Gurkan Yildirim

Influence of Hydrated Lime Addition on the Self-Healing Capability of High-Volume Fly Ash Incorporated Cementitious Composites

AbstractThis paper comprehensively studies the influence of hydrated lime usage on the repeatability and pervasiveness of the self-healing mechanism in engineered cementitious composites (ECC) incorporating high-volume fly ash (HVFA). Repeatability of self-healing was evaluated by repeatedly preloading the specimens up to 70% of their original deformation capacities at the end of each specified cyclic wet/dry exposure. Resonant frequency (RF) and rapid chloride permeability tests (RCPT) were used to assess the extent of deterioration. Crack characteristics were also presented to account for the changes observed in cracks throughout the RF tests. To monitor the pervasiveness of self-healing, RF measurements were recorded from both the top and middle portions of the specimens. Experimental results strongly suggest that the self-healing mechanism in cementitious composites can be made far more repeatable and pervasive with the addition of hydrated lime to the HVFA-ECC mixtures; this can have a significant im...

Repeatability and Pervasiveness of Self-Healing in Engineered Cementitious Composites

This paper investigates the intrinsic self-healing ability of engineered cementitious composites (ECCs) coupled with multiple microcrack formation under mechanical loading based on two robustness criteria: repeatability and pervasiveness. To this end, two different composites containing Class F fly ash and slag were investigated. To generate microcracks, specimens were repeatedly preloaded up to 70% of their deformation capacities under mechanical loading at the end of each specified cyclic wet/dry conditioning period. Resonant frequency (RF) and rapid chloride permeability tests (RCPT) were used to assess the extent of damage and self-healing, and final results were supported by microscope observations. RF measurements were recorded from two different parts of each specimen (the top and middle portions) to monitor whether self-healing takes place in certain regions or whether it is pervasive over the entire specimen. Results of the experimental study show that depending on the type of mineral admixture used and the duration of initial curing before deterioration, ECC specimens can recover up to 85% of their initial RF measurements, even after six repetitive preloading applications. The recovery rates observed in the middle portion are similar to those in the top portion for both ECC mixtures (to a slightly lesser extent), which implies that self-healing is quite pervasive. Furthermore, after repeated application of severe preloading, RCPT results for both mixtures satisfy low or moderate chloride ion penetrability levels in accordance with ASTM C1202. Due to the enhanced self-healing capability of specimens, maximum crack width observed over the specimen surfaces was restricted to 190 µm (0.008 in.), even after nine preloadings. These findings suggest that under certain conditions, the ECC materials produced in this study may significantly enhance the functionality of structures by reducing the need for repair and/or maintenance.

Investigation of the Bond between Concrete Substrate and ECC Overlays

AbstractRigid concrete overlays have been used for smoothing damaged surfaces and/or restoring or improving the mechanical capacity of bridge decks for many years. However, engineered cementitious composites (ECCs), which demonstrate superior ductility with high strength and improved durability characteristics, are an attractive alternative to conventional overlay materials if a strong mechanical bond is formed between the overlay and the substrate material. An experimental study was performed to evaluate the bond strength between ECC overlay and an ordinary concrete substrate with smooth and rough surface textures. Microsilica concrete (MSC), generally used as an overlay material, was also prepared as a control mixture. ECC and MSC overlay mixtures were cast over the concrete substrate to determine bonding performance. Slant shear and splitting prism tests were performed with MSC and two ECC mixtures. The experimental results show that when ECC is used as an overlay material, bond strength is significant...

