Nano reinforced cement paste composite with functionalized graphene and pristine graphene nanoplatelets

This study examines and compares the workability, hydration, mechanical, microstructure and transport properties of cement paste composites containing the three forms of graphene-based 2D nanomaterials synthesised from epigenetic graphite deposit, namely, graphene oxide (GO), reduced graphene oxide (rGO), and pristine graphene nanoplatelates (G). Graphene materials were used from 0.01% to 0.16% of cement weight. The rGO and G were treated with salt and surfactant, respectively during synthesis, to improve dispersion in water. Characteristics and physical strength vary among GO, rGO and G, which have influenced the properties of nano reinforced graphene-cement composites (GCCs). The 28-day compressive and flexural strength of graphene (GO, rGO and G) cement composite improved by 28% and 81%, 30% and 84%, and 39% and 38%, respectively, compared to the control mix (cement paste without graphene materials). Finally, microscopic analysis, dynamic vapour sorption (DVS), electrical resistivity and water sorptivity results suggested that graphene materials densify and reinforce the composite microstructure

Seismic retrofit of deficient reinforced concrete shear walls

This research describes an experimental and analytical investigation to evaluate the seismic performance of poorly designed and detailed reinforced concrete (RC) flexural shear walls both in their as-built conditions and after being retrofitted. Older shear walls have several deficiencies which make them vulnerable in case of moderate to severe earthquakes. Full-scale shear wall specimens were constructed and tested under reversed cyclic loading. Two different techniques were chosen to retrofit the deficient walls in order to improve the overall performance. A retrofit technique using Carbon Fibre Reinforced Polymer (CFRP), having minimum intervention, was studied to determine the seismic performance. A more labour-intensive repair technique, including the addition of a reinforced concrete jacket in the critical region (location of potential plastic hinging and lap splices of vertical bars) together with CFRP wrapping was also studied. The responses obtained from experiments were used to develop behavioural models, capable of representing the global responses of the walls, as well as critical failure modes observed in the experiments. These models provide useful tools for predicting the complete reversed cyclic loading responses of shear walls. The analytical models were used to predict the responses of a deficient prototype wall-frame structure in its original condition as well as after retrofit, subjected to different seismic hazard levels. This study enabled an evaluation of the performance of the prototype structure to determine the effectiveness of retrofit and repair measures.Cette recherche présente une étude expérimentale et analytique pour évaluer la performance sismique des murs des contreventements déficients avant et après réhabilitation sismique. Les murs représentent la construction typicalité des 1960's et ils sont plusieurs déficiences. Les murs à grande échelle ont été construits et soumises à des charges cycliques alternées. Deux techniques différentes ont été choisies et examiné pour la réhabilitation sismique des murs déficients. Une méthode de dimensionnement de réhabilitation sismique, avec l'intervention minimale, utilisant de polymères renforcés de fibres de carbone (PRFC). La deuxième technique compris l'ajout d'une chemises en béton armé (renforcés de fibres d'acier et des armatures) dans la région critique (la région de rotule plastique potentielle et du chevauchement des armatures verticales), accompagnée PRFC pour l'amélioration résistance cisaillement de murs. Les réponses obtenues à partir d'expériences fournissent des informations importantes sur les caractéristiques des murs des contreventements qui peuvent être utilisées pour développer modèles comportementaux et calibrer des techniques de prédictions numériques. Ces modèles sont capables de représenter les réponses globales des murs. Les modèles numérique ont été utilisés pour prédire les réponses d'un vieux bâtiment (ossatures résistantes au moment munies de murs de contreventement) de cinq étages en béton armé dimensionne selon le code 1963 de l'ACI ((American Concrete Institute) et Code national du bâtiment 1965 du Canada (CNBC), et pourrait être vulnérables lors de séismes forts ou même modères. Le bâtiment est analyse (statique pushover et l'analyse dynamique de l'historique temporel) dans le régime non-linéaire avant et après réhabilitation séismique des murs

Comparison of Linear Temperature Corrections and Activation Energy Temperature Corrections for Electrical Resistivity Measurements of Concrete

Electrical resistivity measurements are increasingly being used as measurements for concrete acceptance in practice. It has been shown that these measurements are sensitive to temperature. This paper examines the influence of temperature on electrical resistivity measurements in concrete. Two temperature correction approaches that are commonly used by researchers and practitioners were evaluated: a linear temperature correction approach (α) and an activation energy-based temperature correction approach (Ea-cond). These approaches were compared with each other and their predictive capabilities were assessed using measured data from various concrete mixtures. It was found that for cases of low temperature sensitivity (low values of α or Ea-cond), the predictions obtained with α and with Ea-cond were similar. However, the Ea-cond approach was found to provide more accurate corrections (lower error) than corrections using α for measurements conducted at lower temperatures and for systems with higher temperature sensitivities (high values of α or Ea-cond). For saturated concrete specimens, both the linear (α) and activation energy (Ea-cond) approaches are acceptable, whereas the use of the Ea-cond approach provides better predictive capabilities in sealed concrete specimens, especially at low temperatures. The average values for Ea-cond were found to be 29.8 kJ/mol for sealed specimens and 15.8 kJ/mol for saturated specimens, and corresponding average values of α are 3.25 %/°C and 2.00 %/°C, respectively. The values for Ea-cond for saturated specimens are closer to what is expected of a pore solution on its own