Production, Thermal, Durability, and Mechanical Properties of Translucent Concrete and Its Applications in Sustainable Construction: A Review

Abstract

This study examines transparent concrete (TC) utilizing bibliometric analysis of articles from the Scopus database to identify its performance, knowledge gaps, limitations, and applications. TC is a new type of sustainable building material that combines optical fibers with concrete and is lighter in weight than traditional concrete. Incorporating optical fibers in concrete enables light transmission, thereby reducing the need for artificial lighting in TC structures. TC is also referred to as light-transmitting concrete due to its unique properties. By utilizing natural light resources instead of electric lighting, buildings can better harness sunlight, providing both architectural beauty and energy savings. This approach decreases reliance on non-renewable resources and ultimately conserves energy. Scholars have focused a lot of attention on the superb light transmission and decorative appeal of TC. However, its applications in the construction sector have yet to gain traction due to the time-consuming production process, high labor costs, and limited studies on its durability and mechanical properties. This article reviews the applications, production processes, types of TC, bibliometric analysis, cost analysis, and the research findings related to mechanical, thermal, energy-saving, light-transmitting, and durability properties. TC showed a substantial decrease in the building’s total energy use and maintained strength comparable to conventional concrete. It also displayed minimal water resistance, porosity, and density, making it suitable for constructing buildings and lightweight road surfaces. Additionally, it offers notable aesthetic value. The study identifies gaps in durability and standardization while highlighting significant developments in TC’s mechanical behavior, thermal and energy performance, and applications. Furthermore, it summarizes the future research paths for TC, which are likely to enhance its implementation as a promising sustainable construction material.

1. Introduction

For thousands of years, people around the world have established various civilizations and built hundreds of structures. Many of these structures have survived to the present day, but some have been destroyed due to various events (earthquakes, war, etc.). When we look at these civilizations and buildings, people have tried to benefit from daylight in their buildings since the first buildings [1,2,3,4,5,6]. Various domes and arches with windows placed under them, built in the early Roman period, can be given as examples of these, as reported by Fitchen, 1961, pp. 45–47 [7], and Liu, 2014, pp. 114–121 [8]. It would not be an exaggeration to say that the reason for the invention of many building elements was to take advantage of daylight.

Nowadays, when fossil fuels are frequently used, the desire to benefit from renewable energy sources leads to the emergence of very different materials and building types in the field of construction. Many of these structures, defined as green buildings, appear as structures that produce their own electricity and benefit from daylight the most, and such structures are rewarded by various institutions [1,2,3,4,5,6]. Economic growth, increased activities in the field of science and technology, and the rapid increase in the world population have led to a rapid increase in underground and aboveground structures all over the world. In this economic growth cycle, increasing population, increases in people’s incomes, and technological developments increasingly increase people’s dependence on energy.

Energy production is a sector that pollutes the environment a lot and is very expensive in terms of production methods due to the use of too much fossil fuel. According to 2023 data from the International Energy Agency (IEA), in 2023, fossil fuels supplied 82% of global energy, emitting 37.4 Gt CO₂, and this increase will increase the world temperature by an average of 2.4 °C [9]. The increase in greenhouse gases we emit into the atmosphere causes these gases to act as a protective cover, causing less reflection of the sun’s rays from the atmosphere, thus increasing the temperature in the atmosphere (greenhouse effect). That’s why we want to use energy the most efficiently in buildings, as in every field. It is an important responsibility to reduce the effects of global warming on the environment.

Innovations in sustainable construction materials, including bio-based binders, industrial by-products, recycled aggregates, and energy-efficient concretes, have shown decreased environmental impacts and promote circular economy practices [10]. Transparent concrete (TC) is a promising innovative construction material for urban design that can transmit natural light and reduce the need for artificial lighting. Additionally, it is compatible with recycled glass and other waste-based components, thus furthering the integration of sustainable materials in urban settings. In recent years, TC has emerged to make more use of daylight in buildings around the world. This light-transmitting concrete is called translucent concrete or light-transmitting concrete, in which the optical fibers are placed neatly parallel to the light transmission direction of the element, and the light passes from one side to the other through the optical fibers. In addition to being utilized in construction materials and architectural elements, translucent concrete is applied in a broad range of places, including sidewalks, pavements, tunnels, staircases, speed bumps, and road markings [11,12,13]. In addition, it provides sound insulation, improves safety, and enhances the fire resistance of the structures, making it an ideal choice for acoustic panels and load-non-bearing or bearing walls to reduce background noises and to let natural light into structures’ interior spaces, raising the interior environment’s illumination level [14,15,16,17].

In 2001, Hungarian architect Aron Losonczi produced the first translucent concrete. Translucent concrete was first produced by Hungarian architect Aron Losonczi in 2001 by mixing optical fiber and concrete under the name LiTraCon for architectural design purposes [18,19]. Two years later, he founded a company called LiTraCon in Hungary and produced the first block of TC, which was quickly adopted in countries such as China, Germany, and Italy.

The first scientific studies on light-transmitting concrete were conducted in 2005 [20,21]. Two years later, the first scientific studies on light-transmitting concrete were presented at the Canadian Society for Civil Engineering’s annual conference; some simple optical properties and mechanical properties of TC concrete produced using polystyrene optical fibers were examined [22]. In 2009, five Chinese researchers named Zhi Zhou, Jinping Ou, Ying Hang, Ge Ou, and Genda Chen examined what percentage of the light incident on one side of light-permeable concrete incorporating various ratios of plastic optical fibers (POF) could transmit and the effects of POF ratios on the strength of TC [23]. Mainini et al. [24] measured the photometric properties and light transmission abilities of concrete panels containing PMMA (polymethyl methacrylate) fiber and accordingly examined the light transmission performance of concrete panels with radial fiber placement.

The energy savings used in buildings are provided to a great extent by building materials. Therefore, especially in recent years, innovative methods and solutions have been frequently applied in buildings and building materials. This system, which allows buildings to benefit more from sunlight, provides both visual beauty in terms of architecture and energy savings to the buildings. This article provides a comprehensive review of translucent concrete production and applications as a sustainable material and also presents its mechanical, physical, thermal, light-transmitting, energy-saving, and durability properties. Additionally, cost analysis and recommendations for future studies are discussed. TC would help in energy saving in civil, interior, and architectural engineering constructions and provide an extra function by allowing such concretes to emit light in environments where lighting is not possible at night. Energy savings in buildings are largely achieved by utilizing energy-efficient construction materials. Therefore, in recent years, innovative methods and solutions have often been used in buildings and construction materials. This system, which enables buildings to make better use of sunlight, provides both visual beauty for buildings from the architectural design point of view and energy savings. While few studies have explored the properties and applications of translucent concrete, none have yet provided a comprehensive review that synthesizes its use in architectural, infrastructure, and decorative contexts, particularly from a sustainability perspective. Existing literature lacks an integrated analysis of its applications combined with a bibliometric examination, which could reveal emerging trends and research gaps.

