Structural Behavior of Concrete Beams Reinforced with Biaxial Geogrid

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Citation:Kumar, K.R.; Vijay, T.J.;

Bahrami, A.; Ravindran, G. Structural Behavior of Concrete Beams Reinforced with Biaxial Geogrid.

Buildings2023,13, 1124. https://

doi.org/10.3390/buildings13051124 Academic Editors: Ricardo M. S.

F. Almeida and Rita Bento Received: 23 January 2023 Revised: 6 April 2023 Accepted: 11 April 2023 Published: 23 April 2023

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 (https://

creativecommons.org/licenses/by/

4.0/).

buildings

Article

Structural Behavior of Concrete Beams Reinforced with Biaxial Geogrid

K. Rajesh Kumar¹ , Thiruchengode Jothimani Vijay² , Alireza Bahrami^3,* and Gobinath Ravindran¹

1 Centre for Methods and Materials, Department of Civil Engineering, SR University, Warangal 506371, Telangana, India

2 Department of Civil Engineering, PSNA College of Engineering and Technology, Dindigul 624622, Tamil Nadu, India

3 Department of Building Engineering, Energy Systems and Sustainability Science, Faculty of Engineering and Sustainable Development, University of Gävle, 801 76 Gävle, Sweden

* Correspondence: alireza.bahrami@hig.se

Abstract:In recent decades, corrosion in steel reinforcement has been one of the fundamental risks in steel-reinforced concrete (RC) structures. Geosynthetics can be an alternative approach to solve corrosion problems. The current experimental research work investigates the structural performance of geogrid-reinforced concrete (GRC) elements. Initially, five different geotextiles and biaxial geogrid materials were selected and embedded in the concrete specimens separately to study their mechanical properties. The results of the testing showed that the geogrid embedded specimen behaved more mechanically than the conventional concrete (CC) specimens due to increased bonding characteristics.

The limiting moment and load-carrying capacities of the RC and GRC beams were determined with reference to limit state design principles. In order to compare the structural performance of the beams, two RC beams and two GRC beams with the size of 150 mm×300 mm×2100 mm were cast. The structural performances in terms of the load-carrying capacity, energy absorption, stiffness degradation, and ductility were examined. The results of the tests indicated that even though the load- carrying capacity of the GRC beams was slightly lower, they demonstrated enhanced performance by 42%, 40%, and 68% higher in the energy absorption, stiffness degradation, and ductility, respectively, than those of the RC beams on average. The augmented inelastic performance and better bonding properties of the GRC beams aid in noticeable structural performance.

Keywords:reinforced concrete beam; geogrid; load-carrying capacity; energy absorption; stiffness degradation; ductility

1. Introduction

The utilization of geogrids in concrete structures provides a new path for employing geosynthetics in structural elements. Geogrids are being used as reinforcement for asphalt concrete layers, stabilization and confinement of soil retaining structures, and also to reduce the progressive cracking in pavement. The inclusion of a biaxial geogrid in infrastructures is a pioneering evolution in concrete. Geogrid is one of the varieties of geosynthetics, and all these varieties mainly consist of polymeric compounds. It might be polypropylene, polyethylene, polyester, polyamide, polyvinyl chloride, and polystyrene, and are broadly employed in geotechnical structures to afford tensile reinforcement. Geogrids are two- dimensional planar polymeric structures made up of a mesh-like network of interconnected tensile elements known as ribs. Extrusion, bonding, or interlacing are used to connect the ribs, which have holes or apertures. The geogrids are categorized as either uniaxial or biaxial. Uniaxial geogrids are mainly utilized for retaining walls and steep slope separation.

Biaxial geogrids are mostly applied in highway projects because of their tensile capacity in both directions [1–8].

Buildings2023,13, 1124. https://doi.org/10.3390/buildings13051124 https://www.mdpi.com/journal/buildings

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Researchers have investigated the potential benefits of geogrids for the flexural capacity and strength of concrete elements [1–3,7,8]. The placement of steel reinforcements in thin portions, such as concrete shells, folding plates, domes, and some thin architectural structures is difficult. Furthermore, due to insufficient concrete protection, steel reinforcements are prone to corrosion in thin parts. This leads to the strength loss and failure of steel-reinforced concrete (RC) structures. Therefore, the replacement or addition of an anti-corrosive material as reinforcement in RC elements is one of the ideal solutions in corrosive environments. Plastics, which include polymer and geosynthetics, are some of the anti-corrosive materials that are used as reinforcement in geotechnical projects [7,8].

Geogrids have been reported to improve the post-cracking ductility and load-carrying capability, depending on the type of geogrids utilized. Geogrids are used as stabilizing elements in a variety of infrastructures and major civil engineering projects [7,8]. In order to test the viability of employing them as fibers in concrete, long lengths of geosynthetics were positioned perpendicular to the direction of the load application in structural components.

When geosynthetics were used, it was found that the tensile and compressive qualities of concrete were enhanced [9].

The corrosion of steel reinforcements affects the structural behavior of RC components significantly. Corrosion not only causes structural performance to deteriorate prematurely, but it also generates financial issues during the structure’s service life. The effects of corrosion on RC structures have been studied extensively [10].

To enhance the performance of pavement, bountiful experiments have been done by utilizing geosynthetic materials in the past decades, which proved that the load-carrying capacity of a foundation was increased while using geogrids as soil reinforcements [4].

However, only a few studies have been conducted on the application of geogrids as a reinforcing material in the RC industry [11].

Siva Chidambaram and Agarwal [12–14] investigated geogrids as RC elements’ confinement under static and cyclic loads. It was observed that the proper application of geogrids with steel fiber RC can help achieve higher ductile behavior and alter the brittle mode of failure.

Geogrids were found to reduce the drying shrinkage of concrete by about 15% to 20%, influencing the mechanical properties and behavior of concrete elements [15]. Moreover, one more study was carried out based on laboratory experiments and numerical modeling to scrutinize the employment of geogrids in thin concrete overlays. It was resulted that geogrids enhanced the concrete’s performance in the post-cracking regime in terms of strength, ductility, and failure mode [16–18].

Debbarma and Pal [19] studied the strength of fly ash that was reinforced with woven and nonwoven geotextiles in different combinations. A direct shear test was done in the laboratory on unreinforced and reinforced fly ash. The geotextile reinforcement was applied in different zones, such as the top, middle, and bottom layers. Geogrid-reinforced fly ash specimens showed increased strength in the angle of internal friction value when compared with an unreinforced one.

