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

 During the service period, concrete may come into contact with harsh environmental conditions, ultra-high performance concrete can be considered as a suitable option due to its unique strength and durability. In this study, for the first time, the effect of nanoparticles of magnesium oxide and copper oxide with amounts of 0.5, 1 and 2% separately and combined with different amounts of iron slag (2.5, 5 and 10%) on the compressive strength and electrical resistance of UHPC contains a constant content of PVA fibers in two operating modes Standard and accelerated curing (immersion in water at 95°C) were studied for different ages. Moreover, the Scanning Electron Microscopy test (SEM) is conducted on the specimens to understand the concrete's microstructure better. The results show that by using the heat treatment method and microstructure modification in the presence of new nano materials, it is possible to create a higher potential than UHPC in terms of compressive strength and electrical resistivity. So that after 90 days, the compressive strength for each of the specimens containing 1% of magnesium oxide and copper oxide nanomaterials respectively increased the compressive strength by approximately 37.4% and 37.1% compared to the 7-day sample. While the growth of the compressive strength in the accelerated mode for the mentioned specimens was 16.8% and 18.8%, respectively, compared to the standard curing. In addition, by obtaining accurate experimental relationships between the two parameters of compressive strength and electrical resistivity a non-destructive method for predicting compressive strength has been presented.

The necessity of attention to the sustainable development in civil engineering for the progress of modern societies has highlighted concrete as the most widely used construction material for researchers. In this way, Ultra High Performance Concrete (UHPC) has been highly appreciated as one of the newest inventions in the field of concrete technology. The purpose of this article is to: 1- depict outstanding properties of UHPC that make its utilization in construction, rehabilitation and strengthening projects efficient and 2- promote the application of UHPC in bridge engineering in the national scale relying on extensive domestic studies in order to localize it. Much effort has been made to present a comprehensive report on innovations and gained experiences in the field of using UHPC in the bridge industry during the last two decades in all parts of the world and investigate the main direction of future research pointing to the key constraints of the widespread use of this material for constructing and maintaining bridges.

Concrete is the most widely used building material in recent decades, and researchers are innovating in the production of this material to improve some of it’s properties such as strength and durability. A part of these innovative efforts has led to the production of a new class of concrete called ultra-high performance concrete (UHPC). UHPC has the unique mechanical features that provide opportunities for the development of new techniques of construction, repairs and renovation of concrete structures. While most of the recommended relationships in the standards are based on normal strength concrete (NSC), it is necessary to know more about ultra-high performance concrete behavior. This study aimed to investigate bond behavior (the interaction between rebar and concrete) because it directly affects the performance of concrete structures. 24 cubic concrete specimens (20 cm and 25cm wide) with a centered rebar and two bond lengths, using UHPC and NSC, were subjected to pull-out tests. Concrete’s compressive strength and relative cover, bond length, and yield stress of the rebar significantly influence the failure mode. UHPC reduces the embedded length of rebars by increasing bond strength up to 5 times that in NSC. Regarding to the bond-slip curves, plain UHPC (used in this study) had less ductility than NSC. In NSC, increasing the bond length increases the maximum bond stress, while in UHPC, for increasing bond length, the maximum bond stress decreases. New relationships have been proposed to predict bond-slip behavior.