Life Cycle Assessment of a Road Transverse Prestressed Wooden–Concrete Bridge

Abstract

Through its anthropogenic activities in construction, human society is increasingly burdening the environment with a predominantly adverse impact. It is essential to try to use building materials that allow us to build environmentally friendly buildings. Therefore, this article deals with the determination of the environmental performance of a cross-prestressed timber-reinforced concrete bridge using life cycle assessment (LCA) compared with a reinforced concrete road bridge with a similar span and load. The positive environmental performance of the wooden concrete bridge was proved, with a relatively small (22.9 Pt) total environmental damage. The most significant impact on the environment is made by the wood–concrete bridge materials in three categories of impacts: Respiratory inorganics (7.89 Pt, 79.94 kg PM2.5 eq), Global warming (7.35 Pt, 7.28 × 10⁴ kg CO₂ eq), and Non-renewable energy (3.96 Pt, 6.01 × 10⁵ MJ primary). When comparing the wood–concrete and steel concrete road bridge, a higher environmental performance of 28% per m² for the wood–concrete bridge was demonstrated. Based on this environmental assessment, it can be stated that knowledge of all phases of the life cycle of building materials and structures is a necessary step for obtaining objective findings of environmental damage or environmental benefits of building materials or structures.

1. Introduction

With the world’s growing population, it is necessary to travel and overcome longer distances. This is also connected with the broader use of roads and bridge structures. The bridges are becoming more and more loaded, and which necessitates their reconstruction or complete replacement. In the Czech Republic (Central Europe, total area 78,866 km², population 10.52 mil.), there a total of 17,850 bridges, 13.76% of which are in poor condition, 5.03% are in very poor condition, and 0.45% are in critical state condition. For bridges located on the class 2 roads (the connection between the districts) and class 3 roads (the connection between the municipalities or their connection to the other roads), 16.18% of bridges are in poor condition, 6.02% are in very poor condition, and 0.58% of the bridges are in a critical state condition. A significant part of the bridges in poor to critical state conditions are bridges placed on class 2 and class 3 roads [1]. From this information, almost 23% of class 2 and class 3 road bridges need to be renovated or completely replaced.

According to several world studies, infrastructure is the main cause of greenhouse gas (GHG) emissions, as infrastructure designs influence more than half of global climate change emissions [2,3,4]. Therefore, it is necessary to evaluate the time in which structural systems and the materials used for construction have the potential to minimize the impact on the environment [5,6,7]. Several authors, such as Balogun et al. [7], Horvath and Hendrickson [8], Zhang et al. [9], Du and Karoumi [10], and Pedneault et al. [11], conducted detailed studies comparing basic material groups in the construction of bridges, for example, steel, concrete, aluminum, etc., in their environmental impact assessment. Similar publications focused on the environmental impact of bridges [4,12,13,14,15,16] proved that there is a clear need for environmental information at various stages of the life cycle of the bridge structures.

The evaluation of the publication by Niu and Fink [17] confirms the fact that the phase of production of structural materials has the largest share of the environmental impact of bridges. Habert et al. [18] proved that two phases mainly contribute to the environmental impacts: the production of the materials and the maintenance of the bridge. Du et al. [19] found that regardless of the bridge type, the material manufacture phase dominates the whole life cycle in all indicators. The material production stage shall be considered carefully, since it is usually identified to contribute the largest share of environmental impact [17,20].

The bridges where the main structural material is concrete or various material variants of its reinforcement are dealt with by studies [16,21] considering the environmental impact. In publications, there are evaluations of the environmental impact of individual alternative solutions to the change in the material base of the reinforcement. In the case where concrete is used as the material for the main load-bearing structures of the bridge deck, it has been found that in the area of CO₂ emissions, the use of high-performance concrete caused 66% lower emissions than in the case of normal concrete [22]. For example, in the case of steel–concrete main load-bearing structures [23], these bridge decks are more expensive than concrete in terms of price but have a lower environmental impact. As part of material reuse, structural steel in reinforced concrete structures has significantly higher recyclability than concrete—up to 98% recyclability [10,24]. A comparison of composite bridge structures, for example, steel beams connected with an aluminum bridge deck or steel beams connected with a concrete bridge deck, is dealt with in [11]. It is obvious that the material composition of the structure has an important role in the life cycle stages of bridge structures.

