Ac impedance spectroscopy measurements are used to critically examine the end-to-end (two-point) testing technique employed in evaluating the bulk electrical resistivity of concrete. In particular, this paper focusses on the interfacial contact region between the electrode and specimen and the influence of contacting medium and measurement frequency on the impedance response. Two-point and four-point electrode configurations were compared and modelling of the impedance response was undertaken to identify and quantify the contribution of the electrode–specimen contact region on the measured impedance. Measurements are presented in both Bode and Nyquist formats to aid interpretation. Concretes mixes conforming to BSEN206-1 and BS8500-1 were investigated which included concretes containing the supplementary cementitious materials fly ash and ground granulated blast-furnace slag. A measurement protocol is presented for the end-to-end technique in terms of test frequency and electrode–specimen contacting medium in order to minimize electrode–specimen interfacial effect and ensure correct measurement of bulk resistivity.

This paper presents the verification of analytical modeling for reinforced Engineered Cementitious Composite (R/ECC) in the context of a smeared, fixed crack approach. Verification is provided through the analysis of six R/ECC panels subjected to pure shear. The results demonstrate that the proposed models are capable of replicating various responses of the panels well, provided that tensile property of the ECC is calibrated against those obtained from the panel tests. These responses include load-deformation responses, the magnitudes and directions of principal stress and principal strain, and failure modes. The results also demonstrate the possibility of representing the average crack-shear transfer in the ECC with an explicit smeared model. Finally, this paper includes predictions of the shear capacity of R/ECC panels with a wide range of reinforcement ratios and concludes with discussions regarding factors influencing shear strength.

This paper describes an attempt to predict the response of shear-critical ECC members that exhibit strong anisotropic stress and strain fields. The ECC members investigated include pre-cracked ECC plates under stress field rotation, orthogonally-reinforced ECC (R/ECC) panel under pure shear, and shear-critical R/ECC beams under reversed cyclic loading. To achieve a simple yet accurate prediction, the mechanics of the ECC are represented by smeared models using a fixed crack approach. The applicability of these models is demonstrated through a simulation of ECC plates and R/ECC panel responses. This demonstrates the importance of an appropriate shear transfer model in representing essential behaviors of ECC in an anisotropic field. Predictions of these models were then compared against experimental results of shear-critical R/ECC beams with a M/Vd ratio of 1.0 and 0.5. For beams with a M/Vd ratio of 1.0, a good agreement is observed in terms of hysteretic response, crack pattern, and failure mechanisms. For beams with a 0.5 M/Vd ratio, the analysis somewhat underestimates the beam capacity, although it does predict a correct failure mechanism. Overall, this paper demonstrates that practical application of nonlinear finite-element analysis to ECC structural members is possible.

This paper investigates the causes of excessive long-term deflection of PC bridge viaducts by using 3D integrated material-structural analyses to take into account the coupled chemo-physics at various scales from the molecular size of water to the structural members. The excessive deflection observed at site is found to be rooted in the deformation of cement paste stemming from both externally applied loads and internal stresses driven by capillary surface tension and disjoining pressures in micro-pores. Not only the former but also the later effect is focused in the serviceability control of PC viaducts. It is found that the nonlinear, long-term deflection of the bridge viaduct can be approximately separated into the components of deflections provoked by external mechanistic and internal thermodynamic actions, even though each component is nonlinearly associated with the thermodynamic states of moisture in micro-pores of cement hydrates.

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