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Article

Sustainable High-Performance Geopolymer Concrete: The Role of Recycled Industrial Wastes in Strength, Durability, and Microstructure Enhancement

by
Osama Youssf
1,2,*,
Ahmed Mohamed Abbass
1,3,
Ahmed K. Ahmed
1 and
Ahmed M. Tahwia
1
1
Structural Engineering Department, Mansoura University, Mansoura 35516, Egypt
2
Civil Engineering Department, Horus University-Egypt, New-Damietta 44921, Egypt
3
Department of Civil and Environment Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
*
Author to whom correspondence should be addressed.
Infrastructures 2025, 10(9), 241; https://doi.org/10.3390/infrastructures10090241
Submission received: 12 June 2025 / Revised: 22 August 2025 / Accepted: 10 September 2025 / Published: 12 September 2025
(This article belongs to the Special Issue Advances in Reinforced Concrete Infrastructure: Enhancing Structural Resilience and Promoting Sustainability)
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Abstract

High-performance geopolymer concrete (HPGC) is an eco-friendly type of concrete that is traditionally made of slag, silica fume (SF), and quartz sand. Recycling industrial waste in HPGC presents an eco-friendly approach for maximizing sustainability in the construction sector. This study evaluates the impact of incorporating recycled fine aggregates like crumb rubber (CR), glass waste (GW), and ceramic waste (CW) as partial replacements for quartz sand in HPGC at 10%, 20%, and 40% by volume. GW and CW were also used in binder size as full replacements for SF. The novelty of this research lies in its comprehensive evaluation of waste-integrated HPGC under diverse conditions, including mechanical performance, durability (water absorption, sulfate/chloride/acid resistance), thermal stability (up to 600 °C), and microstructure analysis, while addressing critical gaps in eco-friendly construction materials. The results indicate that CW significantly enhanced compressive strength, increasing by 24–29% at 10% and 40% replacement levels, whereas CR reduced strength by 69.2–83.5%. GW effectively decreases water absorption by 66–72% compared to CW and CR. Both CW and GW improved chemical resistance, reducing compressive strength loss by 15–33% under sulfate and acid attacks. CW exhibited superior residual strength at 600 °C, reaching 96.4 MPa, compared to 54.5 MPa for GW. However, fully replacing SF with GW or CW as a binder resulted in performance deterioration, making it unsuitable. This study demonstrates that incorporating recycled waste materials in HPGC enhances its mechanical and durability properties, making it a viable option for sustainable construction. The findings support the integration of CW and GW as eco-friendly alternatives in HPGC applications.

