This document summarizes research on the structural behavior of high-strength concrete (HSC) columns exposed to fire. It finds that HSC columns experience more spalling than normal-strength concrete columns due to higher pore pressures developing in HSC. The fire resistance of HSC columns is affected by material properties like strength, moisture content, and aggregate type as well as structural factors like member size and reinforcement. Experimental tests showed HSC columns with carbonate aggregate had less spalling than those with siliceous aggregate. Lateral ties also improved fire resistance by limiting column expansion.
what is polymer concrete, types, properties, material used in manufacturing process , manufacturing process, applications and their advantages. case study on polymer composite concrete.
Quality Control in Concrete and Durability factors : An overviewbybyRAJESH PRASAD,IRSE, CPM/M, RVNL. KOLKATA. An interesting and informative presentation....
This presentation is about Eco-friendly concrete also known as Green Concrete. It covers the need, material used for the manufacturing of Green Concrete and the advantages & limitations of Green concrete.
Best Regards:
Engr. Muhammad Ali Rehman
this presentation deals with the different types of cracks generated in concrete during its usage and after its application and also methods to retrofit these cracks
This presentation gives an overview on different types of acid attacks on concrete. Mechanism of each attack is discussed with few case studies. Hope it is useful
High-strength concrete is generally used in the shaping of high-rise structures. It has been used in components of building such as columns (especially on lower floors where the loads will be greatest), shear walls, and foundations. High strengths are also occasionally used in bridge applications as well
Vacuum concrete is the type of concrete in which the excess water is removed for improving concrete strength.
The water is removed by use of vacuum mats connected to a vacuum pump.
The main aim of this technique is to extract extra water from concrete surface using vacuum dewatering.
Geopolymer bricks are the new innovation in the field of brick industry. Geopolymer bricks contain fly ash as the source material and an alkaline activator for the activation of polymerization reaction.experimental work is supposed to be performed on geopolymer bricks with fly ash and GGBS as source materials and sodium hydroxide and sodium silicate as an activator. It reduces dead load on structures due to light weight (2.6 kg, dimension: 230 mm X 110 mm X 70 mm).
what is polymer concrete, types, properties, material used in manufacturing process , manufacturing process, applications and their advantages. case study on polymer composite concrete.
Quality Control in Concrete and Durability factors : An overviewbybyRAJESH PRASAD,IRSE, CPM/M, RVNL. KOLKATA. An interesting and informative presentation....
This presentation is about Eco-friendly concrete also known as Green Concrete. It covers the need, material used for the manufacturing of Green Concrete and the advantages & limitations of Green concrete.
Best Regards:
Engr. Muhammad Ali Rehman
this presentation deals with the different types of cracks generated in concrete during its usage and after its application and also methods to retrofit these cracks
This presentation gives an overview on different types of acid attacks on concrete. Mechanism of each attack is discussed with few case studies. Hope it is useful
High-strength concrete is generally used in the shaping of high-rise structures. It has been used in components of building such as columns (especially on lower floors where the loads will be greatest), shear walls, and foundations. High strengths are also occasionally used in bridge applications as well
Vacuum concrete is the type of concrete in which the excess water is removed for improving concrete strength.
The water is removed by use of vacuum mats connected to a vacuum pump.
The main aim of this technique is to extract extra water from concrete surface using vacuum dewatering.
Geopolymer bricks are the new innovation in the field of brick industry. Geopolymer bricks contain fly ash as the source material and an alkaline activator for the activation of polymerization reaction.experimental work is supposed to be performed on geopolymer bricks with fly ash and GGBS as source materials and sodium hydroxide and sodium silicate as an activator. It reduces dead load on structures due to light weight (2.6 kg, dimension: 230 mm X 110 mm X 70 mm).
FIRES AS A CAUSE OF CONCRETE DETERIORATIONMohamed Omer
Presentation outline
Introduction to the subject
What is the causes of fire?
