scholarly journals Experimental analysis of the spalling phenomenon in precast reinforced concrete columns exposed to high temperatures

2018 ◽  
Vol 11 (4) ◽  
pp. 856-875 ◽  
Author(s):  
A. M. GIL ◽  
B. FERNANDES ◽  
F. L. BOLINA ◽  
B. F. TUTIKIAN
Keyword(s):  
High Temperatures ◽  
Concrete Columns ◽  
Concrete Cover ◽  
Concrete Compressive Strength ◽  
Concrete Mixtures ◽  
Strength Tests ◽  
Fire Curve ◽  
Cover Thickness ◽  
Real Scale

Abstract Among the processes that involve the degradation of concrete structures subject to the high temperatures of a fire there is the spalling phenomenon. Its mechanisms are related to the thermal stress of the materials dilatations and pore pressure the process of vaporization of water during heating. The factors that influences in its occurrence are related to concrete properties, structural member characteristics or the exposure conditions, and their parameters are not clearly known yet. This paper aimed to study the influence of three concrete mixtures, four coating thicknesses and two bars diameters of longitudinal reinforcement in the spalling phenomena exposed to ISO 834 fire curve. The characterization of concrete were performed either of the axial compression strength tests, water absorption by capillary and mercury intrusion porosimetry, besides the fire resistance tests in real-scale specimens. It was concluded that the diameter of the bar does not have influence, while the mixture and the concrete cover thickness does. More spalling was recorded for the columns with thicker concrete cover and concrete compressive strength at 61,9 MPa, and although higher strength concrete have less permeability, this characteristic can be balanced with the higher tensile strength of this type of concrete.

scholarly journals Axial Compression Performance and Residual Strength Calculation of Concrete-Encased CFST Composite Columns Exposure to High Temperature

2022 ◽  
Vol 12 (1) ◽  
pp. 480
Author(s):  
Xiaojun Ke ◽  
Wannian Xiang ◽  
Xiuning Peng ◽  
Yu Dan
Keyword(s):  
High Temperature ◽  
Bearing Capacity ◽  
High Temperatures ◽  
Heating Temperature ◽  
Steel Tube ◽  
Concrete Cover ◽  
Tube Diameter ◽  
Composite Columns ◽  
Load Displacement ◽  
Cover Thickness

Concrete-encased concrete-filled steel tube (CFST) composite columns provide high bearing capacity, good seismic performance and an easier connection with arbitrary angle beams, which are widely used in high-rise buildings. Considering the high frequency of building fires, experimental research investigated the axial compressive behavior of the composite columns’ exposure to high temperature in this paper. Fourteen specimens after exposure to high temperatures with different parameters, including the heating temperature, steel tube diameter and concrete cover thickness, were fabricated to test under axial compressive loading. The failure pattern, load-displacement curve, bearing capacity, initial stiffness, deformation performance and damage rule of the specimens were discussed. The test results showed obvious differences in damage of specimens subjected to various high temperatures. The failure of the specimens began with the spalling and crushing of the concrete at the edge and ends in a lantern shape. The load-displacement curves of the specimens were significantly affected by high temperature, while the influence the of steel tube diameter and concrete cover thickness was relatively weak. A method of calculating axially loaded capacity for the composite column exposure to high temperature is proposed considering the effects of the main parameters of heating temperature and steel tube position, and the calculated results are in good agreement with the experimental results.

scholarly journals Thermal damage evaluation of full scale concrete columns exposed to high temperatures using scanning electron microscopy and X-ray diffraction

DYNA ◽  
2018 ◽  
Vol 85 (207) ◽  
pp. 123-128 ◽  
Author(s):  
Bruno Fernandes ◽  
Augusto Masiero Gil ◽  
Fabrício Longhi Bolina ◽  
Bernardo Fonseca Tutikian
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Reinforced Concrete ◽  
High Temperatures ◽  
Concrete Columns ◽  
X Ray Diffraction ◽  
Reinforced Concrete Columns ◽  
X Ray ◽  
Real Scale ◽  
Scanning Electron

When exposed to elevated temperatures, concrete suffers physicochemical changes, resulting in reduction of mechanical properties, cracking and spalling. These macroscopic changes are related to changes in the microstructure of concrete. In this paper, the microstructure of thermally damaged concrete from real-scale reinforced concrete columns was studied, using scanning electron microscopy (SEM) and x-ray diffraction (XRD). Two real-scale reinforced concrete columns, with different concrete mixtures, were exposed to ISO 834 firestandard curve for 4 hours. After heating, concrete core samples were drilled, sectioned and analyzed in different column section depths.Core samples from reference column not exposed to high temperatures, were also obtained. Macroscopic observations showed a change inthe color of concrete exposed to high temperatures. SEM micrographs presented distinct changes in morphology, like coarsening, and thepresence of cracks and voids. XRD diagrams showed a reduction of portlandite and presence of larnite as depth increases.

scholarly journals Use of Ecofriendly Glass Powder Concrete in Construction of Wind Farms

2021 ◽  
Vol 11 (7) ◽  
pp. 3050
Author(s):  
Eva M. García del Toro ◽  
Daniel Alcala-Gonzalez ◽  
María Isabel Más-López ◽  
Sara García-Salgado ◽  
Santiago Pindado
Keyword(s):  
Wind Farm ◽  
Glass Powder ◽  
Wind Farms ◽  
Main Element ◽  
Partial Replacement ◽  
Surface Protection ◽  
Air Content ◽  
Concrete Mixtures ◽  
Strength Tests ◽  
Rate Of Substitution

