Mustafa Sahmaran

Transport Properties of Engineered Cementitious Composites Under Chloride Exposure

This paper presents the results of an experimental investigation on the chloride transport properties of engineered cementitious composites (ECC) under combined mechanical and environmental loads. ECC is a newly developed, high-performance, fiber-reinforced cementitious composite with substantial benefit in both high ductility and improved durability due to tight crack width. By employing micromechanics-based material design, maximum ductility in excess of 3% under uniaxial tensile loading can be attained with only 2% fiber content by volume, and the typical single crack fracture behavior commonly observed in normal concrete or mortar is converted to multiple microcracking in ECC. In this study, immersion and salt ponding tests were conducted to determine chloride ion transport properties. Under high imposed bending deformation, the preloaded ECC beam specimens reveal microcracks less than 50 μm and an effective diffusion coefficient significantly lower than that of the similarly preloaded reinforced mortar beam because of the tight crack width control in ECC. In contrast, cracks larger than 150 μm are easily produced under the same imposed deformation and have significant effects on effective diffusion coefficient of reinforced mortar. Moreover, through the formation of microcracks, a significant amount of self-healing was observed within the ECC cracks subjected to NaCl solution exposure.

Corrosion Resistance Performance of Steel-Reinforced Engineered Cementitious Composite Beams

This paper presents the results of an experimental investigation on steel-reinforced engineered cementitious composite (ECC) beams subjected to accelerated corrosion by an electrochemical method. ECC is a micromechanically-based designed, high-performance, fiber-reinforced cementitious composite with high ductility and improved durability due to tight crack width. An accelerated corrosion test method, which was carried out by imposing a constant potential, was used to induce different degrees of corrosion into the reinforcement embedded in ECC prismatic specimens. Mortar specimens that have an equal compressive strength to the ECC specimens were also used as reference specimens. After inducing different degrees of accelerated corrosion, the cracks and the residual flexural load capacity of the test specimens and the mass loss of reinforcing bars embedded in specimens were determined. From the results of this study, it is concluded that due to its high tensile strain capacity and microcracking behaviors, ECC significantly prolonged the corrosion propagation period while enhancing the ability to maintain the load capacity of the beam. These performances of reinforced ECC (R/ECC) are expected to contribute substantially to improving infrastructure sustainability by reducing the amount of repair and maintenance during the service life of the infrastructure.

Influence of Aggregate Type and Size on Ductility and Mechanical Properties of Engineered Cementitious Composites

The influence of aggregate type and size on engineered cementitious composite (ECC) mechanical and ductility properties was investigated and the results presented in this paper. A micromechanically-based high-performance fiber-reinforced cementitious composite, ECC enjoys improved durability and high ductility due to tight crack width. Microsilica sand (200 μm [0.008 in.] maximum aggregate size) is typically used to produce standard ECC mixtures. There was investigation of ECC mixtures containing either gravel sand or crushed dolomitic limestone sand with maximum sizes of 2.38 or 1.19 mm (0.094 or 0.047 in.) in this study. Three different ECC mixtures with 1.2, 2.2, and 4.2 fly ash/portland cement (FA/C) ratios were cast for each aggregate type and maximum aggregate size. There was experimental determination of crack development, drying shrinkage behavior, and the effects of FA/C, aggregate type, and maximum aggregate size on compressive, flexure, and unixial tensile properties. Experimental results show that strain-hardening behavior with strain capacities, provided that the matrix employs a high FA content, can be compared with the standard microsilica sand ECC mixtures, in ECC mixtures produced with gravel sand and crushed dolomitic limestone sand with higher maximum aggregate sizes. Tensile strengths of these mixtures can be 3.57 to 5.13 MPAa (0.52 to 0.74 ksi), and tensile ductility can maintain, at 28 days of age, 1.96 to 3.23%. Material behavior can be further improved by using crushed dolomitic limestone sand and gravel sand, since they can be drying-shrinkage arrestors in the paste.

Rheological Control in Production of Engineered Cementitious Composites

A study of fresh property rheological control during engineered cementitious composite (ECC) processing for the purpose of more effective realization of mechanical properties using micromechanical design theory optimization is reported on in this paper. To determine their effects on fresh and hardened ECC properties, there was investigation of four factors (amount of viscosity-modifying admixture, amount of high-range water reducer [HRWR], water-binder ratio [w/b], and Class C fly ash [FA] to Class F FA ratio). That the w/b, among investigated factors, most strongly affects ECC mortar (without fiber), which in turn significantly impacts ECC composite tensile strain capacity and ultimate tensile strength, is indicated in test results. The mini-slump flow test and marsh cone flow test were shown to be simple and practical methods for ECCC mortar rheological property characterization. Self-consolidating ECC with optimum rheological properties promoting uniform fiber distribution through the matrix can be produced easily, and micromechanically based optimized ECC mixture design optimized tensile properties can be realized through compliance recommendation for rheological control for ECC production as summarized in this paper.

Assessing Mechanical Properties and Microstructure of Fire-Damaged Engineered Cementitious Composites

In recent years, a number of investigations of engineered cementitious composites (ECC) have been carried out, and the mechanical behavior and durability characteristics of this type of composite are now increasingly better understood. The fire-resistant behavior of this specialized concrete, however, has not yet been studied as extensively. This investigation develops important data on the mechanical properties and microstructure of ECC exposed to temperatures up to 800°C (1472°F). In this study, the mechanical properties (residual compressive strength, stress-strain curve, and stiffness) and mass loss were determined after air cooling, subsequent to temperature exposure. Changes in the microstructure, porosity, and pore size distribution of the fire-deteriorated ECC specimens were identified using scanning electron microscopy and mercury intrusion porosimetry techniques. Test results revealed no significant changes in the mechanical properties for tested specimens exposed to temperatures up to 400°C (752°F) for 1 hour. Microstructural analysis showed the creation of supplementary pores and channels in the matrix due to polyvinyl alcohol (PVA) fibers melting in the 200-400°C (392-752°F) temperature range. After a 1-hour exposure to temperatures of 600 and 800°C (1112 and 1472°F), the mechanical performance of fire-deteriorated ECC mixture is similar to or better than that of conventional concrete incorporating polypropylene or steel fibers, despite a significant reduction in compressive strength and stiffness. Moreover, no explosive spalling occurred in any specimens during the fire test. The promising performance of ECC under fire exposure may be due to the presence of PVA fibers and high-volume fly ash. The beneficial influence of fly ash can be ascribed to the pozzolanic reaction consuming calcium hydroxide in the hydrates. PVA fiber is also beneficial in that it prevents explosive spalling. This introduces additional channels for vaporized moisture in ECC to escape without creating high internal pressure in the material.

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...

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.

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...