Int J Life Cycle Assess DOI 10.1007/s11367-016-1076-y
ROADWAYS AND INFRASTRUCTURE
Life cycle assessment of non-traditional treatments for the valorisation of dry soils in earthworks Gaëtan Blanck 1,2 & Olivier Cuisinier 1 & Farimah Masrouri 1
Received: 10 September 2015 / Accepted: 22 February 2016 # Springer-Verlag Berlin Heidelberg 2016
Abstract Purpose Sustainable development principles are leading earthwork companies to use all-natural materials extracted from the construction site to build the infrastructure. Natural materials with low characteristics must be improved. For dry soils, the common solution is to increase the compaction energy or add important quantities of water to reach the target dry density and bearing capacity. To reduce the environmental impact of their activities, the use of industrial organic products has been proposed. The aim of this study was to assess the potential benefits that could be expected from the use of these non-traditional treatments in earthworks with a wellrecognised environmental impact assessment methodology. Methods Three non-traditional products were selected as follows: an acid solution (AS), an enzymatic solution (ES) and a calcium lignosulfonate (LS). For each of these categories, geotechnical properties such as compaction, bearing capacity, unconfined compressive strength and stiffness were first determined. Based on these results, the construction strategy for which non-traditional additives lead to greater improvement of soil properties was defined. The environmental balance of each option was then determined via a comparative process life cycle assessment study that considered ten impact categories. Results and discussion An experimental study showed the ability of enzymatic and lignosulfonate additives to improve Responsible editor: Holger Wallbaum. * Olivier Cuisinier
[email protected]
soil characteristics with significant savings of water at the construction stage. The purpose of the study was also to compare the global environmental impact of each treatment strategy defined from laboratory investigations. The life cycle assessment results showed that some construction strategies lead to a significant reduction in the environmental impact compared with the reference strategy. However, these environmental improvements are strongly linked to the choice of the construction strategy and site conditions as discussed in the sensitivity analysis. Conclusions Within the three tested non-traditional additives, enzymatic and lignosulfonate treatments showed an association of technical and environmental interest for the compaction of dry soils. As demonstrated in the sensitivity analysis, these benefits are achieved when the production and transport steps have limited environmental impact. Thus, despite an important transportation distance for enzymatic additive, the small quantities that must be used (0.002 % by dry weight) have a limited contribution on the global environmental impact. In contrast, the production step strongly impacts the treatment with lignosulfonates. Moreover, environmental interest remains strongly dependent on the site conditions and construction strategy, which is why the adopted methodology can accurately perform an initial evaluation before implementing a soil treatment with a non-traditional product. Keywords Compaction . Earthworks . Environmental impact . Life cycle assessment . Non-traditional additives . Soil treatment
1 Introduction 1
LEMTA, UMR 7563 Université de Lorraine/CNRS, 2 rue du Doyen Marcel Roubault, 54518 Vandoeuvre-lès-Nancy, France
2
DTP, 1, Avenue Eugène Freyssinet, 78280 Guyancourt, France
In earthworks, sustainable development will play a larger role in future project design and in the assessment of technical
Int J Life Cycle Assess
solutions by contractors. Currently, the reduction of the environmental impact of earthworks is a growing issue. One of the major challenges facing earthwork companies is the need to use a majority of natural materials extracted within the construction site, including fine soils with very low geotechnical characteristics or extreme hydric states. On the one hand, wet soils are commonly improved by the addition of quicklime, cement or fly ash; on the other hand, dry soils must be wetted and/or compacted, which requires a high level of energy. However, sustainable development principles require a reduction in the consumption of water and non-renewable energies as a way to limit the global environmental impact. In this context, soil treatment with various non-traditional additives has been considered. These additives are diverse in nature, and some of them are derived from the industrial transformation of renewable raw materials. They are also beneficial owing to their efficiency at low dosages, thereby limiting the environmental impact and cost of their use. However, before in situ implementation, the environmental benefits of such additives must be compared with classical construction solutions that would achieve the same performance. 