However, in connection with structural materials, the construction design phase is also a very important phase of the life cycle of construction. This phase mainly affects the method of use, the amount of material used, and the impact on CO₂ emissions [25]. The SEGRO algorithm was used to design prefabricated bridges made of two isostatic beams with a double U-shaped cross-section and isostatic spans. [26]. It has been shown that using the algorithm in the bridge design phase reduces CO₂ emissions. The combination of bridge length with material and construction solutions also has an impact on the environment [27,28]. It is obvious that the design solution can affect not only the choice of the bridge material used but especially its environmental impacts during the life cycle.

Therefore, this article deals with determining the environmental performance of material composition on the classification and quantification of environmental impacts of a transverse prestressed Wooden–Concrete Bridge (WCB) for road transport (with a small bridge up to 10 m). In the next step, the design level and its environmental impacts are evaluated, and the WCB is compared with a similar Steel Concrete Bridge (SCB) per m² of the bridge area.

2. Materials and Methods

2.1. Characteristics of the Road Transverse Prestressed Wooden–Concrete Bridge (WCB)

The transverse prestressed wooden–concrete bridge (WCB) for road transport is in the village of Bohunice in the Czech Republic (Central Europe) (

Table 1. Structural units and materials composition of WCB and SCB bridges.

			WCB		SCB
Structural Elements	Material	m3	t	m3	t
Abutments and piers	Concrete C30/37	65.160	162.900	31.009	77.523
	Reinforcement B500B	0.917	7.200	0.480	3.765
Capping beam	Concrete C30/37	3.507	8.767	13.166	32.915
	Reinforcement B500B	0.022	0.172	0.019	0.149
Abutment wall	Concrete C30/37	3.163	7.908	3.163	7.908
	Reinforcement B500B	0.006	0.047	0.006	0.047
Main construction and bridge deck	Concrete C30/37	17.100	43.180	16.801	42.003
	Glued laminated timber GL32h	33.000	20.483	-	-
	Steel	-	-	1.670	13.128
	Reinforcement B500B	0.080	0.626	0.803	6.302
	Shear connections—engineering steel	0.036	0.279	0.041	0.320
	Prestressing elements	0.220	0.600	-	-
Bridge bearing	Elastomer	0.178	0.570	0.031	0.100
Bridge top	Polyurea	0.082	0.004	-	-
	Asphaltic concrete	-	-	2.898	6.376
	Connecting spray PS	-	-	0.090	0.019
	Medium grain aggregates (16+)	-	-	2.898	4.637
	Mastic asphalt	-	-	1.932	2.125
	Concrete	-	-	1.932	4.250
Bridge equipment	Railings structural steel	27.300	0.493	0.139	1.090
	Concrete monolithic parapet C30/37	4.100	10.430	5.148	12.870
	Reinforcement B500B	0.038	0.301	0.147	1.151

, Figure 1, Figure 2 and Figure 3). The bridge is located on road 2 class, and it was designed as a single-field bridge (one field between two supports) to short span; the length is 13.650 m with a total width of 6.230 m. The reconstruction of the bridge was focused on the part of the substructure and on the superstructure. The foundations of abutments and piers, of which the originals were retained, were designed as spread footing. Bridge abutments, capping beams, and abutment walls are made of concrete with strength class C30/37 with a resistance to corrosion induced by chlorides and a resistance to alternate freeze and thaw attacks. The description of the concretes used in the construction is specified in European standard [29]. The concrete is reinforced with steel-bar reinforcement. The shaft width of concrete abutments is 2.725 m. The capping beams and the abutment wall are reinforced with concrete reinforcement with a diameter of 12 mm and the binder bars with a diameter of 8 mm by 200 mm. The linear elastomer bridge bearing system was chosen and placed on the capping beam mainly due to its low height, with dimensions of the elastomer system 200 × 52 × 300 mm. The structure was also anchored in the horizontal and transverse directions by means of steel loop with a bolt. The superstructure of the bridge was placed on the bridge bearings. The horizontal bearing structure is a patented system, coupling load-bearing wooden parts and reinforced concrete. The wood–steel part is made of transversely prestressed beams made of spruce glued laminated timber (GLT) of strength class GL32h. The height of the wooden beams is 600 mm, and the width is 100 mm. The prestress is realized by means of high-strength steel bars. The prestressing bars are equipped with large steel backplates and nuts on both sides. The beams are protected by polyurea insulation spray. The wood–steel load-bearing structure was placed directly on the elastomer bridge bearings and anchored with an anchoring loop. The roadway was reinforced and cast on the self-supporting structure. The bridge deck is reinforced concrete with strength class C30/37 with resistance to corrosion induced by chlorides and with the resistance to alternate freeze and thaw attacks with a maximum height of 300 mm. The transverse prestressing bars are 14 mm in diameter at an axial distance of 100 mm. Coupling between the wood–steel part and the concrete deck was performed using special coupling screws VB-48-7.5x165. All steel elements were heat galvanized. The roadway of WCB is directly movable with short parapets made of reinforced concrete C30/37. Both parapets are fitted with 1.100 m high steel railings made of structural steel with a yield strength of 235 MPa (S235). The parameters of the steel used are given in [30].