Researchers are making numerous attempts to devise an alternative method to reduce the constant use of steel and control the associated limitations. In recent developments, steel reinforcement has been replaced in concrete by the inclusion of synthetic fibers, glass, rubber, and plastics, or natural fibers such as jute, sisal, coconut, and hemp [20–26]. To improve the tensile strength of concrete, polymer sheets, plates, and carbon sheets have also been evaluated experimentally [27–30]. The presence of fibers in corroded beams clearly demonstrated that the fibers provided approximately 18% more strength to the corroded beams at the loading stage than the control beam before failure [31–33]. Concrete cubes and beams reinforced with polypropylene reinforcement bars were investigated [34]. The results revealed that the treaded reinforcements behaved better in terms of the energy absorption and ductility properties. Geogrid-reinforced concrete (GRC) slabs were evaluated under the drop weight impact tests [27]. The results illustrated that the GRC slab specimens effectively resisted the impact force better than the RC slab specimen.

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The past research results clearly indicated that the geosynthetic materials, particularly geogrid, effectively enhanced the mechanical properties of plain concrete.

Research Significance

An inadequate number of studies have been conducted to examine the viability of geosynthetics as flexural reinforcements in RC structures. Globally, geosynthetics are readily accessible. Geosynthetics, on the other hand, behave in a way that is similar to steel reinforcements in tensile situations. Due to this comparable behavior, a replacement attempt was undertaken for geosynthetics used as flexural reinforcements in concrete structures. In order to investigate the compressive and flexural behaviors of different geosynthetic materials embedded in structural elements, five different types of geosynthetics were examined by embedding them in concrete. The geosynthetic material with the best mechanical properties was chosen for the flexural test under two-point static loading in a simply supported condition. The geogrid and RC beams were to be designed for the same quantity of moment-carrying capacity and considered for the flexural test.

2. Materials and Methods 2.1. Materials

Ordinary Portland cement of grade 53, confirming to ASTM [35] Type I with a specific gravity of 3.125, was used for this research work. In this investigation, coarse aggregates passing through a 12 mm sieve size and retained in a 10 mm sieve size were utilized to maintain effective gradation and achieve better penetration of coarse aggregates into the geosynthetic material. The fineness modulus of coarse aggregates was 2.72 with a specific gravity of 2.77. Local river sands with a specific gravity of 2.62 and a fineness modulus of 2.75 were employed [36,37]. With reference to [38], the mix design ratio for M20 concrete was calculated based on the initial tests results. The specimens were cast with a 1:2.35:1.99 design mix ratio and a 0.5 water-cement (W/C) ratio. The total cement content of the mix was calculated to be 400 kg/m³. The coarse aggregates volume in concrete was set at 37%

(796 kg/m³), while the fine aggregates volume was set at 44% (939 kg/m³).

2.2. Tension Test

Five types of geosynthetics were utilized herein: geotextile (GT), woven geotextile (WG), polypropylene multifilament geotextile (PMG), polyester woven multifilament geotextile (PWMG), and geogrid (GG). Each piece of the geosynthetic materials was cut to a size of 20 cm in width and 30 cm in length, which was rigidly fixed between the geosynthetic testing apparatus to test its tensile strength with reference to ASTM [35]. The universal testing machine (UTM) with 1000 kN capacity was employed to test the tensile property of geosynthetics. Figure1displays the tension test setup arrangement along with the geogrid material in UTM. A slow strain rate was maintained to study the tensile test performance of different geosynthetic materials. The mechanical properties of the geosynthetic materials were calculated with reference to the tested force versus elongation relationship of each geosynthetic material. Table1lists the mechanical properties of different types of geosynthetics. The WG material gave an elongation of about 27%, which was the highest among the geosynthetic materials. The elongation up to the yield stage in the WG material was lesser, and further increasing the loading rate, a drastic increase in elongation was observed. Although the increased elongation reduced the material’s Young’s modulus, it resulted in comparatively higher tensile strength. The failure pattern of WG is presented in Figure2. In particular, the PMG and PWMG materials exhibited almost similar ultimate strength and Young’s modulus, furthermore, they had lower elongation than the GT and WG materials. The higher stiffness of the PMG and PWMG materials resisted excessive elongation and helped resist the in-plane tensile forces. This point aids in improving the tensile strength of the materials. The GG material demonstrated the highest resistance to elongation of 12% with the highest ultimate tensile strength of 65.5 N/mm²compared with all the other materials. The noticeable stiffness property at the junction of ribs increased the

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tensile strength along with the ductile property. This helped the material behave better in tension compared with all the other geosynthetic materials. In particular, the GG material showed an enriched yield strength of 34.67, 27.75, 50.45, and 63.07 times higher than that of the GT, WG, PMG, and PWMG materials, respectively. Similarly, Young’s modulus of the GG material was 119%, 250%, 25%, and 27% higher than that of the GT, WG, PMG, and PWMG materials, respectively. The elongation offered by the GG material was 22%, 125%, 17%, and 25% less than that of the GT, WG, PMG, and PWMG materials, respectively.

The WG, PMG, PWMG, and GG materials indicated higher tensile strength than the GT material. The GT specimen failed to resist the tensile force due to its inadequate stiffness.

Therefore, the WG, PMG, PWMG, and GG materials were taken for the next stage of the research.

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elongation than the GT and WG materials. The higher stiﬀness of the PMG and PWMG materials resisted excessive elongation and helped resist the in-plane tensile forces. This point aids in improving the tensile strength of the materials. The GG material demonstrated the highest resistance to elongation of 12% with the highest ultimate tensile strength of 65.5 N/mm² compared with all the other materials. The noticeable stiﬀness property at the junction of ribs increased the tensile strength along with the ductile property. This helped the material behave better in tension compared with all the other geosynthetic materials. In particular, the GG material showed an enriched yield strength of 34.67, 27.75, 50.45, and 63.07 times higher than that of the GT, WG, PMG, and PWMG materials, respectively. Similarly, Young’s modulus of the GG material was 119%, 250%, 25%, and 27% higher than that of the GT, WG, PMG, and PWMG materials, respectively.

The elongation oﬀered by the GG material was 22%, 125%, 17%, and 25% less than that of the GT, WG, PMG, and PWMG materials, respectively. The WG, PMG, PWMG, and GG materials indicated higher tensile strength than the GT material. The GT specimen failed to resist the tensile force due to its inadequate stiﬀness. Therefore, the WG, PMG, PWMG, and GG materials were taken for the next stage of the research.

Figure 1. Setup of geogrid tension test.

Table 1. Properties of geosynthetics.

