Investigating the performance of ternary cementitious systems incorporating wollastonite powder and lime sludge in concrete

The production of cement results in a significant amount of energy consumption and CO2 emissions, which are major contributors to environmental pollution. Researchers have developed a ternary blended mix concrete to address these concerns by partially substituting cement with a combination of lime sludge (LS) and wollastonite powder (WP). This study investigated the mechanical properties (compressive strength, spilt tensile strength, and flexural strength) of a ternary blended concrete mix with a grade of M30. 180 specimens, including 60 cubes, 60 cylinders, and 60 prisms, were prepared for testing. The blended concrete mix was produced using different percentages of cement replacement by LS (5%, 10%, 15%) and WP (10%, 15%, 20%). The compressive strength for the ternary mix at 10% LS and 15% WP was 44.78% higher than the conventional mix, the flexural strength ternary mix at 10% LS and 15% WP was 25.46% higher than the conventional mix, and spilt tensile strength ternary mix at 10% LS, and 15% WP was 27.30% higher than the conventional mix at 28 days and trend is almost same for 7,56 and 90 days . The results showed that a ternary mix containing 75% cement, 10% LS, and 15% WP exhibited the best mechanical properties.


Introduction
Using concrete as a construction material is widespread due to its strength, durability, and versatility. The composition of concrete involves combining cement, water, and aggregates, which may include materials like sand, gravel, or crushed stone [1]. The production and use of concrete have significant environmental impacts, primarily due to carbon dioxide emissions relatedto cement production. The production of cement demands a significant amount of energy and results in the release of substantial greenhouse gases, such as CO 2 , that contribute to the problem of global warming [2]. In addition, the extraction of raw materials used in concrete production, such as sand and gravel, can negatively impact natural habitats, landscapes, and ecosystems [3]. In order to tackle these issues, researchers are investigating methods to diminish the ecological footprint of concrete through the creation of more sustainable manufacturing processes and the integration of alternative materials., such as lime sludge, wollastonite powder, fly ash, and slag. Additionally, using concrete in construction can have a positive environmental impact by improving the energy efficiency and lifespan of buildings and infrastructure [4]. As the demand for sustainable construction continues to grow, developing environmentally friendly concrete production and use practices is becoming increasingly important [5].
The utilization of supplementary cementitious materials(SCMs) is a strategy aimed at mitigating the environmental impact associated with the production of concrete [6]. SCMs are materials that can partially replace traditional cement in concrete production.By doing so, the energy consumed and the greenhouse gas emissions linked to cement manufacturing can be decreased. Common SCMs include fly ash, slag, lime Sludge, wollastonite, and silica fume, waste products from industrial processes [7]. These materials can enhance strength, durability, and workability and reduce the cement content needed [8]. In addition, utilizing SCMs will Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
improve the long-term performance of concrete by reducing shrinkage and cracking, improving resistance to chemical attack and freeze-thaw cycles, and increasing the lifespan of structures [9]. Incorporating SCMs in concrete production shows the potential to decrease the ecological footprint of building practices while enhancing the durability and functionality of concrete constructions [10]. Different approaches to improve concrete performance is to use ternary and quaternary binders, which involve the addition of SCMs to traditional cement mixtures. Numerous studies have been conducted with the aim of investigating the microstructure, strength, and durability of quaternary concrete composites, considering the influence of multiple factors [11,12]. Furthermore, research has been conducted into the fracture parameters and efficacy of concretes that utilize quaternary blended cements, using techniques such as digital image correlation [13][14][15]. More recently, the influence of acrylamide in situ polymerization on the mechanical properties and microstructure of a specific quaternary system has been studied [16]. In the present study, a ternary blended mix was formed by using lime sludge and wollastonite powder.
Lime sludge is a paper waste material generated during the production of paper. It is a byproduct of the kraft process, one of the most widely used methods for papermaking [17,43]. In this process, wood chips are treated with chemicals to break down the lignin and extract the cellulose fibers used to make paper [18]. The chemicals used in this process include NaOH and sodium sulfide, which react with the lignin and produce a waste material known as lime sludge [19]. Lime sludge is a mixture of calcium carbonate, calcium sulfide, and other impurities left over from the chemical reaction during the kraft process [20]. Lime sludge, which typically exhibits a low pH level and high moisture content, appears as a grayish-white substance with a composition that may vary depending on factors like the type of wood utilized, the specific kraft process chemicals, and processing conditions [21]. Disposing of lime sludge has been a significant environmental challenge for the paper industry for many years. It is a bulky and heavy material that is difficult to transport and store, and it can also be a source of pollution if it is not managed correctly [22]. Traditionally, lime sludge was dumped into landfills or discharged into nearby waterways, negatively impacting the environment and public health [23]. Sustainable and eco-friendly methods for managing lime sludge have recently become a growing focus [24]. One of the most promising approaches is to use it as a soil amendment. Lime sludge contains high levels of calcium, which can help to improve the pH level of acidic soils and provide essential nutrients for plant growth [25].