This article addresses this gap by offering a comprehensive overview of translucent concrete, focusing on its production and applications as a sustainable material through a unique bibliometric analysis, as well as its mechanical, physical, thermal, light-carrying, energy-saving, and durability characteristics. In addition, cost analysis and recommendations for future studies are discussed. TC is still comparatively expensive relative to traditional concrete material, and very limited examples can be found around the world. Moreover, the high level of design and technical expertise required for both the production and the installation process implies a slower response from the construction industry. However, with the increasing emphasis on sustainable development, the environmental benefits driven by the material itself, and the potential for visually attractive architecture, TC is likely to draw more and more attention in the construction market. This review is motivated by the fact that despite growing research interest, TC is an emerging material with great potential for sustainable construction, daylighting, and energy efficiency, but there has been no systematic analysis of its optical, mechanical, and durability properties, and there has been no discussion of standardization and circular economy integration. This review is intended to synthesize recent advances, identify challenges, and propose prioritized directions for future research. The remaining sections of this manuscript are organized as follows: Section 2 describes the production of TC; Section 3 discusses the bibliometric analysis; Section 4 presents TC applications in green constructions; Section 5 discusses the evaluation of TC, including thermal and energy-saving properties, mechanical and physical properties, and light-transmitting and durability properties; Section 6 outlines cost analysis; Section 7 identifies the limitations of TC; and finally, Section 8 and Section 9 summarize the conclusions and future research recommendations, respectively.

2. Production of Translucent Concrete

There is no particular or complicated process for producing translucent concrete; the process is almost the same as for producing normal concrete. The sole distinction is the use of translucent materials in the aggregate and cement mixture. Translucent concrete consists of four main components: fine aggregate, cement, water, and one of the translucent materials, nano optical fibers, polymer resin, waste glass, glow-in-the-dark powder, epoxy resin rods, acrylic rods, plastic pipes, or glass rods [25,26,27,28,29]. Optical fiber is the most widely used and well-liked translucent material for developing TC because it has the best light transmittance characteristics compared to other translucent materials. Overstressed fibers should be avoided, and optical fibers should be positioned parallel to one another in the mold and tightened at both ends. Superplasticizers (Glenium 51, Polyplast SP HPC, and Neoplast) and mineral admixtures (fly ash, GGBFS, and silica fume) can be used to improve the properties of TC. Translucent concrete generally does not contain coarse aggregates, as they can harm the fibers and obstruct light from passing through concrete. However, some investigators [16,30,31] utilized coarse aggregates for structural purposes with maximum size ranges of 10–12 mm. The size of the aggregate is specified based on the distance between the optical fibers arranged inside the mold. Although fine aggregates are not chemically active, they also affect the strength of the material as they fill the voids created and reduce porosity. Figure 1 summarizes the production and evaluation tests of TC containing different translucent materials.

3. Bibliometric Analysis

A bibliometric analysis was performed utilizing the Scopus database because it offers thorough coverage of peer-reviewed literature. The review study employed various keywords and their variants to capture the variety of terminology found in the literature. In particular, “Transparent concrete OR Translucent concrete AND Applications OR Mechanical OR light-transmitting OR thermal insulation OR Thermal and Energy-Saving OR water absorption OR tensile OR durability” were among the main keywords. Nevertheless, to prevent noise and duplication, these keywords were removed from the final dataset because they produced very few additional pertinent records. The data imported in RIS format was analyzed using VOSviewer software version 1.6.19, which produced co-authorship, keyword co-occurrence, and citation network visualizations by applying a filter of at least 31 occurrences per word. Importantly, relying solely on one database (Scopus) may result in the exclusion of pertinent publications that are indexed elsewhere. When interpreting the results, these factors were taken into account.

Book chapters, publications, and editorials written in languages other than English were not included; only journal articles and conference papers published between 2005 and 2024 were included. To identify significant studies, a citation threshold of three or more citations per publication was implemented.

This information allowed for the discovery of 72 documents that were published between 2005 and 2024, as shown in Figure 2. Transparent concrete became more well-known after 2018, as evidenced by the rise in publications on the subject. However, the quantity of research on transparent concrete is still very low compared to more pertinent subjects like conventional and green concrete.

The keywords in Figure 3 are organized into three distinctive groups according to their relationship with the transparent concrete. The one with the highest occurrence, distinguished by red, deals with topics related to the properties of transparent concrete, such as energy saving, light transmission, compressive strength, thermal conductivity, and key information on materials used in the production of transparent concrete, such as POF. Next to it is the green group related to the application of transparent concrete (architectural concrete, precast concrete, concrete slabs, and lightning). The third group is the blue group that relates words to each other with the topic of utilization of TC as an eco-friendly construction material for energy efficiency and intelligent buildings.

As regards the countries of origin of the publications highlighted in this bibliometric analysis, the following are particularly notable: China, with sixteen publications; India, with fourteen publications; Egypt and the United States of America, each with six publications; Germany with four publications; Italy with three publications; and countries such as Switzerland, Singapore, South Africa, Poland, Peru, Hungary, Czech Republic, and the Russian Federation, with two publications in each country. Although it is noted that the geographical scope of these studies is fairly uniform, other countries that have a significant demand for green and energy-efficient concrete do not appear to be particularly unique in this context. With its focus on transparent concrete applications and its mechanical, thermal, and energy-saving qualities, it is hoped that this bibliometric review will increase the number of TC-specific studies.

4. Translucent Concrete Applications in Green Constructions

Today, TC has gained great popularity among designers all over the world. This concrete is a unique modern material that manages to combine an attractive appearance, energy saving, and durability. The potential applications for TC are almost infinite; it may be utilized in interior and architectural design of the structures and in constructing energy-efficient buildings to minimize power costs by allowing more daylight to enter the buildings. Furthermore, TC can be used in exterior and interior walls, lamps, construction of floors, lighting of speed bumps on roads, outdoor memorials, night lighting of sidewalks, pavements, lane signs on roads, and lighting dark subway stations and tunnels. However, there are only a few studies [13,32,33,34,35,36] in the literature regarding the use of TC in the infrastructure and construction sectors, indicating the necessity for more in-depth investigation. The following sub-sections detail some of the potential applications of TC.

4.1. Facades and Cladding

TC provides architects with a versatile and visually striking material for enhancing building facades and cladding systems, offering a combination of aesthetic appeal, sustainability, and functionality [17,37,38,39,40]. Its unique properties open up new possibilities for innovative architectural design solutions in both commercial and residential structures [24,41,42]. Transparent concrete facades and cladding have a unique and interesting appearance due to light and shadows being able to pass through the material. Depending on the type and direction of light, patterns of light and dark can be seen on the surface of the concrete, creating a visually dynamic effect. However, even without light passing through it, the surface of transparent concrete always seems to appear brighter and more inviting than traditional concrete. These visual aspects allow for a new degree of expression in architectural design through the various application possibilities of light and shadows. Additionally, incorporating a significant amount of glass facades or windows in new constructions can result in significant heat gain during the summer and heat loss during the winter, impacting the overall energy efficiency of the building [43,44]. Studies indicate that traditional windows and glass facades constitute about 40% of the energy used by a building [45]. Consequently, improving indoor visual comfort through the use of TC facades and cladding is possible without compromising the building envelope’s thermal insulation.