Physical and chemical response to fire
Spalling of concrete
Factors influencing the explosive spalling
How to improve the concrete structures in the fire resistance?
Case study - Concrete structure subjected to a fire in U.A.E
Rehabilitation methods and the repairing plan
Recommendation and conclusions
Heat of Hydration in Raft Foundation and Thick Walls, Modeling the heat of hydration by the use of IQ-drum technology considering the weather and materials in Saudi Arabia. Prepared by Khaldoon Slaiai (Concrete Research Manager at Saudi Readymix Concrete Company)
Permeability of concrete, chemical attack, acid attack, efflorescence, Corrosion in concrete. Thermal conductivity, thermal diffusivity, specific heat. Alkali Aggregate Reaction
Rapid hardening cement (RHC) is a type of cementsudeshphdce
Rapid hardening cement (RHC) is a type of cement that achieves higher early strength development compared to ordinary Portland cement (OPC). It's formulated to set and harden rapidly, often within a few hours, allowing for faster construction processes. Here's an overview of its characteristics and uses:
Composition: Rapid hardening cement typically contains a higher proportion of tri-calcium silicate (C3S) and finer particles compared to OPC. These characteristics contribute to the rapid hydration and strength gain.
Setting Time: RHC has a shorter setting time compared to OPC. While OPC may take several hours to set, RHC can set in as little as a few minutes to a few hours, depending on the specific formulation and environmental conditions.
Early Strength Development: One of the primary advantages of RHC is its ability to achieve high early strength. This allows for quick demolding of concrete elements, early removal of formwork, and faster construction schedules.
Applications:
Emergency Repairs: RHC is often used for emergency repairs, where quick strength gain is essential to minimize downtime.
Cold Weather Concreting: In cold weather conditions, where low temperatures can slow down the hydration process, RHC can be used to accelerate strength development.
Pre-cast Concrete: RHC is commonly used in pre-cast concrete applications where fast turnaround times are required.
Highway Repairs: For rapid repairs of roads and highways, RHC can be advantageous due to its quick-setting properties.
Limitations: While RHC offers benefits in terms of early strength development and faster construction, it may have lower ultimate strength compared to OPC. Therefore, it's essential to consider the specific requirements of the project and balance the need for early strength gain with long-term durability.
Overall, rapid hardening cement is a valuable material in construction projects where time is of the essence, allowing for efficient and timely completion of tasks.
RESIDUAL COMPRESSIVE STRENGTH OF TERNARY BLENDED CONCRETE AT ELEVATED TEMPERA...Ijripublishers Ijri
The extensive use of concrete as a structural material for the high rise buildings, storage tanks, nuclear reactors and
pressure vessels increase the risk of concrete being exposed to high temperatures. This has led to a demand to improve
the understanding of the effect of temperature on concrete. The behavior of concrete exposed to high temperature is a
result of many factors including the exposed environment and constituent materials.
Concrete structures are exposed to fire when a fire accident occurs. Damage in concrete structures due to fire depends
to a great extent on the intensity and duration of fire. The distress in the concrete manifests in the form of cracking and
spalling of the concrete surface.
Performance of Concrete at Elevated Temperatures: Utilizing A Blended Ordinar...IOSR Journals
This study aimed at investigating the effect of subjecting concrete, produced with cement being
partially replaced with saw dust ash (SDA) to elevated temperatures. The performance of the test concrete cubes
was done by exposing them to elevated temperatures of 200oC, 400oC, 600oC and 800oC, and allowed to cool
down to room temperature before testing for their properties. Both the physical and thermal properties of the
concrete cubes were determined. The concrete produced by blending cement with 10% SDA with an average
percentage loss of 23.04% retained more of its compressive strength when exposed to the different
temperatures, than concrete produced using only OPC, which has an average percentage loss of 29.11%. It is
also found that, at an elevated temperature of 800oC, concrete fail totally in flexure due to the effect of high
heat on binding elements. The flexural strength of both the control concrete (at 0% OPC replacement) and
OPC/SDA blended concrete (at 10% OPC replacement) decreased as the temperature is increased. The
replacement of OPC by 10% SDA increased the thermal shock resistance of the concrete by 11 cycles than the
0% OPC concrete at the same temperature. The concrete produced with OPC has better thermal conductivity
than the concrete produced by blending OPC with SDA, as a result, the dislodgement of the concrete edges is
relatively lower in the SDA blended cement concrete than in the OPC concrete. The result shows that, blending
OPC with SDA in concrete performed better at elevated temperatures than concrete produced with only OPC.