In addition, the calcium carbonate in lime sludge can help to improve soil structure and water-holding capacity. Another potential use for lime sludge is in the production of construction materials. Studies have indicated that lime sludge can serve as an alternative to sand or cement in manufacturing construction materials such as concrete and bricks [26]. By utilizing lime sludge in construction, it is possible to mitigate the ecological effects of the building sector while also providing the paper industry with a beneficial source of raw materials. In summary, lime sludge is a form of paper waste produced during the kraft process [27]. It is a challenging material to manage, but many promising approaches exist for its sustainable and eco-friendly use. By finding new ways to utilize lime sludge, the paper industry can reduce its environmental impact and contribute to a more sustainable future [28]. Due to its strength and durability, wollastonite powder is an essential additive in concrete, a popular construction material used in various applications. When added to concrete, wollastonite powder can improve its properties in various ways, making it a versatile and practicalmaterial [5].
One of the primary benefits of adding wollastonite powder to concrete is that it can improve its strength and durability. Wollastonite powder has a unique needle-like structure that reinforces the concrete, making it more resistant to cracking and other forms of damage [6]. In addition, wollastonite powder has a high aspect ratio, meaning it has a large surface area compared to its volume. As a result, it serves as a helpful filler material that can aid in lessening the amount of cement needed in concrete production, thereby cutting costs and mitigating the environmental impact [29,30]. Another benefit of adding wollastonite powder to concrete is that it can improve its workability. Wollastonite powder is a delicate material that can be easily mixed into the concrete mixture, improving its flowability and reducing the water required [31]. The result can be concrete that is simpler to handle, leading to decreased labor and time required to complete construction projects.Wollastonite powder can also improve the thermal properties of concrete [32]. It has a low thermal conductivity, which can help reduce heat loss in buildings and other structures. This can lead to a more comfortable living or working environment and lower energy costs [33]. In addition, wollastonite powder can improve the chemical properties of concrete. It has a high pH level, which can help to prevent the growth of bacteria and other microorganisms that can cause damage to the concrete [34,35]. This can improve the lifespan of the concrete, reducing the need for costly repairs or replacements.Overall, wollastonite powder is a valuable additive in concrete that can improve its properties in various ways [36]. It can increase strength, improve workability, and enhance thermal and chemical properties, making it a versatile and effective material for various construction applications [37]. Its use in concrete can also help to reduce costs and minimize environmental impact, making it a sustainable and eco-friendly choice for builders and contractors [38].
In this research it was planned to investigate the use of wollastonite powder and lime sludge as two of the three materials in a ternary blended concrete mixture. While previous studies have explored the use of wollastonite and other materials in binary blended concrete mixtures, few have investigated the addition of lime sludge to create a ternary blend. The primary goal of this investigation is to optimize the ternary concrete mix by utilizing a combination of lime sludge and wollastonite powder. To attain this goal, an extensive experimental program was developed in order to determine the most practical combination of lime sludge and wollastonite powder percentages that could be utilized to partially substitute cement in the mixture. To determine the optimal combination for the ternary blended concrete mix, different proportions of cement replacement using Lime sludge (5%, 10%, 15%) and wollastonite powder (10%, 15%, 20%) were tested, and the mechanical characteristics of each mixture were assessed in comparison to the conventional mix. The potential benefits of this approach are significant. The strength and durability of concrete are recognized to be enhanced by the incorporation of wollastonite powder, while also reducing its carbon footprint by decreasing the need for cement. By converting lime sludge, which is a byproduct of the paper industry, into a cementitious material, it is possible to repurpose it and thereby decrease the ecological footprint of concrete manufacturing. Through a series of experimental tests, we will investigate the effect of adding varying proportions of wollastonite powder and lime sludge to a concrete mixture, and compare the resulting mechanical properties and durability to traditional concrete mixtures. This research will provide new insights into the feasibility and effectiveness of using ternary blended concrete mixtures with wollastonite powder and lime sludge, and its potential impact on sustainable construction practices. Overall, this research represents a novel approach to improving the mechanical properties of concrete mix, and has the potential to contribute to the growing body of knowledge on alternative materials in construction.