Over the past ten years, there has been a rise in the application of TC in the construction sector. An example of a built structure in 2006 utilizing TC technology is the Radhous building in Erfurt, Germany. Its translucent facade, measuring about 6 m in width, 70 m in length, and 3 to 8 m in height, is composed entirely of newly developed, highly insulated eight-chamber polycarbonate panels, which are partially enhanced with foil patterns and decorations in shades of silver and gold [46]. Two other examples of structures that make use of TC technology are Italy’s booth at China’s 2010 Shanghai World Expo, where 1887 m², or more than 40% of the building envelope, was covered by 3774 TC panels [47], and Al-Aziz Mosque in Abu Dhabi. The mosque was constructed using 525 m² of TC panels, and it opened its doors in 2015 [48]. A much smaller application of TC takes place at the European Gate in the Hungarian city of Komárom, which symbolizes Hungary’s entry into the European Union. In the morning and late afternoon, the sun illuminates the statue’s 11.5 m TC, and at night, the embedded light sources provide an even more impressive sight [49]. The buildings in Figure 4 are arranged chronologically to provide an overview of applications of TC in diverse buildings across the world [38,46,50,51,52,53,54].

4.2. Top Surfaces

Nowadays, interior designers are focusing more on simplicity and moving away from traditional lighting sources. Translucent concrete is being used as a replacement for roof lights, as it allows light to pass through its fibers. The design of translucent concrete can be customized to create different effects based on the desired aesthetic. Using translucent concrete as a roofing material can help reduce the need for additional indoor lighting, leading to an eco-friendlier design. This type of concrete is often used in areas with ambiguous lighting needs, such as bathrooms and hallways, providing a soft and gentle illumination that adds a touch of luxury without straining the eyes, as shown in Figure 5.

4.3. Walls

The majority of walls in modern homes are painted or embellished with wallpaper for aesthetic purposes, with the exception of concrete rough walls that are only mildly embellished to fit the overall design scheme. These days, walls are mostly utilized for commercial decor, map displays, and tourist attractions. Transparent concrete can significantly reduce resource waste by taking the role of traditional advertising and computer screens. When transparent concrete is used in conjunction with artificial and natural lighting, it may provide a different ambiance and impact, leaving visitors with a fresh impression and infusing the interior space with new vitality. One of the main benefits of using this concrete for walls is that it is beautiful, energy-efficient, and environmentally friendly. Special light and color effects can be produced by using white or colored illumination elements [57]. Figure 6 shows examples of TC walls in different structures around the world.

4.4. Partitions

When TC is used as an interior partition, natural light can flow through the concrete during the day from one end of the room or lobby to the other at night. This creates a feeling of lightness and beauty in contrast to the heavy, dull feeling of traditional concrete partitions (Figure 7a–c). Using the TC as external walls and an interior partition in the Karolinska Institute in Sweden, natural light from outside the building can be reflected through the transparent concrete and light interior spaces and enter the building, increasing the sustainability of the institute and creating a different atmosphere from the artificial lighting (Figure 7a,d).

4.5. Floors and Highways

The primary functions of a building’s floor include separating spaces, protecting structural elements, meeting user needs, and offering various types of insulation. It is also important for the floor to be strong, durable, flat, and free of dust. Safety features such as electrical insulation, non-slip surfaces, and corrosion resistance are essential. Additionally, the floor should be aesthetically pleasing with specific colors, patterns, textures, elasticity, and sound-absorbing qualities [39,54,58]. Using TC as a flooring material can improve aesthetics while preserving the original characteristics of the floor. Translucent concrete in outdoor areas can unify the park, illuminate at night, and guide passersby. In addition, night-time street and footpath lighting is possible thanks to TC lighting technology; the footpath is illuminated only when a walker passes through it. This increases road safety and renders costly permanent illumination obsolete while also being ecologically beneficial. Figure 8 shows examples of the use of TC in flooring, exterior paving, walking paths, and road signs.

4.6. Staircase and Stairs

The incorporation of TC in stairs improves safety in the event of night power failures and can be used in stairwells illuminated by either LED lamps from below or linear LED lamps, as shown in Figure 9. Most recently (2018), a 14 m high staircase at the Capital Bank of Jordan was clad with 30 mm thick TC panels [51]. Millions of POFs have been placed on the panels, allowing light to shine through and creating a dynamic shadow-light interaction that changes throughout the day. The staircase is naturally illuminated during the day, but at night, the built-in LED strips enhance the effect by projecting the outline of the interior occupants onto the exterior walls, creating a shadow theater effect. This building is a great example of how TC can improve architectural design while at the same time providing practical benefits and a visual appeal (Figure 9c).

Transparent concrete can be used to create logos and other attractive decorations. Creating these works of art requires a deductive reasoning secretariat. It can also be utilized in a variety of applications, including exterior and interior walls, outdoor memorials, lamps, furniture, tunnels and dimmed lighting of metro stations, and green building construction to save energy costs by allowing more natural light into buildings [13,63]. Garcia et al. [13] carried out studies to explore the feasibility of using TC to create road tunnel pergolas. Research has shown that the use of TC can guide sunlight into the tunnel while preserving daylight saving [13].

Figure 9. TC stairs: (a) lit up from below side [58], (b) with linear LED fixtures [64], (c) Capital Bank in Amman, Jordan, 2018 [55], and (d) transparent concrete interior stairs [55].

Figure 9. TC stairs: (a) lit up from below side [58], (b) with linear LED fixtures [64], (c) Capital Bank in Amman, Jordan, 2018 [55], and (d) transparent concrete interior stairs [55].

By incorporating optical fibers into concrete, the TC smart lane separator can transmit light, act as a lane marker for drivers, and provide useful real-time information on road conditions, including traffic density and accidents. In addition, TC may illuminate dark passages and speed bumps to increase night vision [65]. However, the use of TC in the field of transport safety still requires more research and refinement. When TC is used in a building’s external structural components, daylight enters the interior during the day, producing ambient lighting. However, at night, light from the illuminated interior rooms spills outside, creating an ambient glow that makes the building’s facades appear to radiate light. The area surrounding the building may be sufficiently lit by the light passing through the walls, reducing the need for external lighting.

5. Evaluation of Light-Transmitting Concrete

As illustrated in Figure 1, there are eight primary assessments of TC being carried out in the literature. The next subsections go into depth about different TC evaluations, focusing on its thermal and energy-saving properties, mechanical and physical properties, light transmittance properties, and durability properties.

5.1. Thermal and Energy-Saving Properties

Transparent concrete, recognized as a sustainable material, has the potential to decrease energy consumption by minimizing the need for daytime artificial lighting and reducing winter’s heating requirements, although it might elevate summer’s cooling demands [66]. To reduce the increased cooling demand caused by heat gain in TC, several methods can be used: applying low-emissivity coatings or reflective coatings, integrating hybrid systems with shading, and utilizing external shading devices to reduce solar exposure to enhance indoor thermal energy efficiency and comfort. This section provides an overview of past studies focusing on transparent concrete’s thermal and energy-saving properties assessments.