1.1 Literature review Various additives have been tested for improving the compaction of dry soils to avoid dust generation and for increasing the durability of uncovered roads (Scholen 1995; Santoni et al. 2002). Additionally, additives have been tested to stabilise erodible soils (Velasquez et al. 2006). Mechanical properties, such as unconfined compressive strength (Santoni et al. 2002; Tingle and Santoni 2003) or swelling potential of plastic soils (Katz et al. 2001; Rajendran and Lytton 1997) have also been studied. Tingle and Santoni (2003) listed seven non-traditional categories based on the major active component and classified them as salts, acids, enzymes, lignosulfonates, petroleum emulsions, polymers and tree resins. Acids are low-pH aqueous solutions containing sulfonated molecules such as naphthalene or limonene (Katz et al. 2001). For enzymatic solutions, the presence of proteins was confirmed by Velasquez et al. (2006). Lignosulfonates are organic polymers derived from lignin extracted by the sulphite processing of cellulose in the wood pulp and paper industries. According to Tingle et al. (2007), petroleum emulsions contain asphalt or synthetic iso-alkane fluids suspended in emulsions by a surfactant, polymer emulsions contain vinyl acetates or acrylic copolymers and tree resins are diverse, emulsified by-products of the timber and paper industries. Nevertheless, many of these products also include secondary additives such as surfactants or ultraviolet inhibitors, which may react with the soil minerals or modify the soil water properties and thus influence the mechanical behaviour of the treated soils.
To determine the best construction strategy from both technical and environmental aspects, it is also necessary to consider the environmental impact of treatments to account for sustainable development issues during the design phase of a project. One possible way is based on the life cycle assessment (LCA) approach, which permits the global impact of a system to be assessed from the extraction of mineral resources towards its end of life (AFNOR NF EN ISO 14040 2006; AFNOR NF EN ISO 14044 2006). In civil engineering, LCA research focused on buildings or structures are widespread (Erlandsson and Borg 2003), whereas studies dedicated to earthworks are relatively scarce. Earthwork stages were considered in a case study involving the construction of a building’s platform (Li et al. 2010). This study includes the excavation of 60,000 m3 of soil and the construction of retaining walls. The study uses the endpoint ‘Environmental Priority Strategies’ (EPS) (Steen 1999) based on the monetization of environmental impacts. The results indicate that the phase of earthworks (excavation and backfilling) represents 26 % of the environmental impacts and mainly affects human health through dust emissions. In the literature, many life cycle assessment methodologies are available, and current trends look beyond the single environmental aspect of integration cost and consider social aspects; see, for example, Klöpfer (2008) or Hendrickson et al. (2006) for economic input–output analysis. The field of road construction is relatively rich in LCA studies as detailed, for example, by Kucukvar et al. (2014), Noori et al. (2014) and Muench (2010), who listed 14 LCA studies published between 2000 and 2009. Mroueh et al. (2001) compared four variants for improving road sub-base founded on compressive clay. The available solutions were soil substitution with aggregates, soil stabilisation with cement, soil improvement by deep mixing or vertical drains. The environmental impacts were evaluated in 12 categories (NOx, dust, CO2, SO2, fuel, etc.). The most harmful solution was that corresponding to soil stabilisation with cement, followed by deep mixing, the solution to replace the ground with granular materials and finally, drainage. According to the authors, the first two solutions are particularly impacted by the use of cement, whose production consumes much energy and generates significant CO2 emissions. Some studies were conducted on the use of substitute materials for natural aggregates such as fly ash, blast furnace slag or recycled concrete (e.g., Muench 2010; Chowdhury et al. 2010; Fevre-Gautier et al. 2012). An example of a result can be illustrated by the energy needed in the case of road construction. Mroueh et al. (2001) compared different pavement structures involving fly ash, blast furnace slag and recycled concrete. Their results showed that the use of substitute materials does not always lead to a reduction in energy consumption. The authors also found evidence that the manufacturing phase of construction material is the most consumptive phase compared to the construction step.
