APPLICATION OF A RECENTLY DEVELOPED GEOTECHNICAL CARBON CALCULATOR IN EUROPE APLICAÇÃO DA RECÉM DESENVOLVIDA CARCULADORA DE CARBONO PARA

Recent research regarding soil stabilization has been increasingly concerned with environmental performance. The present paper applies the newly developed CO2(eq) geotechnical calculator, created by the European Federation of Foundation Contractors and the The Deep Foundations Institute, to assess the behavior of three different binders used in the construction of cutter-soil mixing columns, which formed an embankment/bridge transition wedge. The binders were based on ordinary Portland cement, on a blast furnace slag and cement blend and alkali activated fly ash. Results show that the last two binders are significantly more effective, in terms of environmental performance, than the more traditional cement-based binder. Although the blast furnace slag cement, at this early stage of the geopolymeric binders, appears as the most interesting option, the fact that the CO2/cost ratio of both options is very similar stands out.


Introduction
The environmental protection issues are becoming more and more important and European specifications and standards are being stricter which has the necessary implications in the daily work of companies and institutions.The carbon calculator studied in this work aims to encourage the construction industry, namely the geotechnical area, to contribute to the environmental sustainability.The carbon calculator helps companies to do a more conscious choice of constructive solutions, by evaluating the release of greenhouse gases of the different technical activities necessary for their implementation.
The European Federation of Foundation Contractors (EFFC) and The Deep Foundations Institute (DFI) have created a tool to calculate the carbon dioxide emissions of foundation and geotechnical works.It considers all the CO2 sources from materials, energy, transport, equipment mobilization, people transport and waste, being developed using verifiable, standardized data to enable accurate benchmarking of competing project proposals.
Prior to its development there existed no single standardized tool for calculating CO2 emissions for these types of ground works.The aim is not only to evaluate the carbon footprint of a work, but also to establish a comparison between various solutions in order to find the best.Unlike other calculators, its parameters and databases have been developed and targeted for special geotechnical works.One of the points assessed by the calculator is the cost, the key issue for making a comparison of emission per unit of cost.This may be an argument that, together with emissions, becomes decisive for both the contractor and the project owner.
This study is of great importance to the construction industry as it prepares the companies for the forthcoming laws and rules limiting carbon emissions.At present, these regulations do not totally cover this sector, but with increasing environmental requirements, the construction industry will be soon affected.The application of the carbon calculator to R. Bras.Planej.Desenv., Curitiba, v. 4, n. 2, p. 84-93, jul./dez.2015 these particular cases not only allowed a better understanding of its operation, but also led to a greater knowledge of the construction methods.

The EFFC/DFI carbon calculator
Along with all the other carbon footprinting standards, the underlying principle of this calculator consists in the multiplication of activity data by emission factors, as indicated in equation 1.These factors convert the emission associated with each activity into an equivalente amount of carbon dioxide (CO2eq) based on their global warming potential.
where Ai is the activity data (e.g., kwh of natural gas, tons of steel, etc…) and EFi is the emission factor (e.g., CO2eq/kwh of natural gas, etc... -Materials: embodied carbon in materials, due to their manufacturing (cement, steel…) -Energy: energy consumed on the construction site (grid electricity, diesel, gasoline…) 87 R. Bras.Planej.Desenv., Curitiba, v. 4, n. 2, p. 84-93, jul./dez.2015 -Freight: materials transportation, from factory to construction site (trucks, train, boat...) -Mob/demob: equipment's transportation -People's transportation to the construction site -Assets: equipment's manufacturing (depreciation) -Waste: waste transportation, from construction site to treatment site and waste treatment These emission sources are classified into primary or secondary according to relative contribution to the global footprint of the technique: a secondary source represents less than 5% of the total amount of CO2eq, while a primary emission source represents at least 5%.
Generally, primary emission sources are from materials, energy and freight and represent around 90% of total carbon footprint.Since secondary emission sources have a minor influence on the total footprint, the carbon calculator provides simplified methods to estimate their contribution.The first method consists in obtaining the secondary emission source as a percentage of the primary emission source.The second method consists in having standardized activity data by assuming a predefined ratio or value that will represent the activity data needed for a secondary emission source.Nevertheless, a refined mode can always be implemented in more detailed approaches if real values are available for the secondary emission sources.

Methodology followed in this work
In this paper, the carbon calculator was applied to a transition wedge project with cutter soil mixing (CSM) columns.Transition zones between embankments and bridges or viaducts are often treated with cemented soils compacted in a swedge to provide a smooth transition between a flexible foundation (as a soil embankment) and rigid structures like bridges or viaducts generally founded on piles.In this case, the smooth stiffness transition is implemented by using CSM columns whose length is maximum near the bridge/viaduct abutment and decreases as the distance to the abutment increases.
Having defined the type of geotechnical construction to be analysed by the carbon calculator, the different emission sources identified above should be conveniently quantified.
Being materials the source which represents the larger portion of CO2 it was decided to keep the other sources constant and analyse three different materials as described below.This allowed a comparison between different solutions for the binder used in the CSM columns.R. Bras.Planej.Desenv., Curitiba, v. 4, n. 2, p. 84-93, jul./dez.2015 The quantities of each material were therefore calculated in detail and introduced in the carbon calculator, while standard values were assumed for the other sources which were kept constant in the three analysis.