Therefore, the replacement of OPC with 10% SDA can be applied as a fire resisting bonding material in
concrete.
This Presentation Covers and creates the awareness on understanding the mass concreting and its temperature effects during Concreting. Data compiled from varous papers and presentations.
Underground Construction provides construction, technical and management services to its customers. The company specializes in power, communications, airport fueling and heavy engineering. Since laying its first pipe in 1936, Underground Construction has completed thousands of projects throughout the United States.
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Self-curing concrete is achieved by means of replacing a part of aggregate by lightweight aggregate or adding chemical admixtures. The self-curing process of concrete takes place from inside to outside, thus reducing the autogenous shrinkage and self-desiccation, especially for the high-performance concrete with relatively low water/binder ratio.
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Trenchless construction. Trenchless construction includes such construction methods as tunneling, microtunneling (MTM), horizontal directional drilling (HDD) also known as directional boring, pipe ramming (PR), pipe jacking (PJ), moling, horizontal auger boring (HAB) and other methods for the installation of pipelines and cables below the ground with minimal excavation.
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A stressed ribbon bridge (also stress-ribbon bridge or catenary bridge) is a tension structure (similar in many ways to a simple suspension bridge). The suspension cables are embedded in the deck which follows a catenary arc between supports. Unlike the simple span, the ribbon is stressed in traction, which adds to the stiffness of the structure (simple suspension spans tend to sway and bounce).
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The process of self-healing of cracks or self-filling up of cracks by the help of bacterial reaction in the concrete after hardening is known as Self-Healing Concrete. It can be observed that small cracks that occur in a structure of width in the range of 0.05 to 0.1mm gets completely sealed in repetitive dry and wet cycles.
Autoclaved aerated concrete (AAC) is a lightweight, precast, foam concrete building material suitable for producing concrete masonry unit (CMU) like blocks. Composed of quartz sand , calcined gypsum , lime , cement , water and aluminum powder , AAC products are cured under heat and pressure in an autoclave .
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A submerged floating tunnel, also known as submerged floating tube bridge, suspended tunnel, or Archimedes bridge, is a proposed design for a tunnel that floats in water, supported by its buoyancy. The tube would be placed underwater, deep enough to avoid water traffic and weather, but not so deep that high water pressure needs to be dealt with—usually 20–50 m is sufficient. Cables either anchored to the Earth or to pontoons at the surface would prevent it from floating to the surface or ...
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The bundled tube structure meant that "buildings no longer need be boxlike in appearance: they could become sculpture." Hybrids. Hybrids include a varied category of structures where the basic concept of tube is used, and supplemented by other structural support(s).
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marble slurry dust as cement additive , The research on the use of marble dust in concrete , , disadvantages of marble dust and quarry dust additive in concrete; Chat Now; disadvantage of using quarry dust in concrete
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Computer Ethics: Ethics is a set of moral principles that govern the behavior of a group or individual. Therefore, computer ethics is set of moral principles that regulate the use of computers. Some common issues of computer ethics include intellectual property rights (such as copyrighted electronic content), privacy concerns, and how ...
CIVIL SEMINAR REPORT :USE OF GEOGRIDS IN FLEXIBLE PAVEMENT. Geogrids can also prevent aggregate penetration into the subgrade, depending on the ability of the geogrid to confine and prevent lateral displacement of the base/sub-base. However, the geogrid does not prevent intrusion of subgrade soils up into the base/sub-base course,...