2.2. Characteristics of the Road Steel Concrete Bridge (SCB)

The composite steel-reinforced concrete bridge, Steel Concrete Bridge (SCB), for road transport is in the village in the municipality of Glovčín (Czech Republic, Central Europe) (Table 1, Figure 4, Figure 5 and Figure 6). The SCB was designed as part of road class 2. It is a single-field (one field between two supports) bridge construction with a total bridge length of 11.064 m. The total width of the bridge is 5.1 m. The reconstruction of the bridge was focused on the part of the substructure and on the superstructure. The bridge abutments were founded at strip foundation, which remains as the original, made of reinforced concrete with strength class C25/30. The substructure of the bridge includes two monolithic reinforced concrete abutments. The shaft of abutments, capping beams, and abutment walls were designed from the reinforced concrete with strength class C30/37 with resistance to corrosion induced by chlorides and a resistance to alternate freeze and thaw attacks. The description of the concretes used in the construction is specified in the European standard [29]. The width of the abutments shaft is 1.300 m. The load-bearing structure was mounted on two rectangular reinforced elastomeric bridge bearings on each abutment. The elastomer bearings were located on capping beams in the axes of the main beams. Elastomer bearings were anchored, i.e., structurally secured against movements in the open joint between the bearings and the subsequent construction. One omnidirectionally movable elastomeric bearing and one longitudinally movable elastomeric bearing were designed on abutment 1. One transversely movable elastomer bearing, and one fixed elastomer bearing were designed on abutment 2. The SCB bridge was designed as a full-beam girder with a lower steel–concrete bridge deck. The load-bearing structure of the bridge includes two main longitudinal beams with a span of 12.0 m.

The main beams were designed as welded I profiles with a height of 1.47 m with both-side column bracing. The mutual axial distance of the beams is 4.75 m. The beams are interconnected in the bottom part by an oblique end and perpendicular intermediate crossbeams at a distance of 1.5 m. The bottom bridge deck is made of a system of longitudinal beams and cross beams. Crossbeams with a span of 4.75 m were designed from cold-rolled profile HEB 260 and carry internal longitudinal beams, which are also designed from cold-rolled profiles HEB 260 at a mutual distance of 1.50 m. For the structural coupling of the reinforced concrete slab of the bridge deck with steel structure, perforated coupling strips made of the structural steel with a yield strength of 355 MPa were welded to the upper flanges of the bridge deck steel crossbeams. The properties of the steel used are specified in the European standard [30]. A railing with vertical infill made of structural steel with a yield strength of 235 MPa (S235) was welded to the upper flange of the main load-bearing beams. The load-bearing steel beams were composed of structural steel with a yield strength of 355 MPa (S355). The bridge deck slab was designed as monolithic reinforced concrete, 4.736 m wide and 13.06 long. The thickness of the slab is variable. The minimum slab thickness is 200 mm. The slab is designed from reinforced concrete C30/37, and it supports the roadway. The crossbeams and reinforced concrete slab are connected in the roadway part. Coupling was realized by means of the coupling strip made of 12 mm thick sheet steel, which is perforated with a diameter of 30 mm holes and welded to the upper flange of the crossbeams by a T-filled weld. The bottom primary load-bearing reinforcement of the concrete slab was passed through the holes at the coupling strip. The roadway structure on the bridge comprises asphalt concrete with a thickness of 40 mm, connecting spray, coated medium grain aggregates, 35 mm thick mastic asphalt, and NAIP insulation on the sealing layer. On both sides of the bridge, monolithic parapets are composed of reinforced concrete with strength class C30/37 with resistance to corrosion induced by chlorides and with the resistance to alternate freeze and thaw attacks. The monolithic parapets are 618 mm wide. On both sides of the bridge, a 1.30 m high railing is designed with a vertical infill made of structural steel, which is anchored to the parapet via anchor plates by means of glued anchors.

