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Article

Pistachio Shell Ash in Agro-Waste Cement Composites: A Pathway to Low-Carbon Binders

by
Mahmut Durmaz
* and
Murat Doğruyol
Department of Civil Engineering, Faculty of Engineering, Siirt University, Siirt 56000, Türkiye
*
Author to whom correspondence should be addressed.
Sustainability 2025, 17(9), 4003; https://doi.org/10.3390/su17094003
Submission received: 17 March 2025 / Revised: 8 April 2025 / Accepted: 20 April 2025 / Published: 29 April 2025
(This article belongs to the Special Issue Sustainable Biomass Energy: Opportunities and Challenges for a Green Future)
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Abstract

:
This study evaluates pistachio shell ash (PSA) as a sustainable cement substitute and investigates its effect on setting time, strength and microstructure. In this study, pistachio shell ash (PSA) obtained from the kiln flue gas filter of pistachio shells burnt at 300–350 °C in an industrial kiln was used. PSA was substituted for ordinary Portland cement (OPC) at 5, 10, 15, 20, 25 and 30%. PSA increased the SO3 value in the cement mortars, so 5% PSA substitution delayed the cement setting time by up to 174%. However, it increased the water requirement of the cement mortar by about 2%. While it increased the early strength (22% on day 1, 15% on day 2, and 5% on day 7), the 28-day strength decreased slightly (about 4.5%) due to low pozzolanic activity. Microstructural analyses such as SEM-EDX and XRD showed that the calcite and gypsum phases of PSA provided early strength gains, but there were long-term losses. With a 5% replacement rate, PSA provides significant environmental benefits by reducing CO2 emissions while maintaining optimum mechanical performance and supports the circular economy through the efficient use of agricultural waste.

