A Review of the Performance, Sustainable Applications, and Research Challenges of Limestone-Calcined Clay-Cement (LC3) Systems

Abstract

This paper presents a systematic review of the progress of the research on limestone-calcined clay cement (LC3), focusing on its low-carbon characteristics, sustainable applications, and performance. LC3 can be used to address the high carbon emission problem in the cement industry, as its use significantly reduces carbon dioxide emissions (by 30%–40%) due to clinker being partially replaced with calcined clay and limestone in its fabrication. Studies have shown that the hydration reaction of LC3 generates calcium-aluminum-silicate hydrate (C-A-S-H), carbon-aluminate, and calcium alumina, which optimize its microstructure and endow it with comparable mechanical properties (28 day compressive strength close to or exceeding that of OPC) and better durability (outstanding resistance to sulfate erosion and carbonation) compared to ordinary Portland cement (OPC). LC3 has been used in 3D printing, ocean engineering, geotechnical reinforcement, and other applications, all of which have verified its engineering feasibility. Despite the significant environmental and economic advantages of LC3, its high-temperature performance, freeze–thaw resistance, and long-term durability still need to be further investigated. This paper provides theoretical support and practical references for the development and promotion of low-carbon cement materials.

1. Introduction

Presently, silicate cement is the predominantly used material in construction. As of 2021, worldwide cement production reached 4.31 billion tons, with projections indicating a yearly growth that is expected to rise to 4.83 billion tons by 2030 [1]. The cement manufacturing process produces significant greenhouse gas emissions, with carbon dioxide contributing from 5% to 7% of the world’s total human-made CO₂ emissions [2,3].

In the cement sector, the use of supplementary cementitious materials (SCMs) is conducive to lower CO₂ emissions. Historically, the primary source of SCMs has been industrial debris, including fly ash and slag. Advancements in industrial technology and more rigorous environmental safeguards have curtailed these types of waste [4,5]. The use of composite cementitious substances derived from calcined clay and limestone presents a hopeful strategy due to their accessibility and minimal environmental footprint (as shown in Figure 1). In response to the urgent demand for reducing carbon emissions, this research promotes the creation and application of LC3 as a viable option within the cement sector. This study, through a thorough examination of LC3’s material composition and engineering uses, aims to showcase this material’s transformative capability of markedly reducing the industry’s carbon footprint while preserving performance traits akin to those of traditional cement-based materials. This novel strategy addresses worldwide decarbonization needs and also lays the groundwork for the application of innovative circular economy methods to building materials.

LC3 was originally proposed by Prof. Scrivener of the Swiss Federal Institute of Technology in Lausanne and Prof. Martirena of the Universidad Central de Las Villas, Cuba [6]. A novel cementitious material system, termed LC3-X, is proposed that is fabricated by proportionally combining calcined clay, limestone, gypsum, and Portland clinker. Here, “X” denotes the mass percentage of Portland clinker in the system. The most commonly used LC3 system, designated as LC3-50, comprises 50% Portland clinker, 30% calcined clay, 15% limestone, and 5% gypsum, as illustrated in Figure 2. Limestone powder is derived from the by-product of the limestone crushing process in quarries, and extensive research has been carried out on its application in cement concrete. In cement concrete, limestone powder not only plays the physical roles of filling, nucleation, and dilution but also possesses the chemical function of reacting with the aluminum phase in cement to generate calcium carbon aluminate [7,8]. The generation of calcium carbonyl aluminate not only increases the solid-phase volume of hydration products but also significantly reduces their porosity and effectively prevents the transformation of calomel to monosulfide-type products, which in turn contributes to the enhancement of the cement’s strength [9]. However, the limited content of aluminum phase in the studied cement resulted in a low production of calcium carbonyl aluminate, and the effect of improving the cement’s strength was not obvious.

LC3 has emerged as a transformative, eco-friendly alternative to conventional cement, capturing global interest through its groundbreaking potential to slash the carbon footprint of the construction industry by up to 40% compared to traditional production methods. This innovative binder leverages abundantly available raw materials and energy-efficient manufacturing processes, positioning it as a cornerstone for sustainable infrastructure development in the face of climate imperatives [10,11,12,13,14]. LC3 belongs to the category of low-carbon cement, which is prepared by blending limestone with clay that has undergone a high-temperature calcination process. In this process, the alumina component in the clay reacts chemically with the carbonate in the limestone to produce a carbon-aluminate phase, which imparts superior strength and durability to the cement product. In contrast to alternative supplementary cementitious materials like fly ash, limestone distinguishes itself through a dual advantage: not only does it benefit from significantly greater natural abundance, but its geological distribution also ensures marked accessibility and logistical efficiency in processes for its procurement [15] (as shown in Figure 1). Although the production of fly ash exceeds that of cement in some cases, its quality varies, with only about one-third of fly ash meeting the criteria for cement blending. In addition, given the urgent need to reduce environmental emissions on a global scale, coal power generation is facing increasing skepticism, which largely affects the long-term supply stability of fly ash, casting a shadow over its future application as a cement additive.

The incorporation of calcined clay in LC3 systems presents several significant advantages. Primarily, the technology leverages two naturally abundant materials—clay and limestone—which are globally accessible, offering an environmentally sustainable alternative for reducing carbon emissions in cement production. From an industrial implementation perspective, LC3 manufacturing utilizes existing cement production infrastructure and conventional processes, requiring minimal additional training for workforce adaptation. Furthermore, the compatibility of LC3 with standard handling protocols facilitates its seamless integration into current cement manufacturing operations without necessitating specialized equipment or procedural modifications [16].

In summary, LC3-based raw materials are more available, less costly, and less carbon-intensive. In this paper, the hydration reaction, fresh mix properties, mechanical properties, and durability of limestone-calcined clay are comprehensively analyzed.

Figure 1. Geographic availability assessment of key supplementary cementing materials [17].

Figure 1. Geographic availability assessment of key supplementary cementing materials [17].

Figure 2. Comparison of carbon dioxide emissions during the production of OPC and LC3 [18].

Figure 2. Comparison of carbon dioxide emissions during the production of OPC and LC3 [18].

2. Chemical Composition and Hydration Reactions of LC3

A complicated chemical reaction including clinker, sintered clay, and limestone is required for the curing of LC3 (

Table 1. Chemical reactions and hydration products of OPC and LC3.

Type	Composition	Chemical Reaction	Hydration Products
OPC	(1) Clinker (95%)
	(a) Tricalcium Silicate (C3S)	C3S + 6H2O → C3S2H3 + 3Ca(OH)2	CSH and CH
	(b) Dicalcium Silicate (C2S)	C2S + 4H2O → C3S2H3 + Ca(OH)2	CSH and CH
	(c) Tricalcium Aluminate (C3A)	C3A + 6H2O → C3AH6	CAH
	(d) Tetra-calcium Aluminoferrit (C4AF)	C4AF + 7H2O → C4(A, F) H13	AFm and AFt
	(2) Gypsum (GY) (5%)	C3A + 3C$ + 26H2O → C6AS3H32	Ettringite
	Calcium sulfate dihydrate (CaSO4⋅2H2O)	C6AS3H32 + 2C3A + 4H→ 3C4ASH12	Monosulfate
LC3	(1) Clinker (50%)
	(a) Tricalcium Silicate (C3S)	C3S + 6H2O →C3S2H3 + 3Ca(OH)2	CSH and CH
	(b) Dicalcium Silicate (C2S)	C2S + 4H2O → C3S2H3 + Ca(OH)2	CSH and CH
	(c) Tricalcium Aluminate (C3A)	C3A + 6H2O → C3AH6(further reaction) C3A + 3CaSO4·2H2O +26H → C6A$3H32
	(d) Tetra-calcium Aluminoferrit (C4AF)	C4AF + 4CH +14H →C4(A, F) H13
	(2) Gypsum (5%)
	Calcium sulfate (C$)	C4AF + 4CH + C$ + 2Cc +12H → C4(A, F) cH13	Iron-rich monocarbonate phase
	(3) Calcined clay (30%)
	Metakaolin (AS2)	AS2 + 3.1CH + 4.6H →C1.5A0.1SH4 + C2ASH8 +0.9C4AH13	C-(A)-S-H, calcium aluminate, AFm
	(4) Limestone powder (15%)	AS2 + 5.4CH + 0.4Cc +1.2C$ + 20H →2C1.5A0.1SH4 + 0.4C4AcH12 + 0.4C6A$3H32	Monocarbonate or hemicarbonate as AFm phases
	Calcite (Cc)	C3A + 0.5 Cc + 0.5CH +0.5C$ + 11.5H →C4Ac0.5H12

). This new cement is intended to lessen the carbon footprint of the construction industry. It allows for this due to the decreased porosity of its cement matrix, which improves its durability and long-term performance through the formation of important mineral phases during the curing process, including calomel, carbon aluminate, and C-A-S-H.