1. Introduction

The escalating global population and proliferation of high-rise infrastructure have positioned Portland cement as the most widely used construction material globally. Nevertheless, its production poses substantial environmental challenges due to the emission of large quantities of CO2 [1]. As highlighted by Mokhtar and Nasooti [2], the energy-intensive manufacturing process of Portland cement concrete further exacerbates its ecological footprint. In response, research efforts have focused on developing sustainable binder alternatives, such as geopolymer-based materials, to mitigate these environmental impacts [3,4].
Geopolymer concrete (GC) emerges as an environmentally sustainable construction material, synthesized from aluminosilicate precursors with fine particle sizes comparable to cement. These precursors, rich in silicon (Si) and aluminum (Al), undergo alkaline activation to initiate the geopolymerization process. Common aluminosilicate sources include ground granulated blast furnace slag (GGBFS), low-calcium fly ash (FA), silica fume (SF), and metakaolin [3,5]. Alkaline activators, such as sodium hydroxide (SH) and sodium silicate (SS), are critical for dissolving aluminosilicate minerals, enabling the formation of amorphous three-dimensional networks through Si-O-Al-O linkages—a defining feature of GC synthesis [6]. The reaction products predominantly comprise amorphous aluminosilicate matrices intertwined with sodium/calcium aluminosilicate hydrate (C(N)-A-S-H) gels. Research indicates that these N-A-S-H and C-A-S-H phases are pivotal in achieving high early-age compressive strength (exceeding 50 MPa within 24 h) in GC systems [7].
While traditional GC has been extensively studied, limited research has addressed the development of high-performance geopolymer concrete (HPGC), which is engineered to surpass conventional GC in mechanical strength (more than 70 MPa) [8], durability, and environmental resilience. HPGC employs advanced material formulations and innovative methodologies to meet the demands of high-stress structural applications. For instance, Ambily et al. [9] synthesized HPGC using aluminosilicate precursors such as GGBFS and SF.
As a transformative innovation in construction materials, HPGC exhibits enhanced mechanical properties, prolonged durability, and heightened resistance to chemical, thermal, and mechanical stressors. These improvements stem from optimized mix designs that refine microstructural density and integrate waste materials, thereby elevating strength and degradation resistance. Such advancements position HPGC as a cornerstone for sustainable infrastructure development [10,11].
Recent studies emphasize the role of industrial waste integration and refined design strategies in optimizing HPGC performance [11]. Incorporating recycled materials not only enhances sustainability but also improves key attributes, including thermal stability, chemical resistance, and reduced water permeability [12]. Notably, geopolymer binders reinforced with waste-derived additives have achieved compressive strengths surpassing 90 MPa, enabling their use in high-load applications like bridges, skyscrapers, and critical infrastructure [13].
Durability assessments under extreme conditions—such as elevated temperatures, sulfate exposure, and chloride ingress—reveal HPGC’s superior long-term performance compared to conventional concrete. Its dense microstructure and tailored chemical composition mitigate degradation in aggressive environments, underscoring its viability for resilient infrastructure [14]. Furthermore, HPGC demonstrates exceptional fire resistance, avoiding the spalling and strength loss typical of traditional concrete under high temperatures. This thermal stability makes it ideal for fire-prone structures and industrial settings [15,16].
To address energy consumption in curing processes, recent research has prioritized the development of GC capable of ambient-temperature curing [1,3,17]. Concurrently, the construction industry’s excessive reliance on natural sand has raised significant ecological concerns, including resource depletion and disruption of aquatic ecosystems [18,19]. In response, studies have explored the substitution of natural sand in GC with waste-derived materials such as medical waste, industrial byproducts, brick debris, glass waste, ceramic waste, and crumb rubber [18,19,20].
Recycled glass waste (GW) has been investigated as a partial or full sand replacement in concrete. Ismail and Al-Hashmi [21] reported that substituting 20% of sand with GW enhanced flexural and compressive strengths by 11% and 4.23%, respectively, compared to conventional mixes. Conversely, Rashad et al. [22] observed that incorporating GW as a binder in slag-based geopolymer pastes increased water absorption and reduced compressive strength, particularly after exposure to 400–600 °C. However, at higher temperatures (800–1000 °C), GW exhibited a beneficial effect on strength retention.
Ceramic waste (CW), sourced from discarded tiles, sanitary ware, and electrical insulators, constitutes a major fraction of construction waste in the European Union [23]. Classified as nonhazardous, CW has been repurposed as fine or coarse aggregates in concrete, though outcomes vary depending on substitution methods and material composition [23,24,25]. For instance, previous researchers [26] achieved a 7% compressive strength increase with 5% CW content, while other researchers [27] reported an 8% increase with 100% replacement. Other studies [28,29] reported a 9% strength gain with full CW substitution. Medina et al. [16] documented an 11% increase with 25% CW, whereas a 14% enhancement with 100% replacement was recorded [30]. In contrast, studies by Elemam et al. [31], Reddy [32], Zeng and Wan [33], Cabral et al. [34], and De Brito et al. [35] reported compressive strength reductions of 3%, 5%, 9%, 28%, and 44%, respectively, at full sand replacement. Gomes and De Brito [17] further observed a 24% strength decline with 30% and 50% CW substitutions. Despite these inconsistencies, workability remained comparable to conventional concrete [23]. The integration of crumb rubber (CR) from end-of-life tires into concrete, proposed three decades ago, addresses both waste management and resource conservation challenges [36,37]. In Australia, over 50 million tires reached their end-of-life in 2014, with only 5% recycled domestically, 16% landfilled, 32% exported, and the remainder disposed of improperly, exacerbating environmental risks such as groundwater contamination from leached toxins [38,39,40,41]. While CR substitution reduces reliance on natural aggregates [42], compressive strength declines by up to 90% at high replacement levels (e.g., 100% sand substitution) [43].
As per the above literature, the effect of using waste materials to partially replace quartz sand in HPGC is not well-covered. This study evaluates the feasibility of producing eco-friendly HPGC by incorporating recycled GW, CW, and CR. Quartz sand was replaced with these wastes at doubling increments of 10%, 20%, and 40% volumetric ratios, while SF was substituted with GW and CW as supplementary binders. Mechanical, thermophysical, and microstructural properties were assessed through slump tests, unit weight measurements, water absorption analyses, chemical resistance evaluations, high-temperature exposure tests (up to 600 °C), and scanning electron microscopy (SEM). The chemical resistance of HPGC was measured under aggressive medias of 5% concentrations for 30 and 90 days, including magnesium sulfate (Mg2SO4), hydrochloric acid (HCl), and sodium chloride (NaCl) solutions. The findings aim to advance sustainable construction practices by promoting waste valorization and minimizing ecological impacts.

2. Materials and Methods

2.1. Materials Type and Characterization

The HPGC mixtures utilized slag and SF as the principal precursors, conforming to ASTM C1240-5 specifications [44]. Slag exhibited a specific gravity of 2.9 and a surface area of 390 m2/kg, whereas SF demonstrated a lower specific gravity (2.29) but a substantially greater surface area of 19,500 m2/kg. Quartz sand, characterized by a particle size of 800 μm, a specific gravity of 2.65, and a bulk unit weight of 1420 kg/m3, served as the primary fine aggregate. Additional properties included a fineness modulus of 2.20 and a water absorption rate of 0.34%. Superplasticizer (SP) (a water reducer and accreting admixture) was used in all mixes. Post-preparation images of the raw materials are depicted in Figure 1. Particle size distributions of the source materials, analyzed via laser granulometry (LA-950), are presented in Figure 2. Detailed physical properties of the raw materials and the chemical compositions of slag, SF, and quartz sand are summarized in Table 1.
In this study, GW, CW, and CR were integrated as partial substitutes for quartz sand in HPGC production. The CW aggregates, sourced from discarded wall tiles provided by local manufacturers, underwent drying in an electric furnace at 110 °C for 24 h, followed by pulverization using a Los Angeles abrasion machine to achieve fine particles. The processed CW exhibited a specific gravity of 2.62, a fineness modulus of 3.0, and a water absorption rate of 0.55%. Similarly, GW aggregates, obtained from crushed glass supplied by industrial facilities, were ground into fine particles using the same method. The resulting GW displayed a specific gravity of 2.49, a fineness modulus of 2.4, and a water absorption rate of 0.09%. As detailed in Table 1, GW contains substantially higher silica content but lower aluminum content compared to CW.
CR aggregates, derived from mechanically milled scrap car tires, featured a specific gravity of 0.98, a fineness modulus of 4.85, and a unit weight of 530 kg/m3. To optimize workability, a polycarboxylate-based superplasticizer (SP) was added at 1.5% of the total binder mass, with a specific gravity of 1.08. The alkaline activator comprised a blend of sodium hydroxide (SH) and sodium silicate (SS). SH (99.99% purity) and SS (specific gravity: 1.28, water content: 57 wt.%, silica modulus [Ms]: 2.5) were combined at a weight ratio of 1:2.5 (SH:SS). The SH solution, formulated at a 16M concentration, was prepared 24 h prior to casting by dissolving SH flakes in deionized water, followed by cooling to ambient temperature. This protocol minimized exothermic heat during mixing, ensuring a stable activator solution for HPGC synthesis.

