Effect of Various Moisture Contents, Variety and Dosage of Fibers on Explosive Spalling and Residual Compressive Strength of High Performance Concrete Subjected to High Temperatures

Fire resistance of concrete structures could be improved by add of polypropylene fibres in to the concrete mixture in butch from 1 to 2 kg per 1 m3 of fresh concrete. This method is effective, but it is not possible to use it for existing concrete and existing reinforced concrete structures. The new method which has good potential for fire protection of existing structures is based on creation of capillary pore and micro cracks system, which allowed water vapour evaporate from concrete. This study deals with determination of appropriate temperature in which is created adequate network of capillary pores and micro cracks which has no influence on strength and durability of the concrete. The formation of macro cracks and bigger pores could cause rapid reduction of compressive and tensile strength, decrease of resistance to aggressive substances and decrease of the frost resistance. The high performance concrete (HPC) has very low porosity, which can cause explosive spalling while the water vapour tries to evaporate from concrete structure during the fire. The HPC concrete has high compressive strength and high density. The HPC samples were exposed to temperatures 150, 250, 350 a 450°C, and after cooling down to normal ambient were carried out tests to define changes in porosity by mercury porosimetry, mass looses and compressive strength changes. The heated HPC concrete is regaining humidity into its structure from surrounding atmosphere, which can cause rehydratation of some chemical compounds. [1] For verification of these hypotheses the HPC samples were kept in water storage for 4 weeks and then tested.

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Contribution of Reinforcing Fiber Types on the Mechanical Properties of High Performance Concrete Subjected to High Temperature

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.368-370.1052 ◽

2013 ◽

Vol 368-370 ◽

pp. 1052-1055

Author(s):

Seung Jo Lee ◽

Jung Min Park

Keyword(s):

Mechanical Properties ◽

Compressive Strength ◽

High Temperature ◽

Weight Reduction ◽

High Performance ◽

High Performance Concrete ◽

Reduction Ratio ◽

Fiber Types ◽

Residual Compressive Strength ◽

Reinforcing Fiber

The aim of the study is to improve the understanding of the influence of reinforcing fiber types on the mechanical properties of high performance concretes (HPC) subjected to high temperature. The mechanical properties measured include residual compressive strength, weight reduction ratio, outward appearance property, and failure mode. Nylon, polypropylene, and steel fiber were added to enhance mechanical property of the concretes. After exposure to high temperatures ranged from 100 to 800°C, mechanical properties of fiber-toughened HPC were investigated. For HPC, although residual compressive strength was decreased by exposure to high temperature over 500°C, weight reduction ratio was significantly higher than that before heating temperature.

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Transport Properties and Resistance Improvement of Ultra-High Performance Concrete (UHPC) after Exposure to Elevated Temperatures

Buildings ◽

10.3390/buildings11090416 ◽

2021 ◽

Vol 11 (9) ◽

pp. 416

Author(s):

Yunfeng Qian ◽

Dingyi Yang ◽

Yanghao Xia ◽

Han Gao ◽

Zhiming Ma

Keyword(s):

Compressive Strength ◽

Transport Properties ◽

High Temperatures ◽

High Performance ◽

High Performance Concrete ◽

Ultrasonic Pulse Velocity ◽

Ultrasonic Pulse ◽

Pulse Velocity ◽

Capillary Absorption ◽

Self Healing

Ultra-high performance concrete (UHPC) has a high self-healing capacity and is prone to bursting after exposure to high temperatures due to its characteristics. This work evaluates the damage and improvement of UHPC with coarse aggregates through mechanical properties (compressive strength and ultrasonic pulse velocity), transport properties (water absorption and a chloride diffusion test), and micro-properties such as X-ray diffraction (XRD), Mercury intrusion porosimetry (MIP), and Scanning electronic microscopy (SEM). The result demonstrates that polypropylene (PP) fibers are more suitable for high temperature tests than polyacrylonitrile (PAN) fibers. The result shows that 400 °C is the critical temperature point. With the increase in temperature, the hydration becomes significant, and the internal material phase changes accordingly. Although the total pore volume increased, the percentage of various types of pores was optimized within 400 °C. The mass loss gradually increased and the ultrasonic pulse velocity gradually decreased. While the compressive strength first increased and then decreased, and the increase occurred within 25–400 °C. As for the transport properties, the chloride migration coefficient and capillary absorption coefficient both increased dramatically due to the higher sensitivity to temperature changes. The results of the property improvement test showed that at temperatures above 800 °C, the compressive strength recovered by more than 65% and the ultrasonic pulse velocity recovered by more than 75%. In terms of transport properties, compared to the results before self-healing, the chloride migration coefficient decreased by up to 59%, compared with 89% for the capillary absorption coefficient, after self-healing at 800 °C. With respect to the enhancement effect after exposure to high temperatures, the environment of a 5% Na2SO4 solution was not as good as the clean water environment. The corresponding changes in microstructure during the high temperatures and the self-healing process can explain the change in the pattern of macroscopic properties more precisely.