Research significance
The research mainly focuses on the utilization of lime sludge and wollastonite powder in concrete. The use of these materials in concrete could become more widespread, leading to a more sustainable and environmentally conscious approach to construction. The utilization of lime sludge and wollastonite powder in concrete has become a topic of substantial research interest, as they offer the potential to enhance concrete properties and provide eco-friendly alternatives for the building sector.As a byproduct of the pulp and paper sector, lime sludge presents an opportunity as an affordable substitute for conventional concrete components. By utilizing lime sludge in concrete production, the material's compressive strength, workability, and longevity may all be enhanced.
Additionally, lime sludge has a high pH level, which can help to neutralize the acidic properties of other concrete components, reducing the likelihood of corrosion and other forms of damage.Wollastonite powder, a naturally occurring mineral, has been found to enhance the properties of concrete by improving its strength, durability, and thermal and chemical properties [39]. Wollastonite powder has a unique needle-like structure that reinforces the concrete and can also reduce the amount of cement required in the mixture, making it a costeffective and sustainable option [36]. The utilization of lime sludge and wollastonite powder in concrete has the potential to provide several significant benefits. Incorporating these materials can lessen the ecological effects of construction by using both natural minerals and waste products, thereby reducing the necessity for resourceintensive traditional materials [40]. Additionally, the improved properties of concrete can increase its lifespan and reduce the need for costly repairs and replacements, leading to more sustainable and cost-effective construction practices.
With reference to the literature and the available recent studies, the combinations proposed for the study are considered essential to check mechanical properties. Hence, the study findings can be treated to replace the conventional mix. The paper's novelty is planned to find the replacement of the conventional mix with the selected materials. Initially, lime sludge was fixed at 5% replacement, and the wollastonite powder percentage varied between 10 to 20%. Secondly, lime sludge was fixed at 10% replacement, and the wollastonite powder percentage varied between 10 to 20%. Finally, lime sludge was fixed at 15% replacement, and the wollastonite powder percentage varied between 10 to 20%. The replacement combinations in this study are considered a novel approach that allows finding the performance of the ternary mix.

Materials
In this research,53 grade Ordinary Portland Cement (OPC) in accordance with IS: 12269-1987, with a specific gravity of 3.12 and specific surface area of 225 m 2 g −1 , and initial and final setting times of 45 and 480 min, respectively. Fine aggregate conforming to Zone II as per IS: 383-1970 was used in the study, with specific gravity and bulk density of 2.65 and 1.47 g cc −1 ., respectively, obtained from a nearby river. Locally available 20 mm granite, conforming to IS: 383-1970, was used as the coarse aggregate with a specific gravity of 2.81 and bulk density of 1.51 g cc −1 . The wollastonite powder used in the research was sourced from Vijayawada and had a specific gravity of 2.90. Lime Sludge with a specific gravity of 1.98 was obtained from the Bhimavaram paper mill, and potable water was used for mixing and curing. Table 1 presents the chemical compositions of the cement, Lime sludge, and wollastonite powder used in the study, while table 2 outlines the mix proportions of the concrete.

Mix proportioning
A total of 180 concrete specimens were prepared in this study, including 1 control mix and 9 ternary blended mixtures. The control mix consisted of Portland cement, fine aggregate, and coarse aggregate, while the ternary blended mixtures consisted of Portland cement, fine aggregate, coarse aggregate, wollastonite powder, and lime sludge. The mix proportions were determined using a target compressive strength of 40.35 MPa at 28 days, and the mixtures were prepared using a standard laboratory mixer in accordance with IS 10262: 2019 standard.

Specimen preparation
The concrete mixtures that were prepared were utilized to produce test specimens for the purposes of conducting compressive, split tensile, and flexural strength tests.. A total of 60 cubic specimens (150 mm × 150 mm × 150 mm) for compressive strength test were casted, 60 cylindrical specimens (150 mm × 300 mm) for split tensile strength test were casted, and 60 prismatic specimens (100 mm × 100 mm × 500 mm) for flexural strength test were casted. The Specimens were demoulded after 24 h of casting and were cured for 7, 28, 56, and 90 days in a moist room before testing in accordance with IS 516: 1959 standard.

Testing
The compressive, split tensile, and flexural strengths of the specimens were tested using compressive and universal testing machine in accordance with IS 516-2002 and IS 516: 1959 standard. The compressive strength testing was conducted on cubic specimens, while the split tensile strength testing was conducted on cylindrical specimens. The flexural strength testing was conducted on prismatic specimens.

