Analysis of the Life Cycle and Properties of Concrete with the Addition of Waste Car Glass

Abstract

Sustainable construction aims to reduce the negative environmental impact of buildings throughout their life cycle, which includes design, construction, use, demolition and recycling. Taking into account the successive stages of the concrete life cycle and the elements of sustainable construction, the need to carry out research and analysis of the properties of concrete with additives was noticed in aspects of the concrete life cycle, e.g., the production stage, its durability during operation and the possibility of re-use after demolition. It was also noticed that the use of additives in the form of waste materials brings many benefits, including improvement of some parameters of concrete while saving natural resources. The article presents a detailed analysis of all four phases of the assessment of the life cycle of concrete modified with the addition of waste car glass: goal and scope definition, inventory analysis, impact assessment and interpretation. The progressive increase in the amount of glass waste produced each year around the world made it necessary to start the search for new recycling methods. During the research, concrete mixes were prepared according to a new, laboratory-calculated recipe containing glass fibers, natural aggregate (sand with a fraction of 0–2), crushed aggregate (basalt with a fraction of 2–8) and Portland cement (52.5 MPa). Concrete has been designed in four variants, which differ based on n the amount of tempered glass added. The first variant W1 was modified with 66.67 kg/m³, the second variant W2 contained the addition of 111.11 kg/m³ and the third variant W3—155.56 kg/m³. After 28 days, volumetric densities, values of the modulus of elasticity and thermal properties were determined; strength tests were also carried out during which the compressive strength (Reference = 70.30 MPa; W1 = 68.18 MPa; W2 = 70.13 MPa; W3 = 68.60 MPa), tensile strength in bending (Reference = 5.70 MPa; W1 = 5.63 MPa; W2 = 5.70 MPa; W3 = 5.27 MPa) and tensile strength in splitting were determined. On the remains of the samples from the strength tests, microstructure tests were performed. The conclusions and considerations on the further direction of the research were included in the discussion. The novelty of our research is related to the elimination of the glass waste processing process, which was described in detail in the Introduction.

1. Introduction

The processing of insulated automotive glass is a very complex and high-energy process, which nowadays becomes unprofitable due to the costs of electricity and the amount of gas necessary to achieve a temperature above 1000 degrees Celsius; therefore, attempts have been made to use this type of glass in concrete without the need to waste processing. Due to the fact that insulating glass consists of different layers in addition to the glass itself, e.g., adhesives and foils, its processing is difficult and, above all, very harmful to the environment. During the melting of such glass, many poisonous compounds from the combustion of the above-mentioned layers are released into the environment. Companies processing such material must have special gas purification systems, which are both expensive to explore and require very high energy consumption, which contradicts the principles of sustainable energy management adopted by the European Union. An innovative solution introduced by the authors is the direct use of glass cullets made of insulated glass as a substitute for natural aggregate in the concrete structure. This not only results in savings on glass processing but also leaves natural aggregate necessary for the production of concrete in nature. Therefore, innovative options for recycling waste glass must be developed. One significant option is to use waste glass for construction materials. The recycling of waste glass not only decreases the demand for landfill sites in the building sector but also significantly helps in decreasing the carbon footprint and saving resources.

The purpose of the study was to analyze the impact of the structure made of concrete modified with the addition of waste car glass on the environment throughout its life, from the extraction of raw materials to its demolition with subsequent disposal or reuse. According to the above, the research included designing concrete with the addition of waste tempered glass to determine the effect of glass on the properties of fresh concrete mix and hardened concrete and to test the thermal properties of concrete modified in this way. The reason for starting research on the concrete admixture in the form of waste glass was the information obtained regarding the recycling rate of glass waste, which is quite low in many countries compared with other solid wastes [1]. For example, in the United States, 11.38 million metric tons of waste glass were produced in 2017, but 26.6% was recycled and mainly used for the production of containers and packing, and 60.37% was landfilled [2]. In Hong Kong, 4063 and 7174 metric tons of glass waste were generated in 2018 and 2019, respectively, and the recovery rate was about 16.3% in 2018. The total amount of used glass containers that ended up in landfills in 2018 was 77,400 metric tons [3]. In Singapore, 72.8 million metric tons of glass were disposed of in 2011, but only 29% was recycled [1]. In the United Kingdom, 1.85 million metric tons of waste glass are collected annually, and for container glass, the municipal recycling rate is 34% [4].

The amount of recycled glass is small compared to its annual production. Due to the high usage of glass for packaging purposes, the recycling methods currently available on the market are not efficient enough to fully process all the waste generated. Some of the packaging is also not suitable for traditional recycling. Therefore, there is a need to search for alternative recycling methods [5,6,7]. About 50% of all the packaging in the world is single-use [8,9], hence it generates various types of waste that takes hundreds of years to decompose. This leads to serious environmental problems that could result in health issues, animal degradation, or even water pollution [10,11,12]. Materials that cannot be reused in the food industry could alternatively be processed in order to later be incorporated into concrete. This would make the material that accounts for 3% of the world’s total energy consumption more environmentally friendly [13].

Nowadays, concrete additives are derived from recycling or special treatment of waste materials [14,15,16,17,18,19,20,21]. Waste should be recycled at first, but their use in the concrete mix recipe is definitely possible [22,23,24]. For example, ash, old tires, foil or plastic packaging and glass bottles [25,26,27] can be given a second life as components of a concrete facade, foundation, or beam of a building [28,29].

Concrete is a material that allows for the disposal of waste [27,30,31,32,33,34,35,36,37]. The literature proves that the addition of various types of waste improves some physical and mechanical properties of concrete, e.g., improvement in bending performance of reinforced concrete beams produced with waste lathe scraps [38] and improving bond performance of ribbed steel bars embedded in recycled aggregate concrete using steel mesh fabric confinement [39].

Investigation of the physical-mechanical properties and durability of high-strength concrete with recycled PET as a partial replacement for fine aggregates [40] showed that PET-concrete is recommended for non-structural applications (such as pavements and sports stadiums, wall panels and channel liners), with a replacement ratio of no more than 25%.

Different studies have indicated that independent of the form of marble waste (as powder, fine aggregate or coarse aggregate), aggregate replacements of up to 50% can yield significant changes in the concrete compressive strength [41].

