- Email: [email protected]
Torsional Strengthening Of Normal Weight Concrete And Light Weight Concrete Using Steel Fibres
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 4 (2017) 9846–9850
www.materialstoday.com/proceedings
ICEMS 2016
Torsional Strengthening Of Normal Weight Concrete And Light Weight Concrete Anto Georgea,*, A.Sofib a
Student, M.Tech Structural Engineering, b Associate Professor, School of Civil and Chemical Engineering (SCALE), VIT University, Vellore, TN, India, 632014
Abstract Forces that twist a member about a longitudinal axis are called torsional loads. Modern day structures using conventional concrete which are tall and aesthetically pleasing is in need of torsional strengthening. In this study, torsional behaviour of normal weight concrete (NWC) and light weight concrete (LWC) is analysed. Coconut shell aggregate is used instead of broken granite to make light weight concrete. Torsional strengthening is done using crimped steel fibres. A torsion-loaded member will result in torsional cracking commencing before the flexural failure, as the torsional strength is highly dependent on the tensile strength, which is the weakest component in brittle concrete. Steel fibres in optimum amount can impart homogeneous tensile properties in concrete, which in turn increases torsional capacity. Fibres are added in 0.5% percentage by volume to both NWC and LWC. Basic mechanical properties such as compressive strength, split tensile strength and flexural strength are analyzed using cubes, cylinders and prism for 7 days and 28 days. Torsional strengthening studies are carried out on beams of size 1100x150x100mm. Comparative study of results in NWC and LWC are done with control mixes of corresponding mixes. Comparison between torsional behaviour of NWC and LWC is also done. Torque-Angle of twist responses of all mixes is also found. LWC showed more torque value and angle of twist than NWC. Steel fibres enhanced these properties in both mixes. * Corresponding author. Tel.: +919995248720 E-mail address: [email protected] 2214-7853 © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International Conference on Recent Trends in Engineering and Material Sciences (ICEMS2016).
Anto George, A Sofi / Materials Today: Proceedings 4 (2017) 9846–9850
9847
© 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International Conference on Recent Trends in Engineering and Material Sciences (ICEMS-2016).
Keywords: Fibre reinforced concrete, Normal weight concrete (NWC), Coconut Shell Concrete (CSC), Torsion, Steel fibre
1.
Introduction Concrete has relatively high compressive strength, but much lower tensile strength, limited ductility and little
resistance to cracking. Tensile stresses are induced in concrete resulting the cracking of concrete. Steel reinforcement is used to absorb these tensile stresses and to prevent the cracking to some extent. The addition of steel reinforcement significantly increases the strength of concrete but to produce concrete with homogeneous tensile properties the micro cracks developed in concrete should be suppressed [1]. It has been found that the addition of fibres to concrete would act as crack arresters and would substantially improve its static and dynamic properties [2]. Steel fibre reinforced concrete has superior resistance to cracking and crack propagation. Structural LWC offers design flexibility and cost savings due to weight reduction, improved seismic response, and lower foundation costs. Coconut shell concrete (CSC) could be used in places where coconut is abundant and may also be used where the granite aggregates are costly. Researches proved that wood based materials, being hard and of organic origin, will not contaminate or leach to produce toxic substances once they are bound in concrete matrix [3]. The recent building trends are focused on the concepts of being more economical and space efficient and aesthetic design in which the structural members are designed to be irregular or curved in shape. The curved members will be eccentrically loaded, which will induce torsion in the members. Typical examples of torsion-loaded structures include utility poles, eccentrically structures, spiral staircases, spandrel beams and curved beams. Addition of steel fibres enhances the torsional behaviour. But the study on torsional behaviour is limited, especially in the case of light weight concrete. This study aims at understanding effect of steel fibres in normal weight concrete (NWC) and coconut shell concrete (CSC). 2. Experimental Program 2.1. Materials Used Ordinary Portland Cement (OPC) of 53 grade, sand from Palar river as fine aggregate, crushed stone aggregate with a maximum particle size of 12.5- 20 mm as coarse aggregate, coconut shell (CS) of 12.5mm average size in saturated surface dry condition, silica fume, Cera Hyperplast XR-W40 super plasticizer, grooved steel fibres of 50mm length and 1mm diameter and potable water were used for the study. M20 mix was used for this work. Table 1 shows physical properties of CS and granite aggregates.
9848
Anto George, A Sofi / Materials Today: Proceedings 4 (2017) 9846–9850
Table 1. Physical Properties of CS and granite aggregates.