Property GT WG PMG PWMG GG

Yield stress (N/mm²) 1.6 2 1.1 0.88 55.5

Ultimate stress (N/mm²) 5.33 13.33 16.67 16.67 65.5 Percentage of elongation (%) 14.58 27 14 15 12

Strain at rupture (mm/mm) 0.15 0.27 0.14 0.11 0.16

Young’s modulus (N/mm²) 80 50 140 138 175

Figure 1.Setup of geogrid tension test.

Table 1.Properties of geosynthetics.

Property GT WG PMG PWMG GG

Yield stress (N/mm²) 1.6 2 1.1 0.88 55.5

Ultimate stress (N/mm²) 5.33 13.33 16.67 16.67 65.5

Percentage of elongation (%) 14.58 27 14 15 12

Strain at rupture (mm/mm) 0.15 0.27 0.14 0.11 0.16

Young’s modulus (N/mm²) 80 50 140 138 175

Figure 2. Failure pattern of WG.

2.3. Casting of Concrete Specimen

The tests results clarified that the WG, PMG, PWMG, and GG materials performed better in terms of the mechanical properties. Therefore, properties including the compressive strength, splitting tensile strength, and flexural strength were studied for the WG, PMG, PWMG, and GG materials by embedding them in conventional concrete (CC) individually. The cube with the size of 150 mm × 150 mm × 150 mm, the cylinder with the size of 150 mm in diameter and 300 mm in height, and the prism with the size of 500 mm × 100 mm × 100 mm were, respectively, utilized to test the compressive strength, splitting tensile strength, and flexural strength of geosynthetic embedded concrete, according to [39,40].

The WG, PMG, PWMG, and GG materials were cut oﬀ in a specific manner that suited their corresponding specimen molds. A layer of 140 mm × 140 mm, a diameter of 130 mm, and a layer of 450 mm × 80 mm were, respectively, embedded in cubes, cylinders, and prisms. Two layers of geosynthetics were placed at 1/3 and 2/3 distances from the bottom of the specimens before laying concrete. In order to increase the bonding between the geotextile materials and concrete, holes were made in the geotextile materials before embedding them in the concrete molds. Figure 3 depicts the placement of tailored geotextiles and geogrids for the tests. The geosynthetic embedded concrete specimens were kept in under water curing conditions for 28 days.

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Figure 3. (a) Geosynthetic samples, (b) Geosynthetic sample with holes, and (c) Casting of prism.

Figure 2.Failure pattern of WG.

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2.3. Casting of Concrete Specimen

The tests results clarified that the WG, PMG, PWMG, and GG materials performed better in terms of the mechanical properties. Therefore, properties including the compressive strength, splitting tensile strength, and flexural strength were studied for the WG, PMG, PWMG, and GG materials by embedding them in conventional concrete (CC) individually. The cube with the size of 150 mm×150 mm×150 mm, the cylinder with the size of 150 mm in diameter and 300 mm in height, and the prism with the size of 500 mm×100 mm×100 mm were, respectively, utilized to test the compressive strength, splitting tensile strength, and flexural strength of geosynthetic embedded concrete, according to [39,40]. The WG, PMG, PWMG, and GG materials were cut off in a specific manner that suited their corresponding specimen molds. A layer of 140 mm×140 mm, a diameter of 130 mm, and a layer of 450 mm×80 mm were, respectively, embedded in cubes, cylinders, and prisms. Two layers of geosynthetics were placed at 1/3 and 2/3 distances from the bottom of the specimens before laying concrete. In order to increase the bonding between the geotextile materials and concrete, holes were made in the geotextile materials before embedding them in the concrete molds. Figure3depicts the placement of tailored geotextiles and geogrids for the tests. The geosynthetic embedded concrete specimens were kept in under water curing conditions for 28 days.

Figure 2. Failure pattern of WG.

2.3. Casting of Concrete Specimen

The tests results clarified that the WG, PMG, PWMG, and GG materials performed better in terms of the mechanical properties. Therefore, properties including the compressive strength, splitting tensile strength, and flexural strength were studied for the WG, PMG, PWMG, and GG materials by embedding them in conventional concrete (CC) individually. The cube with the size of 150 mm × 150 mm × 150 mm, the cylinder with the size of 150 mm in diameter and 300 mm in height, and the prism with the size of 500 mm × 100 mm × 100 mm were, respectively, utilized to test the compressive strength, splitting tensile strength, and flexural strength of geosynthetic embedded concrete, according to [39,40].

The WG, PMG, PWMG, and GG materials were cut oﬀ in a specific manner that suited their corresponding specimen molds. A layer of 140 mm × 140 mm, a diameter of 130 mm, and a layer of 450 mm × 80 mm were, respectively, embedded in cubes, cylinders, and prisms. Two layers of geosynthetics were placed at 1/3 and 2/3 distances from the bottom of the specimens before laying concrete. In order to increase the bonding between the geotextile materials and concrete, holes were made in the geotextile materials before embedding them in the concrete molds. Figure 3 depicts the placement of tailored geotextiles and geogrids for the tests. The geosynthetic embedded concrete specimens were kept in under water curing conditions for 28 days.

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Figure 3. (a) Geosynthetic samples, (b) Geosynthetic sample with holes, and (c) Casting of prism. Figure 3.(a) Geosynthetic samples, (b) Geosynthetic sample with holes, and (c) Casting of prism.

3. Results and Discussion on Strength Properties

Tests on the compressive and splitting tensile strengths were conducted based on [39]

using UTM with 1000 kN capacity. The flexural strength tests were done in accordance with [39] utilizing the flexural testing machine with 100 kN capacity. Table2summarizes the mechanical properties of CC and embedded geosynthetic concrete specimens. A linear behavior (the increment difference between the load and deflection values for loading at the nth and (n−1)th steps was similar) was observed up to 45% of the ultimate load in the embedded GG concrete specimens and followed a gradual nonlinear behavior (the increment difference between the load and deflection values for loading at the nth and (n−1)th steps was not similar) until reaching the ultimate load. However, a linear behavior was seen for only about 35% of the ultimate load for the embedded WG, PMG, and PWMG concrete specimens. Further increasing the load, a sudden failure was witnessed due to high deformation with a slight increase in the load capacity in the concrete specimens embedded with WG, PMG, and PWMG along the contact surface of concrete to the geotextile materials (WG, PMG, and PWMG). Compared with the CC specimen, the 28-day compressive strength of the embedded WG, PMG, PWMG, and GG concrete specimens was increased by 17%, 4%, 12%, and 26%, while their 7-day compressive strength was improved by 25%, 10%, 10%, and 47%, respectively.

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Table 2.Strength properties.

