Poly-Methyl-Methacrylate Rods in Light-Transmitting Concrete: A Critical Investigation into Sustainable Implementation

Abstract

The development of special concrete focussed on sustainability and energy conservation has been approached through the use of recycled materials, novel techniques and processes, and materials that harness natural energy. This paper presents the results of one such study on the development of light-transmitting concrete using a novel polymeric transmitting media, poly-methyl-methacrylate, and a detailed analysis of the results obtained. Four variants based on the diameter and number of rods have been studied, with 5 and 10 mm diameter rods incorporated into 100 mm cube samples. A positive correlation between the area of rods and transmittance has been established; however, a loss in compressive and flexural strength was observed. Seasonal and monthly variation results indicate higher transmittance in summer, with the highest transmittance being observed in the month of May and the monsoon having the lowest transmittance, specifically in the month of July. The results of a case study of the application of the material have also been presented. The cost of construction has been studied, and the prediction of electricity consumption during operations has been carried out. The results have indicated the feasibility of use, even with the high initial cost. Variants have been shown to return the investments in a period of 7–31 years. Additionally, three of the four variants showed a sharp decrease in total CO₂ emissions by eliminating the need for energy for daylighting and eliminating the consumption of electricity throughout the service life. Variants have been shown to return the investments in a period of 7–31 years. Additionally, three of the four variants show a sharp decrease in total CO₂ emissions by eliminating the need for energy for daylighting and eliminating the consumption of electricity throughout the service life.

1. Introduction

The evolution of concrete has been one of the pivotal points in infrastructure development and has provided an impetus to global modernisation. With an increased focus on sustainable construction and the environmental impact of construction activities, there is a pressing need to find materials that can achieve these sustainability goals while meeting the requirements of existing materials. This has been the inspiration behind several modern developments in material sciences.

There have been several attempts with varying degrees of success in implementing agricultural, industrial, and manufacturing waste and recycled concrete materials to assist in solid waste management. The use of agro-industrial wastes as alkali-activated binders has been one of the areas of modern research in concrete production as a means to control the carbon footprint [1,2]. Cashew-nut shell ash as a binder is one example of an agro-industrial waste material that has been implemented as a supplementary cementitious material in order to reduce the amount of cement while retaining the properties of concrete [3]. The use of supplementary cement materials, alternate aggregates, and building materials has been an attempt to reduce the dependency on natural and non-renewable materials for conservation and energy-conscious constructions [4,5]. The development of special concrete and high-strength concrete has also caused a reduction in the total quantity of concrete required to construct the same spaces and aid in the vertical development of cities [5]. Better construction practices and optimised processes have also been implemented to reduce waste of material, workforce, and energy [3]. Concretes have been developed to reduce pollution by absorbing airborne affluents and purifying contaminated water. Studies have successfully induced NOx de-pollution using activated charcoal as an additive in concrete [6]. Photocatalysts of copper, titanium, and silicon have been used to self-clean and depollute built environments [7]. Runoff water has been purified using materials like porous concrete with the incorporation of photocatalytic materials like nano-TiO₂ [8,9]. Marine structures have also been constructed with photocatalytic materials to reduce marine oil pollution [10]. While environmental concerns are being addressed through different perspectives, there has also been the development of light-transmitting concrete that attempts to incorporate natural light into buildings and structures as a means of aesthetic design, reduce energy consumption, and improve the productivity and mental wellness of the inhabitants.

Light-transmitting concrete in its present form was envisioned and conceptualised by Hungarian architect Aron Losonczi in 2001, who created a variant of light-transmitting concrete panels by embedding 4 mm transmitting units in a mortar mix. The material was precast, manufactured by precise machines, and sold as panels of various thicknesses and dimensions. This led to an explosion in research in this area, with several researchers worldwide aiming to develop and explore the possibilities of this novel material. Research has progressed into developing a material for illumination and temperature control, which has led to various approaches being undertaken.

Light-transmitting concrete has the potential to be a unique solution to a long-standing problem of sustainable construction. The material paves the way to incorporate sunlight as a source of daylighting while improving the insulation of the spaces it is used in, compared to windows. The combination of light transmittance and insulation can reduce the required heating loads as well as energy losses in cooling that can occur through windows. The ability to harness sunlight results in reducing the consumption of energy, which has a vast economic and environmental impact. In theory, the material has an immense impact on built environments and green construction, but there are practical challenges being addressed through research. A detailed review on pellucid concrete using plastic optic fibres has also determined how there is an increase in the cost of manufacture of translucent concrete while highlighting how glass fibres show better transmittance than glass rods [11], while another comprehensive review of translucent and transparent solar facades concluded with an observation on the lack of consideration of the technical-economical feasibility of the integration of the technology into construction practices [12].

The study of energy efficiency of light-transmitting building envelopes as thermal insulators involves using phase change materials. A study on the effect of using translucent concrete panels on energy characteristics found that a fibre volumetric ratio of 6% can reduce energy consumption by around 18% when compared to a room wholly deprived of sunlight. It was also observed that the energy expenditure in the USA decreased by 18.26% when 64 (6%) fibres were present in a TC panel. Also, a fibre density of 5.59% in ultra-lightweight cement composite panels can save up to 20.5% of energy expenses [13]. A study was conducted on using thinly sliced marble panels as a translucent and cooling building envelope. The results of the study revealed that the use of a translucent façade can reduce electricity consumption by 11% and overall energy demand by 4% for the site. [14]. Light-transmitting cementitious composites using microencapsulated phase change materials have been found to retain and liberate heat in order to improve insulation and reduce energy demand for heating of built environments [15]. Using silica aerogels to induce translucence and high insulation in bricks for building envelopes has been achieved successfully, wherein the glazed surfaces enhance transmission and daylighting [16]. A study on the daylighting performance of translucent building envelopes through simulation and analysis indicated how an increased area of transmittance resulted in an increase in the transmittance and observed the dependence of transmittance on the time of the year as well as the time of measurement [17]. These scientific advancements use various phase change materials, such as silica aerogels, to retain thermal energy and reduce space heating costs while enhancing the illumination of building spaces. The thermal retentivity properties of these materials and their transmissibility make them ideal for such applications.

Concurrently, there have been several scientific advancements in the use of glass, waste glass, and acrylic materials as transmitting media integrated into concrete [18,19]. A study attempted to use waste glass pieces bound with resin as a transmission media. The novel technique aimed to reduce solid waste while improving the transmittance of light. The studies, however, found that due to the variable size and angularity of the glass pieces, the panel thickness and the overall size of the glass pieces determined the transmittance characteristics. The limitation on the thickness results in the possibility of a reasonable production of 10 mm thick tiles with 9 mm glass pieces [20]. A different study also attempted to enhance transmittance by implementing perforated shells [21], while a separate study attempted to develop glow-in-the-dark and colour-tunable concrete [22].

