Robustness is defined as the capacity of cement-based materials to retain fresh properties when subjected to either small variations in the constituent elements or small changes in the mixing procedure. Compared to normal concrete, self-consolidating concrete (SCC) may show less tolerance to those changes. Most robustness studies focus on initial rheological properties or workability, but concentrate less on the evolution of these properties within the first hour(s). This paper presents the results of an investigation aimed at evaluating the change of yield stress and plastic viscosity with time of cement pastes with SCC consistency, which is mainly affected by variations in the water content and the adding time of the superplasticizer. A change in water content also influences the initial rheological properties, and these differences are amplified over time. The difference due to the different adding time of the superplasticizer is, however, reduced or even reversed over time.

The number of applications where self-consolidating concrete (SCC) is used is rising considerably worldwide because of its advantages over conventional concrete. Large-scale SCC production with good degrees of reliability has encouraged engineers to further study the stability of different SCC mixture designs in terms of robustness. The robustness of a SCC mixture is the stability of its properties when the original mixture design is affected by errors in weighing the constituents. To evaluate the robustness of SCC, six different SCC mixture designs were selected. Variations were applied to them, simulating large-scale production errors, and their properties in fresh and hardened states were evaluated. The influence of such errors on concrete properties was analyzed by means of analysis of variance. In addition, tolerances generally accepted by codes were compared to statistical distributions of errors obtained from real data provided by several Spanish concrete producers. In general, tolerances for traditional concrete have proved to be valid for SCC as well. Errors in weighing water and fines contents are of capital importance and are admissible up to ±6%.

A finite element (FE) model is proposed to simulate the corrosion-induced cracking of reinforced concrete (RC) beams. The smeared cracking approach is used to model the cracking of ordinary concrete, ductile fiber-reinforced cementitious composites (DFRCC), and engineered cementitious composites (ECC). The model simulates the cracking of ordinary concrete beams and RC beams containing ECC and DFRCC materials. The strains obtained from the FE models are compared with that measured by the fiber-optic strain sensor (FOSS) gauge, which is placed between longitudinal steel bars at midspan of RC beams during the accelerated corrosion test. The model could predict the corrosion-induced damage tolerance of ECC and DFRCC materials and found that it is several times higher than that of ordinary concrete. The model predicted the uniform damage in the ECC and the DFRCC materials due to corrosion compared with localized damage in ordinary concrete. The model also predicted that the delamination of the cover of the RC beams containing ECC/DFRCC materials will occur at a higher level of steel loss compared with that of an ordinary concrete beam. The better performance exhibited by the RC beam containing ECC/DFRCC materials is due to their higher tensile strain capacity, strain hardening, and multiple cracking behavior.

Broad applications of fiber-reinforced polymer (FRP) reinforcement are hindered by its elastic brittle behavior, which results in reduced structural ductility. In addition, due to the lower modulus of elasticity, serviceability considerations such as deflection and crack width control present serious challenges to designers. This paper reports new means to address these issues by introducing engineered cementitious composite (ECC), which is designed based on micromechanics principles and exhibits higher tensile and shear ductility, to replace brittle concrete matrix. Three series, totaling 16 GFRP reinforced beams with various shear span-depth ratios and longitudinal reinforcement ratios, were tested. The results reveal that, under the same reinforcement configurations, ECC beams exhibit significant increases in flexural performance in terms of ductility, load-carrying capacity, shear resistance, and damage tolerance (such as crack width or spalling) compared with the counterpart high-strength concrete (HSC) beam. The extent of improvement strongly depended on the failure mode; that is, when the limit state was dominated by matrix behavior, more significant improvement was observed. Moreover, ECC beams without shear reinforcement demonstrate better performance than HSC beams with dense steel stirrups, which suggests that elimination of shear reinforcement is feasible when the concrete matrix is replaced by ECC.

A laboratory test program was undertaken to determine the effects of variation in concrete constituents and proportions of response of a nuclear water/cement content gage. A total of 14 separate test series were evaluated in the program. The evaluations included study of the effects of the following variables on the nuclear gage’s determination of cement and water contents: 1) air content; 2) hold time; 3) Classes C and F fly ash; 4) ground, granulated blast furnace slag (GGBFS); 5) maximum size of coarse aggregate; 6) limestone coarse and fine aggregates; 7) basalt coarse aggregate; and 8) temperature. The testing showed that the cement content probe is sensitive to all materials containing calcium atoms; therefore, the gage must be calibrated with exactly the same materials as will be used on the job in question. While the water probe is, in theory, only sensitive to hydrogen atoms, there are some effects from other materials; therefore, calibrations using job materials are also required. With proper calibration, the cement gage is capable of determining cement content of fresh concrete to within approximately 10 to 20 lb/yd3 (6 to 10 kg/m3). The water gage is capable of determining water content to within approximately 2 to 4 lb/yd3 (1 to 2 kg/m3). From the predicted standard errors in water and cement contents, an error in calculated water-to-cement ratio (w/c) of as much as 0.03 may be expected. As entrained air decreases concrete density, which appears to have an effect on the gage response, it is necessary to control air content within very close tolerances (± 1 percent) in both laboratory calibrations and field work with the gage.