Property CC WG PMG PWMG GG

Compressive strength (N/mm²)

7 days 17.5 21.8 19.18 19.18 25.72

28 days 24.9 29.16 25.8 27.85 31.47

Splitting tensile strength (N/mm²)

7 days 1.5 1.8 1.9 2.08 2.35

28 days 3.6 4.7 3.77 3.6 5.05

Flexural strength (N/mm²) 7 days 1.7 1.85 2.35 2.85 3.75

28 days 3.2 3.25 3.85 3.15 5.25

The 28-day splitting tensile strength of the embedded WG, PMG, PWMG, and GG concrete specimens was, respectively, increased by 31%, 5%, 0%, and 40%, while their 7-day splitting tensile strength was, respectively, enhanced by 20%, 27%, 39%, and 57%

compared with those of the CC specimen. Similarly, the 28-day flexural strength of the embedded WG, PMG, PWMG, and GG concrete specimens was changed by 2%, 20%,−2%, and 64%, however, their 7-day flexural strength was improved by 9%, 38%, 68%, and 121%, respectively, compared with those of the CC specimen. It was also witnessed that the splitting tensile strength of the embedded WG, PMG, PWMG, and GG concrete specimens was approximately 14%, 16%, 15%, 13%, and 16% of their corresponding compressive strength, respectively. Moreover, the flexural strength of the embedded WG, PMG, PWMG, and GG concrete specimens was approximately 13%, 11%, 15%, 11%, and 17% of their corresponding compressive strength, respectively. The embedded GG concrete specimen exhibited a higher percentage of splitting tensile and flexural strengths than compressive strengths. This clearly elucidates that the concrete specimens cast with the GG material behaved better from all strength aspects than the concrete specimens cast with the other geotextile materials. Even though the concrete specimen with WG, PMG, and PWMG resulted in higher yield and ultimate tensile strengths than the CC specimen, it failed to behave better than the embedded GG specimen. The poor bonding of the WG, PMG, and PWMG materials with concrete led to the sudden loss of strength. Figure4a illustrates the bonding failure of the PWMG material embedded in concrete. This indicated the pure bonding of the geotextile specimen. This issue clarifies that the bond between concrete and geotextile is not adequate to transfer the load effectively, and there is an inadequate transfer of stress through the subsequent layers of the concrete matrix.

The layer of the geotextile material did not have effective openings in the surface to develop the bond with concrete. This resulted in reduced bonding characteristics in those specimens. However, the embedded geotextile concrete specimens demonstrated a slight increase in the strength behavior compared with CC. In addition, the embedded GG concrete specimen gave a better strength performance thanks to the enhanced bonding characteristics of concrete. The adequate aperture size available in the embedded GG concrete specimen formed good concrete continuity throughout the specimen, and each aperture opening acted as a shear key of each layer. Through the grid’s opening, concrete might flow to succeeding levels [12,14], and as a result, this aids in excellent bonding in the geogrid specimens. Consequently, the geogrid-based specimen outperformed previous geotextile-based specimens. Figure4b depicts that the geotextile has weak bonding, and Figure4c displays that GG has good bonding. Since the selection of the geosynthetic material is the most essential stage of this inquiry, the material chosen must meet the requirements for the RC performance. In conclusion, the GG material was used in the experiments of this research.

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specimens. However, the embedded geotextile concrete specimens demonstrated a slight increase in the strength behavior compared with CC. In addition, the embedded GG concrete specimen gave a better strength performance thanks to the enhanced bonding characteristics of concrete. The adequate aperture size available in the embedded GG concrete specimen formed good concrete continuity throughout the specimen, and each aperture opening acted as a shear key of each layer. Through the grid’s opening, concrete might flow to succeeding levels [12,14], and as a result, this aids in excellent bonding in the geogrid specimens. Consequently, the geogrid-based specimen outperformed previous geotextile-based specimens. Figure 4b depicts that the geotextile has weak bonding, and Fig- ure 4c displays that GG has good bonding. Since the selection of the geosynthetic material is the most essential stage of this inquiry, the material chosen must meet the requirements for the RC performance. In conclusion, the GG material was used in the experiments of this research.

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Figure 4. Bonding failure in geosynthetic materials; (a) Inadequate bonding in prism by geotextile, (b) Crack pattern in geotextile incorporated prism, and (c) Good bonding at geogrid.

4. Structural Investigations 4.1. Derivation for Limiting Moment

In order to examine the structural performance of the geogrid material, it was embedded as the flexural reinforcements in a concrete beam as an alternative to steel reinforcements. In the current investigation, the reinforcements area was designed and provided in the GRC and RC beams in such a way that it should resist the limiting moment capacity of the section. The derivations of limiting moment-carrying capacity (M^{u lim}) for the RC and GRC rectangular beam cross-sections were done with reference to the stress- strain block diagrams shown in Figures 5a and 6a for the RC and GRC beam cross-sections, respectively. Figures 5b and 6b illustrate the stress-strain performance of RC and GRC beam specimens. Table 3 presents the derivation of M^{u lim} for the RC and GRC rectangular beam cross-sections according to [41]. In the table, X^u, e^cu, e^su, e^gu, A^st, A^g, f^y, f^yg, and d are the neutral axis depth from the top (depth of the compression zone), the ultimate strain in concrete, the ultimate strain in steel, the ultimate strain in geosynthetics, the area of steel, the area of geogrid (one rib), the yield strength of steel, the yield strength of geosynthetics, and eﬀective depth, respectively. From the tensile test results of geogrid and steel, the values of e^cu, e^su, e^gu, f^y, and f^yg were, respectively, found to be 0.0034, 0.0037, 0.02, 478.75 MPa, and 55.5 MPa. The aperture size of the geogrid used in this study was 65 mm

× 65 mm, and the area of one rib was 9 mm². The size of one rib in geogrid was 3 mm × 3 mm in cross-section. The thickness of one layer was 3 mm.

Figure 4.Bonding failure in geosynthetic materials; (a) Inadequate bonding in prism by geotextile, (b) Crack pattern in geotextile incorporated prism, and (c) Good bonding at geogrid.

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specimens. However, the embedded geotextile concrete specimens demonstrated a slight increase in the strength behavior compared with CC. In addition, the embedded GG concrete specimen gave a better strength performance thanks to the enhanced bonding characteristics of concrete. The adequate aperture size available in the embedded GG concrete specimen formed good concrete continuity throughout the specimen, and each aperture opening acted as a shear key of each layer. Through the grid’s opening, concrete might flow to succeeding levels [12,14], and as a result, this aids in excellent bonding in the geogrid specimens. Consequently, the geogrid-based specimen outperformed previous geotextile-based specimens. Figure 4b depicts that the geotextile has weak bonding, and Fig- ure 4c displays that GG has good bonding. Since the selection of the geosynthetic material is the most essential stage of this inquiry, the material chosen must meet the requirements for the RC performance. In conclusion, the GG material was used in the experiments of this research.