2.3. Life Cycle Assessment Methodology

The Life Cycle Assessment (LCA) method was chosen for the environmental impact assessment [31,32]. The system boundaries for LCA included in the assessment were divided into construction materials (product stage for raw material supply, transport to the manufacturer, and manufacturing). The materials in Table 1 were included in the inventory analysis. The functional unit was the whole WCB selected for the WCB environmental performance calculation. For the comparison of WCB and SCB, a functional square meter (1 m²) of bridging was chosen to consider the different bridging lengths and different widths of bridge structures, and thus the results can be used for other environmental comparisons for low-span road bridges.

The SimaPro 9 database software [33] and the IMPACT 2002+ method [34] were used for life cycle impact assessment (LCIA). LCIA was evaluated at midpoints of environmental damage: Respiratory inorganics (kg PM2.5 eq), Global warming (kg CO₂ eq), Non-renewable energy (MJ primary), Land occupation (m²org.arable), Terrestrial ecotoxicity (kg TEG soil), Non-carcinogens (kg C₂H₃Cl eq), Carcinogens (kg C₂H₃Cl eq), Mineral extraction (MJ surplus), Terrestrial acid/nutria (kg SO₂ eq), Aquatic ecotoxicity (kg TEG water), Respiratory organics (kg C₂H₄ eq), Ionizing radiation (Bq C-14 eq), Ozone layer depletion (kg CFC-11 eq), Aquatic acidification (kg SO₂ eq), and Aquatic eutrophication (kg PO₄ P_-lim). The dataset covers all relevant process steps and technologies over the supply chain of the represented cradle-to-gate inventory with good overall data quality [35].

3. Results and Discussion

3.1. Life Cycle Impact Assessment of WCB

The largest overall impact has the WCB structural elements: Abutments and piers (56.7%, 13 Pt), followed by the Main construction and bridge deck (33.4%, 7.66 Pt), and Bridge equipment (3.41%, 0.78 Pt) (Figure 7). A Monte Carlo simulation on a single score of the whole WCB showed a mean of 22.27, median of 22.26, standard error of the mean (SEM) of 0.23, standard deviation (SD) of 3.06, and coefficient of variability (CV) of 13.75%. In the environmental impact categories at the midpoints (

Table 2. WCB environmental damage (Pt), midpoint categories, SimaPro, IMPACT 2002+: 1. Abutments and piers, 2. Capping beam, 3. Abutment wall, 4. Main construction and bridge deck, 5. Bridge bearing, 6. Bridge top, 7. Bridge equipment.

