This paper introduces the possibility of in-situ assessment of loading and remaining strength in concrete structures by means of measuring discharge of electric current from loaded specimens.The paper demonstrates that the techniques have been applied to other rock-like materials, but that for the first time they are applied to cement based materials and a theoretical model is proposed in relation to the appearance of electrical signals during sample loading and up to fracture.A series of laboratory experiments on cement mortar specimens in simple uniaxial compression, and subsequently in bending -hence displaying both tension and compression -are described and show clear correlations between resulting strains and currents measured. Under uniaxial loading there is a well-defined relationship between the pressure-stimulated current (PSC) as a result of a monotonic mechanical loading regime.Similar results are observed in the three-point bending tests where a range of loading regimes is studied, including stepped changes in loading.While currents can be measured at low strains, best results seem to be obtained when strains approach and exceed yield stress values.This technique clearly has immense potential for structural health monitoring of cementbased structures. Both intermittent and continuous monitoring becomes possible, and given an ongoing campaign of monitoring, remaining strength can be estimated.

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The electrical signals emitted during the application of uniaxial compressive mechanical stress upon cement mortar specimens are observed and discussed in this paper. This work discusses the electrical signals that are detected when the specimens are excited by a stepwise uniaxial stress increase from a low level (σ L ) to a higher level (σ H ) at a fast or slow rate and consequently remain at a high pressure regime for a long time. When maintaining constant mechanical stress for a long time, creep phenomena are evident in the specimen and the corresponding electrical emissions are recorded and analyzed. The characteristics of the electrical signal give clear information regarding the breaking stress (σ F ) of the material. The electrical emission recordings are of great interest when the applied σ H is located in the vicinity of the failure stress; the emitted electrical current increases greatly due to the sequential formation and propagation of cracks that occurs in this stress region. Thus, by correlating the strain rate variations to the electrical emissions this methodology can be used to predict failure due to compressive stress in cement mortars.

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