While these studies incorporate different materials as transmitters, the primary focus of all developments has been on the inclusion of plastic or glass optical fibres in concrete. Several studies have emphasised and elaborated on various ways to develop light-transmitting cementitious materials, while some others have deliberated on the properties of the concrete that encapsulates these fibres. Studies have been conducted on the use of poly-methyl-methacrylate (PMMA) fibres in cement mortar using a woven-fabric technique that has demonstrated a drop in the compressive and flexural strength of concrete. [23]. In an attempt to reduce this loss of strength, further studies were carried out using a sulfoaluminate cement mortar. This technique allowed for reduced strength loss whilst maintaining the transmission characteristics and behaviour [24]. Another study attempted to integrate self-healing and translucence in cementitious materials with the incorporation of glass fibres, wherein the inclusion of glass fibres increased the transmittance in the non-structural material [25]. A study explored the strength characteristics of resin translucent cement mortar, wherein the inclusion of epoxy resins in translucent concrete with plastic optic fibres was attempted in order to reduce strength loss. The addition of resin as a replacement for plastic optic fibres increased strength, while the addition of resin along with optic fibres caused a reduction in the overall strength in compression [26].

Nam et al. embedded light-transmitting units in a high-strength mortar to improve both the load-taking ability and the transmittance of light-transmitting concrete. The research successfully achieved a strength of 80 MPa by incorporating fine sand, cement, fly ash, and blast furnace slag in the mortar with 5, 10, and 15% addition of optical fibres. The orientation and volume fraction of fibres did not affect the strength characteristics, and the addition of pozzolanic materials also enhanced the workability of the mortar. The larger volume fractions performed better in transmittance testing but also had higher absorption coefficients. Even after being subject to elevated temperatures for a considerable duration, the polymeric optical fibres retain transmittance properties [27]. Tahwia et. al. designed high-performance concrete (HPC) and ultra-high-performance light-transmitting concrete (UHPC) by adding 12 mm downsize coarse aggregates and steel fibres to concrete with silica fume and limestone powder. Further, 1 and 2 mm fibres were incorporated in volumetric ratios between 1% and 4% for HPC and 1% for UHPC. Compressive strengths ranging from 37 to 46 MPa for HPC and 147 to 154 MPa for UHPC were achieved. The peak transmittance achieved was 21% at 1.00 p.m. for the 2 mm diameter fibres with 4% volumetric inclusion [28], which reinforces the previous research by Navabi et al. Poly-Methyl that the transmittance is a direct dependent of both area and volume fraction of fibres [29]. A study by Henriques et al. indicated that the addition of optical fibres is detrimental to the strength of concrete in compression and flexure. The loss in strength is attributed to the reduced grip strength and smooth texture of the optical fibres [30]. Palalanisamy et al. determined the strength and transmittance of light-transmitting concrete incorporating optical fibres in three different volume fractions in an M20 grade concrete [31].

Light-transmitting concrete containing optical fibres has been modelled and analysed using various techniques in several studies [13,17,32]. A study by Chiatti et al. used the same technique to determine the energy saving of a photoluminescent building envelope [33]. Su et al. conducted multiple studies on the transmittance and daylighting characteristics of translucent concrete with the help of a ray tracing model developed to determine the efficiency. The parameters of the analysis were the transmittance and losses of the optical fibres as well as the volume fraction and facing area of the fibres in the transmitting surface. The studies found that maximum transmittance happened between 12:00 and 1:00 p.m., due to the angle of incidence and availability of sunlight, which was experimentally determined and validated with modelling analysis [17]. It was further identified that the optimal angle of incidence for transmittance was 10°, as a lower angle of incidence reduced the availability of sunlight in the acceptance cone, whereas higher angles of incidence caused losses due to total internal reflection at the back end of the surface [34]. The dynamic transmittance characteristics of optic fibres in translucent concrete were further studied; these studies aimed to produce panels with inclined fibres in order to reduce the dependence on high numerical aperture optic fibres. Thermal analysis based on heat gain-loss analysis indicated that there might be an increased heat gain during summers and a reduced heat loss during winters, which can result in lower heating energy demand during winters but a higher cooling energy demand during the summer [35]. A study on the combination of windows and translucent concrete panels and its effects on daylighting and energy performance showed that the use of translucent concrete panels reduced glare index but when used in combination with windows, the change in glare index for indoor illumination was negligible. The use of translucent concrete was also found to reduce daylighting and heating loads but increase the cooling load and energy demand [36]. The effect of elevated temperatures on the transmittance, as well as the transmission of heat through light-transmitting concrete, have also been characterised, and the research has concluded that the fibre properties are resilient to heat and transmission of heat through the fibres is insignificant except for in extreme cases [37].

The current state of research in light-transmitting concrete is limited to a handful of materials such as glass fragments, optical fibres, and phase change materials. While the panels that incorporate glass are purely aesthetic and lack load-taking abilities, the arrangement and orientation of waste glass particles also pose a challenge. Phase change materials and chemicals have been used for thermal more than illumination demand and are both uneconomical and complicated in construction. The most feasible method to produce light-transmitting concrete available is the incorporation of optical fibres, be it with glass or PMMA cores. The optical fibres are highly efficient in transmittance but are expensive, and producing such concrete is labour-intensive.

The present study aims to find a novel and alternate transmission medium, namely, PMMA or acrylic rods as they are colloquially known. These rods are available at a fraction of the cost of optical fibres in various cross-sections and diameters. While the material in itself is less efficient than optical fibres in transmittance, the difference in cost, ease of incorporation, and the sheer area of these large dimension bars can make it a feasible alternative that can bring the light-transmitting concrete technology more accessible to a large segment of the population. This study is a step taken to determine the optical and mechanical properties of concrete, including these rods, and to determine the financial feasibility through detailed modelling and simulation studies.

2. Materials, Mix Design, and Casting Process

2.1. Materials

Materials were procured from locally available sources and then rigorously tested to determine the compatibility and suitability for the experimental investigation.

2.1.1. Cement

Ordinary Portland Cement (OPC) of 43 grade was procured, conforming to IS 8112:2013 [38]. The compressive strength of the cement was a minimum of 43 MPa after 28 days of curing. The specific gravity of cement was 3.15, and the chemical and mechanical properties of OPC were evaluated and compared with the relevant code for conformity.

2.1.2. Fly Ash

Fly ash is the mineral admixture used in the current study. Fly ash is an industrial byproduct of the coal-burning process. It has large proportions of calcium oxides, silica, and alumina, which are highly reactive due to their fineness, which makes it a pozzolanic material. The use of fly ash increases the proportion of fines, increases workability and strength, and uses a material that would otherwise be a pollutant in the soil. This solution resolves solid waste management issues and improves the workability and strength properties of concrete, which is why it was chosen in the current study. Class F fly ash was preferred in the study as the primary functionality of the mineral admixture was to enhance the rheological properties of the concrete. The properties of fly ash were tested to determine whether it conforms to class F, and the same are detailed in

Table 1. Properties of Fly ash.

Properties	Unit	Results of Tests on Fly Ash	Codal Provisions and Limits
			IS 3812:2003 Part 1 [39]	ASTM C 618, Class F [40]	BSEN 450 [41]
Fineness (Retention on 45 micron sieve)	%	17.05	34 max	34 max	40 max
LOI	%	1.67	5 max	6 max	7 max
Moisture	%	0.25	2 max	3 max	NA
Fineness-specific surface by Blaine’s Permeability method	m2/kg	377.2	320 min	NA	NA
Lime reactivity	N/mm2	5.1	4.5 min	NA	NA
Autoclave Expansion	%	0.04	0.8 max	0.8 max	0.8 max
SiO2 + Al2O3 + Fe2O3	%	88.88	70 min	70 min	70 min
Silica as SiO2	%	58.61	35 min	NA	NA
MgO	%	1.8	5 max	NA	NA
Sulphate as SO3	%	0.16	3 max	4	3
Chloride as Cl	%	0.016	0.05 max	NA	0.1 max
Na2O	%	0.16	1.5 max	NA	NA

.