After research on the shear performance of reinforced expansive concrete beams utilizing aluminum waste, it was observed that the load capacity of the Al refuse combined RCBs rose as the vacancy of the stirrup reinforcement reductions increased compared with reference RCBs. Furthermore, it was found that the load capacity of the RCBs reduced as the Al refuse quantity in the concrete mixture increased from 0% to 3%. However, it was found that the decrease in load capacity for 1 vol.% aluminum waste could be tolerated. For this reason, it can be stated that aluminum waste (AW) in reinforced concrete shear beams will contribute to the beam up to 1% [42].

There are also studies in the literature in which waste fire clay (WFC) was consumed by replacing fine aggregate (FA) in confident amounts. It has been targeted to remove the current sustainable complications by confirming the consumption of WFC in reinforced concrete beams (RCBs) as raw materials [43].

This is very important in the case of non-biodegradable or hardly decomposable materials such as glass waste [44,45,46]. For example, Federico and Chidiac [47] analyzed the kinetic and performance properties of cementitious mixes with glass powder. Mirzahosseini and Riding [48] investigated the impact of curing temperature and glass type on the pozzolanic reaction and properties of concrete with glass powder.

Many scientists have tested concrete with glass aggregate as a replacement for coarse aggregate, fine aggregate, or cement in order to use waste glass in the concrete industry [49,50,51]. Yu et al. [52] reported that the glass cullet used as aggregate in concrete enhanced its mechanical properties. Limbachiya et al. [53] and Tittarelli et al. [54], however, obtained the same mechanical performances for concrete mixes with the addition of glass sand up to 15%. It was found that the use of glass cullet as a replacement for coarse aggregate is not satisfactory owing to the reduction of bonding between the aggregate and the cement matrix and a reduction in strength [55]. The effect of the size of glass particles on the properties of fresh mix and hardened samples was analyzed by Ling and Poon [56] and Yousefi et al. [57]. However, the impact of fibers on the properties of a cement-glass composite has rarely been reported.

On the other hand, the production of building materials is responsible for significant energy consumption and CO₂ production [13,58,59], thus it is necessary to look for new materials that can replace the currently used ones [60,61], preferably recycled materials.

It should also be recalled that glass fiber-reinforced composite materials were used in several industrial applications due to their excellent mechanical properties, lack of corrosion and low lifetime maintenance costs [62]. Khan et al. [63] showed a positive glass fiber influence on composite parameters.

The mechanical and thermal properties of epoxy laminates with different fibers (carbon and glass) were tested. Both tensile strength and modulus, as well as strain percentage increased with the increase in fiber content. The tensile strength and modulus of epoxy laminates modified with carbon fibers were remarkably higher than those of laminates modified with glass fibers, regardless of their compositions (around four times higher). In comparison to the base samples, an average three-fold increase in these parameters was noted for samples modified with glass fibers (60% modification). Viet et al. [64] investigated a new glass fiber-reinforced polymer for use in bridge structures and buildings. The stiffness of the connections of the new polymer increased by about 90% after the reinforcement with eight layers of glass fiber. A significant improvement in the final load on the connections for all three types of modifications was determined. The final loads increased as the number of glass fiber layers grew. After toughening, the average end loads increased approximately 1.7, 2.2 and 2.6 times for the two, four and eight layers of glass fibers, respectively [31].

Research is also being conducted on the Analysis of the life cycle of waste car glass [65,66,67]. Badino V., et al. [65] state that a critical point of the analysis involving recycled materials is the energy content of the secondary materials; this case study of LCA application in the automotive industry offers a good example to evaluate the importance of this critical point and to give rise to discussion about the energy content of scrap.

The research conducted by Guignone G. [66] evaluated both the technical and environmental performance of structural concrete elements, considering the partial substitution of cement with glass waste powder and a baseline scenario with conventional concrete. The environmental impacts have been evaluated through the life cycle assessment tool. The results have indicated that incorporating waste glass powder in the prestressed hollow-core slabs as a partial cement replacement can improve durability-related properties and mitigate environmental impacts. It also showed that the manufacturing phase is the most impactful and that glass powder can significantly reduce the impact of maintenance.

In the research described in this article, concrete has been designed in four variants, which differ in the amount of glass added. The first variant W1 was modified with 66.67 kg/m³, the second variant W2 contained the addition of 111.11 kg/m³ and the third variant W3—155.56 kg/m³. The last, fourth variant was a reference sample that was not modified in any way and constituted a reference point for evaluating the results. Prior to the preparation of standardized samples, consistency tests were carried out using the cone drop method and air content in the concrete mix using a porosimeter. After 28 days, when the concrete gained full strength, volumetric densities, values of the modulus of elasticity and thermal properties were determined. In addition, strength tests were carried out during which the compressive strength, tensile strength in bending, and tensile strength in splitting were determined. On the remains of the samples from the strength tests, microstructure tests were performed.

The last point of the thesis was the analysis of the impact of the structure made of modified concrete with the addition of waste automotive glass on the environment throughout its lifetime, from the extraction of raw materials to its demolition with subsequent disposal or reuse.

2. Description of the Test Method

The Bukowski method [68] was used to design the concrete mix. It belongs to the computational and experimental methods based on the three equations method. It consists of determining the amount of individual components of the concrete mix, i.e., cement, aggregate and water, using three equations—strength, tightness and water demand.

The base of the concrete mix is:

• Portland cement, CEM I 52.5 R—SR5,
• Natural fine aggregate—sand with fraction 0–2—(K1),
• Coarse natural aggregate—basalt fraction 2–8—(K2),
• tap water,
• fluidizing admixture.

The concrete mix was made in four variants. After mixing all of the other components for 2 min, the waste glass was added to the mortar mix. The whole mixing process lasted five minutes. After that, the samples were formed in molds with dimensions depending on the test and then compacted on a vibrating table. All samples were produced in laboratory conditions (21 °C temperature and 50% humidity) and stored in water according to EN 12390-2:2019-07 [69].

The first variant is the reference, i.e., a mixture unmodified with any additive, which is a comparison point, and there are three variants modified with the addition of crushed tempered glass from car windows of waste origin. Glass was added in the amounts of 66.67 kg/m³, 111.11 kg/m³ and 155.56 kg/m³. These values were determined experimentally, taking into account the appropriate workability and ease of compaction of the mixture.

