Ahmed A. Abouhussien

Experimental and Empirical Time to Corrosion of Reinforced Concrete Structures under Different Curing Conditions

Reinforced concrete structures, especially those in marine environments, are commonly subjected to high concentrations of chlorides, which eventually leads to corrosion of the embedded reinforcing steel. The total time to corrosion of such structures may be divided into three stages: corrosion initiation, cracking, and damage periods. This paper evaluates, both empirically and experimentally, the expected time to corrosion of reinforced concrete structures. The tested reinforced concrete samples were subjected to ten alternative curing techniques, including hot, cold, and normal temperatures, prior to testing. The corrosion initiation, cracking, and damage periods in this investigation were experimentally monitored by an accelerated corrosion test performed on reinforced concrete samples. Alternatively, the corrosion initiation time for counterpart samples was empirically predicted using Fick’s second law of diffusion for comparison. The results showed that the corrosion initiation periods obtained experimentally were comparable to those obtained empirically. The corrosion initiation was found to occur at the first jump of the current measurement in the accelerated corrosion test which matched the half-cell potential reading of around −350 mV.

Application of acoustic emission monitoring for assessment of bond performance of corroded reinforced concrete beams

This article presents the results of an experimental investigation on the application of acoustic emission monitoring for the evaluation of bond behaviour of deteriorated reinforced concrete beams. Five reinforced concrete beam–anchorage specimens designed to undergo bond failure were exposed to corrosion at one of the anchorage zones by accelerated corrosion. Two additional beams without exposure to corrosion were included as reference specimens. The corroded beams were subjected to four variable periods of corrosion, leading to four levels of steel mass loss (5%, 10%, 20% and 30%). After these corrosion periods, all seven beams were tested to assess their bond performance using a four-point load setup. The beams were continuously monitored by attached acoustic emission sensors throughout the four-point load test until bond failure. The analysis of acquired acoustic emission signals from bond testing was performed to detect early stages of bond damage. Further analysis was executed on signal strength of acoustic emission signals, which used cumulative signal strength, historic index (H(t)) and severity (Sr) to characterize the bond degradation in all beams. This analysis allowed early identification of three stages of damage, namely, first crack, initial slip and anchorage cracking, before their visual observation, irrespective of corrosion level or sensor location. Higher corrosion levels yielded significant reduction in both bond strength and corresponding acoustic emission parameters. The results of acoustic emission parameters (H(t) and Sr) enabled the development of a damage classification chart to identify different stages of bond deterioration.

Acoustic emission monitoring for bond integrity evaluation of reinforced concrete under pull-out tests

This article presents the results of an experimental investigation on the application of acoustic emission technique for monitoring the steel-to-concrete bond integrity of reinforced concrete structures. A series of direct pull-out tests were performed on 54 reinforced concrete unconfined prism samples with variable rebar diameter (10, 20, and 35 mm), embedded length (50, 100, and 200 mm), and concrete cover (20, 30, and 40 mm). The samples were tested under incrementally increasing monotonic loading while being continuously monitored via attached acoustic emission sensors. These sensors were utilized to acquire different acoustic emission signal parameters emitted throughout the tests until failure. Also, an acoustic emission intensity analysis was implemented on acoustic emission signal strength data to quantify the damage resulting from loss of bond in all tested specimens. This analysis employed the signal strength of all recorded acoustic emission hits to develop two additional parameters: historic index (H (t)) and severity (Sr). The results of bond behavior, mode of failure, and free end slip were compared with the recorded acoustic emission data. The results showed that the cumulative number of hits, cumulative signal strength, H (t), and Sr had a good correlation with different stages of bond damage from de-bonding/micro-cracking until bond splitting failure and bar slippage, which caused cover cracking or delamination. The analysis of cumulative signal strength and H (t) curves enabled early identification of two progressive stages of bond degradation (micro-cracking and macro-cracking) and recognized the various modes of failure of the tested specimens. The variations of bar diameter, concrete cover, and embedded length yielded significant impacts on both the bond behavior and acoustic emission activities. The results also presented developed intensity classification charts, based on H (t) and Sr, to assess the bond integrity and to quantify the bond deterioration (micro-cracking, macro-cracking, and rebar slip) in reinforced concrete structures.

Influence of Metakaolin and Curing Conditions on Service Life of Reinforced Concrete

AbstractThis investigation focuses on studying the effect of using metakaolin (MK) and/or different curing conditions on service life of reinforced concrete exposed to chloride-induced corrosion. T...

Influence of pouring techniques and mixture's fresh properties on the structural performance of self- consolidating concrete beams

An experimental investigation was conducted to study the influence of pouring techniques and mixture’s fresh properties on the shear strength, cracking behavior and mid-span deflection of largescale Self-Consolidating Concrete (SCC) beams. SCC beams were poured in two different techniques: the first technique was to pour the concrete from one side of the formwork only, while the second technique was to move the pouring point along the full beam length. The variables were: the concrete type, length and depth of beams, and the viscosity and yield stress of SCC mixture. The study also included a comparison between the experimental shear strength results and the predictions of some major code-based equations. The results obtained from this investigation proved that different pouring techniques, viscosity and/or yield stress of SCC mixtures did not have a significant effect on the structural performance of SCC beams. However, beams cast with lower yield stress appeared to have slightly higher shear strength and minimum average crack heights. Also, SCC beams with higher viscosity mixture tended to have lower stiffness compared to SCC mixtures with normal viscosity mixture.