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Waste water purification using cnstructed wetlandsAglaia Connect
Constructed Wetlands Treatment of Municipal Wastewater (PDF) (166 pp, 1.6 MB, About PDF) This document describes using constructed wetlands as a functional part of wastewater management. This document is not intended to be guidance or a support document for a specific regulatory program.
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Hybrid optimization of pumped hydro system and solar- Engr. Abdul-Azeez.pdffxintegritypublishin
Advancements in technology unveil a myriad of electrical and electronic breakthroughs geared towards efficiently harnessing limited resources to meet human energy demands. The optimization of hybrid solar PV panels and pumped hydro energy supply systems plays a pivotal role in utilizing natural resources effectively. This initiative not only benefits humanity but also fosters environmental sustainability. The study investigated the design optimization of these hybrid systems, focusing on understanding solar radiation patterns, identifying geographical influences on solar radiation, formulating a mathematical model for system optimization, and determining the optimal configuration of PV panels and pumped hydro storage. Through a comparative analysis approach and eight weeks of data collection, the study addressed key research questions related to solar radiation patterns and optimal system design. The findings highlighted regions with heightened solar radiation levels, showcasing substantial potential for power generation and emphasizing the system's efficiency. Optimizing system design significantly boosted power generation, promoted renewable energy utilization, and enhanced energy storage capacity. The study underscored the benefits of optimizing hybrid solar PV panels and pumped hydro energy supply systems for sustainable energy usage. Optimizing the design of solar PV panels and pumped hydro energy supply systems as examined across diverse climatic conditions in a developing country, not only enhances power generation but also improves the integration of renewable energy sources and boosts energy storage capacities, particularly beneficial for less economically prosperous regions. Additionally, the study provides valuable insights for advancing energy research in economically viable areas. Recommendations included conducting site-specific assessments, utilizing advanced modeling tools, implementing regular maintenance protocols, and enhancing communication among system components.
Final project report on grocery store management system..pdfKamal Acharya
In today’s fast-changing business environment, it’s extremely important to be able to respond to client needs in the most effective and timely manner. If your customers wish to see your business online and have instant access to your products or services.
Online Grocery Store is an e-commerce website, which retails various grocery products. This project allows viewing various products available enables registered users to purchase desired products instantly using Paytm, UPI payment processor (Instant Pay) and also can place order by using Cash on Delivery (Pay Later) option. This project provides an easy access to Administrators and Managers to view orders placed using Pay Later and Instant Pay options.
In order to develop an e-commerce website, a number of Technologies must be studied and understood. These include multi-tiered architecture, server and client-side scripting techniques, implementation technologies, programming language (such as PHP, HTML, CSS, JavaScript) and MySQL relational databases. This is a project with the objective to develop a basic website where a consumer is provided with a shopping cart website and also to know about the technologies used to develop such a website.
This document will discuss each of the underlying technologies to create and implement an e- commerce website.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
NO1 Uk best vashikaran specialist in delhi vashikaran baba near me online vas...Amil Baba Dawood bangali
Contact with Dawood Bhai Just call on +92322-6382012 and we'll help you. We'll solve all your problems within 12 to 24 hours and with 101% guarantee and with astrology systematic. If you want to take any personal or professional advice then also you can call us on +92322-6382012 , ONLINE LOVE PROBLEM & Other all types of Daily Life Problem's.Then CALL or WHATSAPP us on +92322-6382012 and Get all these problems solutions here by Amil Baba DAWOOD BANGALI
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Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
Cosmetic shop management system project report.pdfKamal Acharya
Buying new cosmetic products is difficult. It can even be scary for those who have sensitive skin and are prone to skin trouble. The information needed to alleviate this problem is on the back of each product, but it's thought to interpret those ingredient lists unless you have a background in chemistry.
