The research methodology encompasses a multifaceted approach, combining experimental investigations and theoretical modelling. Laboratory experiments will be conducted to assess the material properties, mechanical properties, and behaviour steel and GFRP reinforced slabs comprising M-sand and Alccofine. These experiments will involve the fabrication of test specimens, including both traditional steel-reinforced slabs and those incorporating GFRP. Various tests, such as compressive strength, tensile strength, elastic modulus, flexural behaviour, load-deflection, crack propagation, failure mode; strain behaviour will be conducted according to relevant international standards. Additionally, theoretical investigations are carried out to predict the behaviour of the composite slabs to enhance the understanding of the structural response and performance of the slabs.

The materials employed in the experimental program are outlined in Table 1 . The one-way spanning slab specimens were reinforced longitudinally with either 1) GFRP bars coated with sand, having a 12 mm diameter, or 2) 12 mm diameter steel bars. In all instances, 8 mm steel bars were utilized in the transversal direction. The mechanical characteristics of each reinforcement type utilized in the experimental campaign were determined through tensile testing. Table 1 provides key characteristic properties, including elastic modulus (E), ultimate tensile strength (fu), and yield strength (fy) for the steel bars. Notably, no yield strength values are presented for the GFRP bars, as these materials lack a yield point. Figure 1 displays an image of the steel and GFRPs employed in the present investigation.

Four concrete formulations were created, comprising both conventional concrete and Alccofine-based concrete. In each formulation, a combination of normal river sand and M-sand was utilized. The mix proportions and concrete

properties are detailed in Table 2 . The formulations were labelled according to the materials incorporated, with “C” denoting Cement, “RS” for River Sand, “A” for Alccofine, and “MS” for M-Sand.

The test program included the examination of a total of eight one-way reinforced concrete slabs, as outlined in Table 3 . These slabs were divided into four groups based on their reinforcement and binder content. Groups 1 and 2 comprised conventional concrete with steel and GFRP reinforcement, while Groups 3 and 4 consisted of Alccofine-based concrete with the same types of reinforcement. Each group featured two slabs with either river sand or M-sand. A reference system was employed to label each specimen, where the initial part of the name indicated the type of concrete (i.e., Conventional Cement Concrete (C), Alccofine-based Concrete (A), River Sand (RS), and M-sand (MS)), followed by the type of reinforcement (i.e., Steel Reinforcement (S) and GFRP (G)).

The slabs, with dimensions of 2000 mm in length, 600 mm in width, and 125 mm in thickness, utilize 12 mm diameter bars spaced at 280 mm c/c as the primary

reinforcement, and 8 mm diameter bars spaced at 300 mm c/c as distribution reinforcement. A bottom concrete cover of 20 mm is applied. Figure 2 & Figure 3 illustrate the cross-sectional view and reinforcement arrangements of the RC slab. Before casting, strain gauges were affixed to the central longitudinal steel bar using a strong adhesive. These gauges were additionally coated with a thin resin for protection against moisture and damage. The slabs were cast using the mix proportions specified in Table 2 , with concrete mixing carried out manually as depicted in Figure 4 . Following casting, the specimens underwent a curing period of approximately 28 days. After this curing period, the slabs were cleaned, whitewashed, marked for support and loading, and subsequently relocated to the test floor.

A 50-tonne capacity load frame is employed to test slab specimens, with support provided at one end through a roller and at the other end through a hinge. The slabs undergo two-point loading using a line load system facilitated by spreader beams. To prevent local effects, thick rubber or neoprene pads are placed beneath the spreader beams. The support end levels of the slabs are meticulously maintained using spirit levels. Hydraulic jacks with a manual capacity of 250 kN are utilized to apply static loads, monitored by a proving ring. Deformations in the slabs are gauged using dial gauges, strain gauges, and demec gauges. External surface strain gauges are affixed to the bottom surface of the slabs. Dial gauges are positioned at one-third distance from the supports. Demec gauges, employed for strain measurement, necessitate a standard gauge distance, achieved by affixing brass pellets at known distances at the top, center, and bottom. The load is incrementally increased by 1 kN until slab failure occurs. Crack widths at the ultimate condition are measured using a crack width detection microscope. The experimental setup is illustrated in Figure 5 .