The cone slump test was performed in accordance with EN 12350-2:2019-07 standards [70]. Additionally, the initial and end setting times were gauged using a Vicat device sourced from Merazet, Poznan, Poland. Every mixture underwent testing for five separate samples. The air content and pH of the mix were evaluated according to EN 12350-7:2019-08 [71] and PN-B-01810:1986 standards [72], respectively, with five samples inspected for each batch. Tests were executed in the order they were mentioned, immediately following the mixing process. The values recorded for each test represent the mean of the five samples taken from every blend.

The density of hardened mortar samples, each measuring 150 × 150 × 150 mm, was ascertained according to EN 12390-7:2019-08 [73]. Moreover, a Zwick machine capable of applying a force from 0 to 5000 kN, sourced from Zwick, Ulm, Germany, was used to ascertain the mechanical characteristics of the hardened mortar samples, specifically compressive and flexural strengths.

Compressive strength was gauged as per EN 12390-3:2019-07 [74] on 100 × 100 × 100 mm samples. Flexural strength was examined through a three-point bending approach on samples measuring 40 × 40 × 160 mm (beams) in accordance with EN 12390-5:2019-08 [75]. The supports were placed at a standard distance of 100 mm apart, permitting horizontal motion by the rollers.

The split tensile strength was examined on cylindrical samples (0.15 m in diameter and 0.30 m in height) following EN 12390-6:2011 specifications [76]. The modulus of elasticity and Poisson’s ratio were assessed on cylindrical samples with a diameter of 150 mm and a height of 300 mm, as per EN 12390-13:2014-02 [77].

Two resistance strain gauges, each 100 mm long, were attached to the midpoint on two opposite sides of the samples to assess the modulus of elasticity based on the stress-strain relationship. Prior to testing, surfaces exposed directly to compressive stress were polished to confirm the parallelism of the specimens. Longitudinal and transverse linear displacements were measured using Epsilon extensometers, sourced from Epsilon, Jackson, WY, USA.

The samples underwent three load cycles, with the load removed in the lower and upper stress ranges (in accordance with the characteristic compressive strength).

The research incorporated the examination of thermal conductivity, thermal diffusivity and specific heat. All measurements were carried out based on the material’s temperature response to the impulses of heat flow using an ISOMET2114 analyzer from Applied Precision Ltd., Bratislava, Slovakia.

The heat flow was initiated by an electrically heated resistor heater integrated within the probe that was in direct contact with the specimen under test. The probe used had a diameter of 60 mm, and the tested material was at least 25 mm thick.

The thermal conductivity assessment and volumetric heat capacity were derived from the periodic temperature recordings as a function of time within an unrestricted medium for heat transmission. Five measurements for each sample were taken at various locations, with the temperature varying between −15 and 60 degrees Celsius.

This procedure was applied to ten cubes of each concrete mix, each cube measuring 150 × 150 × 150 mm³. The final result was derived as the average of all these measurements. Graining curve of the aggregate mixture—sand 0–2 and basalt 2–8 is shown in the (Figure 1).

Number of standard samples made:

• 27 cubes with dimensions of 150 × 150 × 150 mm—six reference samples and seven samples for each modification,
• 12 cylinders with a diameter of 150 mm and a height of 300 mm—three reference samples and three samples for each modification,
• 12 pieces of beams with dimensions of 100 × 100 × 500 mm—three pieces of reference samples and three pieces of samples for each modification.

The concrete mix recipe is shown in the (

Table 1. Concrete mix recipe.

Concrete Mix Recipe per m3
Aggregate (K1 + K2)	K = 1000/[(Wk/(1 – Wc × ω)) × (ω/ρc + 1) + (1/ρk)] =	2048	[kg/m3]
Water	W = [Wk/(1 − Wc × ω)] × K =	176	[kg/m3]
Cement	C = W × ω =	367	[kg/m3]
Fine aggregate (K1)— Sand 0–2	K1 = K × (K1/K) =	599	[kg/m3]
Coarse aggregate (K2)—Basalt 2–8	K2 = K × (K2/K) =	1449	[kg/m3]
Bulk density of concrete mix—ρ	ρ = C + K1 + K2 + W =	2591	[kg/m3]

).

All designed mixtures were based on Portland cement, which was CEM I 52.5R, in accordance with EN 197-1:2012 [78], and tap water. Chemical composition of cement and its physical and strength properties were determined according to EN 196-6:2019-01 [79] and PN EN 196-1:2016-07 [80].

Cubic samples, in addition to strength tests, were subjected to tests of their thermal properties. During the tests, the probe was placed on the samples perpendicularly and parallel to the layers.

During these tests, the following concrete properties were determined:

• Thermal conductivity—λ
• Thermal capacity—Cp
• Thermal diffusivity—a

On the remains of cubic samples formed after the compressive strength test, a microstructure study was carried out using a light microscope.

The life cycle assessment focused mainly on concrete, with the addition of glass in the second variant (111.11 kg/m³ of tempered glass).

Modified concrete is designed for the following exposure classes:

• XF3—freeze/thaw attack,
• XM2—mechanical attack,
• XA2—chemical attack,
• XD2—corrosion induced by chlorides,
• XC3—corrosion induced by carbonation,

And characterized by the following properties (average values):

• Compressive strength: 70.13 MPa
• Flexural strength: 5.70 MPa
• Splitting tensile strength—cubic specimens: 2.82 MPa
• Splitting tensile strength—cylindrical specimens: 3.08 MPa
• Dynamic Young’s modulus: 46.9 GPa
• Static Young’s modulus: 40.4 GPa
• Thermal properties:

Thermal conductivity coefficient: 1.8496/1.9025 W/m·K

Specific heat: 1.7483 × 106/1.7329 × 106 J/m³·K

Thermal diffusivity: 1.0579 × 10⁻⁶/1.0979 × 10⁻⁶ m²/s

The life cycle of an industrial floor structure made of concrete with the addition of waste car glass is presented below (Figure 2).

Phase I: Goal and scope definition

According to

Table 2. Life cycle of a building structure [81,82].

