Abdulrahman Alhozaimy

Development and Characterization of Hybrid Polyethylene Fiber Reinforced Cement Composites

Research is reported that optimized the combined use of two different fiber types in cementitious matrixes. The two fiber types were a high modulus polyethylene fiber and a fibrillated polyethylene pulp. The details of the study are described, and it is noted that in the case of impact resistance, the positive effect of each fiber was pronounced in the presence of the other fiber type. For flexural strength and toughness, the combined use of polyethylene fiber and pulp produced desirable results as long as the amounts incorporated were below certain limits. The negative effects of fibers on compressive strength were less pronounced when the two fiber types were used in combination. The interactions between polyethylene fiber and pulp in deciding the specific gravity, volume of permeable pores, and water absorption capacity of cementitious materials were either negligible or only moderately significant.

Role of Manganese Sulfide Inclusions in Steel Rebar in the Formation and Breakdown of Passive Films in Concrete Pore Solutions

This study examined manganese sulfide (MnS) inclusions in steel rebar exposed to a simulated concrete pore solution to understand their role in passive film, corrosion, and pit propagation behavior. The passive film was characterized using x-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and electrochemical techniques. The results showed that MnS inclusions adversely affected the nature of the passive film and accelerated corrosion and pit formation. A schematic model was developed to explain the deterioration of passive film formed on steel containing MnS inclusions, and was validated by Raman spectroscopy of the resulting rust formed on such steel.

Development and characterization of hybrid polyethylene-fibre-reinforced cement composites

Abstract The research reported here is concerned with optimizing the combined use of two different fibre types in cementitious matrices. The two fibre types were a high-modulus polyethylene fibre and a fibrillated polyethylene pulp. The effects of different volume fractions of the two fibres and their interaction on the impact resistance, flexural strength and toughness, compressive strength, bulk specific gravity, volume of permeable pores and water absorption capacity of cementitious materials manufactured with a high-performance mixer were investigated through a factorial experimental design. In the case of impact resistance, the positive effect of each fibre was pronounced in the presence of the other fibre type. For flexural strength and toughness, the combined use of polyethylene fibre and pulp produced desirable results as long as the amounts incorporated were below certain limits. The negative effects of fibres on compressive strength were less pronounced when the two fibre types were used in combination. The interactions between polyethylene fibre and pulp in deciding the specific gravity, volume of permeable pores and water absorption capacity of cementitious materials were either negligible or only moderately significant.

Behavior of Wide Shallow RC Beams Strengthened with CFRP Reinforcement

One-way reinforced concrete joist floors with wide shallow beams (WSBs) are used widely in building construction throughout the Middle East. The short- and long-term behavior of WSBs externally strengthened with carbon fiber-reinforced polymer (CFRP) reinforcement was studied on isolated beams and as part of full-scale building. This paper presents the results of the experimental investigation on the flexural performance of isolated WSBs externally strengthened with CFRP reinforcement. A total of six full-scale beams were constructed and tested to failure. The test variables were the amount, type, configuration, and the elastic modulus of CFRP reinforcement. The test results were presented in terms of deflections, ultimate capacities and modes of failure, crack width development, and strains in reinforcement and concrete. The test results showed significant improvement in the flexural performance of the strengthened beams with respect to flexural capacity, flexural stiffness, and crack width. All but one of the strengthened beams failed because of the debonding of CFRP reinforcement; however, the load carrying capacity of WSBs were more than that predicted by relevant design guidelines.

Mechanism of Nucleation and Growth of Passive Film on Steel Reinforcing Bar at Different Durations of its Exposure in Concrete Pore Solution at Nanoscale

The nanoscale passive film formation on steel reinforcing bars at different stages of their exposure in concrete pore solution is characterized by the application of atomic force microscopy, Raman spectroscopy, electrochemical impedance spectroscopy, electrochemical noise, and cyclic voltametry studies. Based on this, a new description of the sequence of reactions during the formation of passive film on steel reinforcing bars is suggested in this paper. The results generated during this investigation revealed that the surface of the steel reinforcing bars prior to their embedding in a concrete pore solution remain covered with a film of ferric hydroxide (Fe(OH)₃). The passive film on the reinforcing bars is formed by the dissolution of this oxide film followed by a series of chemical reactions. The nanotechnological investigations conducted in this paper indicated that a protective passive film on a reinforcing bar’s surface develops within 24 hours of its exposure to the concrete pore solution. Further exposure helps growth of the film over a period of up to 7 days. Beyond this period of exposure, no significant changes in either the structure or the protective property of the film are recorded. In solid concrete, however, the film formation and its growth is slow compared with the concrete pore solution, and a minimum period of 20 days is needed to form a complete protective film on the reinforcing bars embedded in concrete.