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Mechanical Properties of Ultra-High Performance Concrete before and after Exposure to High Temperatures

Materials ◽

10.3390/ma13030770 ◽

2020 ◽

Vol 13 (3) ◽

pp. 770 ◽

Cited By ~ 6

Author(s):

How-Ji Chen ◽

Yi-Lin Yu ◽

Chao-Wei Tang

Keyword(s):

Mechanical Properties ◽

Compressive Strength ◽

High Temperatures ◽

High Performance ◽

High Performance Concrete ◽

Silicon Powder ◽

Supplementary Cementitious Materials ◽

Ultra High Performance Concrete ◽

Splitting Strength ◽

Experimental Group

Compared with ordinary concrete, ultra-high performance concrete (UHPC) has excellent toughness and better impact resistance. Under high temperatures, the microstructure and mechanical properties of UHPC may seriously deteriorate. As such, we first explored the properties of UHPC with a designed 28-day compressive strength of 120 MPa or higher in the fresh mix phase, and measured its hardened mechanical properties at seven days. The test variables included: the type of cementing material and the mixing ratio (silica ash, ultra-fine silicon powder), the type of fiber (steel fiber, polypropylene fiber), and the fiber content (volume percentage). In addition to the UHPC of the experimental group, pure concrete was used as the control group in the experiment; no fiber or supplementary cementitious materials (silica ash, ultra-fine silicon powder) were added to enable comparison and discussion and analysis. Then, the UHPC-1 specimens of the experimental group were selected for further compressive, flexural, and splitting strength tests and SEM observations after exposure to different target temperatures in an electric furnace. The test results show that at room temperature, the 56-day compressive strength of the UHPC-1 mix was 155.8 MPa, which is higher than the >150 MPa general compressive strength requirement for ultra-high-performance concrete. The residual compressive strength, flexural strength, and splitting strength of the UHPC-1 specimen after exposure to 300, 400, and 500 °C did not decrease significantly, and even increased due to the drying effect of heating. However, when the temperature was 600 °C, spalling occurred, so the residual mechanical strength rapidly declined. SEM observations confirmed that polypropylene fibers melted at high temperatures, thereby forming other channels that helped to reduce the internal vapor pressure of the UHPC and maintain a certain residual strength.

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Mechanical Properties of High Performance Concrete Subjected to High Temperature as a Function of Fly-Ash and Fiber Addition

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.912-914.227 ◽

2014 ◽

Vol 912-914 ◽

pp. 227-230 ◽

Cited By ~ 1

Author(s):

Seung Jo Lee

Keyword(s):

Compressive Strength ◽

Fly Ash ◽

Weight Reduction ◽

High Performance ◽

Mechanical Characteristics ◽

High Performance Concrete ◽

Reduction Ratio ◽

Crack Control ◽

Residual Compressive Strength ◽

Heating Up

The purpose of this study is to have a better understanding of the mechanical characteristics of high performance concrete which is produced by mixing reinforcing fiber controlled by high temperatures with fly ash. After heating up the concrete, its appearance, demolition mode, residual compressive strength, weight reduction ratio and other mechanical characteristics were measured. To improve the mechanical characteristics of concrete, it was mixed with nylon, polypropylene, steel fiber and fly ash. The specimen was exposed to 100 ~ 800°C and its crack control, spalling prevention and other mechanical characteristics were reviewed. When the high performance concrete was exposed to 600°C or higher, its residual compressive strength dropped but its weight reduction ratio was significantly higher than it was heated before.

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Thermal properties of jute fiber concrete at high temperature

Journal of Structural Fire Engineering ◽

10.1108/jsfe-09-2016-017 ◽

2016 ◽

Vol 7 (3) ◽

pp. 182-192 ◽

Cited By ~ 2

Author(s):

Mitsuo Ozawa ◽

Gyu-Yong Kim ◽

Gyeong-Choel Choe ◽

Min-Ho Yoon ◽

Ryoichi Sato ◽

...

Keyword(s):

Mechanical Properties ◽

Compressive Strength ◽

Elastic Modulus ◽

High Temperatures ◽

High Performance Concrete ◽

Synthetic Fiber ◽

Jute Fiber ◽

Explosive Spalling ◽

Content Type ◽

Fiber Addition

Purpose The behavior of high-performance concrete (HPC) at high temperatures is very complex and also affects the global behavior of heated HPC-based structures. Researchers have also reported how various types of fibers affected the mechanical properties of cement-based materials at high temperatures. This study aims to discuss the effects of high temperatures on the compressive strength and elastic modulus of HPC with polypropylene (PP) and jute fiber. Design/methodology/approach Adding synthetic fiber (especially the PP type) to HPC is a widely used and effective method of preventing explosive spalling. Although researchers have experimentally determined the permeability of heated PP-fiber-reinforced HPC, few studies have investigated how adding natural fiber such as jute to this type of concrete might prevent spalling. In this study, the effects of high temperatures on the compressive strength and elastic modulus of HPC with PP and jute fiber (jute fiber addition ratio: 0.075 vol.%; length: 12 mm; PP fiber addition ratio: 0.075 vol.%; length: 12 mm) were experimentally investigated. Findings The work was intended to clarify the influence of elevated temperatures ranging from 20°C to 500°C on the material mechanical properties of HPC at 80 MPa. HSC with jute fiber showed a compressive strength loss of about 40 per cent at 100°C before recovering to full strength between 200°C and 300°C. Originality/value The elastic modulus of high-strength concrete decreased by 10-40 per cent between 100°C and 300°C. At 500°C, the elastic modulus was only 30 per cent of the room temperature value. The thermal expansion strain of all specimens was 0.006 at 500°C.

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