2.1.3. Coarse Aggregates

Coarse aggregates were procured from a local supplier. They were mined from a granitic source, and the maximum size of aggregates was 12.5 mm. The gradation distribution and mechanical properties of the aggregates are indicated in

Table 2. Gradation of aggregates.

Coarse Aggregates				Fine Aggregates
Sieve Size	Cumulative % Passing	IS 383 Upper Limit [42]	IS 383 Lower Limit [42]	Sieve Size	Cumulative % Passing	IS 383 Upper Limit [42]	IS 383 Lower Limit [42]
40.000	100.000			10.000	100	100	100
20.000	100.000	100.000	100.000	4.750	99.9004	100	95
12.500	100.000	100.000	90.000	2.360	99.6504	100	85
10.000	97.500	85.000	40.000	1.180	96.5104	100	75
4.750	9.000	10.000	0.001	0.500	67.6904	79	60
2.360	0.500	0.500	0.001	0.300	22.8904	40	12
0.000	0.000			0.150	2.7804	10	0.001

and

Table 3. Mechanical properties of aggregates.

Parameter	Coarse Aggregate	Fine Aggregate
Specific Gravity	2.73	2.17
Moisture Content (%)	0.4	1.0
Water Absorption (%)	0.79	1.19

.

2.1.4. Fine Aggregates

Locally available river sand was the fine aggregate used in the current study. The properties of the sand were tested to ensure the gradation and conformity characteristics, whose results are indicated in Table 2 and Table 3.

2.1.5. Water

Potable water was used for mixing in the current study.

2.1.6. Superplasticiser

Superplasticisers are chemical admixtures that improve the workability and strength of concrete. They are a combination of a plasticizer and a high-range water reducer, which increases the efficiency of mixing water. This results in requiring less water to achieve high workability. Self-compacting concrete (SCC) requires high workability. Additionally, increased fines and mixing water results in drying shrinkage. The use of superplasticisers reduces the shrinkage and enhances workability, hence suitable for the present study.

2.1.7. PMMA Rods

PMMA rods of 5 and 10 mm diameter and circular profiles were used in the study. These polymeric acrylic rods were incorporated in two different variants each, and a total of 4 variants were cast (

Table 4. Mix designations for variants with PMMA rods.

Mix Designation	Specimen Details	Rod Diameter	Number of Rods	The Total c/s Area of Rods in One Face	% Area of Rods to Area of Cube Face
P11	Cube100 × 100 × 100 mm	5	16	314.15	3.14
P12		5	9	176.71	1.77
P21		10	9	706.86	7.07
P22		10	5	392.70	3.93

).

2.2. Mix Design

The SCC was designed for M30 grade, with a characteristic compressive strength of 30 MPa, as it is one of the most commonly used grades of concrete in structures. The design was conducted with reference to EFNARC 2005 [43] and IS 10262:2019 [44]. The guidelines provided were considered to fix the first mix, after which a trial-and-error process was employed to determine the final mix proportions, as shown in

Table 5. Mix proportions of SCC in kg/m³.

Ordinary Portland Cement	Fly Ash	Coarse Aggregates	Fine Aggregates	Superplasticiser	Water
420	180	780	700	2.514	180

.

2.3. Casting Process

Light-transmitting concrete with optical fibres has been cast using different techniques. Some studies have implemented a layering method where alternate thin layers of concrete and optic fibres were laid repeatedly until the desired size was achieved [45,46]. This method is labour-intensive to execute or requires highly precise equipment. Additionally, the use of coarse aggregates causes the fibres to bend, and the ends are lost in the concrete, causing reduced availability of fibres for transmission. The other most common procedure followed is weaving fibres into a fabric, which is then incorporated into the mould, after which concrete is poured [23,24]. The weaving of these fibres can be conducted physically, and the distribution of the fibres is disturbed during pouring and finishing processes. The third method involves weaving and restricting fibres individually and pouring the concrete mix subsequently [31,47,48]. The second and third methods require specialised moulds to hold and distribute the fibres while incorporating concrete. Compaction is also a challenge; the concrete should contain aggregates whose sizes depend upon the interwoven fibres’ spacing. Weaving is also a tedious process, which tends to make the whole process expensive and time-consuming.

The use of rods brings in the element of stiffness of the material, which makes the process much easier. The rigidity of the rods helps hold shape during placement. The rods do not bend under the weight of the wet concrete or with vibration. This helps maintain the uniform distribution of rods across the cross-section of the sample. These traits make it easier to manufacture LTC with PMMA rods.

The major challenge during casting is that the PMMA rods tend to uplift through the wet matrix. Concrete is denser than rods and as the rods are freely placed, they tend to move to the top of the formwork. During this study, this was restricted by applying weight to hold the rods in place during setting and hardening of concrete. The weights were removed along with the formwork.

3. Experimental Program

The experimental program consisted of three major stages. The properties of concrete in fresh and hardened stages were evaluated. The optical characteristics under thermal radiations, artificial luminance, and natural solar conditions were carried out. Finally, these results were validated with statistical tools and simulation studies, and the impact of this material on cost and energy was estimated.

3.1. Fresh Properties

The design of SCC has a special focus on fresh properties, mainly divided into flowability, passing ability, filling ability, and segregation resistance. EFNARC 2005 [43] specifies specific tests to ascertain each of these properties, and based on this, L-Box, V-Funnel, Slump Flow, T5, and T500 tests were carried out for the concrete mix. These tests were carried out per the procedure given in EFNARC 2005 [43] and IS 10262:2019 [44].

3.2. Strength Properties

The strength of concrete is essential to understand the applicability of the material in various structural and non-structural applications. 100 × 100 × 100 mm cube samples were cast and tested for compressive strength. Three specimens were tested for 7, 14, and 28 days. The stiffness of the rods could impact the strength of concrete, and hence the material has the possibility of being anisotropic. This possibility was further explored by testing each sample in directions where the compressive load was applied along and across the rods. Additionally, each variant’s flexural strength was evaluated on prismatic samples of 100 × 100 × 600 mm sizes for 28 days of curing.

3.3. Microstructural Imaging

The relatively large size of the PMMA rods impacted the possibility of Scanning Electron Microscopic (SEM) analysis of the samples. The 5 mm and 10 mm rod sizes were too large, making the extraction of an undisturbed sample challenging and further hindered the procedure for testing under SEM as the maximum sample sizes used in SEM usually range only up to 5 mm. Instead, the samples were tested with an optical microscope under 40.00× magnification. This is indicative of the behaviour of the interfacial zones and brings clarity to the behaviour of the material.