Impact of Extremely Hot Weather and Mixing Method on Changes in Properties of Ready Mixed Concrete during Delivery

Riyadh is located in central Saudi Arabia. Its extremely hot, dry environment was used to investigate concrete compressive strength, slump, and temperature changes during ready mixed concrete (RMC) delivery. Representing three plants employing a truck-mixing method and three plants employing a central-mixing method in their operations, testing was performed using a total of 80 delivery trucks. Differences in RMC property changes that were not significant were indicated by study results during delivery in both Riyadhs extremely hot, dry summertime environmental conditions and the midwestern United States much milder summer conditions. The study showed that during summertime delivery, concrete slump lost 37% of its initial value and concrete temperature increased by an average of 1.1 degrees Celsius (2.0 degrees Fahrenheit). There was a slightly higher compressive strength at the site than at the plant. Long travel times did not significantly affect compressive strength. Effective control of adverse hot weather effects on concrete production and delivery, even under the regions extremely hot prevailing weather conditions, was shown possible by controlling concrete temperature, avoiding delivery during noon hours, and using water-reducing and retarding admixtures, per ACI 305R recommendations. In this study, there was no observation of the anticipated increased slump loss rate problem associated with hot weather use of water-reducing and retarding admixtures.

Evaluation of Powdered Scoria Rocks from Various Volcanic Lava Fields as Cementitious Material

AbstractIn this study, the large deposits of volcanic scoria rocks (SRs) of the Arabian Peninsula were investigated as cement replacement materials. The powdered SRs procured from three separate regions (SR1, SR2, and SR3) were incorporated in concrete mixtures at three replacement levels (10%, 20% ,and 30%, by cement weight). Additionally, two reference concrete mixtures with silica fume (SF) and ground quartz sand (GS) were fabricated for benchmarking. Fresh properties, compressive strength, chloride-ion penetration resistance, and pore-size distribution from mercury intrusion porosimetry (MIP) were obtained. Microstructural and elemental spot analyses using field emission scanning electron microscopy (FESEM) analyses of samples from concrete mixtures were performed. The results showed that powdered SR samples exhibit clear variations in morphology and mineralogical compositions depending on the volcanic lava field. The strength activity index (SAI) of SR3 was higher than SR1 and SR2 indicating higher p...

Accelerated Rusting of Reinforcing Bars: The Role of Manganese Alloying in Concrete Reinforcement Steel Bars

The role of alloying of manganese in mild carbon steel reinforcing bar on the rate of atmospheric rusting is investigated. Four types of steel reinforcing bar from different producers having variations in the rate of atmospheric rusting were collected and exposed to the atmosphere of Jamshedpur, India for 3 years. The corrosion rates of the exposed reinforcing bar samples were evaluated by determining the loss in weight of the samples. A direct relationship has been recorded between the rate of corrosion and the manganese content in the steel. The corrosion products formed on the surface of the exposed reinforcing bar samples were characterized by Raman spectroscopy and X-ray diffraction techniques. Electro-chemical impedance spectroscopy and DC polarization studies of the reinforcing bar samples were also performed to understand the causes for the difference in their rates of rusting. The mechanism for the accelerated rate of rusting recorded for the higher manganese-containing steel is discussed by proposing a schematic model incorporating different stages of reactions.

Effect of Reinforcing Bar Microstructure on Passive Film Exposed to Simulated Concrete Pore Solution

Use of thermomechanically treated (TMT) reinforcing bars has become popular in the concrete construction industry after their introduction in the 1980s. This can be attributed to the fact that thermomechanical treatment enhances the strength and ductility of reinforcing bars remarkably. However; limited research is available on the corrosion behavior of TMT reinforcing bars after they are embedded in concrete. To enhance knowledge and insights into this area, the authors investigated the protective properties of two types of steel reinforcement bars (reinforcing bars)-namely tempered martensite (TM) and pearlite-ferrite (PF)-after exposing them to concrete pore solution. The microstructures of both types of reinforcing bars were investigated, and their kinetics of growth and mechanism of nucleation were recorded by employing electrochemical impedance spectroscopy and polarization. Studies reveal that protective film on the surface of steel with TM microstructure develops at a significantly higher rate and is more stable compared to that on steel with PF microstructure. This superior protective nature is attributed to the development of a compact and adherent oxide film on TM steel. A model is proposed to explain the results obtained during the study. Raman spectroscopy of passive films formed on the surface of reinforcing bars exposed to concrete pore solution supports the proposed model.

Protection against Reinforcement Corrosion Using Phosphoric Acid-Based Rust Converter

The protective properties of a newly developed phosphoric acid based rust converter are investigated for reinforcement corrosion under chloride-contaminated concrete environment. The electrochemical evaluation of specimens after 6 years (2 years of wet-dry exposure in 3.5% sodium chloride solution and 4 years in dry laboratory environment) demonstrated that treating the reinforcing bar with the newly developed product significantly reduced the corrosion rate compared to the control reinforcing bar. Based on the results of Raman spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy, a new mechanism is described for the transformation of unstable rust phases into stable phases. It is observed that iron phosphate remains entrapped with corrosion products formed on the surface of the treated steel reinforcing bar, even after 6 years of exposure.