Highlights of the Paper
- The innovation of geogrids and steel bars as hybrid reinforcement system.
- A new term of “Geogrids’ proof-strain” was defined.
- Value engineering study of geogrids and steel bars as hybrid reinforcement.
- “Uniaxial geogrids pre-stressed concrete” concept was suggested for future studies. Which is expected to reduce the plastic deformation, enhance the mechanical properties, and increase the benefits to cost ratios.
- This hybrid reinforcement system could decrease the influence of corrosion due to environmental actions, as part of the system is not subjected to corrosion (geogrids). Accordingly, will contributing to reducing its degree of damage, its effect on the structural behavior, and the associated cost and time with repair, moreover, it provides higher benefits to cost ratios compared to the conventional reinforcement of steel bars.
2. Literature Review
Main Conclusions of the Literature Review
- The use of geogrids as additional reinforcement to the steel bars in concrete slabs provided better results, as it provided a higher first crack load and higher ultimate load than the cases of using conventional reinforcement of steel bars or using uniaxial geogrids as main reinforcement; meanwhile, it led to an increase in the deflection values. The decrease of the reinforcement ratio of steel bars to 0.13% led to a decrease in the contribution and effectiveness of geogrids as concrete slab reinforcement. Accordingly, geogrids cannot be depended on as the main reinforcement for concrete slabs.
- The impact resistance and impact energy capacity of concrete slabs increased by using geogrids as an additional reinforcement to steel bars with a positive correlation to the number of geogrids’ layers.
- Geogrids as concrete beams reinforcement provide ductile post cracking behavior, high fracture energy, increase absorbed energy, high flexural strength, and large deformation values according to the tensile strength, number of layers, and the type of geogrids in descending order of uniaxial, biaxial, and triaxial geogrids.
- The confining effect of geogrids plays a significant role in the properties of concrete.
- Crack width is reduced as the tensile strength of geogrids is increased.
- Both of the triaxial geogrids post-failure observations and the strain measurements suggest that there was no pullout or slippage between the triaxial geogrids and the concrete.
- Geogrids should not be used in concrete structures or members that might be subjected to fire. On the other hand, geogrids include a lack of susceptibility to corrosion, higher ratios of strength to weight, and lower costs.
- The circular-shaped geogrids reinforcement was effective in the control of crack opening.
- The size of the coarse aggregate should be less than the aperture size of geogrids.
3. Specifications of the Used Materials
4. Experimental Program
5. Test Set-Up and Loading Arrangement
6. Failure Mechanism and Crack Patterns
7. Experimental Results Analysis and Discussions
7.1. Load Versus Vertical Displacement Behavior
7.2. Cracking Load, Steel-Yield Load, Ultimate Load, and Flexural Strength
7.3. Displacement Ductility Behavior
7.4. Energy Dissipation Behavior
7.5. Bottom Reinforcement Strain-Load Behavior
7.6. Value Engineering
8. Conclusions and Recommendations
- The reinforcement steel bars had the minimum reinforcement ratio, due to the fact that the minimally reinforced concrete sections are brittle structures, to provide one flexural crack in the control concrete slab, and to depend more on the geogrids and deeply study its behavior as additional reinforcement to the steel bars. Accordingly, the loading period of the concrete slabs under this research included the following load points: First-crack load associated with initial-peak load, a sudden load drop in conjunction with a sudden deflection increase, steel-yield load, post-peak load, and failure load in sequential order. Such a loading period demonstrated post cracking ductility. The concrete Slabs loading behavior when using uniaxial geogrids as additional bottom reinforcement to the reinforcement steel bars is most preferred as it provides lower load drops and higher load values, with nearly equal deflections values at the steel yield load when compared with the triaxial geogrids; however, it provided higher deflection values at the post-peak load.
- The number of flexural cracks, deflection, load, flexural strength, displacement ductility index, and energy dissipation has a positive correlation with the tensile strength of geogrids and the number of geogrids’ layers. The case of using uniaxial geogrids as additional bottom reinforcement to the reinforcement steel bars is most preferred as it provides higher values of these parameters when compared with the triaxial geogrids; however, it provided higher deflection values at the post-peak load.