Osman Gencel et al. [67] reported that TC has the potential to greatly increase the lighting efficiency of both residential and commercial structures. Compared to ordinary windows, TC may save up to 14% of energy and transmit up to 12.4% of artificial light. An experimental investigation on a TC panel studied thermal and light emission characteristics by modeling the fibers placement in the concrete throughout 12 months of exposure to simulated sunlight. The results showed that TC has good mechanical and thermal properties [68].

Ahuja and Mosalam [69] utilized a fiber volumetric ratio of 10.56% in a TC panel measuring 300 mm × 300 mm × 100 mm to study the model’s light transmission characteristics in Berkeley, California, weather. The TC panel’s solar heat absorption was modeled and calculated using an algorithm over the course of a 12-month-long simulation. The study’s findings were useful in producing a formula for estimating how much light will enter a building when TC is used. This will affect the subsequent design choices that are made in the ventilation, heating, and air conditioning design process.

As a follow-up to the previous work [69], a new study was conducted to estimate the ideal optical fiber ratio for TC panels to save as much energy as possible and to provide lighting and thermal evaluations [70]. Panels that were identical in size to the computer model from the earlier study [69] were constructed in the lab for the study, which was carried out in a model room that measured 3000 mm × 3000 mm × 2895 mm. The model was developed to calculate and simulate the heating and cooling loads of the ventilation, heating, and air conditioning systems, along with other thermal and light assessments, to identify the optimal optical fiber ratio for TC panels that have the highest potential for energy savings. Based on this, utilizing fiber with a volumetric ratio of about 6% results in an 18% decrease in energy consumption.

Pagliolico et al. [26] conducted both simulations and an experimental study of a high-resistance self-compacting mortar panel incorporating coarse waste glass and measuring 500 mm × 500 mm × 25 mm to study the effect of light transmittance on lighting energy consumption. According to his estimates, the lighting consumption is reduced by 6 to 20.6% as the light transmittance of the TC panels increases.

Additionally, an experimental and computational study was conducted on the thermal, mechanical, and light transmittance properties of a novel type of resin-based transparent cement-based concrete (TCBC) [71]. Findings revealed that TCBC has a 60% lower heat conductivity (0.382 W/m.K) than conventional concrete (0.894 W/m.K), as shown in Figure 10.

Juan Shen et al. [72] studied the natural light illumination, clarity, and shielding performance of a new polymethyl methacrylate resin-embedded concrete building envelope material. Flat plate and optical power methods were used to measure the heat conductivity and light transmission of a resin-based TCBC, respectively. Daylight and energy simulations were performed using Autodesk Ecotect Analysis software version (19.0.0.1) to evaluate daylight levels and the building’s energy consumption. The natural lighting factor increased by around 100%, while the illumination homogeneity improved by around 50% and the operating time of the artificial lighting system reduced by 57%. Moreover, under current test conditions, the heating and cooling loads can be reduced by approximately 20%. The results showed excellent light transmittance and thermal conductivity of resin-transparent cement-based concrete. Additionally, resin-transparent cement-based materials might be used to increase visual comfort and interior illumination.

In 2020, research was conducted to simulate the influence of various factors on the flow of light via TC. [73]. The fiber size simulation is also used to determine the ideal lighting ratio when using TC. Few studies have measured light transmission via TC or contrasted the translucent concrete’s thermal performance and light transmission with that of conventional concrete; nonetheless, the investigations that have been done so far have shown a generally positive energy demand indication.

Amorim et al. [74] developed experimental equipment for testing heat conductivity and transmittance in a transparent concrete block incorporating 0% and 4.1% optical fiber. The tests revealed that the addition of 4.1% optical fibers to the concrete improves its thermal insulating properties. Results showed that TC conducts less heat than that incorporating 0% fiber concrete.

A recent study by Vasudevan et al. [75] revealed that the thermal resistance of TC incorporating poly methyl methacrylate optical fiber is much higher than that of normal concrete, and increasing the poly methyl methacrylate optical fiber ratio allows more daylight in and lower heat gain and thermal conductivity.

5.2. Mechanical and Physical Properties

Compressive strength is the most important mechanical property of TC because the concrete’s strength is proportional to all of its other properties. Thus, compressive strength results may be utilized to assess concrete’s ability to withstand compressive failure. The test of flexural strength, on the other hand, is designed to measure the bending property of TC, which is commonly utilized in transparent partitions or walls.

5.2.1. Compressive Strength

The effect of optical fiber content and shape (filamentous and bunchy) on the compressive strength property of TC was investigated by Li et al. [76]. They reported that the compressive strength of TC incorporating 10% and 20% optical fiber is significantly lower than that incorporating 0% optical fiber. However, the compressive strength was slightly higher when the fibers were in filamentous form as opposed to bunchy form. Thiago et al. [77] also reported that the compressive strength of TCBC incorporating 5% optical fiber is 20% less than that incorporating 0% optical fiber, which is slightly higher than the results reported by Kumar and Ahlawat [16] and Altlomate et al. [52]. The reduction in compressive strength when incorporating optical fibers may be attributed to the formation of voids and fiber-matrix debonding. Luhar et al. [78] found that TC’s compressive strength was almost similar to that of conventional concrete. In their research investigation, they used optical fibers with a diameter of 1 mm and spaced them 8 mm apart horizontally. The authors reported that conventional concrete cubes had an average compressive strength of 39.50 MPa, whereas the comparable value of TC containing 5% fibers was 36.70 MPa. As a result, their study has demonstrated that TC may be encouraged for structural building without concern about compressive strength. This is a key step toward recognizing TC as a potentially long-lasting, unique building material for the infrastructure and construction sectors. The compressive strength of TC facade panels made using optical fibers was investigated by Tuaum et al. [40]. The inclusion of optical fibers in TC panels reduced compressive strength by 3.8 to 23.4% compared to that of conventional TC panels. Regardless of the type of translucent components utilized, augmentation with bright elements reduces the compressive strength of the resulting TC. Light transparent materials’ mechano-physical properties should be identified before including them in the concrete mixture, since their qualities have a direct impact on the properties of the overall concrete mix. For example, according to Henriques et al. [77,79,80,81], optical fibers are hydrophobic and smooth, which leads to poorer bonds at the fiber-matrix interfaces. Previous studies [76,82,83,84] also found that an increase in the volumetric proportion of the POF corresponds with a reduction in the compressive strength of TCBC. Additionally, Salih et al. [85,86] found that increasing POF content reduces compressive strength, while aging enhances it. They proposed that increasing the proportions and sizes of POF could yield lightweight boards by lowering TC density. The authors experimented with various volumetric ratios (2%, 3%, and 4%) and diameters (1.5, 2, and 3 mm) of POF in a self-compacting mortar to formulate TC. This TC achieved a compressive strength between 31.1 MPa and 40.4 MPa at 28 days.

