Estimating carbon emission of rigid pavement: a case study of Palur Flyover

. All construction activities will inevitably produce CO 2 emissions from the production process of materials, transportation, the usage of plant and equipment, the construction process, up to building demolition. Therefore, it is very important to understand the construction process and the amount of CO 2 emissions released at each stage of the construction process. This research aims to estimate the amount of CO 2 emissions during the construction process of a rigid pavement project. Data collection is done by observing rigid pavement of Palur Flyover project as a case study. The results show the total CO 2 emissions during the construction process equals 92.901 tonnes CO 2e , consisting of 91.334 tonnes CO 2e (98.3%) of off-site activities, and 1.567 tonnes CO 2e (1.7%) of on-site activities. The highest emission from off-site activities coming from material production of cement and steel rebars of 88.166 tonnes CO 2e (94.9%), and the material transportation process of 3.168 tonnes CO 2e (3.4%). This research shows that off-site construction activities, i.e. material production and transportation significantly influence the extent of CO 2 emissions in this rigid pavement project. Therefore, it is recommended that strategic efforts for reducing the CO 2 emissions of other typical rigid pavement projects should focus on these two.


Introduction
Global warming has been considered as a real threat to the world. Not only it has a negative effect on living things, but also could damage the environment sustainability. Environmental pollution has been considered as the main contributors to the global warming. There are various types of environmental impact indicators, such as greenhouse gas (GHG) traces, eutrophication potential (EP), acidification potential (AP), human health particles (HH), ozone depletion, and haze [1]. The environmental pollution has also been considered as a major challenge in the construction industry.
Based on data from the USA, the construction projects are accounted 39% of CO 2 gas emissions. It is far greater than the transportation field and industry [2], while data from the European Union mentioned 11% of CO 2 emissions [3] and 18.1% in Australia [4]. The construction process has a significant impact on the degradation of environmental quality. One of the construction processes that produce relatively large CO 2 emissions is road construction project. The CO 2 emission originates from the energy released during the life cycle of the construction project, starting from the production stage, the construction stage, the operational stage, and the demolition stage [5]. Therefore, it is necessary to apply the principle of sustainable development with a green construction perspective. The concept of green construction means environmentally friendly construction through work methods, usage of materials, usage of construction equipment, management, and supervision [6].
The adoption of green construction that implements environmentally friendly construction on an infrastructure project is known as green infrastructure. Green infrastructure is a natural and semi-natural area network, strategically planned with other environmental features, designed, and managed to provide a variety of eco-systemic services and benefits [7]. The application of green infrastructure concept in road projects is known as green road. Green road is a standard to measure sustainable development practices related to road design and construction. Green road is a system which is expected to improve accessibility and mobility, maintain, protect, and improve the performance system, as wel as the environment in the project location [8].
The evaluation of environmental impacts due to CO 2 emissions from road construction, rehabilitation, and operations has become an important issue, and a global concern [9]. This evaluation is done by tracking and measuring carbon levels in each activity. A study on a highway construction project in Michigan used the Project Emission Estimator tool in estimating and calculating carbon footprints [10]. A project in India developed a computer program toolkit (Carbon Footprint Calculator) to measure the carbon footprint of various pavement systems [11]. Some research on carbon footprints on road projects is mostly dominated at the stage of material production and construction. A study on one of the road projects in the US mentioned that, surfacing roads using asphalt has higher emission level of 6730 CO 2e (tonnes) than concrete of 3872 CO 2e (tonnes), and overlay using asphalt of 5598 CO 2e (tonnes) [12]. Considering the unique characteristic of every construction project, the research results may vary among the different projects. The aim of this study is to estimate the total CO2e emissions during the construction process of a rigid pavement project.

Road construction
Roads are lines of lands on earth made by humans with various shapes, sizes, and types of construction as the path for people, animals, and vehicles that transport goods from one place to another easily and quickly [13]. Typically, rigid pavement consists of three layers, i.e. concrete slab, subbase course and subgrade (figure 1). Unlike the flexible pavement, the rigid pavement is not made continuously along the road. This is done to prevent large expansion on the pavement surface which can cause some cracks, and to prevent continuous cracking if there is a crack at one point on the pavement [14]. Another way of prevention is by constructing a joint system to connect each segment of the rigid pavement. There are three joint systems, i.e. jointed plain concrete pavement (JPCP), jointed reinforced concrete pavement (JRCP), and continuously reinforced concrete pavement (CRCP). Typical rigid pavement construction is shown in Figure 1.