Aggregate Type Coconut shell
Maximum size(mm) 12.5
Moisture content 9.7%
Specific gravity 1.31
Water absorption 23.7 %
Granite
20
0.3%
2.78
0.5%
2.2. Mix Design Total of four mixes were made for this investigation. Two of the mixes were normal weight concrete (NWC) using granite aggregates and two were coconut shell concrete (CSC) using coconut shell as coarse aggregate. 0.5% steel fibres by volume of concrete was added to mixes and designated as NWFRC (Normal weight fibre reinforced concrete) and CSFRC (Coconut shell fibre reinforced concrete). NWC was designed as per IS 10262-2009. CSC was designed based on work of K.Gunasekaran et.al [3] and Soon Poh Yap [1]. Silica fume was added at 10% by weight of cement. The mix design obtained are tabulated in Table 2. Table 2 Mix Design
Mix
OPC (kg/m3))
Silica fume
Water (kg/m3)
Sand (kg/m3)
Granite (kg/m3)
CS (kg/m3)
Steel fibre (% vol)
NWC
384
-
192
678
1190
-
0
NWFRC
384
-
192
678
1190
-
0.5
CSC
550
55
186
830
-
550
0
CSFRC
550
55
186
830
-
550
0.5
2.3. Specimens for tests For testing the mechanical properties of each mix proportion, 100mm cubes, 200mm length 100mm diameter cylinders and flexural testing on 500mm x 100mm x 100mm prisms were casted for compression test, split tensile test and flexural test as per IS specifications. Tests were conducted on 7days and 28 days. Torsion studies were carried out on beams of effective length 1m and overall dimension 1100mm x 150mm x 100mm. 2.4. Test procedures For compressive strength, split tensile strength and flexural strength methods where followed as per IS specifications. Torsion testing was done on a Universal Testing Machine. The test setup was made using I-sections and plates [3]. The torsion test setup and schematic setup of end support.is shown in Figure 1.
Anto George, A Sofi / Materials Today: Proceedings 4 (2017) 9846–9850
(a)
9849
(b)
Fig 1. (a)Torsion test setup in UTM for beams (b) Schematic setup of end support 3. Results and Discussions 3.1. Workability and Density NWC mix exhibited higher workability of 75mm against the 50mm workability of CSC mix. A high amount of cement paste is required for the formation CSC aggregate-cement paste bond, which reduces the flowability of the mix. When 0.5% fibre was added the workability of both mixes reduced. NWFRC mix had a workability of 45mm and CSFRC had a workability of 20mm. The density of NWC mix was found to be 2398 kg/m3 and that of CSC was 1995 kg/m3, hence classified as light weight concrete. By the addition of 0.5% steel fibre, the densities increased to 2493 kg/m3 and 2089 kg/m3 for NWFRC and CSFRC respectively. 3.2. Mechanical properties Table 3 shows the test results of compressive strength, split tensile strength and flexural strength. The mixes where compared on the basis of strength. Hence the 28-days compressive strength of both the mixes were made approximately same Table 3 Test results Mix
Compressive
Split tensile strength
Flexural Strength
Cracking
Ultimate
strength (N/mm2)
(N/mm2)
(N/mm2)
torque
torque
7-day
28-day
7-day
28-day
7-day
28-day
(kNm)
(kNm)
NWC
23.9
32.2
2.01
2.69
8.67
9.42
2.146
2.55
NWFRC
37.7
44.2
2.643
3.206
9.67
10.41
3.825
4.05
CSC
21.9
30.17
1.84
2.35
5.5
7.25
4.35
4.8
CSFRC
27.6
32.64
2.63
3.18
6.5
9.58
5.1
5.325
9850
Anto George, A Sofi / Materials Today: Proceedings 4 (2017) 9846–9850
3.3 Torsional behaviour Torsion test results are shown in Table 3. The NWC beam exhibited first crack at torsional moment of 2.146 6
CSC
CSFRC
NWC
NWFRC
Torque (kNm)
5
kNm. The ultimate torque was 2.55 kNm. And angle of twist was 0.0624 rad/m. NWFRC mix had a cracking torque of 3.825 kNm and ultimate torque of
4
4.05 kNm with an angle of twist of 0.084 rad/m. The
3
CSC mix showed more torsional strength than NWC
2
mix. It had a cracking torque of 4.35 kNm and
1
ultimate torque of 4.8 kNm. Angle of twist at ultimate load was 0.077 rad/m. The CSFRC mix
0 0
0.05
0.1
0.15
Angle of twist (rad/m)
Fig 2 Torque – Angle of twist curve for all mixes
exhibited highest values for cracking and ultimate torque. The cracking toque was 5.1 kNm and ultimate torque was 5.325 kNm. The angle of twist
