Effect of Different Material Schemes on Carbon Emissions in Construction Material Production Stage

Introduction: Building energy consumption accounts for a large proportion of global energy consumption, and it is urgent to reduce building carbon emissions. There are many different components in the Building, each of which produces a somewhat different amount of carbon emissions, such as column, beam, floor, exterior wall and interior wall. This Paper is focusing on looking for the components’ differences in carbon emission in order to provide some valuable advises in choosing building materials. Methods: Using the building information model, the sample building is divided into five parts: column, beam, floor, exterior wall and interior wall. Firstly, the quantities of each part of the building is calculated from building information model. Secondly, the method of permutation and combination is performed by choosing different materials including concrete, steel, wood, brick and glass, and then forming 14 schemes. Finally, carbon emissions at production stages are calculated of all 14 schemes by known carbon emission factors. Conclusion: The average proportion of each part of carbon emissions is obtained both with the carbon emissions from different materials. Choosing the lowest and highest theoretical scheme in order to analysis the influence of different materials on carbon emissions in construction production stage, so that the effective data reference for building energy saving and emission reduction can be concluded.


Introduction
Construction, industry and transportation are the three energy consumption industries in cities, among which construction accounts for about 40% of global energy consumption and 30% of greenhouse gas emissions are related to construction [1]. Accordingly, the urgent need is to calculate and analysis the building carbon emission correctly while providing reduction measures [2]. From the viewpoint of design solutions and marital selection, this paper analysis the effect of different material selection schemes on carbon emissions in material production stage [3].
Building carbon emissions are derived from four stages including material production stage, construction stage, operation stage, demolition and recovery stage [4], and the proportion of carbon emissions in each stage is about 5%-20%, 0.4%-4%, 75%-95% and 0.05%-5% respectively. Therefore, the annual carbon emissions per unit accounts for separately as 55%-90%, 2%-12%, 5%-32% and 0.2%-25% based on 50-years-building [5]. The sum of carbon emissions both in construction stage and demolition and recovery stage is only 9%, which can be ignored. Because of the large percentage of carbon emissions in material production stage, this paper is focused on the effect of different material selection schemes on carbon emissions in that particular stage.
In order to facilitate the calculation process, the building model has been hypothesized as follows: 1) from the viewpoint of foundation construction, there's no difference between varies schemes; 2) glasses are chosen for all the windows and doors with frame and skeleton ignored; 3) if glasses are chosen for internal and external walls, vertical boat and bracket steel dosage should be ignored; 4) stairs and roofs use uniform parameters and which do not count in; 5) indoor water, electricity and heating pipelines, decoration and home decoration are consistent, which does not count in.

Basic Information
There are 5 floors above-ground and each floor is 3 meters high with a single storey area of 674.14 m² and a gross floor area of 3370.7 m². The model (see Figures 1 and 2) is established.

Building Data
The building is consist of five parts including columns, beams, floors, external walls and internal walls. Each material selection scheme with data is derived from the building, and shows in table 1.

Combined Scheme Inventoried
There can be 288 combination schemes theoretically according to the material selection listed above. Considering the construction feasibility and data comparability, 14 schemes are chosen as representative to conduct detail analysis and comparison shown in Table 2.

Calculation of Each Scheme
According to the statistic quantities, carbon emission for each scheme is calculated through carbon emission factor (see table 4 [6]). The data above is sorting by carbon emission from small to large, and it is illustrated in carbon emission comparison table (see  table 5) and in average carbon emission ratio chart (see Figure 3) of each different component.

Best and Worst Scheme and Comparison
The theoretical best and worst scheme (M and N) are found by the carbon emission data listed as follows:  All the schemes are summarized and sorted, as shown in Figure 4.

Conclusion
Building production phase is also called embodied carbon of building, in which the carbon emission is calculated through different schemes, comes out the conclusions: (1) Low density and small carbon emission factor building materials can reduce carbon emission significantly, such as wood and concrete blocks with low density and small factor. (2) Minimize the size of building components when meeting the function. (3) Slab is the largest carbon emission component, which should be considered at the outset, then should be beam, external wall and column. (4) Carbon emission of wood and concrete blocks is much lower than that of H-beam steel, concrete and clay bricks. So these two materials can be preferred when choosing building materials. Wood is a kind of renewable resource which causes little damage to ecosystem and creates less pollution than other materials such as steel and concrete. (5) From the viewpoint of lower the carbon emission factor, improving the manufacturing technique of building materials, elevating the energy conversion efficiency in production process, and optimizing logistics allocation technology can reduce the carbon emission.