Construction of rigid pavement
Some heavy equipment is needed for constructing the rigid payment, e.g. excavators, bulldozers, vibrating rollers, dump trucks, mixer trucks, etc. The biggest use of heavy equipment is usually in the process of quarrying and layering the road foundation. For the next process, even though the use of heavy equipment is not as much as at the sta ge of quarrying, the equipment will be used mainly for handling a larger volume of materials, especially cement and aggregate.
In the rigid pavement construction stage, the sequence of work starts from concrete leaning, formwork installation, geotextile installation, rebar installation, casting, grooving, and cutting. Grooving and Cutting a. Grooving the surface so that the surface will not be slippery. b. Cutting the concrete on the expansion joint. c. Applying joint sealer on the expansion joint.
The production process of each material is different, thus the CO 2 emissions produced will be different as well, depending on how much the volume of materials needed in the construction process. The conversion factors for CO 2 emissions caused during the construction process are shown in the table 2. The scheme of estimating CO 2 equivalent emissions (CO 2e ) used in this study is shown in figure 3. The emissions are reviewed based on off-site and on-site activities. The off-site activities include the production stage of materials, such as cement materials, fine aggregates, coarse aggregates, fly ash/fillers, and rebar, and the transportation of materials, includes emissions from transporting vehicles, such as dump trucks and cement trucks. The on-site activities include the concrete production and concrete laying stages. The production of concrete utilizes batching plant, generators and truck mixers, while the concrete laying uses some equipment such as concrete vibrators, concrete cutters, and generators. This research used the rigid pavement of Palur Flyover project as a case study to estimate the amount of CO 2e gas emissions generated during the construction of the rigid pavement. The project was located in the border of Surakarta -Palur (Karanganyar), with the road section being reviewed was STA. 0 + 350 to 0 + 450 (100 m) with 2 lanes of a 3 m width, and areas of 600 m 2 .
Data was obtained by site observation and interview with contractor personnel on site, e.g. site manager, logistic managers, heavy equipment operators, etc. Observation was made on the carbon footprint during the rigid pavement construction process, including levelling concrete, rebar installation, and casting process. Data obtained from observations include stages of the rigid pavement process, heavy equipment usage and their respective capacities, as well as any other variables that cause CO 2 gas emissions in the process. While interviews were conducted to find out the amount of fuel consumption of each heavy equipment and as well as to identify where the materials come from.
The formulas in equations 1, 2, and 3 are used for estimating the amount of CO 2 emissions produced by each activity.
The ECO 2ePM , ECO 2eTM , and ECO 2ePA are the total of CO 2e gas emissions in material production activities, material transportation, and heavy equipment usage on construction site, in units of tonCO 2e . The volume of material (V) is calculated based on the amount of material needed during the construction activities, both at the material production stage and the construction stage. FC PM , FC TM , FC PA are CO 2 emission conversion factors according to the types of sources, such as materials and fuel. As for the conversion factor of material production (PM), unit in kgCO 2 /ton is used, while unit of kgCO 2 /litre is used for transportation materials (TM), and kg CO 2 /litre is used for heavy equipment on the construction site (PA). TFC TM and TFC PA are the total fuel consumption used in the material transportation and the use of heavy equipment during construction.

Results and analysis
This section explains the results and analysis of the estimate CO2e emissions from the off-site and on-site construction activities.

CO2e emissions in material production
CO 2e emissions produced during the construction process are caused by material production, material transportation, and the use of heavy equipment. Table 3 shows the calculation of CO 2e emissions caused by the production process of the materials of the rigid pavement. It is found that cement contributes the highest CO 2e emissions in terms of material production with 80.040 tonnes CO 2e . This is because of the long production process of cement, where each ton of cement production will produce emissions of 1ton CO 2e [15]. The results of the estimated CO 2 emissions are shown in the figure 4.

