Structural characteristics of geopolymer concrete beams using alkali-modified blended ash: a comparative evaluation with conventional beams

ABSTRACT

This study evaluates the fresh-state rheology and flexural performance of ambient-cured geopolymer concrete (GPC) as a sustainable alternative to M35 grade concrete. Using fly ash and GGBS activated by sodium hydroxide (SH) and sodium silicate (SS), the research investigated a parametric molarity range from 4M to 12M. Fresh-state analysis showed that increasing SH concentration significantly raised dynamic viscosity, reducing slump by up to 79%. An 8M threshold was identified for optimal workability and compaction. Mechanical testing revealed 8M as the robust performance optimum, achieving a 28-day compressive strength of 57.53 MPa (23.7% above control) and a flexural load of 112 kN. While GGBS enabled rapid early-strength gain (reaching up to 93% of 28-day strength within 7 days), the 4M configuration was insufficient for structural use. All GPC beams exhibited an under-reinforced failure mode with extensive strain-hardening, yielding capacity ratios between 1.43 to 2.50. Despite the superior ductility and energy absorption of GPC-8M, the findings are presented as indicative performance trends due to the reliance on single-beam specimens per configuration. Furtheremore, the absence of quantitative Life Cycle Assessment or durability profiles necessitates a cautious interpretation of GPC. These findings establish a deterministic benchmark for optimizing molarity in structural geopolymer applications.

Keywords:
Geopolymer concrete; Parametric optimization; Molarity threshold; Fresh-state rheology; Ductility index; Ambient curing.

1. INTRODUCTION

Concrete production has reached exponential levels due to expanding infrastructure and global population growth. Conventionally, Ordinary Portland Cement (OPC) is the primary binder; however, its annual production of 3 billion tonnes accounts for approximately 8% of global CO₂ emissions, ranking the cement industry third in greenhouse gas emissions after the power and road sectors [¹,²,³]. This environmental burden, coupled with the depletion of natural resources, has necessitated a transition toward sustainable construction materials [⁴]. Simultaneously, the aggressive expansion of industrialization generates vast quantities of by-products such as fly ash, copper slag (CS), ground granulated blast furnace slag (GGBS), and silica fume whose disposal remains a significant environmental and health challenge [⁵,⁶,⁷]. The reuse of these industrial wastes is inevitable for developing sustainable concrete. Specifically, FA and GGBS-based geopolymers emit 55–75% fewer greenhouse gases than traditional cement [⁸]. The term “Geopolymer,” introduced by Davidovits, refers to inorganic binders that eliminate cement entirely, potentially reducing CO₂ emissions by over 60% while offering superior engineering properties [⁹,¹⁰,¹¹,¹²,¹³].

Recent studies emphasize the synergy of combining diverse industrial precursors to optimize these binders. For instance, investigations into the hybrid use of FA and GGBS show that the chemical interaction between calcium-rich slag and aluminosilicate-rich ash significantly refines the pore structure, enhancing both mechanical strength and durability under various curing conditions [¹⁴, ¹⁵]. Additionally, emerging research suggests that the integration of nano-materials and bio-fillers within these geopolymeric matrices can further arrest micro-cracking and improve the interfacial transition zone (ITZ) between the paste and reinforcement [¹⁶].

Since 2005, research has focused heavily on FA-based geopolymers [¹⁷, ¹⁸]. Despite extensive research into geopolymerization, a significant gap persists between the massive generation of industrial waste and its effective large-scale utilization in construction. A primary technical barrier to the adoption of FA-based geopolymer concrete is its reliance on heat curing (65–80°C) to achieve structural-grade strength, which restricts its practical application in cast-in-situ projects [¹⁹]. To overcome this, the strategic incorporation of GGBS into FA-based systems has emerged as a transformative solution, facilitating a dual reaction that enables strength development under ambient conditions [²⁰, ²¹].

While recent studies have significantly expanded the understanding of these blended precursors [²²], a critical research deficit remains regarding their behavior at the component level. For instance, MUTHUMANICKAM and MOHAN [²³] demonstrated that ambient-cured reinforced geopolymer concrete beams can achieve flexural capacities comparable to OPC, yet highlighted significant variations in stiffness. Furthermore, NITHIN et al. [²⁴] and CHENet al. [²⁵] have shown that while higher GGBS content enhances early-age strength, it can also lead to more brittle failure modes compared to conventional concrete.

To contextualize these component-level variations, recent structural evaluations of reinforced geopolymer concrete beams have focused heavily on balancing shear, flexure, and bond mechanisms. Recent investigations by SHARMA and KHAN [²⁶] demonstrated that the crack propagation path in ambient-cured binary beams is highly sensitive to the binder matrix density, often resulting in narrower crack widths but a faster transition to final failure compared to OPC controls. This is closely linked to the interfacial bond strength; as established by PATEL[²⁷], the chemically distinct ITZ of an optimized FA-GGBS matrix alters the transfer length of reinforcing bars, which directly dictates structural stiffness degradation under progressive loading. Consequently, while empirical code provisions for conventional concrete often underestimate the ultimate flexural capacity of RGPC beams, they frequently overestimate their post-cracking serviceability.

Furthermore, the structural performance of ambient-cured binary beams cannot be decoupled from the chemistry of their activation. Recent structural testing by Al-MASAEID [²⁸] revealed that altering the alkaline solution-to-binder ratio directly impacts the macro-ductility of reinforced structural elements. Low-molarity systems often fail prematurely due to incomplete geopolymerization and weak aggregate interlocking, whereas excessively high molarities induce micro-brittleness within the binder paste, accelerating shear-compression failure in beams. While these contemporary studies have isolated the effects of either extreme slag substitution or single-molarity activators, a comprehensive systematic mapping of structural ductility across a progressive molarity spectrum remains absent.

1.1. Research gap and novelty

Despite these findings, there remains a critical gap in understanding how a balanced 50:50 FA–GGBS ratio which avoids the brittleness of high-slag mixes influences the full load-deflection curve and energy absorption across a range of alkaline molarities (4M to 12M). The novelty of this study lies in identifying the “Critical Molarity Threshold” required for this specific 50:50 blend to surpass conventional M35 concrete. This research provides a unique structural benchmark for serviceability and ductility that is currently missing from the literature on ambient-cured binary geopolymers.