Impact Category	Unit	Total	1	2	3	4	5	6	7
Total	Pt	22.9	13.0	0.461	0.296	7.66	0.731	4.76 × 10−³	0.781
Respiratory inorganics	Pt	7.89	4.54	0.152	9.09 × 10−2	2.64	0.206	1.34 × 10−³	0.254
Global warming	Pt	7.35	4.63	0.175	0.121	2.00	0.142	9.23 × 10−4	0.289
Non-renewable energy	Pt	3.96	2.17	7.93 × 10−2	5.27 × 10−2	1.18	0.310	2.01 × 10−³	0.155
Land occupation	Pt	1.22	0.202	7.26 × 10−³	4.73 × 10−³	0.988	3.04 × 10−³	1.98 × 10−5	1.13 × 10−2
Terrestrial ecotoxicity	Pt	1.14	0.659	2.18 × 10−2	1.28 × 10−2	0.387	2.71 × 10−2	1.76 × 10−4	3.31 × 10−2
Non-carcinogens	Pt	0.729	0.455	1.44 × 10−2	7.98 × 10−³	0.221	9.36 × 10−³	6.09 × 10−5	2.13 × 10−2
Carcinogens	Pt	0.539	0.285	8.65 × 10−³	4.46 × 10−³	0.197	2.95 × 10−2	1.92 × 10−4	1.33 × 10−2
Mineral extraction	Pt	4.57 × 10−2	2.75 × 10−2	7.69 × 10−4	3.39 × 10−4	1.48 × 10−2	9.55 × 10−4	6.22 × 10−6	1.41 × 10−³
Terrestrial acid/nutri	Pt	3.86 × 10−2	1.93 × 10−2	1.06 × 10−³	9.60 × 10−4	1.38 × 10−2	1.63 × 10−³	1.06 × 10−5	1.77 × 10−³
Aquatic ecotoxicity	Pt	2.36 × 10−2	1.47 × 10−2	4.58 × 10−4	2.46 × 10−4	7.20 × 10−³	6.15 × 10−4	4.00 × 10−6	4.09 × 10−4
Respiratory organics	Pt	1.27 × 10−2	7.57 × 10−³	2.31 × 10−4	1.21 × 10−4	3.79 × 10−³	6.20 × 10−4	4.04 × 10−6	3.68 × 10−4
Ionizing radiation	Pt	3.87 × 10−³	1.65 × 10−³	7.30 × 10−5	5.79 × 10−5	1.47 × 10−³	4.29 × 10−4	2.79 × 10−6	1.82 × 10−4
Ozone layer depletion	Pt	6.47 × 10−4	3.64 × 10−4	1.34 × 10−5	8.94 × 10−6	1.97 × 10−4	4.52 × 10−5	2.94 × 10−7	1.85 × 10−5
Aquatic eutrophication	Pt	-	-	-	-	-	-	-	-
Aquatic acidification	Pt	-	-	-	-	-	-	-	-

and

Table 3. WCB characterization, midpoint categories, SimaPro, IMPACT 2002+: 1. Abutments and piers, 2. Capping beam, 3. Abutment wall, 4. Main construction and bridge deck, 5. Bridge bearing, 6. Bridge top, 7. Bridge equipment.

Impact Category	Unit	Total	1	2	3	4	5	6	7
Respiratory inorganics	kg PM2.5 eq	79.935	46.018	1.540	0.921	26.778	2.088	0.014	2.577
Global warming	kg CO2 eq	7.28 × 104	4.58 × 104	1.73 × 103	1.20 × 103	1.98 × 104	1.40 × 103	9.14	2.86 × 103
Non-renewable energy	MJ primary	6.01 × 105	3.30 × 105	1.21 × 104	8.00 × 103	1.80 × 105	4.70 × 104	3.06 × 102	2.36 × 104
Land occupation	m2org.arable	15,293.188	2544.069	91.185	59.383	12418.011	38.155	0.248	142.137
Terrestrial ecotoxicity	kg TEG soil	1.98 × 106	1.14 × 106	3.77 × 104	2.22 × 104	6.70 × 105	4.69 × 104	3.05 × 102	5.73 × 104
Non-carcinogens	kg C2H3Cl eq	1846.830	1151.506	36.526	20.225	560.850	23.717	0.154	53.852
Carcinogens	kg C2H3Cl eq	1364.350	722.252	21.919	11.296	499.937	74.840	0.487	33.619
Mineral extraction	MJ surplus	6950.275	4176.453	116.894	51.509	2245.212	145.210	0.945	214.052
Terrestrial acid/nutri	kg SO2 eq	508.365	254.687	13.911	12.648	182.140	21.524	0.140	23.315
Aquatic ecotoxicity	kg TEG water	6.45 × 106	4.01 × 106	1.25 × 105	6.72 × 104	1.97 × 106	1.68 × 105	1.09 × 103	1.12 × 105
Respiratory organics	kg C2H4 eq	42.308	25.220	0.771	0.402	12.610	2.065	0.013	1.226
Ionizing radiation	Bq C-14 eq	1.31 × 105	5.58 × 104	2.47 × 103	1.96 × 103	4.97 × 104	1.45 × 104	9.43	6.15 × 103
Ozone layer depletion	kg CFC-11 eq	0.004	0.002	0.000	0.000	0.001	0.000	0.000	0.000
Aquatic acidification	kg SO2 eq	44.843	10.394	1.814	2.263	20.710	6.258	0.041	3.365
Aquatic eutrophication	kg PO4 P-lim	8.873	5.089	0.196	0.137	2.706	0.471	0.003	0.271