was 0.134 rad/m. Torque v/s Angle of twist graph is shown in Figure 2. 4. Conclusions Steel fibres enhances the torsional strength reinforced concrete beams subjected to torsion. Coconut shell concrete produces beams of higher torsional resistance than normal weight concrete. Addition of steel fibres caused a decreased workability of NWC and CSC mix by 40% and 60% respectively. 0.5% steel fibres caused increase of torsional resistance by 58.8% in NWC and 11% in CSC. The cracking torque values of fibre reinforced concretes are closer to ultimate torque because fibres prevent crack formation at early stages. Angle of twist values are more fore fibre reinforced concretes. CSFRC mix underwent maximum twist and was able to resist maximum torque. References [1] Soon Poh Yap, Kuan Ren Khaw, “Effect of Fibre aspect ratio on the torsional behaviour of steel fibrereinforced normal weight concrete and lightweight concrete” Eng Struct 2015 (101)24–33 [2] S. A. Mahadik, S. K. Kamane, “Effect of Steel Fibers on Compressive and Flexural Strength of Concrete.” International Journal of Advanced Structures and Geotechnical EngineeringISSN 2319-5347, Vol. 03, No. 04, October 2014 [3] K.Gunasekaran,P.S.Kumar, “Long term study on compressive and bond strength of coconut shell aggregate concrete.” Construction and Building Materials 208–215, October 2011 [4] A.Sofi, B.R.Phanikumar,“An experimental investigation on flexural behaviour of fibre reinforced pond ashmodified concrete.” Ain Shams Engineering Journal, December 2015, Pages1133–1142 [5] A.Sofi, B.R Phanikumar,” Effect of pond ash and steel fibre on engineering properties of concrete.”Ain Shams Engineering Journal, April 2015 [6] Okay F, Engin S.“Torsional behavior of steel fiber reinforced concrete beams.”Constr Build Mater 2012;28:269–275.
ScienceDirect Materials Today: Proceedings 4 (2017) 9846–9850
www.materialstoday.com/proceedings
ICEMS 2016
Torsional Strengthening Of Normal Weight Concrete And Light Weight Concrete Anto Georgea,*, A.Sofib a
Student, M.Tech Structural Engineering, b Associate Professor, School of Civil and Chemical Engineering (SCALE), VIT University, Vellore, TN, India, 632014
Abstract Forces that twist a member about a longitudinal axis are called torsional loads. Modern day structures using conventional concrete which are tall and aesthetically pleasing is in need of torsional strengthening. In this study, torsional behaviour of normal weight concrete (NWC) and light weight concrete (LWC) is analysed. Coconut shell aggregate is used instead of broken granite to make light weight concrete. Torsional strengthening is done using crimped steel fibres. A torsion-loaded member will result in torsional cracking commencing before the flexural failure, as the torsional strength is highly dependent on the tensile strength, which is the weakest component in brittle concrete. Steel fibres in optimum amount can impart homogeneous tensile properties in concrete, which in turn increases torsional capacity. Fibres are added in 0.5% percentage by volume to both NWC and LWC. Basic mechanical properties such as compressive strength, split tensile strength and flexural strength are analyzed using cubes, cylinders and prism for 7 days and 28 days. Torsional strengthening studies are carried out on beams of size 1100x150x100mm. Comparative study of results in NWC and LWC are done with control mixes of corresponding mixes. Comparison between torsional behaviour of NWC and LWC is also done. Torque-Angle of twist responses of all mixes is also found. LWC showed more torque value and angle of twist than NWC. Steel fibres enhanced these properties in both mixes. * Corresponding author. Tel.: +919995248720 E-mail address: [email protected] 2214-7853 © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International Conference on Recent Trends in Engineering and Material Sciences (ICEMS2016).
Anto George, A Sofi / Materials Today: Proceedings 4 (2017) 9846–9850
9847
© 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International Conference on Recent Trends in Engineering and Material Sciences (ICEMS-2016).
Keywords: Fibre reinforced concrete, Normal weight concrete (NWC), Coconut Shell Concrete (CSC), Torsion, Steel fibre
1.