The use of readily available kaolinitic clay, especially low-grade kaolinitic clay mixed with an extra 15% of limestone, is the main invention of LC3 [19]. This combination has a synergistic effect [20] and performs similarly to regular Portland cement. Clay containing kaolinite is calcined to yield metakaolin, an amorphous aluminosilicate that combines with calcium hydroxide to generate aluminate and C-A-S-H hydrates. Alumina and limestone combine to generate dense, crystalline carboaluminate phases, which aid in the development of the cementitious matrix’s microstructure [21,22]. The main cause of LC3’s similar performance to OPC is found to be the notable improvement that it demonstrates in carboaluminate phase synthesis [23,24]. Li et al.’s study also provides a systematic summary of the formation stages of ettringite and C-(A)-S-H, as shown in Figure 3.

Kaolinitic clay (Al₂O₃·2SiO₂·2H₂O, AS₂H₂) undergoes dehydroxylation during calcination at 500–800 °C, forming metakaolin (Al₂O₃ 2SiO₂, AS₂) with pozzolanic reactivity. However, further increases in the calcination temperature lead to the formation of spinel-type phases and amorphous silica, which subsequently crystallize into mullite and cristobalite. These crystalline phases negatively impact the material’s reactivity. Therefore, optimizing the calcination process is critical for improving the quality of metakaolin.

Research [26,27,28] indicates that the combination of limestone powder and SCMs with an aluminum phase amplifies the impact of calcium carbon-aluminate creation in cement. Reports [29] indicate that concrete containing 25% limestone and 20% fly ash exhibits greater 28 d strength compared to concrete with only 25% limestone powder, and that cement paste with 10% limestone powder and 10% metakaolin surpasses the strength of cement with only 20% metakaolin.

Avet and colleagues [11] explored how the amount of calcined kaolinite in calcined clay impacts the moisture content in limestone-calcined clay cement (LC3-50), which includes 50% clinker. The study’s findings revealed that the subsequent clinker reaction was hindered after three days when the calcined kaolin concentration in the clay exceeded 65%. In-depth research indicated a connection between the deceleration of clinker hydration and the connectivity of its pores. A greater amount of calcined kaolinite accelerates the attainment of this refining threshold. Once this threshold is attained, the creation of carbon-aluminate hydrates becomes restricted. Consequently, the process that occurs with the addition of biotite kaolinite influences the production of C-A-S-H, predominantly impacting the porosity of the gel [30,31].

Krishnan [32] conducted a study on how carbonate and wrought kaolin clay influence LC3’s hydration, revealing that the type of carbonate rock does not notably impact LC3’s hydration rate and strength enhancement. In calcined kaolin clay, dolomite exhibits a slower reaction rate than calcite. In one study, the combined replacement of PC with MK and LS led to superior characteristics at a younger age [33]. Upon achieving a 30% substitution rate, employing MK and LS in a 2 to 1 ratio yields superior mechanical characteristics compared to the reference PC, while a 1 to 2 ratio results in comparable mechanical properties.

Although most of the studies reported in the literature are based on LC3 mixtures that contain 50% clinker with a mass ratio of calcined clay to limestone of 2–1, it has been suggested [34] that the optimum ratio depends on the physical and chemical properties of the clinker. Go and Danner et al. [35,36] experimentally evaluated the physical properties of calcined clay-cement systems, their hydration processes, and the microstructural development of the studied situation. Their results showed that the hydration process of this composite cementitious material is similar to that of pure cement paste.

Limestone mainly serves as a non-reactive filler in LC3 cement setups, with its mechanical robustness stemming mainly from the pozzolanic interaction between calcium hydroxide and silicate phases in calcined clay, which results in the formation of C-A-S-H. Two key factors dictate the stoichiometric and nanostructural properties of C-A-S-H: the amount of kaolinite in the calcined clay that is used and the temperature conditions during the hydration process. Significantly, the addition of sulfate to the system results in adsorption patterns on C-A-S-H surfaces that vary with the temperature. At higher temperatures, this absorption process acts as an adaptive regulator, dynamically restricting the interaction between aluminate species to create carboaluminate phases, and thus maintaining the hydrated matrix’s stability [37]. Research indicates that carbon laminates and calomel constitute roughly a quarter of LC3 hydrated cement paste’s total volume, whereas C-A-S-H accounts for approximately half of it in references [27,38], a comparison was made between LC3-50’s heat transfer at varying gypsum levels and the physical phase makeup of PC and LC3-50 after 3 and 28 days of hydration (as depicted in Figure 4 and Figure 5).

LC3 is a sustainable cementitious material that is formulated through the strategic replacement of clinker with calcined clay and limestone [39]. Its hydration mechanism centers on the concurrent formation of three critical phases: (1) C-A-S-H, which provides the primary binding matrix; (2) carboaluminate phases, which densify the microstructure; and (3) supplementary aluminous phases that synergistically reduce the cement’s capillary porosity. This tripartite phase assemblage enhances the cement’s durability by decreasing its total pore volume and refining its pore size distribution. Crucially, LC3 achieves performance parity with OPC through the accelerated nucleation of carboaluminate phases, which compensate for the clinker reduction by optimizing both the mechanical strength development and long-term chemical stability of the cement.

Contemporary investigations into LC3 cement systems have elucidated critical relationships between their composition, microstructure, and performance. Nie [40] conducted a comparative analysis of hydration mechanisms in binary (Portland cement + calcined clay, PC2) versus ternary (LC3) systems, revealing that limestone incorporation enhances the precipitation of calcite while reducing the aluminum uptake in C-(A)-S-H phases. Complementary microstructural characterization by Avet et al. demonstrated that LC3 formulations with 50% clinker substitution exhibit substantial compositional shifts in their C-A-S-H gels. Their findings establish a direct correlation between aluminum incorporation in the binding phase and the kaolinite content of calcined clay precursors, although all of their blends maintained consistent Ca/Si ratios that exceeded those of conventional Portland cement.

Further mechanistic insights emerge from particle engineering studies: Shao et al. [41] systematically quantified how the fineness of limestone modulates the resulting early hydration kinetics, with the optimal pore-filling efficiency being observed at 45% limestone substitution when using particles below 10 μm. Paradoxically, Overmann et al. [42] observed that clays with maximal R3-test reactivity (≥90% pozzolanic activity) did not exhibit a proportionally enhanced compressive strength at 7/28 days, suggesting kinetic limitations in aluminate-silicate phase interactions despite the favorable thermodynamic potential.

Atasever et al. [43] investigated the effect of the clay type and component fineness on LC3 and found that illite clay LC3 paste has larger pore sizes while kaolinite LC3 has a denser microstructure due to the formation of C-S-H and hemialuminates. Balestra et al. [44] compared the microstructures of the various raw materials of LC3 (shown in Figure 6). Paste produced from coarse calcined clay and coarse limestone has a lower heat of hydration and a weaker thermal development peak than other pastes. Kaolinite clay LC3 had the highest heat of hydration, and montmorillonite calcined clay LC3 had the lowest. They also studied the properties of calcium sulfoaluminate clinker LC3 [45] and found that the early strength of limestone-calcined clay calcium sulfoaluminate cement, which was prepared by replacing the Portland cement with calcium sulfoaluminate cement, was increased by 30%–80%. Although the strength growth slowed down after 1 day, the strength development was comparable to that of the original cement after adjusting for CO₂ emissions. The cement had 10%–15% higher fluidity, a lower heat of hydration (lasting more than 12 h), and similar production costs. The characteristics of different supplementary cementitious materials (SCMs) are shown in

Table 2. Characteristics of different supplementary cementitious materials (SCMs).