ImageJ Image Processing

ImageJ ver. 1.51 is an open-source image processing software used to determine various parameters of images based on analysis. The program allows users to identify, scale, measure, and annotate images while also helping in using colour grading techniques to identify borders, particles, and distribution of these in the figure. The current study used the program to identify bond characteristics between concrete and PMMA rods to study the bond patterns. Bond efficiency was measured as a ratio of the bonded length to the overall length of the interface.

3.4. Thermal Characteristics

Thermal characteristics were measured using a lightbox arrangement with an infrared lamp. Readings were taken on the exposed and internal surfaces of the cubes, and the temperature difference was expressed as a coefficient. The experiment was repeated for various distances and exposure durations to characterise the material’s thermal transmission. The lightbox arrangement is indicated in Figure 1a.

3.5. Behaviour in Artificial Illumination

The lightbox was again used to determine transmittance characteristics in artificial illumination, with the infrared lamp being replaced by an electric LED lamp. The variations were based on distance, and each specimen was analysed to characterise the behaviour.

3.6. Behaviour in Natural Sunlight

The behaviour in natural sunlight is essential to estimate the behaviour of this material in natural conditions for practical applications. Sunlight is dynamic, with a variation in intensity, angle of incidence, and position, with additional effects from climate, cloud cover, surrounding structures, etc. The determination of this transmittance is not absolute and subject to several conditional variables. The testing was conducted using a vertical mounting apparatus, as shown in Figure 1b. The specimen was placed on the top aperture, which was 90 × 90 mm in size, and the sensor of the lux meter was placed inside the lightbox, which was subsequently closed to eliminate the entry of ambient light into the test setup. Two readings were taken at the top and bottom of the lightbox and then averaged to determine transmittance. This procedure was conducted for all four mixes. Considering the average working hours to be 9:00–17:00 h, and the availability of sunlight during the time of the day, to assess the effect of the time of the day, seasonal variations, and an annual average, hourly readings were taken between 09:30 and 16:30 every five days for a calendar year.

3.7. Modelling and Simulation

Simulation modelling is essential in a research investigation aimed to obtain information without altering the actual system, attain a clearer perspective on the performance and operation of the system, and improve the system by developing operating policies and testing new concepts or systems before they can be implemented practically [49].

3.7.1. Integrated Environmental Solutions—Virtual Environment

Integrated Environmental Solutions—Virtual Environment (IESVE) version 2023.3.0.0 is a modelling and simulation software that estimates heat and light transmittance for a given plan of given materials. The various light-transmitting concrete specimens were analysed and modelled into the program, after which a real-time analysis was conducted on an academic block at Manipal Institute of Technology, Manipal, as shown in Figure 2. The subsequent energy characteristics were then obtained through simulation analysis for various sun incidence angles and intensities that occurred through the year at the floor level of the rooms and modelled with the Mangalore International Airport weather data, which were programmed as the control variables, as shown in Figure 3.

3.7.2. Nine-Point Method of Transmittance

It was essential to determine the coefficient of transmittance of various specimens to model them in IESVE. The determination of the coefficient of transmittance of a material is usually conducted through spectroscopy. While spectroscopy is accurate for single-wavelength sources, the method is very inaccurate when measuring light from scattered sources and transmission. To consider all the light available after transmission, the materials were tested for average transmittance using the nine-point method, as specified by the Bureau of Energy Efficiency guidelines and previous lux measurements in other research [50,51]. The area of each specimen was divided into nine squares, and an illuminance reading was taken at the centre of each of these divisions using an 18 W LED lamp as the light source. Transmittance was then determined for each point, and the overall average transmission considering the edges, corners, and centre was determined. The experiment was then repeated with a 12 W LED, 100 W incandescent lamp, and 200 W incandescent lamp for validation. The overall average transmittance thus obtained has been considered the baseline for modelling and simulation.

3.8. Estimation and Costing

The estimation and costing for three cases were considered. Three standalone rooms, a staff room, a classroom, and a laboratory space on the third floor of the Manipal Institute of Technology were considered for this study. The location and dimensions of the room are shown in Figure 2. A comparative costing analysis of the structures was conducted considering construction using two techniques, the present masonry structural design and a design that implements light-transmitting concrete at the external walls. The design of the foundation or the bottom stories has yet to be considered since the weight of the concrete block masonry and light-transmitting concrete masonry is comparable, and the replacement would not affect this construction in any appreciable way.

3.9. Projection and Forecasting

The operational cost of the structure has to be determined in order to ascertain the overall feasibility of the use of the material. The initial approach was to accumulate the historical prices of electricity, which was achieved from resources provided by official government records. The data were then forecasted using a univariate equation, and a linear and polynomial trend was obtained. The nature of univariate forecasting caused these trends to underestimate or overestimate the degree of cost escalation, as linear variation did not fit the data suitably, and the polynomial trend tended to infinity, which is an unrealistic projection. In order to find a more accurate forecasting model, machine learning was used, and factors like the cost of coal, inflation, GDP, import of electricity, export of electricity, and the distribution of generation over various sources were considered.

3.10. Carbon Emission Characteristics

Carbon emission calculations were conducted for the location of the Manipal Institute of Technology campus of the case study for all the cases considered. The distances were calculated based on the source of material available, and production emissions were taken from various available resources, as indicated in

Table 6. Parameters considered for calculation of carbon emissions.

Name.	Material Production Emissions			Material Transportation Emissions				Total Emissions
	Quantity (kg)	Unit	Reference	Distance from Source	Capacity of Vehicle (kg)	Quantity (kg)	Unit	Quantity (kg)	Unit
Cement	0.82	per kg	[52]	55	10,000	0.003256	per kg	0.823256	per kg
Fly Ash	0.027	per kg	[52]	640	10,000	0.037888	per kg	0.064888	per kg
Sand	0.0139	per kg	[52]	59	7000	0.00499	per kg	0.01889	per kg
Coarse Aggregates	0.0408	per kg	[52]	59	7000	0.00499	per kg	0.04579	per kg
Cement blocks	2.90	per block	[53]	37	250	0.087616	per block	2.247616	per block
Paint	0.659	per litre	[54]	65	7000	0.005497	per litre	0.664497	per litre
PMMA rods	0.438	per kg	[55]	1100	20,000	0.03256	per kg	0.47056	per kg
Electricity	0.919	per kW	[56]					0.919	per kW

. Construction and operational emissions were calculated based on an assumption of a design life of 50 years as a basic consideration criterion taken for the design of educational institutions. Emission for the production of electricity was considered constant, as there was no data availability and limitations in the forecasting abilities, as technological advancements and institutional policies were the major governing criteria, which were unpredictable.

4. Results

4.1. Fresh Properties

The fresh properties of the obtained mixes are plotted in Figure 4, along with the limits and classifications specified in EFNARC 2005 [43]. According to this, the fresh concrete conforms to viscosity VS2/VF2 (>2 s T₅₀₀, 9–25 s V-funnel time), passing ability class PA2 (≥0.80 with three rebars), and slump flow class SF1 (550–650 mm spread).

According to the provisions, this concrete is most suitable for roof and floor slabs. While the present research uses concrete as a binding medium for PMMA rods, it is essential to note the properties of the concrete used.