To bridge the gap between material rheology and component-level structural behavior in sustainable construction, this study systematically evaluates an ambient-cured, binary 50:50 FA–GGBS geopolymer matrix through six interconnected objectives. The primary objective is to quantify the rheological interaction between varying sodium hydroxide molarities (4M to 12M) and the fresh-state fluidity of the 50:50 FA–GGBS matrix, thereby establishing the precise threshold where liquid-phase dynamic viscosity restricts horizontal slump and extends Vee Bee remolding time. Concurrently, the study aims to evaluate early-age mechanical kinetics under ambient curing conditions, isolating how the active soluble calcium ions from the 50:50 slag inclusion govern rapid compressive strength development at 7, 14, and 28 days without thermal assistance. To define structural boundaries, the investigation is designed to identify the “Critical Molarity Threshold” required to meet or exceed an M35 structural grade baseline, while clarifying the microstructural mechanisms responsible for the sub-critical binder activation and structural capacity deficits observed in low-molarity (4M) configurations.

Scaling up to the structural component level, the research analyzes the full-scale flexural behavior of reinforced geopolymer concrete beams under four-point loading configurations, specifically comparing the first-crack initiation parameters and ultimate load-carrying capacities against M35 reference elements. This structural mapping is extended to characterize the structural serviceability limits, ductility indices, and energy absorption capacities of the ambient-cured binary GPC components by continuously tracking load-deflection profiles, mid-span settlements, and initial stiffness degradation. Ultimately, the synthesis of these multi-scale datasets aims to establish the optimum performance window within the 8M to 10M range that balances the critical trade-offs among peak mechanical resistance, macro-structural energy dissipation, fresh-state workability boundaries, and carbon emission reductions for practical cast-in-situ construction applications.

2. MATERIALS AND METHODS

Building upon the foundation of sustainable construction, Geopolymer concrete’s production involves an innovative blend of fly ash, GGBS, alkaline solution, super plasticizer, and aggregates.

2.1. Source materials (SM)

To explore sustainable alternatives to OPC, this investigation sourced low-Calcium fly ash (ASTM class F) from the Tuticorin thermal power plant in Tamil Nadu, India, as a primary material for Geopolymer concrete synthesis. It appeared dark grey as displays in Figure 1 with a specific gravity of 2.20. To elucidate the suitability of fly ash for Geopolymer synthesis, its chemical composition was analyzed, with key findings summarized in Table 1.

Figure 1
Source materials.

Table 1
Chemical composition of fly ash.

CHEMICAL COMPOUND	SiO2	AI2O3	Fe2O3	TiO2	CaO	K2O	P2O5	MgO	SO3
Weight (%)	55.41	29.69	8.48	2.02	1.39	1.01	0.70	0.45	0.32

The other binding substance is GGBS, which has a specific gravity of 2.80 and an off-white color as shown in Figure 1. Table 2 shows the chemical composition of GGBS determined by XRF analysis. Because of the higher amount of calcium oxide (CaO) in GGBS (approximately 40%), the addition of GGBS in Geopolymer concrete is extremely helpful in curing the specimens under ambient conditions.

Table 2
Chemical composition of GGBS.

CHEMICAL COMPOUND	CaO	SiO2	AI2O3	MgO	SO3	MnO	TiO2	Fe2O3	K2O	BaO
Weight (%)	39.79	31.72	16.91	6.23	1.62	1.18	1.11	0.61	0.47	0.11

2.2. Cement

Ordinary Portland Cement (43 grade), used in this study shown in Figure 2, and satisfies IS 8112 (part1): 2013 for the preparation of control concrete specimens. The cement had a consistency of 30% and a specific gravity of 3.15. The physical properties of the cement are listed in Table 3. The required amount of cement was determined, procured from a local supplier, and kept in a dry place to avoid cement clotting.

Figure 2
Cement.

Table 3
Physical properties of cement.

SL. NO	PHYSICAL PROPERTIES	VALUE
1	Specific Gravity	3.15
2	Standard Consistency	30 %
3	Initial Setting Time	90 mins
4	Final Setting Time	210 mins
5	Fineness	5 %
6	Soundness Test	0.95 mm
7	Compressive Strength	44.58 MPa

2.3. Activation solution (AS)

Two types of alkaline activating solutions are used to prepare the Geopolymer concrete: sodium-based or potassium-based. The alkaline solution used in this study was a combination of sodium hydroxide and sodium silicate solutions.

2.3.1. Sodium hydroxide solution

Sodium hydroxide solution is a commonly used solution for the activation of source material in Geopolymer concrete production. According to the molarities of SH, the required amount of sodium hydroxide pellets with a purity of 98% need to be dissolved in potable water to prepare the sodium hydroxide solution. Heat is liberated from the solution during this dissolution process because it is an exothermic reaction.

2.3.2. Sodium silicate solution

Sodium silicate is commercially available in liquid form with a mass ratio of soluble silica to sodium oxide of 2.20. This ratio is a prime factor in understanding the reactivity of the metal. It is vicious in nature and was purchased from a local dealer.

2.3.3. Preparation of activation solution

Sodium hydroxide and sodium silicate solutions were combined to create an alkaline solution, as shown in Figure 3. By maintaining an SS/SH ratio of 2.5, the anticipated alkaline solution was proportionally split into sodium hydroxide and sodium silicate solutions [²⁹]. The sodium silicate and sodium hydroxide solutions were calculated as 125 and 50 litre/m³ for an alkaline solution to source material ratio of 0.35. The SH pellets (8 × 40 g = 320 g) were dissolved in one litre of potable water to make a one molarity SH solution. Because the dissolution of SH pellets is an exothermic reaction, heat is generated. Hence, the SH solution was prepared 24 h before the concrete mixing time, and extreme caution was required throughout the development of the SH solution. The manufactured SH solution was blended with a readymade SS solution during concrete mixing.

Figure 3
Preparation of alkaline solution.

2.4. Aggregate

A better packing density can be achieved using aggregates of various sizes. Therefore, locally available granite metals of 20 mm and 12.5 mm size which represented in Figure 4 with specific gravities and fineness moduli of 2.80, 2.96, and 7.37, 6.97, respectively, were selected as coarse aggregates. Due to the scarcity of natural river sand, M-sand from zone II conforming to IS 383:2002 with a specific gravity of 2.72 and a fineness modulus of 2.50 was used as the fine aggregate. The gradation curve for the aggregates is given in Figure 5. Prior to the mixing operation, the Saturated Surface Dry condition of the aggregate was attained.

Figure 4
Aggregate.

Figure 5
Gradation curve for aggregate.

2.5. Super plasticizer

A Polycarboxylic ether-based super plasticizer with a pH and specific gravity of 7 and 1.08, respectively, was used as an additive to enhance the fresh concrete characteristics.