Int J Life Cycle Assess
1.2 Aim of the study Even if some studies showed that non-traditional products could improve the geotechnical characteristics of fine soils, there is a lack of knowledge on their optimal conditions of use and the relative environmental benefits they could bring compared with conventional solutions. In this context, the main concern of this study was to determine the conditions under which the use of non-traditional stabilisers could be beneficial from both technical and environmental points of view. This study is performed to test the technical and environmental performance of non-traditional products and the real environmental benefits with regard to site conditions and does not consider in a first approach a life cycle cost analysis. The selected methodology is a process-based LCA defined in the French standard for environmental evaluation of construction materials (AFNOR NF P01-010). This standard selected 10 environmental impact categories such as energy consumption, water depletion and air pollution. 1.3 Selection of additives The emphasis was put on non-traditional additives that would lower the environmental impact of soil treatment in the earthworks industry. Therefore, only the products derived from the transformation of renewable organic matters—acids, enzymes and lignosulfonates—were considered. For each of these categories, geotechnical properties such as compaction, bearing capacity, unconfined compressive strength and stiffness were first determined to characterise the technical benefits that could be expected from those products. These results permitted construction strategies to be defined for their optimal use. The environmental balance of each option was then determined. These analyses were carried out from different scenarios of use and compared with a reference scenario that excludes the use of treatment product. A sensitivity analysis was performed to quantify the relative contribution of each stage of the life cycle and test the influence of the hypotheses that were taken. The emphasis was also put on the effect of the life cycle inventory (LCI) input data related to the additives, especially for enzymatic treatment, for which input data do not directly exist.
2 Material and methods 2.1 Non-traditional additives The acid solution (AS) tested in this study was a concentrated solution of sulfuric acid mixed with D-limonene, a by-product of citrus processing. For this kind of product, typical dosages tested in the literature comprise between 0.01 and 0.2 %. As shown by different authors, unconfined compressive strength (UCS) compaction and clay mineralogical properties were not
affected by dosage increase (e.g., Rauch et al. 2003). Thus, a dosage of 0.01 % of concentrated product by dry weight of soil was tested in this study. The tested enzymatic solution (ES) is a biodegradable brown aqueous solution with an acidic pH of 4.6. For this type of product, typical dosages comprise between 0.002 and 0.1 %. However, according to Tingle and Santoni (2003) and Velasquez et al. (2006), the geotechnical properties of soils treated with an enzymatic additive were independent of the application rate. Therefore, a dosage of 0.002 % was selected. To guarantee these very low dosages, the concentrated product was first diluted in water down to the level of real conditions in the field. The product was mixed with a quantity of water corresponding to a 3 % increase in the soil water content. The tested lignosulfonate (LS) was a biodegradable, organic and water-soluble calcium salt used in powder form. The insoluble components were less than 0.5 %, the moisture content was approximately 7 % and the reducing sugar content was approximately 7 % by dry weight of lignosulfonates. Previous results indicated an optimal additive content of 5 % (Santoni et al. 2002; Surdahl et al. 2007) for improving the UCS. However, Gow et al. (1961) demonstrated that maximum density and bearing capacity values were obtained for a dosage of 0.5 %. For LS treatment, three dosages (0.5, 2.0 and 5.0 %) were considered. 2.2 Tested soil A natural, fine-graded soil of low plasticity often encountered in earthwork projects in the Paris Basin, classified as ML in the Unified Soil Classification System (USCS), was tested in this study (Table 1). X-ray diffraction investigations indicated that the main minerals were quartz and calcite (8.0 % by weight determined by calcimetry). The 17.8 kN m−3) by modifying the water content of the soil and/or the compaction energy (Table 3). 1 The soil is treated with 0.002 % of enzymatic product diluted in the water used for treatment. The required mass water content for compaction is then only 11.5 %. 2 The soil is first mixed with some lignosulfonate as a dry powder in a first step, and the water content is then increased to 11.5 % before compaction. 3 Water is added up to a target water content of 14 %, then the untreated soil is compacted to the target dry density with standard Proctor energy. 4 Water is added up to 11.5 %, and the compaction energy is increased beyond standard Proctor energy to reach the target dry density. Laboratory tests demonstrated that this can be accomplished if the compaction energy is increased by 70 %. Thus, for enzymatic and 2.0 % lignosulfonate treatments, compaction can be carried out at a water content of 11.5 % instead of 14.0 %. This difference of 2.5 % of water content represents water savings of 44.5 m3 for 1000 m3 of compacted soil. This is all the more significant because dry soils are mostly found in arid areas where access to water is a key issue. Moreover, it is also possible to compact the untreated soil at a target water content of 11.5 % and provide a 70 % increase in compaction energy. In this case, the use of non-traditional stabilisers can lead to a reduction in the energy consumed on the construction site. Significant savings can be expected from non-traditional stabilisers. However, the production of the stabilisers, their transport and the modification of the construction procedures could also generate environmental impacts that must be assessed over the built embankment life cycle. The main goal of the next section is to compare the impact of each of the four construction strategies listed earlier.
