4.2.1. Fresh Density and Particle Packing
Figure 10 shows the results of the fresh density and packing density values of the studied mixtures. As depicted in the figure, M40 grade concrete has the highest fresh density at 2390.5 kg/m
3, highlighting the significant impact of crushed stone aggregate on density, especially when compared to mixtures using only CS aggregate replacement. However, its packing density, standing at 0.794, suggests a potential inefficiency in the arrangement of solid particles. In contrast, the LWAC-Control mix, characterized as UGGBS slurry-replaced non-fibrous concrete, exhibits a lower fresh density of 1792.4 kg/m
3 with a 25% decrease but compensates with a relatively higher packing density of 0.887. The incorporation of BF follows a consistent trend, resulting in increased fresh density across all mixes. LWAC-0.15% demonstrates a fresh density of 1821.6 kg/m
3, while the LWAC-1% mix achieves a fresh density of 1855.1 kg/m
3, with a 24% and 22% reduction compared to M40-grade concrete, respectively.
The addition of BF further enhanced the packing efficiency for fibrous mixes. The mix with 0.15% BF resulted in a packing density of 0.901, and the 1% BF-added mix achieved an even higher packing density of 0.915. These findings indicate that the inclusion of BF fosters a more effective arrangement of solid particles within the mixture, leading to increased packing density. The impact of fiber type on raising packing density is visually depicted in
Figure 11. The incorporation of BF as flexible fibers consistently raised both fresh and packing densities in all concrete mixtures. This improvement in density values signifies the valuable role of BF in enhancing the overall density and packing efficiency of concrete mixes, potentially leading to improved mechanical and durability characteristics.
4.2.2. Saturated Surface Dry Density and Surface Cracking
The study investigated fresh density, 1-day demold density, and densities at 7 and 28 days under SSD conditions for the concrete samples. The acquired data offers insights into the evolution of concrete density over time and the influence of incorporating BF. The results of density for the mixtures are shown in
Table 6. It can be observed that all mixtures subjected to packing density considerations yielded lightweight concrete densities. This aligns with existing literature, which typically categorizes lightweight concrete as having densities lower than 2000 kg/m
3 according to EN 206-1 [
77]. When examining the 1-day demolded density, it becomes evident that all mixtures show a slight increase compared to their fresh densities.
For the 7- and 28-day periods under SSD conditions, an increase was noted, reflecting an upward trend in density for all mixtures. In general, the results suggest that incorporating BF enhances the density properties of concrete, contributing to improved packing and densification. After 28 days of water curing, minor cracks were observed on the surface of the CS aggregate-replaced concrete samples, as depicted in
Figure 12. These cracks may be attributed to autogenous shrinkage, which is the uniform reduction of internal moisture due to cement hydration. Autogenous shrinkage is especially prevalent in high-strength concrete, where the water-to-cement ratio is typically lower than 0.42 [
78]. However, these cracks were less pronounced with increasing fiber volumes, indicating the bridging effect of BF-causing reinforcement to reduce the internal stress of the matrix through the microstructure and their ability to prevent decomposition, thereby potentially preserving structural properties [
79]. Moreover, the presence of tensile stress in the fiber results in the formation of a variety of bond stress distributions near the cracks. This, in turn, hinders the development of the crack tip due to the limits and barriers imposed by the fiber. Therefore, the inclusion of fibers in concrete can effectively mitigate autogenous shrinkage and deformation [
80].