The effects of the incorporation of fly ash as a mineral admixture and the superplasticiser, a combination of a viscosity modifying agent and plasticizer, are evident in the mechanistic behaviour of the concrete mix. The additives increase the flowability, passing ability, filling ability, and segregation resistance, as indicated by the slump flow, l-box, and v-funnel tests. Class-F fly ash, with its relatively inert nature, allows for the formation of increased paste volume and causes secondary reactions, hence slowing the setting down. This results in better performance in the T500 test, which is beneficial as it increases the time before setting. Additionally, the use of the viscosity modifying agent in the superplasticiser enhances workability while reducing water demand, which is evident from the slump flow results. The passing ability is further supported by the selection of 10 mm downsize aggregates.

4.2. Compressive Strength

Incorporating PMMA rods into concrete causes a loss in compressive strength. All mixes exhibit a drop in compressive strength at all ages compared to the control mix, and there is an increased loss with an increase in the area of rods, as shown in Figure 5. While there is a drop in the strength at all ages, the 28-day compressive strength of all variants exceeds the design strength of 30 MPa.

An analysis of the influence of the orientation of rods on the compressive strength shows that in all instances, orientation along the loading direction has better strength than loading across the rods. The stiffness of rods seems to influence the load-taking capabilities of the specimens positively.

4.3. Flexural Strength

The incorporation of rods has detrimental effects on the flexural strength of the specimens. All samples undergo heavy strength loss, and none of the mixes achieves the flexural strength of the control mix or even the minimum flexural strength required for structural use. The large area of the rods paired with the smooth surface causes them to pull out with less resistance due to insufficient bonds between them and the concrete matrix (Figure 6).

4.4. Microscopic Photography

Microscopic imaging was carried out to further study the effect of the rods and the interaction between rods and concrete. A few of the resulting images are shown in Figure 7. A close inspection of these figures shows how the interface between the rods and concrete is smooth, and there is no separation between the materials in certain phases. In contrast, a clear distinctive separation is seen in other zones. The surface also shows the distribution of aggregates in the mix.

Seventy such images of various samples were collected for detailed image analysis. The images were visually inspected and then analysed using ImageJ. The images were processed through thresholding and grading before lengths were measured and aggregated. An indicative example of the steps in analysing these samples is given in Figure 8.

Bonding efficiency was calculated as a percentage of the length of bonding, shown in green in Figure 8 to the total length available for bonding. The length of the bonded concrete-rod interface was determined by visual inspection and taken as a cumulative value of the observed specimens and the total available length was also measured by the cumulative length of the sample available for observation in the microscopic images.

In variants P11 and P12, using 5 mm diameter rods, the bond efficiency varied between 42.46% and 89.00%, while in the 10 mm diameter samples P21 and P22, the bond efficiency varied between 31.99% and 84.37%. When cumulated, the average bond efficiency was 62.32% and 59.78% when 5 mm and 10 mm diameter rods were used, respectively. These numbers indicate poor bonding between the rods and the matrix, which explains the loss of flexural strength of all variants.

4.5. Thermal Behaviour

Analysis of thermal transmittance was carried out to determine the transmission of heat by the specimens. The testing was conducted with the help of an infrared lamp for 4 h and at varying distances. The results indicate an increase in temperature differential at the early stages, which reduces over time, as illustrated in Figure 9. This can be attributed to the insulating properties of concrete. The most significant thermal gradient was observed for mix P21, and the correlation between the addition of rods and thermal performance is indicated in the figure.

The thermal transmittance also depends on the exposure duration and the distance from the source. As this distance increases, transmittance reduces. As time passes, there is a drop in transmittance, and for long-term durations, the transmittance is constant. The use of PMMA rods does not seem to have a very high impact on the internal heating of the room, though, even at exposure temperatures as high as 65.78 °C, the internal temperature of the concrete was around 29.1 °C on average. Interestingly, the maximum temperature at the inner surface was 29.42 °C, recorded for the mix P21 at 4 h of exposure, and the minimum internal temperature was 19.67 °C, observed at 5 min of exposure for the variant P12.

To understand the interplay of the factors under consideration, surface fitting was carried out. The R-square values for fitted surfaces ranged from 0.76 to 0.89. The fitted planes are shown in Figure 9. The statistical analysis validates that the duration of exposure and distance from the source impact the thermal transmittance. This indicates that prolonged exposure to a source of heat will increase the heat within the concrete but the transmittance will stabilize after a specific duration, in the case of the experiment, 2 h, after which, the increase in temperature will be negligible under constant temperature.

4.6. Testing under Artificial Light

Samples were tested for transmittance with a focus on three parameters, viz, distance from the source, area of transmitting surface, and diameter of the rods. Figure 10 represents the behaviour of transmittance with a change in distance. The transmittance is inversely dependent on distance, and there is a reduction in transmittance as the distance from the source increases. Additionally, the change is reasonably linear, from the characteristic of linear fitting, which exhibits R² values between 0.95 and 0.97 for all mixes.

Figure 11 illustrates the variation of transmittance as a factor of rod area. It can be seen how there is a definite impact of the area on transmittance and how these are directly correlated. Furthermore, it can be observed how this variation is vast at smaller distances from the source, whereas they reduce when studied for larger distances. This is attributed to the type of luminary used for the study and the least count of the lux meter. In the present experimental setup and conditions, while we can arrive at an understanding that there is an effect of the distance from the source as well as the area of rods, it is not possible to say that there is no effect of the type or size of rods beyond 0.9 m, which is the limitation of the present setup.

4.7. Testing in Natural Light

The results of illumination studies in natural light have been determined for a year and further analysed based on seasonal, annual, and daily variations. Peak transmittance was found around noon, observed at 12:30 or 13:30 h, as illustrated in Figure 12. The transmittance peaked at the hours when the sun was at the zenith, apart from isolated cases during the monsoon wherein the cloud cover impacted the luminance values. The average annual transmittance shows that the overall peaking of luminance happens at midday. An analysis of the variations indicates that there is an increase in transmittance as the diameter and the number of rods increase. As seen in the tests pertaining to artificial light, the variants had similar behaviour in natural light. P21 had the best transmittance behaviour for both natural and artificial light, as can be observed by comparing Figure 10 and Figure 12. The least transmittance was observed for variant P12. This is attributed to the percentage of transmission media available for transmittance, as variant P12 has a higher percentage of fibres per area of concrete, as seen in Figure 11. This trend can be seen in all the variations, be it daily, monthly, seasonal, or annual average transmittance, which are evident in Figure 12, Figure 13 and Figure 14.

Seasonal trends indicate maximum transmittance in summer and reduced transmittance in monsoons, which are attributed to the cloud cover and inclement weather that reduces direct and indirect sunlight incidents on the samples. This trend is clearly seen in Figure 13, which shows monthly and seasonal variations. The seasons have been selected based on the stipulations of the Indian Meteorological Department for the coastal regions of Karnataka, wherein the measurements were undertaken. A study on monthly variations also indicates that while the monsoons affect the luminance highly, there is also a reduction in post-monsoon and winter, owing to the shorter length of day and a lower azimuthal angle than summer.

