Page 6 - Open-Access-August-2019

TECHNICAL PAPER

REsIDUAL PRoPERtIEs

oF BAsALt AnD

PoLYPRoPYLEnE

HYBRID FIBRE

REInFoRCED ConCREtE

ExPosED to ELEvAtED

tEmPERAtUREs S.K. KIRThIKA, S.K. SIngh, S.R. KARADE

Abstract and high heat capacity [1, 2] . However, constituents of concrete
behave differently at elevated temperatures, because of the
One of the important issues about concrete of-late is its difference in their thermal conductivity and coefficient of
behaviour during fire. The mechanical properties of concrete expansion. Consequently, properties of concrete like strength,
decrease on exposure to a temperature above 300ºC. In order Young’s modulus and volume stability may change when
to circumvent this problem, hybridization of two or more types exposed to elevated temperature [3, 4] . These properties vary
of fibres in concrete is gaining importance. A high modulus as a function of temperature and depend on the composition
fibre helps in preventing thermal cracks, whereas low modulus and characteristics of concrete [1, 5 & 6] . Thermal cracking and
fibre (polypropylene, nylon) helps in preventing spalling by spalling have significant influence on the properties of concrete
reducing pore pressure. An experimental study was conducted at elevated temperatures [1-2, 5-7] . Generally, thermal cracks occur
to explore the use of basalt fibres. The aim of this study was due to differential thermal expansion among constituents of
to develop a concrete that shall be able to retain strength and concrete resulting into tensile stresses that exceed the in-place
prevent spalling even after exposure to 800ºC. It has been concrete tensile strength [1, 5, & 7] . Another important effect of
found that hybrid fibre reinforced concrete with polypropylene elevated temperature on the concrete is spalling, which is
(V f =0.25%)+basalt (V f =0.50%) fibres retained upto 70% breaking up of layers or pieces of concrete from the surface
strength when exposed to elevated temperature of 800ºC, of a concrete member [1-9] . Successive spalling in a concrete
whereas control specimens retained only 52% of their original structure may lead to loss of stability and integrity of the
strength. In addition, no spalling was observed for both basalt structure [1, 5-11] . Furthermore, spalling exposes deeper layers of
fibre reinforced concrete (BFRC) and hybrid fibre reinforced concrete, thereby increasing the rate of transmission of heat
concrete (HyFRC) even when exposed to 1000ºC temperature to the inner layers of the member, which makes the exposure
for all mixes. A relationship between residual properties and of reinforcement to elevated temperature leading to loss in its
fibre dosage was developed to optimize fibre dosage for a strength [1, 9-11] .
temperature range of 25ºC ≤ t ≤ 1000ºC.
Efforts are made to improve the properties of concrete against
Keywords: Basalt fibre, Basalt fibre reinforced concrete, elevated temperature. The addition of fibres in concrete has
Elevated temperature, Hybrid fibre reinforced concrete, proven to be an effective solution. Over the years, many kinds
Polypropylene fibre, Residual compressive strength, Spalling, of fibre reinforced concrete (FRC) have been developed .
[11]
Thermal crack.
Experimental studies on the performance of FRC indicate
that incorporating fibres in concrete enhances one or more
1. iNtRoDUctioN properties of concrete like tensile strength, flexural strength,
Concrete, generally offers good fire resistance properties, i.e., toughness, impact resistance, durability and fatigue when
non-combustible, resistance to flame penetration, etc. [1-3] . This compared with normal concrete . This is because of the
[11]
is due to various constituents of concrete, which chemically unique property of randomly distributed fibres, which hinders
combine to form an inert material with low thermal conductivity the formation, and expansion of micro and macro cracks [12-15] .

16 The IndIan ConCreTe Journal | auGuST 2019