scholarly journals Effect of Elevated Temperature on the Bond Strength of Prestressing Reinforcement in UHPC

Materials ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 4990
Author(s):  
Petr Pokorný ◽  
Jiří Kolísko ◽  
David Čítek ◽  
Michaela Kostelecká
Keyword(s):  
Bond Strength ◽  
High Performance ◽  
Elevated Temperatures ◽  
High Performance Concrete ◽  
Future Research ◽  
Ultra High Performance Concrete ◽  
Negative Effect ◽  
Laboratory Investigations ◽  
Increasing Temperature ◽  
Positive Effect

The study explores the effect of elevated temperatures on the bond strength between prestressing reinforcement and ultra-high performance concrete (UHPC). Laboratory investigations reveal that the changes in bond strength correspond well with the changes in compressive strength of UHPC and their correlation can be mathematically described. Exposition of specimens to temperatures up to 200 °C does not reduce bond strength as a negative effect of increasing temperature is outweighed by the positive effect of thermal increase on the reactivity of silica fume in UHPC mixture. Above 200 °C, bond strength significantly reduces; for instance, a decrease by about 70% is observed at 800 °C. The decreases in compressive and bond strengths for temperatures above 400 °C are related to the changes of phase composition of UHPC matrix (as revealed by X-ray powder diffraction) and the changes in microstructure including the increase of porosity (verified by mercury intrusion porosimetry and observation of confocal microscopy) and development cracks detected by scanning electron microscopy. Future research should investigate the effect of relaxation of prestressing reinforcement with increasing temperature on bond strength reduction by numerical modelling.

Advances in Research on Influence of Raw Materials on Workability of Fresh Concrete: A Review

2009 ◽  
Vol 405-406 ◽  
pp. 83-88 ◽  
Author(s):  
Gai Fei Peng ◽  
Zhan Qi Guo ◽  
Piet Stroeven ◽  
Ri Gao ◽  
Jiu Feng Zhang
Keyword(s):  
High Performance ◽  
High Performance Concrete ◽  
Fresh Concrete ◽  
Raw Materials ◽  
Experimental Tests ◽  
Solid Particles ◽  
Future Research ◽  
Negative Effect ◽  
The Relationship ◽  
Positive Effect

A literature review was carried out to identify advances in research on workability of fresh concrete via both experimental tests and modeling, especially high performance concrete and self-compacting concrete. As to the relationship between fluidity of concrete and that of paste, future research can be conducted in two aspects, i.e. one is the influence of the quantity of paste in concrete, and another is the influence of fluidity of paste affected by a couple of factors. Most literature proved that the flow of concrete depends both on positive effect and negative effect, the former promote fluidity, such as dispersing, filling and lubricating, and the latter restricts fluidity, such as formation of particle coagulation, an increase of wettable surface of solid particles and mechanical interlock.

scholarly journals Materials for Production of High and Ultra-High Performance Concrete: Review and Perspective of Possible Novel Materials

Materials ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4304
Author(s):  
Markssuel Teixeira Marvila ◽  
Afonso Rangel Garcez de de Azevedo ◽  
Paulo R. de de Matos ◽  
Sergio Neves Monteiro ◽  
Carlos Maurício Fontes Vieira
Keyword(s):  
High Performance ◽  
High Performance Concrete ◽  
Review Article ◽  
Cement Matrix ◽  
Bibliographic Databases ◽  
Future Research ◽  
Chemical Additives ◽  
Ultra High Performance Concrete ◽  
Conventional Concrete ◽  
Essential Components

This review article proposes the identification and basic concepts of materials that might be used for the production of high-performance concrete (HPC) and ultra-high-performance concrete (UHPC). Although other reviews have addressed this topic, the present work differs by presenting relevant aspects on possible materials applied in the production of HPC and UHPC. The main innovation of this review article is to identify the perspectives for new materials that can be considered in the production of novel special concretes. After consulting different bibliographic databases, some information related to ordinary Portland cement (OPC), mineral additions, aggregates, and chemical additives used for the production of HPC and UHPC were highlighted. Relevant information on the application of synthetic and natural fibers is also highlighted in association with a cement matrix of HPC and UHPC, forming composites with properties superior to conventional concrete used in civil construction. The article also presents some relevant characteristics for the application of HPC and UHPC produced with alkali-activated cement, an alternative binder to OPC produced through the reaction between two essential components: precursors and activators. Some information about the main types of precursors, subdivided into materials rich in aluminosilicates and rich in calcium, were also highlighted. Finally, suggestions for future work related to the application of HPC and UHPC are highlighted, guiding future research on this topic.