- The initial-peak load has a weak positive correlation with the tensile strength of geogrids and the number of geogrids’ layers; meanwhile, the post-peak load has a normal positive correlation with the tensile strength of geogrids and the number of geogrids’ layers. The reason is that, when the first-crack occurs, the geogrids’ ribs control the crack propagation, and the crack opening leads to geogrids’ ribs elongation, resulting in geogrids’ ribs being tension-stressed, and accordingly, geogrids provide better performance when tension-stressed. Therefore, geogrids are recommended to be tension stressed before the concrete casting as this condition can expedite and enhance its participation in carrying the tensile force. This condition can be achieved by the uniaxial geogrids; meanwhile, it is difficult to achieve by the triaxial geogrids.
- As the friction between the geogrids and concrete interface is weak, the mechanism of geogrids to carry tensile force is; the uniaxial geogrids’ transverse bars or the triaxial geogrids’ integral nodes are entirely confined by the concrete, keeping its location, and preventing tensile force transmission to the following uniaxial geogrids’ ribs portions or triaxial geogrids’ hexagon pitches. This gives the geogrids’ ribs the ability to control the crack propagation, and the crack opening leads to geogrids’ ribs elongation and carrying the tensile force. As the triaxial geogrids’ integral nodes are uniformly staggered distributed to the whole area, the triaxial geogrids could be cut at any location. Meanwhile, as the uniaxial geogrids’ transverse bars are parallelly distributed with an equal offset, the uniaxial geogrids should be cut at transverse bars location to provide a transverse bar at its beginning and its end.
- The ability of geogrids to carry tensile force as concrete slab reinforcement is limited by the ribs portions or the hexagon pitches where concrete cracks hit the ribs. Accordingly, the geogrids’ performance and benefits as concrete slab reinforcement will be enhanced as the number of concrete flexural cracks increased, spread, and distributed widely throughout the concrete slab tension zone length. This condition can be achieved by using geogrids of the higher experimental tensile strength (like; 103.91 kN/m for UG, 19.45 kN/m for TG, and higher tensile strengths), and as an expectation, it may be achieved by using the geogrids as additional bottom reinforcement to a moderate reinforcement ratio (not a minimum reinforcement ratio) of steel bars.
- As each uniaxial geogrids’ ribs portions cover a larger area than triaxial geogrids’ hexagon pitches and as the number of uniaxial geogrids’ ribs portions contributing to carrying the tensile force is gradually increasing with increasing of the tensile strength of uniaxial geogrids and the number of uniaxial geogrids’ layers; meanwhile, the number of triaxial geogrids’ hexagon pitches contributing to carrying the tensile force kept constant while it duplicated in the case of using double layers of triaxial geogrids with the experimental tensile strength of 19.45 kN/m (based on the number and locations of the flexural cracks), the displacement ductility index value and the energy absorption capacity value were gradually increased for the cases of using uniaxial geogrids as additional reinforcement to steel bars; meanwhile, it had a large increment in the case of using double layers of triaxial geogrids with the experimental tensile strength of 19.45 kN/m. On the other hand, the cases of three uniaxial geogrids’ ribs portions contributing to carrying tensile forces (cases of two occurred flexural cracks), provide higher loads at uniaxial geogrids’ yield-strain when compared with other cases of uniaxial geogrids. Accordingly, it is recommended to use a moderate (not the minimum) reinforcement ratio of the steel bars.
- The uniaxial geogrids material yield-strain is 13% (as proposed by the manufacturer), and the triaxial geogrids material yield-strain is 6.4% (Numerical yield Strain)—which is very far from the concrete slabs elastic range and acceptable plastic range. Accordingly, the term “geogrids’ proof-strain” was defined to guarantee that the geogrids reinforced concrete slabs will not exceed the acceptable concrete slabs behavior ranges (the elastic range or an acceptable plastic range). The geogrids’ proof-strain was chosen to be equal to the reinforcement steel-yield strain value (which varies from 1250 (0.13%) to 2500 (0.25%) micro-stain based on the steel grade) when it is used as additional reinforcement to the steel bars.
