Magnesium potassium phosphate cement (MKPC), made of sintered magnesium oxide and potassium phosphate, is a new material for construction and structural repair. It possesses high early strength and bond capacity, low drying shrinkage, excellent fire resistance and compatibility with concrete. These characteristics render it an ideal material for strengthening reinforced concrete (RC) structures. This study developed a MKPC-based textile reinforced cementitious composite (TRCC) to strengthen RC beams at soffit. Three-point flexural tests were conducted on two control specimens without strengthening and two strengthened specimens. Experimental results showed that the TRCC system exhibits good bonding with substrate concrete. The strengthened specimens failed due to rupture of textile meshes in TRCC. TRCC could improve load capacity by 4-25%, postpone propagation of cracks, reduce tensile strain of main reinforcement and reduce deflection of beams at the same load level. High relative textile ratios contributed to the load resistance while impaired the ductility of strengthened beams. Design formulae are proposed to predict the flexural capacity of beams strengthened by MKPC-based TRCC, and reasonable prediction close to experimental results can be obtained from the formulae.
Chloride-induced corrosion of reinforcement has endangered the safety of reinforced concrete (RC) structures. It is, therefore, necessary to strengthen the corroded RC members to ensure structural safety. This study aims to investigate the effectiveness of alkali-activated slag (AAS) ferrocement jackets in strengthening corroded RC columns. AAS ferrocement specimens with various layers of stainless steel wire mesh (SSWM) were subjected to direct tensile tests. Square RC columns suffered artificially accelerated corrosion and were subsequently strengthened by AAS ferrocement jackets. Axial compressive tests were conducted on the column specimens. Experimental results have shown that corroded specimens suffer severe losses in loading capacity up to 46% as compared with the control one. Volume fraction of transverse SSWM (ρ v) plays primary role in loading capacity and ductility of ferrocement and its confinement on column specimens. Ferrocement with ρ v of 0.266% can rehabilitate loading capacity of specimens with corrosion degrees of 8.9% and 18.3% by 37% and 46%, respectively. Corroded specimen strengthened by ferrocement with ρ v of 0.532% achieves approximately two times the ductility than the one without strengthening. Ferrocement jackets provide better and uniform confinement to core concrete than new stirrups. Analytical models are proposed to predict tensile strength of AAS ferrocement and loading capacity of specimens strengthened by ferrocement jackets. The prediction is in good agreement with experimental results.
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