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Data file handling has been effectively used in the program.
The automated cosmetic shop management system should deal with the automation of general workflow and administration process of the shop. The main processes of the system focus on customer's request where the system is able to search the most appropriate products and deliver it to the customers. It should help the employees to quickly identify the list of cosmetic product that have reached the minimum quantity and also keep a track of expired date for each cosmetic product. It should help the employees to find the rack number in which the product is placed.It is also Faster and more efficient way.
About
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Technical Specifications
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
Key Features
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface
• Compatible with MAFI CCR system
• Copatiable with IDM8000 CCR
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
Application
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
2. CONTENTS
INTRODUCTION
FIRE RESISTANCE OF HSC
EFFECT OF FIRE ON NSC
FACRORS GOVERNING THE FIRE PERFORMANCE OF HSC
EXPERIMENTAL STUDIES
GUIDELINES
PARAMETERS AFFECTED BY FIRE
CONCLUSION
3. INTRODUCTION
WHAT IS HSC?
It is a type of high performance concrete generally with a
specified compressive strength of 40 Mpa or greater.
The compressive strength is measured at 56 days or 90
days or some other specified age depending upon the
application.
4. To put the concrete at service at much earlier age.
To build high rise buildings by reducing column sizes and
increasing available space.
To build the superstructure of long-span bridges and to
enhance the durability of bridge decks.
WHY DO WE NEED
HSC?
5. In recent years, the construction industry has shown more
interest in the use of high strength concrete (HSC).
This is due to the improvements in structural performance,
such as high strength and durability, that it can provide
compared to normal strength concrete (NSC).
Recently, the use of high strength concrete, which was
previously in applications such as bridges, off-shore structures
and infrastructure projects, has been extended to high rise
buildings.
One of the major uses of HSC in buildings is for columns.
6. FIRE RESISTANCE OF HSC
Fire resistance is defined as the ability of a structural element
to withstand its load-bearing function under fire conditions.
It is the time during which a structural member exhibits
resistance with respect to structural integrity, stability and
temperature transmission.
The fire resistance of a structural member is dependent on
following factors:
geometry
materials used in construction
load intensity
characteristics of the exposing fire
7. Generally, concrete structural members exhibit good
performance under fire situations.
The performance of HSC is different from that of NSC
and may not exhibit good performance in fire.
Further, the spalling of concrete under fire conditions is
one of the major concerns due to the low water-cement
ratio in HSC.
8. Spalling is basically caused by the build-up of pore
pressure during heating.
HSC is believed to be more susceptible to this pressure
build-up because of its low permeability compared to
NSC.
Fire performance of HSC and spalling of HSC is affected
by the following factors:
original compressive strength
moisture content of concrete
concrete density
heating rate
specimen dimensions and shape
loading conditions
9. EFFECTS OF FIRE ON NSC
Thermal mismatch
Decomposition of hydrates
Pore pressure
10. THERMAL MISMATCH
When a low strength concrete member is exposed to fire,
the temperature gradient across the depth of the section
will be built up.
The thermal expansion of the outer layer of concrete
under a high temperature is partially restrained by the
inner layer of concrete under a lower elevated
temperature. , and this generates tensile thermal
stresses in the concrete.
The steeper the temperature gradient, the higher will be
the thermal stresses.
11. Concrete is a brittle composite material that consists of
binder (cement) paste and aggregates (fine and coarse
aggregates).
These materials have different mechanical and physical
properties, including different coefficients of thermal
expansion.
So because of this different co-efficient of thermal
expansion, LSC leads to thermal mismatch.
12. DECOMPOSITION OF HYDRATES
The mechanical properties of concrete depend
largely on the hydration products (calcium silicate
hydrate gel, calcium hydroxide) formed during the
hydration reaction between the cementitiuous
constituents and water.
When concrete is exposed to a fire attack, free
water in the concrete matrix will firstly be removed
through a physical process such as evaporation at
a lower elevated temperature.