Introduction Concrete has relatively high compressive strength, but much lower tensile strength, limited ductility and little
resistance to cracking. Tensile stresses are induced in concrete resulting the cracking of concrete. Steel reinforcement is used to absorb these tensile stresses and to prevent the cracking to some extent. The addition of steel reinforcement significantly increases the strength of concrete but to produce concrete with homogeneous tensile properties the micro cracks developed in concrete should be suppressed [1]. It has been found that the addition of fibres to concrete would act as crack arresters and would substantially improve its static and dynamic properties [2]. Steel fibre reinforced concrete has superior resistance to cracking and crack propagation. Structural LWC offers design flexibility and cost savings due to weight reduction, improved seismic response, and lower foundation costs. Coconut shell concrete (CSC) could be used in places where coconut is abundant and may also be used where the granite aggregates are costly. Researches proved that wood based materials, being hard and of organic origin, will not contaminate or leach to produce toxic substances once they are bound in concrete matrix [3]. The recent building trends are focused on the concepts of being more economical and space efficient and aesthetic design in which the structural members are designed to be irregular or curved in shape. The curved members will be eccentrically loaded, which will induce torsion in the members. Typical examples of torsion-loaded structures include utility poles, eccentrically structures, spiral staircases, spandrel beams and curved beams. Addition of steel fibres enhances the torsional behaviour. But the study on torsional behaviour is limited, especially in the case of light weight concrete. This study aims at understanding effect of steel fibres in normal weight concrete (NWC) and coconut shell concrete (CSC). 2. Experimental Program 2.1. Materials Used Ordinary Portland Cement (OPC) of 53 grade, sand from Palar river as fine aggregate, crushed stone aggregate with a maximum particle size of 12.5- 20 mm as coarse aggregate, coconut shell (CS) of 12.5mm average size in saturated surface dry condition, silica fume, Cera Hyperplast XR-W40 super plasticizer, grooved steel fibres of 50mm length and 1mm diameter and potable water were used for the study. M20 mix was used for this work. Table 1 shows physical properties of CS and granite aggregates.
9848
Anto George, A Sofi / Materials Today: Proceedings 4 (2017) 9846–9850
Table 1. Physical Properties of CS and granite aggregates.
Aggregate Type Coconut shell
Maximum size(mm) 12.5
Moisture content 9.7%
Specific gravity 1.31
Water absorption 23.7 %
Granite
20
0.3%
2.78
0.5%
2.2. Mix Design Total of four mixes were made for this investigation. Two of the mixes were normal weight concrete (NWC) using granite aggregates and two were coconut shell concrete (CSC) using coconut shell as coarse aggregate. 0.5% steel fibres by volume of concrete was added to mixes and designated as NWFRC (Normal weight fibre reinforced concrete) and CSFRC (Coconut shell fibre reinforced concrete). NWC was designed as per IS 10262-2009. CSC was designed based on work of K.Gunasekaran et.al [3] and Soon Poh Yap [1]. Silica fume was added at 10% by weight of cement. The mix design obtained are tabulated in Table 2. Table 2 Mix Design
Mix
OPC (kg/m3))
Silica fume
Water (kg/m3)
Sand (kg/m3)
Granite (kg/m3)
CS (kg/m3)
Steel fibre (% vol)
NWC
384
-
192
678
1190
-
0
NWFRC
384
-
192
678
1190
-
0.5
CSC
550
55
186
830
-
550
0
CSFRC
550
55
186
830
-
550
0.5
2.3. Specimens for tests For testing the mechanical properties of each mix proportion, 100mm cubes, 200mm length 100mm diameter cylinders and flexural testing on 500mm x 100mm x 100mm prisms were casted for compression test, split tensile test and flexural test as per IS specifications. Tests were conducted on 7days and 28 days. Torsion studies were carried out on beams of effective length 1m and overall dimension 1100mm x 150mm x 100mm. 2.4. Test procedures For compressive strength, split tensile strength and flexural strength methods where followed as per IS specifications. Torsion testing was done on a Universal Testing Machine. The test setup was made using I-sections and plates [3]. The torsion test setup and schematic setup of end support.is shown in Figure 1.
