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Pumping changes the rheological properties, workability and construction performance of fresh concrete. However, there were limited knowledges on influences of discharge rates and pumping distances on the fresh properties of concrete. In this paper, effects of various discharge rates and pipeline lengths on rheological properties of self-consolidating concrete (SCC) after pumping were studied. A total of 12 SCC mixtures with the slump flow of 650–745 mm were pumped in pipelines with measured lengths of 342 m, 545 m, and 1044 m by constant discharge rates ranging between 5.1 and 11.4 L/s. Rheological properties were measured before and after pumping. Physical conditions of SCC during pumping, including pressure, shear, and temperature were estimated theoretically and experimentally. Moreover, the total organic carbon in the pore solution of SCC mixtures was measured to evaluate the change of superplasticizer adsorptions after pumping. Test results indicated that, due to pumping, the yield stress increased; the initial tangential viscosity decreased and the shear-thickening phenomenon was eliminated. The changes of yield stresses and viscosity were encouraged by discharge rates. Besides, lower initial slump flow of SCC exhibited a larger slump flow loss after pumping due to a higher shear rate experienced during pumping. The yield stress and viscosity after pumping increased with the increase of pipeline length at similar discharge rates, but decreased with the pipeline length under similar pumping pressures. The adsorption of superplasticizer increased after pumped at relative low discharge rates (5.2–5.7 L/s), but decreased at discharge rates of 7.7–10.8 L/s. [ABSTRACT FROM AUTHOR]

• Resistivity evolution of fresh HSC were measured to characterize the early age hydration process in HSC. • Influence of pumping on early age hydration in HSC were evaluated. • Changes in dynamic yield stress of HSC after pumping were related to corresponding changes in hydration process. The pumping process exerts high pressure and strong shearing on fresh concrete, which may affect the hydration process and rheological behavior of concrete. In this paper, full-scale pumping circuits with lengths of 348-, 600-, and 924-m were established to evaluate the effect of pumping on hydration and rheology of concrete. Electrical resistivity measurement was employed to indirectly evaluate the hydration process of concrete. Ten high-strength concrete (HSC) mixtures with slump flow of 680 ± 50 mm and strength grades of C60-C100 were pumped, and HSC mixtures were sampled before and after pumping for rheological properties and electrical resistivity measurements. Findings indicated that the hydration process, determined by the electrical resistivity evolution, was accelerated after pumping. The end of the dormant period of fresh concrete was decreased by 10.3%-27.3%, and the end of the setting period was shortened by 15.6%-28.4% after pumping. The reduction in the dormant period can be well correlated with the drop in slump flow or increase in dynamic yield stress after pumping. [ABSTRACT FROM AUTHOR]

The rheological properties of fresh concrete can be characterized by the function between shear rate and shear stress. However, neither shear rate nor shear stress can be measured directly, but transformed from the rotation speed and torque logged by the rheometer. Therefore, the relationship between the rheological model and the torque-rotation speed function needs to be established. In order to describe the nonlinear rheological behavior of fresh concrete, the Robertson-Stiff model was proposed in this paper, and the relationship between rotation speed-torque and rheological parameters measured by the coaxial cylindrical rheometer was derived. Eight concrete mixtures were made, and its rheological properties were tested with ConTec 5 viscometer. Then raw data was utilized to validate the model. The results showed that the Robertson-Stiff model could be used to describe the rheological behavior of fresh concrete. [ABSTRACT FROM AUTHOR]

• Changes in rheological properties of high-strength concrete due to pumping were systemically investigated. • Fresh concrete was sampled in dismantled pipes for the rheological test. • Shear-thickening in high-strength concrete was eliminated after pumping. • Shearing energy during agitation and pumping was estimated and correlated to the changes in viscosity. Pumping of high-strength concrete (HSC) in high-rise or long-span structures is of paramount importance in constructions. However, pumping technology in practice is highly dependent on practical field experience, and full-scale testing that is carried out for complex projects involving new materials or long pumping distances. In this paper, a long pumping circuit was built to study changes in fresh properties of HSC due to pumping. In total, 10 HSC mixtures with strength grades of C60 to C100 were pumped at constant flow rates in pipelines measuring 348, 600 and 924 m in length. Rheological properties, workability characteristics, and concrete temperature were measured on concrete specimens sampled before and after pumping. Rheological properties of concrete sampled in dismantled pipes shortly after the end of pumping were also determined. Test results indicated that the yield stress increased, the initial tangential viscosity decreased and the shear-thickening phenomenon was eliminated due to pumping. The increase in yield stress mostly occurred in the first half of the pipeline, and the tangential viscosity decreased nearly linearly along the pipe length. The levels of drop in initial tangential viscosity were found to positively correspond to the calculated shearing energy, which is estimated given the shear rate, apparent viscosity and elapsed time during agitation and pumping. [ABSTRACT FROM AUTHOR]