As the temperature further increases, disintegration
of hydrates and loss of chemically bonded water
13. The decomposition of calcium hydroxide occurred at
about 350°C.
Then partial volatilization of calcium silicate hydrate gel
commenced at about 500°C.
The pore size and porosity of the hydrate matrix will
increase, and the mechanical properties (strength and
elastic modulus) of the hydrates will be weakened.
14. Moreover, at 573°C, the crystal structure of quartz
in a siliceous aggregate transforms from a low
temperature - phase to a high temperature - phase.
Such transformation is accompanied by an
approximately one percent volume increase, which
accelerates the disintegration process of the
hydrates.
15. PORE PRESSURE
The pore pressure developed in a heated concrete is
derived from the evaporation of water within the porous
media and from the decomposition of C-S-H gel and
calcium hydroxide.
The highest pore pressure occurred between 220°C and
240°C in high strength concrete (HSC) and between
190°C and 210°C in normal strength concrete (NSC).
The magnitude of the pore pressure depends on
moisture level
permeability of concrete
heating rate
16. The maximum pore pressure could reach 3 MPa for HSC
and 1 Mpa for LSC.
Low permeability and dense microstructure of HSC are
probably the causes for creating high pore pressure that
has been considered as a key factor for explosive
spalling of concrete.
The concrete with compressive strength of less than 60
MPa, no spallling would take place.
17. FACTORS GOVERNING THE
PERFORMANCE OF HSC
Fire characteristic
Material characteristic
Concrete strength
Concrete moisture content
Concrete density
Fibre reinforcement
Type of aggregate
Structural features
Specimen dimension
Lateral reinforcement
Load intensity and type
18. FIRE CHARACTERISTICS
The type of fire, the fire size and heat output, has
significant influence on the fire performance of a
concrete structural system.
The high rate of temperature rise can induce
spalling in concrete members.
This is mainly due to high temperature gradients
that develop within a cross section, which in turn
increases the pore pressure generated in the
concrete.
This effect can lead to significant spalling in HSC
members.
19. MATERIAL CHARECTERISTICS
CONCRETE STRENGTH
Strength of concrete has significant influence on fire
performance of concrete members.
The higher the strength, the higher will be the
probability of spalling.
Further, the loss of strength with temperature is
higher for HSC as compared to NSC.
20.
21. It can be seen that the rate of loss of strength is higher
(and significant) for HSC over the entire temperature
range.
In addition, the fire-induced spalling of HSC is
significantly higher than that for NSC.
22. SILICA FUME
Based on fire resistance tests, while for NSC
columns (concrete strength of about 40MPa) a fire
endurance of about 6 h was obtained.
For HSC columns (concrete strength of about
114MPa), with similar confinement, fire endurance
of only about 4 h was obtained.
In these tests, the extent of spalling was very
significant in columns with high silica fume content
(about 15%).
23. The higher silica fume, and associated compressive
strength, increases the extent of spalling, and leads
to decreased fire endurance.
This could be attributed to the fact that the addition
of silica fume appears to reduce the permeability of
the concrete, restricting the loss of moisture during
curing, drying, and the fire test.
24. MOISTURE CONTENT
The moisture content, expressed in terms of relative
humidity (RH), influences the extent of spalling.
Higher RH levels lead to greater spalling.
Fire-resistance tests on full-scale HSC columns and HSC
blocks have shown that significant spalling occurs when
the RH is higher than 80%.
The time required to attain an acceptable RH level (below
75%) in HSC structural members is longer than that
required for NSC structural members.
25. CONCRETE DENSITY
The effect of concrete density was studied by means of
fire tests on normal-density (made with normal-weight
aggregate) and lightweight (made with lightweight
aggregate) HSC blocks.
The extent of spalling was found to be much greater
when lightweight aggregate is used.