2.6. Water

Potable water conforming to the specifications of IS 456:2000 was used for the preparation of sodium hydroxide solution and manufacturing of conventional concrete. The results of the water quality analysis are shown in Table 4.

Table 4
Water quality analysis test results.

SL. NO	PROPERTIES	VALUE	MAXIMUM PERMISSIBLE LIMIT	REFERENCE CODE
1	pH	7.5	6.0–9.0	IS: 3025 (Part 11)-1983 (2002)
2	Hardness	85	1000	IS: 3025 (Part 21)-2009
3	Chloride	50	500	IS: 3025 (Part 32)-1988 (2003)
4	Sulphate	10	400	IS: 3025 (Part 24)-1986 (2009)

2.7. Steel reinforcement

Steel rods were used as reinforcement in the Geopolymer and conventional concrete beams. High yield strength deformed (HYSD) steel bars with diameters in the range of 8–12 mm and grade Fe500 were selected for this research. The steel bars with different diameter were tested in the Universal Testing Machine (UTM) by conducting a tension test to find its yield and ultimate strength, and the results are tabulated in Table 5.

Table 5
Tension test results of steel reinforcements.

SL. NO.	DIAMETER OF ROD (mm)	NOMINAL AREA (mm²)	YIELD STRENGTH (N/mm²)	ULTIMATE STRENGTH (N/mm²)
1	8	50.3	558	624
2	10	78.5	554	637
3	12	113.1	531	672

3. METHODOLOGY

The experimental framework utilized a binary binder matrix composed of a balanced 50:50 weight ratio of low-calcium Class F Fly Ash and GGBS to enable ambient-temperature setting and accelerated early-age strength development. To systematically map the “Critical Molarity Threshold,” an alkaline activator solution was formulated by blending sodium and sodium hydroxide across a progressive spectrum of concentrations: 4M, 6M, 8M, 10M, and 12M. The liquid activators were dissolved 24 hours prior to use to ensure thermal equilibrium. All geopolymer concrete variations maintained a constant precursor mass, fixed aggregate volumes and a uniform solution-to-binder ratio of 0.35. A conventional concrete mix designed with Ordinary Portland Cement served as the structural baseline control variable (CC-M35).

The fresh-state workability was immediately evaluated using two complementary configurations: a standard Slump Cone apparatus, and a Vee Bee Consistometer. Immediately after rheological testing, the fresh matrices were cast into 150 mm steel cube molds and structural reinforced beam molds embedded with high-yield strength deformed steel reinforcing bars. The GPC specimens were demolded after 24 hours and transferred directly to an ambient laboratory environmental chamber, while the control CC-M35 elements were submerged in water. The development of hardened mechanical properties was quantified at curing intervals of 7, 14, and 28 days using a calibrated 2000 kN capacity Compression Testing Machine on triplicate cube specimens, with quality control verified via Standard Deviation.

To bridge the gap between material properties and structural response, full-scale reinforced concrete beams were tested under a four-point bending configuration inside a rigid loading frame to evaluate their complete load-deflection behavior, ultimate flexural capacity, cracking patterns, ductility index, and energy absorption capacity. Mid-span deflections were continuously recorded using linear variable differential transformers synchronized with a digital data acquisition system. The resulting structural and mechanical datasets were evaluated alongside the dual-gel polymerization kinetics—chemically governed by the co-existence of Sodium Aluminosilicate Hydrate and Calcium Aluminosilicate Hydrate gels—to validate the sustainability claim of this 50:50 binary blend, which targets a 55–75% reduction in embodied carbon footprint compared to traditional OPC binders.

4. MIX PROPORTION

4.1. Proportioning of geopolymer concrete

There are no standard specifications for the mix design of Geopolymer concrete. A novel mix design methodology for FA-based Geopolymer concrete is only partially supported by research findings [³⁰,³¹,³²,³³]. Because designing a Geopolymer concrete mix takes time and is dependent on several factors, there is a lack of studies in this area. For this investigation, the concrete density was assumed to be 2400 kg/m³. Based on a literature review [²⁹,³⁰,³¹,³²,³³], 70% of the weight of concrete was engaged by aggregates, and the ratio of fine aggregates to coarse aggregates was taken as 0.35. It was decided to keep the sodium hydroxide solution to sodium silicate solution ratio as 2.5. The proportioning of materials for making one cubic meter of Geopolymer concrete is quantified in Table 6.

Table 6
Proportioning of materials for making 1 m³ of Geopolymer & OPC concrete.

MIX ID*	SH MOLARITY	FLY ASH (kg/m³)	GGBS(kg/m³)	FINE AGGREGATE (kg/m³)	COARSE AGGREGATE (kg/m³)		SH SOLUTION		SS SOLUTION (lit/m³)	SP (kg/m³)
					12.5 mm	20 mm	kg	lit
GPC-4M	4	250	250	435	498	747	8	50	125	20
GPC-6M	6	250	250	435	498	747	12	50	125	20
GPC-8M	8	250	250	435	498	747	16	50	125	20
GPC-10M	10	250	250	435	498	747	20	50	125	20
GPC-12M	12	250	250	435	498	747	24	50	125	20
CC-M35	–	390 (Cement)		703	544	772	Water – 158 (W/C – 0.4)			15

4.2. Mix design of conventional concrete

Ordinary Portland cement concrete of M35 grade was produced and selected as the control concrete for comparison with the test results of the Geopolymer concrete. The mix design of the control concrete was performed by referring to the Indian Standard specifications IS: 10262, 2019 and the proportions are included in Table 6.

5. EXPERIMENTAL SETUPS

The load-deflection characteristics, load-carrying capacity, failure mode, and crack pattern of Geopolymer and conventional concrete beams were investigated using a four-point bending test. All beams were 150 mm wide, 250 mm deep and 2000 mm long. Figure 6 depicts the reinforcement details of the reinforced concrete beam. In compliance with IS: 456-2000, the beams were under-reinforced with an effective span of 1800 mm. For the comparison of test findings, five different Geopolymer concrete beams were cast with different alkaline solution concentrations, in addition to one control concrete beam. Other variables, such as the tension reinforcement percentage, shear span-to-depth ratio, clear cover, and mix proportions, were kept constant.

Figure 6
Reinforcement details of the concrete beam.