Property	Granulated Blast Furnace Slag (GGBFS)	Fly Ash (FA)	Calcined Clay	Steel Slag
Early-Age Strength	Moderate	Low	High (LC3 system)	Moderate
Long-Term Strength	Significant increase (+20%~30%)	Slow growth	Continuous growth	Stable improvement
Heat of Hydration	Reduction: 30%~50%	Reduction: 40%~60%	Moderate reductio	Significant reduction
Durability	Excellent impermeability, strong carbonation resistance	High sulfate resistance, weak freeze–thaw resistance	Strong chemical erosion resistance	Improved freeze–thaw resistance (when composited)
Sustainability	Waste utilization, 37% carbon reduction	Waste utilization, 30% carbon reduction	40%~50% carbon reduction	20%~30% carbon reduction

.

In the field of modeling research, Krishnan et al. [34,46] developed a numerical method that was aimed at determining the optimal proportioning scheme for limestone, calcined clay, and cement clinker. Yang et al. [47], on the other hand, predicted the effects of chloride on the service life of concrete by simulating the diffusion behavior of chloride in the LC3 cementitious system. In addition, Park et al. and Wang et al. [48,49] optimized the central particle hydration model in their studies by taking several factors into account, such as the mineral composition of the admixtures, the water–cement ratio, and the ambient temperature. However, it is worth noting that most of the current studies on the hydration model of LC3 concrete focus on the incorporation of the hydration products of the LC3 cementitious system, while an in-depth exploration of the kinetic process of its hydration is still required.

In summary, the hydration reaction of LC3 results in the formation of key mineral phases, such as C-A-S-H, carbon-aluminate, and calomel, which reduce the cement’s porosity and enhance its properties. LC3 has an effectively reduced carbon footprint due to the partial replacement of clinker with calcined clay and limestone, and maintains comparable properties to those of conventional cement.

3. Fresh Mix Performance

The fresh-state performance of LC3-based concrete is governed by multiple compositional and rheological parameters, including the water–binder (w/b) ratio, the dosage of high-range water reducers (HRWRs), and the proportional balance between calcined clay, limestone, and clinker. While LC3 systems typically demonstrate enhanced workability compared to conventional concretes—which is attributed to the high specific surface area of calcined clay particles improving the particle packing efficiency and acting as a supplementary pozzolan to stabilize the system’s fluidity—their fresh properties exhibit heightened sensitivity to mix design variations. This dichotomy arises from competing mechanisms: calcined clay’s nanoscale morphology facilitates lubrication between aggregates, yet its rapid adsorption of HRWR molecules can reduce the admixture’s effectiveness, necessitating precise dosage calibration. Concurrently, limestone’s nucleation effects accelerate early C-A-S-H gel formation, further complicating the slump retention dynamics. Empirical studies confirm that LC3 formulations with 30%–40% clinker replacement maintain optimal workability when paired with polycarboxylate-based HRWRs at 0.8%–1.2% binder mass, although localized fluctuations in clay mineralogy or limestone fineness may necessitate mix-specific adjustments [50,51,52,53]. These interdependent factors underscore the importance of holistic formulation strategies to reconcile LC3’s inherent workability advantages with its susceptibility to fresh-state variability in practical applications [54].

The workability of LC3 concrete hinges on three key parameters: water–cement ratio optimization, the incorporation of high-performance superplasticizers, and the balanced proportioning of calcined clay and limestone components. This innovative binder system inherently exhibits favorable workability characteristics due to its high fine content and the pozzolanic reactivity of calcined clay, which functions similarly to natural volcanic ash in enhancing the mixture’s fluidity. However, when substituting traditional cement with LC3 in concrete or mortar formulations, adjustments may be required to maintain consistent fresh properties such as slump retention and pumpability, as the unique particle distribution and hydration kinetics of LC3 can influence the initial mixture behavior.

In the study of Nguyen et al. [55,56], it was found that, with the increase in general-purpose cement substitutes, a decrease in concrete compatibility has been observed. The same was indicated in the study of Nair et al. [57], where the slump retention performance of concrete with LC2 as a mineral additive was less than satisfactory when compared to the normal silicate cement system unless the substitution level was kept below 30%. At a substitution level of 45%, all of the studied concretes failed to achieve the desired slump retention performance. Therefore, excessive flow times must be avoided when using limestone-calcined clay-based binders [58].

Ferreiro et al. [59] investigated the ease and strength properties of different LC3s. The results indicated that the strength of blended cement could be optimized by adjusting the SO₃ content, the ratio of calcined clay to limestone, and the active alumina content of the clay. The calcined clay content significantly affects the cement’s workability, especially since 1:1-type clay exhibits a reduced superplasticizer efficiency. However, the delayed addition of plasticizer or the addition of fly ash improved the rheology of calcined clay-containing cement and maximized its strength while maintaining the same workability.

The use of LC3 in mortar and concrete might slightly alter the new characteristics of the final mixtures. The study by Chen et al. [60] study revealed that, due to its enhanced specific surface area and water absorption, LC3 concrete needs a greater amount of water compared to regular concrete. Research conducted by Yu and colleagues [61] found that LC3 mixtures with extremely large volumes exhibited notable thixotropy and a swift decline in their slump. Thixotropy refers to a material’s capacity to exhibit reduced viscosity when subjected to shear and temporal forces, a beneficial characteristic of concrete during its placement and transit. Hou et al. determined the clustering of clay particles within the LC3 system [62] to be the fundamental process behind the key thixotropic characteristics of LC3 concrete.

A popular technique for assessing freshly mixed concrete is the slump test. According to a study by Yu et al. [61], the slump value of their chosen concrete was 235 mm after 10 min of mixing and the slump flow rate was 415 mm. However, the slump value dropped to just 100 mm after 25 min of mixing [63].

The impact of partially substituting calcined clay and limestone for OPC in cement pastes on its setting time was examined in a study by Shah et al. [52]. They tested the initial setting time and the standard consistency of the resulting mixtures using a range of replacement amounts, including 10%, 15%, 20%, 30%, and 50%. As the amount of OPC replacement increased, the mixtures’ standard consistency rose as well, suggesting that more water was needed to make them as compatible as the OPC mixtures.

In comparison to Portland cement-based slurries, LC3 blends have a longer setting time and a larger dosage of water reduction agent, according to recent research by Balestra et al. [44]. LC3 with fly ash demonstrated the best overall performance, and the addition of spherical particles increased the slurry’s fluidity and decreased the amount of water reducer.

To sum up, when contrasted with OPC, there was a slight increase in the solidification period of limestone-calcined clay mixtures at reduced replacement rates; yet, these mixtures solidified more rapidly. Additional studies are needed to explore how different quantities of replacements impact the characteristics of concrete. Employing limestone and calcined clay as partial replacements for OPC in cement pastes could enhance their setting time and other characteristics.

4. Mechanical Properties

4.1. Compressive Properties

One important metric for assessing concrete’s resistance to external loads and stresses is its compressive strength. Numerous factors influence the compressive strength of LC3 concrete, but one of the most significant ones is the percentage of calcined clay. In general, concrete’s compressive strength decreases as the percentage of calcined clay increases. Furthermore, two important variables that influence the development of LC3 concrete’s strength are the temperature and humidity during the curing phase. The ratio of cement to water is another crucial factor in determining LC3 concrete’s compressive strength. There is a substantial amount of research in the literature on the effects of different parameters since compressive strength is a crucial component in the design of all construction.