This is mainly because the light weight aggregate
contains more free moisture, which creates higher vapour
pressure under fire exposures.
26. FIBRE REINFORCEMENT
Addition of polypropylene fibres minimizes spalling
in HSC members under fire conditions.
One of the most accepted theories on this is that by
melting at a relatively low temperature of 170 C, the
polypropylene fibres create ‘‘channels’’ for the
steam pressure within the concrete to escape, thus
preventing the small ‘‘explosions’’ that cause
spalling.
The amount of polypropylene fibres needed to
minimize spalling is about 0.1–0.15% (by volume)
27. In some studies, addition of steel fibres was found to be
beneficial in enhancing fire endurance of HSC column.
The presence of steel fibres increases the tensile
strength of concrete, at high temperatures, and thus
reduces spalling and enhances fire resistance.
Also, the increased deformation capacity from the
addition of steel fibres contributes to minimising spalling.
28. TYPE OF AGGREGATE
Of the two commonly used aggregates, carbonate
aggregate (predominantly limestone) provides
higher fire resistance and better spalling resistance
in concrete than does siliceous aggregate.
This is mainly because carbonate aggregate has a
substantially higher heat capacity (specific heat),
which is beneficial in preventing spalling.
The fire endurance of HSC columns made with
carbonate aggregate concrete is about 10% higher
than HSC columns made with siliceous aggregate
Concrete.
29. STRUCTURAL FEATURES
SPECIMEN DIMENSION
The risk of explosive thermal spalling increases
with specimen size.
This is due to the fact that specimen size is directly
related to heat and moisture transport through the
structure.
Therefore, careful consideration must be given to
the size of specimens when evaluating the spalling
problem
30. LATRERAL REINFORCEMENT
Higher fire endurance in HSC columns can be achieved
by providing improved tie configuration (provision of bent
ties at 135° back into the core of the column and
increased lateral reinforcement) and with closer tie
spacing.
32. These improved tie provisions also minimize the extent of
spalling in HSC columns. This increased fire endurance and
reduced spalling are mainly due to ties holding the longitudinal
rebars, firmly in place, under fire exposure condition.
This mechanism helps to minimize the movement and
buckling of longitudinal bars which in turn reduces the strains
induced in concrete.
Columns containing only 90°ties would typically lose a
significant portion of the columns section upon failure.
33.
34. LOAD INTENSITY AND TYPE
The fire endurance of a RC column increases with
a decreasing load.
A higher load intensity leads to lower fire
resistance, since the loss of strength with a rise in
temperature is greater for HSC than for NSC.
This has been confirmed through number of fire
tests where a loaded HSC structural member was
more susceptible to higher spalling than an
unloaded member.
35. This occurs because a loaded structural member is
subjected to stresses due to load in addition to the pore
pressure generated by steam.
Further, the extent of spalling is higher if the load is of an
eccentric (or bending) type since this will induce
additional tensile stresses.
36. EXPERIMENTAL STUDIES
TEST SPECIMEN
The experimental program consisted of conducting fire
resistance tests on three reinforced concrete columns.
Two of these columns, HSC1 and HSC2, were of high
strength concrete while the third one, NSC1, was made
with normal strength concrete.
All columns were 3810 mm long and were of square
cross section of 305 mm size.
37. •The dimensions of the column cross section and
other specifics of the columns are given in Table
1.
38. Columns HSC1 and HSC2 had eight, 20 mm,
longitudinal bars, while Column NSC1 had four, 20
mm, longitudinal bars.
In the HSC columns, the bars were tied with 10 mm
ties at a spacing of 225 mm; while in the NSC
columns, the bars were tied with 8 mm ties at a
spacing of 305 mm.
The main reinforcing bars and ties had a specified
yield strength of 400 MPa.
39. Three batches of concrete were used in fabricating the
columns.
The mix for Batch 1 and Batch 2 used HSC, while the mix
for Batch 3 used NSC.