- The using of uniaxial geogrids as additional reinforcement to the steel bars provide more efficient utilization than the using of triaxial geogrids as additional reinforcement to the steel bars as it has higher benefits to cost ratios, especially for uniaxial geogrids with the experimental tensile strength of 103.91 kN/m and 143.46 kN/m, as it has the highest benefits values (steel yield load, post-peak load, displacement ductility index, and energy absorption capacity), while they provided benefit to cost values higher than the lower uniaxial geogrids’ tensile strength. Meanwhile, the triaxial geogrids provided lower deflection values, especially for the deflection at the post-peak load.
- Based on the applied configuration of the geogrids and steel bars hybrid reinforcement system for concrete slabs under this study (the geogrids was applied for the whole slab area and with minimum reinforcement ratio of the steel bars), the hybrid reinforcement system provides a higher benefit to cost ratios when it compared with the case of using conventional reinforcement of steel bars (concrete control slab). In some cases, it nearly provided double benefits values when compared with the concrete control slab. Meanwhile, In order to increase the benefit to cost ratios of the hybrid reinforcement system, the geogrids are recommended to be applied only for the tension zone with suitable development lengths (decreasing its cost) and with the use of moderate (not the minimum) reinforcement ratio of the steel bars (increasing its benefits values, as an expectation).
9. Future Studies
- Study the efficiency of pre-tensioning the uniaxial geogrids before the concrete casting to provide uniaxial geogrids pre-stressed concrete slabs. Based on the above-mentioned conclusions and recommendations, uniaxial geogrids are expected to provide better performance as concrete slabs reinforcement if it were tension-stressed before the concrete casting; on the other hand, the uniaxial geogrids material yield-strain is 13%, which is considerably higher than the concrete slabs elastic range and an acceptable plastic range; meanwhile, the geogrids proof-strain is varying from 0.13% to 0.25%; accordingly, uniaxial geogrids could be tensioned before the concrete casting up to a strain of 8% (for example), providing uniaxial geogrids pre-stressed concrete slabs and adding a new utilization concept of uniaxial geogrids in structural engineering. This concept is expected to reduce the plastic deformation, enhance the mechanical properties, and increase the benefits to cost ratios.
- Study the efficient steel bars reinforcement ratio for the hybrid reinforcement of geogrids and steel bars.
- Study the efficiency of geogrids and steel bars hybrid reinforcement system in the two-ways concrete slabs.
- Study the ways to enhance the bonding at the geogrids-concrete interface.
- Study the effect of dynamic loads on geogrids reinforced concrete.
- Study the effect of cyclic loading on geogrids reinforced concrete.
- Study the effect of span to depth ratio on the geogrids reinforced concrete slabs.
- Study the shear behavior on the geogrids reinforced concrete slabs.
- Study the effect of high-temperature changes on the geogrids reinforced concrete.