Production phase	A1	Extraction and production of raw materials
	A2	Transport
	A3	Production of construction materials
Construction phase	A4	Transport
	A5	Construction
Use phase	B1	Use
	B2	Maintenance
	B3	Repair
	B4	Replacement
	B5	Refurbishment
	B6	Energy consuption
	B7	Water consuption
End-of-life phase	C1	Demolition
	C2	Transport
	C3	Waste processing
	C4	Disposal

, the following concrete parameters allow for the maximum load on the floor in the form of:

• Design point load—wheels—40 kN,
• Design point load—shelves—25 kN,

Selection of slab thickness depending on concrete parameters and loads is presented in

Table 3. Selection of slab thickness depending on concrete parameters and loads [83].

Design Point Load—Wheels [kN]	Design Point Load—Shelves [kN]	Concrete Class	Water/Cement Ratio	Concrete Slab Thickness [cm]
				Daily Intensity
				n ≤ 10	n ≤ 50	n ≤ 100
10	15	C25/30	≤0.55	≥16	≥16	≥18
20				≥16	≥18	≥20
30	25	C30/37	≤0.50	≥16	≥18	≥20
40				≥18	≥20	≥22
60	35		≤0.45	≥20	≥22	≥24
80				≥22	≥24	≥26
100	50	C35/45		≥24	≥26	≥28
120				≥26	≥28	≥30
140			≤0.42	≥28	≥30	≥32

.

For these load values, concrete parameters and a daily intensity smaller than 50, a concrete slab thickness of 20 cm was selected.

To make a 20 cm-thick concrete slab on an area of 500 m², you need 100 m³ of concrete mix and approximately 2000 kg of steel fibers (

Table 4. Amount of ingredients needed to make 100 m³ of concrete mix.

Component	Amount	Unit
Cement CEM I 52.5 R	36,700	kg
Fine aggregate—sand 0–2	59,900	kg
Coarse aggregate—basalt 2–8	144,900	kg
Water	17,600	kg
Car glass	11,111	kg

).

Phase II: Inventory analysis

At this stage, the balance of all elements entering and leaving the system that have an impact on the natural environment is created. The data covers the consumption of natural resources and any negative environmental impacts in the form of emissions throughout the life cycle of the component.

When assessing the environmental impact of a structure, particular attention should be paid to the carbon footprint of concrete and the depletion of natural resources.

1.

Inventory analysis—production phase

The carbon footprint in the product phase covers the emission of carbon dioxide generated as a result of the extraction of raw materials from the ground, their transport and the processes of their transformation into construction products. During the production of one ton of CEM I Portland cement, the amount of carbon dioxide produced is approximately 700 kg [66]. This is mainly due to the clinker burning process, which accounts for over 95% of the cement composition, during which calcium carbonate is decarbonated to calcium oxide, with carbon dioxide being a side product.

2.

Inventory analysis—construction phase

The construction phase takes into account processes ranging from the transport of materials from the factory to the entire construction process until the completion of the works. This stage includes the consumption of resources during the transport, storage and use of materials and any emissions from these activities.

The average fuel consumption of a truck with a load of 20 tons was assumed to be approximately 30 L for each 100 km traveled, which gives the environment emissions of approximately 78 kg of CO₂ per 100 km. The distance at which all transport of raw materials and other materials takes place was also assumed to be equal to 100 km.

3.

Inventory analysis—exploitation phase

This phase occurs from the completion of construction works to the demolition of the structure; therefore, it covers the entire period in which the element is used. It includes all emissions during use and the input of raw materials used in repair, maintenance or replacement.

Floor repairs will be carried out periodically every five years throughout the service life and in critical situations, when damage occurs that must be repaired immediately.

4.

Inventory analysis—end-of-life phase

This stage occurs after the object (or element) is withdrawn from use. Its scope covers the processes taking place during the demolition and the impacts resulting from transport during the demolition of the element.

The estimated impact of the construction on the environment throughout its life cycle is presented in

Table 5. Estimated environmental impact of construction throughout its life cycle.

Parametr	Amount	Unit
Emissions to the environment
Global warming potential—CO2—eqv	33,509	kg
Depletion of natural resources
Fine aggregate—sand 0–2	64,692	kg
Coarse aggregate—basalt 2–8	156,492	kg
Water	19,008	kg
Limestone and aluminosilicates	38,448	kg
Gypsum	1188	kg
Depletion of energy sources
Fuel—Diesel	2356	L
Electricity—coal	587	kg
Thermal energy—coal	3425	kg
Thermal energy—RDF alternative fuel	3171	kg

.

Phase III: Impact assessment

Tempered glass from car windows of waste origin was added to the designed concrete mix as an addition. Currently, glass used in the automotive industry is produced in the Float technology. First, large panes of glass are made, from which panes of a specific shape, structure and purpose are then created. Glass is produced from five basic components:

• Sand: approximately 72%
• Soda: approximately 13%
• Limestone: approximately 8%
• Dolomite: approximately 4%
• Alumina: approximately 1%

Glass exists in various colors and types, with various chemical components. Figure 3 and Figure 4 show the chemical compositions of different colors and types of typical glass, respectively.

The physical and mechanical properties of crushed waste glass are listed in Figure 5 and Figure 6, respectively.

Car windows are mainly made in two variants: laminated and toughened. Laminated glass is used as a windshield and is made by placing a transparent polyvinyl butyl (PVB) film between two glass panes. Such construction of the glass makes it much safer for vehicle users because, after the glass breaks, all its pieces stick together and the crack itself does not significantly limit visibility through the glass. Tempered glass is most often used in side and rear car windows. This type of glass is more impact- and bend-resistant than standard glass. As a result of the breakage of such a glass, very small, unsharp pieces are formed, which eliminates the risk of dangerous wounds and cuts. Such properties of tempered glass are obtained by initial, controlled heating to a temperature of about 650 °C and then by rapid cooling. Tempering the glass in this way causes internal stresses in the glass structure, which improve its resistance to mechanical actions, while increasing its fragility.

Glass waste used for the production of concrete is marked in the standard for the classification of glass waste as code 16 01 20, i.e., waste from car windows resulting from the disassembly, inspection and maintenance of vehicles.

Tempered glass from car windows - before and after fragmentation is shown in (Figure 7).