The beams were simply supported at the ends, and the load was applied using a 500 kN hydraulic jack. The applied load was measured using a load cell with a capacity of 250 kN and a least count of 0.1 kN. The load was applied to the concrete beam in the pure bending zone using a spreader beam. The experimental model setup is shown in Figure 7. The load was gradually applied in increments of 2 kN, and the loading rate was set at 1 kN/30sec. The load at which the first crack appeared was observed and recorded. The deflection of the beam caused by the load application was measured using a Linear Variable Differential Transformer (LVDT) fixed at the mid-span and loading point on the soffit of the concrete beam. The applied load and corresponding deflection were recorded using a digital data acquisition system. Figure 8 indicates the actual experimental setup used during the application of the load.

Figure 7
Model experimental setup for flexure test.

Figure 8
Actual experimental setup during bending test.

6. EXPERIMENTAL RESULTS

6.1. Workability

The degree of mobility or fluidity of freshly prepared concrete is referred to as “workability.” It must be measured to produce the desired level of compaction, as both parameters are interconnected. A Slump Cone test and a Vee Bee Consistometer test were performed on fresh Geopolymer concrete to determine its workability. The Slump Cone test is a widely used method for determining the consistency of concrete, whereas the Vee Bee Consistometer is preferred when the consistency of concrete is very dry.

6.1.1. Slump cone test

Conventional cement concrete was produced with a slump value of 100mm. All Geopolymer concrete mixes had lower slump values than the control concrete. Slump values significantly decreased, illustrating a reduction from 95 mm to 21 mm, as the molarity of SH increased from 4M to 12M, indicating reduced workability at higher SH concentrations. Compared to the slump value of conventional concrete, the Geopolymer concrete mixtures demonstrated an exponential reduction in workability, losing 5%, 17%, 36%, 69%, and 79% of their slump at sodium hydroxide concentrations of 4M, 6M, 8M, 10M, and 12M, respectively. This profound slump loss confirms that scaling SH molarity increases the dynamic viscosity and cohesiveness of the alkaline activator solution, heavily restricting flowability [³⁴, ³⁵]. As documented by MEMON [³⁴], high concentrations of NaOH introduce a larger fraction of dissolved solids, making the liquid medium highly viscous. Furthermore, this trend matches established literature indicating that higher OH⁻ concentrations accelerate early-stage silica and alumina leaching, triggering rapid initial polymerization, gel formation, and a subsequent reduction in fresh concrete workability [³⁶]. This was also highlighted by a previous study [³⁷]. Based on these findings, it is clear that the concentration of the alkaline activator significantly affects the workability of the Geopolymer concrete. The slump values of various Geopolymer concrete mixes were compared with the slump value of the control concrete, as revealed in Figure 9. According to MEHTA and SIDDIQUE [³⁸], when the molarity of SH increased, a considerable reduction in slump was observed in Geopolymer concrete. This could be due to the presence of excess solid content in the alkaline solutions. Another factor contributing to slump loss is GGBS’s rough and irregular surface, whereas fly ash particles have a smooth surface that aids in the lubrication of concrete mixtures [³⁹, ⁴⁰].

Figure 9
Comparison of slump values for geopolymer and cement concrete mixes.

6.1.2. Vee Bee consistometer test

The Vee Bee Consistometer test was performed on fresh Geopolymer and conventional concrete mixes. The workability of concrete is indirectly measured using this laboratory test. The Vee Bee degree is the time in seconds required to convert a conical concrete shape into a full cylindrical shape. According to the findings, all Geopolymer concrete mixes took a longer duration to convert to their final shape than the ordinary cement concrete. The Vee Bee degree for the control concrete was 3 s, which was taken as a reference value to compare the Vee Bee degrees of the Geopolymer concrete mixes, as shown in Figure 10. The Vee Bee time increased from 7.5 to 23.6 s as the molarity of SH increased from 4M to 12M. This indicates that the increasing molarity of SH indirectly delays the time required for concrete shape conversion. A higher value of the Vee Bee degree indicates that the degree of workability is very stiff or dry. The Vee Bee degree of Geopolymer concrete prepared with varying concentrations of SH was around 4-21 seconds higher when compared to Vee Bee seconds of cement concrete. The maximum and minimum values of 23.6 and 7.5 s were observed in the GPC-12M and GPC-4M mixes, respectively.

Figure 10
Vee Bee degree comparison of GPC and OPC concrete mixes.

6.1.3. Rheological implications and practical limits

The observed workability trends are driven by the liquid-phase rheology of the alkaline activator. Higher SH concentrations increase the dynamic viscosity of the solution and the total solid content, which reduces the thickness of the lubricating water film between the angular and irregular GGBS particles [⁴¹, ⁴²]. From a rheological perspective, the high Vee-Bee time (23.6 s) for GPC-12M indicates a high yield stress, the internal friction of the mix is so great that significant mechanical energy is required to initiate flow. Based on the synchronization of fresh-state data and hardened properties, 8M is identified as the practical workability threshold. Beyond 8M, the excessive viscosity hinders effective compaction, likely leading to the slight reduction in ultimate load capacity observed in the 10M and 12M beam specimens. The rheological categorization including solid content, viscosity and super plasticizer with practical workability limits of GPC Mixes are summarized in Table 7.

Table 7
The rheological practical workability limits of GPC mixes.

Sl No.	Mix ID	SLUMP (mm)	SLUMP LOSS vs. CC (%)	WORKABILITY CATEGORY [43]	RHEOLOGICAL IMPLICATIONS
1	GPC-4M	100	–	High	Reference water-lubricated mix.
2	GPC-6M	95	5	High	Low activator viscosity; high “free water.
3	GPC-8M	83	17	Medium	Balanced ionic strength and flow.
4	GPC-10M	64	36	Medium	Practical Limit: Optimal yield stress.
5	GPC-12M	31	69	Low	High viscosity; SP efficiency decreases.
6	CC-M35	21	79	Very Low	Excess solid content; high internal friction.

6.2. Compressive strength

The compressive resistance of Geopolymer concrete mixes with different SH concentrations was investigated at 7, 14, and 28 days of ambient curing using triplicate cube specimens. Similar to conventional concrete, increasing the curing time enhanced the compressive strength of the Geopolymer concrete. However, compared to conventional and fly ash-based Geopolymer concrete, the fly ash and GGBS-based Geopolymer concrete achieved the required strength at a faster rate. Furthermore, adding GGBS to Geopolymer concrete improved the early age properties under ambient curing conditions, such as 90% of the 28-day compressive strength attained within 7 days of curing which is consistent with literature [⁴⁴]. Figure 11 shows a visual representation of the compressive strength results of Geopolymer concrete mixes. The test results concluded that a higher concentration of SH participates in higher strength development, whereas the GPC-4M mix could not resist more load during the compression test at an early curing age. The average compressive strength and associated standard deviations for the GPC and control mixes are summarized in Table 8. As shown in Table 8, the standard deviations for all Geopolymer Concrete and control mixes remain below 2.0 MPa. This results in a Coefficient of Variation within the range of 3% to 6%, which demonstrates high quality control standards and material consistency during the fabrication process.