2.2. Preparation of Specimens

The mix designs for the concrete formulations are outlined in Table 2. The control mixture (CC) was formulated with standard HPGC constituents, including slag, SF, quartz sand, alkaline activator, and superplasticizer (SP). In modified mixtures, CR, GW, and CW were substituted for quartz sand at volumetric ratios of 10%, 20%, and 40%. These replacement ratios were selected to measure the effect of doubling the increment in replacing the original material. Mix nomenclature reflects the replacement material and percentage (e.g., CR10, GW20). In GW100SF and CW100SF formulations, SF was entirely replaced by GW-derived powder (GWP) and CW-derived powder (CWP), respectively. For all other mixes, SF content was fixed at 10% by volume. Slag, sodium hydroxide (SH), sodium silicate (SS), and SP contents remained fixed at 90, 12.86, 32.14, and 1.5 vol.%, respectively. The alkali activator-to-binder ratio was held constant at 0.45 for all mixes.
The mixing procedure commenced with a 3 min dry blending of all solid constituents. Subsequently, the alkali activator was introduced, and the mixture underwent an additional 3 min of mechanical mixing. The freshly prepared concrete was transferred into molds and subjected to vibration to expel entrapped air. Specimens were cured under ambient conditions (27 °C, 90% relative humidity) for 24 h before demolding. Post-demolding, the samples were heat-cured in an electric oven at 80 °C for 48 h to facilitate complete geopolymerization.

2.3. Experimental Methods

The workability of HPGC was quantified via slump testing, performed using a mini-slump cone apparatus (height: 114 mm, top diameter: 38 mm, base diameter: 76 mm) in compliance with the AS1012.3.5 standard [43]. Compressive strength was evaluated at 7-, 28-, and 56-day intervals using triplicate 50 mm3 cubic specimens per test age. Testing was executed on a 600 kN universal compression machine under a controlled loading rate of 0.6 MPa/s, adhering to ASTM C109 [45].
Water absorption was determined at 28 days following ASTM C1585-13 [46]. Specimens (50 mm3) were oven-dried at 100 °C for 24 h, followed by gravimetric measurement of dry mass. Subsequent immersion in tap water for 48 h enabled saturation, after which saturated mass was recorded. Water absorption (%) was calculated as:
W a t e r   a b s o r p t i o n = S a t u r a t e d   m a s s − D r y   m a s s D r y   m a s s × 100
Post 28-day curing, 12 specimens per mix were thermally conditioned in an electric oven. Samples were heated to 300 °C and 600 °C at a ramp rate of 8 °C/min and held isothermally for 1.5 or 3.0 h. Controlled cooling within the furnace mitigated thermal shock risks. Residual compressive strength was reassessed post-exposure to quantify thermal degradation.
Microstructural analysis of ultra-high-performance geopolymer concrete (UHPGC) was conducted via scanning electron microscopy (SEM; JSM-6510LV, Mansoura University, Mansoura, Egypt). Thin sections (0.5 mm) of ambient-cured samples were analyzed to elucidate the microstructural characteristics and interfacial bonding mechanisms within the geopolymer matrix.
Chemical resistance was evaluated by immersing 50 mm3 cubes in 5% solutions of Mg2SO4, NaCl, and HCl for 30- and 90-day immersion periods. Post-immersion, mass loss and compressive strength degradation were measured to assess material performance in aggressive chemical environments.

3. Result and Discussion

3.1. Workability

The measured slump values for the HPGC mixes are shown in Figure 3. The control mix recorded a slump of 8.5 cm. Among the mixes incorporating CR, the highest workability was observed in the CR10% mix with a slump of 7.8 cm, whereas the CR40 mix had the lowest slump. In the case of GW, the GW40 mix exhibited the highest slump value of 8.6 cm, while the GW10 mix had the lowest slump of 8.2 cm. For CW, the CW10 mix achieved the highest slump of 7.75 cm, whereas the CW40 mix recorded the lowest at 6.0 cm. Overall, the results indicate that the inclusion of CR and CW negatively impacted the workability of HPGC, whereas incorporating GW led to a slight improvement in workability. It can also be observed that the workability increased with the inclusion of GW, and further increased by raising the GW dosage. The reason for this phenomenon is the low friction coefficient and low water absorption of glass particles, which enhance the flow rate. On the other hand, when 10%, 20%, and 40% of fine aggregate were replaced by CR, the workability decreased. Therefore, the inclusion of 40% CR had the lowest workability owing to the hydrophobic characteristic and high friction coefficient of rubber particles that increases the flow resistance.

3.2. Physical and Mechanical Properties

3.2.1. Unit Weight

The unit weight of all HPGC mixtures was assessed using 28-day-cured compressive strength specimens, as depicted in Figure 4. The unit weights exhibited a range of 2019.1 kg/m3 to 2267.5 kg/m3. Results revealed that CW-modified mixes yielded the highest unit weight values, exceeding the CC due to the elevated water absorption characteristics of CW aggregates, which reduced pore formation during curing. Conversely, GW-incorporated mixes demonstrated unit weights comparable to the control, attributed to the lower water absorption capacity and advantageous particle morphology of GW. Notably, a 10% GW substitution for quartz sand exhibited negligible impact on unit weight. In contrast, CR integration reduced unit weight significantly, a consequence of the inherently low density and hydrophobic properties of rubber particles, which increased void content (after free water evaporation) within the matrix and hence lowered unit weight.