Portland cement, Aalborg White CEM I 52.5 R—SR5, was used to design and make the concrete mix. This cement is characterized by high stability, low alkali content, high resistance to sulfates and a white color that comes from the limestone (chalk) and fine-grained sand from which it is produced (

Table 6. The most important properties of cement are CEM I 52.5 R—SR5.

Essential Characteristics	Usable Properties	Unit
Compressive strength
1 day	21–27	MPa
2 days	40–48	MPa
7 days	53–65	MPa
28 days	66–76	MPa
Initial setting time	110–160	min
Standard consistency	30
Constant capacity	0.5	mm
Cement fineness (wg Blaine’a)	400	m2/kg
Specific mass (absolute density)	3090–3190	kg/m3
Bulk-specific weight	1080	kg/m3
Heat of hydration	550	kJ/kg
Chemical properties of clinker
C3S	73	%
C2S	16	%
C3A	5	%
C4AF	1	%
Chemical properties of cement
SO3	1.8–2.3	%
MgO	0.6	%
Na2O	≤0.3	%
Chloride	≤0.04	%
roasting loss	1	%
Insoluble residue	0.1	%
Water-soluble Cr + 6	≤2	mg/kg

).

The fine aggregate used to make the concrete mix is sand with a fraction of 0–2. This aggregate is very popular due to its high availability and wide use in construction. Fine sand can be used for mortars, concrete, plaster and floors. An important advantage of this aggregate is its purity, i.e., no clay or organic substances.

Basalt with a fraction of 2–8 was used as the coarse aggregate. Basalt grit belongs to the group of crushed aggregates, and it is nothing more than basalt stones crushed to the appropriate fraction. Basalt, as a raw material, is formed from magma smelted deep below the Earth’s surface. In conditions of very high temperatures and enormous pressure, it becomes extremely hard, compact, durable and is additionally resistant to factors such as:

• Temperature variables (from −70 °C to 150 °C),
• Moisture,
• Emphasis,
• Action of bases, acids and salts,
• UV radiation,
• dirt,
• Abrasion.

Tap water was used to create the concrete mix. It is pure water that does not contain any impurities that could adversely affect the concrete mix or mature concrete. No testing is required when using this type of water.

Atlas Duruflow PE-531 concrete fluidizing admixture was used in the preparation of the mix. It affects e.g.:

• Facilitating the distribution and compaction of the concrete mix,
• Improving water and frost resistance,
• Improvement of the early and final strength of concrete.

The life cycle analysis was mainly related to the building material, concrete, with the addition of car glass. Due to the use of glass as an additive to concrete, it has a marginal impact on improving its environmental performance compared to unmodified concrete. The cement industry has a large impact on the natural environment in the production of concrete, which, due to its high energy consumption, consumes large energy sources, and at the same time generates large amounts of carbon dioxide emissions for the environment.

A more optimal solution would be to use car glass as a partial replacement for cement or aggregate. This would reduce the amount of cement or aggregate used in the production of concrete, which would undoubtedly have a better effect on the environment. However, it should be noted whether such a modification of the concrete would be rational in terms of the obtained strength parameters and other properties.

The positive side of the use of toughened glass as an additive to concrete from an ecological point of view is the utilization of waste, which in many cases cannot be reused without significantly deteriorating the mechanical properties of the concrete. Additionally, a positive aspect of the use of glass in concrete is the re-use of natural raw materials in a processed form, because for each ton of glass cullet there is approximately 800 kg of sand, 250 kg of soda and 180 kg of limestone flour.

Phase IV: Interpretation

The proposed application of the concrete mix in the test is industrial floors. This proposed use-like structure, due to its small size and the traditional method of execution, has a relatively small impact on the natural environment, but taking into account that there are thousands of such structures around the world, the impact on the environment becomes significant. In construction, the scale on which it operates is very important; there is no place on Earth where construction would not be used, and concrete is the basis for the construction of all kinds of facilities. Therefore, it is important to strive to minimize its impact on the natural environment in all aspects of its existence, from reducing the consumption of natural resources to reducing all kinds of emissions.

3. Results

The concrete mix was designed in four variants, differing in the content of car glass [84,85,86,87,88,89]. The first variant W1 was modified with 66.67 kg/m³, the second variant W2 contained an addition of 111.11 kg/m³ and the third variant W3—155.56 kg/m³. The last fourth variant is the reference samples, which have not been modified and are the reference for the evaluation of the results. Before making standard samples, the consistency class was determined by the concrete slump test and the air content in the concrete mix with the use of a porosimeter. After 28 days, when the concrete reached its full strength, the bulk density, the values of the Young’s modulus were determined and the strength tests were carried out, during which the compressive strength, flexural strength and splitting tensile strength were determined.

The density of the reference variant classifies it at the upper limit of ordinary concrete, and all modified variants have been classified as heavy concrete. These values are due to using a large amount of aggregate in the form of basalt with a density of 3000 kg/m³.

The test of the consistency of the concrete mix was carried out using the cone-drop method. In this method, a frustoconical mold is filled in layers with concrete mix, each layer being compacted by stabbing. After filling the entire cone, the last layer is leveled, then the form is dynamically lifted up and then the difference in the height of the mixture in the cone and after its removal is measured (Figure 8). The result obtained allows the mixture to be classified into one of five consistency classes (

Table 7. Consistency classes according to the cone drop method.

Class	Cone Drop [mm]	Tolerance [mm]
S1	10–40	±10
S2	50–90	±20
S3	100–150	±30
S4	160–210	±30
S5	≥220	±30

).

All variants of the concrete mix were qualified for consistency class S1 (

Table 8. Obtained consistency classes.

Variants	Cone Drop [mm]	Consistency Class
Reference	30	S1
Variant 1	37	S1
Variant 2	7	S1
Variant 3	5	S1

).

The smallest drop of the cone was created during the testing of the concrete mix with the largest amount of the additive in the form of tempered glass and amounted to 5 mm. On the other hand, the largest slump of 37 mm was obtained with the smallest amount of additive.

The air content was tested using a porosimeter. It is a pressure method consisting of filling the device with a concrete mixture in layers with appropriate compaction. Then, using a hand pump, the pressure in the device chamber is defined and opening the overflow valve equalizes the pressure in a container filled with the mixture. The pressure drop in the vessel shows the amount of air contained in the concrete mix. When testing the air content with a porosimeter, values of 5% were obtained for all variants of the concrete mix. This amount of air in the mixture is sufficient to obtain frost resistance.

