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Microstructural and corrosion characteristics of Quenched and Self-Tempered (QST) steel reinforcing bars
Highlights Poor quality cross-sectional phase distribution in TMT/QST rebars identified and categorized. Reduction of chloride threshold in poor quality QST rebars. Sensitizedthe impact of inadequate Tempered Martensite phase on the durability of RC structures.
Abstract Quenched and Self-Tempered (QST) steel reinforcing bar (rebar, herein) is widely used in the reinforced concrete (RC) systems across the world. A typical QST steel rebar cross-section consists of a ductile ‘ferrite-pearlite’ (FP) core and a hard ‘tempered-martensite’ (TM) periphery. A good quality QST steel rebar is expected to have an FP core encircled by a uniformly thick, continuous, and concentric TM ring/phase. This study assessed the cross-sectional phase distribution (CSPD) of QST steel rebars produced in various countries using macroetching. These countries include Australia, Bahrain, Germany, Hungary, India, Italy, Japan, Malaysia, Russia, Singapore, SriLanka and Switzerland. Unfortunately, many rebars with 8, 12, and 16 mm diameter revealed inadequate CSPD with discontinuous and/or non-uniform TMphase. Also, the adverse effects of this inadequate CSPD on the corrosion resistance were evaluated using Cyclic Potentiodynamic Polarization (CPP) tests. For this, the FP and TM plate/coupon specimens (15 × 15 × 3 mm) were extracted from a QST steel rebar and metallographic type specimens were prepared. Then,thespecimens were immersed in chloride (Cl−) contaminated simulated concrete pore solution (denoted as SCPS). Then, the CPPtests were done after incremental addition of Cl− in SCPS to identify the Cl− threshold (Clth) of TM and FP. The FP exhibited about 10–15% lesser Clth than TM. An analytical case study showed that the use of such QST steel rebars with inadequate CSPD can result in about 20% reduction in service life. Then, bend tests were conducted on 8 mm good quality and poor quality QST steel rebars used for stirrups. Poorquality rebars with inadequate CSPD showed visible surface-cracks in some products, which could lead to severe crevice corrosion, even without the presence of chlorides. Hence,better quality control in the quenching and self-tempering process is required to improve the corrosion resistance of QST steel rebars.
Microstructural and corrosion characteristics of Quenched and Self-Tempered (QST) steel reinforcing bars
Highlights Poor quality cross-sectional phase distribution in TMT/QST rebars identified and categorized. Reduction of chloride threshold in poor quality QST rebars. Sensitizedthe impact of inadequate Tempered Martensite phase on the durability of RC structures.
Abstract Quenched and Self-Tempered (QST) steel reinforcing bar (rebar, herein) is widely used in the reinforced concrete (RC) systems across the world. A typical QST steel rebar cross-section consists of a ductile ‘ferrite-pearlite’ (FP) core and a hard ‘tempered-martensite’ (TM) periphery. A good quality QST steel rebar is expected to have an FP core encircled by a uniformly thick, continuous, and concentric TM ring/phase. This study assessed the cross-sectional phase distribution (CSPD) of QST steel rebars produced in various countries using macroetching. These countries include Australia, Bahrain, Germany, Hungary, India, Italy, Japan, Malaysia, Russia, Singapore, SriLanka and Switzerland. Unfortunately, many rebars with 8, 12, and 16 mm diameter revealed inadequate CSPD with discontinuous and/or non-uniform TMphase. Also, the adverse effects of this inadequate CSPD on the corrosion resistance were evaluated using Cyclic Potentiodynamic Polarization (CPP) tests. For this, the FP and TM plate/coupon specimens (15 × 15 × 3 mm) were extracted from a QST steel rebar and metallographic type specimens were prepared. Then,thespecimens were immersed in chloride (Cl−) contaminated simulated concrete pore solution (denoted as SCPS). Then, the CPPtests were done after incremental addition of Cl− in SCPS to identify the Cl− threshold (Clth) of TM and FP. The FP exhibited about 10–15% lesser Clth than TM. An analytical case study showed that the use of such QST steel rebars with inadequate CSPD can result in about 20% reduction in service life. Then, bend tests were conducted on 8 mm good quality and poor quality QST steel rebars used for stirrups. Poorquality rebars with inadequate CSPD showed visible surface-cracks in some products, which could lead to severe crevice corrosion, even without the presence of chlorides. Hence,better quality control in the quenching and self-tempering process is required to improve the corrosion resistance of QST steel rebars.
Microstructural and corrosion characteristics of Quenched and Self-Tempered (QST) steel reinforcing bars
Nair, Sooraj A.O. (author) / Pillai, Radhakrishna G. (author)
2019-09-27
Article (Journal)
Electronic Resource
English
CE , Counter Electrode , Cl<sup>−</sup> , Chloride , Cl<inf>th</inf> , Chloride threshold , CPP , Cyclic Potentiodynamic Polarization , CSPD , Cross-sectional Phase Distribution , FP , Ferrite-Pearlite , MSP , Meta-Stable Pitting , OCP , Open Circuit Potential , QST , Quenched and Self-Tempered , RE , Reference Electrode , Rebar , Reinforcing bar , SCE , Standard Calomel Electrode , SCPS , Simulated Concrete Pore Solution , SP , Stable Pitting , TM , Tempered Martensite , TMT , Martensite , Ferrite , Pearlite , Cyclic voltammetry , Polarization , Pitting
Geometrical and Material Characterization of Quenched and Self-Tempered Steel Reinforcement Bars
| Online Contents | 2016
Geometrical and Material Characterization of Quenched and Self-Tempered Steel Reinforcement Bars
| British Library Online Contents | 2016