Rajeh Z. Al-Zaid

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.

Contact between a circular plate and a tensionless edge support

Abstract In this paper the extent of contact between a circular plate and its tensionless edge support is studied. The solution is obtained by employing the Ritz method. The displacement function is approximated in terms of the functions which satisfy exactly one of the boundary conditions. The other boundary condition is satisfied approximately by taking the harmonic average. The numerical results showing the effects of the configuration of loading and the stiffness of the support on the extent of the contact and on the edge displacement of the plate are presented in various diagrams. The results which correspond to a very low support stiffness are compared with those of a rigid plate, and very good agreement is found.

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.

Influence of non-standard curing on the strength of concrete in arid areas

Abstract The influence of non-standard curing practice on the strengths of specimen and in-situ concrete is evaluated by experimental testing. Samples were collected randomly from construction sites distributed over two areas of distinct climatic conditions: 1) hot and dry (arid) climate, and 2) hot and moist coastal climate. The in-situ strength of concrete was evaluated by strength testing of cores taken from slab, beam, and column elements. The curing methods were simulated by water sprinkling twice a day for 7 days with and without burlap cover. The strength results for cubes and cores so cured indicate that curing employing water sprinkling, twice a day, and without burlap cover is far below the ACI-318 requirements. The results also indicate the need to account for the high variability of the strength ratio of field to standard cured concrete in the assessment of curing procedures specially in arid areas. It is recommended that the curing procedures shall be improved when strength of field cured cylinders is less than 85 percent of that of companion laboratory-cured cylinders in coastal humid areas and 75 percent in arid areas.