3.2.2. Water Absorption

Figure 5 illustrates the 28-day water absorption (WA) characteristics of HPGC mixtures. At 10% CR substitution for quartz sand, the WA measured 2.4%. Increasing CR content to 40% elevated WA by 15%, a phenomenon linked to heightened void formation (after free water evaporation) caused by suboptimal interfacial bonding between hydrophobic rubber particles and the geopolymer matrix.
CW-modified HPGC exhibited WA values spanning 1.33% to 3.35%, with the control mix (1.68%) demonstrating the lowest absorption. GW outperformed both CR and CW, achieving the minimal WA across all substitution levels. A 10% GW replacement yielded a WA of 1.85%, with further increments reducing absorption by ~66%, attributable to GW’s low porosity and enhanced particle packing.
At 40% CW replacement, WA surged by 150% relative to the 10% CW mix, driven by unreacted Al- and Si-rich ceramic particles accumulating within the matrix. WA values for 10%, 20%, and 40% CW substitutions were 1.33%, 3.3%, and 3.35%, respectively, consistent with prior studies documenting gel phase evolution in CW-incorporated systems [47,48]. While Rashad et al. [22] reported reduced WA in ultra-HPGC with ceramic powder, the current results align with established thresholds, corroborating the existing literature. In summary, GW demonstrated superior efficacy in minimizing WA, with incremental substitution significantly enhancing HPGC durability by mitigating water ingress.

3.2.3. Compressive Strength

Compressive strength, a critical metric for assessing HPGC, serves as a primary indicator of structural integrity. The evolution of HPGC’s mechanical performance was evaluated through compressive strength testing at 7-, 28-, and 56-day intervals, as depicted in Figure 6, Figure 7 and Figure 8. Experimental results demonstrated that waste material incorporation significantly influenced strength development, with CR substitution exhibiting the most pronounced compressive strength degradation (Figure 6).
The control mix achieved compressive strengths of 90 MPa (28 days) and 94 MPa (56 days). A 10% CR substitution reduced strength by 7.45% relative to the control, a marginal decline attributed to the synergistic interaction of sodium hydroxide (SH) and sodium silicate (SS) in the alkaline activator. Pretreatment of CR particles with SH partially mitigated interfacial incompatibility, attenuating strength loss at lower substitution levels [39]. However, higher CR replacements (20% and 40%) induced pronounced strength degradation, yielding 28-day values of 56.6 MPa (−37.1%) and 24.5 MPa (−72.7%), respectively. This marked deterioration correlates with incomplete SH-mediated surface modification of CR particles, resulting in unreacted, smooth-surfaced rubber aggregates that weakened interfacial adhesion. Additionally, CR’s low elastic modulus generated localized tensile stresses, promoting premature matrix cracking and strength reduction [42].
The hydrophobic nature of CR further exacerbated void formation, as air bubbles nucleated on rubber surfaces during mixing and propagated through the matrix [38,49,50]. Elevated air content, a well-documented consequence of rubber incorporation, reduced load-bearing capacity by introducing discontinuities in the geopolymer network [39,49]. These findings align with prior studies, underscoring the trade-off between waste valorization and mechanical performance in rubberized HPGC.
Figure 7 illustrates the compressive strength evolution of HPGC mixtures incorporating varying proportions of GW as a quartz sand substitute. The 40% GW formulation exhibited peak compressive strengths of 94.8 MPa (7 days), 96.7 MPa (28 days), and 102.4 MPa (56 days), demonstrating a positive correlation between GW substitution levels and mechanical performance. Specifically, incremental replacement of quartz sand with GW yielded progressive strength gains, culminating in a 12.9% and 18.6% enhancement at 40% GW relative to 20% and 10% substitutions, respectively.
This strength enhancement is mechanistically linked to the pozzolanic reactivity of amorphous silica in GW, which promotes microstructural densification through the formation of calcium–sodium–silicate–hydrate (C-N-S-H) phases. These reaction products enhance interfacial cohesion within the geopolymer matrix, thereby optimizing load-bearing capacity. The observed trend aligns with the superior particle packing efficiency and chemical compatibility of GW-derived silica, which facilitates robust geopolymerization kinetics compared to lower substitution levels. The reason the glass-containing mix (GW) showed a traditional strength gain pattern, unlike the CC mix, lies in the nature of its chemical reactions following a normal, healthy strength development curve because its main strength-enhancing component (the crushed glass) works over the long term. This is a desirable trait, as it indicates a more durable concrete that will continue to gain strength over time.
Figure 8 delineates the compressive strength progression of CW-modified HPGC mixtures. The 40% CW formulation exhibited peak mechanical performance, attaining compressive strengths of 108 MPa (7 days), 110 MPa (28 days), and 121.1 MPa (56 days). This aligns with findings by Rashad and Essa [51], who reported accelerated early-age strength development in alkali-activated CW systems, particularly within the initial 7-day curing period.
The enhanced mechanical properties are attributed to CW-induced modulation of cross-linked aluminosilicate networks, which govern microstructural evolution within the geopolymer matrix. In the control mix, optimal dissolution kinetics of aluminosilicate precursors under alkaline activation facilitated the formation of calcium–aluminum–silicate–hydrate (C–A–S–H) and sodium–aluminum–silicate–hydrate (N–A–S–H) phases. These reaction products densified the microstructure, thereby augmenting load-bearing capacity.
The superior strength gain in CW-incorporated systems arises from the synergistic co-precipitation of calcium–sodium–silicate–hydrate (C–N–S–H) and calcium–silicate–hydrate (C–S–H) phases. This is driven by the elevated bioavailability of amorphous aluminosilicate species derived from ground granulated blast furnace slag (GGBFS) and reactive silica nanoparticles, which act as nucleation sites for geopolymer gel formation. The resultant matrix exhibits reduced porosity and enhanced interfacial cohesion, corroborating the observed mechanical superiority of high-CW formulations.
Figure 9 demonstrates that full replacement of SF with GWP or CWP in HPGC formulations significantly reduced compressive strength. The CW-substituted mix exhibited a 32% strength reduction compared to the control, while GW substitution resulted in a milder 17% decline. This disparity underscores SF’s critical role in geopolymerization, where its high amorphous silica content accelerates the formation of calcium–silicate–hydrate (C–S–H) and sodium–aluminosilicate–hydrate (N–A–S–H) phases. These reaction products enhance matrix densification and interfacial bonding, which are pivotal for mechanical strength. The inferior performance of CWP and GWP highlights their limited pozzolanic reactivity relative to SF, impeding optimal geopolymer network development.
Based on the above results, it is clear that when 10%, 20%, and 40% of sand were replaced with industrial waste materials, the CW mixes consistently achieved the highest compressive strength, while the CR mixes consistently showed the lowest.