Study on the transfer and anchorage length of steel strand in ultra high performance concrete material

2020 ◽  
Vol 10 (2) ◽  
pp. 153-164
Author(s):  
Hui Zheng ◽  
Dongdong Zhou ◽  
Xinfeng Yin ◽  
Lei Wang
Keyword(s):  
Bond Strength ◽  
High Performance ◽  
Failure Modes ◽  
High Performance Concrete ◽  
Protective Layer ◽  
Experimental Results ◽  
Ultra High Performance Concrete ◽  
Anchorage Length ◽  
Pull Out ◽  
Steel Strand

Ultra-high-performance concrete (UHPC) material, a new type of cement-based composite material, is usually employed in the bridge engineering. The transfer and anchorage length of steel strand in UHPC material is different from that in ordinary concrete; nevertheless, few design standards are found that how to anchor the transfer and anchoring length of steel strand in UHPC material under normal curing. Through central pull-out test under the different conditions of protective layer thickness and embedded length, the load-slip curves, failure modes, and bond strength of 36 UHPC material specimens under normal curing were studied. The experimental results showed that the ultimate bond stress between UHPC material and steel strand under natural curing conditions is 7.01∼11.68 MPa. When the compressive strength of cube was 157 MPa; the bond strength under natural curing was smaller than that under thermal curing; when the thickness of the protective layer of steel strand with a diameter of 15.2 mm is greater than 30 mm, it had a little influence on bond strength. The regression analysis of the test results based on the experimental results proves that the recommended formulas for the design of transfer length and anchorage length of steel strand in UHPC material were in great agreement with the results of published studies.

Study on Interfacial Properties of Ultra-High Performance Concrete Containing Steel Slag Powder and Fly Ash

2011 ◽  
Vol 194-196 ◽  
pp. 956-960 ◽  
Author(s):  
Yan Zhou Peng ◽  
Kai Chen ◽  
Shu Guang Hu
Keyword(s):  
Fly Ash ◽  
Bond Strength ◽  
High Performance ◽  
Steel Fiber ◽  
High Performance Concrete ◽  
Steel Slag ◽  
Interfacial Zone ◽  
Ultra High Performance Concrete ◽  
Slag Powder ◽  
Steel Slag Powder

The interfacial properties of reactive powder concretes (RPCs), other known as ultra-high performance concrete (UHPC), containing steel slag powder and ultra fine fly ash are studied in this paper. The microstrctural characterization of interfacial transition zones (ITZs), including the aggregate-cement paste interfacial zone and the steel fiber-paste interfacial zone, is investigated by SEM. The microhardness of the aggregate-paste ITZ and the steel slag-paste ITZ is studied and the bond strength of steel fiber in matrix is tested through fiber pullout tests. The results indicate that the microhardness of the steel slag-paste ITZ is slightly higher than that of the aggregate-paste ITZ, which implies the advantage of the substitution of quartz powder with steel slag powder in preparation of RPCs to some degrees. Moreover, the hardness of these two ITZs is higher than that of the hardened paste. A certain amount of hydration products has been observed exsiting on the surface of steel fiber by SEM and the bond strength of steel fiber-martix is up to 9.3MPa. These interfical properties are definitely critical to obtain high performance of UHPCs containing steel slag powder and fly ash.

scholarly journals Study of Toughness and Macro/Micro-Crack Development of Fibre-Reinforced Ultra-High Performance Concrete After Exposure to Elevated Temperature

Materials ◽  
2019 ◽  
Vol 12 (8) ◽  
pp. 1210 ◽  
Author(s):  
Piotr Smarzewski
Keyword(s):  
High Performance ◽  
Elevated Temperatures ◽  
High Performance Concrete ◽  
Three Dimensional ◽  
Polypropylene Fibre ◽  
Crack Development ◽  
Furnace Chamber ◽  
Flexural Test ◽  
Ultra High Performance Concrete ◽  
Dimensional Measurements

