Browsing by Author "Ozbay, Erdogan"

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Dual effectiveness of freezing-thawing and sulfate attack on high-volume slag-incorporated ECC
(ELSEVIER SCI LTD, 2013) Ozbay, Erdogan; Karahan, Okan; Lachemi, Mohamed; Hossain, Khandaker M. A.; Atis, Cengiz Duran; 0000-0003-3459-329X; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü; Atis, Cengiz Duran
This study investigated the dual effect of freeze–thaw cycles with sodium sulfate solution on the performance of non-air-entrained Engineering Cementitious Composites (ECCs) with high volumes of slag. ECC specimens containing three different levels of slag content as a replacement for cement (55%, 69% and 81% by weight of total cementitious material) were exposed to aggressive sodium sulfate solution under freezing–thawing cycles. The load–deflection response associated with ultimate mid-span deflection and flexural strength/stiffness was determined, along with crack development behavior. For comparison purposes, the freezing–thawing resistance (in water) of control ECC specimens was also evaluated. Modified point count method air-void parameters, compressive strength, porosity, water absorption and sorptivity tests were also conducted on the virgin ECC specimens (those not exposed to freezing–thawing cycles in water or aggressive sodium sulfate solution). The test results for the virgin specimens revealed that increased slag content (S/PC) improved the ductility, hardened air content, water absorption, porosity and sorptivity of ECC, while marginally decreasing the compressive and flexural strengths. Freeze–thaw cycles in water or sodium sulfate solution showed that the ductility of ECC specimens decreased remarkably, irrespective of slag content and applied freezing–thawing process. Reduction in mass loss was at minimal levels and no significant behavior change was monitored between the specimens undergoing freeze–thaw cycling in water and the aggressive sodium sulfate solution. Moreover, the decrease in flexural stiffness was more evident than the reduction of the flexural strength for all ECC mixtures.
Fresh, Mechanical, Transport, and Durability Properties of Self-Consolidating Rubberized Concrete
(AMER CONCRETE INST, 2012) Karahan, Okan; Ozbay, Erdogan; Hossain, Khandaker M. A; Lachemi, Mohamed; Atis, Cengiz Duran; 0000-0003-3459-329X; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü; Atis, Cengiz Duran
This paper presents the fresh, mechanical, transport, and durability performances of self-consolidating rubberized concretes (SCRCs). Fresh concrete properties were determined with slump flow, V-funnel, J-ring, and L-box tests. Mechanical, transport, and durability properties were determined by measuring compressive, flexural, and splitting tensile strengths; bond strength characteristics; water porosity; water absorption; water sorptivity; rapid chloride-ion permeability; and freezing-and-thawing and corrosion resistance. SCRC mixtures with a water-binder ratio (w/b) of 0.32; total binder content of 500 kg/m(3) (842 lb/yd(3)); and crumb rubber content of 0, 10, 20, and 30% by fine aggregate volume were produced and tested. Fresh properties testing revealed that the use of crumb rubber as a fine aggregate diminished the filling and passing ability of SCRC. A gradual reduction in mechanical properties was also observed with an increase in crumb rubber content; however, the rate of compressive strength reduction was more evident than that of tensile strength. Despite the fact that water porosity, water absorption, and chloride-ion permeability increased slightly with the use of crumb rubber, a remarkable decrease was observed in the initial and secondary water sorptivity of SCRC. No significant decrease was observed in the freezing-and-thawing and corrosion resistance of SCRC with 10% crumb rubber. Beyond that level, however, durability performance was significantly affected.
Investigation of Properties of Engineered Cementitious Composites Incorporating High Volumes of Fly Ash and Metakaolin
(AMER CONCRETE INST, 2012) Ozbay, Erdogan; Karahan, Okan; Lachemi, Mohamed; Hossain, K. M. A.; Atis, Cengiz Duran; 0000-0003-3459-329X; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü; Atis, Cengiz Duran
This study was carried out to develop engineered cementitious composites (ECCs) incorporating binary blends of high volumes of fly ash (FA) and metakaolin (MK) for the purpose of achieving low drying shrinkage and high composite strength with adequate ductility and improved durability. ECC, an ultra-ductile cement-based composite reinforced with short random fibers, exhibits strain-hardening and multiple-cracking behavior in uniaxial tension and bending. Standard (M45) and high-volume FA ECC mixtures are typically produced by replacing portland cement (PC) with 55% and 70% of FA, respectively (FA-to-cement ratio of 1.2 and 2.2 by weight). In this study, the (FA + MK)/PC ratio was maintained at 1.2 and 2.2 and the FA/MK ratio was maintained at 4.5. Two replacement levels of MK with FA were adopted. The investigation used 10% and 12.5% MK by weight of total binder content, respectively. For the purposes of comparison, standard and high-volume FA ECCs were also studied. To determine the effect of binary blends of FA and MK on the properties of ECC, this study focused on the evaluation of free drying shrinkage, flexural and compressive strengths, porosity and water absorption (WA), sorptivity, and chloride-ion permeability. The experimental results showed that the drying shrinkage, porosity, absorption, sorptivity, and chloride-ion permeability properties were significantly reduced with the use of binary blends of FA and MK, while ECC's ultra-high ductility and strain-hardening properties were preserved at an adequate level.