Effects of Compressive Strength, Autogenous Shrinkage and Testing Methods on the Bond Behavior of HES-ECC

An experimental study was undertaken to assess the bond characteristics of high-early-strength engineered cementitious composites (HES-ECC) with characteristics of high ductility and low early-age shrinkage. For comparison purposes, a mixture of repair material (REP), which is commercially available and extensively used for fast and durable repair of infrastructures, was used to compare the bonding performance. For the evaluation of bond characteristics, slant shear and tensile pulloff tests were performed. In this study, the influence of compressive strength and autogenous shrinkage on individual bond strength results is also discussed, along with the basic mechanical properties of the proposed materials. Experimental results indicate that the influence of compressive strength and autogenous shrinkage on bond strength results varies significantly depending on the test method. It was also shown that the use of HES-ECC mixtures significantly improves the bond characteristics of a repair assembly in comparison to REP. Enhanced bond performance of HES-ECC mixtures over REP is more evident in the case of direct pulloff tests than in slant shear tests, both in terms of bond strength results and failure type.

Influence of Cyclic Frost Deterioration on Water Sorptivity of Microcracked Cementitious Composites

AbstractEngineered cementitious composites (ECCs) are relatively new construction materials characterized by strain-hardening behavior under excessive tensile loading. Unlike conventional concrete materials, which generally show failure after first tensile cracking, ECCs strain-harden upon excessive loading by creating multiple closely-spaced microcracks. Given the fact that crack widths in ECCs are at micron levels, water movement into these cracks through capillary suction requires further attention, especially under frost action. This paper therefore explores the effectiveness of frost action on water movement into microcracked ECCs. The experimental study covered the sorptivity measurements of ECC mixtures produced with mineral admixtures with different chemical compositions after exposure to cyclic freezing and thawing (F/T), in accordance with ASTM C 666, Procedure A. Air-void characteristics of ECCs were also compared. Experimental findings showed that air-void parameters are not the sole influenti...

Effect of Corrosion on Shear Behavior of Reinforced Engineered Cementitious Composite Beams

The objective of this study was to evaluate the effect of corrosion level on shear behavior of engineered cementitious composite (ECC) beams. Reinforced normal concrete (R-NC) specimens with compressive strength equal to the ECC specimens were also used for control purposes. Ten reinforced concrete beams (five ECC and five NC) with dimensions of 150 x 220 x 1400 mm (5.91 x 8.66 x 55.12 in.) were manufactured for the study. Using accelerated corrosion through the application of a constant current of 1 ampere, four levels of corrosion were established at 5%, 10%, 15%, and 20% of mass loss of the reinforcing bars. To ensure the highest probability of shear failure mode, all beams were tested under a four-point loading system with a shear span-effective depth ratio of 2.5. General structural behavior, strength, stiffness, failure mode, and energy absorption capacities of ECC and R-NC beams subjected to different corrosion levels were evaluated and compared. Experimental results showed a high correlation between calculated mass loss and measured mass loss in reinforcing bars due to accelerated corrosion. Compared to NC, ECC beams exhibited significantly higher strength, stiffness, and energy absorption capacity, along with superior performance in terms of the restriction of damage caused due to corrosion. The increase in corrosion level negatively influenced the structural behavior of the ECC beams tested.

Tests of high-performance fiber-reinforced concrete beams with different shear span-to-depth ratios and main longitudinal reinforcement

Test results of 12 reinforced concrete (RC) beams having three shear span to effective depth ratios and two main longitudinal reinforcement amounts are reported. Six of the test specimens were produced with engineered cementitious composites (ECCs) and another corresponding six with ultra high-strength fiber-reinforced cementitious composite (RMC). The shear span to effective depth ratios of test specimens were selected low to investigate the shear performance of ECCs and RMC characterized by ultra high ductility-moderate strength and ultra high strength-moderate ductility, respectively. Shear-carrying capacity and ductility ratios of large-scale reinforced ECC and RMC beams were compared and interpreted for different shear spans, energy absorption capacities, and stiffnesses. The experimental results showed that for the three different shear spans, the RMC beams had higher shear capacity results than the ECC beams. Using both concrete types markedly restricted shear cracking and led to flexural failure. Overall findings suggest that RMC beams have higher shear capacity and yield stiffness than ECC beams, while ECC beams have a higher deflection ductility ratio and energy absorption capacity.