Steel bars in reinforced concrete are protected from corrosion by the high pH environment of the surrounding concrete. This alkaline environment is destroyed by the reaction of atmospheric CO, with the Ca(OH), of the concrete mass. When this process, called carbonation of concrete, reaches the reinforcing bars, corrosion of the latter may commence. In this paper, the physiochemical processes in this phenomenon are presented and modeled mathematically. The mathematical model is fairly complex, but certain simplifying assumptions are possible, which lead to the formation of a "carbonation front" and to a simple analytical expression for the evolution in time of this front, in terms of the composition parameters of cement and concrete and of the environmental conditions. This simple expression is in very good agreement with experimental results obtained in this and in previous studies. The effect of some parameters on the carbonation front propagation is also discussed. Porosity at t,, -0 Porosity decrease due to hydration AeH -Z ([i],AcFi) Constituent i C,S C S C,A C,AF M-K. x lo3 (kg/mol) 228.30 172.22 270.18 485.96 AV, x lo6 (m3/mol) 53.28 39.35 149.82 112.81 AF,, -3.85 . m'/mol AFcsH -15.39 . m3/mol *Computed with molecular weights and molar volumes of the principal constitu-**The terms involving the unhydrated and subject to carbonation C,S and C S ents of Portland cement and parameters used in conjunction with 4 . 2 5 .can be omitted because their contribution to porosity change is negligible.

This chapter is the only one in the book devoted exclusively to existing concrete buildings. It builds on:-Chapter 1, for the seismic performance requirements that may be apply to existing buildings and to their upgrading, -Chapter 2, for the demonstration of the inherent vulnerability of substandard existing buildings, -Chapter 3 for the quantification of the cyclic force and deformation capacity of concrete members, including the effect of poor detailing or retrofitting, and on -Chapter 4 for the estimation of the seismic response via (mainly nonlinear)analysis.The first part of the chapter is mainly devoted to seismic assessment of the as-is building. The rest to its upgrading through appropriate and cost-effective retrofitting. One section, namely Section 6.5, is specific to Part 3 of Eurocode 8. Retrofitting strategies and techniques commonly used today and in the foreseeable future for a concrete building as a whole and for its members, respectively, are described and their scope, pros and cons highlighted. Procedures, rules and expressions are given for practical member retrofit design. Finally, practical retrofitting is illustrated through two real applications.

Synopsis Plastics reinforced with continuous glass fibres have outstanding tensile strength in the fibre direction and excellent corrosion resistance, but are characterized by low modulus and low compressive strength. It is proposed to develop composite members in which a prefabricated FRP (fibreglass-reinforced-plastic) casing is used initially as the form to cast plain concrete, and thereafter to confine the concrete, act as tensile reinforcement and provide corrosion protection. Significant cost savings are possible with the proposed combination of materials, especially in exposed structures, such as bridges. An experimental investigation of FRP-encased concrete cylinders in axial compression and of rectangular FRP-encased beams in bending is presented. The results demonstrate the excellent strength and ductility characteristics of FRP-encased members. The behaviour of circular FRP-encased concrete beam-columns is described also, in terms of analytically obtained moment-axial-load and ductility-axial-load interaction diagrams and moment-curvature relations. The weathering characteristics and the fire resistance of the FRP are discussed, and measures to improve these environmental properties are reviewed.

The effects of masonry infills on the global seismic response of reinforced concrete structures is studied through numerical analyses. Response spectra of elastic SDOF frames with nonlinear infills show that, despite their apparent stzening effect on the system, infills reduce spectral displacements and forces mainly through their high damping in the first large post-cracking excursion. Parametric analyses on a large variety of multi-storey infilled reinforced concrete structures show that, due to the hysteretic energy dissipation in the infills, if the infilling is uniform in dl storeys, drifts and structural damage are dramatically reduced, without an increase in the seismic force demands. Soh-storey effects due to the absence of infills in the bottom storey are not so important for seismic motions at the design intznsity, but may be very large at higher motion intensities, if the ultimate strength of the infills amounts to a large percentage of the building weight. The Eurocode 8 provisions for designing the weak storey elements against the effects of infill irregularity are found to be quite effective, in general, for the columns, but unnecessary and often counterproductive for the beams.

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