Int J Life Cycle Assess
Dry unit weight (kN/m3)
19.0
untreated
0.01 % AS
0.002 % ES
2.0 % LS
dry unit wt.
Bearing cap.
60
18.0
50
17.0
40
16.0
30
15.0
20
14.0
10
13.0 8.0
10.0
12.0
14.0
16.0
18.0
20.0
Bearing capacity (-)
Fig. 1 Impact of treatment with non-traditional stabilisers on compaction characteristics and un-soaked bearing capacity
0 22.0
Water content (%)
3 Life cycle assessment
3.1 Definition of the system
The applied approach is governed by standards of life cycle assessment (ISO 14040 and ISO 14044). The life cycle of a system is commonly divided into five stages: the extraction of raw materials and production of additives and fuels; the transportation of these products and the construction, the use of the system and its end of life. To calculate the environmental impact of a system, the first step of LCA aims to identify and quantify its inputs and outputs. The life cycle impact assessment (LCIA) procedure can then be conducted based on collected life cycle inventory data. In this study, the method used for the LCIA is defined by the standard NF P 01-010 (AFNOR 2004) partially based on CML 2001 methodology (Guinée et al. 2002). It relies on ten indicators: energy consumption, mineral resource depletion, water depletion, solid waste production, climate change, terrestrial acidification, stratospheric ozone depletion, photochemical oxidant formation, air pollution and water pollution.
The main object of the study is to compare the use of nontraditional additives with common embankment construction practices. To compare the environmental impact of the different construction strategies, the first step was to define the studied system and its boundaries. The functional unit is a volume of 1000 m3 of compacted soil at the same target dry density of 17.8 kN m−3. For all tested construction strategies, the initial conditions were the same, and an initial water content of 9 % was considered. All life cycle steps, which were identical in the four construction strategies, were excluded from the system, and the other ones were included in the analysis. The first stage of the life cycle corresponds to the extraction of the volume of soil required to build the embankment, the extraction of raw materials, the manufacturing of the treatment products, the production of the construction machines, the production of energy and the water supply. In this study, all steps regarding the extraction of the soil were similar among all strategies and were thus excluded from the system. Because the duration of the construction operations was short compared to the life duration of the machines, this step was also excluded from the system. Thus, only the production and transportation of the non-traditional stabilisers, energy and water supply were considered in the analysis (Fig. 3). The second stage covers the transportation to the construction site of the extracted soil, the machines, the treatment products, etc. Because the machines to be used are not specific to perform the treatment of the soils with the non-traditional products, they are assumed to be directly available on the construction site; thus, machine transportation was excluded from the analysis. Therefore, only the transportation of the treatment products and water was retained in the system.