3.2.4. Residual Compressive Strength Under Elevated Temperatures

The thermal performance of HPGC is a critical determinant of its structural resilience in fire-prone or high-temperature environments. This investigation analyzes the residual compressive strength of HPGC formulations incorporating CR, CW, and GW as partial/full substitutes for conventional aggregates, following exposure to 300 °C and 600 °C for 1.5 and 3.0 h (Figure 10). Results revealed no linear correlation between heating duration and residual compressive strength, with variability attributed to the heterogeneous thermal response of waste-modified matrices.
The integration of CR into HPGC formulations induced nonlinear compressive strength fluctuations at 300 °C, a phenomenon linked to CR’s proximity to its thermal decomposition threshold (~300 °C) [52,53]. The irreversible thermoplastic degradation of CR, compounded by heterogeneous thermal gradients, precipitated significant mechanical variability. Specimens with 40% CR substitution (R40) exhibited a 60% strength reduction relative to the control mix, whereas R10 formulations demonstrated a mitigated decline of 27.6%, highlighting the inverse proportionality between rubber content and thermal stability.
In contrast, CW-modified HPGC displayed superior residual compressive strength across all thermal regimes (300–600 °C) [54]. At 600 °C with 3 h exposure, CW substitutions (10–40%) retained 50–60% of their ambient-temperature strength. This enhancement is mechanistically attributed to alkali-activated sintering of unreacted crystalline phases within CW, which promotes matrix densification via solid-state reactions at elevated temperatures [51]. Additionally, CW’s role as a thermally stable fine aggregate mitigates interfacial debonding at the binder-aggregate interface under thermal stress. Two synergistic mechanisms underpin CW’s efficacy: (1) pore occlusion by thermally softened CW particles, which reduces microcrack propagation, and (2) interfacial bond reinforcement through partial surface nitrification of CW at 600 °C, as observed in prior studies [51].
GW-incorporated HPGC exhibited lower residual strength than CW, a consequence of GW’s coarser particle size distribution (D50 >150 µm) and propensity for void nucleation under thermal cycling. However, GW partially offset aggregate-binder debonding caused by differential thermal expansion, albeit at the expense of increased matrix porosity. Despite these limitations, GW-modified mixes retained structural integrity without spalling, preserving >97% of baseline strength at 300 °C (10% GW) and exhibiting only a 3% strength reduction under prolonged 600 °C exposure. Notably, 40% GW substitution achieved 50% higher residual strength than 10% GW, a counterintuitive result attributed to partial rehydration of degraded calcium–sodium–silicate–hydrate (C–N–S–H) gels and hydroxyl group depletion, offset by GW’s latent pozzolanic reactivity [55].

3.2.5. Thermo-Physical Appearance and Mass Change

Visual inspection serves as a diagnostic tool for evaluating thermomechanical behavior, including chromatic alterations, microfracture propagation, and spalling resistance. Table 3 catalogs the post-thermal morphological evolution of control and modified HPGC specimens (CR-, GW-, and CW-incorporated mixes at incremental quartz sand substitutions, alongside full SF replacement with GWP/CWP) across elevated temperatures. Below 300 °C, specimens exhibited negligible macroscopic morphological alterations. At 300 °C, the control mix underwent a chromatic transition to grey, while GW-modified formulations (GW10, GW20, GW40) and the control displayed analogous spectral shift to darker brown hues between 300 °C and 600 °C. In contrast, CW20 and CW40 mixes developed pronounced dark brown discoloration, attributed to the elevated iron oxide content (3.87 wt.%) in CW aggregates relative to GGBFS (1.2 wt.% Fe2O3).
Volumetric moisture loss during thermal exposure attenuated thermally induced discoloration at 600 °C. Surface microfractures manifested predominantly in control and CW-modified specimens (CW10–CW40) after prolonged 600 °C exposure (3.0–6.0 h). Conversely, GW incorporation suppressed crack nucleation under equivalent thermal regimes, demonstrating enhanced interfacial compatibility and thermal stress dissipation within the geopolymer matrix.
Based on the experimental data above, it was established that under conditions of elevated temperature, CW incorporation consistently yielded superior compressive strength results across all tested replacement percentages (10%, 20%, and 40%). Conversely, the inclusion of CR uniformly resulted in the lowest compressive strength values across the same substitution spectrum.
Post-spalling analysis involved quantifying the residual mass of each specimen to compute mass loss, inclusive of moisture evaporation. In alignment with the classification by Tahwia et al. [56], severe spalling was defined as a mass reduction exceeding 20%. This investigation evaluates the impact of integrating CR, GW, and CW on the thermogravimetric behavior of HPGC under thermal stress. Figure 11 and Figure 12 delineate the mass loss profiles of HPGC formulations exposed to 300 °C and 600 °C for 1.5 h and 3.0 h intervals, respectively. Regardless of the mix ingredients, increasing the replacement ratio or the temperature exposure time increased the concrete mass loss due to the decomposition of C-S-H.
As depicted in Figure 11, CR incorporation markedly amplified the thermogravimetric response of HPGC at 300 °C. The CC exhibited a minimal mass reduction of 0.7% after 1.5 h exposure, while the 40% CR formulation (R40) demonstrated an 8.44% mass loss—a 12.1-fold increase. This trend persisted across CR-modified mixes, with mass loss escalating from 0.75% to 8.1% between 1.5 h and 3.0 h exposures, driven by volatilization of free/interlayer water and progressive thermoplastic degradation of CR [57,58].
Figure 12 delineates mass loss dynamics at 600 °C, revealing accelerated mass reduction due to CR decomposition and surface exfoliation. By 300 °C, free and chemically bound water had largely evaporated [57,58], leaving residual mass loss at 600 °C dominated by advanced geopolymer gel dehydration (tri-sulfate, mono-sulfate, and C–S–H phases) [54,59]. Consequently, mass loss plateaued at 600 °C regardless of exposure duration, contrasting with the time-dependent escalation observed at 300 °C.
GW-modified mixes displayed maximal volumetric expansion at 300 °C, with mass loss correlating positively with CW content. This phenomenon is attributed to microstructural pore collapse during bound water egress. At 600 °C, however, GW content exerted negligible influence on mass loss. Despite higher thermogravimetric losses, GW formulations exhibited suppressed crack propagation relative to CW mixes, underscoring GW’s superior interfacial thermal stability.
These findings highlight GW’s efficacy in enhancing HPGC’s thermal resilience, whereas CR exacerbates mass loss via thermoplastic decomposition. Such insights are critical for informing the design of thermally resilient HPGC formulations for extreme environments.

