Assem A. A. Hassan

Effect of Metakaolin and Silica Fume on Rheology of Self-Consolidating Concrete

The rheology of self-consolidating concrete (SCC) containing metakaolin (MK) versus silica fume (SF) was compared. Plastic viscosity and yield stress were evaluated at different slump-flow values using a concrete viscometer. The effects of high-range water-reducing admixture (HRWRA) dosage, the total time for flow, the time to reach 19.68 in. (500 mm) diameter (T50), and the final diameter of the slump-flow test, as well as the influence of the mixture viscosity on the flowability and passing ability were investigated. Plastic viscosity and yield stress increased with the increased percentage of MK, but not with that of SF. However, the yield value sharply increased with the increased percentage of SF. Good correlations between slump-flow diameter and yield stress, viscosity and T50, viscosity and total slump-flow time, as well as viscosity limits for SCC mixtures based on the mixture usage, construction requirements, and member characteristics were established.

Effect of Metakaolin on the Rheology of Self-Consolidating Concrete

This study deals with the rheological properties of self-consolidating concrete (SCC) incorporating various percentages of metakaolin (MK) and silica fume (SF) as a partial replacement of cement. Plastic viscosity and yield stress were evaluated at different slump flow values using a concrete viscometer. The effect of high range water reducing admixture (HRWRA) dosage and the total time for flow, the time to reach 500 mm diameter (T50), and the final diameter of the slump flow test were also investigated and studied in this research program. The results showed that the plastic viscosity and the yield stress increase with the increase of the percentage of MK. The results also demonstrated a correlation between the final slump flow diameter and the yield stress similar to that presented in the literature.

Ductility and Cracking Behavior of Reinforced Self-Consolidating Rubberized Concrete Beams

AbstractThis paper investigates the applicability of using optimized self-consolidating rubberized concrete (SCRC) and vibrated rubberized concrete (VRC) mixtures in structural applications. The curvature ductility, ultimate flexural strength, and cracking characteristics of different SCRC and VRC mixtures were tested using large-scale reinforced concrete beams. The variables were crumb rubber (CR) percentage (0–50% by volume of sand), different binder contents (500–550  kg/m3), inclusion of metakaolin (MK), use of air entrainment, and concrete type. The performance of some design codes were evaluated in predicting the cracking moment and crack widths of the tested beams. The results indicated that although the flexural capacity of the tested beams decreased with the addition of CR, adding CR improved the beams’ curvature ductility and reduced its self-weight. Adding CR into concrete also appeared to limit the flexural crack widths but with a slightly higher number of cracks compared to beams without CR. ...

Performance of Full-Scale Self-Consolidating Rubberized Concrete Beams in Flexure

This research investigated the performance of full-scale self-consolidating rubberized concrete (SCRC) and vibrated rubberized concrete (VRC) beams in flexure. The beam mixtures were developed with a maximum possible percentage of crumb rubber (CR) (0 to 50% by volume of sand) while maintaining acceptable fresh properties and minimum strength reduction. The mixture variables included different binder contents, the addition of metakaolin, and the use of air entrainment. The performance of the tested beams was evaluated based on load-deflection response, concrete strain/stiffness, cracking behavior, first crack load, ultimate load, ductility, and toughness. In general, increasing the CR content decreased the mechanical properties, first crack load, stiffness, and self-weight of all SCRC and VRC beams. However, using up to 10% CR enhanced the deformation capacity, ductility, and toughness of tested beams without affecting the flexural capacity. This improvement in the deformation capacity, ductility, and toughness appeared to continue up to 20% CR (but with a slight reduction of the flexural capacity) and then reduced with further increases in the CR content. The results also indicated that although it was possible to produce VRC beams with higher percentages of CR (50% compared to 40% in SCRC), this increased percentage only gave VRC beams an advantage in terms of self-weight reduction, while it had a limited contribution in enhancing the structural performance of the beams.

Impact Resistance and Mechanical Properties of Self-Consolidating Rubberized Concrete Reinforced with Steel Fibers

AbstractThis study evaluates the impact resistance and mechanical properties of a number of developed self-consolidating rubberized concrete (SCRC) mixtures reinforced with steel fibers (SFs). In this research, SFs were used to compensate for the reduction in tensile and flexural strength that resulted from adding high volumes of crumb rubber (CR). SFs were also used to exploit the beneficial interaction between SFs and CR to develop low-density concrete with higher impact resistance. The experimental variables were different replacement levels of fine aggregate volume by CR (0–40%), binder content (550–600  kg/m3), SF volume fractions (0, 0.35, 0.5, 0.75, and 1%), and size of SFs. Tests included fresh properties, compressive strength, splitting tensile strength (STS), flexural strength (FS), and impact loading (drop-weight on cylindrical specimens and flexural impact loading on small-scale beams). The results indicated that adding CR to concrete improved the impact energy absorption and ductility, wherea...

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.

Steel-Fiber Self-Consolidating Rubberized Concrete Subjected to Impact Loading

This investigation was carried out to evaluate the combined effect of crumb rubber (CR) and steel fibers (SFs) on improving the impact resistance of self-consolidating concrete (SCC) mixtures. Seven SCC mixtures were developed with varied percentages of CR (0–15% by volume of sand) and SF’s volume of 0.35%. The performance of the developed mixtures was evaluated by testing the fresh properties, compressive strength, splitting tensile strength (STS), flexural strength (FS), and impact loading (drop weight on cylindrical and beam specimens). The results indicated that inclusion of CR decreased the compressive strength, STS, and FS of the tested mixtures, while the impact resistance obviously increased. Reinforcing CR mixtures with 0.35% SFs could compensate the reduction in the tensile strength resulting from adding rubber and further increase the resistance of mixtures to impact loading, achieving mixtures with promising properties for multiple structural applications.

Probabilistic and Statistical Modeling of Chloride-Induced Corrosion for Concrete Containing Metakaolin

AbstractThis paper presents new models for computing the chloride-induced corrosion period based on combining Monte Carlo simulation and statistical analysis methods. The study is divided into two ...