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

Improving the energy efficiency of buildings with hollow core slabs: A numerical investigation

Thermal mass is the capacity of a material to store heat. Concrete or masonry has a higher heat storage capacity than air; therefore, there is significant potential in using the natural thermal mass of buildings to reduce and to shift peak load energy demands. Most residential and commercial buildings have adequate thermal mass that can be utilized to reduce and shift peak energy load. In particular, hollow core slabs that utilize air passing through the slabs to transfer heat in and out of concrete, have the potential to reduce and to shift peak load requirements. This paper presents a numerical investigation that aims to investigate design parameters of hollow core slabs for the maximum energy efficiency, particularly with respect to peak energy demand reduction and shifting. Results reveal that hollow core slab system can be actively used to improve the energy efficiency of buildings. The use of phase change materials (PCM) along with the thermal mass of hollow core slabs enhances both peak load reduction and phase shift; therefore, composite systems that combine the thermal mass of concrete with PCMs emerge as feasible design alternatives to commonly used flat slab systems

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

Simulating waste temperatures in an operating landfill in Québec, Canada

A bioreactor landfill operated in Sainte-Sophie, Québec, Canada was instrumented to better understand the waste stabilization process in northern climates. Instrument bundles were placed within the waste to monitor temperature, oxygen, moisture content, settlement, total load, mounding of leachate and electrical conductivity. A finite element model was developed to simulate the heat fluxes to and from the waste, as well as heat generation within the waste from both anaerobic and aerobic processes. The results of the analysis suggest the majority of the aerobic activity occurs in the top portion of the waste lift exposed to ambient air. In addition, the model indicates that frozen waste lifts require a significant amount of heat to thaw the liquid fraction. The model also demonstrates that when a lift of cold waste is placed at the bottom of the landfill, the subsurface acts as a significant source of heat

Numerical and experimental investigations for safer transportation of dangerous goods

Transportation of dangerous goods (DG) represents an important portion of the overall transport of freight in the world. Ground transport (excluding pipelines) moves approximately 21% to 31% of the total tonnage of DG in Canada. Accidents involving DG might occur at any time, at any location along transport routes or within storage areas and they not only affect people and the environment but also have a great impact on the national economy. This paper presents the details of experimental investigation studying the blast attenuation capability of suppressive shield panels (SSP). Moreover, the performance of one type out of four designed suppressive shield panels (SSPs) using a numerical approach to verify an experimental study. The technology can be used for the storage, processing and transport of explosive materials, or can also be applied to protecting attractive targets and infrastructure that is deemed vulnerable to explosive attacks, including those attacks accompanied by the threat of fragment bombs. Various configurations of commercially-available steel angles were assembled as SSPs and were evaluated for their capability to attenuate blast pressure from detonating Pentolite charges. Results obtained from the experimental test