The destruction of life or property is caused by fire in buildings and infrastructure
It is essential to understand the strength and decomposition properties of concrete using additives subjected to elevated temperatures in order to assess the reaction of those structures during and after susceptibility to high temperatures
Ordinary Portland cement of 53 grade was procured from local suppliers. The standard consistency of cement is 32 percent, and the initial setting time and final setting time are 56 and 259 minutes. The properties of cement are shown in
Standard Consistency |
Specific gravity |
Final setting time |
Initial setting time |
Fineness |
Soundness (Le Chatelier method) |
(%) |
- |
(min) |
(min) |
(m2/kg) |
(mm) |
32 |
3.15 |
259 |
56 |
300 |
1.2 |
Sand confirming to Zone -II was used as fine aggregate, and additional materials, if any, are removed from sand by passing it through a sieve size of 4.75mm. Crushed stone of 20mm size is used as coarse aggregate. Fine and coarse aggregates were brought from local suppliers.
Properties |
FA |
CA |
Fineness modulus |
3.18 |
7.6 |
Specific gravity |
2.65 |
2.79 |
Bulk-density (kg/m3) |
1520 |
1416 |
Nano silica of average particular size 17nm was procured from Asstra chemicals, Chennai, India. Alccofine of size 4-6µm was obtained from local dealers. The properties of nano-silica (Ns) and alccofine (Al) are given in
Item |
Ns |
Al |
Calcium oxide |
0.06% |
32.1-34.3% |
Silicon dioxide |
99.88% |
33-35% |
Aluminum oxide |
0.01% |
18.0-20.0% |
Ferric oxide |
0.00% |
1.8-2% |
Magnesium oxide |
- |
8.0-10.0% |
Sulfur trioxide |
- |
0.30-0.70% |
Avg. particle size |
17nm |
4-6µm |
Conplast SP430 DIS, with brand name Fosroc, is a brown liquid that is immediately soluble in water and is based on Sulphonated Naphthalene Polymers to improve the workability of concrete. It is combined with water and added to the concrete.
Mix design of three concrete grade M40, M50, & M60 was done using according to the IS10262:2019 and IS 456:2005. In this study, the comparison of control mixes and mixes using nano-silica and alccofine was made. The percentage of nano-silica and alccofine is taken as 15% and 3%. The mix proportions of all the mixes are given in
Mix |
SCM |
Notations |
Water (Kg/m3) |
Cement (Kg/m3) |
Fine agg. (FA) (Kg/m3) |
Coarse agg. (CA) (Kg/m3) |
Alccofine (AL) (Kg/m3) |
Nano silica (NS) (Kg/m3) |
w/c |
M40 |
0 |
M4 |
160 |
400 |
667 |
1248 |
- |
- |
0.4 |
AL+Ns |
M4AlNs |
160 |
328 |
667 |
1248 |
60 |
12 |
0.4 |
|
M50 |
0 |
M5 |
159 |
440 |
642 |
1243 |
- |
- |
0.36 |
AL+Ns |
M5AlNs |
159 |
360.8 |
642 |
1243 |
66 |
13.2 |
0.36 |
|
M60 |
0 |
M6 |
158 |
527 |
596 |
1218 |
- |
- |
0.3 |
AL+Ns |
M6AlNs |
158 |
432.2 |
596 |
1218 |
79 |
15.8 |
0.3 |
Relative compressive strength (RCS) is the ratio of compressive strength at a particular temperature to compressive strength at room temperature. Relative compressive strength values of the concrete blends at different temperatures and fire durations are demonstrated in
Furthermore, as the fire duration at 600°C increased, the RCS of M4, M5, and M6 mixes ranged from 0.95 to 0.72. While M4AlNs, M5AlNs, and M6AlNs mixes ranged from 0.78 to 0.59. At 800°C, the RCS of all the concrete mixes was less than 0.6. And the RCS subsequently decreased to 0.24 for the Al+Ns mix and 0.32 for the control mix at 12 hours. The dense morphology is mainly impervious, which is harmful at high temperatures. It prevents water from escaping, contributing to the development of pore water pressure and thereby leading to microcrack formation, resulting in rapid degradation of RCS
Ultrasonic Pulse Velocity test is one of the most powerful and versatile indirect techniques used for assessing the damage level in concrete subjected to fire, regarding the loss of strength and durability
Developing a mathematical relationship for calculating concrete residual compressive strength at higher temperatures is a valuable technique for designing concrete structures
Source |
Relations |
Eurocode et al. |
