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    Influence of cracking and healing on the gas permeability of cementitious composites
    (Elsevier Sci Ltd, 2015) Yildirim, Gurkan; Sahmaran, Mustafa; Balcikanli, Muzeyyen; Ozbay, Erdogan; Lachemi, Mohamed
    The main objective of the study presented in this paper was to investigate the influence of cracking and self-healing on the gas permeability of Engineered Cementitious Composites (ECC). To deliberately introduce microcracks, specimens were pre-loaded to different deformation levels under splitting tensile loading and exposed to different environmental conditionings for the assessment of self-healing. Gas permeability (GP) and resonant frequency (RF) tests, crack characteristics observation and microstructural analysis were conducted to analyze the effect of cracking and healing on the properties of cementitious composites. Test results indicate that the self-healing effect determined through GP and RF tests was strongly influenced by changes in the chemical compositions of the mixtures. Application of pre-loading led to significant increases in GP results, so that even microcracks of less than 50 mu m caused a GP coefficient fifty times higher than that of sound specimens. However, the recovery in GP results could be escalated up to 96% after only a month through proper material design and conditioning. It therefore appears that microcracking and subsequent healing is influential on the GP recovery rates of specimens, but not on RF recovery rates. (C) 2015 Elsevier Ltd. All rights reserved.
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    Repeatability and Pervasiveness of Self-Healing in Engineered Cementitious Composites
    (Amer Concrete Inst, 2015) Sahmaran, Mustafa; Yildirim, Gurkan; Noori, Rezhin; Ozbay, Erdogan; Lachemi, Mohamed
    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 (RP) a,id 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 selfish) 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 mu m (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.
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    Self-healing ability of cementitious composites: effect of addition of pre-soaked expanded perlite
    (Ice Publishing, 2014) Sahmaran, Mustafa; Yildirim, Gurkan; Ozbay, Erdogan; Ahmed, Karwan; Lachemi, Mohamed
    This study assessed the use of pre-soaked expanded perlite aggregate (PS-EPA) on the self-healing of cementitious composites by replacing a proportion of normal aggregate with PS-EPA at different replacement rates. Specimens with and without PS-EPA were stored in water for 28 d and then mechanical loading was applied to produce specimen deterioration. At the age of 28 d, pre-loaded and sound specimens were exposed to continuous air (CA) exposure for 30 d. The degree of deterioration as a result of mechanical pre-loading and the degree of self-healing were determined via characterisation of crack numbers and widths, transport (chloride ion permeability) and mechanical properties (splitting tensile strength), and specimens with and without PS-EPA were compared. The test results revealed that increased PS-EPA content significantly improved the compressive strength and chloride ion permeability of specimens, and that it further enhanced the hydration and healing capability of specimens under CA exposure after pre-loading.