According to Zhandarov et al. [87], TC containing recycled glass also showed the same problem because of the glass’s pitiful geometry particles and the weak adhesion between the cement paste and glass, which was discovered in studies of how the interfacial bond strength determines the characteristics of heterogeneous systems like TC. The compressive strength of TC incorporating 0, 2.5, and 3.5% organic glass elements was investigated in [88], and the results showed that the organic glass elements had a positive effect on the compressive strength of TC. However, the compressive strength of concrete specimens incorporating 2.5% organic glass is higher than those incorporating 3.5%. Additionally, results showed that a further increase in the content of transparent elements (>3.5%) leads to a sharp decrease in compressive strength and is not recommended in practice. Incorporating recycled aggregate and other waste materials, TC may support circular economic principles by improving material recyclability and sustainability [89]. Sangeetha et al. [90] investigated the effect of the diameter and spacing of POF on the compressive strength of TC after 7, 14, and 28 days of cure. Four TC cubes with 0.5 mm, 0.75 mm, 1 mm, and 2 mm diameter POF, along with two different spacings (10 mm and 20 mm), were prepared and tested. The results revealed an increase in compressive strength with increasing both the curing period and optical fiber diameter, as displayed in Figure 11. The 28-day compressive strength of 10 mm spacing increased from 5.5 to 18.7% as the fiber diameter increased from 0.5 to 2 mm. Similarly, the compressive strength of 20 mm spaced specimens rose from 6.5 to 22% when the fiber diameter increased from 0.5 to 2 mm. Krishnamurthy et al. [91] also reported similar results: an increase in the compressive strength of TC compared to conventional concrete and an increase in compressive strength with increasing curing period from 7 to 28 days.

Tahwia et al. [35] studied the influence of the diameter and volume ratio of POF on the compressive strength of both ultra-high-performance transparent concrete and high-performance transparent concrete. Results showed an increase in compressive strength as the volume ratio and diameter of POF increased. However, the effect of optical fiber diameter on increasing compressive strength is more than that of the volume ratio. Zhou and Ou [68] and Paul et al. [92] found that when the volume ratio of POF increased, the compressive strength of TC decreased. As a result, increasing transmittance indefinitely by raising the POF volume ratio would be harmful to the mechanical properties of TC. While Momin et al. [93] determined that TC incorporating glass optical fibers performed similarly to ordinary concrete, it was less effective than TC incorporating glass rods due to the glass optical fiber’s lower rigidity. In the study [27], TC specimens incorporating glass optical and rod fibers at varying ratios were prepared and compared to ordinary concrete. According to the findings, the compressive strength of ordinary concrete specimens was higher than those incorporating optical and glass rod fibers, and the compressive strength of optical fiber TC was higher than that of glass rod TC.

The compressive strength of printed TC cubes incorporating PMMA was evaluated by [33], and the results showed that increasing fiber content increased the compressive strength of 3D printer TC when loaded perpendicular to the fiber orientation but reduced it when loaded parallel to the fiber orientation. According to studies [77,79,94], the use of silica fume as a partial substitute for cement in TC is necessary to reduce microcracks caused by POF in TC. Juan and Zhi studied the effect of area resin ratio on the compressive strength of TCBC and reported a slight reduction in compressive strength of 0.43% to 3.49% as the area resin ratio increased from 1.13% to 6.2%, as shown in Figure 12. The primary cause of the reduction in compressive strength was that as the ratio of resin volume increased, the interface area increased, leading to faster formation of cracks at the interface and thus reducing specimen’s strength. Consequently, the area ratio should be maintained below 5%.

5.2.2. Flexural Strength

The flexural strength of the concrete reflects the bending resistance of TC when used in translucent partitions or walls. Several factors affecting the flexural strength of TC include fiber diameter, ratio and spacing, aggregate size and shape, curing and moisture conditions, water-to-cement ratio, unit weight, air content, and the production conditions of the concrete. Shitote et al. [95] reported that TC’s flexural tensile strength gradually decreased as its optical fiber content increased. Li et al. [83,84] and Henriques et al. [77,79] investigated the flexural strength of cement-based PMMA fibers and POF, respectively, and discovered a similar pattern. Prior studies [6,7] also found that when the volumetric ratio of the optical fiber increased, the flexural strength of cement-based TC decreased. The flexural strength results obtained at various fiber content levels show a gradual reduction, as illustrated in Figure 13.

Salih et al. [85] studied the flexural strength of TC reinforced with self-compacting mortar and POF. The results showed that the incorporation of POF frequently decreased the flexural strength of TC. However, it appeared that the flexural strengths of TC changed in response to variations in POF’s volume and diameter. It was found that TC incorporating 2 mm diameter PMMA fibers exhibited higher flexural strength than those incorporating 1 mm or 2 mm. Furthermore, a study carried out by Tutikian and Marquetto [96] evaluated TC walls constructed with a random distribution of optical fibers for use in precast buildings in Brazil. The experimental results demonstrated a decrease in the tensile strength of TC with increasing optical fiber content. In contrast, Robles et al. [97] found that increasing the fiber diameter decreases the fiber-matrix interfacial area and enhances the tensile strength of TC. Awetehagn et al. [40] also reported that the flexural strength of TC specimens incorporating 2 mm and 3 mm POF diameters with 2%, 4%, and 6% POF ratios was less than that of the normal concrete. However, the flexural strength of TC specimens containing 3 mm POF diameter was higher than those containing 2 mm POF diameter.

Summarizing earlier studies in Section 5.1 and Section 5.2.1, a research deficiency exists, connecting the optimal optical fiber content in TC to achieve both better mechanical properties and maximum energy savings, as illustrated in Figure 14. Additionally, compressive strength and energy efficiency must be traded off for TC performance, as shown in Figure 14. The increase in POF ratio from 1% to 5% improved light transmission, and the energy costs were reduced through natural lighting. However, because of fiber clustering and weak bonding interfaces, this increase in POF content resulted in decreased compressive strength. A POF content of 4.5% is typically the ideal amount for load-bearing structural members. This range maintains an acceptable compressive strength, 12.3% less than that incorporated with 0% POF, offers considerable daylighting benefits, and saves energy by about 24.4%. However, it is strongly advised that structural members that are not load-bearing or that are lightly loaded have a POF of greater than 6% since this greatly increases energy savings. Therefore, to maintain balance between compressive strength and saving energy, designers should choose fiber content with the TC’s frequent use in mind.

