جستجوی مقالات مرتبط با کلیدواژه "high-performance concrete (hpc)" در نشریات گروه "عمران"

The main objective of the present study is to investigate the effects of incorporating the low ratios of different Nanosilica types on concrete resistivity against bars corrosion embedded in High-Performance Concrete (HPC). Three ratios of water to binder are considered in the experiment: very low, low, and moderate ratios equal to 0.25, 0.30, and 0.35, respectively. In addition to implementing different ratios of w/b, different types of nanosilica were applied, a coarser and a finer one, respectively, with specific surface areas of 200 and 380 . Moreover, two low ratios of nanosilica 0.75% and 1.50% were considered to replace with cement according to previous studies. Compressive strength test, electrical resistivity, and non-destructive ultrasonic test were conducted in this study. In addition, the workability of the mixtures was kept constant by adjusting the superplasticizer. Although the performance of different types and ratios of nanosilica were variable due to its great activity, it was significant that nanosilica with a lower specific surface area outperformed the control specimen and the specimen with finer one. It should be noticed that due to very much fine size of pyrogenic nanosilica used in this study, it was highly agglomerated. Thus, by using a high shear speed mixer, nanosilica was mixed with partial mixture water. It was shown that a lower water-to-binder ratio had more compressive strength and also, more electrical resistivity was addressed indicating more durability due to lower water-to-binder ratios. It was also noticeable that using nanosilica in mixtures made the HPC more durable and increased compressive strength. Nanosilica of Coarser grade sounded quite better in terms of durability characteristics and also, showed more corrosion resistivity based on ACI222r01. As a result, mixtures of lower water-to-binder ratio with higher replacement of cement (1.5%) with coarser nanosilica (lower specific surface area) had the most compressive strength, electrical resistivity, and non-destructive ultrasonic pulse velocity, indicating the best concrete resistivity against corrosion of deformed bars.

In blended Portland cement, clinker is replaced partially with supplementary materials such as Pozzolanic materials, which may improve the mechanical, physical and durability characteristics of cement and concrete. Sirjan Tuff is volcanic natural pozzolan that is in vicinity of Sirjan mountain and using for producing pozzolan cement in cement companies of Kerman-Iran. Use of blended cements has advantages such as reducing air pollution, saving natural resources and reducing energy consumption. The properties of blended cements with high volume pozzolan have been investigated in this research. For this purpose, pozzolanic materials including silica fume (SF) and a natural pozzolan (NP) were investigated. The concrete mixes include one plain mixture with 100\% Portland cement type II, three admixtures containing 3, 6 and 9 percent of cement replaced with Silica fume as binary blended admixtures, two mixes with natural pozzolan replacement levels 40 and 60 as binary blended admixtures and six mixtures containing both silica fume and natural pozzolan as ternary blended mixtures. The purpose of 40\% and 60\% replacement of cement with natural pozzolan was investigating mechanical and durability properties of concrete containing high volume natural pozzolan. The results indicated that, natural pozzolan used in this research did not have significant effect on concrete chloride resistance in 28 days, however in long term it shows effective improvement. Combined use of silica fume with natural pozzolan enhanced significantly the compressive strength and chloride resistance of concretes containing natural pozzolan, particularly at early ages. Using the natural pozzolan at high volumes reduced the compressive strength especially at early ages in comparison with ternary mixtures containing silica fume and natural pozzolan and the control admixtures. Nonetheless, the differences between compressive strength of mixtures decreased by increasing the curing age up to 90 days. Regarding the capillary absorption test results, binary mixtures containing silica fume or natural pozzolan did not show any significant effect on reduction of capillary absorbed water, but ternary mixtures with silica fume and natural pozzolan show reduction of capillary absorption content. Considering the water absorption test and sulfuric acid resistance ternary admixtures containing silica fume and natural pozzolan did not indicate any desirable effect.