Abdulaziz I. Al-Negheimish

Investigation of potential uses of electric-arc furnace dust (EAFD) in concrete

This paper presents the results of an investigation for the possible uses of electric-arc furnace dust (EAFD) by-product in concrete manufacturing. The effects of EAFD on the properties of fresh and hardened concrete are investigated. The results of standard tests on fresh concrete indicate that EAFD can be used as an effective set retarder. In addition, other standard tests appear to indicate that EAFD will enhance engineering properties of hardened concrete without any side-effects.

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.

Effect of manufacturing process and rusting on the bond behavior of deformed bars in concrete

The paper presents the results of an experimental program to assess the effects of manufacturing process and rusting due to extended periods of site exposure on the bond behavior of deformed bars in concrete of ordinary strength. The specimens are exposed to seven exposure periods (0, 3, 6, 12, 18, 24 and 36 months) in the severe environment of the Arabian Gulf. A total of 63 pullout tests covering bars with three different geometries and two manufacturing processes are conducted. For each test, the bond stress vs. slip is recorded until failure. Test results have shown that bond performance of the bars is improved by short exposure; however, an extended exposure tends to adversely affect the bond performance. The decrease in bond strength after 36 months of site exposure is found to be about 10% of that of fresh bars. The manufacturing process has significant impact on the mass loss vs. exposure duration with the quenching process showing superior performance compared to the hot-rolled process. However, this is not reflected in the bond performance of bars from the two processes as they showed similar bond behavior irrespective of the manufacturing process.

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.

Effect of basic design parameters on IC debonding of CFRP-strengthened shallow RC beams

Bonding of fiber-reinforced polymer (FRP) plates to the tension face is an effective technique for strengthening reinforced concrete (RC) beams. However, an important design issue is the sudden and premature failure by intermediate crack (IC) debonding of the externally bonded FRP plates from the concrete surface of the strengthened beams. The objective of this paper is to examine the effect of basic design parameters on the IC debonding of the FRP-strengthened RC beams and to assess the accuracy of prediction models of IC debonding in international codes and guidelines. A total of 13 RC beams were constructed and tested for this purpose. The test variables include steel reinforcement ratio, compressive strength of concrete, depth of the beam, and the width of the FRP reinforcement. None of the test variables caused a change in the IC debonding failure mode, except for the strengthened beam with FRP area covering its full width. Among studied variables, only the compressive strength of concrete had a significant effect on the debonding strain of the FRP plates. The results of this experimental work were compared with IC debonding prediction models—currently in effect—of international codes and guidelines. Among these codes, ACI 440.2R-08 and the Italian guide CNR DT200 showed the most accurate and consistent prediction of the IC debonding strain.

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...

Blended Cement Containing High Volume Ground Dune Sand and Ground Granulated Blast Furnace Slag for Autoclave Concrete Industry

This paper presents the results of using ground dune sand (GDS) and ground granulated blast furnace slag (slag) as high volume cement replacement materials. In this study, plain and four blended mixtures were fabricated and cured under normal and autoclave conditions. For the blended mixtures, 40% GDS by weight of the total binder materials and different percentages of slag (15%, 30% and 45%) were incorporated as partial cement replacement materials. The effect of curing conditions (normal and autoclave) on the compressive strength of prepared mixtures was studied. The results showed that, for the autoclave cured mixture, up to 85% of cement can be replaced by GDS and slag without significant drop in the compressive strength. Microstructure analyses using scanning electron microscope (SEM) and X-ray diffraction analysis (XRD) were carried out to examine the microscale changes of the hydrated mixtures. The SEM revealed the formation of thin plate-like calcium silicate hydrate and compacted microstructure of autoclave cured mixture. XRD showed the elimination of calcium hydroxide and existence of residual crystalline silica of all blended mixtures.

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.

Pitting Susceptibility of Concrete Reinforcing Steel Bars Having Manganese Sulfide Inclusions

Long-term wetting-drying treatment of specimens with reinforcing bars having manganese sulfide (MnS) inclusions in their microstructure showed a strong pitting tendency under sufficient chloride concentration. On the other hand, reinforcing bars free from MnS inclusions tested under identical conditions did not exhibit such pitting. The mass loss for both types of reinforcing bars computed after 3 years of exposure were comparable. However, the mortars embedded with manganese sulfide inclusion (MSI) reinforcing bars exhibited cracking after 3 years of wet/dry treatments. No such cracks were found for inclusion-free (IF) reinforcing bars. Scanning electron microscopy, space and time-dependent electro-chemical alternate current (AC) impedance, and potential studies were performed to examine the kinetics and mechanism of these reinforcing bars. The accelerating effect of chloride on pitting of metals and alloys with MnS inclusions has been explained in this paper considering the theory of acid regeneration cycle, increased solution conductivity, and the availability of high charge density on these ion forming compounds, which destabilized the passive layer. Raman spectroscopy and X-ray diffraction studies indicated the formation of ferric chloride in the rust layers of severely pitted MSI reinforcing bars. It is suggested that this ferric chloride, in the presence of oxygen and moisture, regenerated hydrochloric acid and lepidocrocite, resulting in autocatalytic chain reactions on the surface of MSI reinforcing bars.