4.2.3. Water Absorption and Porosity
Table 7 presents the detailed results of water absorption and the volume of permeable voids for the mixtures. Previous studies [
79,
80,
81] have shown that BF is effective in reducing the water absorption of concrete mixtures. This phenomenon can be attributed to the enhanced compactness of the concrete; the addition of BF blocked the development of cracks and plugged the pores, causing a decrease in water absorption and permeability [
81,
82,
83]. Water absorption of CS aggregate concrete samples showed a similar increase in the range of 260–286%, compared to granite aggregate concrete. The mechanisms behind the significant increase in water absorption in LWAC with CS aggregates compared to granite aggregates can be attributed to the porous structure of the CS aggregates, which inherently absorb more water [
84]. Additionally, the systematic increase in the use of coconut shell aggregates of varying sizes, according to the packing density method in concrete, further enhances water absorption. Despite achieving higher packing density values, the intrinsic porosity of the CS leads to increased water uptake, explaining the substantial rise in water absorption compared to less porous granite aggregates. Gunasekaran et al. [
85] conducted a study on the water absorption of coconut shell aggregate concrete under full water curing conditions. In early ages, the absorption of water by the specimens does not appear to have a significant impact. This phenomenon may be attributed to the water that is absorbed by the CS during the soaking process and subsequently stored, acting as a reservoir. However, at later ages, there were notable disparities in the curing process, with a reduction of 16% at 56 days and 24% at 90 days, respectively. A similar trend is evident when examining the volume of permeable voids. The M40 grade concrete exhibited the lowest value at 9.19%, signifying a diminished volume of voids capable of permitting fluid passage. In contrast, the LWAC-Control and the mixtures with BF show higher volumes of permeable voids, indicative of the increased porosity despite having higher packing density values. The results indicate that M40 concrete displays comparable lower water absorption and lower permeable voids compared to LWAC mixtures. The introduction of CS aggregates into lightweight mixes leads to increased water absorption and porosity. Notably, the incorporation of BF in the mixes generally has a marginal impact on these properties.
4.2.4. Sorptivity
The sorptivity test results from 1 to 24 h reveal distinctive differences in absorption rates among various concrete mixes for earlier and later ages.
Figure 13 illustrates the water sorptivity test results for all mixes. Specifically at 1 min for LWAC-Control concrete, a 1351% rise was observed compared to M40 concrete, which has a significantly high sorptivity value, highlighting its inferior resistance to immediate water penetration. The LWAC-Control mix exhibits remarkably high sorptivity at these early time intervals, indicating its susceptibility to rapid water ingress. The 0.15% and 1% BF-added mixes demonstrate intermediate sorptivity values with 465% and 358% rises compared to M40 concrete, respectively, suggesting that the inclusion of BF contributes to reducing early water absorption rates. This trend revealed itself by having 275%, 197%, and 66% increases for LWAC-Control, LWAC-0.15%, and LWAC-1% mixtures compared to M40 concrete, respectively, in 24-h duration. At the early stage, the LWAC-Control mix shows a high sorptivity of approximately 6 mm, while the M40 mix remains low at about 0.5 mm, illustrating the control mix’s rapid initial water uptake. The introduction of 0.15% BF reduces this early sorptivity to 2.5 mm, and 1% BF further lowers it to around 2 mm, indicating a reduction of over 58% and 67%, respectively, compared to the control. Over the longer term, the LWAC-Control’s sorptivity reaches around 12.5 mm, while the LWAC-0.15% and LWAC-1% mixes exhibit reductions to approximately 8 mm and 7 mm, reflecting 36% and 44% lower sorptivity, respectively. The M40 mix remains consistently low, at about 4 mm, but the LWAC-1% mix’s final sorptivity value demonstrates a significant improvement, bringing its performance closer to that of M40 concrete. The analysis also reveals that while increasing BF content from 0.15% to 1% continues to reduce sorptivity, the rate of improvement decreases, suggesting diminishing returns at higher BF levels.
As evident in the figure, the sorptivity values of M40 concrete remain consistently low. Notably, the mix incorporating 1% BF displays a consistently lower sorptivity trend compared to the control mix. Over time, sorptivity values of the LWAC-1% mix increase at a slower rate, approaching those observed for M40 concrete. For the increased rate of BF mixes, both the LWAC-0.15% and LWAC-1% formulations demonstrate significant reductions in sorptivity compared to the LWAC-Control mix at both testing intervals, which may be attributed to the fact that the inclusion of BF imparts effective, sustained protection against water penetration owing to the filler effect by blocking the capillary pathways [
86,
87]. Furthermore, the contrast in sorptivity between early and late-age results is more pronounced in the LWAC-Control mix than in the BF-added mixes. This implies the critical role of BF reinforcement in sustaining consistently lower sorptivity values over time. Overall, the findings underscore the significant role of BF in reducing sorptivity, with particular emphasis on the 1% BF-added mixture, which achieves sorptivity values akin to those of M40-grade concrete. These findings contribute to the understanding of how BF incorporation can effectively control sorptivity, offering valuable insights for enhancing the durability and performance of concrete structures.
