Page 11 - Open-Access-August-2019

TECHNICAL PAPER

which shows superior mechanical properties. The increase aggregates. The whitish grey or white colour of the concrete
in compressive, splitting tensile, flexural strength and elastic specimens at 800ºC is found probably due to decomposition of
modulus of HyFRC 1 was in order of 28.24, 60, 44.47 and 31.08% calcium carbonate or lime present in concrete. Similar trends in
over control concrete, which are higher than that of BFRC 1. BFRC and HyFRC specimens are observed except some black
This is due to positive synergistic effect of basalt and PP fibres in spots on the surface due to melting and evaporation of PP
concrete. fibres.

3.2.1. visual observations There was no visible change in texture of concrete surface up
to 400ºC for both BFRC and HyFRC. However, some fine cracks
The colour changes of basalt fibres at different temperatures are
shown in the Figure 5. The surface texture and colour of basalt were observed on surface of control specimens. A few and very
fine surface cracks were observed in BFRC & HyFRC specimens
fibres remained same from ambient to 400ºC, beyond this the at 600ºC. Well pronounced surface cracking was observed in
colour changes, fibres become soft and observed to be golden
yellow in colour and elongated after exposing to 600ºC. The control specimens at 1000ºC, whereas the cracking in BFRC and
charring of fibres started at 800ºC and were broken into pieces. HyFRC was restrained due to presence of fibres. Table 5 shows
The colour of the fibres turn to black at 1000ºC. surface crack widths. The crack width in control specimens after
exposing to 800ºC was 0.40 mm, whereas in BFRC and HyFRC it
120 -200 was only 0.20 and 0.12 mm, respectively. This is probably due to
Furnace Rate -6 C/min 30 fibres in the BFRC and HyFRC help in arresting the cracks and
o
1200 Specimen Rate -0.5°C/min ASTM E-119-14 100 -150 25 thus stopping the propagation of the cracks further. However, in
1000 Exposure ISO 834-12 80 -100 Microvolt Endo Up (µV) 20 control specimens cracks develop and further propagate.
Temperature ( o C) 800 Experimental - - Weight (%) 60 -50 Vee-Bee Time (seconds) 15 table 5: crack width measurement of various
Furnace
10
Experimental
40
600
Specimen
0
400
20
0 5 concrete mixes
200 0 50 Specimens Casted tYPE CRACK WIDtH (mm)
0 200 400 600 800 1000
0 200ºC 400ºC 600ºC 800ºC 1000ºC
0 200 400 600 800 1000 Temperature (˚C) Control BFRC 1 BFRC 2 BFRC 3 HyFRC 1 HyFRC 2 HyFRC 3
Time (min) Control No cracks 0.02-0.03 0.24- 0.30 0.34-0.40 0.50-1.00
TGA DTA
Figure 4: Vee-Bee time of concrete vs various concrete mixes.
BFRC 1 No cracks No cracks 0.07-0.09 0.18-0.20 0.20-0.45
table 4: Hardened properties of concrete HyFRC 1 No cracks No cracks 0.03-0.04 0.10-0.12 0.12-0.35
mixes at ambient temperature
110 60 ConCREtE ComPREs- tEnsILE FLExURAL ELAstIC
Control
6
sIvE
Ultrasonic Pulse Velocity (km/s)
100 50 sPECImEn stREnGtH stREnGtH stREnGtH moDULUs
BFRC 1
Residual Mass (%) 90 40 tIons 4 (mPa) 3.00 4.63 BFRC 3
(GPa)
5nA-
DEsIG
(mPa)
(mPa)
BFRC 2
80
30
28.21
HyFRC 1
38.25
Control
70
3
35.25
HyFRC 3
60 Residual Compressive Strength (MPa) 20 BFRC 1 48.50 4.20 6.70 HyFRC 2
2
10
50 0 BFRC 2 46.54 4.50 6.45 36.01
1
0 200 400 600 800 1000 1200 0 200 400 600 800 1000 BFRC 3 40.28 4.00 6.30 35.75
o
Temperature ( C) Temperature ( C) HyFRC 1 49.05 4.80 6.70 36.98 Ambient 200ºC 400ºC
0
o
Control BFRC 1 BFRC 2 BFRC 3 Control BFRC 1 BFRC 2 BFRC 3 0 200 400 600 o 800 1000 1200
4.57
HyFRC 1 HyFRC 2 HyFRC 3 HyFRC 1 HyFRC 2 HyFRC 3 HyFRC 2 45.48 Temperature ( C) 6.51 35.67
HyFRC 3 40.08 4.05 6.45 35.50
3.3. Residual Properties of the concrete Mixes
The typical colour changes of concrete specimens at different
40 Control 0.8 HyFRC temperatures are shown in Figure 6. The colour of all the
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 changes from dark grey at 200ºC to buff colour at 1000ºC. Figure 5: Colour change of basalt fibres exposed to different elevated
Volume Fraction of Fibres (%)
concrete specimens including control, BFRC and HyFRC
35
BFRC 1
0.75
y = 6E-05x + 0.553
600ºC
800ºC
1000ºC
0.7
BFRC 3
0.7
25
0.65
The colour of control specimens turns pink at 400ºC and
HyFRC 1
0.65
20
0.62
0.604
0.6
600ºC, which is due to the presence of iron compound in the
HyFRC 2
temperature.
0.6
15
0.573
0.57
0.587
0.566
0.596
HyFRC 3
0.559
0.55
0.55
10
0.5
0.5
0 5 0.45 0.45 The IndIan ConCreTe Journal | auGuST 2019 21
0.4
0 200 400 600 800 1000 1200 0.4
0 200 400 600 800 1000 1200
Temperature ( C) Temperature ( C) 0 200 400 600 800 1000 1200
o
o
o
Temperature ( C)