To sum up, during the tests of fresh concrete mix, all designed variants obtained the consistency of the S1 class, and during the test of air content, values of approximately 5% were obtained for each of the tested variants (

Table 9. Concrete mix test results.

	Reference	W1	W2	W3
Density [kg/m3]	2591	2658	2702	2747
Consistence class	S1	S1	S1	S1
Air content [%]	5.0	5.1	5.0	5.2

).

The bulk density of concrete was determined on the basis of cubic samples and is the ratio of the sample weight to its volume (

Table 10. Volume densities of cubic samples.

	Volume Densities of Cubic Samples [kg/m3]
	Reference	W1	W2	W3
1	2483.7	2516.7	2548.1	2448.4
2	2548.0	2472.4	2504.3	2454.7
3	2518.1	2507.3	2463.6	2494.1
4	2503.3	2530.1	2459.7	2484.4
5	2498.7	2488.0	2476.1	2452.9
6	2529.8	2508.7	2421.3	2456.1
7	-	2425.9	2472.9	2496.4
Average value	2513.6	2492.7	2478.0	2469.6

, Figure 9 and Figure 10).

The obtained results show a downward trend with the increase of the tempered glass additive. The highest average bulk density was achieved by the reference variant, and the lowest variant with the addition of 7000 g of glass for the batch. This is due to the partial substitution of heavier basalt (3 g/cm³) for lighter glass (2.5 g/cm³) in the samples. All variants in terms of the obtained bulk density qualify for ordinary concrete.

Compressive strength tests were carried out on cubic samples with dimensions of 150 × 150 × 150 mm using a strength pair. The samples were placed in the press perpendicular to the direction in which they were made, and the load acted on the entire surface of the sample (Figure 11).

The results of the compressive strength tests are presented in the

Table 11. Compressive strength.

Variant	Destructive Force F [kN]	Compressive Strength [MPa]	Average Compressive Strength [MPa]	Standard Deviation	Confidence Interval [MPa]
Reference	1533.6	68.2	70.30	1.836	64.71–75.89
	1612.1	71.6
	1600.7	71.1
W1	1547.7	68.8	68.18	1.992	64.51–71.84
	1591.7	70.7
	1505.1	66.9
	1492.2	66.3
W2	1560.2	69.3	70.13	1.905	66.62–73.63
	1639.4	72.9
	1542.5	68.6
	1567.3	69.7
W3	1513	67.2	68.60	1.643	65.58–71.62
	1549.7	68.9
	1518.4	67.5
	1592.1	70.8

.

The reference variant obtained the highest average compressive strength of 70.30 MPa. Among the glass-modified samples, the best results were obtained by the variant modified with 5000 g of additive, which achieved an average strength very similar to the reference variant, equal to 70.13 MPa, and the worst result of 68.18 MPa was achieved by the first variant with the addition of 3000 g of glass.

For concretes, the confidence of measurements is taken at the level of 95%, and the presented compressive strength results differ by less than 5%, i.e., they are within the measurement error. This proves that the additive does not significantly affect the compressive strength of concrete but only affects other concrete strength tests.

The bending tensile strength test was performed on 100 × 100 × 500 mm beams. The three-point bending method used consists in resting the beam on two shafts and then loading it with a centrally acting point force. Before the test, the test stand was properly prepared by properly centering the beam in relation to the support points and removing any impurities (Figure 12).

The results of the flexural tensile strength tests are presented in the

Table 12. Flexural tensile strength.

Variant	Destructive Force F [kN]	Flexural Tensile Strength [MPa]	Average Flexural Tensile Strength [MPa]	Standard Deviation	Confidence Interval [MPa]
Reference	10.38	6.2	5.70	0.458	4.31–7.09
	8.75	5.3
	9.32	5.6
W1	8.68	5.2	5.63	0.451	4.26–7.01
	9.38	5.6
	10.22	6.1
W2	9.31	5.6	5.70	0.557	4.01–7.39
	8.67	5.2
	10.28	6.3
W3	8.89	5.3	5.27	0.058	5.09–5.44
	8.75	5.3
	8.65	5.2

.

During the flexural tensile strength test, the three variants of the concrete obtained similar results. The reference variant and the second modification obtained the same average tensile strength of 5.70 MPa; the first variant achieved a slightly weaker result of 5.63 MPa, and the lowest tensile strength of 5.27 MPa was obtained when testing concrete containing 7000 g of glass.

The addition of glass to the concrete in the amount of 7000 g, which has a bulk density of 155.56 kg/m³, began to affect the decrease in tensile strength when bending. Further increasing the amount of additive would further reduce the tensile strength.

The method of conducting the splitting tensile strength test is very similar to testing the compressive strength of concrete. The difference in carrying out these tests is due to the way the load is transferred to the samples. In the tensile strength test, the force acts on the sample linearly through the washers. The samples during the test should be placed very precisely against the washers, and after the test, any contamination should be removed from the machine (Figure 13).

The results of the tensile strength when splitting cylindrical samples tests are presented in the

Table 13. Tensile strength when splitting cylindrical samples.

Variant	Destructive Force F [kN]	Tensile Strength When Splitting [MPa]	Average Tensile Strength When Splitting [MPa]	Standard Deviation	Confidence Interval [MPa]
Reference	269.2	3.8	3.53	0.275	2.70–4.37
	238.4	3.25
	254.2	3.55
W1	221.1	3.15	3.43	0.275	2.60–4.27
	243.0	3.45
	262.4	3.7
W2	218.2	3.1	3.08	0.625	1.18–4.99
	260.0	3.7
	171.9	2.45
W3	232.5	3.3	3.20	0.100	2.90–3.50
	212.8	3.1
	226.3	3.2

.

When testing the tensile strength during splitting of cylindrical samples, the best results were obtained with the reference variant (3.53 MPa). The strength of the samples modified with the addition of tempered glass decreased compared to the references, and the worst results were achieved by the second variant with the addition of 5000 g of glass with an average of 3.08 MPa.

The longitudinal modulus test was carried out on cylindrical samples with a diameter of 150 mm and a height of 300 mm, which were previously weighed. The weights of the samples were entered into the computer, and the samples were placed in sequence in the device. Based on the measurement of the velocity of the sound wave flow through the sample, the dynamic and static moduli of elasticity were determined (Figure 14).

