Effects of moisture evaporation (weight loss) on fracture properties of high performance concrete subjected to high temperatures

2011 ◽  
Vol 46 (8) ◽  
pp. 543-549 ◽  
Author(s):  
Binsheng Zhang
Keyword(s):  
Weight Loss ◽  
High Temperatures ◽  
High Performance ◽  
High Performance Concrete ◽  
Moisture Evaporation ◽  
Fracture Properties

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

Buildings ◽  
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.

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

Materials ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 770 ◽  
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.

Evolution from High Strength Concrete to High Performance Concrete

2014 ◽  
Vol 629-630 ◽  
pp. 49-54
Author(s):  
Vlastimil Bílek ◽  
Vladimíra Tomalová ◽  
Petr Hájek ◽  
Ctislav Fiala
Keyword(s):  
High Strength Concrete ◽  
High Performance ◽  
High Performance Concrete ◽  
High Strength ◽  
Maximum Size ◽  
Point Of View ◽  
Fracture Properties ◽  
Strength Concrete ◽  
Time Period ◽  
Long Term Observation

High strength concrete for the production of concrete railway sleepers was designed more than 20 years ago. The compressive strength of the concrete was very high from the start, but flexure strengths showed some irregular development - a decrease in time. Later, also a significant decrease of fracture properties was recorded. Microcracking was found to be the reason for this; therefore some modifications were performed to avoid this happening (especially the reduction of the maximum size of aggregates from 22 mm to 16 mm or 11 mm). Some problems concerning frost resistance of the concrete with a slag addition were reduced by applying ternary binders. All of the results are discussed from the point of view of a long-term observation of the strengths and fracture properties ́ development during the time period of 5 years or even more.

Fracture properties of high-performance concrete containing fly ash

2012 ◽  
Vol 226 (2) ◽  
pp. 170-176 ◽  
Author(s):  
P Zhang ◽  
Q Li ◽  
H Zhang
Keyword(s):  
Fly Ash ◽  
Crack Opening Displacement ◽  
High Performance ◽  
High Performance Concrete ◽  
Crack Opening ◽  
Ash Content ◽  
Crack Mouth Opening Displacement ◽  
Opening Displacement ◽  
Fracture Properties ◽  
Fracture Parameters

A parametric experimental study has been conducted to investigate the effect of fly ash on the fracture properties of high-performance concrete (HPC), with four fly ash contents used. By means of three-point bending method, the fracture toughness, fracture energy, effective crack length, critical crack opening displacement, and maximum crack opening displacement of the specimen were measured, respectively. The results indicate that fly ash has great improvement on the fracture parameters, and these fracture parameters gradually increase when the content of fly ash increases from 10 per cent to 20 per cent. However, these fracture parameters begin to decrease after the fly ash content exceeds 20 per cent. Besides, as the fly ash content increases from 10 per cent to 20 per cent, the relational curves between the vertical load and the mid-span deflection ( PV– δ), crack mouth opening displacement ( PV– CMOD), and crack tip opening displacement ( PV– CTOD) become plumper and plumper, which indicates that the capability of HPC containing fly ash to resist crack propagation is becoming stronger and stronger, while the curves become shriveled after the fly ash content exceeds 20 per cent. The contribution of fly ash on the fracture properties of HPC containing fly ash seems to be performed only when the fly ash content does not exceed 20 per cent.

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