1. Introduction

Portland cement is a special material produced by a specific process in which the clinker obtained by firing calcite and clay at a high temperature (1400 °C) is finely ground with gypsum (about 3% of the weight of the clinker) [1]. It is observed that CO2 emissions from the combustion of conventional fuels and raw materials vary between 0.84 and 1.15 kg/kg of clinker [2]. As cement remains significant in meeting housing and modern infrastructure requirements at a global level, humanity faces difficulties in increasing CO2 emissions, as well as the destruction of material and energy resources [3]. Global cement production, increasing more than 30 times since 1950, accounts for 8% of all emissions worldwide [4,5]. The cement industry remains responsible for significant global anthropogenic CO2 emissions, although research scientists have worked for a long time to tackle environmental issues [6].
In the materials where cement and reinforced concrete are used, it is seen that most of the industrial wastes are used together with the natural resources used in order to minimize the plain cement dosages. Within the concrete industry, it helps to significantly reduce silica fume, fly ash, blast furnace slag, and CO2 emissions in order to contribute to the mechanics and strength of concrete and serves as practical and successful supplementary cementitious materials (SCMs) for this gain [7,8,9]. Pozzolans or thinner materials are also eco-efficient products with a reinforced strength force [10]. The cement and concrete industry employs SCMs to mitigate alkali-silica reaction (ASR) induced expansions while simultaneously enhancing the durability and sustainability of the final products [11,12]. These materials are utilized in a cost-effective manner, demonstrating both economic viability and environmental benefits [13,14].
Tosti et al. [15] demonstrated that incorporating biomass ash in cement formulations presents a viable waste management solution, as uncontrolled disposal of these ashes may lead to the leaching of potentially hazardous pollutants that can compromise soil ecosystem integrity. While the effects of SCMs in Portland cement concrete systems have been extensively characterized, ongoing research continues to explore novel materials to further enhance performance and sustainability [16,17].
Isperto et al. [7] state that the abundant amount of rice husk ash they have made in the Philippines can increase the compressive strength of cement mortars when it is replaced with 10% cement by weight. Groundnut shells [18] and many other ashes from coconut shells [19] cause local contamination. In addition to various studies on the use of industrial wastes and biomass ashes in the production of pozzolans cement systems, there are also some studies on the use of hazelnut shell ash (HA) in cement, mortar and concrete products [20]. In addition to these additives in recent studies, pistachio shell ash has also been used in the cement and concrete industry as a remarkable material. In particular, recent developments have introduced agricultural waste by-products such as pistachio shell ash (PSA) as a sustainable and innovative additive in cementitious composites, showing promising potential for improving material performance [14,21,22].
Turkish Statistical Institute data report that Türkiye ranks third behind Iran and the US in pistachio production. The amount of pistachio produced in 21 countries in the world is 1,158,519 tons per year [23]. Pistachio production in Turkish cities, including Gaziantep, Şanlıurfa, and Siirt, is increasing due to growing demand. Turkish Statistical Institute data also report a significant increase in pistachio production in recent years, and annual production in Türkiye has reached around 244 tons [24]. Shells obtained from pistachios are used as fuel in furnaces. However, the ashes remain as waste.
If the peanut shell is used as fuel, it must not be constant in burning conditions. However, if this ash is to be used in the cement and concrete industry, both the burning and cooling of the obtained ash must be performed under certain conditions [25]. When the peanut shell burning process is carried out in a controlled temperature range of 400 °C to −600 °C and the cooling of the obtained ash is fast, the silica in the ash turns into an amorphous structure [26,27]. Peanut shell ash, which contains more amorphous silica, is obtained as a highly reactive pozzolanic material with a high surface area and excellent grains [28]. It has been demonstrated that the ash obtained by burning the peanut shell at temperatures of 800 °C and above compared to low-temperature degrees has a high SiO content, high pozzolanic reactivity, and a larger specific surface area [29]. The use of pistachio shell ash, which is a pozzolanic material, in cement and concrete provides advantages such as reducing the permeability of concrete, resistance to chemical effects, resistance to alkali-silica reaction, improvement in workability properties, and thus strength and durability of concrete [30].
Pistachio shells are commonly utilized as biomass fuel in various industrial applications. However, the combustion process generates volatile ash residues that pose significant environmental concerns due to their potential for particulate emissions and leaching of alkaline components. When the shell is burned, it produces whitish-colored ash (Figure 1b) residues containing 1.2% by weight [21], some silica and some carbon.
The utilization of pistachio shells in the production of cement and concrete is a factor for the sustainability goals of the cement industry as well as for the disposal of waste piles in the pistachio processing industry.
This study comprehensively evaluates the feasibility of using PSA as a SCM through a systematic investigation of basic mortar properties. The experimental investigation examines PSA incorporation at replacement levels of 5-10-15-20-25-30% of OPC on basic fresh state properties (standard consistency and setting time), hydration water requirements, mechanical performance (compressive strength development) and Microstructural development (through SEM-EDX and XRD analysis). This research aims to reduce natural resource consumption and minimize the environmental footprint of cement production by utilizing regional agricultural waste. The findings are expected to contribute to the improvement of waste management strategies and the development of sustainable construction materials, especially in regions where pistachio production is important.

