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- MakaleYalnız künye2013The effects of antifreeze use on physical and mechanical properties of concrete produced in cold weather
Çullu, Mustafa; Arslan, Metin
This study examined the effects of antifreeze on the physical and mechanical properties of the concrete which are produced in cold weather. 30% Calcium Nitrate and 5% hydroxyethylaminemixture (HEA), Calcium Nitrate (KN) and Polyhydroxy Amine (PA) were used as additives in antifreeze. Prepared concrete samples were placed in a formwork and exposed to the frost at 0 °C, -5°C, -10°C, -15°C and -20°C for 2 days. Afterwards, concrete samples in the freezer were cured at the room temperature until the 28th day and permeable pore space volume, water absorption ratio, density, capillarity ratio, impermeability, compressive strength, static modulus of elasticity, Poisson's ratio and tensile strength values of the concrete samples were determined after the curing. In conclusion, 30% Calcium Nitrate and 5% hydroxyethylaminemixture (HEA) were found to be giving the best performance among the antifreeze types. The physical and mechanical properties of the concrete were negatively affected from all antifreeze types due to the temperature decrease of the exposed fresh concrete.
- MakaleYalnız künye2013The effects of high temperature on mechanical properties of cementitious composites reinforced with polymeric fibers
Çavdar, Ahmet
Polymeric fibers are cheap and popular materials used in the concrete industry, and they may improve the mechanical properties of cementitious composites under high temperature. In this study, three different types of polymeric fibers - Copolymer Polypropylene/polyethylene (CPP), Homopolymer Polypropylene (HPP), and Aramid (AR) - are added to cement mortars with the aim to investigate their mechanical contributions to mortars under high temperature, comparatively. These fibers are added into mortars in five different ratios (0.0%, 0.3%, 0.6%, 0.9% and 1.2%) by volume. The mortars are subjected to following temperatures: 21 °C (normal conditions), 100 °C (oven dry), 450 °C, 650 °C and 850 °C. It is concluded that polymeric fibers used in this study contribute to the flexural strength of mortars under normal dry conditions (100 °C). This effect continues clearly up to 450 °C and polymeric fibers show effects on flexural strength especially at 450 °C. Each fiber shows the best performance different addition ratio when flexural and compressive strength are taken into consideration at the same time under high temperature. The highest increase in flexural strength and the lowest decrease in compressive strength are at 0.3-0.9% fiber addition ratio for HPP, at 0.3-0.6% fiber addition ratio for CPP and at 0.9% fiber addition ratio for AR for every temperature.
- MakaleYalnız künye2012A study on the effects of high temperature on mechanical properties of fiber reinforced cementitious composites
Çavdar, Ahmet
The flexural strength and ductility properties of cementitious composites (mortar) under high temperature may be significantly improved by incorporating different types of fibers. In this study, four different types of fibers are added to cement mortars with the aim to investigate their mechanical contributions to mortars under high temperature, comparatively. Polypropylene (PP), carbon (CF), glass (GF) and polyvinyl alcohol (PVA) fibers are chosen for research. These fibers are added into mortars in five different ratios (0.0%, 0.5%, 1.0%, 1.50% and 2.0%) by volume. The mortars are subjected to the following temperatures: 21°C (normal conditions), 100°C (oven dry), 450°C and 650°C. The mechanical properties investigated are flexural strength, deflection and compressive strength of the cement mortars. In addition, thin sections of mortars are investigated to obtain changes in mortar because of high temperature. It is concluded that all fiber types contribute to the flexural strengths of mortars under high temperature. However, this contribution decreases with an increase in temperature. The samples with PVA show the best flexural performance (75-150%) under high temperature. CF which does not melt under high temperature also gives high flexural strength (11-85%). The compressive strengths of the mortars reduce under high temperature or with fiber addition. The highest increase in flexural strength and the lowest decrease in compressive strength is at 0.5-1.5% for CF if all temperature conditions are taken into consideration. The optimum fiber addition ratios of the samples containing PP and GF are 0.5% by volume. And for PVA, it is between 0.5% and 1.5% by volume.