4.2.5. Compressive Strength
The 1-, 7-, and 28-day compressive strengths of tested specimens are shown in
Figure 14. Notably, in the context of 1-day compressive strength, a remarkable observation developed in the UGGBS slurry-replaced mixtures. The 1-day compressive strength of the LWAC-Control, LWAC-0.15%, and LWAC-1% mixes are 49%, 49%, and 61% of M40 concrete. Insignificant early compressive strength difference between LWAC-Control and LWAC-0.15% mixtures due to the low fiber content of BFs which is lower compared to that of LWAC-1%. The results also align with Wu et al. [
88] that low fiber content has negligible impact on the early compressive strength of LWACs. All packing density optimized LWAC mixtures demonstrated substantial strength development even after a one-day curing period, a characteristic that is distinctive in comparison to the high cement content LWAC behavior as presented in the existing literature [
89,
90]. The enhanced packing density of both UGGBS slurry with cement as paste and coarse-fine aggregate combination is likely effective in this early-age strength development. These findings align with existing literature, where UGGBS-based concretes accelerated early-age strength attributed to the activation efficiency [
36,
91].
The 7-day compressive strength shows a similar pattern compared to 1-day results, where the UGGBS slurry-replaced LWAC-Control, LWAC-0.15%, and LWAC-1% mixtures had 85%, 86%, and 94% of the compressive strength of M40 concrete, respectively. The results imply that these mixtures have the potential to attain strength levels comparable to traditional concrete within a relatively short curing period. The relatively higher compressive strength of LWAC mixes compared to the existing literature can also be attributed to the influence of fine content in decreasing total porosity, improving compactness, and enhancing the microstructural development of concrete [
92]. Hence, the enhancement in the strength of LWACs is not solely attributable to hydration reactions but also the grain size distribution associated with the formation of particle interlocking within the matrix [
93]. It is crucial to emphasize that the incorporation of BF also contributes to this increased strength development, likely attributable to their reinforcing effects and the potential enhancement of packing density [
94,
95,
96]. These outcomes reveal that BF incorporation can develop both the early- and long-term strength of concrete.
The data emphasizes the remarkable early-age strength attributes of UGGBS slurry-replaced mixtures [
36], owing to the synergistic influences of UGGBS and CS aggregates, which potentially improved packing density both in mortar [
61] and aggregate [
46] phases. The incorporation of BF further increases both early-age and long-term strengths, positioning these mixtures as promising contenders for diverse concrete applications. These results represent the importance of optimizing packing density, aligning with insights from the existing literature regarding early-age strength development in concrete.
The compressive strength results demonstrate that the LWAC-1% mix consistently outperforms the LWAC-Control and LWAC-0.15% mixes across all curing times. At 1 day, the LWAC-1% mix achieves a compressive strength of 15.2 MPa, notably higher than the 12.2 MPa and 12.3 MPa of the LWAC-Control and LWAC-0.15% mixes, respectively. By the 7th day, this mix further distinguishes itself, reaching 36.7 MPa, which is approximately 10% higher than the LWAC-Control. At 28 days, the LWAC-1% mix attains a compressive strength of 40.4 MPa, showing a significant 17.4% improvement over the LWAC-Control and marking the highest strength among the LWAC mixes. This performance underscores the critical role of higher BF content in enhancing both early and long-term compressive strength, making it particularly advantageous for applications requiring rapid strength development and durability.
Results of the investigated mixtures revealed that the 28-day compressive strengths of M40 concrete exhibit a higher development compared to other concretes, characterized by its conventional composition with higher cement content, which exhibits a steady and consistent development in strength, resulting in a final compressive strength of 52 MPa. In contrast, the UGGBS slurry-replaced LWAC-Control mixture, despite demonstrating comparable early-age strengths, displays a relatively lower 28-day strength of 34.4 MPa. This difference can be attributed to the prolonged pozzolanic reaction of GGBS, which tends to result in slower strength gain beyond the initial 7 days [
97,
98]. However, with the introduction of BF, particularly evident in the 1% BF mixture, a noticeable enhancement in 28-day strength is observed (40.4 MPa). The addition of BF reinforces the tension of capillary pores induced by water evaporation, thereby mitigating the formation of microcracks. Consequently, the long-term compressive strength of BF-reinforced concrete demonstrates an increase compared to non-fibrous concrete [
99]. Moreover, as can be seen from the above results, the influence of packing density remains significant in shaping the 28-day strengths of these mixtures. It is important to state that a negligible increase in strength was observed between the 7th and 28th days for the LWAC-Control, LWAC-0.15%, and LWAC-1% concrete mixtures with 4%, 6%, and 10% rises, respectively.