Equivalent CO2 emissions in material transportation
The calculation of CO 2e emissions from the transportation of rigid pavement materials can be seen in table 5. In this calculation, it is assumed that the vehicle used is new so that the fuel consumption of each vehicle is the same, and the speed of the vehicle is the same as the speed of the vehicle in an empty load state. The emissions generated by transportation of geotextile materials and joint sealants are considered minimal, and are not taken into account. For the material transportation, cement contributes to the highest CO 2e emissions of 1.037 tonnes of CO 2e . This is because of the long distance of the source of material from Gresik City to the project location in Palur of 341 km. Moreover, as there is a large amount of material needed, causing a great number of transportation trips as well. The CO 2e emissions produced by the transportation of fine aggregate are almost as much as the CO 2e emissions from the cement transport. This is due to the large volume of material and the distance of the material source from Muntilan to Palur, Karanganyar which is 41 km a way, thus causing large amount of energy usage. The CO 2e emissions produced by other materials are presented in figure 5.

On-site construction activities
The CO 2e emissions in the construction stage are produced by the heavy equipment used for the compaction and casting process. The emissions are estimated based on machine operating time, machine fuel consumption per hour, and conversion rates for the fuel used. The amount of CO 2e emissions during the rigid pavement construction can be seen in the table 6.  Figure 6 shows the summary of the estimated CO 2 emissions heavy equipment used in this project. Estimated CO 2e emissions produced during concrete production come from generators that drive batching plants which are 0.479 tonnes of CO 2e . The size of the CO 2 emissions produced depends on the volume of concrete needed. After the concrete production process, the concrete is ready to be distributed to the project location, which will then be laid out. During the distribution process, the heavy equipment that contributed the most CO 2 emissions was the mixer truck which is 0.810 tonnes of CO 2e . This is because the demand for concrete is very high so that the operational time of the truck will also be large, which affects the amount of fuel used. The CO 2 emissions produced by heavy equipment during concrete production and the complete spreading is presented in the figure 6.

Discussion
Emissions generated during the production process, material transportation, and heavy equipment usage are based on the areas of the rigid pavement. The total CO 2e emissions from the construction of the rigid pavement under review is equal to 92.901 tonnes CO 2 e.   Figure 7 shows a schematic diagram revealing the sources and the values of the CO 2e emissions of the rigid pavement under review. In this rigid pavement construction process, the largest CO 2e emissions are produced during the material production, which is 88.166 tonnes CO 2e , equivalent to 94.9% of the total CO2e emissions. The production process of cement and rebar produces very high CO 2e emissions, because they are produced through a long process and require very high energy usage. Innovative efforts are needed to create new technologies that produce alternative materials that have material properties similar to cement, but with more durability and sustainability, so that the CO 2e emissions can be reduced.
Building structures engineering using green cement and wood materials will reduce carbon emissions significantly [17]. One alternative material that is more environmentally friendly is to use CO 2 Eco -Structure. CO2 Eco-Structure is a casting method using CO 2 and silica sand. It consists of two types, i.e. yielding Type I and yielding Type II. Type I is made by injecting CO 2 into silica sand, so that it only has compressive strength. The aim is to be used for areas affected by surface subsidence. Type II is made of Type I which has impregnated with epoxy resin, creating a structure that has compressive strength equals to tensile strength [18].
The use of energy and the highest carbon producer occurs at the operational stage, this should be a concern for the structural engineers to be more innovative in producing designs [19]. Recycled materials for road pavement at the base and subbase layers can potentially reduce global warming by 20%, energy consumption by 16%, water consumption by 11%, and hazardous waste generation by 6% [20]. Similarly, research in Australia states that recycled material which is reused as a coating material has lower emission levels than new material [21]. By adopting the principle of environmentally friendly road planning using the concept of low-impact procedures in producing materials and utilizing recycled materials, it will have great potential to reduce environmental impacts [22] From the case study, it can be learned that the most CO 2 emissions are produced from the process of material production and transportation from the factory to the project site with an estimate of around 98%, while in the implementation of construction on site is only 1-2%. The high emission in the production process is due to the many stages to produce materials in the factory. This is in line with research which found that concrete, aluminium, and steel are among the materials with the highest energy and they are also responsible for a large amount of CO 2 emissions [23]. For this reason, innovation and efficiency during the production period are needed in creating green construction, particularly green road of rigid pavement.