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Figure 4. Bonding failure in geosynthetic materials; (a) Inadequate bonding in prism by geotextile, (b) Crack pattern in geotextile incorporated prism, and (c) Good bonding at geogrid.

4. Structural Investigations 4.1. Derivation for Limiting Moment

In order to examine the structural performance of the geogrid material, it was embedded as the flexural reinforcements in a concrete beam as an alternative to steel reinforcements. In the current investigation, the reinforcements area was designed and provided in the GRC and RC beams in such a way that it should resist the limiting moment capacity of the section. The derivations of limiting moment-carrying capacity (M^{u lim}) for the RC and GRC rectangular beam cross-sections were done with reference to the stress- strain block diagrams shown in Figures 5a and 6a for the RC and GRC beam cross-sections, respectively. Figures 5b and 6b illustrate the stress-strain performance of RC and GRC beam specimens. Table 3 presents the derivation of M^{u lim} for the RC and GRC rectangular beam cross-sections according to [41]. In the table, Xu, ecu, esu, egu, Ast, Ag, fy, fyg, and d are the neutral axis depth from the top (depth of the compression zone), the ultimate strain in concrete, the ultimate strain in steel, the ultimate strain in geosynthetics, the area of steel, the area of geogrid (one rib), the yield strength of steel, the yield strength of geosynthetics, and eﬀective depth, respectively. From the tensile test results of geogrid and steel, the values of ecu, esu, egu, fy, and fyg were, respectively, found to be 0.0034, 0.0037, 0.02, 478.75 MPa, and 55.5 MPa. The aperture size of the geogrid used in this study was 65 mm

× 65 mm, and the area of one rib was 9 mm². The size of one rib in geogrid was 3 mm × 3 mm in cross-section. The thickness of one layer was 3 mm.

Figure 4.Bonding failure in geosynthetic materials; (a) Inadequate bonding in prism by geotextile, (b) Crack pattern in geotextile incorporated prism, and (c) Good bonding at geogrid.

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4. Structural Investigations

4.1. Derivation of Limiting Moment-Carrying Capacity

In order to examine the structural performance of the geogrid material, it was embedded as the flexural reinforcements in a concrete beam as an alternative to steel reinforcements. In the current investigation, the reinforcements areas were designed and provided in the GRC and RC beams in such a way that they should resist the moments of the sections.

The derivations of limiting moment-carrying capacity (M_{u lim}) for the RC and GRC rectangular beam cross-sections were done with reference to the stress-strain block diagrams shown in Figures5a and6a for the RC and GRC beam cross-sections, respectively. Figures 5b and6b illustrate the stress-strain performance of RC and GRC beam specimens. Table3 presents the derivations of M_{u lim} for the RC and GRC rectangular beam cross-sections according to [41]. In the table, X_u, e_cu, e_su, e_gu, A_st, A_g, f_y, f_yg, and d are the neutral axis depth from the top (depth of the compression zone), the ultimate strain in concrete, the ultimate strain in steel, the ultimate strain in geosynthetics, the area of steel, the area of geogrid (one rib), the yield strength of steel, the yield strength of geosynthetics, and the effective depth, respectively. From the tensile test results of geogrid and steel, the values of e_cu, e_su, e_gu, f_y, and f_ygwere, respectively, found to be 0.0034, 0.0037, 0.02, 478.75 MPa, and 55.5 MPa. The aperture size of the geogrid used in this study was 65 mm×65 mm, and the area of one rib was 9 mm². The size of one rib in geogrid was 3 mm×3 mm in cross-section. The thickness of one layer was 3 mm.

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Figure 5. (a) Stress-strain block for RC rectangular beam cross-sections. (b) Stress-strain curve of steel specimen.

(a)

0.002; 478.75 0.0037; 502.5

0 100 200 300 400 500 600

0 0.001 0.002 0.003 0.004

Stress (MPa)

Strain

Figure 5.(a) Stress-strain block for RC rectangular beam cross-sections. (b) Stress-strain curve of steel specimen.

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(a)

(b)

Figure 5. (a) Stress-strain block for RC rectangular beam cross-sections. (b) Stress-strain curve of steel specimen.

(a)

0.002; 478.75 0.0037; 502.5

0 100 200 300 400 500 600

0 0.001 0.002 0.003 0.004

Stress (MPa)

Strain

(b)

Figure 6. (a) Stress-strain block for GRC rectangular beam cross-sections. (b) Stress-strain curve of geogrid specimen.

Table 3. Mulim for RC and GRC rectangular beam cross-sections.

Mulimit for RC Rectangular Beam Mulimit for GRC Rectangular Beam

Tension = Compression (Equation (1)) Tension = Compression (Equation (1))

T = 0.87 fy Ast T = 0.87 fyg Ag

C = 0.36 fck b Xu C = 0.36 fck b Xu

0.87 fy Ast = 0.36 fck b Xu 0.87 fyg Ageo = 0.36 fck b Xu

(Xu/d) = (0.87 fy Ast)/(0.36 fck b d) (Xu/d) = (0.87 fyg Ageo)/(0.36 fck b d) By similar triangle concept

(ecu/Xu) = [esu/(d − Xu)] (ecu/Xu) = [egu/(d − Xu)]

(Xu,max/d) = [ecu/(esu + ecu)] (Equation (2)) (Xu,max/d) = [ecu/(egu + ecu)] (Equation (2)) Substituting value of ecu and esu in Equation (2) Substituting value of ecu and egu in Equation (2)

(Xu,max/d) = 0.479452055 (Xu,max/d) = 0.14893617

Mu = T (d − 0.42 Xu) or C (d − 0.42 Xu)

Mu = 0.36 fck Xu b (d − 0.42 Xu) Mu = 0.36 fck Xu b (d − 0.42 Xu)

Mulim = 0.36 fck (Xu,max/d) d² b (1 − 0.42 (Xu,max/d)) (Equation (3)) Mulim= 0.36 fck (Xu,max/d) d² b (1 − 0.42 (Xu,max/d)) (Equation (3)) Mulim = Q fck b d² Mulim = Q fck b d²

Substituting value of (Xu,max/d) in Equation (3) Substituting value of (Xu,max/d) in Equation (3)

Q = 0.13784575 Q = 0.0503

Mulim = 0.138 fck b d² Mulim = 0.05 fck b d²

As a result, Mulim values of the RC and GRC beam cross-sections were calculated according to [41,42], respectively, as Mulim= 0.138 fck b d² (if Fe415 used) and Mulim= 0.05 fck

b d² (if geogrid used).