2. Materials and Methods

2.1. Material

In this study, pistachio shell ash (PSA) was obtained by combusting pistachio shells in an industrial oven at 300–350 °C (Figure 1a), with the resulting ash collected from the chimney filter (Figure 1b). Ordinary Portland cement (OPC), compliant with EN 196-1 standards [31], was used in the preparation of mortar samples. The OPC, supplied by Limak Kurtalan Cement Plant (Siirt, Türkiye), had a Blaine fineness of 3274 cm2/g and a density of 3130 kg/m3, while the PSA exhibited a Blaine fineness of 3167 cm2/g and a density of 2350 kg/m. A detailed comparison of the chemical composition of OPC and PSA used in the experiment with other biomass wastes is given in Table 1.
Table 1 presents the chemical compositions of pistachio shell ash (PSA), hazelnut shell ash (HA) and coconut shell ash (CHA) from ashes obtained from agricultural wastes in comparison with ordinary Portland cement (OPC). The analyses show that PSA and HA exhibit significantly high alkaline properties with K2O contents of 33.77% and 27.73%, respectively. This property suggests that both materials will offer potential advantages in alkali-activated binder systems. The 12.96% SO3 content of PSA can be considered a functional additive in cementitious material formulations, especially due to the setting-accelerating effect of sulfate [14]. On the other hand, the 50.48% CaO content of HA is suitable for partial cement substitution applications. CHA, on the other hand, has a total S+A+F (SiO2, Al2O3 and Fe2O3) value of 9.94% with S+A+F and stands out as the biomass-based material with the highest pozzolanic activity potential thanks to this balanced composition. These findings reveal the suitability of these agricultural waste ashes for different application areas in the development of sustainable building materials.
Table 1 reveals that PSA contains high concentrations of Na2O, K2O, SO3 and MgO and shows lower CaO and SiO2 content compared to OPC. However, when the combustion temperature was increased (at 850 °C for 30 min), it was shown that these PSA contents improved [14]. This particular chemical profile significantly influences the setting behavior of cementitious systems, where high alkali content tends to reduce setting times while decreasing Al2O3 and SiO2 content produces an opposite effect by prolonging both initial and final setting times [14]. The observed particle aggregation behavior may be attributed to the material’s elevated potassium content (K+), as corroborated by findings from Shakouri et al. [33] and Kamau et al. [34], who established that K+ concentrations in agricultural by-products are influenced by both plant species and fertilizer applications. Given the high total alkali content (Na2Oeq > 0.60%), particular caution must be exercised to avoid potential alkali-silica reaction (ASR) when employing PSA with reactive aggregates containing amorphous silica, such as andesite, dacite, or rhyolite [12]. The high SO3 content of PSA (12.96%) can trigger the formation of excessive etrengite (Ca6Al2(SO4)3(OH)12·26H2O) in the cement matrix Equation (1), which can increase the water demand of the mortar and have a negative impact on long-term performance. [8,9,21,35]. The pozzolanic reaction occurs when a siliceous or aluminous material comes into contact with Ca(OH)2 in the presence of moisture, resulting in the formation of compounds with cementitious properties [36]. Highly amorphous siliceous ash added to mortars reacts with Ca(OH)2 and forms calcium silicate hydrates (C-S-H) Equation (2) [37,38].
C 3 A + 3 K 2 S O 4 + 2 C a ( O H ) 2 + 24 H 2 O ⇾ C a 6 A l 2 ( S O 4 ) 3 ( O H ) 12 · 26 H 2 O + 6 K O H
C a ( O H ) 2 + S i O 2 + H 2 O ⇾ C a O · S i O 2 · H 2 O
XRD analysis of PSA revealed distinct crystalline phases, including SiO2 identified by its characteristic peak at 2θ ≈ 21.29° [39] and calcite (CaCO3) as the dominant phase evidenced by the intense diffraction peak at 2θ ≈ 29.4° [40]. While the crystalline silica was detected, it should be noted that amorphous silica typically exhibits superior reactivity in pozzolanic reactions due to its disordered atomic structure and higher surface energy, which facilitates faster dissolution kinetics [41]. The analysis also confirmed the presence of potassium sulfate (K2SO4), a non-flammable, water-soluble crystalline compound widely utilized in fertilizers as a dual source of potassium and sulfur.
Particle size distribution analysis provides critical insights into the suitability of ash as a cementitious material substitute for ordinary OPC. The results demonstrate that approximately 80% of the particles fall within the 0.010–0.100 mm range, exhibiting a granulometric profile comparable to OPC (Figure 2). The presence of a fine fraction (<20%) in the 0.001–0.010 mm range enhances the reactive surface area, thereby promoting pozzolanic activity (Figure 2). Notably, a minor proportion (<5%) of coarser particles up to 1 mm suggests potential aggregate effects. This bimodal distribution indicates the material’s dual functionality as both binder and filler when used as an OPC replacement. However, additional grinding may be required to optimize the particle size distribution for improved performance, particularly to reduce the coarse fraction and increase the proportion of particles in the 0.1–10 μm range, which is most favorable for pozzolanic reactions. The observed distribution profile aligns with previous studies on biomass ash utilization in cementitious systems [42], though the relatively broad particle size range may necessitate blend optimization to achieve optimal packing density and strength development.