Most research findings indicate that LC3 cement’s compressive strength at 28 days matches that of standard silicate cement made with comparable clinker, although its efficacy differs across various ages [55,64,65]. In particular, at the three-day mark, LC3 and its concrete exhibited marginally less strength compared to OPC, yet surpassed the strength of slag or fly ash blended cements [66]. This highlights a key benefit of LC3, namely its capacity to be manufactured with clinker levels ranging from 40% to 50% while maintaining its mechanical characteristics over time. Observations revealed that, within a week, LC3’s strength neared or surpassed that of OPC, and by the 28th day, a slight enhancement in compressive strength was noted [67], a pattern which is corroborated by additional research. Initial research has indicated that elements like the size of individual particles, the makeup of the clinkers, the ambient temperature, and the alkali levels are crucial in determining the potency of LC3 [34,68,69].

Dhandapani and their team [66,70] analyzed the growth in compressive strength of LC3 cement, standard silicate cement, and concrete based on fly ash. The study used ordinary Portland cement (OPC) conforming to IS 12,269 (Grade 53). Siliceous fly ash sourced from Ennore near Chennai was employed to produce Portland Pozzolana cement (PPC) with a 30% replacement level (70% OPC + 30% fly ash), designated as FA 30, at a laboratory scale. LC3 (limestone calcined clay cement) from a pilot industrial production trial in Gujarat, India, was utilized. For the LC3 mixture in this study, the composition by mass was clinker–calcined clay–limestone–gypsum = 50:31:15:4, with a water–binder (w/B) ratio of 0.42. The concrete mix included fine aggregates, comprising graded river sand with a nominal maximum aggregate size of 4.75 mm, and coarse aggregates of 10 mm and 20 mm crushed granite. A polycarboxylate ether (PCE)-based high-range water reducer (superplasticizer, SP) with 34% solid content was used to achieve the target slump range of 80–120 mm. The investigation focused on the efficacy of three distinct concrete blends: two of which were designed to have identical strength levels (namely, M30 and M50 grades) and contained varied cementing substances; the third was fabricated to guarantee uniformity in the composition of cementitious materials and their water–cementitious proportion. The study’s findings indicated that, following a 28 day curing period, the compressive capacities of M30 and M50 concretes matched those of OPC and LC3 concretes, as depicted in Figure 7. Nonetheless, it is important to mention that, during the initial phases (e.g., utilizing 100% OPC as a benchmark), the FA30 concrete mixture exhibits comparatively low strength. Fascinatingly, over a span of 28–365 days, FA30 and LC3 mixtures demonstrated greater strength improvements than OPC concrete, as noted by Mo and colleagues [71]. The study analyzed how various combinations of limestone and calcined clay impact the mechanical characteristics of LC3 concrete, discovering that concrete with 15% calcined clay exhibited a more robust long-term compressive ability compared to other experimental groups.

In their study on LC3 formulation, the Portland clinker used was supplied by Cementos Molins, S.A. (Barcelona, Spain), and was ground and sieved to a particle size < 80 μm. The limestone and gypsum, provided by LABKEM (Labbox, Barcelona, Spain), had purities of >98.5 wt% and >99 wt%, respectively. The raw kaolinitic clay, sourced from Minerals i Derivatis, S.A. (Tarragona, Spain), underwent both thermal (calcination) and mechanical activation before being incorporated as a supplementary cementitious material (SCM) in LC3. Thermal activation was performed in a laboratory oven at 800 °C for 1 h. Mechanical activation was carried out using a planetary ball mill (PM 400, RETSCH, Haan, Germany) in a 125 mL zirconia jar under conditions that were consistent with the authors’ previous work: zirconia balls (10 mm diameter) occupied approximately 20% of the jar volume, with a rotational speed of 350 rpm and a grinding duration of 120 min. The LC3 produced under these conditions is illustrated in Figure 8.

Huang and colleagues recently conducted a study [72] that examined the mechanical characteristics and resistance to chlorination of limestone and calcined clay cement ultra-high performance seawater-sand concrete (UHPSSC-LC3) in various curing scenarios, and found that the UHPSSC-LC3 demonstrated superior compressive and flexural strength across all ages and curing conditions, surpassing UHPC and UHPSSC. Utilizing seawater curing solutions led to similar or marginally greater compressive and flexural strengths than conventional curing methods, offering a straightforward solution for UHPSSCLC3 in marine engineering applications. Compared to UHPSSC-LC3, the heated water method proved superior in enhancing the initial compressive strength of UHPC and UHPSSC due to UHPSSC-LC3’s lower cement levels, for which the impact of rapid cement hydration is minimal. Furthermore, the impact of treatment with heated water on the development of the cement’s compressive strength proved to be more significant than its impact on the cement’s flexural strength.

Overall, the research done on LC3 in terms of its compressive properties has been relatively comprehensive, with LC3 concrete exhibiting similar compressive properties to ordinary silicate cement concrete. Nonetheless, further research could explore other factors that may affect the strength development of LC3 mixes, such as the curing conditions, aggregate type, and particle size distribution.

4.2. Other Mechanical Properties

Although information on the compressive strength of LC3 concrete is available in the literature, data on other mechanical properties are lacking. In order to fill this gap, in terms of flexural strength, Yu et al. [17] compared the flexural strength of LCC-50 (50% limestone-calcined clay cement), LCC-60, LCC-70, LCC-80, FA-25 (25% fly ash blend), and PC-100 (100% Portland cement) at curing ages of 3, 7, 28, and 90 days. The results of the study showed that the flexural strength of LC3 concrete increased by 2%–10% compared to ordinary Portland cement concrete.

Pertaining to the elasticity modulus. Dhandapani and their team [67,70] analyzed the static modulus of various LC3 concrete mixtures, discovering that the elasticity modulus of LC3 concrete paralleled that of FA30 and standard OPC concrete. Their findings suggest that LC3 concrete could possess mechanical properties similar to those found in OPC concrete for structural applications.

In terms of its bending properties, LC3 concrete demonstrates enhanced strength, which can be attributed to its high concentration of crystalline aluminates and C-A-S-H in comparison to OPC concrete [73,74]. Within the framework of dynamic load resistance, Long and his team’s research [75] highlighted remarkable outcomes, demonstrating the superior efficacy of LC3 fiber-reinforced materials (FRMs) in enduring dynamic stress.

Zhu et al.’s research [76] revealed that LC3-based engineering cementitious composites (ECCs) exhibit a greater strain capacity and narrower crack widths than OPC-based ECCs. Research conducted by Yu’s team [77] revealed that LC3-ECC containing merely 20% clinker attained a tensile strength of around 5 MPa, which diminished as the w/b ratio rose. Other studies [78,79] have deduced that the fineness of limestone influences the tensile flexibility, breadth, and density of cracks in LC3-ECC that is it used in.

In summary, the compressive characteristics of LC3 are similar to those of standard silicate cement at 28 days, being initially slightly less (3 days) yet nearing or surpassing OPC’s strength after 7 days. Regarding additional mechanical attributes, LC3 has shown enhancement in its flexural and bending qualities relative to OPC, exhibiting superior mechanical qualities; however, further research is needed.

5. Durability

The robustness of concrete is characterized by its ability to endure various damaging factors in practical applications and to maintain its practicality and visual appeal for a prolonged period in order to guarantee the safety and consistent use of concrete structures. This type of performance is vital for ensuring the lasting steadiness and security of structures.

Reports indicate that the pore configuration of LC3 is more delicate compared to those of OPC and mixed fly ash cements [37]. The observed increased blending of hydration products suggests that the observed pore refinement might stem from these products precipitating on the calcine’s larger surface, which leads to a more uniform distribution of these products across the microstructure [80]. The reduced porosity could also stem from larger proportions of less dense crystalline phases, such as calcite and carbon aluminate. It has been demonstrated that this delicate pore configuration leads to reduced permeability, making the concrete more resilient under various exposure scenarios. Diminished permeability is marked by decreased capillary absorption, less chloride entry, and heightened concrete resistance, with LC3’s finer pore configuration forming sooner than other cement types. Consequently, the cement becomes more resistant to the shortening of its lifespan due to inadequate upkeep (Figure 9).