fc`T = fc`, T ≤ 100 ◦Cfc`T = fc` × (1.067 − 0.00067 × T) ≥ 0, 100 ≤ T ≤ 400 ◦Cfc`T = fc` × (1.44 − 0.0016 × T) ≥ 0, T ≥ 400°C |
Raza et al. |
fc`T = fc` (-3E-06x2 + 0.0014x + 0.9365), 25 ≤ T ≤ 800°C |
Li and Purkiss et al. |
fc`T = fc` × (0.00165 × ( |
Hassan et al. |
fc`T = (20731.45 x fc` + 11.76 × T1.708) ∕ (20731.45 + T1.708), 20 ≤ T ≤ 800°C |
Concrete mix |
Relation |
R |
M4 |
fc`T/fc`27 = -9E-07T2 + 6E-05T + 1.0571 |
0.9452 |
M4AlNs |
fc`T/fc`27 = -1E-06T2 + 0.0004T + 1.0359 |
0.9369 |
M5 |
fc`T/fc`27 = -9E-07T2 + 0.0001T + 1.0374 |
0.9771 |
M5AlNs |
fc`T/fc`27 = -9E-07T2 + 0.0003T + 1.0414 |
0.8912 |
M6 |
fc`T/fc`27 = -9E-07T2 + 0.0001T + 1.0302 |
0.9833 |
M6AlNs |
fc`T/fc`27 = -1E-06T2 + 0.0004T + 1.0315 |
0.9575 |
Compared to other relations,
The percentage difference between experimental and predicted values is determined for each of the concrete blends mentioned in
Temp. (°C) |
M4 |
M5 |
M6 |
||||||
Exp. values |
Pred. values |
% Error |
Exp. values |
Pred. values |
% Error |
Exp. values |
Pred. values |
% Error |
|
27 |
40.94 |
42.82 |
-5% |
46.95 |
49.24 |
-5% |
54.80 |
57.08 |
-4% |
200 |
47.08 |
44.05 |
6% |
53.01 |
50.02 |
6% |
63.22 |
58.72 |
7% |
400 |
40.82 |
42.41 |
-4% |
46.42 |
47.77 |
-3% |
53.90 |
56.53 |
-5% |
600 |
38.81 |
37.50 |
3% |
44.66 |
42.13 |
6% |
50.77 |
49.95 |
2% |
800 |
24.25 |
29.31 |
-21% |
24.68 |
33.12 |
-34% |
31.06 |
38.99 |
-26% |
1000 |
18.38 |
17.85 |
3% |
22.31 |
20.72 |
7% |
19.53 |
23.65 |
-21% |
Temp. (°C)
|
M4AlNs |
M5AlNs |
M6AlNs |
||||||
Exp. values |
Pred. values |
% Error |
Exp. values |
Pred. values |
% Error |
Exp. values |
Pred. values |
% Error |
|
27 |
52.80 |
55.87 |
-6% |
56.56 |
58.79 |
-4% |
66.15 |
68.28 |
-3% |
200 |
58.45 |
54.55 |
7% |
60.72 |
57.77 |
5% |
70.40 |
67.09 |
5% |
400 |
51.98 |
49.48 |
5% |
55.31 |
52.79 |
5% |
64.00 |
61.27 |
4% |
600 |
41.32 |
40.61 |
2% |
42.78 |
43.74 |
-2% |
51.11 |
50.68 |
1% |
800 |
23.25 |
27.94 |
-20% |
26.80 |
30.62 |
-14% |
33.03 |
35.34 |
-7% |
1000 |
17.30 |
11.46 |
34% |
15.29 |
13.43 |
12% |
18.97 |
15.23 |
20% |
The conclusions are being drawn based on the findings in the present research. The relative compressive strength was greater than 1 at 200°C after 4 and 8 hours, indicating an increase in strength for both control and Al+Ns mixes. But as the temperature and fire duration increased, the relative compressive strength decreased. M4AlNs, M5AlNs, and M6AlNs mixes had the lowest relative strength of 0.08 to 0.09 at 1000ºC for 12 hours. The relative compressive of M4AlNs, M5AlNs, and M6AlNs mixes was less compared to M4, M5, and M6 at all temperatures. As exposed to a fire for 4 and 8 hours at 200ºC, all concrete mixes had UPV values greater than 4.5, indicating excellent quality. The ultrasonic pulse velocity reduced as the temperature and duration of the fire increased, with the percentage decrease being greater for M4AlNs, M5AlNs, and M6AlNs mixes at all temperatures. The dramatic decrease in the ultrasonic pulse velocity values of all concrete mixes beyond 400ºC clearly showed a rapid degradation in the physical state of the concrete specimens. At 1000°C, the ultrasonic pulse velocity values were reduced to zero for all concrete mixes due to increased porosity. The proposed equations in polynomial form had a correlation coefficient R2 almost equal to 1 for all the concrete mixes, and it showed acceptable reliability compared to other relations.
As the temperature rose above 600
Since lightweight aggregates have a lower heat conductivity, in future research, we can study the performance of concrete using lightweight aggregates, alccofine, and nano-silica at high temperatures.
RCS |
Relative compressive strength |
Al |
Alccofine |
Ns |
Nano-silica |
Al+Ns mix |
Concrete using alccofine and nano-silica |
UPV |
Ultrasonic Pulse Velocity |
fc`T |
Cylindrical compressive strength at temperature ‘T’ |
fc`27 |
Cylindrical compressive strength at temperature ‘27ºC’ |
fc` |
Cylindrical compressive strength at room temperature |
T |
Temperature |