فهرست مطالب maziar zareechian

Plastic shrinkage occurs in fresh concrete usually within few hours after mixing the concrete and risk of its cracks endangered concrete structures especially in the elements with high surface to volume ratio such as slabs or highway pavement. An experimental investigation on capillary pore pressure, tensile strength and plastic shrinkage of concrete is presented here. The aim of research is to study the relationship between capillary pore pressure build up in concretes, early age tensile strength and plastic shrinkage strain. Capillary pore pressure apparatus was created for the first time in Iran for this research. Test was done in a climate chamber with the constant evaporation rate of 0.7 kg/m²/h .Eight types of concrete in two categories such as normal concrete and self-consolidating concrete were tested including mixture without any mineral admixtures and containing of pozzolanic materials such as silica fume and metakaolin. The results indicated that there is no strong relationship between capillary pore pressure and plastic shrinkage strain and it can be concluded that other parameters such as tensile strength development can play an important role in the plastic state of concrete. However, it should be mentioned that capillary pressure is the main cause and driving force of concrete shrinkage and the onset of capillary pressure is directly related to the onset of shrinkage. The results also showed that early age tensile strength can be effective factor in controlling cracks of concrete. No cracks appeared in the mixtures containing of silica fume and metakaolin in comparison with the reference mixture. However capillary pore pressure in these mixtures was higher than pressure in the reference mixture.

In this study, the effects of spraying nanoparticles with different geometries (nano-SiO2, nano-halloysite, and nano-montmorillonite) on surface characteristics of concrete pavement in terms of microstructure. The initial and final setting times of mixtures were determined to investigate the proper spraying time for applying on the pavement surface at early ages. To precisely investigate the microstructural properties, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and atomic force microscopy (AFM) were used. The results revealed that spraying nanoparticles improved the abrasion and skid resistance as well as transport properties of the concrete surface, especially at the initial setting time. According to the tribology testing, the surface friction coefficient of sprayed samples compared to the reference sample (not sprayed) was increased 28%, on average. AFM results verified that this growth is due to the improved surface roughness and van der Waals forces. Based on the FTIR results, the abrasion resistance of the samples gradually diminished by increasing the depth due to reduction of nanoparticles penetration, thus, reducing its positive effect. In addition, a good relationship with regression coefficient of 0.79 was found between the surface tensile strength and the abrasion resistance of the specimens.

Plastic shrinkage occurs in fresh concrete usually within few hours after mixing the concrete and risk of its cracks endangered concrete structures especially in the elements with high surface to volume ratio such as slabs or highway pavement. An experimental investigation on capillary pore pressure, tensile strength and plastic shrinkage of concrete is presented here. The aim of research is to study the relationship between capillary pore pressure build up in concretes, early age tensile strength and plastic shrinkage strain. Capillary pore pressure apparatus was created for the first time in Iran for this research. Test was done in a climate chamber with the constant evaporation rate of 0.7 kg/m²/h .Eight types of concrete in two categories such as normal concrete and self-consolidating concrete were tested including mixture without any mineral admixtures and containing of pozzolanic materials such as silica fume and metakaolin. The results indicated that there is no strong relationship between capillary pore pressure and plastic shrinkage strain and it can be concluded that other parameters such as tensile strength development can play an important role in the plastic state of concrete. However, it should be mentioned that capillary pressure is the main cause and driving force of concrete shrinkage and the onset of capillary pressure is directly related to the onset of shrinkage. The results also showed that early age tensile strength can be effective factor in controlling cracks of concrete. No cracks appeared in the mixtures containing of silica fume and metakaolin because of tensile strength improvement up to 55 and 32 percent respectively, in comparison with the reference mixture. However capillary pore pressure in these mixtures was higher than pressure in the reference mixture.