Yazar "Lachemi, M." seçeneğine göre listele

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    Physical and Chemical Actions of Nano-Mineral Additives on Properties of High-Volume Fly Ash Engineered Cementitious Composites
    (Amer Concrete Inst, 2016) Al-Najjar, Y.; Yesilmen, S.; Al-Dahawi, Majeed; Sahmaran, M.; Yildirim, G.; Lachemi, M.; Amleh, L.
    Unlike conventional concrete, the material design process for engineered cementitious composites (ECC) involves micromechanics-based design theory, paving the way for the use of high volumes of fly ash (HVFA) as a major component. Using high volumes of fly ash (up to 85% weight fraction of cement) in ECC mixtures enables improved tensile ductility (approximately a 3% increase in long-term tensile strain) with reduced crack widths, although it also leads to significantly reduced early-age compressive and tensile strength and chloride ion resistance. However, nanomineral additives are known to improve mechanical strength and durability of HVFA systems. The study emphasizes the effects of different fly ash (FA)/cement ratios on various properties (hydration and microstructural characteristics, transport and mechanical properties) of ECC mixtures designed with different mineral additives. Experimental results confirm that although different optimum levels can be selected to favor various ECC properties, optimum weight fraction of FA is dependent on the mechanism of nanomodification (that is, type of modifier). The optimum level of fly ash weight fraction that yields the highest rate of improvement through nanomodification of ECC varies for different mechanical and transport properties.
  • [ X ]
    Öğe
    Self-Healing of Cementitious Composites to Reduce High CO2 Emissions
    (Amer Concrete Inst, 2017) Sahmaran, M.; Yildirim, G.; Aras, G. Hasiloglu; Keskin, S. Bahadir; Keskin, O. K.; Lachemi, M.
    Existing concrete structures worldwide are suffering from deterioration/distress. With ever-growing urban population and global warming, higher CO2 concentrations in the atmosphere are likely to further weaken the chemical stability of concrete material, and it is very important to understand how its effects will impair the material. To help moderate the harmful effects of increased CO2 concentrations, an experimental study was undertaken in which efforts were made to accelerate the capability of engineered cementitious composites (ECCs) with different pozzolanic materials (PMs) to self-heal its own damage (for example, cracks) in a CO2-rich environment. Self-healing was assessed by electrical impedance (EI) and rapid chloride permeability tests (RCPTs) on 28-day-old specimens. Experimental findings show that self-healing in a CO2-rich environment is more pronounced than it is in normal atmospheric conditions. The findings also show that PM type can be very decisive on self-healing performance in a CO2-rich environment, depending on testing method. Results suggest that proper material design can lead to the development of environmentally friendly ECC options with superior mechanical and durability characteristics.