3.2.6. SEM Observation

The microstructural features correlate directly with the mechanical and durability properties of HPGC. Figure 13a illustrates the microstructure of GC containing 10% SF, 90% FA, and aggregates of 20% CR and 80% quartz sand. The matrix exhibits a heterogeneous morphology with calcium–silicate–hydrate (C-S-H) gel and calcium hydroxide (C-H) crystals, indicative of partial pozzolanic reactions between SF and residual calcium from FA. Pores, likely formed due to CR incorporation and water evaporation during curing, reduce mechanical strength but may enhance thermal insulation. Microcracks near CR particles and within the matrix suggest shrinkage stresses or weak interfacial bonding, exacerbated by thermal mismatch between rubber and the geopolymer paste. While the use of CR aligns with sustainable practices, the porous and fractured microstructure underscores the need for optimizing interfacial adhesion and curing conditions to improve durability.
Figure 13b depicts GC with 10% SF, 90% FA, and 20% GW aggregates. A dense, fibrous C-S-H phase dominates the microstructure, attributed to secondary hydration reactions involving reactive SF and GW-derived silica. However, unreacted C-H crystals and microcracks near GW particles highlight incomplete geopolymerization and interfacial stress from thermal expansion mismatches. The smooth, inert surface of GW likely weakens bonding with the geopolymer matrix, increasing permeability and susceptibility to environmental degradation. Despite these challenges, GW enhances pozzolanic reactivity, suggesting that surface treatments (e.g., etching) or optimized particle gradation could mitigate cracking and improve performance.
Figure 13c shows GC formulated using 10% SF, 90% FA, and 20% CW. The presence of C-S-H gel, formed via interactions between SF and calcium from FA or CW, enhances early-age strength and matrix densification. However, residual C-H and microcracks near porous regions signal incomplete geopolymerization and shrinkage-induced stresses. The rough surface of CW improves mechanical interlocking compared to smoother aggregates like GW or CR, yet cracks at aggregate boundaries suggest interfacial weakness. Reducing porosity through refined curing protocols or enhanced particle packing could strengthen the composite while leveraging CW’s sustainability benefits.
Figure 13d (10% GW, 90% FA, 100% quartz sand) reveals a hybrid microstructure with C-S-H, C-H, and ettringite formation. Ettringite, typically associated with Portland cement hydration, arises from sulfate–calcium–aluminum interactions in FA or GW, contributing to early strength but posing risks of expansion-induced cracking. Pores and microcracks further compromise mechanical integrity, emphasizing the need to balance geopolymer and traditional hydration reactions through compositional adjustments.
Figure 13e (10% CW, 90% FA, 100% quartz sand) demonstrates concurrent hydration and geopolymerization, evidenced by C-S-H and C-H phases. Microcracks, likely from shrinkage or thermal stresses, propagate along CW–matrix interfaces, underscoring interfacial incompatibility. Despite these flaws, the rough CW texture enhances load transfer, suggesting that tailored curing conditions (e.g., controlled humidity) could minimize cracking while preserving sustainability advantages.
The microstructural analysis underscores a critical balance between the sustainability benefits achieved through waste material (WM) integration and the inherent performance challenges posed by porosity and cracking in geopolymer composites. To address these limitations, targeted optimization strategies have been proposed, including interfacial engineering approaches such as acid treatment or surface modification to enhance bonding between aggregates (e.g., glass or ceramic waste) and the geopolymer matrix. Additionally, curing protocols involving steam or controlled heat could be refined to accelerate geopolymerization and mitigate shrinkage-induced stresses. The incorporation of microfibers offers a viable pathway to arrest crack propagation, while optimizing aggregate particle gradation may reduce void content and improve packing density, thereby enhancing mechanical integrity. Collectively, these findings highlight the promise of WM-enhanced geopolymer composites as sustainable alternatives to traditional concrete, provided that microstructural flaws are systematically addressed through advanced material design and processing techniques.

