Improvement of historic reinforced concrete/mortars by impregnation and electrochemical methods

Old reinforced concrete (RC) structures often exhibit unsatisfactory performances in terms of both residual serviceability and seismic behavior. The durability requirements were not considered at all at the age of design and construction, exposing such structures to severe decay in aggressive urban and/or industrial environment; in the meantime, the use of plain steel bars (with poor bond strength) was common at the age of construction and this jeopardizes the RC performance under cyclic load reversals like those induced by earthquakes. In this paper, the deep impregnation of cement-based mortars and concrete with a solution of ethyl silicate and with electrochemical treatments by means of a solution of sodium carbonate was investigated, with a twofold aim: (1) increasing the bond strength of the embedded plain steel bars in existing structures without any need for demolition and (2) increasing the durability and safety of the reinforced concrete elements. Both the treatments are already exploited in other fields: ethyl silicate solutions are widely used for stone consolidation (and only recently proposed for concrete surface protection), while migration of sodium carbonate under DC voltage is used for RC realkalization. In the present study these treatments are expected to penetrate inside mortar and concrete and to modify their microstructure, hence improving their properties. The effects of the treatments are investigated by comparing the characteristics of treated and untreated mortar and concrete samples reinforced with plain bars, in terms of penetration inside the samples, pull-out strength, water absorption, pore size distribution, carbonation resistance and corrosion resistance