5.3. Light-Transmitting Property

According to Hoyos [98], light transmittance is an optical property that occurs when a material dissipates energy in the form of light by passing through it from one side to the other; the energy dissipated on the output side is equal to the energy dissipated on the input side, and after completely passing through the material, the light beam exits with a final reduced intensity that is nothing other than the transmitted intensity. This light transmittance can be measured using mathematical formulas, through a spectrophotometer [98], and also by a luxmeter [99]. The majority of the studies have performed light transmittance tests to validate the characteristics of TC based on several criteria. Light transmittance tests have been employed in numerous studies to validate the properties of TC based on various criteria. It was highlighted that no recommendations or standards for assessing TC’s light transmittance properties had yet been devised. Each researcher used a different testing device and experimental design. For example, there are two possible experimental setups for light transmittance testing: enclosed and open spaces [13,24,32,83]. Henriques et al. [79] and Altlomate et al. [52] created an enclosed region for TC transparency evaluation to prevent light dispersion and ensure that all light rays from the light source are directed toward TC specimens. The information obtained is unique because of the uncertainties brought on by the resistance and accuracy of the measuring equipment, even though differences in measuring equipment may not significantly affect transparency measurements. Consequently, a light-transmittance ratio that lowers measurement errors caused by different measuring devices has been validated by some researchers [24,25,82,95]. A study was conducted both experimentally and computationally on the TC panel [26]. The influence of employing coarse waste glass fragments was investigated in terms of energy consumption and light transmittance for illumination. The testing findings revealed promising applications for TC panels with a light transmittance of 5% as a function of glass volume. As a result, simulations showed a reduction in energy consumption for lighting ranging from 12.7% to 16% with a light transmittance of 5%. Internal walls, rather than envelope components, are an even better application for the investigated concrete panels.

The transmitted luminous flux utilizing optical fibers with varying diameter and volume ratios was experimentally examined to assess the importance of figuring out the fiber volume ratio in TC panels and how it affects the quality of daylight transmission [66]. Specimens incorporating optical fibers with a 3 mm diameter and a 5% volume ratio showed the best results.

Although this is not available during the actual construction process, the results suggested that the bending radius should be less than 15 times the fiber diameter because it affects the performance of light transmission. Additionally, to measure the amount of light that enters a space from the outside, the study tested various translucent concrete panels with varying thicknesses (3, 6, and 10 mm) that were intended to replace windows. The results of the illuminance test verified that the distribution and spacing between fibers were important factors that affected the amount of daylight that entered space. The light transmittance properties of TC were investigated by Sangeetha et al. [90], where a lux meter was used to measure the quantity of light in lumens, with a range of 0.1 to 100,000 lux. A 16W LED fiber mini optic tiny kit was utilized as the light source. TC cubes were kept in a 610 mm × 610 mm wooden box to avoid light losses. The lux meter measurements were taken. On both sides of the TC cubes, the optical fibers were securely coiled and affixed with insulating tape. The fibers were connected to the lux meter on one side and the LED tiny kit light source’s intensity on the other.

The findings demonstrated that light transmission is influenced by the spacing and diameter of optical fibers. Light transmission increases as the horizontal and vertical spacing between fibers decreases. These findings are similar to those reported in [40,100]. Following that, Kim et al. [28] produced weightless TC by replacing optical fibers with transparent plastic pipes and rods. The study showed that the transmission of light is inversely related to the length of the pipe and the rod. Another investigation [67] developed a new light-transmitting cementitious-based (LTCB) composite that replaces microencapsulated phase-shift material used in buildings, with the aim of reducing energy consumption of buildings through light carried out by LTCB composite. The findings revealed that composite slabs had up to 12.4% artificial light transmittance, resulting in a significant boost in the lighting efficiency of residential and commercial structures. The findings of this investigation can be applied to increase the effectiveness of artificial lighting in buildings, which will encourage the creation of environmentally friendly constructions. Figure 15 shows the relationship between fiber spacing and content and light transmission.

The light-transmitting property of TC concrete was simulated multiple times using Autodesk Ecotect Analysis software version (19.0.0.1) [71,102,103], and it was found that TC increases the amount of light entering the room and its brightness by as much as 30%. One of the most significant issues with evaluating TC is the lack of standard testing methodologies, particularly for light transmission. As a result, creating ASTM or ISO norms is critical to guarantee that TC evaluations are consistent and comparable.

Table 1. Thermal, energy-saving, mechanical, physical, and light transmission characteristics were collected from existing studies.

Ref. #	Fibers				Mechanical Properties Compared to Normal Concrete			Thermal and Energy-Saving	Light-Transmission (LT)
	Type	Diameter (mm)	Spacing (mm)	Ratio (%)	* CS/FS	Effect	Increase or Decrease Percentage (%)
[76]	Glassy optical fiber (filamentous)	0.05	0.125	10	CS	Decrease	27.5	-	Increase LT by increasing fiber diameter and parallel arrangement of the fibers
				20		Decrease	12.1
		0.0625		10		Decrease	19.8
				20		Decrease	11.3
	Glassy optical fiber (bunchy)	0.05	0.125	10		Decrease	26.7
				20		Decrease	11.7
		0.0625		10		Decrease	18.5
				20		Decrease	11.1
[77]	Polymeric optical fibers	0.4	0.1	2	CS	Decrease	11.4	-	LTC containing 5% polymer optical fibers increases the LT by 100%.
				3.5			14.9
				5			19.9
				2	FS	Decrease	20.6
				3.5			31.7
				5			25.4
[16]	POF	0.5	0.1	0.25–1.5	CS	Decrease	4.6–0.8	-	Increasing LT as the fiber volume increases
				1.75–2		Increase	1.1–2.7
				2.5–4		Decrease	1.1–15.2
[52]	POF	0.3–0.75	0.5–1	0.06–0.36	CS	Decrease	15–1.3	-	Increase in LT as the fiber ratio decreases and the fiber diameter and spacing increase
		0.75–1.5	1	1.43–1.59		Increase	28.8–3.4
[78]	POF	1	8	1	CS	Decrease	5.0	LTC may be used for energy saving in commercial and residential buildings.	-
[40]	POF	2–3	1–6	2–6	CS	Decrease	3.8 to 23.4	-	-
		2–3	6.5–14.5	2–6	FS	Decrease	2–21.5
[90]	POF	0.5	10	-	CS	Increase	5.5	-	POF with 10 mm spacing and 2 mm diameter provides optimum lighting and is suited for manufacturing LTC.
		2					18.7
		0.5	20				6.5
		2					22
[91]	POF	2	5	4	CS	Increase	9.7–10.8	LTC is an energy-efficient building material.	LT decreases as the fibers’ spacing increases.
[35]	POF	1, 2	16	1	CS	Increase	2.5–17.6	LTC is more cost-efficient and energy-efficient than conventional concrete.	The LT increased significantly from 10% to 21.35% as the POF rose from 1% to 4%.
[33]	PMMA	1–3	10	2.16	CS	Increase	2–4	Thermal conductivity of LTC is 19% less than that of normal concrete.	LT decreased with light incident angles but increased with POF diameters and reflection coefficients.
[85]	PMMA	1.5–3	10	2–4	FS	Decrease	15–47.3	-	-
[67]	Glass fibers	0.013	Regular distribution	0.5	CS	Decrease	The addition of 10% of microencapsulated phase-change material decreased CS by about 28%.	LTC may save up to 14% of energy.	Transmission of up to 12.4% of the light
					FS	In 28 days, it is almost like normal concrete.	The addition of 10% of microencapsulated phase-change material slightly affects TS by about 28%.
[70]	PMMA	5	Dispersed over 90˚ angles	5.6	-	-	-	LTC saved up to 18% of energy.	Increasing fiber content provided sufficient daylight illumination.
[26]	Flat glass	-	9	5	-	-	-	LTC saved up to 16% of energy.	LT ranged from 1.3 to 4.9 percent depending on the glass openings of the panels tested.
[71]	Resin cylindrical rod	15–22	6		CS	Slight decrease	0.42–3.5% as the resin content increases from 1.13–6.2%	TCBC has a 60% lower heat conductivity than conventional concrete.	Within a 100 mm thickness range, LT was 93%; as thickness increased, it dropped to 60%.
[74]	POF	3.2	12–13	4.1	-	-	-	LTC incorporating 4.1% POF improved thermal insulation and reduced heat conduction by 8% compared to that incorporating 0% of POF.	TC can provide energy savings, as it can partially illuminate the space using only sunlight or electricity from another environment.
[75]	PPMA	1	2.5–5	-	-	-	-	Thermal insulation improved as fiber content increased.	LT increased with increasing of the fiber content.