Table 2 Impact of non-traditional products on compaction references of the tested soil Treatment
Untreated Acid solution Enzymatic solution Lignosulfonate
Dosage
wopt
γdmax
(%)
(%)
(kN/m3)
Bearing capacity at wopt (%)
/ 0.01 0.002 0.5 2.0 5.0
15.5 15.0 14.5 15.0 13.5 14.0
18.2 18.3 18.6 18.4 18.5 18.3
15 19 14 13 14 5
Int J Life Cycle Assess 19.0
Fig. 2 Definition of different compaction strategies to meet a compaction objective of 98 % of the maximum dry density of the untreated soil
untreated 0.002 % ES
18.0
17.0
compaction
Dry unit weight (kN/m3)
2.0 % LS
16.0 wetting wi = 9.0 % 15.0 8.0
10.0
12.0
14.0
16.0
18.0
20.0
22.0
Water content (%)
The implementation phase is related to the construction of the embankment. It includes all stages prior to the final levelling. Only the operations related to the treatment (product spraying and mixing) of the water content adjustment and the compaction were considered. All other operations were regarded as identical whether non-traditional products were used. The next stage considered the operations linked with the life of the embankment, including all potential operations of maintenance. This stage also included the emissions in the air or water due to potential leaching and degradation of the treatment products. Finally, the last stage was related to the end of life of the embankment. The progress of these two stages was not significantly altered by the construction technique. They were thus excluded from the system.
The inputs considered are the treatment product, the water and the fuel. The volume of all other inputs was regarded as similar for all construction strategies. As an example, the volume of soil required for the construction is given by the final volume of the embankment to be built. The data concerning the consumption of the different machines and their productivity were provided by the French company DTP a subsidiary of Bouygues Construction.
3.2 Life cycle inventory
3.2.2 Amount of fuel for transportation operation
The inventory step consists of an estimation of the different inputs required during the life cycle of the system. For each input, data on their life cycle inventory must be collected.
Paris (France) has been defined as the location of the project for the calculation of transport distances. The water was pumped from a river located 1 km from the project and transported directly by sprinkler. The enzymatic product was
Table 3 Construction strategies to build the embankment with a target dry density of 17.8 kN m−3 1 2 3 4
Treatment with 0.002 % enzymatic product Treatment with 2.0 % lignosulfonate Untreated soil Untreated soil
3.2.1 Amount of water and non-traditional additives The amount of water is directly calculated from the difference between the initial and final water content. The estimations of the quantities of additives were based on the amount of each product required for the treatment of the functional unit.
Initial water content wi (%)
Compaction water content wf (%)
Compaction energy –
9.0
11.5
Standard Proctor energy
9.0
11.5
Standard Proctor energy
9.0 9.0
14.0 11.5
Standard Proctor energy Standard Proctor energy increased by 70 %
Int J Life Cycle Assess Fig. 3 Diagram of the system considered for the life cycle impact assessment step
Petroleum raw material
Vegetal raw material T
T
Site preparation, transportation of workers, ...
Transformation plants
Oil refinery T
T
Water
T
T
Embankment
Soils T
Production of machines
Fuel consumption of machines Sprinkler Spreader Stabilizer Compactor
manufactured in the USA (California). Transportation therefore requires travel by land and sea routes (Table 4). The production of lignosulfonate was located in a factory in Karlsruhe (Germany), and only road transport has been retained for the purpose of the study. Regarding road transportation, the calculation of fuel consumption was performed of the AFNOR recommendation (AFNOR FD P01-015 2006), which considers trucks with a load capacity (Cr) of 24 t, gas oil consumption of 38 L per 100 km and an unloaded return rate of 30 %. For the transport of a load Q, the amount of gas oil consumed qg is given by the following relationship (Eq. 1):
qg ¼
38 1 Cr 2 2 ⋅d⋅ ⋅ þ þ 0; 3 : :N 100 3 24 3 3 Q N¼ Cr
ð1Þ
Transport distance of water and non-traditional products
Water Enzymatic product Lignosulfonate
Travel distance by road (km)
Travel distance by sea (km)
1 2950 560
0 8000 0
T
Transportation step System boundary Element excluded from the system Element included in the system
a consumption of 0.0026 kg per ton of transported product per kilometer. Therefore, the amount of fuel qfuel required for travel by sea is given by the following relationship: qfuel ¼ 0:0026⋅d⋅Q
ð2Þ
The transportation of water between the pumping area and the construction site is facilitated by a water spraying machine. The fuel consumption (Eq. 3) is determined from the hourly consumption ch (L h−1) of the water sprayer along with its speed v (km h−1) and the travel distance d (km). It is a function of the total amount of water Q (L) and the volumetric capacity of the water sprayer Cr (L). In this study, ch = 8 L h−1, Cr = 15,000 L, v = 30 km h−1 and d = 1 km. qgasoil ¼ ch ⋅
where d is the distance between the manufacture and construction sites and N is the number of trucks required. Following AFNOR FD P01-015 2006, only boats with a capacity higher than 80,000 t are considered. Their power is equal to 0.11 kW per ton with a speed of 15 km h−1. The energetic value of the fuel used is 0.35 kg kW h−1. This gives
Table 4
Excavator Dumper Motor scraper Grader ...