Conflicts of Interest
- Saranyadevi, M.; Suresh, M.; Sivaraja, M. Strengthening of Concrete Beam by Reinforcing with Geosynthetic Materials. Int. J. Adv. Res. Educ. Technol. 2016, 3, 245–251. [Google Scholar]
- Maxwell, S.; Kim, W.-H.; Tuncer, B.E.; Benson, C.H. Effectiveness of Geo-Synthetics in Stabilizing Soft Subgrades; University of Wisconsin-Madison: Madison, WI, USA, 2005. [Google Scholar]
- Webster, S.L. Geogrid Reinforced Base Course for Flexible Pavements for Light Aircraft: Test Section Construction, Behaviour under Traffic, Laboratory Tests, and Design Criteria; National Technical Information Service: Springfield, VA, USA, 1992. [Google Scholar]
- Sharbaf, M. Laboratory Evaluation of Geogrid-Reinforced Flexible Pavements. Master’s Thesis, University of Nevada, Las Vegas, NV, USA, May 2016. [Google Scholar]
- Al-Hedad, S.A.; Bambridge, E.; Muhammad, N.S. Influence of Geogrid on The Drying Shrinkage Performance of Concrete Pavements. Construct. Build. Mater. 2017, 146, 165–174. [Google Scholar] [CrossRef]
- Al Basiouni Al Masri, Z.; Daou, A.; Haj Chhade, R.; Chehab, G. Experimental and Numerical Assessment of the Behavior of Geogrid-Reinforced Concrete and Its Application in Concrete Overlays. J. Mater. Civ. Eng. 2018, 30, 04018332. [Google Scholar] [CrossRef]
- Itani, H.; Saad, G.A.; Chehab, G.R. The use of geogrid reinforcement for enhancing the performance of concrete overlays: An experimental and numerical assessment. Constr. Build. Mater. 2016, 124, 826–837. [Google Scholar] [CrossRef]
- Khodaii, A.; Fallah, S. Effects of Geo-Synthetic Reinforcement on The Propagation of Reflection Cracking in Asphalt Overlays. Int. J. Civ. Eng. 2009, 7, 131–140. [Google Scholar]
- Walubita, L.F.; Nyamuhokya, T.P.; Komba, J.; Tanvir, H.A.; Souliman, M.; Naik, B. Comparative assessment of the interlayer shear-bond strength of geogrid reinforcements in hot-mix asphalt. Constr. Build. Mater. 2018, 191, 726–735. [Google Scholar] [CrossRef]
- Tang, X.; Chehab, G.R.; Kim, S. Laboratory study of geogrid reinforcement in Portland cement concrete. In Proceedings of the 6th RILEM International Conference on Cracking in Pavements, Chicago, IL, USA, 16–18 June 2018; pp. 769–778. [Google Scholar]
- Ahmed Shaban, A.H.G. Strengthening of Reinforced Concrete Slabs Using Different types of Geo-Grids. Int. J. Civ. Eng. Technol. 2019, 10, 1851–1861. [Google Scholar]
- Al Qadi, A.N.; Al-Kadi, Q.N.S.; Al-Zaidyeen, S.M. Impact Strength of Oil-Palm Shell on Lightweight Concrete Slabs Reinforced with a Geo-Grid. J. Mater. Civ. Eng. 2015, 27, 04014264. [Google Scholar] [CrossRef]
- Tang, X.; Mohamad, N.; Higgins, J.; Higgins, I. Concrete Slab-on-Grade Reinforced by Geogrids. In Proceedings of the Eight International Conference on Case Histories in Geotechnical Engineering, Philadelphia, PA, USA, 24–27 March 2019. [Google Scholar] [CrossRef]
- El Meski, F.; Chehab, G.R. Flexural Behavior of Concrete Beams Reinforced with Different Types of Geogrids. J. Mater. Civ. Eng. 2014, 26, 04014038. [Google Scholar] [CrossRef]
- Shobana, S.; Yalamesh, G. Experimental study of concrete beams reinforced with uniaxial and biaxial geogrids. Int. J. ChemTech Res. 2015, 8, 1290–1295. [Google Scholar]
