand obtained in the vicinity of Riyadh, Saudi Arabia was investigated to be used as partial cement replacement materials. Physical and chemical properties of dune sand were evaluated. Dune sand is inert and chemically inactive under normal curing condition. In this study, three different methods including chemical, mechanical and thermal activation were employed to enhance the reactivity of dune sand. The final products obtained were further analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), differential thermal analysis (DTA) and the thermogravimetric analysis (TGA) to investigate the promoting mechanism of the compressive strength. Replacement of cement with 30% dune sand displayed the highest compressive strength and lowest free Ca(OH)2 content when it was subjected to the thermal activation under autoclave curing.