Annual variations have been essential to understanding the changes that occur throughout the year and also have been instrumental in forming the basis of costing and estimation. The detailed study of annual variation indicates the variable trend of available luminance and the performance of various variants throughout the year. It can be seen that during monsoon, when the level of luminance is lower, the difference in transmittance amongst different mixes also reduces. In contrast, the difference is more evident during the brighter seasons of summer and winter, which is in agreement with studies involving optic fibres [57]. Figure 14a indicates the annual variation of mix P12 and the variation of data points available throughout the day. Figure 14b compares the variation of yearly average luminance based on the mixes. There is a definite improvement in transmittance when the area of rods increases, thus validating the results obtained during testing with artificial luminaries. The distance between the source and surface has a reduced effect on transmittance compared to artificial luminaries, as the amount of possible variation in distance is negligible when considering the distance between the sun and the surface of the specimen.

4.8. Coefficient of Transmission

The coefficient of transmission was quantified through the nine-point method using an LED lamp. The values of the same are given in

Table 7. Coefficient of transmittance by the 9-point method.

Ref. Point	P11		P12		P21		P22
	IC Lamp	LED	IC Lamp	LED	IC Lamp	LED	IC Lamp	LED
1	0.130	0.175	0.058	0.066	0.155	0.212	0.137	0.189
2	0.209	0.264	0.093	0.077	0.333	0.331	0.220	0.264
3	0.121	0.180	0.057	0.071	0.184	0.209	0.164	0.183
4	0.186	0.268	0.091	0.075	0.345	0.326	0.228	0.262
5	0.383	0.261	0.100	0.119	0.546	0.362	0.417	0.283
6	0.193	0.271	0.090	0.086	0.317	0.330	0.215	0.267
7	0.118	0.187	0.059	0.071	0.219	0.203	0.181	0.174
8	0.211	0.277	0.092	0.068	0.299	0.336	0.255	0.260
9	0.130	0.187	0.066	0.063	0.202	0.201	0.176	0.173
Average	0.187	0.230	0.078	0.077	0.289	0.279	0.221	0.228
Coefficient of Transmittance	0.209		0.078		0.284		0.225

, and the reference points are shown in Figure 15. The variants have a very low coefficient of transmission as compared to traditional transmission media like glass. This is because the PMMA rods have low efficiency and cover a small percentage of the cross-sectional area. It can be seen that the coefficient of transmission depends on the area of rods present. The coefficient of transmission was further validated by using an incandescent lamp (IC lamp) and determining the coefficient independently. The average of the two is presented and taken for analysis.

4.9. Modelling Analysis

Modelling analysis of three different rooms in an academic setting was undertaken for the study, as detailed in the plan. The exposed side of these structures was modelled as light-transmitting concrete variants based on the coefficient of transmissions obtained to understand light distribution throughout the room and ascertain the material’s effectiveness, as shown in Figure 16. The illumination distribution of the various rooms for all the variants is shown. These are characteristics based on the annual average considering the solar positions and weather data available for the nearest meteorological landmark, Mangalore International Airport. It can be seen how the intensity of transmitted illumination is highest at the walls and gradually dissipates as we move away from it. It can also be observed that the maximum required range of lighting for these rooms is 300 lux as per IS 3646-1 (1992) [58]. Every part of the room is illuminated beyond this range; hence, the structure effectively implements the same. The thus obtained annual average was considered the basis for estimating energy characteristics.

Of the variants, P21 exhibits the best transmittance behaviour as the larger diameter and area of PMMA rods result in better transmission and more effective distribution. P12, on the other hand, contains the lowest area and has the lowest coefficient of transmission and hence fails in both the staff room and the laboratory to provide the required illumination levels. It must be noted that the results represented are the average annual transmittance and not daily transmittance characteristics, which vary based on solar angle, time of day, and weather conditions. To assess this further, the dimmer function in IESVE was used to determine the total energy consumption and savings throughout the year for illumination purposes. The results of those analyses are shown below.

4.10. Costing Analysis

The detailed costing report, along with the assumptions and considerations for a classroom for normal construction and a P11 variant are shown in

Table 8. (a) Costing report for the classroom for normal concrete. (b) Costing report for the classroom for light-transmitting concrete variant P11.