Workability
Workability is a crucial characteristic of concrete that refers to its ability to be mixed, transported, placed, and compacted without excessive segregation or bleeding. The workability of concrete affects the ultimate quality of the end product, the duration and labor required for the construction process, and the project's overall cost. It is influenced by factors such as the water cement ratio, the size and shape of the aggregates, chemical admixtures, and the properties of SCMs used in the mix [41]. A concrete mix with good workability is easier to handle, leading to faster and more efficient construction processes. Table 3 delineates the formulation of nine distinct types of ternary concrete mixtures, each composed of different ratios of lime sludge, wollastonite powder, and cement. The workability of the concrete was measured using the slump cone test, following the IS 1199-1959 standard. The slump of the OPC concrete was recorded as 85 mm. As shown in figure 1, an increase in slump was observed in all ternary mixes as the lime Sludge and wollastonite powder contents increased till the optimum mix, the rest of the ternary mixes showed a downtrend. The improved workability linked to an increase in wollastonite powder concentration can be attributed to its unique particle shape.; The particle shape helps to fill the voids in the concrete mixture and improves the particle packing, increasing the mixture's density. This density increase allows less water to be used in the mixture while maintaining almost the same level of workability. Additionally, wollastonite powder is often coated with a layer of calcium hydroxide on the surface. This acts as a lubricant and reduces the friction between the particles in the mixture, which makes the mixture easier to mix and place. It helps to prevent segregation. As wollastonite powder content increases, there will be improved particle packing, reducing bleeding and preventing these issues. An increase inthe addition of wollastonite powder to concrete can improve workability due to the unique particle shape, lubricating properties, reduction in bleeding, and control of setting time. Adding lime sludge to concrete does not typically affect the workability of the mixture. This is because lime sludge is not known to have properties that improve concrete handling and shaping characteristics. Unlike wollastonite powder, which can improve workability by improving particle packing, reducing friction, and controlling bleeding, lime sludge does not have properties that directly affect these aspects of concrete. However, lime sludge can have other potential benefits when added to concrete. For example, lime sludge contains calcium, which can act as a binder  Once incorporated into the concrete mix, it interacts with the calcium hydroxide produced during cement hydration, forminga calcium silicate hydrate (C-S-H) gel that enhances the strength and longevity of concrete. This pozzolanic reaction between lime sludge and cement increases the strength of the concrete. Secondly, the wollastonite powderacts as a filler in the concrete matrix. Adding to the concrete fills the voids and spaces, making the concrete more compact and dense. By enhancing particle packing in concrete, this filling effect results in an improvement in compressive strength. Furthermore, lime sludge and wollastonite powder reduce the water-cement ratio of concrete, meaning less water is required to attain the intended level of workability in the concrete mix. This results in a denser and stronger concrete mix. Finally, adding lime sludge and wollastonite powder increased the rate and extent of cement hydration. These materials provide additional sources of calcium and silicates, which are required for the formation of Calcium silicate hydrates gel [42]. The increased hydration of cement leads to a denser and stronger concrete matrix, improving the compressive strength of the concrete.
In summary, adding lime sludge and wollastonite powder enhances concrete's chemical and physical properties, resulting in a stronger and more durable material. Figure 2 illustrates the combinations of the selected materials varying between 5 to 20 percent. The ternary mix of 10% lime sludge and 15% wollastonite powder had the highest compressive strength at 7, 28, 56, and 90 days.

Split tensile strength
Split tensile strength was evaluated following the IS 516-1959 standard, and the results showed that all nine mixes containing ternary components demonstrated higher Split tensile strength when compared to M30 grade OPC concrete at 7, 28, 56, and 90 days as shown in figure 3. Additionally, the results indicated that the mix containing 10% lime sludge and 15% wollastonite powder showed the highest Split tensile strength at 7, 28, 56, and 90 days, with an increase of approximately 25% compared to OPC concrete. The observed increase in Split tensile strength with adding lime sludge and wollastonite powder to concrete can be attributed to their unique properties. Lime sludge contains fine particles and reactive silica and alumina, which act as a pozzolanic material in the concrete mix. It reacts with the calcium hydroxide created during hydration after mixing with cement. It produces extra calcium silicate hydrate (C-S-H) gel, which enhances the robustness and longevity of the concrete, leading to a rise in Split tensile strength.Wollastonite powder, a fibrous mineral, improves concrete's mechanical and chemical properties. It acts as a micro-reinforcement in the concrete matrix, preventing the formation and propagation of cracks. Incorporating wollastonite powder in concrete reduces its permeability, making it more resilient against chemical and water damage. Hence, adding lime sludge and wollastonite powder to the ternary mix results in better mechanical characteristics and durability of the concrete, leading to a noteworthy enhancement in Split tensile strength.