Silicon is the main element in the composition of glass and it has been seen that it can be used as a partial replacement for cement in the manufacture of concrete. Different dosages of glass powder and cement were applied to manufacture the concrete mixes. Initially, the characteristics of fresh concrete were studied, such as consistency, air content, apparent density and workability. Secondly, compressive strength tests were performed on the different concrete mixtures produced. The consistency tests allowed us to classify these concretes within the group of fluids. The air content of these concretes increased with the rate of substitution of cement by glass powder, resulting in lighter concretes. Density tests showed that this parameter decreased as the rate of substitution of cement increased. A coefficient k has been calculated for the substitution of glass powder by cement in the binder, using the Bolomey formula. Also, a mathematical model has been proposed to further analyze the experimental data. Major contributions of this work were to study the possible application of this concrete in different dispersions as a surface protection layer against the action of corrosion, in wind turbine foundations as well as the stabilization of the wind farm roads.

scholarly journals Characterization of wheat MYB genes responsive to high temperatures

2017 ◽  
Vol 17 (1) ◽  
Author(s):  
Yue Zhao ◽  
Xuejun Tian ◽  
Fei Wang ◽  
Liyuan Zhang ◽  
Mingming Xin ◽  
...  
Keyword(s):  
High Temperatures ◽  
Myb Genes

Purification and characterization of two isoforms of native α amylase from Ok-Rong mango (Mangifera indica Linn. cv. Ok-Rong)

2017 ◽  
Vol 42 (6) ◽  
Author(s):  
Raksmont Ubonbal ◽  
Saijai Porsoongnoen ◽  
Jureerut Daduang ◽  
Sompong Klaynongsruang ◽  
Sakda Daduang
Keyword(s):  
High Temperatures ◽  
Fruit Ripening ◽  
Specific Activity ◽  
Mangifera Indica ◽  
Ripening Stage ◽  
Purification And Characterization ◽  
Tropical Plant ◽  
Short Period ◽  
Structure Properties

AbstractIntroduction:The tropical plant amylases involved in the fruit ripening stage is outstanding for their high activities in converting starch to sugars within a short period at high temperatures over 40°C.Methods:The α amylase iso-enzymes from Ok-Rong mango (Results:The enzyme was purified 105-fold with a final specific activity of 59.27 U mgConclusion:Two α amylase iso-enzymes were classified as members of the low-pI group of amylases with identical structure, properties and functions. They are mesophilic with high possibilities for application for many purposes.

scholarly journals Relations between indirect tensile and flexural strengths for dry and plastic concretes

2013 ◽  
Vol 6 (6) ◽  
pp. 854-874 ◽  
Author(s):  
J. T. Balbo
Keyword(s):  
Tensile Strength ◽  
Concrete Slab ◽  
Plane Stress State ◽  
Concrete Mixtures ◽  
Technological Control ◽  
Strength Tests ◽  
Indirect Tensile ◽  
Actual Strength ◽  
Basic Concepts ◽  
Set Up

Indirect tensile strength is not usually used for concrete mixtures proportioning and its technological control; flexural strength tests under third point loads arrangement are the pattern for such goals. Indeed, neither of such tests have the capability to set up the actual strength of a concrete slab since its response is under plane stress state. A critical review of the basic concepts on both kinds of tests allows foreseeing its limitations as well as how to overcome such shortcomings. At last correlations between the two kinds of tensile strength are presented considering dry and plastic concretes typically applied on paving, corroborating to former results achieved for plastic concretes.

Effect of High Temperatures and Heating Rates on High Strength Concrete for Use as Thermal Energy Storage

2010 ◽  
Author(s):  
Emerson E. John ◽  
W. Micah Hale ◽  
R. Panneer Selvam
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Molten Salt ◽  
High Temperatures ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Heat Transfer Fluid ◽  
Heating Rates ◽  
Storage Media ◽  
Concrete Mixtures

In recent years due to rising energy costs as well as an increased interest in the reduction of greenhouse gas emissions, there is great interest in developing alternative sources of energy. One of the most viable alternative energy resources is solar energy. Concentrating solar power (CSP) technologies have been identified as an option for meeting utility needs in the U.S. Southwest. Areas where CSP technologies can be improved are improved heat transfer fluid (HTF) and improved methods of thermal energy storage (TES). One viable option for TES storage media is concrete. The material costs of concrete can be very inexpensive and the costs/ kWhthermal, which is based on the operating temperature, are reported to be approximately $1. Researchers using concrete as a TES storage media have achieved maximum operating temperatures of 400°C. However, there are concerns for using concrete as the TES medium, and these concerns center on the effects and the limitations that the high temperatures may have on the concrete. As the concrete temperature increases, decomposition of the calcium hydroxide (CH) occurs at 500°C, and there is significant strength loss due to degeneration of the calcium silicate hydrates (C-S-H). Additionally concrete exposed to high temperatures has a propensity to spall explosively. This proposed paper examines the effect of heating rates on high performance concrete mixtures. Concrete mixtures with water to cementitious material ratios (w/cm) of 0.15 to 0.30 and compressive strengths of up to 180 MPa (26 ksi) were cast and subjected to heating rates of 3, 5, 7, and 9° C/min. These concrete mixtures are to be used in tests modules where molten salt is used as the heat transfer fluid. Molten salt becomes liquid at temperatures exceeding 220°C and therefore the concrete will be exposed to high initial temperatures and subsequently at controlled heating rates up to desired operating temperatures. Preliminary results consistently show that concrete mixtures without polypropylene fibres (PP) cannot resist temperatures beyond 500° C, regardless of the heating rate employed. These mixtures spall at higher temperatures when heated at a faster rate (7° C/min). Additionally, mixtures which incorporate PP fibres can withstand temperatures up to 600° C without spalling irrespective of the heating rate.

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