The present paper reported an investigation on the personality correlates of alcohol and tobacco use of male college students with Eysenck Personality Questionnaire. The results demonstrated significant associations of alcohol and tobacco use with extraver-sion-introversion and psychoticism. The moderate and heavy drinkers and daily smokers scored higher on both extraversion and psychoticism. Besides, daily smokers had lower scores on lie scale.
The engineering properties of alkali activated materials (AAMs) mainly depend on the constituent materials and their mixture proportions. Despite many studies on the characterization of AAMs, guidelines for mixture design of AAMs and their applications in engineering practice are not available. Extensive experimental studies are still necessary for the investigation of the role of different constituents on the properties of AAMs. This paper focuses on the development of alkali-activated fly ash (FA) and ground granulated blast furnace slag (GBFS) paste mixtures in order to determine their suitability for making concretes. In particular, the influence of the GBFS/FA ratio and liquid-to-binder (l/b) ratio on the slump, setting, strength, and autogenous shrinkage of the alkali activated pastes is studied.It is shown that fresh properties largely depend on the type of precursor (GBFS or FA). The slump and setting time of GBFS-rich pastes was significantly reduced. These pastes also have higher compressive strength than FA-rich pastes. The study identifies important practical challenges for application of the studied mixtures, such as the behavior of their flexural strength and high amplitudes of autogenous shrinkage of GBFS-rich mixtures. Finally, the optimum GBFS/FA ratio for their future use in concretes is recommended.
The microstructures of Portland cement paste (water to cement ratio is 0.4, curing time is from 1 day to 28 days) are simulated based on the numerical cement hydration model, HUMOSTRUC3D (van Breugel, 1991; Koenders, 1997; Ye, 2003). The nanostructures of inner and outer C-S-H are simulated by the packing of monosized (5 nm) spheres. The pore structures (capillary pores and gel pores) of Portland cement paste are established by upgrading the simulated nanostructures of C-S-H to the simulated microstructures of Portland cement paste. The pore size distribution of Portland cement paste is simulated by using the image segmentation method (Shapiro and Stockman, 2001) to analyse the simulated pore structures of Portland cement paste. The simulation results indicate that the pore size distribution of the simulated capillary pores of Portland cement paste at the age of 1 day to 28 days is in a good agreement with the pore size distribution determined by scanning electron microscopy (SEM). The pore size distribution of the simulated gel pores of Portland cement paste (interlayer gel pores of outer C-S-H and gel pores of inner C-S-H are not included) is validated by the pore size distribution obtained by mercury intrusion porosimetry (MIP). The pores with pore size of 20 nm to 100 nm occupy very small volume fraction in the simulated Portland cement paste at each curing time (0.69% to 1.38%). This is consistent with the experimental results obtained by nuclear magnetic resonance (NMR).
Recently, blast furnace slag, fly ash and limestone powder are increasingly used as blending materials in producing concrete. The use of these materials not only has economical and environmental advantages, but also improves the mechanical properties, durability and workability of concrete. In this paper, the results of experimental investigations on the evolution of hydration heat and the development of microstructure of Portland cement blended with blast furnace slag, fly ash or limestone powder are presented. These results show that three blending materials accelerate the hydration of Portland cement, but result in less heat release during the first 72 hours. The Portland cement with blast furnace slag has a denser pore structure than the others.
Experiments were performed on several types of high performance concrete, including high strength concrete and self compacting concrete with different dosages of polypropylene fibers. Differential thermal and thermo gravimetric analyses were used to capture the physcial and chemical developments with temperature. After a special heating process, scannning electron microscopy and mercury instruction porosimetry were applied to investigate the microstructure. Gas permeability test was carried out in order to determine the effect of micro-structural changes on the permeability. Based on the results, the cause of micro structure development with elevated temperature was analyzed. The melting of polypropylene fibers was captured and its influence on the micro structure was also discussed. The relationship between micro structure and gas permeability and the factors affecting gas permeability were also investigated. The conclusions are helpful for understanding the spalling of high performance concrete at elevated temperatures, and would promote further usage of high performance concrete.
When a concrete structure is exposed to high temperature, the mechanical damage and chemical transformation take place simultaneously, which will change the microstructure of material. On the other hand, the mechanical properties and transport properties depend on the development of microstructure of cement paste. In order to study the microstructure changes at high temperature, in this contribution the cement paste samples were firstly heated to varied temperatures from 100 °C to 1000 °C with heating rate of 5 °C/min, and then naturally cooled to indoor temperature. In the microstructural analysis program, the environmental scanning electron microscope (ESEM), mercury intrusion porosimetry (MIP) and thermogravimetry analysis (TGA) were used. The images captured by ESEM were analyzed by segmentation and binary image processing in order to calculate the volume fractions of hydration products and porosity. The change on density distribution of hydration products was characterized by histogram of ESEM image at different temperatures. The porosity and pore size distribution of same samples were studied by MIP and the chemical decomposition was analyzed by TGA as well. Through the analysis of the information obtained from TGA and microstructure measurements, it is found that hydrated calcium silicate (CSH gel) and portlandite dehydrated into sparse crystalline particles when temperature reached 1000 °C. The porosity and the connectivity of pore of cement paste increased along with temperature increase. The results of this research provide a fundamental understanding on how the fire sapling occurs when concrete structures were exposed to high temperature.
Micro-cracks in concrete cover are big problem for both mechanical properties and durability issue. To minimize the damage due to micro-cracks in concrete structure, especially on the concrete cover, one can use the idea of self-healing materials concept to recover concrete cracks from the potential damage. In general, low water/cement ratio is often used in high performance concrete (HPC). The high fraction of anhydrous cement particles left after the reaction with water at a certain age, these anhydrous cement particles can be treated as a reservoir for further hydration. When a microcrack develops, fresh anhydrous surfaces are exposed. If the anhydrous is soaked in water, hydration starts again on these crack surfaces. The newly forming hydrates rapidly fill the crack and seal it. This phenomenon can be simulated by computer numerical model
Abstract Experiments on a vanadium recovery method from vanadium containing BOF‐slag using both a Tamman furnace (3 kg scale) and an induction furnace (150 kg scale) were conducted. The vanadium was extracted into the slag phase by bubbling oxidation gas into a metal bath consisting mainly of V (1–10 mass%), Si (less than 1 mass%) and P (about 1 mass%). The first experiments revealed that the slag formed during oxidation reaction had considerably high phosphate capacity. High phosphorus content would rule out the possibility of using the slag as a raw material for the production of ferrovanadium of high quality. In order to reduce the P‐content in the slag, addition of slag former to reduce phosphate capacity was necessary. A suitable slag system (having the initial composition 40 mass% Al 2 O 3 ‐ 25 mass% CaO ‐ 35 mass% SiO 2 ) and a suitable atmosphere, by using CO 2 , that enhanced the oxidation of vanadium, but limit the oxidation of iron and phosphorus was found. However, more efforts should be put forward, e.g. study of the phase diagram, the viscosity of the slag and even oxide activities to gain more insight into the slag formed by selective oxidation.