Figure 11
Compressive strength variation of Geopolymer & cement concrete mixes.

Table 8
Mean compressive strength of GPC & OPC mixes at various curing age.

SL. NO.	MIX ID	AGE OF CURING
		7 DAYS		14 DAYS		28 DAYS
		MEAN COMP. STRENGTH (Mpa)	STANDARD DEVIATION (Mpa)	MEAN COMP. STRENGTH (Mpa)	STANDARD DEVIATION (Mpa)	MEAN COMP. STRENGTH (Mpa)	STANDARD DEVIATION (Mpa)
1	GPC-4M	16.49	0.73	27.74	1.05	33.34	1.07
2	GPC-6M	43.58	1.85	45.61	1.46	49.10	1.34
3	GPC-8M	45.76	1.48	50.55	1.39	57.53	1.90
4	GPC-10M	48.81	1.78	51.64	1.41	55.14	1.69
5	GPC-12M	49.25	1.17	52.30	1.26	52.74	1.14
6	CC-M35	32.08	0.92	40.42	1.19	46.50	1.21

Extending the curing period to 7 and 14 days yielded approximately 49%–93% and 83%–99% of the 28-day compressive strength, respectively. This proves that the inclusion of GGBS improved the early age strength. The presence of soluble calcium ions contributed to this, and the rapid reaction with an alkaline activating solution resulted in the formation of an amorphous Geopolymer gel [⁴⁵,⁴⁶,⁴⁷,⁴⁸]. The presence of alumina and silica in fly ash and calcium in GGBS significantly increased the compressive resistance of Geopolymer concrete at ambient temperature. The polymerization reaction between an alkaline solution and silica-alumina-rich precursors yields sodium aluminate silicate hydrate (NASH) and calcium aluminate silicate hydrate (CASH) gels, which drive strength development in geopolymer concrete [⁴⁹]. Concurrently, the available calcium content generates auxiliary calcium silicate hydrate (C-S-H) phases, mirroring the traditional hydration products observed in Ordinary Portland Cement concrete [⁵⁰].

Compared with OPC concrete, the strength of Geopolymer concrete mixes of GPC-4M and GPC-6M showed 8.93–9.56% and 5.60–6.23% higher 28-day compressive strengths, respectively. The maximum compressive strength of 57.53 MPa was recorded in the Geopolymer mix of GPC-8M at 28 days of ambient curing, which is 23.72% higher than that of the control concrete. Beyond the GPC-8M mix (GPC-10M and GPC-12M), a slight decline in compressive strength was observed at 28 days of curing. This occurred because of the excess leachable silica content, which hampers the polymerization reaction [⁵¹]. Because the quantity of SS and SH influences the microstructure of Geopolymer concrete, it affects its compression resistance [⁵²]. The polymerization process may be affected by the higher concentration of the alkaline solution, resulting in lower strength development [⁵³, ⁵⁴]. The strengths of the Geopolymer concrete mixtures,GPC-6M, GPC-8M, GPC-10M, and GPC-12M, were higher than that of the conventional concrete at all curing ages. However, the GPC-4M mix achieved lower strength compared to the control concrete, indicating that the activating solution concentration was insufficient to activate the source materials. Similarly, the rate of increase in strength was low compared to the other Geopolymer mixes and conventional concrete. The results indicated that the ambient-cured Geopolymer concrete mixtures of GPC-6M, GPC-8M, GPC-10M, and GPC-12M are suitable for replacing conventional concrete while maintaining an equivalent 28-day compressive strength threshold.

6.3. Flexure test on reinforced concrete beam

The flexural behavior of reinforced Geopolymer concrete beams cast with different alkaline solution concentrations of 4M, 6M, 8M, 10M, and 12M were investigated by applying a monotonic load. The findings of the flexure tests performed on the Geopolymer concrete beam specimens were compared with those of the conventional reinforced cement concrete beam. The experimental results were used to evaluate the structural parameters, such as the first crack load, yield load, ultimate load, neutral axis depth, theoretical and actual moment capacity, deflection under loading points, ductility, initial stiffness, energy absorption capacity, and energy index.

6.3.1. Load–deflection characteristics

A typical OPC concrete beam and five different reinforced GPC beams with variable concentrations of SH were tested under an increasing loading rate until failure, and the resulting deflections for each load application were observed. For the GPC mixes, the load-deflection curves were constructed between the applied loads and the achieved midspan deflections, as shown in Figure 12, which also represents the load-deflection behavior of a control reinforced concrete beam. For all the Geopolymer concrete and cement concrete beam specimens, a similar pattern was identified in the load-deflection responses cited in literatures [⁵⁴, ⁵⁵].

Figure 12
Load-deflection responses of reinforced geopolymer and cement concrete beam.

Two key stages are generally identifiable in the load-deflection behavior. Initially, there was a linear line with a steep slope corresponding to the uncracked condition of the beam. However, the slope continued to decline as cracks began to appear. Subsequently, the deflection is minimized at similar load levels owing to the increasing compressive resistance of concrete [⁵⁶]. In addition, the deflection of the beam specimen reached its maximum value before failure, regardless of the alkaline solution concentration. Accordingly, GPC-4M, GPC-6M, GPC-8M, GPC-10M, GPC-12M, and CC-M35 attained maximum deflections of 21.80 mm, 28.40 mm, 34 mm, 32.60 mm, 31.50 mm, and 26 mm, respectively.

The depicted load-deflection curves were used to calculate the yield load using a bilinear trend. While the yield load of a control concrete beam specimen was 50 kN, the obtained yield loads for Geopolymer mixes made with SH molarities of 4M to 12M at an increment of 2M were found to be 38, 60, 70, 68, and 66 kN, respectively. The Geopolymer mix of GPC-8M achieved the maximum yield load, which was 40% higher than that of conventional concrete. The tensile reinforcement attained its yield strength before failure because all the test beams were designed as under-reinforced sections. The following sections present the impact of various parameters on the flexural behavior of the reinforced concrete beam specimens.