2d Q ⋅ v Cr
ð3Þ
3.2.3 Amount of fuel required during the construction stage Construction operations are performed via the use of several machines. An embankment is constructed by successive layers of a few tens of centimetres, each with a target dry density of 17.8 kN m−3. In our study, we selected a thickness of 0.30 m for each layer of soil, which is a standard value for the type of soil considered (Corté and Havard 2003). For each layer, the same unit operations are considered. First, the soil is spread all over the surface. The soil water content is then adjusted with the water sprayers up to the target value. The soil stabiliser is used to mix the added water, soil and treatment product. For lignosulfonate, a spreader is required. The last stage of construction corresponds to the compaction of the soil layer to the desired dry density.
Int J Life Cycle Assess
The fuel consumption of the water sprinkler during the water spraying is calculated by Eq. 5: qgasoil ¼ ch ⋅
qgasoil
Su f ⋅n Sh
Vuf ¼ ch ⋅ e ⋅n v⋅L
ð4Þ
ð5Þ
where ch (L/h) is the hourly consumption. Suf (m2) is the surface to be wetted. Sh (m2 h−1) is the total surface covered by the water sprinkler during 1 h. Vuf (m3) is the volume of the functional unit (1000 m3). e (m) is the thickness of the soil layer to be compacted. v (m h−1) is the speed of the water sprinkler. L (m) is the width of the water sprinkler. n is the number of passes. The spreader fuel consumption was also calculated with Eq. 5. The hourly consumption ch is 18 L h−1. Only one pass is required for a lignosulfonate dosage of 2 %. The width L of the binder spreader considered in this study is 2.1 m. The soil stabiliser hourly consumption ch is equal to 57 L h−1, with mean productivity of 250 m3 h−1. The volume of gasoil needed in the case of the functional unit defined in this study is given by this relationship: qgasoil ¼ ch ⋅
Vuf Vh
ð6Þ
The consumption during the compaction stage was estimated with French technical guides, which provide the conditions to reach the desired density as a function of the class of compactor, the nature of soils and the thickness of the compacted layer. The consumption of the compactor is given by the following relationship: qgasoil ¼ ch :
Vuf k⋅Q⋅L
ð7Þ
where Q (m3/h m) is the productivity of a compactor with a width of 1 m.L (m) is the width of the drum of the compactor.k (−) is a practical coefficient of efficiency, taken to be 1 in this estimation. For the compactor type retained in this study, class V5 according to French technical guide (Corté and Havard 2003), the hourly consumption was evaluated at 15 L h−1 for a width of 2.1 m. The analysis showed that the amount of water, treatment products and fuel fluctuates as a function of the construction strategy (Table 5). An initial analysis of LCI results showed that the use of non-traditional stabilisers induces a large reduction in the consumption of water (44,500 instead of 89,000 L for untreated soil (strategy 3)). Additionally, a large difference appears in the fuel consumption, which especially depends on the number of passes of the stabiliser and the consumption of
the trucks. For example, for the comparison of the use of untreated soil at optimal water content (strategy 3), the water content adjustment from 9 to 14 % must be performed in two passes (associated fuel consumption = 456 L) according to the technical requirement. In comparison, the treatment with the enzymatic product (strategy 1) required only one pass (associated fuel consumption = 228 L). Therefore, the use of the enzymatic product leads to a reduction in the fuel consumption of approximately 50 % during the construction stage. For the lignosulfonate treatment, two passes of stabiliser are required. One must be conducted after the water content adjustment, and the second is conducted after the lignosulfonate has been spread over the soil. Thus, the fuel consumption of the soil stabiliser is equivalent to the untreated case because two passes are