The coarse aggregate in Batches 1 and 3 was carbonate
while in Batch 2 it was siliceous aggregate.
Columns HSC1, HSC2 and NSC1 were fabricated from
Batch 1, Batch 2 and Batch 3, respectively.
40.
41. The moisture condition at the centre of the column
was also measured on the day of the test.
The moisture conditions of Columns HSC1, HSC2
and NSC1 are approximately equivalent to those in
equilibrium with air of 69% relative humidity (RH),
63% RH and 75% RH, respectively, at room
temperature.
42. TEST APPPARATUS
The tests were carried out by exposing the columns to
heat in a furnace specially built for testing loaded
columns.
The furnace consists of a steel framework supported by
four steel columns, with the furnace chamber inside the
framework.
The test furnace was designed to produce conditions,
such as temperature, structural loads and heat transfer,
to which a member might be exposed during a fire.
The furnace has a loading capacity of 1,000 t.
43. TEST CONDITION AND
PROCEDURE
The columns were installed in the furnace by
bolting the endplates to a loading head at the top
and to a hydraulic jack at the bottom.
The conditions of the columns were fixed-fixed for
all tests.
For each column, the length exposed to fire was
approximately 3000 mm.
For columns tested fixed at the ends, an effective
length of 2000 mm represents experimental
behaviour.
44. Column HSC1 was subjected to a load of 2000 KN.
Column HSC2 was subjected a load of 1700 KN.
Column NSC1 to a load of 1067 KN.
The load was applied approximately 45 min before the
start of the fire test and was maintained until a condition
was reached at which no further increase of the axial
deformation could be measured.
The load was maintained constant throughout the test.
45. RESULTS AND DISCUSSION
The temperature-time curves for the external
surface and for various depths in concrete are
plotted.
For all three columns, the temperatures inside the
column rose rapidly to about 100°C and then the
rate of increase of temperature decreased.
Both the NSC and HSC columns expanded until the
reinforcement yielded and then contracted leading
to failure.
46. It can be seen that deformation in the HSC columns was
slightly less than that for the NSC column.
The deformation in the columns resulted from several
factors, such as load, thermal expansion and creep.
Initial deformation of the column was mainly due to the
thermal expansion of concrete and steel.
While the effect of load and thermal expansion is
significant in the intermediate stages, the effect of creep
becomes pronounced in the later stages due to the high
fire temperature.
47. This is one of the main reasons that the deformations are
quite large before the failure of the columns.
All three columns failed in compression mode.
In the NSC column, no significant spalling occurred until
the failure of the column.
In the case of HSC columns, there was noticeable
spalling at the end of the test.
48. The cracks in these HSC columns progressed at the
corners of the cross section, with the increase in time,
and led to spalling of chunks of concrete.
This spalling was significant at about mid-height.
While minute cracks could be noticed in about 20 to 30
min, the widening of these cracks occurred after about 60
min or so.
In the case of Column HSC1 (carbonate aggregate
concrete), the spalling was less compared to Column
HSC2 (siliceous aggregate).
49. This could be attributed to the effect of aggregate
used in the concrete mix and also to the intensity of
load.
For the NSC column, the fire resistance was
approximately 366 min.
For Columns HSC1 and HSC2, it was 225 and 189
min, respectively.
54. GUIDELINES
High-strength concrete is a high-performing material that
offers a number of advantages. Engineers can enhance
its fire performance by adopting the following guidelines:
Use normal-weight aggregate (instead of lightweight
aggregate) to minimize spalling.
Add polypropylene fibres to the mix to reduce spalling.
Add steel fibres to enhance tensile strength and
reduce spalling.
55. Use carbonate aggregate (instead of siliceous
aggregate) to reduce spalling.
Employ both closer tie spacing and cross ties to
improve fire resistance.
Install bent ties (at 135° back into the concrete core)
instead of straight ties.
Take appropriate precautions to prevent spalling when
concrete strength exceeds 55 MPa.