The study conducted by Zolfagharnasab and his colleagues [81] demonstrated that incorporating calcined clay in mixtures with varying grades of calcined clay enhanced the binding and diffusion rates of chloride ions in both binary and ternary mixtures, which surpassed those in LS10 and OPC mortars. Avet and colleagues [82] investigated how pH levels influence the chloride ion adherence of limestone-based calcined clay cement, discovering that C-A-S-H’s ability to adsorb chloride ions is also pH-dependent, as indicated by the minimal adsorption that was observed in all mixed systems. As the pH levels rose, the reduction in chloride concentration within the solid solution and the diminished adsorption ability of C-A-S-H led to a decrease in the total chloride binding capacity.

The corrosion of reinforcing steel due to chloride intrusion is a key factor that can shorten the service life of reinforced concrete structures [83,84,85]. By incorporating auxiliary cementitious materials, the secondary hydration reaction with calcium hydroxide can be promoted to generate additional C-S-H gels, which are effective in filling the pores and micro-cracks within the cement stone and thus enhance the performance of the material [86,87]. A study by Guo et al. revealed that the addition of calcined clay and limestone to recycled aggregate concrete was able to optimize its phase composition and cause the matrix interface to become denser. The study by Pillai et al. [84] further showed that LC3 cement not only has a more homogeneous and superior internal bonding after the incorporation of calcined clay but also exhibits greater resistance to external chloride ion attack compared to ordinary silicate cement.

According to Maraghechi and colleagues [80], mortar specimens (cylindrical: 110 mm diameter × 300 mm height; cube: 40 mm edge length) and paste specimens (30 mm diameter × 50 mm height) were prepared following the EN 196-1 standard [88], although the exact sample size per group was not specified. Chloride penetration tests revealed that, after 2 years of immersion, ordinary Portland cement (PC) exhibited a chloride penetration depth exceeding 40 mm, while the LC3-50 system (with 50% metakaolin replacement) showed a significantly lower depth of ~10 mm. The apparent chloride diffusion coefficient decreased by two orders of magnitude (PC: ~1 × 10⁻¹² m²/s; LC3-50: ~1 × 10⁻¹⁴ m²/s). Although standard deviations or confidence intervals were not provided, the reliability of the data was ensured through micro-X-ray fluorescence (μ-XRF) multi-point measurements (at least 10 points per depth). Mercury intrusion porosimetry (MIP) analysis indicated that the enhanced chloride resistance of LC3-50 primarily stemmed from pore refinement (smaller critical pore size), while the chloride binding capacity (via Friedel’s salt formation and C-A-S-H adsorption) played a lesser role. The LC3-50 system with 50% metakaolin achieved optimal performance without requiring high-purity clay. Carbonation depth data were also included, but limited information on the sample size and statistical uncertainties was provided. The conclusions of the study were primarily based on mean values and phase analysis.

In the study by Scrivener et al. [27], an LC3-50 formulation demonstrated a significantly lower chloride penetration depth compared to ordinary Portland cement (PC), with enhanced performance being observed at a calcined clay–limestone ratio of 2:1. This improvement was attributed to pore refinement, as validated by mercury intrusion porosimetry (MIP). Carbonation depth analysis revealed that the LC3 exhibited higher carbonation rates than PC but outperformed fly ash- and slag-based systems. Extended curing periods effectively mitigated carbonation, and this issue was negligible in high-humidity environments (e.g., tropical regions). Regarding chloride penetration resistance, the LC3-50 system showed a lower apparent chloride diffusion coefficient than PC, with a performance that was comparable to or better than fly ash- or slag-modified systems. However, the document did not explicitly provide experimental details such as the sample size, standard deviations, or confidence intervals. The results were primarily presented through qualitative descriptions and graphical trends (Figure 10).

In the study by Jan et al. [89], the use of limestone-calcined clay cement with 70% clinker content (LC3-70) significantly enhanced the durability of mortar. Regarding chloride resistance, LC3-70 exhibited a 40%–60% reduction in its chloride penetration depth compared to traditional CEM II. Under salt spray exposure, the penetration depths for LC3-70 were 4.4–5.3 mm (vs. 9.8–12.3 mm for CEM II), while under immersion conditions, the depths were 7.7–8.9 mm (vs. 18.7–24.8 mm for CEM II). The acid-/water-soluble chloride content decreased by approximately 50%, with the standard deviations consistently ranging from ±0.1 to 0.7 mm. In carbonation tests, both the natural carbonation depth (3.0–5.5 mm) and accelerated carbonation depth (2.8–5.1 mm) of LC3-70 were significantly lower than those of CEM II (5.0–6.4 mm and 8.3–10.6 mm, respectively), with standard deviations of ±0.2–0.7 mm. Although the incorporation of recycled sand (RS1/RS2) slightly increased the chloride penetration (+20%–30%) and carbonation depth (+15%–25%), LC3-70 still demonstrated superior overall performance. This highlights its potential as a highly sustainable material for use in recycled aggregate concrete, as it can effectively extend the concrete’s structural service life and reduce its environmental impact (Figure 11).

The research by Dhandapani and colleagues [66] on the chloride levels in concrete mixtures post-56 days of chloride solution exposure yielded findings akin to those reported by Maraghechi and their team. The research conducted by Dixit and colleagues [90] involved measuring the resistivity in samples measured at 28 and 91 days. The outcomes of the resistivity tests mirrored those of the RCPT experiments. Compared to the benchmark mixtures, there was a notable rise in the mixtures’ resistivity, as evidenced by a 200% surge in the MA and LH levels of the clays. Despite varying kaolinite levels, the resistance measurements for clay MA and LH remained comparable. The resistivity increases observed in the 28–91-day mixture samples were significant and correlated with the RCPT data. Moreover, given that the pH of the pore solution in LC3 is slightly lower compared to that used in other cements (e.g., OPC, which has a pH of approximately 13.8) at approximately 13.2 [11], it can be predicted that the chloride-induced corrosion process will be initiated under lower chloride concentration conditions. In addition, the slower water mobility and higher resistivity characteristics exhibited by LC3 concrete both imply that, even if the corrosion process is initiated, it may progress at a relatively slow rate [84].

The resilience of LC3 against the alkali-silica reaction was assessed by gauging the expansion of mortar bars immersed in alkaline environments. Experimental findings indicate that LC3 mortars remain unaffected by the swelling of the alkali-silica reaction (ASR), even when reactive aggregates are present [91]. This result was expected, as LC3’s alkalinity is naturally lower compared to that of other cement varieties, and the alumina emitted from the calcined clay’s pores significantly slows down the aggregate’s dissolution. Compared to other cement types, LC3 is less prone to swelling and cracking when exposed to sodium sulfate [92]. As the proportion of limestone- and calcined clay-substituted clinker increases, LC3 becomes more resistant to sulfate. This may be related to the process of the conversion of carbonyl aluminate to the relatively innocuous chalcocite, but this speculation needs to be further explored. Although accelerated test conditions using MgSO4 have been reported to be more severe than in practice, the performance of LC3 under these conditions still needs to be thoroughly investigated [93]. Currently, no modeling studies have been found for the service life of LC3 concrete under sulfate exposure.

Dhandapani et al. [66] summarized the air permeability as well as the water absorption of different concretes at 28 and 90 days and showed that LC3 concrete performs better than normal concrete in both aspects.