3.3. Effect of Aggressive Chemical Attacks

This study evaluated the chemical resilience of HPGC under aggressive media, including sulfate (Mg2SO4), hydrochloric acid (HCl), and sodium chloride (NaCl) solutions. Specimens were fully immersed in 5% concentrations of each solution for 30 and 90 days, followed by compressive strength testing and visual inspection to quantify degradation. Figure 14, Figure 15 and Figure 16 illustrate compressive strength variations across mixes post-exposure, with the 28-day ambient-cured strength serving as the baseline.
As shown in Figure 14, sulfate immersion induced progressive compressive strength loss. However, GW and CW substitutions mitigated deterioration. GW20–GW40 mixes exhibited residual strength reductions of 5.0–23% (30 days) and 2.5–12.5% (90 days), while CW20–CW40 formulations showed 14.8–30% (30 days) and 7.5–26% (90 days) reductions. The enhanced durability might be due to the GW/CW’s pore-refining effect, which limits sulfate ingress. SF and slag further optimized microstructural densification by reducing porosity and promoting calcium–aluminosilicate–hydrate (C–A–S–H) gel formation, corroborating prior studies [54,60].
Figure 15 and Figure 16 reveal analogous strength degradation in NaCl and HCl environments. Increased CR content (10–40%) exacerbated mechanical deterioration across all media, while 10% GW/CW substitutions minimized strength loss, achieving optimal durability.
Based on the experimental data above, it was established that under exposure to aggressive chemical environments—specifically, 5% concentrations of magnesium sulfate (Mg2SO4), hydrochloric acid (HCl), and sodium chloride (NaCl) solutions—the CW incorporated mixes consistently exhibited the highest compressive strength values. Conversely, the inclusion of CR uniformly resulted in the lowest strength across all tested replacement ratios (10%, 20%, and 40%).

4. Conclusions

This study comprehensively evaluated the feasibility of incorporating recycled industrial wastes—CW, GW, and CR—as sustainable alternatives in HPGC. The findings demonstrate that CW and GW significantly enhance the mechanical and thermal properties and durability of HPGC, while CR exhibits limitations in structural applications. Specifically, replacing quartz sand with 10–40% CW improved compressive strength by 24–29%, achieving up to 121.1 MPa at 56 days, due to enhanced geopolymerization and the formation of dense calcium–sodium–silicate–hydrate (C-N-S-H) gels. CW also exhibited exceptional thermal stability, retaining 96.4 MPa residual strength at 600 °C, outperforming conventional HPGC and GW-based mixes. This superior performance is attributed to CW’s ability to mitigate interfacial damage under high temperatures through pore-filling and improved aggregate–matrix bonding.
In contrast, GW demonstrated outstanding durability, reducing water absorption by 66–72% compared to CW and CR, and enhancing resistance to sulfate, chloride, and acid attacks. Its low permeability and smooth particle morphology contributed to a refined microstructure, making GW ideal for environments requiring chemical resistance. However, CR incorporation led to substantial strength reductions (up to 83.5%) due to poor interfacial adhesion and increased porosity, though its lightweight and thermal insulation properties suggest potential for non-structural applications. Critically, full replacement of SF with waste-derived binders (GWP/CWP) in this study degraded performance.
The study highlights that the utilized materials not only address resource scarcity but also improve fire resistance and durability, critical for infrastructure in extreme environments. Based on this research, the concrete mix contained CR can be used in enhancing insulations, building facades, precast roofs in green buildings, and other non-structural components where insulation is a priority rather than the strength. CW can be a great choice for concrete under aggressive media and building subjected to high temperatures. GW has a good resistance under aggressive media and it can be used in offshore constructions.
Future research should focus on optimizing CR composites through surface treatments or hybrid fiber reinforcement, scaling CW/GW applications in precast elements, and exploring synergistic effects of multi-waste blends. In addition, a comparison of the carbon footprint reduction value against conventional concrete is recommended for future extension of this work. By bridging the gap between waste valorization and high-performance construction, this work advances the development of eco-efficient materials, offering a roadmap for resilient, sustainable infrastructure in the face of global environmental challenges.

