Page 9 - Open-Access-August-2019

TECHNICAL PAPER

2.6. Residual Properties of the concrete 2.6.6. Average optimum volume fraction of
2.6.1. visual observations fibres
The specimens were taken out of the furnace after 12 hours and A relation with experimental data with error analysis, with
observations were noted in terms of colour changes, cracking respect to residual compressive strength and residual elastic
patterns, crack widths, etc. to ascertain the degree of damages in modulus has been developed to optimize percentage volume
concrete specimens. In addition, the change in colour of basalt fraction of basalt fibre in BFRC and in HyFRC (with 0.25% volume
fibre was also studied for different elevated temperatures. The fraction of PP fibres) exposed to different temperatures. The
assessment in the colour change of PP fibres was not possible, as validation of the formulation was carried out using experimental
it melts at low temperature around 160ºC and evaporated. The results.
crack width formed in all specimens after temperatures exposure
were measured with crack-width microscope. Formulation
A function f 1 (x) is defined for a property varying with percentage
120 -200
o
Furnace Rate -6 C/min volume fraction (x) of the fibre for a particular exposure 30
100
-150
1200 Specimen Rate -0.5°C/min ASTM E-119-14 temperature t 1. The ‘z’ is a maximum value of percentage 25
80ion for the property, i.e., in a sufficiently close
1000 Exposure ISO 834-12 volume fract -100 Microvolt Endo Up (µV) 20
Weight (%)
Temperature ( o C) 800 Experimental - - values of f 1 (x) is smaller than f 1 (x=z). The first derivative of the Vee-Bee Time (seconds) 15
neighbourhood of the point, all values of ‘x’ are associated with
60
Furnace
-50
10
600
40
Experimental
[49]
function is the extremum where the slope becomes zero . In
Specimen
5
the present study, a quadratic equation for residual compressive
0
400
20
200 strength for various percentage volume fraction of fibre at a 0 Specimens Casted
0
50
given temperature based on the experimental results as given:
1000
200
400
0
800
600
0
0 200 400 600 800 1000 Temperature (˚C) 2 Control BFRC 1 BFRC 2 BFRC 3 HyFRC 1 HyFRC 2 HyFRC 3
Time (min) P for a given temperature = f 1 (x) = ax + bx + c (1)
1
TGA DTA
Figure 2: Surface temperature vs time for temperature exposure where,
at 800ºC.
P 1 – Residual compressive strength (Property 1)
2.6.2. Residual mass x – Percentage volume fraction of fibres.
Residual mass depicts the effect of exposure temperature on At f’ 1 [49]
110
60
reduction in density of concrete. The percentage residual mass to obtain the value of ‘x’, which yields an extremum of the 6 Control
100
Residual Mass (%)
50
of the concrete specimens for each exposure temperature with function f 1 (x). Similarly, the quadratic function for residual elastic 5 BFRC 1
BFRC 2
90
40
respect to control specimens (25ºC) was calculated after 12 modulus is given below: BFRC 3
80
hours of cooling. Residual Compressive Strength (MPa)(x) = 0, is a critical value of the argument ; among them (2) Ultrasonic Pulse Velocity (km/s) 4 3 HyFRC 1
30
P for a given temperature = f 1 (x) = Ax + Bx + C
2
2
70
HyFRC 2
2.6.3. Ultrasonic pulse velocity (UPv) where, 20 2 HyFRC 3
60
10
50
The UPV was used to ascertain the degree of damages in terms P 2 – Residual elastic modulus (Property 2). 1
0
1200
800
0
200
400
600
1000
of quality of the concrete exposed to different temperatures. 0 200 400 600 800 1000
Temperature ( C) x – Percentage volume fraction of fibres for the same 0
o
o
Temperature ( C)
An UPV instrument of PUNDIT LAB PLUS of Proceq make with 0 200 400 600 800 1000 1200
Control BFRC 1 BFRC 2 BFRC 3 temperature at which the value of P is obtained. BFRC 3
BFRC 2
Control
BFRC 1
1
transducers of 54 kHz frequency was used. The wave pattern of HyFRC 1 HyFRC 2 HyFRC 3 Temperature ( C)
o
HyFRC 3
HyFRC 2
HyFRC 1
the concrete specimens exposed to different temperatures were Similarly, at f’ 1 (x) = 0, is a critical value of the argument; among
also recorded. them to obtain the value of x, which yield an extremum of the
function f 1 (x).
2.6.4 Residual compressive strength
A new function is defined as Y 1 (P 12, x) = f 1 (x) + f 1 (x) and its first
Residual compressive strength of all the concrete specimens derivative Y 1’ (P 12, x) is determined to seek the value of x, which
40
exposed to different temperatures were measured using UTM. yield an extremum of the function for that particular temperature 0.8
Control
HyFRC
Residual Elastic Modulus
35
BFRC 1
0.8
The failure modes of each specimens were noted in order to of study for the combined property. Experimental investigations 0.75 y = 6E-05x + 0.553
Volume Fraction of Fibres
30
0.75
0.7
assess the efficacy of fibres in concrete. BFRC 2 was carried out with three different percentage volume fraction 0.65
y = 1E -05x + 0.5937
BFRC 3
25
0.7
0.654
(GPa)
(PP+BF)%
0.65
20
0.607
0.603
HyFRC 2
2.6.5. Residual elastic modulus HyFRC 1 of basalt fibre (0.5, 0.75 and 1%) for six different temperatures Volume Fraction of Fibres (%) 0.6 0.57 0.559 0.566 0.573 0.604 0.62
0.6
15
0.587
and for two properties. In a similar way, the extremum point of
0.596
HyFRC 3
0.55
0.553
10
Elastic modulus were calculated for all the mixes exposed to percentage volume fraction for all the six temperatures were 0.55
0.5
0.5
5
0.45
different temperatures by drawing a slope of the corresponding determined for residual compressive and elastic modulus. A 0.45
0
0.4
600
800
1000
1200
400
0
stress-strain curve at 40% of maximum stress of the specimens. graph was plotted with extremum percentage volume fraction 0.4
200
400
1200
600
800
1000
200
0
Temperature ( C) Temperature ( C) 0 200 400 600 800 1000 1200
o
o
o
Temperature ( C)
The IndIan ConCreTe Journal | auGuST 2019 19