Regarding the resistance to carbonation of LC3, Scrivener and colleagues [16] conducted a study on the extent of its carbonation following two years of natural exposure, both inside and outside, at the Federal Institute of Technology in Lausanne, Switzerland. Their findings indicated superior carbonation resistance in LC3 concrete compared to regular concrete. Cheng and colleagues [94] conducted research to thoroughly examine how blocking fine-pore water in standard silicate cement and limestone-based clay cement pastes impacts their accelerated carbonation, employing a unilateral nuclear magnetic resonance (NMR) monitoring method. The research focused intently on how CO₂ levels influence the carbonation of cement pastes, emphasizing the water content distribution in both types of cement. Employing a one-sided nuclear magnetic resonance method for water profiling, the scientists discovered consistent water levels in the small pores (encompassing spaces between layers and gel pores) at the forefront of carbonation, even under rapid carbonation scenarios of 5% and 1%, which indicated a blockage effect. Consequently, extracting water from the delicate pores becomes challenging, which makes it necessary to manage the carbonation mechanism. Yet, this blockage phenomenon did not manifest in natural carbonation scenarios, as evaporation typically comes before the carbonation process. The research emphasizes the need for the precise characterization of cementitious materials’ characteristics in natural carbonation scenarios, which necessitates the deliberate restriction of CO₂ levels to prevent the clogging effect from disrupting the outcomes. Furthermore, the works [89,95] also played a role in the study of cements’ resistance to carbonation.

Kong and colleagues recently conducted a study [96] that explored how Ca(OH)₂ and gypsum influence the resistance to carbonation and the mechanical characteristics of low-activity gangue-based LC3. Gangue’s usage in LC3 is constrained by its minimal activity and weak resistance to carbonation. The research revealed that incorporating 7.15% Ca(OH)₂ and 10% gypsum into LC3, along with 60% gangue substitution, decreased the depth of carbonation from 19.3 mm to 17.0 mm and enhanced the cement’s compressive strength to 31.9 MPa. Conversely, adding 20% gypsum to the composite with 30% gangue substitution decreased the carbonation depth to 10 mm and boosted the compressive strength to 39.3 MPa. These results hold great importance for the sustainable optimization of cement materials.

Studies have shown that LC3 cement exhibits superior resistance to swelling and cracking in sodium sulfate environments compared to other types of cement [11,92]. As the proportions of limestone and calcined clay-substituted clinker increase, the sulfate resistance of LC3 cement also shows an enhanced trend. Although the transformation of carbontalcite to caliche may be considered as a relatively low-impact process, an in-depth understanding of the mechanisms by which it enhances the resistance of cement is yet to be obtained. In addition, although the accelerated test conditions for the use of magnesium sulfate were more severe than in practice, a full assessment of the specific effects of magnesium sulfate on LC3 still needs to be supported by more research.

Detailed investigations into the efficacy of LC3 in fire and high-temperature environments are scarce. LC3 binder is similar to fly ash, silica fume, and kaolin, is fabricated at 300 °C, and has a higher relative strength than OPC. Furthermore, unlike fly ash, it is similar to metakaolin and silica fume. That is, at 900 °C, the relative strength of LC3 binder is lower than that of OPC [97]. Research has further revealed an increase in the proportion of clinker substituted by limestone and calcined clay, which leads to a corresponding rise in the decrease in remaining compressive strength.

Studies on the effect of cyclic freezing and thawing on the performance of LC3 concrete have not been reported. Experimental data indicate that quaternary composite cements incorporating silica fume (SF) or metakaolin (MK) exhibit exceptional freeze–thaw resistance. Specifically, the PCSFASF system (with silica fume) achieved a freeze–thaw durability factor (DF) of 80%, meeting frost resistance requirements. It also demonstrated the lowest initial surface absorption rate (ISA-10) at 25 × 10⁻² m/m²/s and a chloride diffusion coefficient of 8.6 × 10⁻¹¹ m²/s under water curing, significantly outperforming ordinary Portland cement (OPC) and high-limestone binary systems (e.g., PCLS45, DF < 60%). This performance enhancement is attributed to the highly reactive silica fume and metakaolin, which refine the pore structures of cement through filler effects and secondary hydration reactions. These mechanisms reduce harmful interconnected porosity and delay freeze–thaw damage. In contrast, high-limestone binary systems like PCLS45 showed coarsened porosity, leading to a significantly higher ISA (78 × 10⁻² m/m²/s) and chloride permeability (15.5 × 10⁻¹¹ m²/s), along with markedly reduced frost resistance. The data confirm that the synergistic effects of multi-component cementitious materials in composite cements can optimize pore structures, thereby improving the freeze–thaw durability of cement [98].

LC3 demonstrates exceptional long-term durability in real-world environments. Its core advantage lies in the synergistic optimization of its material composition and microstructure to enhance erosion resistance. Notably, LC3 exhibits superior chloride resistance, with chloride diffusion coefficients that are reduced by 50%–60% compared to those of conventional cement. The formation of carboaluminate phases further binds free chloride ions, extending the cement’s maintenance intervals from 15 years (traditional materials) to 25 years in coastal projects in India.

Additionally, LC3’s low porosity (30%–50% lower than OPC) and dense interfacial transition zone (ITZ width reduced to 10 μm) significantly delay carbonation and sulfate attack. After 150 wet–dry cycles, its expansion rate is only 1/4 that of OPC. Field validations in India, Cuba, and other regions reveal over 95% structural integrity in LC3 applications after 4+ years of service, with its lifecycle costs being reduced by 30%. Although the initial costs are 5%–10% higher, LC3’s outstanding resistance to degradation (e.g., low deterioration rates under combined chloride-carbonation effects) and sustained strength development (15%–20% increase in 90 day strength) make it an ideal choice for sustainable infrastructure in harsh environments. Future research should focus on optimizing its performance under extreme climates and dynamic loading.

To sum up, it has been demonstrated that LC3 concrete is more resistant to sulfate attacks, rendering it ideal for areas with elevated sulfate levels. Additionally, LC3 concrete’s reduced permeability lessens the penetration of water and other aggressive materials. This characteristic aids in safeguarding the integrated reinforcement of the concrete and enhances its longevity. Additionally, LC3 exhibits enhanced resistance to carbonation. Regarding its longevity, further investigation into the resilience across varied settings is necessary. The research on the long-term durability of LC3 is evidently insufficient.

6. Applications of LC3

LC3 is seen as an alternative to OPC in the construction industry, and as such, its main application areas are cement-based construction facilities, the covering of conventional concrete, 3D concrete printing technology, plastering operations, roof tile manufacturing, use for precast materials, concrete block production, paver applications, and use as a cement additive. Nevertheless, the large-scale popularization and application of LC3 is still in the developmental stage, and further efforts are needed to achieve its widespread application within the construction industry. In order to assess the effectiveness of LC3 in practical applications, we consider LC3 as a potential alternative option, using OPC as a reference. This section explores and analyzes the evidence found in the relevant literature on the use of LC3 in different construction applications.

LC3 demonstrates targeted performance advantages in various application scenarios: In marine and coastal engineering, its porosity is reduced by 30%–50% compared to ordinary Portland cement (OPC), with its chloride ion diffusion coefficients being decreased by 50%–60% and the formation of carboaluminates extending its maintenance cycle to 25 years (compared to 15 years for traditional materials). In high-sulfate soil environments, it exhibits an expansion rate of only 0.03% after 150 wet–dry cycles (vs. 0.12% for OPC), with its strength loss rates being reduced to one-third of that of OPC. For high-temperature industrial settings, its hydration temperature rise is lowered by 10–15 °C, and industrial waste like fly ash can be incorporated to enhance its corrosion resistance. In general construction, LC3 achieves a 28 day compressive strength of 45–55 MPa (with 50% clinker content) and long-term strength growth of 15%–20% (vs. 5%–8% for OPC). In cold regions, its dense interfacial transition zone (ITZ width of 10 μm) and sulfur–aluminum formula optimization (SO₃ content 3.0%–3.5%) ensure frost resistance. In resource-constrained areas, it can be adapted to material shortages using non-kaolinite clays like montmorillonite (calcined above 800 °C), as seen in India’s Bharatmala Highway Project, which reduces CO₂ emissions by 15 million tons annually. Future efforts should focus on validating its extreme-environment performance, dynamic formula adjustments (e.g., gypsum content), and updating standardization systems to solidify LC3’s role in achieving carbon neutrality goals.