- Murekar, A.; Devikar, D.; Singandhupe, J.; Faizan Farooqui, M.; Ghodmare, S. Comparative Study and Analysis of PCC Beam and Reinforced Concrete Beam using Geogrid. Int. J. Sci. Technol. Eng. 2017, 3, 247–253. [Google Scholar]
- Ahmed Alamli, A.S.; Yousif, M.A.; Mohammed, M.H. Reinforced Concrete Strengthening by Using Geotextile Reinforcement for Foundations and Slabs. Int. J. Civ. Struct. Environ. Infrastruct. Eng. Res. Dev. 2017, 7, 35–46. [Google Scholar] [CrossRef]
- Ali, Y.S.; Awad Waryosh, W.; Yousif, M.A. Increasing Ultimate Strength of Reinforced Concrete Slab by Using Geogrid. Glob. J. Eng. Sci. Res. Manag. 2018, 5, 83–94. [Google Scholar]
- Tharani, K.; Mahendran, N.; Vijay, T.J. Experimental Investigation of Geogrid Reinforced Concrete Slab. Int. J. Eng. Adv. Technol. 2019, 8, 158–163. [Google Scholar]
- Ramakrishnan, S.; Arun, M.; Loganayagan, S.; Mugeshkanna, M. Strength and Behaviour of Geogrid Reinforced Concrete Beams. Int. J. Civ. Eng. Technol. 2018, 9, 1295–1303. [Google Scholar]
- Tang, X.; Higgins, I.; Jlilati, M.N. Behavior of Geogrid-Reinforced Portland Cement Concrete under Static Flexural Loading. Infrastructures 2018, 3, 41. [Google Scholar] [CrossRef]
- Meng, X.; Chi, Y.; Jiang, Q.; Liu, R.; Wu, K.; Li, S. Experimental investigation on the flexural behavior of pervious concrete beams reinforced with geogrids. Constr. Build. Mater. 2019, 215, 275–284. [Google Scholar] [CrossRef]
- Chidambaram, R.S.; Agarwal, P. Flexural and shear behavior of geo-grid confined RC beams with steel fiber reinforced concrete. Constr. Build. Mater. 2015, 78, 271–280. [Google Scholar] [CrossRef]
- Sivakamasundari, S.; Daniel, A.J.; Kumar, A. Study on Flexural Behavior of Steel Fiber RC Beams Confined With Biaxial Geo-Grid. Procedia Eng. 2017, 173, 1431–1438. [Google Scholar] [CrossRef]
- Chidambaram, R.; Agarwal, P. The confining effect of geo-grid on the mechanical properties of concrete specimens with steel fiber under compression and flexure. Constr. Build. Mater. 2014, 71, 628–637. [Google Scholar] [CrossRef]
- Aluri, A.K.; Anand, Y.B. A Complete Study on Behaviour of Concrete Columns by Using Biaxial Geogrid Encasement. SSRG Int. J. Civ. Eng. 2015, 2, 10–17. [Google Scholar]
- Dong, Y.-L.; Han, J.; Bai, X.-H. Numerical analysis of tensile behavior of geogrids with rectangular and triangular apertures. Geotext. Geomembranes 2011, 29, 83–91. [Google Scholar] [CrossRef]
- Carmona, J.R.; Ruiz, G.; Del Viso, J.R. Mixed-mode crack propagation through reinforced concrete. Eng. Fract. Mech. 2007, 74, 2788–2809. [Google Scholar] [CrossRef]
- Susumu, I. Ductility and Energy Dissipation of Concrete Beam Members and Their Damage Evaluation Based on Hysteretic Dissipated Energy. Ph.D. Thesis, Kyoto University, Kyoto, Japan, January 1994. [Google Scholar]
- Rao, G.A.; Vijayanand, I.; Eligehausen, R. Studies on ductility of RC beams in flexure and size effect. In Proceedings of the 6th International Conference on Fracture Mechanics of Concrete and Concrete Structures, Catania, Italy, 17 June 2017; Volume 2. [Google Scholar]
- AACE International. Skills and Knowledge of Cost Engineering, 6th ed.; Hastak, M., Ed.; AACE International: Morgantown, WV, USA, 2015. [Google Scholar]