2.2. Methods

In this study, OPC and PSA, obtained by burning pistachio shells at 300–350 °C in an industrial furnace and collected from the chimney filter, were used. In addition to the reference mix (100% OPC), PSA was included as a partial replacement in the cement at 5%, 10%, 15%, 20%, 25% and 30% by weight to evaluate its effect on the chemical, physical and mechanical properties of the cementitious system. The specimens were demoulded after 24 h and cured in saturated lime solution at 20 ± 2 °C and R.H. ≈ 95% for 1, 2, 7 and 28 days.
The standard consistency of water, initial setting time, and final setting time were determined using a Vicat apparatus in accordance with EN 196-3 [43]. Compressive strength testing was conducted on 40 × 40 × 160 mm prismatic mortar specimens at 1, 2, 7, and 28 days of curing, following EN 196-1 [31]. The compressive strength test was carried out on 40 × 40 × 160 mm prismatic mortar specimens at curing times of 1, 2, 7 and 28 days in accordance with EN 196-1. The mix proportions used in this research are detailed in Table 2.
For microstructural and crystallographic analysis, samples from both ambient and high-temperature conditioned specimens were extracted and prepared for scanning electron microscopy (SEM) and X-ray diffraction (XRD) characterization.
The samples were carefully cut to obtain suitable dimensions for SEM analysis. To facilitate high-resolution imaging, the sample surfaces were made conductive by gold plating using a sputter coater (Au/Pd target). The prepared samples were loaded into the vacuum chamber of a Hitachi SU3500 SEM system (Tokyo, Japan), where the surface morphology was studied at multiple magnification levels. XRD analysis parameters and XRD characterization were carried out using the following experimental configuration. Radiation: Cu-Kα (λ = 1.5406 Å) Angular range: 10–90° (2θ), step size: 0.02°, scanning speed: 2°/min.

3. Results

3.1. Amount of Water and Setting Time of Blended Cement

It was determined that there is a relationship between the amount of PSA in the cement and the setting time. The initial setting time of blended cement is presented in Figure 3a. It was also observed that as the PSA substitution rate increased, the initial setting time of cement increased significantly. Due to the 5% PSA substitution, the initial setting time increased by approximately 73%. As the PSA substitution rate increased, the increase in setting time continued, and at a PSA substitution rate of 30%, the first setting time increased by almost 174%. The final setting times of the cement are given in Figure 3b. As the amount of PSA substitution increased, there was a significant increase in the final setting times. Following the 5% PSA substitution for cement, a significant increase in the final setting time was observed (51%). As the PSA rate of substitution for cement increased, the increase in the final setting times continued, and with 30% PSA substitution, there was approximately 126% increase in the final setting time.
In a study on coconut shell ash, Utseve and Taku [19] observed that coconut shell ash substitution increased the initial and final setting times of cement, reporting that 10% coconut shell ash substitution almost quadrupled the setting times of cement.
Therefore, it is possible to employ the PSA as a set of retarding additives apart from the other properties to be discussed below [14].
The S-O set is used to adjust the cement setting time. Zunino reported that SO3 cement delayed the setting time [44]. The amount of SO3 in PSA is around 12%. While this reduces the initial and final setting times, the low Al2O3 and SiO2 amount in PSA increases the initial and final setting times [14]. The amounts of Al2O3, SiO2 and SO3 in PSA are presented in Table 1. Also, as can be seen in Figure 4, the water requirement of the cement paste increased as the PSA replacement rate increased. This increase is thought to be due to the increase in surface area due to the small particle size of PSA. In addition, the increase in ettringite formation with PSA is another factor that increases the water requirement [21] (Equation (1)). Due to this increase in water requirement, both the initial and final setting times were increased.