Liang and colleagues [99], in their research on engineering cementitious composites, (ECC) delved into the extensive features and minute details of limestone-calcined clay-based recycled sand cementitious composites (LC3-ECCs). The research revealed that LC3 contributes to the production of environmentally friendly cement materials. Likewise, Wang and colleagues [100] investigated the impact of different preparation techniques on the microstructure and longevity of engineered cementitious composites made of LC3. The results showed that the printed LC3-ECC’s tensile strength and strain capacity decreased by 16.6%~22.7% and 43.3%~54.6%, respectively, relative to its initial state, while a 2% strain capacity was preserved and the material showed tendencies for multiple cracks to form. Zhang and colleagues [78] additionally noted favorable results in this aspect of the study.

Yan and their team [101,102] explored the use of 3D concrete printing (3DCP) with combined sustainable ECC using LC3 and light fine aggregates, and methodically analyzed the progression of innovative 3D-printed LC3-based lightweight engineered cementitious composites (LL-ECCs) from new to solidified forms, and from the material stage to the component stage. Their findings indicate that LL-ECC stands out as an effective and hopeful composite, offering a harmonious blend of printability, mechanical characteristics, and eco-friendliness in 3D printing.

In terms of its application to UHPC, Huang et al. [64,72,103] investigated the mechanical properties and chloride ion erosion resistance of limestone-calcined clay-cement ultra-high-performance seawater sea sand concrete (UHPSSC-LC3) under different curing conditions, and the results of the study showed that, although the application of limestone-calcined clay-cement ultra-high-performance seawater sea sand concrete (UHPSSC-LC3) in building sustainable marine structures offers a promising solution, research on the mechanical properties of UHPSSC-LC3 is rather limited and its resistance to chloride ions has not yet been investigated.

Regarding the use of these materials in 3D printed concrete (3DPC), the findings of Wu and colleagues [104,105] demonstrated that combining LC3 with SF led to significant water absorption and clumping of the cement paste, enhancing the mortar’s yield stress and viscosity. The elevated yield stress led to improved buildability and reduced deformation in 3D printed mortars. Additionally, employing LC3 markedly enhanced the percentage of structural recovery.

In terms of its application to geotechnical engineering, OPC has been widely used in the foundation treatment of problematic soils such as expansive soils, loess soils, contaminated soils, organic soils, etc., from a geotechnical engineering perspective [106]. These types of soils exhibit a low bearing capacity and consist of unfavorable soil properties such as low shear strength, expansion and contraction behavior, and cracking phenomena. Some studies have shown that LC3 exhibits potential benefits in treating problematic soils. Specifically, Ijaz et al. [107] carried out a comprehensive study in 2022 that delved into the mechanism of LC3 stabilization for the treatment of problematic expansive soils. The mechanism involves the invasion of LC3, a process that promotes the formation of C-S-H (calcium-silica) and C-A-S-H (calcium-aluminum-silica) gels, which combine with calcium alumina produced under high-pH conditions to fill soil voids. These calcium aluminates are critical for enhancing the strength of soil, eliminating swelling, and reducing the cement’s permeability. In addition, the synergistic interaction between CC/MK and LSP, which is essential for the formation of calcite alunite, is a major factor in the formation of compact microstructures [108].

To date, LC3 building materials have been widely used in construction facilities in many regions and of various scales [109,110]. The latest statistics show that LC3 has been adopted as the main building material in more than 25 projects. For example, in Chamshi, India, LC3 was used as a core building material in the design and construction of a model house which utilized 26.6 tons of industrial waste, resulting in an environmental benefit of 15.5 tons of CO₂ reduction. In addition, LC3 has been used in the offices of the Swiss Agency for Development and Cooperation (SDC) at the Swiss Embassy in Delhi, in a river dam project in Orchha, India, and in sidewalks on the campus of the UCLV in Cuba, which demonstrates the adaptability of the LC3 system to different types and scales of construction, as shown in Figure 12.

LC3 faces multiple challenges in industrial standardization and large-scale adoption. It faces raw material constraints such as global variations in clay mineral composition (requiring 40%–60% kaolinite content) and the need for precise calcination temperature control (700–850 °C) to avoid a loss of reactivity, both of which pose significant hurdles. It also faces production challenges such as the fact that traditional cement plants require equipment upgrades (e.g., additional calcination kilns) with high initial costs (5%–10% increase in capital investment), while the uneven regional distribution of suitable clay resources destabilizes supply chains. As well, it faces standardization gaps such as the fact that current building codes lack mandatory durability criteria for LC3 (e.g., chloride-binding capacity, sulfate resistance), and its lower early-age strength (1–3 days strength at 80% of ordinary cement) limits its construction compatibility. Policy and industry misalignment is also an issue: incomplete carbon trading mechanisms weaken economic incentives for emission reduction, and cross-sector collaboration gaps hinder technology dissemination. Market barriers are also an issue: misconceptions about material properties (e.g., color variations) and the absence of lifecycle cost assessment frameworks further delay the adoption of LC3. To overcome these barriers, multidimensional efforts, including in the technological (e.g., rapid clay characterization tools, integrated processing equipment), policy (inclusion in green building certifications), and industrial (regional industry alliances) spheres, are required. These steps are critical to transitioning LC3 from pilot projects to mainstream construction materials.

In the latest research, Marangu and colleagues [111] conducted experiments on the use of LC3 to strengthen extensive soil roadbeds. A comparison was made between the impact of LC3 and OPC on the mechanical characteristics of the soil in the roadbed. Mixing of the two at concentrations of 1%, 1.5%, and 2% of the soil’s dry weight was conducted, in that sequence. The findings indicated that LC3 and OPC both increased the soil’s plastic threshold and reduced its plastic index, liquid limit, and linear contraction. Adding cement enhanced the soil’s peak dry density while reducing its ideal water content. The greatest enhancement in CBR and MDD, along with a reduction in OMC, was noted at the ideal 2% cement level. LC3’s efficacy matched that of OPC in roadbed treatment. Mugambi and colleagues [112] examined LC3’s stabilizing impact on clay soils used in road building, employing dosages of 1%, 3%, and 5% and contrasting the results with those obtained for OPC. XRD, SEM, and TGA studies uncovered changes in the mineralogy and microstructure of LC3. As the dosage of LC3 and OPC rose, there was a reduction in the plasticity index, line shrinkage, and ideal moisture level of the soil, alongside an increase in its maximum dry density and CBR. The creation of C-S-H and semicarbonylaluminate enhanced the characteristics of the soil. When the cement ratio reached 5%, the characteristics of LC3 matched those of OPC.

7. Discussion of Economic Feasibility and Environmental Aspects

LC3 adeptly tackles sustainability’s three key aspects—ecological, financial, and societal—especially regarding engineered materials, and is distinguished by its safety and usability (encompassing engineering efficiency). The major benefit it offers lies in its sustainability. Composed of limestone, calcined clay, and various additives, LC3 boasts a reduced carbon footprint compared to conventional Portland cement, cutting down on energy use and greenhouse gas emissions owing to its lower production temperatures. Implementing LC3 in building processes not only cuts down on waste but also preserves natural resources. Furthermore, LC3 stands out as an economical and readily accessible raw material in resource-scarce regions, and its production in current cement plants with slight alterations lessens the necessity for additional infrastructure and enhances its financial feasibility. The financial benefits have been evidenced in various places [113,114,115].

In cement production, as in any other industrial process, the contribution of infrastructure and the operational phase need to be taken into account. In using LCA, the importance of the frame structure has been proven. Economically, this aspect was analyzed by considering OPEX and CAPEX. Considering the production and operating costs of LC3, a comparison between the environmental and monetary costs of cement production can describe the environmental and economic impacts of two stages of a cement plant’s life cycle: construction and operation, and day-to-day operations. Figure 13 shows results achieved using the BAT. From an environmental perspective, almost all impacts came from the operational phase (cement production) rather than from the initial construction of infrastructure (cement plant). However, from the point of view of real costs, this figure was quite the opposite. The initial construction of a cement plant was indeed the main cost of the production of one ton of cement, rather than the operating cost of fuel and raw materials.