Materials description
The following binders were considered in this work: -Ordinary Portland cement (OPC) without main additions also named as CEM I by ASTM C 150 ( 2004); -Blast furnace low-heat/sulfate-resistant cement CEM III/B 32,5 (EN 197, 2000); -Geopolymeric binder made by the alkaline activation (AA) of fly ash; The first two materials are recommended by Bauer ( 2004) as adequate for CSM works, the third is a new binder commonly associated with a low carbon emission (TURNER; COLINS, 2013).In fact, while OPC production is responsible for emission the almost 1 ton of CO2 per ton of OPC produced, AA uses a waste by-product from thermoelectric power plants (fly ash).
Blast furnace cement is created through the addition of granulated blast furnace slag (GGbs) with Portland cement clinker and gypsum reducing the amount of Portland cement clincker that generates such amount of CO2 emissons.Blast furnace slag is a byproduct of the iron and steel manufacturing process.In the production of steel, iron orea mixture of oxides of iron, silica, and aluminatogether with a fuel consisting of coke, natural gas, oxygen and pulverised coal and also limestone as a fluxing agent, are fed into a blast furnace, which consists of a large vertical chamber through which large volumes of hot air are blasted.
Generally a blast furnace operates on a continuous basis and produces approximately 250 -300 kg of slag/ton of iron produced (worldcement.com).In the particular case of CEM III/B, there are 27% of Portland cement and 73% of GGbs, which substancially reduces its carbon footprint.
Geopolymers are inorganic polymeric materials, as defined by Davidovits (1991), created by the chemical reaction between alumino-silicate oxides and alkali metal silicate (iv) bonding of undissolved solid particles and hardening into a solid structure.This binder has been recently studied for soil improvements works as described in Cristelo et al. (2011) and Rios et al. (2015).

Geometric and mixture properties
In this study it was assumed two transitions wedges in each side of the bridge in a length of 30 m and 20 m of width, resulting in 1200 m 2 of treated area.The columns disposed in quadratic mesh of 3.5 m have an average length of 6 m which corresponds to 600 m of columns.In Table 1 the geometric data of the columns is presented where a standard CSM equipment was considered.In the three projects, it was considered 0,4 m 3 of grout per m 3 of treated soil.The properties of the grouts are indicated in Table 2.The properties of the geopolymeric binder were obtained from the G8 mixture of Cristelo et al. (2013).The other information required by the carbon calculator is similar for the three solutions so it will not influence the comparison of footprints between solutions.For that reason, data related to the location and respective distances of transport, equipments, wastes, people, etc… are not detailed in this paper.

Results and discussion
In agreement with most geotechnical techniques available in the carbon calculator, in the case studied in this paper the most important emission source is materials, followed by energy with a much lower contribution, as presented in Figure 1 for the CEM I solution although similar distributions were also found for the other two binders.As a consequence, according to the classification indicated above, only materials and energy are considered primary emission sources, while the others are secondary with less than 5% of contribution to the global carbon footprint.This highlights the importance of studying CO2 emissions of different material solutions available for the same geotechnical technique.OP cement, blast furnace slag cement and alkali activated fly ash were used to improve the mechanical behaviour of transition wedge, through cutter-soil mixing columns.
The financial analysis showed that the cement-based solutions are more advantageous.
However, it should be noted that the application of alkali activation to soil improvement is still at an early stage, i.e. it is not fully optimised.For instance, the use of industrial waste as the main activator component is being addressed by several research teams, which would significantly decrease the financial and environmental cost of this solution.
A thorough assessment of the mechanical performance of each type of binder should be carried out, as well as a financial and environmental assessment of their respective applications in different techniques, like jet grouting or deep mixing columns.
The main conclusion from the presented results is that the alkali activated ash grout is already competitive, at such an early stage of its development, with traditional cementbased grouts.Also significant is the capacity of this new carbon calculator tool to quantify and help defyning, based on solid and supported argumentation, the ups and downs of any binder and/or technique to be used in geotechnical works.

Figure 1 -
Figure 1-Total carbon footprint divided by the different emission sources evaluated by the carbon calculator (CEM I case)

Figure 2 -
Figure 2 -Total carbon footprint obtained in CSM technique using different binders

Figure 3 -
Figure 3 -Total carbon footprint per project cost obtained in CSM technique using different binders

Table 3 :
Material costs