3.2. Oxide Composition of Blended Cement

The chemical composition of blended cement formulations was systematically calculated based on varying PSA replacement ratios (5–30 wt.%) and evaluated against the compositional limits specified in EN 197-1 [45] Table 3. Notably, the PSA-modified systems exhibited significantly elevated alkali metal oxide content (Na2O + K2O = 11.9%) compared to the reference mortar (≈1%). These compounds form alkaline silica gels with a very high water absorption capacity and cause an expansion in the cement [12]. The chemical composition data reveal a progressive increase in SO3 content (2.54% to 5.62%) with higher PSA substitution (0–30%), exceeding the EN 197-1 limit of ≤4.0% beyond 15% replacement. This elevated SO3 derives primarily from potassium sulfate (K2SO4) decomposition in PSA, as evidenced by the concomitant rise in K2O (0.75% to 9.72%). While SO3 initially enhances early-age strength by optimizing C-S-H formation through gypsum (CaSO4·2H2O) regulation of C3A hydration, concentrations > 4.0% may induce deleterious effects. Furthermore, comparative analysis revealed that PSA contains markedly higher MgO content Table 1 relative to conventional CEM I 42.5 N cement. MgO is known to adversely affect cementitious systems through delayed hydration reactions, potential formation of expansive brucite (Mg(OH)2), and long-term durability concerns related to volumetric instability [46]. The parallel LOI increase (2.89% to 11.58%) further suggests unburned carbon may adsorb sulfate ions, exacerbating uneven hydration.

3.3. Microstructural Analyses

The pore formed in the cement with 5% PSA substitution is shown in Figure 5b. The pistachio shell ash substitution for cement increased pore sizes in the cement paste. Increases in pore size led to a decrease in strength. Unburned carbon particles (LOI = 5.08% at 5% PSA) act as nucleation sites for void formation [47]. In a previous study conducted with nutshell ash, it was observed that nutshell ash substitution increased the pore sizes in the cement and decreased the strength [20]. A strong relationship was found between pore size and strength in cement [48].
SEM-EDX of 5% PSA substituted cement is presented in Figure 6. As can be seen in Figure 6c, the ratios of Ca, Si, C and O are high, and Ca, Si, and O are the proof of the formation of C-S-H [49]. This increased the binding property of cement. In addition, the presence of C may have caused the formation of calcium carbonate (CaCO3) [50].
The silica and alumina content of PSA is very low. This indicates the expectation of limited puzzolanic activity. C-S-H formation depends on the reaction with Ca(OH)2 in the cement matrix. Low SiO2 may reduce the efficiency of this reaction Figure 7a.
The alkali is a factor that accelerates the hydration of the cement [51]. The high alkali content of PSA added in the cement paste caused the increase. The high alkali content of PSA caused the formation of calcium belit (2CaSO4·K2SO4) in the cement paste [52]. Thus, ettringite crystals in a needle-like shape, calcium alumina formation hydrates, and calcium monosulfoalumina hydrates are thought to reduce the viscosity of cement paste [53]. Additionally, ettringite crystals are pretty stable and cause an enormous expansion in the cement paste [54]. The crystal morphology of K2SO4 predominantly exhibits a classical cuboid shape. The crystalline product was characterized by X-ray diffraction. A comprehensive analysis of the particle size revealed that the average size of the crystals obtained by suction filtration ranges between 10–120 μm and exhibits an unimodal distribution [55,56]. With the high K2O and SO3 content of PSA, the formation of K2SO4 crystals observed in the SEM image in Figure 7b may be critical for strength and durability [57,58]. It may cause problems such as setting delays or expansion in cement. Figure 7c,d voids resulting from unburnt organic residues can inhibit hydration reactions or increase porosity [59].
X-ray diffraction (XRD) analysis revealed significant crystallographic differences between the plain cement mortar (Figure 8a) and the 5% PSA substituted mortar (Figure 8b). The control sample exhibited characteristic portlandite [Ca(OH)2] peaks at 18° and 34.15° 2θ and more intense SiO2 peaks at 20.67°, 21.88°, 27.60°, and 29.91° 2θ. In contrast, the 5% PSA sample showed significantly increased gypsum (CaSO4·2H2O) and calcite (CaCO3) peaks superimposed on these baseline patterns. The prominent gypsum diffraction signals (especially at 27.60°, 29.24°, and 34.75° 2θ) correlate with the setting time delay observed in PSA-modified mortars [60] attributable to sulphate-induced hydration interference. This finding is in agreement with the established role of sulfate phases in retarding cement hydration kinetics. In particular, while calcite formation suggests carbonation effects, comparative studies [61,62] show that calcite-containing systems provide faster early-age strength development (7 days) than fly ash or silica fume mixtures, but long-term strength gains (28 days) are limited.