Given clinker’s status as cement’s most energy-demanding element, diminishing its amount through the incorporation of LC3 can markedly lower the energy usage and emissions in cement applications. While additional cement-based substances like fly ash and slag are typically seen as non-emissive and energy-efficient, clays also play a role through their calcination process. However, it is important to recognize that clay undergoes calcination at temperatures which are significantly lower than those used in clinker production, and its breakdown process does not emit carbon dioxide. From a statistical standpoint, the energy needed for calcinating clay constitutes merely around 60% of the energy needed for producing clinker [116], and the related CO₂ emissions account for just about 30% of the energy consumed in clinker production [117]. Directly contrasting the energy usage and emissions of various cement types presents challenges due to several elements like raw material transportation and fuel consumption, which greatly influence the total energy consumption and emissions associated with cement.

An economic analysis for the Indian market revealed that LC3 is commercially viable compared to Portland volcanic ash cement (PPC) in most cases [113]. A study of the Cuban market reached similar conclusions, showing that the adoption of LC3 not only reduces CO2 emissions, but also lowers the monetary cost of cement production.

Typically, the overall energy emissions from LC3 production are about 15% lower than those for OPC, while the resulting CO₂ emissions are reduced by about 30% to 40% [116,118,119]. However, while the energy consumption during LC3 production may be slightly higher than that of PPC, its emission level may be lower. These studies emphasize the importance of developing an exhaustive carbon emission inventory.

Research conducted by the Swiss Federal Institute of Technology in Lausanne [120] suggests that LC3’s manufacturing expense is approximately 10%–20% less than that of Portland cement. Investigations also revealed that enhancing the calcination method and substituting industrial waste for clay could further lower the expenses associated with LC3. Research focusing on the long-term viability of reinforced concrete subjected to CO₂ and chloride exposure has been documented [121].

Although LC3 has demonstrated a number of advantages in concrete production, its economic viability still faces a number of challenges. The first issue is the lack of a mature production and distribution supply chain infrastructure, which may lead to higher transportation costs and an unstable supply chain [39], thus increasing the overall cost of LC3. In addition, the adoption of LC3 requires technological innovations and the appropriate training of building professionals, all of which entail high upfront investment and may discourage some stakeholders from adopting it. Furthermore, the cost of LC3 is significantly affected by the geographic location and availability of raw materials. For countries where limestone and clay resources are scarce, high transportation costs and a lack of local supply chains may make LC3 less economically viable.

To sum up, the financial feasibility of using LC3 for producing concrete is limited by various elements such as raw material prices, manufacturing methods, the extent of infrastructure enhancement, and the effectiveness of the supply chain. Nonetheless, it is important to recognize that LC3 has shown promise in reducing costs by decreasing production expenses, offering possible advantages in carbon credit trading, and ensuring long-term viability. As the need for eco-friendly construction materials increases, thorough investigation of LC3 and further funding of research in this vein are anticipated to promote broader acceptance and additional savings.

8. Potential Research Areas for LC3

Based on a comprehensive literature review, the findings of this study suggest that the use of LC3 in concrete technology has been promoted due to its economic and environmental benefits. In the most recent study, Manosa and Han et al. [122,123] assessed the evolution of research on LC3 through a bibliometric analysis. LC3, as a newly developed binder, has the potential to reduce the rate of cement clinker that is used and the resulting environmental impact. The results of the analysis show that the LC3 technology has received increasing attention, with a significant increase in the number of publications and collaboration among researchers being observed. Research on LC3 is essential to reducing the carbon footprint of the cement industry, and LC3 is considered to be a viable and reliable approach. Although LC3 has proved to be a very promising cementitious composite material, there are shortcomings that should be noted:

• Optimization of Clay Purification and Calcination Processes

Challenges: the complex impurity distribution in clay minerals and their low reactivity due to conventional calcination methods.

Directions: integrate advanced impurity removal techniques (e.g., redox-based leaching) with innovative calcination methods (e.g., suspension calcination, flash calcination) to enhance the purification efficiency and product reactivity of LC3 for industrial scalability;

2.

Refinement of LC3 Hydration Thermodynamic and Kinetic Models

Issues: existing models lack universality for raw materials (e.g., low-grade calcined clays) and environmental variables (e.g., temperature, admixtures).

Directions: multi-factor coupled models that incorporate reactivity components, temperature effects, and mix ratios should be developed. The applicability of LC3 should be validated across diverse raw material systems to improve prediction accuracy;

3.

Workability Regulation and Compatibility of Admixtures

Current status: there is a poor compatibility of PCE-based water reducers with LC3 systems, leading to suppressed early hydration with excessive dosing.

Directions: the interaction mechanisms between clay structures and functional groups of water reducers should be investigated. LC3-specific admixtures with low adsorption and high dispersion should be designed to balance rheology and strength development;

4.

Development of Alternative Al/Si Sources and Impurity Control

Objective: high-grade calcined clays and limestone should be replaced with industrial by-products (e.g., red mud, clay tailings) to improve the cost-effectiveness of LC3.

Challenges: reactivity assessment methods (e.g., Al/Si ratio, loss on ignition) should be established and the impurity impacts (e.g., alkali metals) of LC3 on hydration products (e.g., C-A-S-H gel formation) should be clarified;

5.

Long-Term Performance Evaluation and Standardization Framework

Current status: there is limited field validation of LC3-based materials and absence of unified standards in China.

Directions: long-term monitoring of the durability (e.g., combined chloride-carbonation effects) and structural stability (e.g., shrinkage, microcrack evolution) of LC3 should be conducted. Standards for its production, testing, and application (e.g., clay reactivity grading, performance benchmarks) should be established.

9. Conclusions

To sum up, the innovative limestone-calcined clay-cement (LC3) system, a low-carbon cement material, demonstrates significant promise in diminishing the carbon footprint within the cement sector. This research, through an in-depth examination of LC3’s hydration reaction, functionality, longevity, and real-world engineering uses, uncovers its viability and advantages as a long-lasting substitute for traditional silicate cement.

The key innovation of LC3 is the use of calcined clay with limestone to partially replace clinker, a process that not only reduces raw material costs, but also significantly reduces CO₂ emissions. The kaolinite clay in calcined clay forms metakaolin after calcination, which reacts with calcium hydroxide to form C-A-S-H and aluminate hydrate, effectively enhancing the microstructure and durability of the cement matrix. In addition, the hydration process of LC3 involves the formation of various mineral phases, such as the carbon-aluminate phase and calcite, which further reduce the porosity and enhance the overall performance of the material.

In terms of mechanical properties, although the compressive strength of LC3 is slightly lower than that of OPC in the early stages (e.g., at 3 days), it approaches or exceeds that of OPC at 7 days, with a small increase in compressive strength still being present at 28 days. This trend was confirmed in several studies, suggesting that LC3 can be produced with lower clinker contents without sacrificing its mechanical properties in the short term. In addition, LC3 concrete exhibits a higher flexural strength and better chloride binding capacity, which further broadens its range of applications.

In terms of its durability performance, LC3 concrete exhibits excellent resistance to sulfate attack and carbonation. It was also found that the durability and service life of LC3 concrete can be further enhanced by optimizing its proportioning and curing conditions. In addition, the economic viability of LC3 in concrete production is widely recognized, especially when considering its low-carbon and environmental advantages.

It is worth noting that, although significant progress has been made in the study of the LC3 system, there are still many outstanding issues and challenges to be solved. For example, a deeper understanding of the effects of the clay composition, calcination parameters, and impurities on the performance of LC3 is needed; meanwhile, the performance of LC3 under extreme conditions such as high temperatures and fire needs to be further explored. In addition, promoting the large-scale popularization and application of LC3 also requires policy support and market promotion.

Overall, the limestone-calcined clay-cement system, as a low-carbon, environmentally friendly, and high-performance cement material, has broad application prospects and far-reaching social significance. Future research should continue to focus on the optimization of LC3 performance, cost control, and the promotion of its application in order to promote its sustainable development in the construction industry.