جستجوی مقالات مرتبط با کلیدواژه "خصوصیات مقاومتی" در نشریات گروه "عمران"

It is very important to improve the strength and permeability characteristics of concrete mixtures used in concrete pavements in order to increase the performance and durability of these pavements. Meanwhile, the use of new materials to improve these characteristics in concrete pavements becomes important. Silica fume and polypropylene macro fibers are among the types of new materials in the pavement industry. The present research has evaluated the effect of silica fume on the resistance and permeability characteristics of air-entrained concrete pavements containing macro polypropylene fibers in different amounts. In this regard, silica fume in consumption amounts of 5% and 7.5% and polypropylene macro fibers in consumption amounts of 0.9 kg/m3 and 1.8 kg/m3 were added to the reference concrete mixture. Also, the strength properties including compressive, splitting tensile and flexural strength and permeability properties including water absorption and penetration depth under the pressure of concrete mixtures have been evaluated according to standard methods. The results indicated that silica fume significantly changes the strength and permeability properties of concrete mixtures containing fibers. With the addition of silica fume, the compressive, tensile, and flexural strength of concrete increased to 44%, 54%, and 27%, respectively. Also, silica fume decreased the amount of water absorption and penetration depth up to 12 and 48 percent. The consumption of silica fume also had a significant effect on the change in the strength behavior and permeability of the concrete pavement. It was observed that among the strength properties, silica fume had the greatest impact on the splitting tensile strength and among its permeability properties, it had the greatest impact on the penetration depth of concrete. In addition, the change in compressive strength is greater than the flexural strength of the concrete pavement.

The addition of fibers with different physical and strength properties has different effects on the strength properties of jointed concrete pavements at rupture and also on the residual flexural strength of the pavement. This study investigates the separate and comparative effect of micro and macro synthetic fibers on the strength properties of jointed concrete pavements, considering the residual flexural strength of the pavement. For this purpose, the effect of adding two types of macro fibers and one type of micro fiber in the content of 1, 2, and 3 kg/m3 on compressive strength, splitting tensile strength, flexural strength, and flexural performance after cracking of concrete pavement were investigated. The results showed that micro fibers in all consumption contents have the least effect on the strength properties of pavement compared to macro fibers. Also, the addition of macro fibers did not have a significant effect on the compressive strength, but the splitting tensile strength, flexural strength, and residual flexural strength of pavement were significantly increased. The effect of macro fibers on improving the splitting tensile strength and modulus of rupture of pavement occurred at dosage rates higher than 2 kg/m3. However, the most significant increase in the equivalent flexural strength ratio of fiber reinforced concrete pavement occurred in the range of 1 to 2 kg/m3, and by adding higher contents of macro fibers, the increasing growth trend of residual flexural strength decreased. It was founded that macro fibers have the most excellent effect on flexural strength and residual flexural strength of the pavement. Also, the performance of twisted and continuously embossed macro fibers in all dosage rates was approximately the same.

The development of new types of high performance concrete such as self-consolidating concrete (SCC) and lightweight concrete (LWC)responds to some of the urgent needs of the construction sector. The use of lightweight aggregates in the production of SCC combines the favorable properties of LWC and SCC in self-consolidating lightweight concrete (SCLC). However, there are few studies on properties of SCLC up to now. In this study, the effects of polypropylene fibers on strength and transport properties of SCLC were investigated. Two types of polypropylene fibers, 6mm and 12mm long, were used in SCLC mixtures at different contents of 0%, 0.025%, 0.05% and 0.1% by total volume of concrete. The fresh properties of SCLCs were observed through slump flow time and diameter, V-funnel flow time and J-ring tests. Unit weight, compressive strength, flexural strength, pulse velocity, water absorption, and sorptivity were measured in all SCLC mixes and compared with that of the control mixture. It has been found that using polypropylene fibers in SCLC can lead to improvement in both strength and transport properties of concrete