Mohammed A. Al-Osta

Capacity of Corrosion-Damaged Eccentrically Loaded Reinforced Concrete Columns

The residual strength of corrosion-damaged eccentrically loaded columns is presented along with a strength-prediction model developed on the basis of a substantial amount of test data generated from the testing of 48 specimens under eccentric axial loading, 36 of which were subjected to accelerated corrosion to induce various degrees of corrosion damage. The test variables included two different cross sections, two different diameters of longitudinal steel, and different corrosion periods. The proposed approach for an estimation of residual strength involves two steps: first, the strength is calculated by conventional mechanics using only the reduced area of steel after metal loss from corrosion, and then this value is reduced by multiplying with a proposed reduction factor developed through a multi-level regression of test data to collectively account for all other corrosion-damage effects. The accuracy of the proposed method has been verified by comparing results with available test data.

Exploitation of Ultrahigh-Performance Fibre-Reinforced Concrete for the Strengthening of Concrete Structural Members

The repair and strengthening of reinforced concrete members are very important due to several factors, including unexpected increases in load levels and/or the damaging impact of aggressive environmental conditions on structural concrete members. Many researchers have turned to using materials for the repair and strengthening of damaged structures or the construction of new concrete structural members. Ultrahigh-performance fibre-reinforced concrete (UHPFRC), characterized by superior structural and durability performance in aggressive environmental conditions, is one of the materials that have been considered for the repair and strengthening of concrete structural members. The repair or strengthening of concrete structures using UHPFRC needs a thorough knowledge of the behaviour of both the strengthening material and the strengthened concrete structure at service load conditions, in addition to an understanding of the design guidelines governing the use of such materials for effective repair and strengthening. In this study, the recent issues and findings regarding the use of UHPFRC as a repair or strengthening material for concrete structural members are reviewed, analysed, and discussed. In addition, recommendations were made concerning areas where future attention and research on the use of UHPFRC as a strengthening material needs to be focused if the material is to be applied in practice.

Finite Element Modeling of CFRP-Strengthened Low-Strength Concrete Short Columns

Carbon fiber-reinforced polymer (CFRP) sheets and plates are now being extensively used as retrofitting/strengthening system, due to high strength, low weight, corrosion resistance, and ease and speed of application. Structures with very low-strength reinforced concrete columns, constructed during the early 1970s and 1980s, are rampant in many countries. These structures are prone to collapse during a seismic event. It is important to investigate if these low-strength concrete columns can be made safe by CFRP sheet strengthening. An experimental and numerical investigation conducted on short circular low-strength concrete column is presented. The results of this study showed that the confinement equations for concrete columns as per ACI and CSA codes give erroneous results for these columns. The CSA code equations require satisfaction of certain constrains, which are not applicable to such columns. Control specimen (unconfined specimens) results showed that both CSA and ACI equations overestimate the ultimate loads of low-strength RC columns by an order in magnitude. For CFRP-confined specimens, the ACI and CSA code equations overestimate the strength by about 13% and 24%.

Evaluation of unconfined compressive strength of carbonate sedimentary rocks in Saudi Arabia using indirect tests

Unconfined compressive strength (UCS) of rocks, determined by loading the rock specimens along their longitudinal axis without lateral restraint, is one of the important engineering properties required for assessing the mechanical behavior of the rocks. However, determining UCS using direct method requires stringent sample preparation and testing that need higher costs and longer time. Therefore, the evaluation of UCS of rocks using the correlations developed empirically between UCS and some relevant parameters obtained through indirect tests on rocks would be an alternative approach. In the present work, 40 samples of carbonate sedimentary rocks, belonging to Cenozoic deposits of the Great Ghawar Uplift geological province, near Ain Dar, Saudi Arabia, were collected. All samples of rocks were tested to determine their mass density, ρ, point load strength index, Is(50), ultrasonic pulse velocity, Vp, and UCS. The test results were analyzed and the correlations of UCS with ρ, Is(50), and Vp were obtained for indirect estimation of UCS of the rocks considered under this study. The relationship between UCS and Vp showed highest degree of fit among three relationships followed by the relationships between UCS and ρ and UCS and Is(50).

Study of heavy fuel oil fly ash for use in concrete blocks and asphalt concrete mixes

Use of heavy fuel fly ash (HFFA) (diesel and cracked fuel) for power generation in Saudi Arabia has generated and accumulated large quantities of HFFA as a byproduct. In this research, HFFA is studied with the emphasis on the utilization of this waste material in concrete blocks and asphalt concrete mixes. Two types of mixes, one with low and other with high cement content, were studied for concrete blocks. Different mixes having varying percentages of HFFA (0% to 25%), as cement/sand replacement or as an additive, were studied. The performance of concrete blocks is evaluated in terms of compressive strength, water absorption, durability and environmental concerns. The results showed that blocks cannot be cast if more than 15% HFFA is used; also there is a marginal reduction in the strength of all the mixes before and after being exposed to the sulfate solution for a period of ten months. HFFA is studied in asphalt concrete mixes in two ways, as an asphalt modifier (3&5%) and as a filler (50%) replacement, the results showed an improvement in stiffness and fatigue life of mixes. However, the stability and indirect tensile strength loss were found to be high as compared to the control mix due to moisture damage, indicating a need of using antistripping agents. On environmental concerns, it was found that most of the concerned elements are within acceptable limits also it is observed that lower concentration of barium is leached out with the higher HFFA concentrations, which indicates that HFFA may work as an adsorbent for this leaching element.