4.2.6. Flexural Strength
The 28-day flexural strength of mixtures is presented in
Figure 15. The flexural strength results at the 28-day illustrate the influence of involving BF in concrete. M40 concrete resulted in a flexural strength of 7.1 MPa; additionally, the LWAC-Control mix demonstrated a marginally lower flexural strength of 7.0 MPa, where the flexural strength of the LWAC-Control mix is notably comparable to that of the M40. Adding 0.15% and 1% of BF raised the flexural strength by 33.80% and 59%, respectively. Previous studies also revealed that the inclusion of BFs enhanced the flexural strength of cementitious LWAC composites. In a study conducted by Zeng et al. [
100], the flexural strength of BF-reinforced concrete specimens increased compared to non-fibrous control mixtures in 0.5%, 1.0%, and 1.5% volume fractions. The flexural strength results at 28 days reveal a clear distinction in performance among the concrete mixtures when BF is incorporated. The M40 concrete and LWAC-Control mix show similar flexural strengths of 7.1 MPa and 7.0 MPa, respectively, indicating that the absence of BF maintains a comparable baseline strength. However, the addition of BF markedly alters this dynamic. The LWAC-0.15% mix reaches a flexural strength of 9.4 MPa, which is 2.4 MPa higher than the LWAC-Control, reflecting a 34% enhancement in flexural capacity. The LWAC-1% mix further improves this value to 11.1 MPa, resulting in a 59% increase over LWAC control. Notably, the incremental improvement in flexural strength from 0.15% to 1% BF (an additional 1.7 MPa) highlights the effectiveness of increasing BF content in significantly boosting the concrete’s flexural performance. These results demonstrate that even a small increase in BF content can lead to substantial gains in the material’s ability to resist bending stresses, with the LWAC-1% mix showing a 4.1 MPa higher strength than the LWAC-Control, underscoring the material’s enhanced structural capacity and potential for broader application in load-bearing scenarios. As the stress increases, the plain concrete initially approaches its maximum flexural strength, resulting in a brittle fracture. When fiber is introduced, the fibers dispersed in a random orientation decrease the stress intensity factor at the crack tip. A higher stress is necessary to initiate fracture propagation and result in material failure for the same matrix material. The high-elastic-modulus fiber enhances the crack resistance during the entire stress process, hence improving the flexural strength of the concrete [
101].
Figure 16 illustrates the crack propagation in the mixtures following the flexural strength test. Notably, all mixtures, except the one containing 1% BF, exhibited a single crack on the surface of the specimen. In contrast, the presence of a double crack in the mixture with 1% BF signifies a bridging effect of the BF, which enhances the bending crack resistance and ductility of LWAC [
102,
103,
104]. This effect results in the transfer of load energy through the BF, providing a positive impact on the structural concrete. Furthermore, the substantial increase in flexural strength observed in the BF-added mixtures indicates the potential for further enhancing the mechanical properties of lightweight structural concrete. These findings indicate that incorporating BF, in conjunction with sustainable mix designs, can be a promising strategy for constructing eco-friendly yet robust structures with improved flexural strength.
4.2.7. Relationship between Compressive and Flexural Strength
Analyzing the 28-day values reveals a clear correlation between compressive and flexural strengths, with a correlation coefficient of 0.967: as the compressive strength increases, so does the flexural strength. This trend is particularly evident in the LWAC-0.15% and LWAC-1% mixes, where the inclusion of basalt fibers significantly enhances the flexural strength compared to LWAC-Control. For instance, the LWAC-0.15% mix shows a modest increase in compressive strength (35.5 MPa) over LWAC-Control (34.4 MPa), but a notable improvement in flexural strength (9.5 MPa versus 7 MPa). Similarly, the LWAC-1% mix achieves a substantial increase in both compressive strength (40.4 MPa) and flexural strength (11.3 MPa).