), the greatest negative impact is found on Respiratory inorganics (34.4%, 7.89 Pt, 79.935 kg PM2.5 eq), followed by Global warming (32%, 7.35 Pt, 7.28 × 10⁴ kg CO₂ eq), and Non-renewable energy (17.2%, 3.96 Pt, 6.01 × 10⁵ MJ primary). Additionally, according to the results of Du et al. [19], Global Warming, Human Toxicity, and Particulate Matter Formation are the most important environmental damage categories. This finding points to a significant negative impact of the construction materials used on the quality of human health, as PM2.5 particles are known to penetrate the pulmonary alveoli of the lower respiratory tract.

Concrete and steel are the biggest contributors to the overall negative impacts. The negative effects of the use of other materials due to their quantity are less significant compared to concrete and steel. The findings of this research are similar to the results of other authors, such as Liu et al. [4], Du et al. [19], and Hettinger et al. [36]. According to Du et al. [19], steel and reinforcement are key materials that affect GWP (global warming potential) and CED (cumulative energy demand), and this means the bridge, which uses steel as the main load-bearing structure, has a much higher potential in the GWP impact mitigation. When looking at the initial construction of equivalent bridge designs, steel-reinforced concrete girders appear to have lower overall environmental effects than steel girders. However, steel girders are reusable and recyclable at the end of their useful life [8]. Habert et al. [18] found that, within concrete structures, the concrete used for the bridge deck clearly dominates in the impact on a conventional bridge. This effect is significantly reduced for a high-performance bridge. The carbon emission of cement is the greatest in the material production stage, which has the greatest impact on the environment in the whole life cycle of the bridge. Therefore, the decarbonization of the cement industry will have a significant impact on the carbon reduction of the infrastructure industry [4].

In the case of the alternative use of concrete reinforcement in bridge construction, namely variants of bars made of different composite materials [16], the net difference between the variants has been shown to be approximately 35.500 kg in CO₂ production. Composite materials in bridge structures [37,38,39] may be an alternative to the currently most widely used steel. Therefore, WCB is trying to replace concrete and steel and instead use composite materials based on renewable raw materials, i.e., wood. In their study, Jena and Kaewunruen [38] compared the use of LCA two bridge systems for footbridges made from modern composite materials. The results showed the importance of composite materials in reducing the environmental demands of bridge infrastructure.

The use of the materials itself seems important, but it is also necessary to point out the structural level of the bridge and its environmental design. Therefore, in the following sections of this article, in addition to examining the uncertainty analysis, the research focuses on comparing the environmental properties of materials for two similar bridges, but on a different design basis and materials basis.

3.2. Comparison of WCB and SCB Environmental Performance

The design level and its environmental impacts are evaluated via a comparison of WCB and SCB (Table 1, Figure 4, Figure 5 and Figure 6) per m² of the bridge area. Ideally, a WCB and an SCB design for exactly the same situation would be the only comparable bridges but using m² is the best solution for bridge structures of different lengths and different widths. LCIA was evaluated with the IMPACT 2002+ method, which contains 15 midpoints of environmental damage (

Table 4. Characterization and environmental damage of WCB and SCB per m² (SimaPro, IMPACT 2002+, midpoint categories).

Impact Category	Unit	WCB	SCB	Unit	WCB	SCB
Respiratory inorganics	kg PM2.5 eq	54.936	88.599	mPt	92.782	128.194
Global warming	kg CO2 eq	57,215.27	81,722.027	mPt	86.419	130.184
Non-renewable energy	MJ primary	468,549.53	701,965.683	mPt	46.540	75.441
Land occupation	m2org.arable	14,194.63	4420.413	mPt	14.310	5.211
Terrestrial ecotoxicity	kg TEG soil	1,333,088.65	2,042,480.86	mPt	13.415	16.439
Non-carcinogens	kg C2H3Cl eq	1126.85	2041.858	mPt	8.575	10.757
Carcinogens	kg C2H3Cl eq	866.241	1339.417	mPt	6.334	6.985
Mineral extraction	MJ surplus	3607.60	8748.035	mPt	0.538	0.773
Terrestrial acid/nutri	kg SO2 eq	622.813	382.403	mPt	0.454	0.650
Aquatic ecotoxicity	kg TEG water	3,830,468.60	5,662,764.03	mPt	0.278	0.225
Respiratory organics	kg C2H4 eq	25.169	49.209	mPt	0.149	0.203
Ionizing radiation	Bq C-14 eq	128,415.22	135,768.087	mPt	0.046	0.077
Ozone layer depletion	kg CFC-11 eq	0.003	0.004	mPt	0.008	0.009
Aquatic acidification	kg SO2 eq	107.981	2.688	mPt	0.000	0.000
Aquatic eutrophication	kg PO4 P-lim	7.292	7.98	mPt	0.000	0.000
Total	-	-	-	mPt	269.847	375.147