Flexural strength
According to IS 516-1959, a flexural test was performed on OPC concrete using a two-point loading test. The 7, 28, 56, and 90 days flexural strengths were measured and found to be 4.52 N/mm 2 , 5.42 N/mm 2 , 5.68 N/mm 2 , and 5.82 N/mm 2 . The results were plotted in a graph ( figure 4) showing the flexural strength variation of all ternary mixes concerning the percentage of Lime Sludge and Wollastonite Powder.The results showed that all nine ternary mixes had higher flexural strength compared to the OPC 30 grade concrete at 7, 28, 56, and 90 days, and this enhancement in strength was due to the formation of more robust interfacial zones in the ternary mixes. Additionally, the flexural strength exhibited the same pattern as compressive strength and split tensile strength at 7, 28, 56, and 90 days. In summary, the ternary concrete mix containing 10% lime sludge and 15% wollastonite powder demonstrated the most substantial improvement in flexural strength at 7, 28, 56, and 90 days, exhibiting an increase of nearly 25% compared to OPC concrete. This finding suggests that the addition of lime sludge and wollastonite powder can significantly enhance the flexural strength of OPC concrete, making it a promising material for construction applications.

Conclusions
This study examines the behavior of M30 grade ternary blended concrete mixes, incorporating various combinations of cement replacement percentages by Lime sludge (5%, 10%, 15%) and Wollastonite powder (10%, 15%, 20%). The study aims to investigate the impact of incorporating Lime sludge and Wollastonite powder on the mechanical properties of the resulting ternary blended concrete mixes, including compressive, split tensile, and flexural strengths.
• The study presents the results of the mechanical properties tests for the ternary blended mix. The study showed that the ternary blended concrete mix had higher compressive strength than the traditional mix. The mix containing 10% lime sludge and 15% wollastonite powder displayed the greatest compressive strength among all the blends tested.  • The improvement in compressive strength is due to the formation of sturdy cementing agents, such as calcium silicate hydrates and calcium aluminum silicates.
• Incorporating lime sludge and wollastonite powder in the concrete mix has been observed to enhance its workability greatly. The increase is due to Lime sludge, a fine powder that can fill in the gaps between the aggregates, resulting in better particle packing and improved lubrication. This enhances the flow of the mix, making it more workable. On the other hand, Wollastonite powder has a unique needle-like structure that helps increase the mix's surface area. This enhances the interaction between the cement and water, resulting in better particle dispersion and improved flow.
• The results of the study showed that the split tensile and flexural strengths of the ternary blended concrete mix were higher than those of the conventional mix. The mix containing 10% Lime Sludge and 15% Wollastonite Powder exhibited the highest split tensile and flexural strengths among all the blends tested.  • At 56 days, the flexural strength of mix containing 10% lime sludge and 15% wollastonite powder showed 25.66% increase of strength when compared to conventional mix and at 90 days, the flexural strength strength of mix containing 10% lime sludge and 15% wollastonite powder showed 25.70% increase of strength when compared to conventional mix.
• This improvement in split tensile and flexural strengths can be attributed to the formation of stronger interfacial zones between the components of the mix and the pozzolanic reactions that occur in ternary mixes, resulting in more durable and structurally sound concrete.

Data availability statement
All data that support the findings of this study are included within the article (and any supplementary files).

Further recommendations
In concern to further studies, the current research can be further adopted by including studies related to longterm durability. Adding lime sludge or wollastonite to concrete has shown promise in increasing strength.
However, further studies are needed to evaluate the long-term durability of such concrete structures and to determine their impact on the service life of the structures. Also, the optimal mixing proportions for lime sludge and wollastonite can vary depending on the source of the materials, their particle size distribution, and the specific application. Therefore, future studies can investigate the optimal mixing proportions for different types of concrete applications, such as pavement or bridge decks. Although using lime sludge and wollastonite as partial replacement materials in concrete can potentially reduce the environmental impact of concrete production, the overall environmental impact of their use needs to be evaluated. Future studies can assess the environmental impact of these materials over the entire life cycle of the concrete structure, including the production, transportation, use, and disposal phases. Finally, economic feasibility is another criterion that assesses the use of lime sludge, and wollastonite can potentially reduce the cost of concrete production by replacing a portion of cement. However, the economic feasibility of their use needs to be further evaluated. Future studies can investigate the cost-effectiveness of using these materials in different concrete applications.