3.4. Strength of Blended Cement

According to Figure 9, the highest 28-day compressive strength result was obtained in the plain mortar with 48.5 MPa, while 5% PSA with 46.4 MPa was obtained in the substituted samples. However, according to the 28-day results, the compressive strength of the cement mortars obtained with 10, 15, 20, 25 and 30% PSA did not meet the compressive strength of the plain specimen and the EN 197-1 standard. Although the early age (1, 2 and 7 days) strength values (21.8, 33.1, 41.0 MPa, respectively) of the 5% substituted designs were superior to the plain mortar (17.8, 28.9, 39.2 MPa, respectively), the 28-day strength value was lower, but it was found to meet the EN 197-1 limit requirement. The intense calcite (CaCO3) peaks observed in the XRD analysis of the 5% substituted mortar (Figure 8b) is an important finding that explains the characteristic early strength behavior of this specimen. It is known in the literature [63] that the presence of calcite catalysis cements hydration reactions and accelerates the early age strength gain. This is consistent with the fact that the 1, 2 and 7-day compressive strength values of this specimen were superior to the control specimen. However, the relative decrease in 28-day strength can be explained by the low pozzolanic activity of PSA and the limitation of the formation of long-term hydration products by calcite.
It can be said that the strength of cement paste is due to the formation of C-S-H gels [64]. In addition, it is estimated that low CaO and SiO2 levels affect the amount of C-S-H gel that can be formed in the structure and thus decrease the strength [65]. C-S-H (calcium silicate hydrate) gel is a product that increases the binding property in cement and provides strength [66]. The results show that the strength decreases as the PSA rate increases. In addition, the strength of the structure is negatively affected as the amount of Na increases [67]. The increase in Na and the decrease in Ca in the structure negatively affect the structure of the C-S-H gel and cause a weaker gel formation [68,69]. The presence of Na alters the morphology of C-S-H. This results in a fibrous network that is less cohesive than the denser structures formed at higher Ca/Si ratios [70].
However, blending 5% PSA into cement appears to be a means of reducing carbon emissions [71,72] and achieving an approximate 5% reduction in the environmental impact score of cement compared to conventional Portland cement. The economic and environmental benefits of 5% PSA substitution in cement production are presented in Table 4.
According to Table 4, a CO2 reduction of 42.5 kg per tonne (with a reference value of 0.85 tCO2/tonne) contributes to environmental sustainability. In terms of cost, a saving of USD 2.85 per tonne has been achieved based on an assumed clinker cost of USD 60/tonne. In addition, resource efficiency has been improved by using 5% (47.5 kg) less clinker instead of the standard 950 kg/tonne clinker. However, these changes result in a 4.5% decrease in compressive strength after 28 days of curing. These results indicate that a balanced optimization of cement production is required.

