Page 7 - Open-Access-August-2019

TECHNICAL PAPER

The hybridisation of two or more fibres to have positive residual physical and mechanical properties like colour change,
synergistic effect in improving properties of the concrete is also mass loss, ultrasonic pulse velocity, compressive strength, elastic
[16]
gaining importance [13-15] . Pliya et al. observed the significant modulus and micro-structural changes with respect to different
improvement in residual properties like residual compressive, exposed temperature of BFRC and HyFRC are studied and
flexural and elastic modulus of concretes containing results are compared with control concrete. The mechanical
polypropylene (PP) and steel fibres compared to concretes properties of control, BFRC and HyFRC are also investigated.
without fibres when exposed up to 600ºC. The combination
of two low melting point fibres like nylon (250ºC) and 2.1. Raw Material characterisation
polypropylene fibres (160ºC) in the concrete showed enhanced
spalling resistance [16-23] , by allowing the escape of pore pressure 2.1.1. cement, aggregate and admixtures
through micro-channels after melting of PP and nylon fibres Ordinary Portland cement (OPC) 43 grade confirming to IS
when exposed to elevated temperature. HyFRC having PP 269 [30] was used in all mixes. River sand of Zone II conforming to
and steel fibres above 400ºC, the residual fracture energy was IS 383 , having specific gravity of 2.64 and fineness modulus
[31]
found more as compared to concrete without fibre . The high of 2.31 was used as fine aggregate. Crushed stone aggregate
[22]
modulus fibre like steel helps in reducing the thermal cracks of maximum size of 20 mm having specific gravity of 2.69 and
formed whereas low modulus and low temperature melting fibre fineness modulus of 6.8 was used as coarse aggregate. Potable
like polypropylene or nylon fibre helps in reducing spalling in tap water was used for mixing and curing concrete specimens.
the concrete by reducing excess pore pressure that build when Third generation carboxylic ether based super-plasticizer
exposed to high temperatures [23, 24] . confirming to IS 9103 was used to attain the desired
[32]
workability.
In the recent years, the use of natural mineral fibres such as
basalt fibres (BF) is gaining importance. It performs exceptionally 2.1.2. Fibres
well being inert- mineral having high thermal stability and good
mechanical properties as compared with other fibres . The Basalt fibres and polypropylene fibres used in the experimental
[25]
applications of basalt fibres are increasing especially in the last investigations were procured from Hydro Design Management
five years [11, 26] . Basalt fibre reinforced concrete (BFRC) retained Company Pvt. Ltd. (HDM), New Delhi and Forta Ferro, USA,
90% of strength even after exposed to 400ºC . Ren et al. respectively. The physical properties of the fibres were tested in
[25]
[27]
observed that for a given temperature, the strain rate, dynamic the laboratory and given in Table 1. The length and diameter of
strength, critical strain and impact toughness of BFRC increase the fibres were measured using Scanning Electron Microscope
with impact velocity. The basalt fibre reinforced plastics showed (SEM). The tensile strength, elastic modulus and percentage
better mechanical properties and temperature resistance elongation break of the fibres were tested using Universal
compared to glass fibre reinforced plastics (GFRP) [28, 29] . Testing Machine (UTM) of capacity of 50 kN. Thermogravimetric
analysis (TGA) and differential thermal analysis (DTA) of
The use of basalt fibre in concrete is an exploratory area. both fibres were carried out with temperature ranging from
Limited investigations on BFRC were reported in the literature. 25ºC - 1000ºC at 10ºC/minute heating rate under nitrogen
However, no attempt has been made to study the behaviour atmosphere to measure the changes in physical and chemical
of concrete with basalt and PP fibres at elevated temperatures. properties. TGA/DTA analysis provides informative data on its
Therefore, experimental investigations on basalt and PP fibre in transformation occurred such as glass transition, crystallization,
concrete were carried out to determine the residual engineering melting, sublimation, etc. [33, 34] .
properties, such as strength, elastic modulus when subjected to
different elevated temperatures up to 1000ºC. Microstructural Table 1: Properties of fibre
changes in the concrete when exposed to elevated temperature PRoPERtIEs BAsALt FIBRE PoLYPRoPYLEnE
has also been studied. A theoretical formulation has been FIBRE
developed to determine the optimum percentage volume Form Monofilament Monofilament
fraction of hybridization to get positive synergistic effect in Colour Brown Grey
HyFRC when exposed to temperature ranging from 200ºC to Length (mm) 24 54.0
1000ºC and the results are validated. Diameter (µm) 160.5 340
Aspect ratio (l/d) 1500 158.8
2. MAteRiALs AND MetHoDs Specific gravity 2.60 0.91
The physical properties of ingredients of the concrete mixture as Tensile strength (MPa) 3200 7.80
well as properties of basalt and PP fibres used in this study are Elastic modulus (GPa) 110 0.68
described in subsequent sections. Mix proportioning, specimens Elongation at break (%) 3.5 19.1
details, casting and heating procedures are also presented. The Melting temperature (ºC) 1400 160

The IndIan ConCreTe Journal | auGuST 2019 17