Page 10 - Open-Access-August-2019

TECHNICAL PAPER

of fibres vs temperature and a trend line was drawn in order The TGA/DTA results of PP fibre as shown in Figure 3 (b) exhibits
to determine the percentage volume fraction for any given that, the fibre melts around 160ºC and becomes vapour at
temperature between 25 and 1000ºC. 342ºC. It also exhibits a slight dilation at melting. The occurrence
of this dilation will help us to understand the effect of PP fibres
Error Analysis in reducing excess pore pressure in the concrete when exposed
The value of the properties P 1 and P 2 for x avg. was obtained to elevated temperatures. This was also corroborated by Kalifa
for every temperature and compared with that of highest et al. and Nazaret .
[33]
[51]
value of experimental study of the property for that particular
temperature and percentage deviation was obtained. This 3.2. Fresh and Hardened Properties of the
process was repeated for all six temperatures for the properties concrete
P 1 and P 2. The largest value of deviation obtained for the P 1 and
P 2 among all the temperatures was considered as the highest The Vee-Bee time of various concrete mixes are shown in Figure
deviation. The result of maximum deviation within 5% error 4. It increases with increase in percentage volume fraction of
should be observed.
fibres in both concrete mixes, i.e., BFRC and HyFRC. This is due
to clinging of concrete mixes resulting in increased adhesion
2.6.7. Microstructural studies
and cohesiveness of fresh concrete. In addition, fibres hold
Scanning Electron Microscope (SEM) analysis performed for the concrete together and thus slow down the settlement of
microstructural studies of all concrete mixes exposed to different aggregates. The reduction in workability was more prominent
temperatures. The specimens were observed after sputtering in BFRC as compared to HyFRC at same volume fraction. This is
them with gold coating. probably due to the positive synergistic effect of hybridisation
on workability. The air content in BFRC and HyFRC was found to
3. ResULts AND DiscUssioN be 0.80 and 0.75%, respectively, whereas in control concrete it
The results of the experimental investigations are presented as was only 0.6%.
follows.
Table 4 shows hardened properties of concrete mixes. The
3.1. tGA/DtA Analysis of Fibres optimum dose of basalt fibres in concrete is 0.5% volume
Figure 3 (a) shows TGA/DTA curves of basalt fibre. The mass fraction (V f ) (BFRC 1) and the enhancement in compressive,
loss is only 1.6% up to 1000ºC. The high melting point of the splitting tensile, flexural strength and elastic modulus of BFRC1
basalt fibres (about 1400ºC) shows its high thermal stability. are 26.80, 40, 44.47 and 24.95%, respectively, as compared to
Matykiewicz et al. [50] reported similar results. In DTA analysis, control concrete. This is due to bridging effect of basalt fibres
basalt fibre undergoes endothermic reaction. Since, the in the concrete mixes. A slight reduction in the hardened
materials, which undergoes endothermic reactions, are generally properties of the concrete is observed as percentage volume
amorphous in nature and have better adhesion with substrate. fraction of fibre increases. This is probably due to the balling
Therefore, basalt fibres have better adhesion with cement effect of fibres in concrete [52-58] . The optimum dose of fibres in
matrix. HyFRC is found to be 0.75% (HyFRC 1) (BF-0.50%+PP-0.25%),

0.676 100 -107
0 -100
120 -200 90
o
Furnace Rate -6 C/min 30 -80
80
Specimen Rate -0.5°C/min ASTM E-119-14 100 Derivative
1200 -150 -5 25 -60
70
1000 Exposure ISO 834-12 80 -100 Microvolt Endo Up (µV) -10 20 -40
60
Temperature ( o C) 800 Experimental - - Weight (%) 60 -50 Derivative Weight (% min) -15 Vee-Bee Time (seconds) Weight (% ) 15 -20 Microvolt Endo Up (μv)
50
Furnace
40
10
0
600
40
Experimental
30
Specimen
5
20
0
400
0
10
200 20 50 -20 20 Specimens Casted 40
0
0 200 400 600 800 1000 0 Dta 60
0 -10
tGa
0 200 400 600 800 1000 Temperature (˚C) Control BFRC 1 BFRC 2 BFRC 3 HyFRC 1 HyFRC 2 HyFRC 3
80
Time (min) -25.51 -20 91.77
TGA DTA -35.84 0 100 200 300 400 500 600 700 800 901.1
Temperature (°C)
(a) (b)
Figure 3: TGA / DTA analysis of fibres : (a) basalt fibre and (b) polypropylene fibre.
110
20 The IndIan ConCreTe Journal | auGuST 2019 6 Control
60
100 50 5 BFRC 1
Residual Mass (%) 90 40 Ultrasonic Pulse Velocity (km/s) 4 BFRC 3
BFRC 2
80
30
HyFRC 1
70
HyFRC 3
60 Residual Compressive Strength (MPa) 20 3 2 HyFRC 2
10
50 0
0 200 400 600 800 1000 1200 0 200 400 600 800 1000 1
Temperature ( C) Temperature ( C) 0
o
o
600
Control BFRC 1 BFRC 2 BFRC 3 Control BFRC 1 BFRC 2 BFRC 3 0 200 400 Temperature ( C) 800 1000 1200
o
HyFRC 1 HyFRC 2 HyFRC 3 HyFRC 1 HyFRC 2 HyFRC 3
40 Control 0.8 HyFRC 0.75 y = 6E-05x + 0.553
0.8
Residual Elastic Modulus (GPa) 30 BFRC 2 Volume Fraction of Fibres (PP+BF)% 0.75 0.603 0.607 y = 1E -05x + 0.5937 0.553 0.654 Volume Fraction of Fibres (%) 0.65 0.57 0.559 0.566 0.573 0.604 0.62
35
BFRC 1
0.7
BFRC 3
0.7
25
HyFRC 1
0.65
20
0.6
HyFRC 2
0.6
15
0.587
HyFRC 3
0.596
0.55
0.55
10
0.5
0.5
0 5 0.45 0.45
0.4
0 200 400 600 800 1000 1200 0.4
0 200 400 600 800 1000 1200
o
Temperature ( C) 0 200 400 600 800 1000 1200
Temperature ( C)
o
Temperature ( C)
o