4. Conclusions

This study comprehensively investigated the usability of pistachio shell ash (PSA) as a replacement material in the cement industry. The findings reveal the effects of PSA on cement properties and its potential as a sustainable building material. The main academic results of the study can be summarised as follows:
  • The experimental results demonstrate that PSA substitution significantly influences the compressive strength development of cement mortars. At early curing stages (1, 7, and 28 days), mortars containing 5% PSA exhibited enhanced strength characteristics compared to the control mixture, with measured values of 21.8 MPa, 33.1 MPa, and 41.0 MPa, respectively, versus 17.8 MPa, 28.9 MPa, and 39.2 MPa for the plain mortar. This improvement in early-age strength can be attributed to the accelerated hydration kinetics facilitated by PSA’s high alkali content (Na2O + K2O = 11.9%) and sulfate (SO3 = 12.96%) components. However, at 28 days of curing, the 5% PSA mixture showed a marginal reduction in ultimate compressive strength (46.4 MPa) compared to the control (48.5 MPa), though it still complied with the EN 197-1 standard requirements. This slight decrease may be associated with PSA’s limited pozzolanic activity (S+A+F = 3.82%) and its interference with long-term C-S-H gel formation.
  • PSA substitution significantly extended the setting times of the cement. A 30% PSA substitution increased the initial setting time by 174% and the final setting time by 126%. This effect is due to the high SO3 content and low pozzolanic activity of PSA.
  • As the PSA substitution rate increased, the water requirement of mortars also increased. This was attributed to the high surface area and fine-grained structure of PSA particles.
  • SEM-EDS and XRD analyses showed that calcite and gypsum phases dominated in the PSA-substituted samples. These phases increased the early age strength but limited the C-S-H gel formation in the long term.
A 5% substitution of pistachio shell furnace filter ash in the cement industry contributes to increasing the compressive strength of cement, recycling regional biomass wastes as a complementary cement material in cement products, the sustainability targets of the world in terms of protecting natural resources and reducing greenhouse gas emissions, and provided environmental and economic benefits to especially the regions where biomass waste is found.

Author Contributions

Conceptualization, M.D. (Mahmut Durmaz) and M.D. (Murat Doğruyol); methodology, M.D. (Mahmut Durmaz); software, M.D. (Murat Doğruyol); validation, M.D. (Murat Doğruyol) and M.D. (Mahmut Durmaz); formal analysis, M.D. (Mahmut Durmaz); investigation, M.D. (Mahmut Durmaz); resources, M.D. (Mahmut Durmaz); data curation, M.D. (Murat Doğruyol); writing—original draft preparation, M.D. (Mahmut Durmaz); writing—review and editing, M.D. (Murat Doğruyol); visualization, M.D. (Murat Doğruyol); supervision, M.D. (Mahmut Durmaz); project administration, M.D. (Mahmut Durmaz); funding acquisition, M.D. (Mahmut Durmaz) and M.D. (Murat Doğruyol). All authors have read and agreed to the published version of the manuscript.

Funding

This study was financially supported by the Siirt University Scientific Research Projects Unit (2018-SİÜMÜH-040).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available by email requirement to the corresponding authors.