Anto George, A Sofi / Materials Today: Proceedings 4 (2017) 9846–9850
(a)
9849
(b)
Fig 1. (a)Torsion test setup in UTM for beams (b) Schematic setup of end support 3. Results and Discussions 3.1. Workability and Density NWC mix exhibited higher workability of 75mm against the 50mm workability of CSC mix. A high amount of cement paste is required for the formation CSC aggregate-cement paste bond, which reduces the flowability of the mix. When 0.5% fibre was added the workability of both mixes reduced. NWFRC mix had a workability of 45mm and CSFRC had a workability of 20mm. The density of NWC mix was found to be 2398 kg/m3 and that of CSC was 1995 kg/m3, hence classified as light weight concrete. By the addition of 0.5% steel fibre, the densities increased to 2493 kg/m3 and 2089 kg/m3 for NWFRC and CSFRC respectively. 3.2. Mechanical properties Table 3 shows the test results of compressive strength, split tensile strength and flexural strength. The mixes where compared on the basis of strength. Hence the 28-days compressive strength of both the mixes were made approximately same Table 3 Test results Mix
Compressive
Split tensile strength
Flexural Strength
Cracking
Ultimate
strength (N/mm2)
(N/mm2)
(N/mm2)
torque
torque
7-day
28-day
7-day
28-day
7-day
28-day
(kNm)
(kNm)
NWC
23.9
32.2
2.01
2.69
8.67
9.42
2.146
2.55
NWFRC
37.7
44.2
2.643
3.206
9.67
10.41
3.825
4.05
CSC
21.9
30.17
1.84
2.35
5.5
7.25
4.35
4.8
CSFRC
27.6
32.64
2.63
3.18
6.5
9.58
5.1
5.325
9850
Anto George, A Sofi / Materials Today: Proceedings 4 (2017) 9846–9850
3.3 Torsional behaviour Torsion test results are shown in Table 3. The NWC beam exhibited first crack at torsional moment of 2.146 6
CSC
CSFRC
NWC
NWFRC
Torque (kNm)
5
kNm. The ultimate torque was 2.55 kNm. And angle of twist was 0.0624 rad/m. NWFRC mix had a cracking torque of 3.825 kNm and ultimate torque of
4
4.05 kNm with an angle of twist of 0.084 rad/m. The
3
CSC mix showed more torsional strength than NWC
2
mix. It had a cracking torque of 4.35 kNm and
1
ultimate torque of 4.8 kNm. Angle of twist at ultimate load was 0.077 rad/m. The CSFRC mix
0 0
0.05
0.1
0.15
Angle of twist (rad/m)
Fig 2 Torque – Angle of twist curve for all mixes
exhibited highest values for cracking and ultimate torque. The cracking toque was 5.1 kNm and ultimate torque was 5.325 kNm. The angle of twist
was 0.134 rad/m. Torque v/s Angle of twist graph is shown in Figure 2. 4. Conclusions Steel fibres enhances the torsional strength reinforced concrete beams subjected to torsion. Coconut shell concrete produces beams of higher torsional resistance than normal weight concrete. Addition of steel fibres caused a decreased workability of NWC and CSC mix by 40% and 60% respectively. 0.5% steel fibres caused increase of torsional resistance by 58.8% in NWC and 11% in CSC. The cracking torque values of fibre reinforced concretes are closer to ultimate torque because fibres prevent crack formation at early stages. Angle of twist values are more fore fibre reinforced concretes. CSFRC mix underwent maximum twist and was able to resist maximum torque. References [1] Soon Poh Yap, Kuan Ren Khaw, “Effect of Fibre aspect ratio on the torsional behaviour of steel fibrereinforced normal weight concrete and lightweight concrete” Eng Struct 2015 (101)24–33 [2] S. A. Mahadik, S. K. Kamane, “Effect of Steel Fibers on Compressive and Flexural Strength of Concrete.” International Journal of Advanced Structures and Geotechnical EngineeringISSN 2319-5347, Vol. 03, No. 04, October 2014 [3] K.Gunasekaran,P.S.Kumar, “Long term study on compressive and bond strength of coconut shell aggregate concrete.” Construction and Building Materials 208–215, October 2011 [4] A.Sofi, B.R.Phanikumar,“An experimental investigation on flexural behaviour of fibre reinforced pond ashmodified concrete.” Ain Shams Engineering Journal, December 2015, Pages1133–1142 [5] A.Sofi, B.R Phanikumar,” Effect of pond ash and steel fibre on engineering properties of concrete.”Ain Shams Engineering Journal, April 2015 [6] Okay F, Engin S.“Torsional behavior of steel fiber reinforced concrete beams.”Constr Build Mater 2012;28:269–275.