Ali Al-Harthy

Pitting corrosion and structural reliability of corroding RC structures: Experimental data and probabilistic analysis

A stochastic analysis is developed to assess the temporal and spatial variability of pitting corrosion on the reliability of corroding reinforced concrete (RC) structures. The structure considered herein is a singly reinforced RC beam with Y16 or Y27 reinforcing bars. Experimental data obtained from corrosion tests are used to characterise the probability distribution of pit depth. The RC beam is discretised into a series of small elements and maximum pit depths are generated for each reinforcing steel bar in each element. The loss of cross-sectional area, reduction in yield strength and reduction in flexural resistance are then inferred. The analysis considers various member spans, loading ratios, bar diameters and numbers of bars in a given cross-section, and moment diagrams. It was found that the maximum corrosion loss in a reinforcing bar conditional on beam collapse was no more than 16%. The probabilities of failure considering spatial variability of pitting corrosion were up to 200% higher than probabilities of failure obtained from a non-spatial analysis after 50 years of corrosion. This shows the importance of considering spatial variability in a structural reliability analysis for deteriorating structures, particularly for corroding RC beams in flexure.

Effect of cement kiln dust (CKD) on mortar and concrete mixtures

Abstract The aim of this study was to investigate the use of cement kiln dust (CKD) as a cementitious material in concrete and mortar. CKD was added to concrete and mortar mixtures to study its effect on the strength and on the ability of the cover zone to absorb water, an important factor in the deterioration process. Experimental results on compressive strengths, flexural strength and toughness of concrete samples containing CKD are reported. The sorptivity and the initial surface absorption tests (ISAT) of mortars were used to measure the absorption characteristics for different mortar samples containing CKD. It was found that substitution of cement with CKD does not lead to strength gain for all samples studied and proper addition of CKD has no negative effects on strength properties. It is also shown that mortars prepared using suitable amounts of CKD have better absorption characteristics. However, above certain limits, the water absorption of the mortar increased with increasing CKD contents and decreasing mortar strengths.

Feed water pretreatment in RO systems: unit processes in the Middle East

Abstract The paper deals with the conventional physical, chemical and biological unit processes that are widely applied in the Middle East for treating feedwater to reverse osmosis (RO) systems which produce potable water from brackish groundwater and saline seawater. Depending on the quality of intake water, membrane process, posttreatment and desired quality of product water, a pretreatment system was designed. Such a system usually comprises a train of unit processes based on technical and cost considerations. Proper decision for selecting unit processes involves a thorough evaluation of available alternatives. Results of previous experiences and present guidelines and schemes that are developed combining unit processes for pretreatment of RO feed are reviewed. Through the process, the combination of pretreatment units is made in such a way so that the quality of feedwater is improved at a minimal cost for pretreatment and with minimal adverse effects on succeeding processes: membranes, storage and supply systems. Conceptual layouts of several such systems of alternatives are presented along with comparative data on expected system performance and cost.

Use of Cement By-pass Dust in Flowable Fill Mixtures

Flowable fill is a self-compacted, cementitious material used primarily as a backfill in lieu of compacted fill. It is generally a mixture of sand, small amount of cement, fly ash, and water. Sand is the major component of most flowable fill mixes. Waste materials such as fly ash, ground granulated blast furnace slag, and foundry sand are commonly used to ensure low maximum compressive strength. Cement by-pass dust (CBPD) is considered a waste material of the production of cement. An estimated 25,000 tons of CBPD are produced annually in the Sultanate of Oman by Oman Cement Company alone. Most of this material is not effectively used and is disposed of on-site without any reuse causing environmental concerns. The main objective of this research is to investigate the potential use of CBPD in flowable fill mixtures as an alternative to fly ash and as a partial substitute for cement. The physical and chemical properties of both CBPD and cement were determined. Cube and cylindrical samples were prepared using different proportions of CBPD and water-to-cement ratios in order to select the optimum mixes that can be used in flowable fill applications. The optimum mixtures were cured in air and covered in plastic bags in order to study the effect of curing method on the compressive strength of flowable fill mixtures. Promising results were obtained with respect to the use of CBPD as a partial or full substitute for cement in flowable fill mixtures. Results also demonstrated that air cured samples gave a higher compressive strength than samples cured in the plastic bags for the mixes where CBPD was used as a partial substitute for cement. However, in mixes where CBPD was used to fully replace cement, samples that were cured in plastic bags produced higher strength than air cured samples at longer curing periods.

Utility of spatially variable damage performance indicators for improved safety and maintenance decisions of deteriorating infrastructure

Corrosion of concrete and structural steel is a primary cause of deterioration of built infrastructure. This deterioration can cause reduced load capacity and on-going and costly maintenance and repair. Typically, this corrosion can be seen on structures to be spatially variable. Few studies have considered the effect of spatial variability of corrosion on structural performance and its effect on structural reliability. Random fields may be used to consider the temporal and spatial deterioration effects on structural performance, and performance indicators may include probability of extent of damage or structural reliability. In the present article, four case studies showing the benefits of using spatially variable damage performance indicators are discussed, for structural steel and reinforced concrete structures. It will be shown how spatially variable damage performance indicators will allow for more informed decision-making about the level of safety and the selection of optimal maintenance and repair strategies.