Several factors contribute to this observed correlation between compressive and flexural strengths. Firstly, M40, a normal-weight concrete, inherently possesses higher compressive and flexural strengths due to its dense matrix and the use of coarse aggregates. In contrast, LWAC mixes utilize lightweight aggregates, such as coconut shells, which generally result in lower densities and strengths. Secondly, the inclusion of basalt fibers in LWAC-0.15% and LWAC-1% mixes provides significant benefits in terms of tensile and flexural performance. Fibers bridge cracks and distribute stresses more evenly, enhancing the composite material’s ability to resist flexural loads. This is evident in the dramatic increase in flexural strength observed with higher fiber content (11.3 MPa in LWAC-1%).
Additionally, the optimized packing density in LWAC-Control contributes to better compaction and reduced porosity, leading to improved compressive strength. However, without fibers, the flexural strength remains limited due to the brittle nature of the lightweight aggregate matrix. The combination of optimized packing density and basalt fiber reinforcement in LWAC-0.15% and LWAC-1% mixes creates a synergistic effect, enhancing both compressive and flexural strengths. The fibers improve ductility and crack resistance, while the dense packing ensures a robust load-bearing matrix. Thus, the correlation between compressive and flexural strengths in these mix designs is influenced by the intrinsic properties of the materials used, the optimization of packing density, and the inclusion of basalt fibers, collectively contributing to the mechanical performance of the concrete mixes.
4.2.8. Impact of Packing Density
The analysis provides valuable insights into the correlation between packing density and various critical properties of concrete. Packing density stands out as a fundamental parameter for evaluating concrete quality, particularly concerning its long-term structural integrity. The correlation values indicate a strong positive correlation between packing density and compressive strength, as well as flexural strength, with correlation coefficients of 0.991 and 0.939, respectively. This suggests that an increase in packing density correlates with a corresponding increase in both compressive and flexural strengths, highlighting the crucial role of effective particle packing in enhancing the material’s mechanical performance. Conversely, packing density exhibits a strong negative correlation with water absorption, porosity, and sorptivity, with correlation coefficients of −0.885, −0.931, and −0.977, respectively. These negative correlations imply that as packing density increases, the water absorption, porosity, and sorptivity of the concrete decrease. This suggests that a denser packing of concrete particles results in reduced permeability and increased resistance to moisture ingress, which are essential attributes for the durability and extended service life of concrete structures.
Figure 17 presents a high-magnification view of a packing density-optimized LWAC structure. The close packing of aggregates significantly enhances the mechanical properties of concrete by optimizing load distribution within the material. By tightly arranging the aggregates, the spaces are minimized, reducing voids and enhancing interlocking between particles. This results in improved load-bearing capacity and structural integrity, making the concrete more resistant to external forces. Additionally, the reduced porosity resulting from close packing diminishes water absorption capabilities, thereby enhancing the concrete’s durability against moisture ingress and chemical attacks. Furthermore, the decreased porosity also leads to lower sorptivity, meaning the concrete absorbs water at a slower rate, contributing to its longevity and resistance to weathering effects. In summary, close packing of aggregates in concrete not only improves its mechanical strength under load but also enhances its resistance to water absorption, porosity, and sorptivity, thereby prolonging its service life and overall performance.
4.2.9. Sustainability
Assessing green building materials considers economic benefits and carbon emissions as important factors. Despite the LWAC mixed with high-volume UGGBS demonstrating approximate compressive strength with a 1% BF addition compared to M40 at 28 days, it is essential to account for manufacturing expenses and carbon footprint.
Table 8 provides a comprehensive assessment of individual and cumulative CO
2 emissions for various components and mixtures. The quantities of materials used in each mix were determined based on the mix design proportions provided in
Table 5. These quantities include cement, GGBS slurry, fine aggregate, crushed stone, coconut shells, basalt fibers, water, and superplasticizer. The CO
2 emission factors for each material were sourced from credible and standardized databases and literature, ensuring accuracy and relevance. The carbon footprint for each mix was calculated by multiplying the quantity of each material by its respective emission factor and then summing these values to obtain the total CO
2 emissions per cubic meter of concrete.