(a)
Sl. No.	Particulars	Quantity	Unit	Rate	Area Weightage @ 10%	Amount
1	KSRB 5-14.1: Providing and constructing load bearing wall with solid concrete blocks having block density not less than 1800 kg/m3 having a minimum average compressive strength of 5.00 N/mm2 confirming to IS 2185 (Part 1) 2005 [59] and constructed with CM 1 A, as per IS 2572: 2005 [60] including cost of all materials labour charges, scaffolding, curing, hire charges of machineries, etc., complete as per specifications. KBS No. 5.4 Size: 400 mm × 150 mm × 200 mm	93.16	Sqm	₹ 953.00	₹ 1048.30	₹ 97,657.04
2	KSRB 15.3: Providing 12 mm thick cement plaster in single coat with cement mortar to brick masonry including rounding off corners wherever required smooth rendering, Providing and removing scaffolding, including cost of materials, labour, curing complete as per specifications. CM 1:4	96.49	Sqm	₹ 205.00	₹ 225.50	₹ 21,757.55
3	KSRB15-3: Providing 20 mm thick cement plaster in single coat with cement mortar to stone masonry and concrete surface including rounding off corners wherever required smooth rendering, including providing and removing scaffolding, cost of materials, labour, curing, etc., complete as per specification. KSRB 15-3.11-do-cement mortar 1:4 (Pg. No. 116, Item No. 15.19, SR 2018-19)	100.95	Sqm	₹ 273.00	₹ 300.30	₹ 30,314.32
4	Providing and applying two coats of wall putty to inside plastered walls and ceiling using white cement putty. Scrapping and levelling the surface using steel blade and preparing the surface even and smooth by using different grade sandpapers, including cost of all materials, cost of labour and scaffolding, etc., complete as per the specification.	96.49	Sqm	₹ 78.00	₹ 85.80	₹ 8278.48
5	KSRB 15-14.1 Providing and applying two coats with oil bound washable distemper of approved brand and shade on wall surface including priming coat with distemper primer after thoroughly brooming the surface free from mortar drops and other foreign matter including preparing the surface to be even and sandpaper smooth, cost of materials, labour, complete as per specifications.do-(Page No. 119 Item No. 15.49.1 SR 2018-19)	96.49	Sqm	₹ 110.00	₹ 121.00	₹ 11,674.79
6	KSRB 15-16.1 Providing and finishing external walls in two coats with waterproof cement paint of approved brand and shade to give an even shade after thoroughly brooming the surface to remove all dirt and loose powdered material, free from mortar drops and other foreign matter cost of materials, labour, complete as per specifications. With Primer Coat (Pg. No. 120, Item No. 15.53.2, SR 2018-19)	100.95	Sqm	₹ 102.00	₹ 112.20	₹ 11,326.23
Total:						₹ 181,008.41
GST @ 18%						₹ 32,581.51
Total:						₹ 213,590.00
Approximation:						₹ 214,000.00
(b)
Sl. No.	Particulars	Quantity	Unit	Rate	Area Weightage @ 10%	Amount
1	KSRB 5-14.1: Providing and constructing load bearing wall with solid concrete blocks having block density not less than 1800 kg/m3 having a minimum average compressive strength of 5.00 N/mm2 confirming to IS 2185 (Part 1) 2005 and constructed with CM 1 A, as per IS 2572: 2005 including cost of all materials labour charges, scaffolding, curing, hire charges of machineries, etc., complete as per specifications. KBS No. 5.4 Size: 400 mm × 150 mm × 200 mm	47.96	Sqm	₹ 953.00	₹ 1048.30	₹ 50,271.64
2	KSRB 5-14.1: Providing and constructing load bearing wall with light-transmitting concrete blocks having block density not less than 1800 kg/m3 having a minimum average compressive strength of 5.00 N/mm2 confirming to IS 2185 (Part 1) 2005 and constructed with CM 1 A, as per IS 2572: 2005 including cost of all materials labour charges, scaffolding, curing, hire charges of machineries, etc., complete as per specifications. KBS No. 5.4 Size: 400 mm × 150 mm × 200 mm	45.20	Sqm	₹ 9724.00	₹ 0.00	₹ 439,545.59
3	KSRB 15.3: Providing 12 mm thick cement plaster in single coat with cement mortar to brick masonry including rounding off corners wherever smooth rendering was required. Providing and removing scaffolding, including cost of materials, labour, curing complete as per specifications. CM 1:4	48.93	Sqm	₹ 205.00	₹ 225.50	₹ 11,033.99
4	KSRB15-3: Providing 20 mm thick cement plaster in single coat with cement mortar to stone masonry and concrete surface, including rounding off corners wherever smooth rendering was required, including providing and removing scaffolding, cost of materials, labour, curing, etc., complete as per specification. KSRB 15-3.11-do-cement mortar 1:4 (Pg. No. 116, Item No. 15.19, SR 2018-19)	51.16	Sqm	₹ 273.00	₹ 300.30	₹ 15,363.86
5	Providing applying two coats of wall putty to inside plastered walls and ceiling using white cement putty. Scrapping and levelling the surface using steel blade and preparing the surface to be even and smooth by using different grade sandpapers, including cost of all materials, cost of labour and scaffolding, etc., complete as per the specification.	48.93	Sqm	₹ 78.00	₹ 85.80	₹ 4198.30
6	KSRB 15-14.1 Providing and applying two coats with oil bound washable distemper of approved brand and shade on wall surface including priming coat with distemper primer after thoroughly brooming the surface free from mortar drops and other foreign matter including preparing the surface to be even and sandpaper smooth, cost of materials, labour, complete as per specifications.do-(Page No. 119 Item No. 15.49.1 SR 2018-19)	48.93	Sqm	₹ 110.00	₹ 121.00	₹ 5920.68
7	KSRB 15-16.1 Providing and finishing external walls in two coats with waterproof cement paint of approved brand and shade to give an even shade after thoroughly brooming the surface to remove all dirt and loose powdered material, free from mortar drops and other foreign matter cost of materials, labour, complete as per specifications. With Primer Coat (Pg. No. 120, Item No. 15.53.2, SR 2018-19)	51.16	Sqm	₹ 102.00	₹ 112.20	₹ 5740.34
Total:						₹ 532,074.40
GST @ 18%						₹ 95,773.39
Total:						₹ 627,848.00
Approximation:						₹ 628,000.00
Difference in Cost:						₹ 414,000.00

below. The estimation has been conducted on the basis of the scheduled rates provided by the Government of Karnataka State. Similar analyses were conducted for the P12, P21, and P22 variants of the classroom as well as all four variants for the laboratory and the staff room, the results of which are represented in Figure 17.

The cost of construction is estimated to increase between 91.11 and 217.53% based on the variations in diameter and the number of bars placed per area of the wall. The cost of the rods is the main factor that increases the price of this technique, while there is a saving when it comes to plastering and painting which are not possible while using this concrete.

While the initial cost is high, the advantages of the material come in the way of reduced electricity consumption.

4.11. Energy Characteristics

The energy characteristics were estimated based on the average illumination values and the predicted cost of electricity. The cost of electricity was collected for the last 25 years, and a forecasting model was implemented to determine the cost for the next 50 years, which is the service life of such commercial structures. The savings in cost were achieved by converting the lux into wattage of an equivalent LED lamp, which was then converted to kWh for 8 h of use. This was then cumulated to determine the energy saving over the structure’s service life. The staff room estimation shows that the additional construction cost for variant P1 is returned in approximately 7.5 years. This varied between 6–9 years for the staff room, classroom, and laboratory, indicating that the average return of investment could be expected in a duration of 9 years, based on the configuration of rods used, and that all variants provide sufficient illumination and eliminate the need for artificial illumination in the structure. Over the design life, the total cost saving varies between 10.63 and 11.45 times the initial investment, making this technology economically and environmentally feasible (Figure 18, Figure 19 and Figure 20).

4.12. Predictive Modelling

The estimation of future electricity demand in terms of cost/kWh is based on seven data points that were gathered from 1971 to 2023 in India [61]. These include the different methods of electricity generation, like thermal power plants, hydroelectric power plants, nuclear power plants, and the power generated from renewable energy sources. Three other factors that impact the cost of electricity, which are the quantity of electricity imports, the quantity of coal imports, and the price index of coal on the global market, have also been considered as primary factors that influence the price of the generation of power.

Additionally, the nature of the consumer has been considered as a factor of secondary impact, which has been broadly classified into six categories as per the data availability. These are consumption by the agricultural sector, industries, domestic/residential sector, commercial sector, transportation sector (specifically railroads), and other/miscellaneous consumption.

The nature of the relationship of these factors was first determined. Figure 21 illustrates the linear relationship that was observed for every variable with the forecasted price of electricity. The associations were considered to strongly impact the price as the R² values for these variables ranged between 0.90 and 0.99. Based on this, a linear regression model was adopted to predict the cost of electricity, which resulted in Equation (1). Hence, forecasting these factors for the target year, Equation (1) can be implemented to predict the cost of electricity for a specific year.

Predicted cost of electricity (/kWh) = 130280.65 − 5.97 (1*) + 1.24324050 (2*) + 1.55583102 (3*) − 2.08934811 (4*) − 1.08502428 (5*) − 7.60566389 (6*) + 2.84420914 (7*) + 5.37428507 × 10⁻¹ (8*) − 2.14152102 (9*) + 2.58644851 (10*) + 5.72888213 × 10⁻² (11*) + 2.56232383 (12*) − 2.66463457 (13*)

(1)

where 1* is electricity generated by thermal plants in GWh, 2* is electricity generated by hydroelectric plants in GWh, 3* is electricity generated by nuclear power plants in GWh, 4* is electricity generated by renewable sources in GWh, 5* is quantity of electricity imports in GWh, 6* is quantity of coal imports in MT, 7* is coal wholesale price index (no unit), 8* is consumption of electricity by the agricultural sector in GWh, 9* is consumption of electricity by the industrial sector in GWh, 10* is consumption of electricity by the domestic sector in GWh, 11* is consumption of electricity by the commercial sector in GWh, 12* is consumption of electricity by the railroad sector in GWh, and 13* is consumption of electricity by others in GWh.