* CS: Compressive strength, FS: Flexural strength.

summarizes the thermal, energy-saving, mechanical, physical, and light transmission characteristics from existing studies.

5.4. Durability Properties

Managing the sustainability of new structures and extending the lifespan of existing ones align perfectly with the principles of a circular economy. In this context, concrete structures’ sustainability plays a crucial role worldwide, with the primary goal of ensuring their reliability in a specific environment over an expected lifespan. Concrete’s durability is defined as its ability to withstand deterioration caused by abrasion, weathering, chemical exposure, or harsh conditions while preserving its appearance and strength throughout its lifespan [104,105]. Concrete’s durability can be dangerously affected by the penetration of aggressive liquids, such as those that have the potential to chemically break down the cement matrix and implanted optical fibers. In practical applications, they may impair light-transmission capabilities and the material’s structural integrity by causing microstructural damage and reducing mechanical performance. Further weakening the cement matrix and thereby increasing the chance of cracking is the leaching of calcium hydroxide by water circulation within the concrete [106]. This liquid penetration depends on the concrete’s permeability, which also determines how easily the concrete can be saturated. Therefore, it is also important in resisting thawing and freezing. Henriques et al. [79] studied the water absorption characteristics of TC incorporating 2%, 3.5%, and 5% fiber. The findings revealed that increasing the fiber content from 2% to 5% increased water absorption by 309% to 400% as compared to conventional concrete. This occurred because adding fiber increases concrete’s porosity. Saleem [11] studied how reagent concentration affects the chemical attack resistance of TC fiber-optic TCs. The permeability of optical fiber TC progressively dropped as fiber content increased; however, this resistance improved after applying an epoxy resin surface treatment. Pilipenko et al. [107] studied permeability, fading, freeze-thaw, water absorption, and chemical attack of fiber-optic TCs. The results revealed that water absorption and unit elongation during thawing and freezing were reduced by 16–20% and 17–20%, respectively. It was also discovered that distributing polymer resin through holes on the surface increases freeze-thaw and chemical resistance.

Overall, there has been little research on the durability of TC compared to light transmission and mechanical properties. However, the durability of the optical fiber TC is important in determining the longevity of the optical fiber TC to withstand deterioration and maintain the efficiency of light transmission over its lifetime. This is due to the weaker interface link between optical fibers and cement, which creates more pores in the cement and provides an invasion channel for aqueous solutions and chemical reactions [79,83]. In addition, when used as a long-term outdoor shield, fiber TC is susceptible to acid rain erosion, weather, freeze-thaw action, and UV radiation. However, there is currently no research on this range of longevity characteristics. Therefore, further studies are needed to investigate the long-term durability of TC under real-life conditions and other durability tests, such as freeze-thaw actions, resistance to chemical exposure or UV radiation, and accelerated aging, to better evaluate TC in real applications.

There are currently few durability studies on TC due to a lack of standardized testing methodologies for its hybrid composition. Instead of employing unique degradation processes such as light transmission loss, heat mismatches, and fiber-matrix interface deterioration, researchers must rely on traditional concrete testing. To ensure uniform and trustworthy results, future studies should follow standardized procedures of existing durability testing, such as freeze-thaw resistance, accelerated chloride penetration, and sulfate attack tests.

6. Cost Analysis

This section shows an average comparison between the costs of making translucent concrete and the costs of making conventional concrete, in relation to the specifics of the concrete’s main materials. The cost of translucent concrete may vary depending on various factors, as with other technological concretes. These factors are the type of optical fibers and other transparent material quality, production method and process, size of the project, requested features, local material, and labor costs. Transparent concrete reduces energy costs because it allows light to pass through. Moreover, it provides earthquake safety by reducing the dead load of the building [108]. However, translucent concrete is more expensive than traditional concrete because more materials and labor are required in production. Additionally, since translucent concrete produces more heat in direct sunlight, it can increase air conditioning costs if used indoors. Translucent concrete has less water permeability. For this reason, the need to take special precautions to prevent water from entering is among its disadvantages [108]. Besides initial production cost, TC needs to be maintained on a regular basis over the course of its 15–20-year service life, mainly by surface cleaning of optical fibers and re-coating of epoxy layers to maintain light transmission effectively. This slightly raises the total cost of TC compared to that of normal concrete, but the energy savings resulting from better natural lighting make operating costs of TC lower, while the long-term life-cycle cost of TC is lower than that of normal concrete. TC and regular concrete have comparable end-of-life recycling costs, which is another balanced life-cycle factor. TC uses daylighting to reduce energy consumption. However, due to polymer optical fibers, epoxy resins and unique production processes, it may contain more embodied carbon, which, due to the scarcity of published studies, is still to be explored.

Figure 16 shows a cost comparison of three transparent materials (polyester resin, POF, and glass aggregate). Among the three transparent materials, glass fiber is the least expensive, and optical fiber is known to be the most expensive transparent material [71], particularly glass optical fiber. As a result, polymer resin and plastic are being used to replace glass optical fiber to lower transparent material costs.

The overall cost of TC production includes the labor and manufacturing process costs. There is no need for extra work to distribute the glass aggregates in the mixture because they are mixed with the concrete during casting. According to Juan and Zhi [71], the difficult layout installation and arrangement of optical fiber hampered large-scale TC manufacturing and decreased the popularity of its uses in the building sector. The use of polymer resin and plastic bars in the production of TC reduces production costs by removing costly procedures for the arrangement and installation of fibers. The only researchers who used GiD powder to make TC blocks were Saleem and Blaisi in 2019. However, the production cost is three times that of normal interlocking blocks. Henriques et al. [77] examined the material production cost per lux for TC with various fiber volumetric fractions. They found that the higher the fiber content, the higher the material production cost. However, this does not guarantee that greater TC costs will result in similar light transmittance returns as the fiber volumetric percentage increases. The findings showed that, in comparison to a fiber content of 3.5%, 5% of the volumetric fraction of fiber was the most advantageous, offering the best translucency with only a slight increase in fiber content.