4.2. Casting of Beams

Two sets of beams with a length of 2.1 m and a cross-section of 0.15 m × 0.3 m were cast. The details of the test specimens are presented in Table 4. The first set with steel reinforcement (RC Beam) was embedded with two numbers of 10 mm diameter steel bars as tension reinforcements, and the second set with geogrid reinforcements (GRC Beam).

The total geogrid area required for GRC to equalize the moment capacity of the RC beam was 582 mm². The area of the single geogrid rib was 9 mm². A total of three numbers of the geogrid ribs were available in one layer of geogrid of 120 mm width (after deducting

0.001; 55.5 0.02; 65.5

0 10 20 30 40 50 60 70

0 0.005 0.01 0.015 0.02 0.025

Stress (MPa)

Strain

Figure 6.(a) Stress-strain block for GRC rectangular beam cross-sections. (b) Stress-strain curve of geogrid specimen.

Table 3.M_{u lim}for RC and GRC rectangular beam cross-sections.

Mu limitfor RC Rectangular Beam Mu limitfor GRC Rectangular Beam

Tension = Compression (Equation (1)) Tension = Compression (Equation (1))

T = 0.87 fyAst T = 0.87 fygAg

C = 0.36 fckb Xu C = 0.36 fckb Xu

0.87 fyAst= 0.36 f_ckb Xu 0.87 fygAgeo= 0.36 f_ckb Xu

(Xu/d) = (0.87 fyAst)/(0.36 fckb d) (Xu/d) = (0.87 fygAgeo)/(0.36 fckb d) By similar triangle concept

(ecu/Xu) = [esu/(d−Xu)] (ecu/Xu) = [egu/(d−Xu)]

(Xu,max/d) = [ecu/(esu+ ecu)] (Equation (2)) (Xu,max/d) = [ecu/(egu+ ecu)] (Equation (2)) Substituting value of ecuand esuin Equation (2) Substituting value of ecuand eguin Equation (2)

(Xu,max/d) = 0.479452055 (Xu,max/d) = 0.14893617

Mu= T (d−0.42 Xu) or C (d−0.42 Xu)

Mu= 0.36 fckXub (d−0.42 Xu) Mu= 0.36 fckXub (d−0.42 Xu)

Mu lim= 0.36 fck(Xu,max/d) d²b (1−0.42 (Xu,max/d)) (Equation (3)) Mu lim= 0.36 fck(Xu,max/d) d²b (1−0.42 (Xu,max/d)) (Equation (3))

Mu lim= Q fckb d² Mu lim= Q fckb d²

Substituting value of (Xu,max/d) in Equation (3) Substituting value of (Xu,max/d) in Equation (3)

Q = 0.13784575 Q = 0.0503

Mu lim= 0.138 fckb d² Mu lim= 0.05 fckb d²

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As a result, M_{u lim}values of the RC and GRC beam cross-sections were calculated according to [41,42], respectively, as M_{u lim}= 0.138 f_ckb d²(if Fe415 used) and M_{u lim}= 0.05 f_ckb d²(if geogrid used).

4.2. Casting of Beams

Two sets of beams with a length of 2.1 m and a cross-section of 0.15 m×0.3 m were cast. The details of the test specimens are presented in Table4. The first set with steel reinforcement (RC beam) was embedded with two numbers of 10 mm diameter steel bars as tension reinforcements, and the second set with geogrid reinforcements (GRC beam).

The total geogrid area required for GRC to equalize the moment capacity of the RC beam was 582 mm². The area of the single geogrid rib was 9 mm². A total of three numbers of the geogrid ribs were available in one layer of geogrid of 120 mm width (after deducting a clear cover of 15 mm from beam width). 22 layers (594 mm²) of geogrid reinforcements of 66 mm thickness were provided to equalize the moment capacity of the RC beam. Therefore, the moment capacities of the RC beam sections and GRC beam sections were the same.

The computations of steel reinforcements and geogrid reinforcements were done based on Equations (1) and (2), respectively. All the beams were commonly provided with two numbers of 8 mm diameter reinforcements as compression reinforcements and two-legged 8 mm diameter reinforcements at 250 mm center-to-center spacing as shear reinforcements.

The geogrid material was first cut into pieces measuring 0.12 m×2.07 m. The 22 layers of geogrid were then stacked one on top of the other and tied together as a monolith with binding wire before concrete was laid.

Table 4.Details of test specimens.

Detail RC Beam GRC Beam

Number of specimens 2 2

Size of specimens 150 mm×300 mm×2100 mm

Tension reinforcements 2 numbers of 10 mm diameter steel bars 22 layers of geogrid material with size of 120 mm×2070 mm

Compression reinforcements 2 numbers of 8 mm diameter steel bars Shear reinforcements 8 mm diameter at 250 mm center to center spacing

Method of curing Gunny bag curing method

Age of specimens during test 28 days 28 days

Type of test Two-point loading test (four-point bending)

Figure 7demonstrates the schematic reinforcement detailing of the RC and GRC beams. Figure8indicates a geogrid layer placed inside the beam mold. The gunny bag curing method was conducted for 28 days. The wetness in the beams was maintained constantly with the help of gunny bags.

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a clear cover of 15 mm from beam width). 22 layers (594 mm²) of geogrid reinforcements of 66 mm thickness were provided to equalize the moment capacity of the RC beam.

Therefore, the moment capacities of the RC beam sections and GRC beam sections were the same. The computations of steel reinforcements and geogrid reinforcements were done based on Equations (1) and (2), respectively. All the beams were commonly provided with two numbers of 8 mm diameter reinforcements as compression reinforcements and two-legged 8 mm diameter reinforcements at 250 mm center-to-center spacing as shear reinforcements. The geogrid material was first cut into pieces measuring 0.12 m × 2.07 m.

The 22 layers of geogrid were then stacked one on top of the other and tied together as a monolith with binding wire before concrete was laid.

Figure 7 demonstrates the schematic reinforcement detailing of the RC and GRC beams. Figure 8 indicates a geogrid layer placed inside the beam mold. The gunny bag curing method was conducted for 28 days. The wetness in the beams was maintained constantly with the help of gunny bags.

Table 4. Details of test specimens.

Detail RC Beam GRC Beam

Number of specimens 2 2

Size of specimens 150 mm × 300 mm × 2100 mm

Tension reinforcements 2 numbers of 10 mm diameter steel bars 22 layers of geogrid material with size of 120 mm × 2070 mm

Compression reinforcements 2 numbers of 8 mm diameter steel bars Shear reinforcements 8 mm diameter at 250 mm center to center spacing

Method of curing Gunny bag curing method

Age of specimens during test 28 days 28 days

Type of test Two-point loading test (four-point bending)

Figure 7. Reinforcement details of RC beam and GRC beam. Figure 7.Reinforcement details of RC beams and GRC beams.