Example Calculation for LWAC-Control Mix:
Cement: 284 kg × 990 kg CO2/1000 kg = 281.16 kg/t
GGBS Slurry: 307 kg × 298.87 kg CO2/1000 kg = 91.80 kg/t
Fine Aggregate: (234 + 58.5 + 97.5) kg × 26 kg CO2/1000 kg = 9.75 kg/t
Coconut Shells: (82 + 374) kg × 19 kg CO2/1000 kg = 8.64 kg/t
Water: 43.5 kg × 0.1 kg CO2/1000 kg = 0.004 kg/t
Superplasticizer: 8 kg × 1.48 kg CO2/1000 kg = 0.011 kg/t
Total CO2 Emission: 281.16 + 91.80 + 9.75 + 8.64 + 0.004 + 0.011 = 391.36 kg/t
Statistical analysis reveals significant variations across the mixes. Notably, LWAC-Control showcases the lowest CO
2 emissions at 391.4 kg/t, representing a reduction of approximately 31.6% compared to M40’s emission rate of 571.1 kg/t. The LWAC-0.15% mix had emissions of 392.4 kg/t, slightly higher than LWAC-Control but still significantly lower than M40. The LWAC-1% mix, despite incorporating more basalt fibers, resulted in emissions of 399.9 kg/t, highlighting the effectiveness of using lightweight aggregates and UGGBS slurry in reducing the overall carbon footprint. Additionally, when evaluating emissions per compressive strength (kg/MPa), LWAC mixes demonstrated lower values than M40, indicating a more efficient use of materials in terms of CO
2 emissions per unit strength. Despite its lower CO
2 emissions, LWAC-Control achieves a compressive strength of 34.4 MPa, suggesting competitive structural performance. However, LWAC-1% emerges as the strongest mix, attaining a compressive strength of 40.4 MPa, surpassing LWAC-Control by approximately 17.4%. Nevertheless, this superior strength comes at the cost of increased CO
2 emissions due to BF inclusion, with LWAC-1% emitting 399.9 kg/t of CO
2. In terms of environmental efficiency, LWAC-Control continues to excel, demonstrating the lowest emission per unit of compressive strength at 11.36 kg/MPa, implying a reduction of 3.62% and 1.3% compared to LWAC-0.15% and LWAC-1%, respectively. This statistical analysis underscores LWAC-Control’s prominence as a sustainable concrete mix, offering competitive performance across environmental and structural metrics.
Table 9 provides a comparison between the current study and previous research regarding the components used in their mix designs and the compressive strength obtained.
Earlier investigations employing CS as coarse aggregates exhibited lower strength levels and required higher cement dosages. The use of high volumes of CS with improved mechanical characteristics emphasizes the importance of the packing density method for the matrix. Furthermore, the wet grinding technique for GGBS enhanced hydration properties by reducing particle size, facilitating the formation of a reliable binder between coarse and fine aggregate particles. The provided table sheds light on various concrete production samples, delineating their composition, properties, and environmental impact. Notably, the LWAC-1% sample stands out with distinctive attributes. LWAC-1% exhibits a remarkable reduction in CO2 emissions. This reduction is attributed to the high-volume cement reduction facilitated by packing density optimization techniques. As a result, LWAC-1% boasts the lowest CO2 emissions per cubic meter among the samples, at 399.9 kg/m3, signifying a notable decrease of approximately 14.6% compared to its counterparts. Additionally, LWAC-1% showcases a commendable compressive strength of 40.4 MPa, outperforming all other samples listed in the table.
LWAC-1% stands out with a reduction of approximately 14.4% in emissions compared to M11, which exhibits the highest emissions. Specifically, for producing 1 MPa of concrete strength, LWAC-1% emits approximately 9.89 kg of CO2. In contrast, M11, which has the highest emissions, produces approximately 19.64 kg of CO2 to achieve the same strength level. This stark difference underscores LWAC-1%s’ efficient resource utilization and balanced approach, making it a compelling option for environmentally conscious projects seeking sustainable concrete solutions.
The lightweight coarse aggregate’s specific gravity in a dry state, ranging between 1/3 and 2/3 of that of normal-weight aggregate, meets the criteria for achieving a 28-day compressive strength of at least 17 MPa [
114], high-strength lightweight aggregate concrete (HSLWAC) that exceeds 40 MPa [
115], and a unit weight of 1120–1920 kg/m
3 [
114]. Therefore, all LWAC mixes produced for this study are classified as structural lightweight aggregate concrete (SLWAC); in particular, the LWAC-1% mix can be defined as HSLWAC [
115]. This implies that, through careful selection of supplementary cementitious materials and systematic mix design optimization, it is feasible to strike a balance between eco-friendliness and structural reliability. This study not only offers a novel approach to address challenges faced by the cement industry but also serves as inspiration for low-cement-content, high-strength LWAC with a greener profile.