Hasan Erhan Yucel

Effect of Fly Ash and PVA Fiber on Microstructural Damage and Residual Properties of Engineered Cementitious Composites Exposed to High Temperatures

This paper discusses the influence of high volumes of fly ash and micro polyvinyl alcohol (PVA) fibers on the fire resistance and microstructure of engineered cementitious composites (ECC). Composites containing two different contents of fly ash as a replacement for cement (55 and 70% by weight of total cementitious materials) are examined. To determine the effects of microfibers and ultrahigh ductility of ECC, ECC matrix mixtures of similar composition except PVA fiber are also produced and tested for the fire resistance. The mixtures are exposed to temperatures up to 800°C for one hour. Fire resistances of the mixtures are then quantified in terms of the residual mechanical properties (strength, stress-strain curve, deflection, and stiffness) and mass loss. The role of PVA fibers and fly ash is discussed through the analysis of microstructure and fiber-matrix interactions as a function of heat treatment. The microstructural characterization is examined before and after exposure to fire deterioration by ...

Combined Effect of Aggregate and Mineral Admixtures on Tensile Ductility of Engineered Cementitious Composites

The mixture proportions of engineered cementitious composites (ECCs) are optimized through micromechanics-based material design theory to attain high tensile ductility. Therefore, ECC ingredients with inappropriate characteristics (such as type and amount of mineral admixture and size and amount of aggregate) from different sources can negatively influence the microstructure of the composite and the tensile ductility of the ECC. In this study, an experimental program is performed to understand the dependence of the composite properties on its mixture composition governed by mineral admixture types and replacement level, and maximum aggregate size and amount. The test results reveal that increasing the size and amount of aggregates does not negatively influence the ductility of ECC when combined with an appropriate mineral admixture type and amount. Instead, an increase in the age of restrained shrinkage cracking and a significant decrease in the drying shrinkage are accomplished.

Self-Healing of Microcracks in High-Volume Fly-Ash- Incorporated Engineered Cementitious Composites

This paper presents the self-healing ability of engineered cementitious composites (ECCs) containing high-volume fly ash (HVFA). Composites containing two different contents of FA (55 and 70% by weight of total cementitious material) are examined. A splitting tensile strength test was applied to generate microcracks in ECC mixtures, where cylindrical specimens were preloaded up to their 85% maximum deformation capacity at 28 days. These specimens were then exposed to further continuous wet (CW), continuous air (CA), and wet/dry (W/D) cycle curing regimes up to 60 days. The extent of damage was determined by using the rapid chloride permeability test (RCPT), splitting tensile tests, and microscopic observation. In terms of permeation properties, microcracks induced by mechanical preloading significantly increase the RCPT values of ECC mixtures. Moreover, increasing FA content is shown to have a negative effect, especially on the permeation properties of virgin ECC specimens at an early age. Without self-healing, however, the effect of mechanical preloading on the chloride-ion penetration resistance of ECC with 70% FA is lower compared to ECC with 55% FA. The test results also indicate that CW and W/D cycle curing contribute and speed up the healing process of the cracks, significantly improve mechanical properties, and drastically decrease the RCPT of ECC. The use of HVFA in ECC production is likely to promote self-healing behavior due to tighter crack width and a higher amount of unhydrated cementitious material available for further hydration. Therefore, it appears that the curing conditions and ECC composition significantly influence self-healing ability.

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...

Effect of Microcracking on Frost Durability of High-Volume- Fly-Ash- and Slag-Incorporated Engineered Cementitious Composites

This paper reports the durability performance of high-volume-fly-ash (FA)- and slag (S)-incorporated engineered cementitious composites (ECCs) when subjected to mechanical loading and freezing-and-thawing cycles. Composites containing two different contents of FA and slag as a replacement of cement (55 and 70% by weight of total cementitious materials) are examined. To find out the effect of mechanical preloading on the frost durability of ECCs, prism specimens were preloaded up to a certain deformation level under four-point bending loading to generate microcracks. Then, the preloaded and pristine (sound) specimens were subjected to the freezing-and-thawing test in accordance with ASTM C666/C666M. Experimental tests consisted of measuring the change in mass and ultrasonic pulse velocity (UPV) and residual flexural properties of ECC specimens exposed to the freezing-and-thawing cycles up to 300. Test results revealed that the frost resistance of ECCs was significantly influenced by the mineral admixture type and amount and preloading deformation. The deterioration with an increasing number of freezing-and-thawing cycles was relatively more for ECC mixtures with FA than for slag mixtures at the same replacement level. In addition, an increase in the FA replacement rate was observed to exacerbate the deterioration caused by freezing-and-thawing cycles. Apart from some reduction in flexural properties and UPV and an increase in mass loss and residual crack width, the results presented in this study, however, confirm the durability performance of ECC material under freezing-and-thawing cycles, even in cases where the material experiences mechanical loading that deforms it into the strain hardening stage prior to exposure. It is important to note that this durability of ECCs under freezing and thawing was achieved without deliberate air entrainment, and contrary to conventional concrete, no relationship of frost resistance was found to the air-void structure of the ECC mixtures.