6.3.2. First crack load and ultimate load

The results of the first crack load and ultimate load-carrying capacity of the Geopolymer and control concrete beam specimens are tabulated in Table 9. Because it is challenging to accurately establish the first crack load from the load-deflection plots, the first crack load was determined during the flexural testing of the appropriate beam specimen. The recorded first-crack loads of higher molarity GPC beam higher than the first-crack load of the control concrete beam, whereas GPC-4M produced the minimum first-crack load among all mixes, which was 15.7% lower than that of the control concrete beam. The results indicated that the mix with better compressive strength was responsible for the delay in initial cracking [⁵⁶]. All the reinforced concrete beams exhibited initial cracking close to the loading point in the pure bending zone.

Table 9
Salient features of load-deflection responses.

SL. NO.	BEAM ID	LOAD IN kN AT			DEFLECTION IN mm AT
		FIRST CRACK	YIELD	ULTIMATE	FIRST CRACK	YIELD	ULTIMATE
1	GPC-4M	32	38	64	4.00	4.80	21.80
2	GPC-6M	46	60	84	3.80	5.30	28.40
3	GPC-8M	56	70	112	3.40	5.40	34.00
4	GPC-10M	50	68	97	3.90	5.80	32.60
5	GPC-12M	48	66	94	3.60	5.80	31.50
6	CC-M35	38	50	78	4.10	5.10	26.00

It was also stated that the Geopolymer concrete mixes with higher SH concentrations improved both the first crack and ultimate load compared to the conventional concrete beam. However, overall, the GPC-4M mix performed inferior than the control and other Geopolymer concrete mixes. The compressive resistance of Geopolymer concrete also had a significant impact on the first crack and ultimate load, particularly when the compressive strength increased from 33.34 MPa (GPC-4M) to 57.53 MPa (GPC-8M). Figure 13 displays the relationship between the ultimate load value and its corresponding deflection.

Figure 13
Ultimate load vs. Ultimate deflection.

6.3.3. Crack pattern and spacing

All the reinforced Geopolymer and conventional concrete beams were tested until their ultimate load-carrying capacity. Initially, no cracks were observed in any of the beam specimens. As the load progressed, all the beams started to deflect, and flexural cracks were formed in the tension zone along the length of the reinforced concrete beam, particularly in the constant moment region. The existing cracks progressed, and additional cracks developed along the beam span as the load increased. As projected, the cracks propagated from the tension face to the compression face, and their width increased as the applied load increased. When the loads approached their maximum capacity, several cracks appeared and expanded. Few shear cracks were formed between the pure bending zone and the support section whenever the applied load was between 70-80% of their ultimate capacity. Variation in the crack width was also observed near the application of the ultimate load. The graphical representations of the number of cracks that manifested and the maximum crack width are shown in Figure 14.

Figure 14
Details of number of cracks and maximum width of cracks.

The transition from GPC-4M to GPC-8M resulted in a significant increase in peak load and a refined crack distribution. This phenomenon is supported by BENDAPUDI [⁵⁷] who observed that increasing alkaline activator molarity enhances flexural strength and bond-anchorage. Furthermore, a denser microstructure in high-molarity GPC helps in resisting micro-crack propagation [⁵⁸], leading to the closely spaced, narrower flexural cracks observed in our 8M and 10M specimens.

As shown in Figure 14, compared to the other Geopolymer and ordinary concrete specimens, the remaining Geopolymer concrete beams cast with lower concentrations of SH (4M and 6M) developed more cracks before collapse. Whereas the GPC-12M and control concrete specimens failed after the formation of seven cracks, the Geopolymer mixes of GPC-8M and GPC-10M deflected with six cracks. This indicates that the mixture with greater compressive strength had deteriorated by a smaller number of thinner cracks [⁵⁶]. Consequently, the maximum crack width of 3.5 mm was observed in the GPC-8M beam specimen, whereas the maximum crack widths of the other beams were 7.5, 6, 4.5, 5, and 5.5 mm for GPC-4M, GPC-6M, GPC-10M, GPC-12M, and CC-M35, respectively. Following this, narrower cracks appeared in the Geopolymer concrete produced with the SH concentrations of 8M, 10M, and 12M when compared to the control concrete beam. The crack patterns of every tested specimen of Geopolymer and OPC concrete are shown in Figure 15a-f.

Figure 15
(a-f) Crack patterns of conventional and Geopolymer concrete beams (a) GPC-4M beam, (b) GPC-6M beam, (c) GPC-8M beam, (d) GPC-10M BEAM, (e) GPC-12M beam and (f) CC-M35 beam.

The crack patterns and their propagation in the Geopolymer concrete beams were nearly identical to the cracking behavior of the control concrete beam [⁵⁹]. In the GPC-8M, GPC-10, and GPC-12M beams, almost all major vertical cracks were visible under the flexure zone. In contrast to the control concrete beam, which showed a few significant shear cracks, the shear spans of the GPC-4M and GPC-6M mixes showed vertical and minor inclined cracks. It reveals that a strong bond between the Geopolymer gel and the aggregate surface enhanced the tensile and shear strength of Geopolymer concrete [¹¹].

6.3.4. Neutral axis depth and mode of failure

For the given section, the Neutral Axis (NA) depth was calculated as 36.15 mm by equating the internal forces (Compression = Tension). The limiting NA depth for Fe-500 steel and given cross section is 97.52 mm. Since, all specimens (GPC and CC) are categorized as highly under-reinforced. This explains the observed ductile failure mode, where yielding of the tension steel occurred significantly before concrete crushing, providing ample warning through the development of progressive flexural cracks. The shallow NA depth leads to a larger lever arm, which, combined with the high molarity of the geopolymer matrix in GPC-8M, resulted in refined crack spacing and a higher number of narrower cracks compared to the CC-M35 control beam.

A significant increase in ultimate load capacity was observed as the NaOH molarity increased, specifically a 75% increase between the GPC-4M (64 kN) and GPC-8M (112 kN) specimens. While the reinforcement ratio remained constant, this behavior is attributed to the accelerated dissolution of reactive silica and alumina at higher alkaline concentrations, leading to a denser sodium aluminosilicate hydrate (N-A-S-H) gel matrix. This denser microstructure significantly enhances the bond strength between the geopolymer matrix and the reinforcement, which minimizes interfacial slip and allows for more efficient load mobilization compared to lower molarity mixes [⁶⁰].