Neither the univariate nor the machine learning multivariate model could accurately capture the trend of the variation in the price of electricity due to the complex nature of the predicted variable, nor the availability of historical data. The prices of electricity are largely influenced by policies, geopolitics, and behavioural trends of the population, for instance, in the installation of personal generation systems. It is also influenced by the development and evolution of technology and the efficiency of present and future infrastructure. Accepting these complexities as variables out of control, while it is not possible to accurately predict the cost of electricity, hence the operational cost, it is possible to compare the obtained results and conclude confidently from Figure 18 and Figure 22 that the increase in the cost of construction of the staff room will be returned between 2046 and 2052 for P11, 2038 and 2043 for P12, 2047 and 2054 for P21, and 2039 and 2044 for P22. Similar results for return on investments and overall fiscal benefit can be obtained for the variants when used in the classroom and laboratory (Figure 23 and Figure 24).

4.13. Carbon Emission Calculations

The emission of carbon dioxide in the production and subsequent operation over the design life has been determined for various mixes as well as the three use cases considered. While mixes P11, P21, and P22 eliminated the need for artificial illumination by providing the required threshold of lux levels throughout the year, mix P12 required artificial illumination as the transmittance and lux levels were below specified limits. The design of illumination requirements and subsequent consumption characteristics have been estimated. In order to quantify the same, illumination was designed for the difference between required illumination, as specified in IS 3646-1 (1992), and available illumination, as indicated in Figure 16. As precise design could not be carried out without an extensive study, the present results are catered to the minimum illumination value observed throughout the year. This overestimates the consumption and hence underestimates the reduction in carbon footprint. The reduction in carbon emissions, hence, can be considered as a minimum threshold and operational reduction can be more than these indicated values. The results of these analyses are provided in

Table 9. Construction and operational emission characteristics of various mixes.

Mix	Carbon Emission (kg)	Reduction in Carbon Emissions (%)	Carbon Emission (kg)	Reduction in Carbon Emissions (%)	Carbon Emission (kg)	Reduction in Carbon Emissions (%)
	Staff Room		Laboratory		Classroom
Control	26,934.283		91,730.071		91,690.963
P11	2813.118	89.55	2448.055	97.33	3358.444	96.34
P12	13,526.587	49.77	55,932.438	39.02	32,817.275	64.21
P21	2863.502	89.36	2540.855	97.23	3490.848	96.19
P22	2842.832	89.44	2502.783	97.27	3436.528	96.25

.

5. Conclusions

The extensive study on the development and usage of light-transmitting concrete using PMMA rods has shed light on the possibility of a cost and energy-efficient building material that can impact sustainable construction as a cost-viable system. The non-load-bearing construction material was developed and studied for strength, transmittance, and use cases over the long term, based on which the following conclusions can be drawn.

• The use of PMMA rods as a transmission media in light-transmitting concrete is suitable for non-structural use of concrete.
• The surface roughness has been an important factor in improving the friction and area of contact between fibre and paste, which impacts the behaviour of these fibres in strength tests, as illustrated in steel fibres [62,63]. The smooth surface finish of PMMA rods reduces friction and increases the void concentration, causing a loss in bond strength as seen in the image analysis. This leads to the presence of failure surfaces in the concrete and negatively impacts the strength performance.
• The best orientation of fibres to enhance the tensile properties is if the fibres are placed along the direction of tensile loads, as demonstrated with steel fibres [64,65]. In the case of light-transmitting concrete, the rod orientation is along the cross-section of the beam samples tested for flexure, which does not contribute to improving the strength. Combined with the lack of bonding, the effect of unidirectional orientation is detrimental to the strength properties, as evident from the results.
• The thermal transmission behaviour indicates that the use of PMMA rods does not cause a considerable increase in the ambient temperature as the thermal transmittance is similar to concrete. This is indicative that the cooling or heating loads of the built environment employing light-transmitting concrete will be comparable to that of a structure built conventionally. There is no adverse impact of using light-transmitting concrete on the heating and cooling loads; hence, the material is suitable for use in construction, irrespective of weather conditions.
• A linear trend was observed between the area available for light and transmittance, which was in line with various historical studies using other transmitting materials like optic fibres [27,45,66].
• Annual transmittance characteristics indicated the transmittance being highest in the months of April and May, during summer when the cloud cover was minimal. Conversely, the monsoon months of July and August were the months with the least transmittance. The best performance was seen in P21, with a maximum monthly average transmittance of 721 lux in the month of May between 12.00 and 01.00 p.m., and the least average monthly transmittance observed between 12.00 and 01.00 p.m. for P21 was 427 lux. The percentage reduction in transmittance was 40.77% in this specific instance. Generally, for all variants, the percentage difference between the highest and lowest transmittance for the same time of testing varied between 38.21% and 56.74%.
• The cost of construction for the use of materials increased between 91% and 217% based on the different variations of rods as well as the different room dimensions and configurations. A major increase in the cost was due to the addition of PMMA rods, which was slightly offset by the deduction of plastering and painting costs, as the light-transmitting concrete variants cannot be plastered or painted.
• The IESVE modelling of the variants indicated the transmittance behaviour and provided evidence of the suitability of the use of the different variants throughout the year, considering the weather conditions of Manipal. Variant P12 exhibited lower average luminance levels compared to P11, P21, and P22, with the annual average being below 300 lux for all three applications. This indicates that the use of P12 needs to be supported by artificial illumination for adequate functionality.
• Projected operational cost and cost saving indicate that all variants are feasible in construction. The return of the increased cost varies between 9 and 31 years, based on the variant used.
• The environmental impact and reduction in CO₂ emissions are significant, as observed in this study. With operational emission reductions estimated as high as 97.33% or even as low as 39.02%, there is an immense impact on sustainable construction. The CO₂ emissions were increased in the construction phase for all cases as the use of PMMA has an increased footprint. That being said, it was offset by the reduction in emissions resulting from the omission of plastering and painting. The major difference in emission was in operational emissions, as some of the variants had zero daylighting emissions, and the average illuminations ranged above the minimum stipulated criteria.

PMMA rods are a novel material that has been used as the transmitting media in light-transmitting concrete. The use of PMMA rods as a transmitting media can be a valuable alternative to the existing technology of light-transmitting concrete using optical fibres and other variations. The material has the scope to be an alternative to these existing methods of manufacturing, making this a material that is accessible to a vast majority of the population.

The case study and simulation studies seem to indicate that the material can be an alternative building material that can reduce the environmental impact by harnessing green energy. The increase in initial cost, while being a drawback, is offset by cost savings in operation. The vast improvement in both cost and emissions in operation makes the material a suitable addition to the sustainable construction material arsenal.

That being said, the loss in strength due to the orientation and surface texture of the rods is a matter of concern that needs to be explored and addressed. The possibility of using non-circular profiles or surface coatings to enhance friction can be an avenue for further research. The loss in bonding strength and the presence of voids at the interaction surface can also impact the durability of the material, and this is an avenue for further research in the area.

6. Patents

Figure 1, Section 3.6 and Section 4.7 implement technology filed for a patent as detailed in “Measuring Optical Transmittance of Materials” by Manipal Academy of Higher Education with inventors being Shenoy, A., Nayak, G., Tantri, A. with application number 202341067180, reference number TEMP/E-1/80087/2023-CHE, filed on 6 October 2023 in India.