Figure 8. Placing of GG material in beam.

5. Results and Discussion on Flexural Performance 5.1. Load-Carrying Capacity and Failure Characteristics

As it was mentioned, the flexural investigation of the RC and GRC beams was done using UTM under two-point loads to examine their structural features. The two-point loads were applied to the beams at 1/3 and 2/3 lengths with simply supported conditions.

The support-to-support distance of the beams sections was kept at 1.8 m. A computerized linear variable diﬀerential transformer (LVDT) was employed to measure the deflection, and a 100 kN hydraulic load jack was utilized to generate the monotonic static load. Fig- ures 9 and 10 show the set-up of the two-point loading testing and two-point loading testing at the laboratory, respectively. The structural results of the tested beams are listed in Table 5. Figure 11 reports the load versus mid-span deflection curves of the RC and GRC beams. The relationships between the ultimate load (kN) and beam deflection (mm) for the RC and GRC beams are presented in Figure 11 too.

Table 5. Structural results of tested beams.

Structural Result RC Beam GRC Beam

Specimen 1 Specimen 2 Average Specimen 1 Specimen 2 Average

Yield load (kN) 12.88 12.13 12.50 16.56 15.44 16.00

Yield deflection (mm) 1.11 1.18 1.15 0.62 0.66 0.64

Ultimate deflection (mm) 7.65 8.15 7.90 12.98 14.69 13.84

Ultimate load (kN) 46.44 43.56 45.00 32.07 28.33 30.20

Ductility 6.89 6.91 6.90 20.94 22.26 21.60

Stiffness (kN/mm) 5.46 5.30 5.38 2.20 2.15 2.17

Energy absorption (kN-mm) 200.00 204.00 202.00 342.57 355.40 349.00

Experimental/Theoretical 1.86 1.74 1.80 1.27 1.13 1.20

Maximum crack width (mm) 1.10 1.10 1.10 3.40 3.60 3.50

The tested RC and GRC beams were not observed with any cracks until the deflection reached the average values of 1.15 mm and 0.64 mm, respectively, with their corresponding average yield loads of 12.5 kN and 16 kN. This issue elaborates that the GRC beams did not exhibit ductile behavior initially. This was due to the higher stiffness offered by the geogrid material because of its effective aperture size, which resulted in higher bonding characteristics at this stage. On average, the GRC beams had 28% higher load-carrying capacity than that of the RC beams at the yield stage. The cracks were initiated by further increasing the loading slightly after the yield stage. Then, the existing cracks formed in the beams were developed to a large length and width in the consecutive loading stages.

It was also seen that the cracks length and width of the RC beams were comparatively less than those of the GRC beams. Initially, the GRC beams behaved rigidly with a linear behavior in the yield stage, followed by a nonlinear higher increase in deflection.

After the yield stage, the GRC beams behaved with larger cracks width and length due to the higher ductile deflection behavior, occurred during the loading, than the RC beams. The RC and GRC beams failed at the average ultimate loads of 45 kN and 41 kN, respectively, with their corresponding average deflections of 7.9 mm and 13.84 mm. On Figure 8.Placing of GG material in beam.

5. Results and Discussion on Flexural Performance 5.1. Load-Carrying Capacity and Failure Characteristics

As it was mentioned, the flexural investigation of the RC and GRC beams was done using UTM under two-point loads to examine their structural features. The two-point loads were applied to the beams at 1/3 and 2/3 lengths with simply supported conditions.

The support-to-support distance of the beams sections was kept at 1.8 m. A computerized linear variable differential transformer (LVDT) was employed to measure the deflection, and a 100 kN hydraulic load jack was utilized to generate the monotonic static load.

Figures9and10show the set-up of the two-point loading testing and two-point loading testing at the laboratory, respectively. The structural results of the tested beams are listed in Table5. Figure11reports the load versus mid-span deflection curves of the RC and GRC beams. The relationships between the ultimate load (kN) and beam deflection (mm) for the RC and GRC beams are presented in Figure11too.

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average, the GRC beams had 9% lower load-carrying capacity than the RC beams. The lower load-carrying capacity of the GRC beams at the ultimate stage than at the yield stage may be due to the degraded stiﬀness caused by the higher flexibility of the geogrid material and the subsequent loss of the aggregates’ interlocking mechanism. The 22 layers provided as a single mat in the GRC beams reduced the bond characteristics, which led to the degradation of the aggregates’ interlocking mechanism and enhanced the rate of the stiﬀ- ness degradation. This caused the loss of the load-carrying capacity in the GRC beams after the yield stage.

The tested RC beams illustrated a permanent crack, and the crack width was not reduced during the unloading process. The maximum crack measured in the RC beams was 3.2 mm on average, which was not reduced during the unloading process. However, the GRC beams displayed a great elastic property. On average, the deflection of the GRC beams was 1.75 times higher than that of the RC beams, however, it provided greater resistance to failure. The deflected shape of the GRC beams was restored to its original position, and the existing cracks were closed by themselves during the unloading process.

In the GRC beams, the reloading was done after the unloading process. The reloading results revealed that the loading capacities of both loading and reloading were almost the same. The failure of both beams was observed to be of the flexural type.

Figures 12 and 13 indicate the cracks patterns of the tested RC and GRC beams, respectively. No spalling was witnessed in either of the beams. The maximum crack width measured in the RC beams at the ultimate stage was 3.5 mm on average, whereas the maximum crack width measured in the GRC beams after unloading was less than 1.6 mm.

The ultimate deflection of the GRC beams was decreased to 1.6 mm on average, and the crack width was reduced to 1.2 mm. It was demonstrated that the GRC beams behaved with an enriched pinching eﬀect and enhanced post-yield behavior. This ensured the enhanced ductility of the GRC beams compared with the RC beams.

Figure 9. Set-up of two-point loading test. Figure 9.Set-up of two-point loading test.

Figure 10. Two-point loading testing.

Figure 11. Load vs. mid-span deflection curves of RC and GRC beams.

Figure 12. Crack patterns of tested RC beams.

Figure 13. Crack patterns of tested GRC beams.