|Concrete–Mix, WC = 0.5, 1.5% Admixture|
|Water||Water Reducing and Super-Plasticizer Concrete Admixture||Cone Slump||Compressive Strength after 28 days|
|400 kg/m3||600 kg/m3||1200 kg/m3||200 kg/m3||6 kg/m3||6.5 cm||40 N/mm2|
|Properties of the Steel Bars|
|Nominal Diameter (mm)||6||Nominal Cross-Area (mm2)||28.29|
|Experimental Weight (kg/m)||0.224||Experimental Cross-Area (mm2)||28.52|
|Experimental Yield Load (kN)||8.4||Experimental Ultimate Load (kN)||13.51|
|Experimental Yield Stress (N/mm2)||296.97||Experimental Tensile Resistance (N/mm2)||477.51|
|Experimental Yield Strain (Micro-strain)||1485||Experimental Elongation After Break Down (%)||32.7|
|Properties||Uniaxial Geogrids (UG) Grades|
|Mass per Unit Area (g/m2)||300||600||800||1000|
|Theoretical Tensile Strength at 2% Strain (kN/m)||11||26||36||45|
|Theoretical Tensile Strength at 5% Strain (kN/m)||25||50||72||90|
|Theoretical Tensile Fesign Strength (kN/m)||21.2||42.4||56.5||75.4|
|Theoretical Yield Point Elongation (%)||11.5||13||13||13|
|Theoretical Peak Tensile Strength (kN/m)||45||90||120||160|
|Experimental Peak Tensile Strength (kN/m)||45.56||79.36||103.91||143.46|
|Experimental Peak Strain (%)||30||30||30||30|
|Material||High-Density Polyethylene (HDPE)|
|Properties||Triaxial Geogrids (TG) Grades|
|Transverse (1)||Diagonal (2)||Transverse (1)||Diagonal (2)|
|Mid-rib depth (D = mm)||1.1||1.4||1.5||1.8|
|Mid-rib width (W = mm)||1.2||1||1.3||1.1|
|Rib pitch (P = mm)||40||40|
|Theoretical Radial Secant Stiffness at 0.5% Strain (kN/m)||360 (−75)||390 (−75)|
|Theoretical Radial Secant Stiffness at 2% Strain (kN/m)||250 (−65)||290 (−65)|
|Hexagon Pitch (mm)||80 (±4)||80 (±4)|
|Radial Secant Stiffness Ratio||0.8||0.8|
|Experimental Peak Tensile Strength (kN/m)||17.21||19.45|
|Experimental Radial Secant Stiffness at 2% strain (kN/m), based on BS EN 1SO 10319:1996||195||245|
|Experimental Peak Strain (%)||14.5||14.5|
|Numerical Yield Strain (%) ||6.4||6.4|
|Material||Polypropylene with a Minimum of 2% Finely Divided Carbon Black Content|
|Slab Number||Cracks’ Locations||The Tensile Force Expected to be Carried by|
|1st Crack||2nd Crack|
|Group Number One Concrete Slabs|
|S3-ST+1UG90||T3||R2 and R3|
|S4-ST+2UG45||T4||R4 and R3|
|S5-ST+1UG120||T3||T4||R2, R3, and R4|
|S6-ST+1UG160||T3||T4||R2, R3, and R4|
|S7-ST+2UG90||R2 adjacent to T3||T4||R2, R3, and R4|
|S8-ST+2UG120||T3||T4||R2, R3, and R4|
|S9-ST+2UG160||T3||T4||R2, R3, and R4|
|Group Number Two Concrete Slabs|
|S10-ST+1TG150||H6-H7||H6-H7 and H-6|
|S11-ST+1TG160||H6-H7||H6-H7 and H-6|
|S12-ST+2TG150||H6||H6-H7 and H-6|
|S13-ST+2TG160||H8||H4-H5||H4, H4-H5, H7-H8, and H8|
|Slab Number||Steel Bars||Geogrids|
|Strain Value at the First-Crack Load (Initial-Peak Load Point)|
|Strain Value after the First-Crack Load (Load-Drop Point)|
|Percentage of Strain Values’ Sudden Increase after the First-Crack Load (%)||Strain Value at the first-Crack Load (Initial-Peak Load Point)|
|Strain Value after the First-Crack Load (Load-Drop Point)|
|Percentage of Strain Values’ Sudden Increase or Decrease after the First-Crack Load (%)|
|Group Number One Concrete Slabs|
|Group Number Two Concrete Slabs|
© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).