In general, the slabs reinforced with steel and GFRP bars displayed a linear response before cracking occurred, followed by the sudden emergence of wide and deep cracks, accompanied by substantial deflections in GFRP reinforced slabs. The initiation and propagation of cracks in steel-reinforced concrete are often more gradual compared to sudden emergence and undergo significant deformation before failure shows the ductile response. The test outcomes and observed failure patterns for the slabs examined in this study are detailed in Table 4 . Figure 6 illustrates the deflected profile of the slabs. Notably, the slab reinforced with GFRP bars experiences a notable decrease in stiffness after the first crack initiation compared to the slab reinforced with steel reinforcements. Additionally, all slabs reinforced with GFRP demonstrate significantly broader crack widths and depths when compared to the slabs reinforced with steel. This divergence is ascribed to the lower elastic modulus of GFRP bars in contrast to steel reinforcements.

Figure 7 illustrates the crack propagation and crack width observed in all slabs, while Table 4 provides details on the failure modes across the slabs. In the case of slabs reinforced with steel (CRS-S, CMS-S, ARS-S, and AMS-S). The mode of failure in these instances was characterized by yielding and ductile failure. Conversely, slabs reinforced with GFRP (CRS-G, CMS-G, ARS-G, and AMS-G) exhibited a minimal number of cracks with wider crack widths. The failure mode in these slabs was brittle, resulting in the rupture of GFRP. Despite the concrete’s ability to continue carrying the load, the GFRP bars experienced rupture failure, rendering them incapable of sustaining the load.

The load-deflection behaviour of all slabs is depicted in Figure 8 . The GFRP-RC slabs exhibited a bi-linear pattern, representing both pre- and post-cracking stages until eventual failure. Similar bi-linear behaviour was observed in previous studies for FRP-RC slabs subjected to static loading [27] [28] . In the case of steel-reinforced slabs, ductility is imparted to the system by the steel bars (rebars). Unlike GFRP, which tends to exhibit a more brittle failure mode, the inclusion of steel reinforcement allows for increased deformation and energy absorption before reaching failure. Consequently, the load-deflection curve of a steel-reinforced slab displays a more gradual and ductile response, lacking a sharp transition between pre- and post-cracking behaviour. Deformation and cracking are more evenly distributed, leading to a failure that is not as abrupt or catastrophic as observed in GFRP-RC slabs.

The diagram in Figure 9 illustrates the load-strain characteristics of both reinforcement and concrete. At the moment of cracking, a sudden decline in strain was observed, followed by a rapid increase in average post-cracking strain for GFRP reinforcement within the strain range of 0 to 4. In contrast, steel reinforcement (within the strain range of 0 to 2) exhibited a slight deviation at the cracking point and a gradual post-cracking strain increase. This behaviour was observed to be influenced by the type of reinforcement material used. It was noted that the concrete strength had a negligible impact on the strain in both steel and GFRP reinforcement bars. In the case of concrete, the strain values across all slabs were nearly identical, ranging from 0 to 2.5. The lack of significant differences in strain values is attributed to the fact that slab failures occurred only under reinforcement conditions (tension failure), and the concrete strain values did not reach the ultimate strain.

The study involved a comparison between experimental test data and design recommendations [13] [29] focusing on failure mode, ultimate load, and deflection. The calculations for reinforcement ratios, maximum loads, and midspan deflections at maximum loads were derived from preliminary material testing data. Table 5 displays the comparison of maximum loads and midspan deflections, presenting both experimental and code predictions, and showcasing the percentage difference. Values less than one indicate under-prediction by the design codes, while values greater than one suggest over-prediction. For example, the Slab CRS-S has load and deflection of 1.24 and 1.19 which is overpredicted by the code recommendation. Notably, slabs with a reinforcement ratio of 0.4 (less than 1) failed due to GFRP bar rupture and exhibited ductility for steel bars. Figure 10 illustrates the load-deflection behaviour, comparing experimental and predicted outcomes.

For the analysis of cracked GFRP reinforced slabs, ACI 440 specifies the use of the effective moment of inertia (Ie) in Equation (1), incorporating an integration factor “γ” based on loading and boundary conditions. Equation (2) accounts for the integration factor in the case of four-point loading, considering the stiffness

along the GFRP reinforced slabs. Additionally, ACI 440 provides Equation (3) to calculate deflections and cracking for four-point loading.

$I_e=\frac{I_{cr}}{1-\gamma {\left(\frac{M_{cr}}{M_a}\right)}^2\left[1-\frac{I_{cr}}{I_g}\right]}\le I_g$ (1)

$\gamma =1.72-0.72\frac{M_{cr}}{M_a}$ (2)

$\text{Δ}=\frac{23P{L}^3}{1296E_c{I}_e}$ (3)