The value of the dynamic modulus of elasticity is presented in the

Table 14. The value of the dynamic modulus of elasticity.

Variant	Modulus of Elasticity [GPa]	The Average Value of the Modulus of Elasticity [GPa]	Standard Deviation
Reference	46.7	47.6	0.902
	48.5
	47.7
W1	46.9	46.8	0.058
	46.8
	46.8
W2	46.9	46.9	0.551
	46.4
	47.5
W3	46.5	46.4	0.153
	46.2
	46.4

and the value of the static modulus of elasticity is presented in the

Table 15. The value of the static modulus of elasticity.

Variant	Modulus of Elasticity [GPa]	The Average Value of the Modulus of Elasticity [GPa]	Standard Deviation
Referencja	40.1	41.2	1.102
	42.3
	41.3
W1	40.4	40.3	0.100
	40.3
	40.2
W2	40.3	40.4	0.702
	39.7
	41.1
W3	39.8	39.7	0.100
	39.6
	39.7

.

During the tests of the modulus of elasticity of concrete, the following results were obtained: the highest average value of the modulus of elasticity, both dynamic and static, was obtained by the reference variant, which was not modified with the addition of glass, and the lowest results were obtained when testing the sample with the addition of glass in the amount of 7000 g per batch.

The average results of all tests for hardened concrete are presented in the (

Table 16. Averag test results for hardened concrete.

	Reference	W1	W2	W3
Mass [g]	8483.3	8413.0	8363.3	8334.9
Bulk density [kg/m3]	2513.6	2492.7	2478.0	2469.6
Compressive strength [MPa]	70.30	68.18	70.13	68.60
Flexural strength [MPa]	5.70	5.63	5.70	5.27
Splitting tensile strength— cubic specimens [MPa]	3.07	3.03	2.82	2.98
Splitting tensile strength— cylindrical specimens [MPa]	3.53	3.43	3.08	3.20
Dynamic Young’s modulus [GPa]	47.6	46.8	46.9	46.4
Static Young’s modulus [GPa]	41.2	40.3	40.4	39.7

).

In the study of the thermal conductivity coefficient, the same set of results was obtained both for the probe applied perpendicularly and parallel to the layers. The highest value of the coefficient was obtained for the variant modified with 3000 g of glass, and the lowest for the variant modified with the largest amount of glass—7000 g. Therefore, in the variants modified with glass, there is a downward trend in the amount of added glass. The reference variant scored lower than the first variant and higher than the second variant. The addition of glass improves the insulation parameters of concrete (

Table 17. Thermal conductivity—probe perpendicular to the layers.

No	Variant	The Value of the Thermal Conductivity Coefficient—λ	Unit
1	Reference	1.8837	[W/m·K]
2	W1	1.9086
3	W2	1.8496
4	W3	1.7336

and

Table 18. Thermal conductivity—probe parallel to the layers.

No	Variant	The Value of the Thermal Conductivity Coefficient—λ	Unit
1	Reference	1.9184	[W/m·K]
2	W1	1.9202
3	W2	1.9025
4	W3	1.8699

).

The highest specific heat value was obtained for the variant modified with the highest amount of the tempered glass additive, and the lowest for the reference (probe parallel to the layers) and the first variant (probe perpendicular to the layers). In both variants of the study, an increasing tendency was observed for glass-modified samples (

Table 19. The right warmth—probe perpendicular to the layers.

No	Variant	The Right Warmth—cp	Size Multiplier	Unit
1	Reference	1.7646	×106	[J/m3·K]
2	W1	1.7049
3	W2	1.7483
4	W3	1.8276

and

Table 20. The right warmth—probe parallel to the layers.

No	Variant	The Right Warmth—cp	Size Multiplier	Unit
1	Reference	1.5591	×106	[J/m3·K]
2	W1	1.5911
3	W2	1.7329
4	W3	1.7673

).

The thermal diffusivity tests show that the highest value, depending on the test method, was obtained by the reference variant (probe parallel to the layers) or the modified variant with 3000 g of glass per batch (probe perpendicular to the layers). The lowest value was obtained for the variant with the largest amount of glass. In addition, in this case, trends were obtained for modified samples—with a greater amount of glass, the value of thermal diffusivity decreased (

Table 21. Thermal diffusivity—probe perpendicular to the layers.

No	Variant	Thermal Diffusivity—a	Size Multiplier	Unit
1	Reference	1.0675	×10−6	[m2/s]
2	W1	1.1195
3	W2	1.0579
4	W3	0.9486

and

Table 22. Thermal diffusivity—probe parallel to the layers.

No	Variant	Thermal Diffusivity—a	Size Multiplier	Unit
1	Reference	1.2305	×10−6	[m2/s]
2	W1	1.2068
3	W2	1.0979
4	W3	1.0581

).

The microstructure study was carried out on the remains of cubic samples formed after the compressive strength test using a light microscope. The photos taken during the test show that the mixture was properly mixed and compacted, and the glass was properly distributed throughout the entire volume (Figure 15, Figure 16, Figure 17 and Figure 18).

4. Research Significance

This research explores the physical characteristics of waste glass. In addition, this study aims to review the literature that discusses the use of recycled waste glass in concrete as a partial or complete alternative to aggregates by focusing on the effect of this waste on the fresh and mechanical properties of concrete in order to demonstrate the possibilities of using recycled waste glass in concrete and to provide practical and brief guidance. Furthermore, we are establishing a foundation for future study on this material and describing research insights, existing gaps, and future research goals [14].

5. Conclusions

During the tests of the fresh concrete mix, all designed variants obtained the consistency of S1 class, and during the testing of the air content, values of approximately 5% were obtained for each of the tested variants.

Strength tests of glass-modified samples showed a negative effect of this additive on the strength properties of concrete. Among the modified samples, the highest compressive strength and flexural strength were achieved by the second variant modified with the addition of 5000 g of glass, but the same variant obtained the lowest splitting tensile strength. The results of the strength tests did not show any tendency depending on the amount of glass added; however, taking all the results into account, it can be assumed that with an increase in the amount of glass added, the strength parameters of concrete deteriorate, as does the durability of the structure.