Figure 16 illustrates the failure modes of the tested reinforced concrete beams. As revealed in Figure 15, it is important to observe that regardless of the alkaline solution concentration, all Geopolymer concrete beams behaved and failed like reinforced conventional concrete beams [⁶¹]. The failure in all the beams was initiated by the yielding of the tension reinforcement in the tension zone, followed by the crushing of concrete, which is also a common failure of under-reinforced beam specimens.

Figure 16
Failure modes of tested reinforced concrete beams.

6.3.5. Experimental vs. calculated moment capacities

The calculated neutral axis depth of 36.15 mm (x_u/d = 0.17) which is substantially lower than the limiting value (x_{u, max}/d = 0.46).This confirms that the failure was governed by steel yielding rather than concrete crushing. Recent study [⁶²] suggest that GPC exhibits a more gradual stress-strain degradation compared to OPC, when combined with a shallow neutral axis, enhances the section’s rotational capacity and ductility. The comparisons between the experimental and calculated flexural capacities are displayed in Table 10.

Table 10
Experimental vs.calculated flexural capacities of GPC & OPC concrete beams.

SL. NO.	BEAM ID	Mexp (kNm)	Mcalc (kN)	ACCURACY RATIO (Mexp/ Mcalc)	FAILURE MODE
1	GPC-4M	19.20	13.45	1.43	Flexure/ Ductile
2	GPC-6M	25.20	13.45	1.87
3	GPC-8M	33.60	13.45	2.50
4	GPC-10M	29.10	13.45	2.16
5	GPC-12M	28.20	13.45	2.10
6	CC-M35	23.40	13.45	1.74

The high (M_exp/M_calc) ratios (up to 2.50) indicate that standard design codes provide conservative estimates for GPC flexural capacity. OMID [⁶³] found that while numerical models based on ACI 318 are applicable for the linear range, they often underestimate post-yield performance. This underestimation is attributed to the extensive strain-hardening of the reinforcement, which is facilitated by the superior interfacial bonding in the GPC matrix compared to OPC [⁶⁴]. According to AL-JABALI et al. [⁶⁴], the denser interfacial transition zone (ITZ) in fly-ash-based geopolymers improves the bond-anchorage between steel and the surrounding matrix, allowing the reinforcement to sustain stresses well beyond its yield point before any bond slip occurs. While the control beam showed a ratio of 1.74, the GPC specimens (except 4M) consistently showed higher values. This suggests that for the same 35 MPa, the flexural toughness of geopolymer concrete is inherently higher. This aligns with findings from AHMED and SHAH[⁶⁵] stating that geopolymer beams often show superior cracking moments and ultimate load-carrying capacities compared to OPC beams of similar grade. The unique alumino-silicate gel structure in GPC provides a “crack-arresting” mechanism that is inherently more efficient than the calcium-silicate-hydrate gel in conventional concrete.

6.3.6. Ductility

Ductility is the ability of a specimen to experience significant deformation without impairing its capacity to support loads before breaking. This is a crucial factor to consider when designing earthquake-resistant buildings. Therefore, the ductility must be measured. The term “ductility” is typically described as displacement, energy, or curvature ratios. In this study, the ultimate deflection was divided by the yield deflection to determine the displacement ductility [⁶⁶]. The displacement ductility was computed using Equation 1.

(1) $$\text{Displacement ductility}{\text{μ}}_{\text{d}}=\frac{\mathrm{\Delta }\mu }{\mathrm{\Delta }\text{y}}$$

Where, ∆u is ultimate deflection; ∆y is yield deflection. A comparison with the results of the conventional concrete beam is shown in the bar chart in Figure 17. The ductility of the Geopolymer concrete mix with SH molarity of 6M, 8M, 10M, and 12M produced better results, which is 5.10, 23.53, 10.20, and 6.47% higher than the ductility of the control concrete beam. In contrast, the ductility of the GPC-4M concrete beam was 10.98% lower than that of an ordinary concrete beam.

Figure 17
Displacement ductility of geopolymer and control concrete beams.

Similarly, all the Geopolymer concrete beams exhibited relative ductility values greater than 1. However, the Geopolymer concrete beam (GPC-4M) produced a relative ductility value of 0.89. The findings demonstrated that the ductility of Geopolymer concrete significantly increased as the SH concentration increased from lower (4M and 6M) to higher (8M and 12M) values. It is consistent with other research [⁶⁷], confirms that limited dissolution of precursors leads to a less dense matrix and higher brittleness at very low concentrations (like your 4M result which was 10.98% lower).Another finding on ambient-cured geopolymer concrete indicates that increasing the NaOH concentration from 4M to 6M can increase fracture parameters (related to ductility) by approximately 21.95% [⁶⁸].

6.3.7. Stiffness

Stiffness is a measure of the essential load required to cause unit deformation. In the present study, the initial stiffness was calculated using the gradient of the tangential taken from the origin of the load-deflection curve. A comparison of the stiffnesses of the Geopolymer and ordinary concrete beams is shown in Figure 18. The Geopolymer concrete beams of GPC-8M and GPC-4M had maximum and minimum stiffness values of 15.55 and 8.08 kN/mm, respectively. The beam specimens, such as GPC-6M, GPC-8M, GPC-10M, and GPC-12M achieved 53.71, 92.45, 58.79, and 63.74% greater values when compared to the stiffness value of GPC-4M concrete beam (lowest molarity), while the same value of the control concrete beam was 21.78% higher. This enhancement is attributed to the more complete geopolymerization process at higher concentrations, which yields a denser and more rigid binder matrix [⁵⁷]. Recent comparative studies under cyclic loading further validate these findings, showing that optimized GPC beams (8M–12M) maintain their structural integrity longer than OPC, demonstrating slower stiffness degradation and8–32% higher cumulative energy absorption [⁶⁹].

Figure 18
Stiffness results of geopolymer and control concrete beams.

6.3.8. Energy absorption capacity

The capacity of a structure to absorb energy is essential when designing it for earthquake resistance. The energy absorption capacity refers to the flexural toughness and is often characterized as the area under the load-deflection plot. The safety of the structure during seismic motion can be assessed by comparing the input energy imparted to the structure by the earthquake with its capacity for energy absorption. A pictorial representation of the energy absorption capacities of various Geopolymer and control concrete beams is provided in Figure 15. As specified in Figure 19, all of the reinforced Geopolymer concrete beams, except GPC-4M, absorbed more energy than the conventional reinforced concrete beam.

Figure 19
Energy absorption capacity of geopolymer and control concrete beams.