). LCIA for bridge comparison thus provides a multicriteria analysis, using not only inputs (Table 1) but also outputs (Table 4, Figure 8), where each bridge has its own different and unique material impact on the environment. Similar conclusions were introduced by Hettinger et al. [36], who state that the environmental profile of the bridges, defined by eleven indicators, is strongly connected to the bill of quantities. Du et al.’s [19] interpretation of their environmental analysis indicates that the bridge’s environmental performance is governed by multiple indicators. Each bridge has a unique performance among different indicators.

From Table 4, where the specific values of emissions to the environment are given at the midpoints (characterizations), and from Figure 9, where the total environmental damage is presented in standard eco point units (mPt, mili eco point), it can be seen that the most significant damage from both bridges is within three categories of environmental damage: Respiratory inorganics (WCB = 54.9, SCB = 88.6, kg PM2.5 eq), Global warming (WCB = 57,215, SCB = 81,722, kg CO₂ eq), and Non-renewable energy (WCB = 468,549, SCB = 701,965, MJ primary). These three categories form the triangle of the most significant environmental damage, accounting for 84% of the total negative environmental impacts for WCB and 89% for SCB (Figure 9).

Pedneault et al. [11] analysis has shown a carbon footprint of 8960 kg CO₂ eq/m² for a concrete deck on steel beams (CD) and 4870 kg CO₂ eq/m² for the aluminum deck (AD) on steel beams according to the scope 2 (complete life cycle without traffic diversion), it is slightly higher than the steel–concrete bridge with 4090 kg CO₂ eq/m² [40] and a few times higher the concrete slab frame bridges with 1370 kg CO₂ eq/m² [19]. The study from Hammervold et al. [12] demonstrates a ten times lower carbon footprint per m² compared to the study from Pedneault et al. [11], but they considered only routine repair actions and studied different bridge designs and lengths.

Compared to this case, the values are about 10 times smaller; for example, the amount of steel in the study of Pedneault et al. [11] is 136.82 kg/m² for CD and 78.08 kg/m² for AD, compared to 114.276 kg/m² for WCB and 418.824 kg/m² for SCB in this study. Pedneault et al. [11] used the same evaluation method but different software to calculate the damage. In addition, this research deals purely with the material level of the bridges with different structural systems and a different scope of inventory analysis. The reserves in the calculations using the database program are also confirmed by Habert et al. [18], which state that for the prestressed steel, it is commonly accepted that this steel is essentially produced using the blast furnace method. However, because the efficiency of a blast furnace plant can be different from one plant to another, it was assumed that the environmental load could be 20% higher than the load calculated with Ecoinvent data. Therefore, trends may be more interesting than absolute numbers. Material damage trends are the same. This means that the greatest damage to the road bridges that were compared is caused by concrete and steel in the construction. The other materials used for WCB and SCB have a significantly smaller impact on the environment than concrete and steel.

Several authors [7,8,41,42] concluded that concrete is a more environmentally friendly material than steel, but steel is used in lower quantities for the same design conditions. It may be similarly advantageous in terms of environmental impact in certain design solutions. By comparing composite constructions, coupling steel beams with an aluminum bridge deck, and steel beams coupled with a concrete bridge deck [11], it is shown that all categories of environmental impact are in favor of aluminum bridge decks. One of the reasons is the environmental contribution of the recycling of steel and aluminum. Their use as a substitute for original material (concrete) can reduce environmental impact by up to 40%. Martínez-Muñoz et al. [28] state that prestressed concrete is the best alternative for bridge lengths less than 17 m. The prestressed cellular concrete deck is the best alternative for bridge lengths between 17 m and 25 m because no box girder solution is used. For lengths between 25 m and 40 m, the best solution depends on the percentage of recycled structural steel. If this value is more than 90%, then the best alternative is a composite box-girder bridge deck. However, if the value of recycled structural steel is lower than 90%, then the most environmentally friendly alternative is a prestressed concrete bridge deck.