This study has investigated the changes that might appear in post-peak flexural response. Before the flexural test, prismatic specimens were placed in a furnace chamber and exposed to elevated temperatures of 400, 600, and 800 °C. The flexural toughness test was carried out on two types of concrete: Plain ultra-high performance concrete (UHPC) and UHPC with different types of fibres (steel fibre (SF) and polypropylene fibre (PPF)) at 0.5%, 1%, 1.5%, and 2% volume fractions. During the flexural test in the macro-crack development analysis, the non-contact ARAMIS system was used to perform three-dimensional measurements of strain and displacement. The results of scanning electron microscope (SEM) observations of micro-crack development in UHPC without and with SF/PPF were also presented. The experimental results showed that in some cases, the load–deflection curve of fibre-reinforced UHPC displayed a double-peak response. The first peak signified the UHPC properties, while the second peak represented the properties of the fibres. Under flexural load, the toughness decreased as the temperature increased. Significant decrease in the load–deflection response and toughness were observed for the polypropylene fibre-reinforced UHPC when the temperature approached 800 °C. The SEM observation results showed that the thermal damage of fibre-reinforced UHPC depends on the pore pressure effect, the thermal mismatch, the decomposition of hydration products, and the formation of micro-cracks.

scholarly journals Effects of Elevated Temperatures on Mechanical’s concrete specimen behaviour

2018 ◽  
Vol 165 ◽  
pp. 22010
Author(s):  
Nesrine Khodja ◽  
Hadda Hadjab
Keyword(s):  
Mechanical Properties ◽  
High Performance ◽  
Elevated Temperatures ◽  
High Performance Concrete ◽  
Concrete Specimen ◽  
Relative Strength ◽  
Cement Matrix ◽  
Initial Strength ◽  
Different Temperatures ◽  
Increasing Temperature

This paper presents an experimental study on the performance of concrete, subjected to high temperatures. Investigation was carried out by using two mixtures: an Ordinary Concrete (OC) and High Performance Concrete (HPC) with 10% of Silica Fume (SF) replaced of cement weight and 1,5% of super plasticizer, the water-binder (w/b) ratio used was 0,5 and 0,32 respectively. The produced concrete specimens are heated at a rate of 7 °C/min up to different temperatures (150, 300, 450, 600 and 900°C). In order to ensure a uniform temperature through the specimen, the temperature is held constant at the temperature stage for one hour before cooling. Mechanical properties at ambient temperature and residual mechanical properties after heating have already been determined. We examined also the effect of high temperature on the aggregate-cement paste interface and aggregate microstructure of the concrete specimens by scanning electron microscopy (SEM) method to reveal changes occurred after the cycle of heatingcooling. The results revealed that relative strength of the concrete specimens decreased as the exposure temperature increased and reaches about a quarter of its initial strength at 900°C. Moreover SEM examinations showed that, increasing temperature caused weakening of the adherence of aggregate and cement matrix by the appearance of cracks and micro cracks.

scholarly journals Application of nanomaterials in ultra-high performance concrete: A review

2020 ◽  
Vol 9 (1) ◽  
pp. 1427-1444
Author(s):  
Changjiang Liu ◽  
Xin He ◽  
Xiaowei Deng ◽  
Yuyou Wu ◽  
Zhoulian Zheng ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Environmental Sustainability ◽  
High Performance ◽  
High Performance Concrete ◽  
Future Research ◽  
The Novel ◽  
Ultra High Performance Concrete ◽  
Engineering Construction ◽  
Superior Mechanical Properties ◽  
Weak Resistance

Abstract In the recent decades, traditional concrete poses a great challenge to the modernization of the construction industry because of low tensile strength, poor toughness, and weak resistance to cracking. To overcome these problems, ultra-high performance concrete (UHPC) with superior mechanical properties and durability is developed for broad application prospect in the future engineering construction. However, UHPC is less eco-friendly because it consumes more cement compared with the traditional concrete. The manufacturing of cement produces large amounts of carbon dioxide and therefore leads to the greenhouse effect. Nanomaterials consist of microstructural features that range from 0.1 to 100 nm in size, which exhibit the novel properties different from their bulk counterparts, including filling effect, surface activity, and environmental sustainability. This paper reviews the effect of various nanomaterials used in UHPC to partially replace the cement or as an additive on the microstructures, mechanical properties, and other properties of UHPC. In addition, the limitations and shortcomings of the current research are analyzed and summarized, and development directions are provided for future research on the application of nanomaterials in UHPC.

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