Summarizing the results of all the tests, the influence of toughened glass from car windows in most cases has a negative effect on the properties of concrete, but it is not a significant impact that would prevent its use.

In the case of thermal parameters, the addition of glass resulted in a decrease in the value of the thermal conductivity coefficient. A downward trend was obtained with an increase in the amount of added glass, which means a positive effect of glass on the thermal insulation properties of the product made of concrete modified in this way.

An interesting continuation of the research could be the use of toughened glass as a substitute for some cement or aggregate and carrying out a series of tests on such material [90].

Moreover, the analysis of the concrete modified with car glass has shown that this additive has little effect on the improvement of the environmental performance of this material. In assessing the impact of concrete on the natural environment, the cement production process plays a significant role, as it is highly material- and energy-consuming, as a result of which a large amount of emissions is generated [91].

Glass in the form of an additive to concrete does not reduce the amount of cement or aggregate necessary to make a concrete mix, which would significantly reduce the carbon footprint and the amount of natural resources used [92,93,94,95].

6. Discussion

In discussing the results and comparing them with other researchers [96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116], the focus was primarily on the recent studies on the use of glass in concrete by other researchers in this field:

• Ali İhsan Çelik, et al. [104]; Mechanical Behavior of Crushed Waste Glass as Replacement of Aggregates.

In this article, which includes the results of research, ground glass powder and crushed waste glass were used to replace coarse and fine aggregates. Based on findings obtained from this study, the researchers recommend a 20% replacement for fine aggregate and coarse aggregate with waste glass, considering both workability and strength [104] (Figure 19).

2.

Ibrahim Almeshal, et al. [15]; Mechanical properties of eco-friendly cements-based glass powder in aggressive medium.

In this article, which includes results of research, eco-friendly mortar containing recycled glass powder as a replacement for cement is submerged in NH₄NO₃ solutions. The results indicated that the maximum compressive strength was attained at the 10% replacement level of cement with glass powder by approximately 60 MPa after 60 days of immersion in NH4NO3 solution [15].

3.

Shaker Qaidi, et al. [14]; Concrete Containing Waste Glass as an Environmentally Friendly Aggregate: A Review on Fresh and Mechanical Characteristics

In this article, which includes the results of research, the literature discussing the use of recycled glass waste in concrete as a partial or complete replacement for aggregates has been reviewed by focusing on the effect of recycled glass waste on the fresh and mechanical properties of concrete [14] (Figure 20) and

Table 23. Bulk density of concrete with content of waste glass for R, W1, W2 and W3.

	Reference	W1	W2	W3
Bulk density [kg/m3]	2513.6	2492.7	2478.0	2469.6

.

4.

Ali İhsan Çelik, et al. [105]; Use of waste glass powder toward more sustainable geopolymer concrete

In this article, which includes results of research, the influence of waste glass powder with fly ash in certain proportions on geopolymer concrete was investigated by exchanging different proportions of molarity and waste glass powder percentages in geopolymer concrete [105] (Figure 21, Figure 22, Figure 23 and Figure 24 and

Table 24. Results of compressive strength tests for R, W1, W2 and W3.

	Reference	W1	W2	W3
Compressive strength [MPa]	70.30	68.18	70.13	68.60

,

Table 25. Results of splitting tensile strength tests for R, W1, W2 and W3.

	Reference	W1	W2	W3
Splitting tensile strength— cubic specimens [MPa]	3.07	3.03	2.82	2.98
Splitting tensile strength— cylindrical specimens [MPa]	3.53	3.43	3.08	3.20

and

Table 26. Results of flexural strength tests for R, W1, W2 and W3.

	Reference	W1	W2	W3
Flexural strength [MPa]	5.70	5.63	5.70	5.27

).

5.

Zeybek Ö., et al. [106]; Influence of Replacing Cement with Waste Glass on Mechanical Properties of Concrete

In this article, which includes the results of research, the effect of waste glass on the mechanical properties of concrete was examined by conducting a series of compressive strength, splitting tensile strength and flexural strength tests. According to this aim, waste glass powder was first used as a partial replacement for cement, and six different ratios of waste glass powder were utilized in concrete production. According to the results obtained, a 20% substitution of WGP as cement has been considered the optimum dose for concrete produced with combined WGP and crashed glass particles. Mechanical properties increased up to a certain limit and then decreased owing to poor workability. Thus, the researchers have considered 10% the optimum replacement level, as combined waste glass shows considerably higher strength and better workability properties [106] (Figure 25).

Summary of the results of past studies on the splitting tensile strength of waste-glass concrete based on the source materials contained in [14] (Figure 26).

Summary of the results of past studies on the flexural strength of waste-glass concrete based on the source materials contained in [14] (Figure 27).

Summary of the results of past studies on the compressive strength of waste-glass concrete based on the source materials contained in [14] (Figure 28).

7. Recommendations

This paper makes the following general recommendations for future research:

• More investigation is required into the mechanical characteristics of high-performance and high-strength waste-glass concrete.
• The effects of different types and sizes of glass particles on concrete mixes should be thoroughly researched in the future.
• Test fewer common types of glass as aggregates in concrete because the vast majority of research only covers soda-lime, borosilicate or lead glass.
• Conduct a comprehensive evaluation of the real environmental effects through a thorough and detailed life-cycle assessment to evaluate the feasibility of using this waste.

8. Further Research

In further research, the authors will focus on testing the durability of the resulting composite and, above all, documenting that it is suitable for construction use by meeting environmental standards, including frost resistance, algae growth resistance, resistance to UV radiation, thermal shock. Thanks to such information, the authors will fully confirm the suitability of this type of composite for general construction applications. Based on the available literature and required standards, these studies are long-term and require a number of samples to be compared with results obtained by other researchers in the discipline.

The improvements to consider regarding the methodology in the future are:

• confirmation of the origin of the glass, as its chemical composition may significantly change the physicochemical properties of the finished composites.
• considering adding more glass in favor of a weaker type of cement, e.g., metallurgical, to reduce the CO₂ footprint.
• the possibility of using glass aggregate as a substitute for all natural aggregate used in the production of concrete composite.
• the possibility of using chemical additives to modify the physical properties of composites, e.g., increasing the strength between cement and glass aggregate or accelerating or slowing down the hydration reaction.