It is desirable to minimize these two main materials (concrete and steel) in bridge structures and to reasonably replace them with a suitable composite material incorporating its design advantages and possibilities.

When comparing the environmental damages of WCB and SCB, it is clear that a difference of 28% per m² is in favor of WCB. The difference in the use of steel in the compared bridges is 304.547 kg/m², and concrete 157.742 kg/m². This means that the use of a composite based on renewable raw material, i.e., wood, and its proper integration into the bridge construction system can significantly affect the overall environmental impacts as well as impacts on the individual components of the environment. The main difference is in the categories of environmental impacts: Global warming (43.765 mPt, 14,506.757 kg CO₂ eq), followed by Respiratory inorganics (35.412 mPt, 33.663 kg PM2.5 eq), and Non-renewable energy (28.901 mPt, 233,416.153 MJ primary). The only two categories of environmental impacts where the WCB has worse results are the Land occupation (9.099 mPt, 9774.217 m²org.arable) and the Aquatic ecotoxicity (0.053 mPt, 183.229 × 10⁴ kg TEG water) (Table 4, Figure 8). This is understandable in context with the use of wood as a construction material. Given their overall impact (Figure 9, Table 4), they appear less significant. Hettinger et al. [36] dealt with a similar topic. The result of this research is that the composite bridge generates significantly less environmental impacts than its equivalent made of prestressed concrete.

As already mentioned, wood as a material is considered one of the main renewable resources. From the point of view of ecology and environmental sustainability, the use of wood and wood-based composite materials is also very advantageous in construction because it is one of the major contributors to greenhouse gas emissions. When comparing different wood products, bricks, concrete, and steel products in terms of global warming impact, it has been shown that concrete and brick are at the lower end of the wood GWP range, and the cement and steel are at the top of the wood GWP range [43]. Wooden beams have become an ecological and cost-effective variant for steel and concrete elements. In terms of the structural system in bridge engineering, wood most often appears as a glued laminated timber (GLT) element in arched, girder, or hybrid structural systems. GLT is, in many cases, combined with steel or concrete in the form of slabs to increase the overall load-bearing capacity of the structural systems [44,45]. The planned timber is most often used for the construction of truss, hanging, and strut-framed constructional systems. The advantage of these systems is not only the use of renewable material but also the use of a lower volume of materials for a larger span than other constructional systems. In terms of mechanical parameters, wood can fully replace other commonly used materials and at the same time contribute to improving the quality of the environment.

4. Conclusions

Human society is increasingly burdening the environment with its anthropogenic activities in construction. It is therefore essential to try to use building materials and construct buildings that are environmentally friendly. Therefore, this article deals with determining the environmental performance of a road wooden–concrete bridge using Life Cycle Assessment (LCA). The research was a comparison of the wood–concrete bridge with the steel–concrete bridge, where both serve as a road bridge for short spans.

When comparing the wood–concrete and steel–concrete road bridges, higher environmental performance for the wood–concrete bridge was demonstrated. The comparison showed that the wood–concrete bridge has more favorable environmental properties. The advantage of WCB is, for example, the use of renewable resources, especially wood, as a material for the main load-bearing structure. WCB is an adequate alternative to steel, concrete, and other composite structural systems with similar load and dimensional parameters. It can be observed that the involvement of renewable bio-material resources in the construction industry in road infrastructure can have a positive impact on the environment. At the same time, it turned out that the environmental properties of wood-based composite materials will have a significant positive effect with the help of a suitable construction solution.

The results can be used for a good comparison of the environmental characteristics of bridge structures, roads, or urban infrastructure. WCB is an innovative design system that has proven to be suitable for environmental impact due to its LCA method evaluation. Based on this environmental assessment, it can be stated that clear knowledge of all phases of the life cycle of building materials and structures is a necessary step to obtain objective findings about environmental damage or the environmental benefits of building materials or structures.