Investigation of the Relationship Between Formation Factor and Fresh Properties of Concrete

Formation factor of fresh cementitious pastes was investigated experimentally as a function of time from initial mixing and mixture design properties such as supplementary cementitious material (SCM) replacement level, water-to-binder ratio (w/cm), and superplasticizer dosage. SCM types included fly ash, slag and silica fume. A total of 54 paste mixtures were studied. The formation factor of each fresh paste was determined at the 30th, 60th, and 90th minutes from initial mixing. It was shown that for a given type of paste mixture (e.g. OPC plus silica fume), formation factor decreases if porosity or w/cm ratio increases, and this relationship can be well formulized by a power function. Although both paste and pore solution resistivity decrease with time in fresh cement paste mixtures until initial setting, their ratio (formation factor) remains relatively constant because it is only indicative of physical formation of solid particles in the pore solution. Formation factor of fresh cement paste is strongly correlated to its porosity through Archie's law, which implies that formation factor decreases if porosity increases. This decrease of formation factor is attributed to the smaller solid particles fraction (i.e., 1-φ) with high resistivity (i.e., lower amount of non-conductive component compared to conductive component). The tortuosity of paste affects the formation factor even at a constant porosity. Smaller size, angular shape, and more even distribution of particles increase the tortuosity of the paste. Slag and fly ash particles considerably decrease tortuosity; whereas silica fume incorporated pastes have almost the same tortuosity as OPC pastes. Superplasticizer addition significantly increases tortuosity through a better distribution of solid particles.Pacific Northwest Transportation Consortium Natural Science and Engineering Research Council of Canad

Formation factor of fresh cementitious pastes

Formation factor of fresh cementitious pastes was investigated experimentally as a function of time from initial mixing and mixture design properties such as supplementary cementitious material (SCM) replacement level, water-to-binder ratio (w/cm), and superplasticizer dosage. SCM types included fly ash, slag and silica fume. A total of 54 paste mixtures were studied. The formation factor of each fresh paste was determined at the 30th, 60th, and 90th minutes from initial mixing. It was shown that the formation factors of fresh cementitious pastes were strongly correlated with porosity, tortuosity and w/cm. Slag and fly ash considerably decreased tortuosity of the pastes, whereas silica fume did not have a significant effect. Superplasticizer addition increased tortuosity through a better distribution of the solid particles. A model representing the formation factor of the tested fresh cementitious pastes was provided. Similar models can be used to determine the initial setting time of cement-based materials and quality control of fresh mixtures in precast and ready-mix concrete plants

Kinetics of passivation and chloride-induced depassivation of iron in simulated concrete pore solutions using electrochemical quartz crystal nanobalance

Kinetics of passivity and chloride-induced depassivation of iron exposed to simulated concrete pore solutions were studied using electrochemical quartz crystal nanobalance (EQCN), electrochemical impedance spectroscopy (EIS), and open circuit potential (OCP) monitoring. Passivation followed a two-stage logarithmic film formation process: protective film mostly formed within the first 10 min to 20 min of exposure to the passivating solutions as indicated by a sharp mass increase accompanied by impedance and phase angle data showing trends toward passivation. After this initial passivation period, mass continued to increase, albeit at a significantly slower rate. Electrochemical indicators during this period remained relatively constant and stable, suggesting that the iron remained passive. The mass increase during the post-passivation period was indicative of the formation of additional oxides, while relative stability of the OCP, impedance and phase angle measurements suggested that these oxides were likely more porous, and therefore, less protective than those that had formed during the first 10 min to 20 min. Chloride addition initially caused mass gain while all electrochemical indicators indicated stable passivity, suggesting an induction period before the first signs of pitting. Mass increase during this period supports the predictions of depassivation models that hypothesize the adsorption and ingress of chlorides though the outer layers of oxides

Alexander Scordelis Memorial Session: Thin Shell Concrete Structures

IASS-IACM 2008 Session: Alexander Scordelis Memorial Session: Thin Shell Concrete Structures -- Note: Video is available for the Keynote Lectures by Billington, Meyer and Willam -- Session Organizers: Maria GARLOCK (Princeton University), John ABEL (Cornell Univ.) -- Keynote Lecture and Video: "Alexander Scordelis: Friend, colleague and mentor" by David P. BILLINGTON (Princeton University) -- Keynote Lecture and Video: "Alexander C. Scordelis and concrete shells" by Christian MEYER (Columbia University) -- Keynote Lecture and Video: "Alexander C. Scordelis: Legacy in finite element analysis of reinforced concrete" by Kaspar J. WILLAM (University of Colorado) -- Keynote Lecture: "Alex C. Scordelis? great achievements in bridge engineering ? From computer programs to the Golden Gate Bridge retrofit" by Ekkehard RAMM (Stuttgart University) -- "3-D pushover analysis of a collapsed reinforced concrete chimney" by Wei HUANG (KPFF Consulting Engineers), Phillip L. GOULD (Washington University) -- "Structural optimization of concrete hyperbolic paraboloid umbrella shells" by Powell DRAPER, Maria E. Moreyra GARLOCK, David P. BILLINGTON (Princeton University) -- "Delamination in a two-layer thin-shell concrete dome with unanticipated construction openings" by Sinead C. MAC NAMARA (Syracuse University) -- "Testing, modeling and constructing wood-plastic composite Catalan vaults" by Edmond SALIKLIS, Kyle WHITE (Cal Poly) -- "Concrete vaulting in Imperial Rome: A structural analysis of the Great Hall of Trajan's Markets" by Renato PERUCCHIO, Philip BRUNE (University of Rochester) -- "Numerical study of steel corrosion in concrete shell members" by O. Burkan ISGOR, Mohammad POUR-GHAZ, Pouria GHODS (Carleton University