5.2. Energy Absorption and Ductility

Energy absorption is a property of an element that can store maximum strain energy without loss of its load-carrying capacity. The area under the load-deflection curve is generally called energy absorption. The ratio of the ultimate deflection to yield deflection is used to calculate the ductility. Figure 14 depicts the energy absorption characteristics of

0 5 10 15 20 25 30 35 40 45 50

0 2 4 6 8 10 12 14 16

Load (kN)

Deflection (mm)

RC Beam - 1 RC Beam - 2 GRC Beam - 1 GRC Beam - 2

RC Beam - Approximation GRC Beam - Approximation

RC Beams, Yield Load = -1.9547x² + 13.15x + 0.0343; R² = 0.9989 RC Beams, Inelastic Load = -0.096x² + 5.3195x + 8.3247; R² = 0.9954 GRC Beams, Yield Load = 3.9899x² + 22.67x - 0.1195; R² = 0.996 GRC Beams, Inelastic Load = -0.0829x² + 2.0812x + 17.135; R² = 0.9876 Figure 10.Two-point loading testing.

The tested RC and GRC beams were not observed with any cracks until the deflection reached the average values of 1.15 mm and 0.64 mm, respectively, with their corresponding average yield loads of 12.5 kN and 16 kN. This issue elaborates that the GRC beams did not exhibit ductile behavior initially. This was due to the higher stiffness offered by the geogrid material because of its effective aperture size, which resulted in higher bonding characteristics at this stage. On average, the GRC beams had 28% higher load-carrying capacity than that of the RC beams at the yield stage. The cracks were initiated by further increasing the loading slightly after the yield stage. Then, the existing cracks formed in the beams were developed to a large length and width in the consecutive loading stages. It was also seen that the cracks length and width of the RC beams were comparatively less than those of the GRC beams. Initially, the GRC beams behaved rigidly with a linear behavior in the yield stage, followed by a nonlinear higher increase in deflection.

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Table 5.Structural results of tested beams.

Structural Result RC Beam GRC Beam

Specimen 1 Specimen 2 Average Specimen 1 Specimen 2 Average

Yield load (kN) 12.88 12.13 12.50 16.56 15.44 16.00

Yield deflection (mm) 1.11 1.18 1.15 0.62 0.66 0.64

Ultimate deflection (mm) 7.65 8.15 7.90 12.98 14.69 13.84

Ultimate load (kN) 46.44 43.56 45.00 32.07 28.33 30.20

Ductility 6.89 6.91 6.90 20.94 22.26 21.60

Stiffness (kN/mm) 5.46 5.30 5.38 2.20 2.15 2.17

Energy absorption (kN-mm) 200.00 204.00 202.00 342.57 355.40 349.00

Experimental/Theoretical 1.86 1.74 1.80 1.27 1.13 1.20

Maximum crack width (mm) 1.10 1.10 1.10 3.40 3.60 3.50

After the yield stage, the GRC beams behaved with larger cracks width and length due to the higher ductile deflection behavior, occurred during the loading, than the RC beams. The RC and GRC beams failed at the average ultimate loads of 45 kN and 41 kN, respectively, with their corresponding average deflections of 7.9 mm and 13.84 mm. On average, the GRC beams had 9% lower load-carrying capacity than the RC beams. The lower load-carrying capacity of the GRC beams at the ultimate stage than at the yield stage may be due to the degraded stiffness caused by the higher flexibility of the geogrid material and the subsequent loss of the aggregates’ interlocking mechanism. The 22 layers provided as a single mat in the GRC beams reduced the bond characteristics, which led to the degradation of the aggregates’ interlocking mechanism and enhanced the rate of the stiffness degradation. This caused the loss of the load-carrying capacity in the GRC beams after the yield stage.

0 5 10 15 20 25 30 35 40 45 50

0 2 4 6 8 10 12 14 16

Load (kN)

Deflection (mm)

RC Beams, Yield Load = -1.9547x² + 13.15x + 0.0343; R² = 0.9989 RC Beams, Inelastic Load = -0.096x² + 5.3195x + 8.3247; R² = 0.9954 GRC Beams, Yield Load = 3.9899x² + 22.67x - 0.1195; R² = 0.996 GRC Beams, Inelastic Load = -0.0829x² + 2.0812x + 17.135; R² = 0.9876

Figure 11.Load vs. mid-span deflection curves of RC and GRC beams.

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The tested RC beams illustrated a permanent crack, and the crack width was not reduced during the unloading process. The maximum crack measured in the RC beams was 3.2 mm on average, which was not reduced during the unloading process. However, the GRC beams displayed a great elastic property. On average, the deflection of the GRC beams was 1.75 times higher than that of the RC beams, however, it provided greater resistance to failure. The deflected shape of the GRC beams was restored to its original position, and the existing cracks were closed by themselves during the unloading process.

In the GRC beams, the reloading was done after the unloading process. The reloading results revealed that the loading capacities of both loading and reloading were almost the same. The failure of both beams was observed to be of the flexural type.

Figures 12 and 13indicate the cracks patterns of the tested RC and GRC beams, respectively. No spalling was witnessed in either of the beams. The maximum crack width measured in the RC beams at the ultimate stage was 3.5 mm on average, whereas the maximum crack width measured in the GRC beams after unloading was less than 1.6 mm.

The ultimate deflection of the GRC beams was decreased to 1.6 mm on average, and the crack width was reduced to 1.2 mm. It was demonstrated that the GRC beams behaved with an enriched pinching effect and enhanced post-yield behavior. This ensured the enhanced ductility of the GRC beams compared with the RC beams.

0 5 10 15 20 25 30 35 40 45 50

0 2 4 6 8 10 12 14 16

Load (kN)

Deflection (mm)

Figure 12.Crack patterns of tested RC beams.

0 5 10 15 20 25 30 35 40 45 50

0 2 4 6 8 10 12 14 16

Load (kN)

Deflection (mm)

Figure 13.Crack patterns of tested GRC beams.

5.2. Energy Absorption and Ductility

Energy absorption is a property of an element that can store maximum strain energy without loss of its load-carrying capacity. The area under the load-deflection curve is generally called energy absorption. The ratio of the ultimate deflection to yield deflection is used to calculate the ductility. Figure14depicts the energy absorption characteristics of the beams. Table5lists the energy absorption and ductility of the beams as well. The average energy absorption and ductility of the GRC beams were, respectively, 73% and 213% higher than those of the RC beams. The energy absorption of the RC beams was initially higher and was reduced less than that of the GRC beams. The higher deflection of the GRC beams without much loss in the load capacity aided the enriched performance in both the ductility and energy absorption. The geogrid material acted as a shear key. This ensured a good bond between GG and concrete, which helped resist the stiffness degradation, and this effective bonding improved ductile behavior by enhancing the inelastic response. The stable crack growth caused large stress redistribution and a release of stored energy, which in turn provided more ductile behavior for the GRC beams.