Author Contributions

Conceptualization, O.Y. and A.K.A.; Data curation, A.M.A.; Formal analysis, A.K.A. and A.M.A.; Methodology, A.K.A. and A.M.T.; Project administration, A.M.T.; Supervision, O.Y. and A.M.T.; Writing—original draft, O.Y., A.K.A. and A.M.A.; Writing—review and editing, O.Y., A.M.A. and A.M.T. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Data is available in the manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Images of the materials used. (a) Slag, (b) SF, (c) CR, (d) GW, (e) CW.
Figure 1. Images of the materials used. (a) Slag, (b) SF, (c) CR, (d) GW, (e) CW.
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Figure 2. PSD of slag, SF, quartz sand and waste materials (CW, GW, and CR).
Figure 2. PSD of slag, SF, quartz sand and waste materials (CW, GW, and CR).
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Figure 3. Slump of the mixes containing waste materials.
Figure 3. Slump of the mixes containing waste materials.
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Figure 4. Unit weight of all HPGC mixes.
Figure 4. Unit weight of all HPGC mixes.
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Figure 5. Water absorption for all HPGC mixes.
Figure 5. Water absorption for all HPGC mixes.
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Figure 6. Compressive strength of HPGC mixes with different ratio of CR.
Figure 6. Compressive strength of HPGC mixes with different ratio of CR.
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Figure 7. Compressive strength of HPGC mixes with different ratio of GW.
Figure 7. Compressive strength of HPGC mixes with different ratio of GW.
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Figure 8. Compressive strength of HPGC mixes with different ratios of CW.
Figure 8. Compressive strength of HPGC mixes with different ratios of CW.
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Figure 9. Compressive strength of HPGC mixes with full replacement of SF with GWP and CWP.
Figure 9. Compressive strength of HPGC mixes with full replacement of SF with GWP and CWP.
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Figure 10. The variation in HPGC residual strength after exposure to elevated temperature.
Figure 10. The variation in HPGC residual strength after exposure to elevated temperature.
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Figure 11. Mass loss of HPGC mixes at 300 °C for 1.5 h and 3.0 h.
Figure 11. Mass loss of HPGC mixes at 300 °C for 1.5 h and 3.0 h.
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Figure 12. Mass loss of HPGC mixes at 600 °C for 1.5 h and 3.0 h.
Figure 12. Mass loss of HPGC mixes at 600 °C for 1.5 h and 3.0 h.
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Figure 13. SEM micrograph analysis of HPGC. (a) CR20, (b) GW20, (c) CW 20, (d) GWP, (e) CWP.
Figure 13. SEM micrograph analysis of HPGC. (a) CR20, (b) GW20, (c) CW 20, (d) GWP, (e) CWP.
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Figure 14. Compressive strength of HPGC after exposure to sulfate attack.
Figure 14. Compressive strength of HPGC after exposure to sulfate attack.
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Figure 15. Compressive strength of HPGC after exposure to chloride attack.
Figure 15. Compressive strength of HPGC after exposure to chloride attack.
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Figure 16. Compressive strength of HPGC after exposure to hydrochloric attack.
Figure 16. Compressive strength of HPGC after exposure to hydrochloric attack.
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Table 1. Oxide compositions of geopolymer binders and aggregates.
Table 1. Oxide compositions of geopolymer binders and aggregates.
NotationsOxides wt. %
CaOSiO2Al2O3Fe2O3SO3MgONa2OK2OSrOTiO2P2O5Mn2O3LOI
Slag43.032.813.40.41.95.50.40.30.80.6<0.10.10.8
Silica fume0.397.80.1--0.70.40.6----5.1
Quartz sand0.4195.50.340.1-0.710.0270.085-0.0130.0030.0013.45
Ceramic waste2.7368.998.983.97--1.041.75-----
Glass waste11.772.611.380.480.090.5613.120.38-0.04--0.22
Table 2. Mixture proportions of HPGC (Vol.%).
Table 2. Mixture proportions of HPGC (Vol.%).
Mix
Code		BinderFine AggregatesThe Alkaline ActivatorSP
SFSlagGWPCWPQuartz
Sand		CRGWCWSHSS
CC1090--100---12.8632.141.5
CR101090--9010--12.8632.141.5
CR201090--8020--12.8632.141.5
CR401090--6040--12.8632.141.5
GW101090--90-10-12.8632.141.5
GW201090--80-20-12.8632.141.5
GW401090--60-40-12.8632.141.5
CW101090--90--1012.8632.141.5
CW201090--80--2012.8632.141.5
CW401090--60--4012.8632.141.5
GWP-9010-100---12.8632.141.5
CWP-90-10100---12.8632.141.5
Table 3. The spalling observation of HPGC after exposure to elevated temperature.
Table 3. The spalling observation of HPGC after exposure to elevated temperature.
Temp.300 °C600 °C
Duration1.5 h3.0 h1.5 h3.0 h
R10Infrastructures 10 00241 i001Infrastructures 10 00241 i002Infrastructures 10 00241 i003Infrastructures 10 00241 i004
R20Infrastructures 10 00241 i005Infrastructures 10 00241 i006Infrastructures 10 00241 i007Infrastructures 10 00241 i008
R40Infrastructures 10 00241 i009Infrastructures 10 00241 i010Infrastructures 10 00241 i011Infrastructures 10 00241 i012
G10Infrastructures 10 00241 i013Infrastructures 10 00241 i014Infrastructures 10 00241 i015Infrastructures 10 00241 i016
G20Infrastructures 10 00241 i017Infrastructures 10 00241 i018Infrastructures 10 00241 i019Infrastructures 10 00241 i020
G40Infrastructures 10 00241 i021Infrastructures 10 00241 i022Infrastructures 10 00241 i023Infrastructures 10 00241 i024
C10Infrastructures 10 00241 i025Infrastructures 10 00241 i026Infrastructures 10 00241 i027Infrastructures 10 00241 i028
C20Infrastructures 10 00241 i029Infrastructures 10 00241 i030Infrastructures 10 00241 i031Infrastructures 10 00241 i032
C40Infrastructures 10 00241 i033Infrastructures 10 00241 i034Infrastructures 10 00241 i035Infrastructures 10 00241 i036
GWPInfrastructures 10 00241 i037Infrastructures 10 00241 i038Infrastructures 10 00241 i039Infrastructures 10 00241 i040
CWPInfrastructures 10 00241 i041Infrastructures 10 00241 i042Infrastructures 10 00241 i043Infrastructures 10 00241 i044
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Youssf, O.; Abbass, A.M.; Ahmed, A.K.; Tahwia, A.M. Sustainable High-Performance Geopolymer Concrete: The Role of Recycled Industrial Wastes in Strength, Durability, and Microstructure Enhancement. Infrastructures 2025, 10, 241. https://doi.org/10.3390/infrastructures10090241

AMA Style

Youssf O, Abbass AM, Ahmed AK, Tahwia AM. Sustainable High-Performance Geopolymer Concrete: The Role of Recycled Industrial Wastes in Strength, Durability, and Microstructure Enhancement. Infrastructures. 2025; 10(9):241. https://doi.org/10.3390/infrastructures10090241

Chicago/Turabian Style

Youssf, Osama, Ahmed Mohamed Abbass, Ahmed K. Ahmed, and Ahmed M. Tahwia. 2025. "Sustainable High-Performance Geopolymer Concrete: The Role of Recycled Industrial Wastes in Strength, Durability, and Microstructure Enhancement" Infrastructures 10, no. 9: 241. https://doi.org/10.3390/infrastructures10090241

APA Style

Youssf, O., Abbass, A. M., Ahmed, A. K., & Tahwia, A. M. (2025). Sustainable High-Performance Geopolymer Concrete: The Role of Recycled Industrial Wastes in Strength, Durability, and Microstructure Enhancement. Infrastructures, 10(9), 241. https://doi.org/10.3390/infrastructures10090241

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