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Title: Using alkali-activated slag ferrocement to strengthen corroded reinforced concrete columns
Authors: Fang, Shuai
Degree: Ph.D.
Issue Date: 2018
Abstract: Chloride-induced corrosion of reinforcement has endangered the safety of reinforced concrete structures. Corrosion weakens cross-sectional area of reinforcements and bonding between concrete and reinforcements. It generates cracks in concrete cover, which accelerates invasion of chloride and causes further corrosion. Corrosion of reinforcement decreases loading capacity and ductility and shortens service life of structural members. It is, therefore, necessary to strengthen corroded reinforced concrete members to ensure structural safety and to extend service life. It is the objective of this study to develop effective strengthening schemes for corroded concrete columns using alkali-activated slag ("AAS") ferrocement. To optimize the mix proportion of AAS, complete factorial experiments and analysis of variance were implemented to investigate effect of alkali content and modulus of activator on flexural strength, compressive strength, drying shrinkage, setting time, and resistance to chloride penetration of AAS mortar. Accelerated corrosion test was conducted on steel bars embedded in AAS mortar to examine protection of AAS and corrosion inhibitors on reinforcements. Tensile strength of AAS ferrocement and its confinement on plain concrete columns were examined and modeled. Seventeen full-scale column specimens were prepared and fourteen of them suffered from artificial accelerated corrosion. Twelve corroded specimens were subsequently strengthened using proposed strengthening schemes. The specimens were tested under axial compression, small eccentricity and large eccentricity to assess effectiveness of strengthening schemes, respectively. Experimental results have shown that rising alkali contents or moduli can increase compressive strength, drying shrinkage, and shorten setting time of AAS. With increasing moduli, there is a steady improvement in compressive strength but a reduction in flexural strength. NaNO2 at 3% of slag mass can reduce the mass loss of reinforcements by 28% and exert nominal influence on the mechanical performance of AAS. An optimal AAS composition was achieved with Na2O content of 3%, modulus of 0.9 and NaNO2 dosage of 3%. Cracking load of AAS ferrocement is closely related to tensile strength of both mortar and stainless steel wire meshes ("SSWM"). With increasing layers of SSWM, peak load of confined square columns improves by 6% to 25%. Corroded columns suffer severe losses in loading capacity up to 46% as compared with control specimens. AAS ferrocement with two layers of SSWM is proved to be an effective strengthening scheme for columns with degree of corrosion of 8.9%. This scheme rehabilitates loading capacity of corroded specimens to a level comparable to or higher than that of control specimens. AAS ferrocement with four layers of SSWM demonstrates its efficiency in strengthening columns with degree of corrosion of 18.3%. It achieves enhancement of 63% and 94% in peak strength and ductility as compared with corroded specimen. Analytical models are proposed to predict tensile strength of AAS ferrocement and loading capacity of specimens strengthened by ferrocement jackets. Prediction is in good agreement with experimental results.
Subjects: Hong Kong Polytechnic University -- Dissertations
Reinforced concrete construction -- Maintenance and repair
Reinforced concrete -- Corrosion
Pages: xx, 179 pages : color illustrations
Appears in Collections:Thesis

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