The GPC-8M Geopolymer concrete beam had a maximum energy absorption capacity of 3125 kN-mm, which is 96.42 percent more than a conventional concrete beam. The other Geopolymer concrete beams, such as GPC-6M, GPC-10M, and GPC-12M absorbed more energy than the OPC concrete beam by 25.02, 65.93, and 54.31%, respectively. But compared to conventional concrete beams, the specimen of a reinforced concrete beam constructed with GPC-4M mix had a 33.44% lower energy absorption capacity. This might be explained by the fact that the formation of a strong interfacial transition zone in Geopolymer concrete enhanced the tensile and shear strength of the concrete [⁷⁰].

6.3.9. Energy index

The energy absorption capacity ratio of ultimate load to first crack load level is referred to as the energy index. Figure 20 compares the energy index of reinforced Geopolymer concrete beams with the relative performance of the control concrete beam. Apart from the GPC-4M concrete beam, the other Geopolymer concrete mix possesses more energy index values as it could absorb greater energy before failure. It is obvious that GPC-10M and GPC-12M Geopolymer concrete mixes produced roughly similar amounts of energy index; however, the GPC-8M concrete beam showed the highest amount of energy index.

Figure 20
Energy index of different reinforced concrete beams.

In contrast to the Geopolymer concrete beam manufactured with 4M molarity of SH, the Geopolymer concrete beam specimens such as GPC-6M, GPC-8M, GPC-10M, and GPC-12M developed relatively 21.79, 72.53, 52.22, and 49.51% superior observations of energy index, respectively. This indicates that the capacity to absorb energy and the assessment of the energy index are both positively affected by the increasing concentration of the alkaline solution.

7. SUSTAINABLITY CLAIMS

The utilization of Fly Ash and GGBS as primary binders suggests a qualitative reduction in the carbon footprint compared to traditional OPC-based concrete, primarily due to the diversion of industrial by-products from landfills and the avoidance of high-temperature clinker production [⁷¹]. However, the net sustainability of the proposed GPC-8 M mix is influenced by the environmental burden of chemical activators, such as Sodium Hydroxide and Sodium Silicate, which are energy-intensive to manufacture [⁷²].

While ambient curing eliminates the thermal energy typically required for geopolymerization, the high molarity (8 M–12 M) used in this study introduces a significant chemical footprint [⁷³]. Therefore, while GPC-8 M shows mechanical potential as an M35 alternative, its sustainability profile remains indicative and requires further quantitative validation through a site-specific Life Cycle Assessment (LCA) to account for transportation and chemical processing impacts [⁷⁴].

8. CONCLUSIONS

This study evaluated the fresh-state rheology and flexural performance of ambient-cured Geopolymer Concrete as a potential sustainable alternative to M35 grade conventional concrete. The following conclusions are drawn:

• Rheological Thresholds: GPC mixes exhibited significantly higher yield stress compared to conventional concrete. Slump values decreased by up to 79% (from 95 mm to 21 mm) as SH molarity increased to 12M, while Vee-Bee times increased from 7.5 s to 23.6 s. This indicates a practical workability limit at 8M, beyond which the increased dynamic viscosity and solid content of the activator hinder effective compaction.

• Compressive Strength Evolution: The inclusion of GGBS facilitated early-strength development through calcium-silicate-hydrate (C-S-H) formation. Except for GPC-4M, all GPC mixes achieved 80–93% of their 28-day strength within 7 days. While GPC-4M attained an M25 equivalent, the GPC-8M mix reached a peak mean strength of 57.53 MPa, exceeding the M35 target by 24%.

• Statistical Significance of Molarity: A clear parabolic trend was observed in mechanical performance. Increasing molarity from 8M to 12M resulted in an 8.3% reduction in compressive strength and a decline in ultimate flexural load. This post-peak decline is statistically significant and correlates with the reduced workability and increased micro-porosity of high-viscosity mixes.

• Structural Flexural Capacity: GPC beams with 6M molarity outperformed the CC-M35 control in both first-crack and ultimate load levels. GPC-8M demonstrated a peak ultimate load of 112 kN (a 43.6% increase over control) and superior energy absorption. Conversely, the GPC-4M beam showed inferior performance, indicating that a 4M activator concentration is insufficient for structural-grade geopolymerization.

• Predictive Accuracy: The standard limit state equations (IS 456 / ACI 318) provided conservative estimates of flexural capacity (M_calc = 13.45 kNm). The high accuracy ratios (from 1.43 to 2.50) are attributed to the strain-hardening of the reinforcement, which is facilitated by the superior bond-anchorage in the geopolymer matrix.

• Serviceability and Ductility: The maximum deflection of GPC-8M (34.00 mm) was 30.7% higher than the control (26.00 mm), indicating enhanced ductility. Initial stiffness varied significantly with molarity, peaking at 15.55 kN/mm for GPC-8M, nearly double that of the 4M mix (8.08 kN/mm).

• Qualitative Sustainability Potential: The replacement of traditional OPC with FA and GGBS-based geopolymer binders significantly enhances the sustainable profile of structural concrete. While the indicative findings affirm GPC’s potential as an eco-friendly M35 alternative, these implications remain qualitative in the absence of quantitative Life Cycle Assessment (LCA) or CO₂ emission data.

9. LIMITATIONS & FUTURE RECOMMENDATIONS

The primary limitation of this research is the reliance on single-beam specimens, which precludes the determination of a Coefficient of Variation. Furthermore, the scope is restricted to short-term flexural behavior under a single aggregate source, without addressing critical factors such as shear capacity, bond strength, or long-term durability. The investigation was limited strictly to ambient curing. While this is more sustainable and practical for field applications, the results may not reflect the potential strength gains achievable through heat or steam curing common in precast geopolymer concrete.

The practical application of high-molarity mixes also faces handling and safety challenges that must be balanced against their mechanical benefits. Consequently, while this study affirms the qualitative sustainability potential of GPC, future research with multiple replicates and quantitative Life Cycle Assessment (LCA) is essential to establish the statistical confidence and durability profiles required for standardized structural design.

10. ACKNOWLEDGMENTS

The authors express their gratitude to the Government College of Engineering, Tirunelveli, and Alagappa Chettiar Government College of Engineering and Technology, Karaikudi for their essential technical support in this research.

11. DATA AVAILABILITY

The full dataset supporting the findings of this study is available upon request to the corresponding author [Sasi Rekha Muniyasamy, Assistant Professor, Department of Civil Engineering, Government College of Engineering, Tirunelveli, India]

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Publication Dates

• Publication in this collection
  10 Aug 2026
• Date of issue
  2026

History

• Received
  20 Nov 2025
• Accepted
  13 July 2026