Acknowledgments

The authors gratefully acknowledge the financial support provided by Siirt University Scientific Research Projects Unit (Project No: 2018-SİÜMÜH-075). We extend our sincere appreciation to the Limak Kurtalan Cement plant for their technical support and material contributions. Special thanks are due to Kürşat TURNA for his valuable insights into cement chemistry, İrem DİRİKOLU for her assistance with experimental procedures, and Abdullilah YILMAZ for his dedicated work in sample preparation and testing.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. (a) industrial oven, (b) PSA, (c) XRD analysis of PSA.
Figure 1. (a) industrial oven, (b) PSA, (c) XRD analysis of PSA.
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Figure 2. Particle size distribution of PSA and OPC.
Figure 2. Particle size distribution of PSA and OPC.
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Figure 3. (a) initial setting time (b) final setting time.
Figure 3. (a) initial setting time (b) final setting time.
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Figure 4. The water content of cement mortars.
Figure 4. The water content of cement mortars.
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Figure 5. (a) Reference cement sample (OPC) (b) Sample with 5% PSA Substitution.
Figure 5. (a) Reference cement sample (OPC) (b) Sample with 5% PSA Substitution.
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Figure 6. Analysis of 5% PSA: (a) SEM image, (b) EDX spectrum, (c) elemental composition (wt.%).
Figure 6. Analysis of 5% PSA: (a) SEM image, (b) EDX spectrum, (c) elemental composition (wt.%).
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Figure 7. SEM images of the sample with 5% PSA substitution (a) hydration products (b) formation of K2SO4 crystals (c,d) voids.
Figure 7. SEM images of the sample with 5% PSA substitution (a) hydration products (b) formation of K2SO4 crystals (c,d) voids.
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Figure 8. XRD analysis of the (a) Plain cement mortar and (b) 5% PSA-substituted mortar sample.
Figure 8. XRD analysis of the (a) Plain cement mortar and (b) 5% PSA-substituted mortar sample.
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Figure 9. Compressive strength values of the specimens.
Figure 9. Compressive strength values of the specimens.
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Table 1. Comparison of OPC with biomass materials.
Table 1. Comparison of OPC with biomass materials.
SiO2Al2O3Fe2O3CaOMgOSO3K2ONa2ONa2Oeq 1LOI 2S+A+F
OPC19.614.923.1563.662.192.540.750.290.782.8927.68
PSA2.40.650.7717.075.9212.9633.778.1330.3518.333.82
PSA (850 °C) 3 [14]18.114.602.9664.492.342.950.660.130.793.3125.67
CHA [32]8.090.761.0927.93-3.1219.85--1.619.94
HA [20]4.890.771.8350.481.673.2027.732.9821.23-7.49
1 Na2Oeq = Na2O + 0.658 K2O, 2 LOI = loss on ignition, 3 PSA (850 °C) = PSA burnt at 850 °C for 30 min [14].
Table 2. Mortar mixture ratios (g).
Table 2. Mortar mixture ratios (g).
Mix IDOPCPSASandWater
Plain450.00.01350225
5427.522.5
10405.045.0
15382.567.5
20360.090.0
25337.5112.5
30315.0135.0
Table 3. Oxide compositions of blended cement (%).
Table 3. Oxide compositions of blended cement (%).
Component0 (100% OPC)51015202530EN197-1 [45]
SiO219.6118.6317.9216.9716.3315.6114.78
Al2O34.924.724.564.34.093.963.79
Fe2O33.153.032.92.782.742.552.46
CaO63.6660.3657.7154.5452.1749.5546.67
MgO2.192.372.462.632.72.963.1≤5.0
SO32.543.073.414.044.495.025.62≤4.0
K2O0.752.123.254.936.217.929.72
Na2O0.290.620.861.311.531.982.28
LOI2.895.086.938.59.7410.4511.58
Table 4. Economic and environmental benefits of 5% PSA blended in cement production.
Table 4. Economic and environmental benefits of 5% PSA blended in cement production.
ParameterValue
(per Ton Cement)		Notes/Source
CO2 Reduction42.5 kg0.85 tCO2/t [4,73]
Cost Savings$2.85Clinker cost: $60/tonne [74]
Clinker Replacement47.5 kg5% of standard 950 kg clinker/ton cement [75]
Compressive Strength Impact4.5% reductionTest result (28-day curing)
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Durmaz, M.; Doğruyol, M. Pistachio Shell Ash in Agro-Waste Cement Composites: A Pathway to Low-Carbon Binders. Sustainability 2025, 17, 4003. https://doi.org/10.3390/su17094003

AMA Style

Durmaz M, Doğruyol M. Pistachio Shell Ash in Agro-Waste Cement Composites: A Pathway to Low-Carbon Binders. Sustainability. 2025; 17(9):4003. https://doi.org/10.3390/su17094003

Chicago/Turabian Style

Durmaz, Mahmut, and Murat Doğruyol. 2025. "Pistachio Shell Ash in Agro-Waste Cement Composites: A Pathway to Low-Carbon Binders" Sustainability 17, no. 9: 4003. https://doi.org/10.3390/su17094003

APA Style

Durmaz, M., & Doğruyol, M. (2025). Pistachio Shell Ash in Agro-Waste Cement Composites: A Pathway to Low-Carbon Binders. Sustainability, 17(9), 4003. https://doi.org/10.3390/su17094003

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