Sawant et al. [101] analyzed the manufacturing cost and payback duration of TC based on light energy savings. They observed that while the cost of producing TC was high, the long-term advantages of reducing light energy use not only compensated for the manufacturing cost but also lowered the carbon footprint, contributing to climate change. In contrast, Ahuja and Mosalam [70], on the other hand, did a thorough analysis of total energy expenditure while utilizing TC, taking into account thermal comfort and light energy consumption in a building. Because transparent materials have heat conductivity properties, light that passes through TC transmits both heat energy and light into the structure. They [70] determined that TC panels with 5.6% fiber content may reduce overall energy consumption by 18% when accounting for HVAC and lighting systems. In summary, TC manufacturing costs are the primary focus of economic viability studies in literature. So far, there has not been a feasibility study that takes light and thermal analysis into account to determine total energy savings. Moreover, most of the research on economic feasibility in the database of current literature concentrates on TC incorporating optical fiber. More research on the economic viability of TC using other types of transparent materials, such as polymer resin and glass aggregate, is urged.

7. Limitations

Although light-transmitting concrete offers great potential for architects and engineers, it is not without its limitations. This section addresses some of the gaps in the literature on TC, such as the use of results from small-scale laboratory work that is unlikely to represent service performance in the real world and the lack of full-scale or pilot-scale applications for assessing structural integrity, long-term durability, and practical viability. All these differences highlight the need for complementary empirical research and well-established field-testing procedures to supplement laboratory work and boost trust in the application of transparent concrete in construction practices. In addition, the maximum size of panels that may be manufactured using light-emitting concrete is limited, typically up to 600 mm × 1200 mm [109], because of the relatively low modulus of fiber rupture. This therefore restricts the application of this material in larger construction projects, as many large precast concrete panels are now used in modern construction, and only a small proportion of these would be able to incorporate light-transmitting concrete. Additionally, light-transmitting concrete is significantly more expensive than more traditional forms of concrete. Overall, the limitations of light-transmitting concrete will necessarily restrict its use to a small number of niches and high-profile projects for the foreseeable future. However, further research and development may yet provide more efficient ways of using the material or even new applications that are not yet possible with traditional construction materials.

8. Conclusions

In this literature review, we discussed the production, components, mechanical properties, light transmission properties, energy-saving and conductivity properties, cost, and bibliometric analysis of transparent concrete (TC) incorporating various types of transparent elements. The following conclusions can be drawn:

• Placing the fiber optics vertically has a significant effect on the transparency of the concrete.
• The mechanical strength of TC decreases when transparent elements are incorporated. However, depending on the type of transparent element and other parameters, increasing the volume fraction of the transparent element may increase or decrease the mechanical and light transmission characteristics.
• The optimal fiber ratio in concrete volume is less than 5% for enhanced mechanical properties and 6% or more for energy savings.
• Transparent concrete will play a crucial role in smart housing designs. Its contribution to electricity, heat, and energy efficiency will enhance the popularity of smart buildings.
• Most current literature has focused on TC utilizing optical fiber. There is considerable potential to incorporate epoxy resin and waste glass into the production of TC; however, insufficient information regarding their properties is available in existing literature.
• Currently, the focus of TC development is primarily on aesthetic and construction applications.
• Nonetheless, TC holds significant promise for infrastructure uses, particularly enhancing traffic safety. However, essential factors such as illuminance levels, mechanical properties, production processes, and design criteria suitable for infrastructure use remain insufficiently researched.
• Nonetheless, TC holds significant promise for infrastructure applications, particularly in enhancing traffic safety. However, essential factors such as illuminance levels, manufacturing processes, mechanical properties, and design criteria suitable for infrastructure use remain insufficiently researched.
• The use of modern materials and technologies enables the creation of new types of decorative concrete, which possess unique aesthetic features.
• The primary factors examined in TC studies include the spacing, amount, and size of transparent components inside the concrete matrix. Additionally, variables such as curing conditions, light intensity, angle of light incidence, and the distance between the light detector and the light source relative to the tested specimen significantly influence TC properties.
• The durability and mechanical properties of TC can be analyzed through microstructural studies, which provide insight into the cohesion between the concrete matrix and optical fibers. Environmental factors affecting the durability of fiber-optic TC, including porosity, chemical attacks, freeze-thaw cycles, and water permeability, have received little attention. Addressing these factors is essential for ensuring sustainability in the building sector.
• The larger the size and volume percentage of the transparent element, the greater the light transmission. In light transmission tests, most experimental data reported luminance values rather than light transmission efficiency, leading to biased and inconclusive results.
• The application range of TC is more limited compared to normal concrete constructions. However, as the durability and mechanical properties of TC are better understood and production costs are reduced, its use will expand even further in the future.

Table 2. TC characteristics versus type of transparency used.

Test	Transparent Concrete
	Epoxy Resin-Based	Polymer Optical Fiber-Based	Waste-Based Glass-Based
Compressive strength	Low, limited data is available	High, extensively researched	Low, limited data is available.
Flexural strength	No data is available	High, extensively researched	No data is available
Light-transmitting property	No data is available	High, extensively researched	Low, limited data is available.
Durability properties	Low, limited data is available.	Moderate, with limited long-term research.	Nil, no data is available
Thermal and energy-saving properties	Low, limited data is available.		Ver low, limited data is available.

summarizes the analysis of the TC gap matrix, comparing the characteristics of the TC (mechanical and physical characteristics, heat and light saving, and durability) with the types of transparency used (waste glass, POF, and resins).

We can conclude that a unique material has emerged in construction, one without any analogues. This material will enable the realization of innovative ideas, resulting in glowing houses, theaters, and other buildings that will captivate with their beauty and brilliance, elevating architecture to a new level and giving rise to new architectural achievements.

9. Future Research

• Further studies are needed to identify the best fiber ratios to be incorporated in TC to improve its mechanical properties and achieve maximum energy savings.
• The durability evaluation of TC containing various types of transparent elements requires further investigation. Additionally, testing for physical characteristics and microstructure analysis should be done to get solid proof for the mechanical and durability analysis of TC.
• Future research should focus more on TC incorporating waste glass and epoxy resin than on transparent fibers. These materials, particularly epoxy resins, have a great deal of potential to replace optical fibers in TC due to their low labor and material costs and simpler production processes.
• Further research is needed to clarify the mechanical behavior of the panel form of the TC and other characteristics such as heat insulation, permeability, and sound insulation, so that TC applications can be widely used in practice.
• Additional research is needed to investigate heat loss over a longer time span, taking into account both daytime and nighttime temperatures.
• More attention should be paid to feasibility investigations on total energy consumption, taking into account heat comfort and light transmittance property.
• The utilization of LTC in the infrastructure in the infrastructure sector, particularly for road markings and tunnels, needs to be investigated.
• Theoretical research on the mechanical strength and overall energy savings of LTCs is suggested as a foundation for engineering design. This enables engineers to estimate the maximum benefit achievable that can be gained from using TC and its characteristics.
• Future research should focus on the development of standardized ASTM or ISO durability and light transmitting test manuals.
• LTC would help in saving energy of construction in the fields of civil, interior, and architectural engineering and would provide an additional function by enabling these concrete structures to provide light in dark environments.