made for the water adjustment of untreated soil (strategy 3). Moreover, the transportation step of 35.7 t of lignosulfonate generates an additive consumption of 379 L of fuel. At this stage of the study, it appears that the lignosulfonate treatment induced the highest fuel consumption of the four studied strategies. Therefore, the lignosulfonate treatment will generate a higher environmental impact than untreated strategy 4, which features an increase in compaction energy for the same water consumption as strategy 2. For the other comparisons, the choice between two construction strategies is not as clear because balance can occur between water and energy consumption or between the environmental impacts of the treatments products. To determine the better construction strategy with regard to environmental issues, it appeared to be necessary to continue the study with the environmental impact assessment step. The completion of this last step required life cycle inventory data for each of the previously quantified inputs. 3.3 Origin of LCI data This section describes the origin of the LCI data and hypothesis used in the impact calculation. The LCI of water depends on its origin. For construction purposes, water can be taken from drinking water networks, rivers or lakes or pumped into a borehole. It is also possible to anticipate the needs of the site by creating ponds to store rainwater. Owing to the diversity in the means of supplying water and the lack of statistical data on the origins of the water used on construction sites, the environmental impact associated with the water supply step will not be considered. This choice will be discussed in Section 5. The LCI of the enzymatic product used in laboratory tests was unavailable. However, it was shown in a specific study that this product alters the compaction characteristics of soils owing to its surfactant properties (Blanck et al. 2014). It was also demonstrated that the effects of the treatment with the enzymatic product are equivalent to those of a common surfactant, sodium dodecyl sulphate (SDS). Therefore, the LCI of
Int J Life Cycle Assess Table 5
Inputs quantities for the different construction strategies
Strategy number
1
2
3
4
Treatment
2.0 % lignosulfonate
Water (L)
0.002 % enzymatic product 44,500
44,500
Untreated soil standard energy 89,000
Untreated soil 170 % standard energy 44,500
Additives (kg) Fuel (L)
Trucks
35.6 2
35,600 379
– –
– –
Water sprinkler Soil stabiliser
2.9 228
2.9 456
5.2 456
2.9 228
Compactor Binder spreader
30 –
30 2.9
30 –
51 –
0.7
–
–
–
Heavy fuel (kg)
the enzymatic product was regarded as equivalent to the LCI of SDS available in Stalmans et al. (1995) and supplemented by data coming from Pittinger et al. (1993) regarding water consumption. The LCI of lignosulfonate was obtained from Modahl and Vold (2011). These data were calculated for a factory located in Sarpsborg, Norway.
4 Results Construction strategy number 1 based on the use of the enzymatic product led to a reduction in seven indicator categories (Fig. 4a) compared with the standard construction strategy without treatment (number 3). As an example, energy consumption is reduced by 40 %, from 18.8 to 10.7 × 103 MJ, and water consumption decreased from 9.1 to 4.6 × 104 L. In contrast, the production of waste increased by a factor of 4.5 with the use of enzymatic product. Nevertheless, this corresponds to an increase of only 2.8 kg per 1000 m3 of compacted soil, which is very low compared with the 5000 kg of waste (industrial, municipal and construction wastes including wasted soils) produced in 2 012 per pe rson in Euro pe (Eurostat 20 15). Construction strategies 1 and 4 have equivalent environmental impacts (Fig. 4b). Compared with strategy 3, the lower water content required only one wetting operation instead of two. Despite the 170 % increase in the required compaction energy, the environmental impact of both strategies is very similar. These results showed that the benefit of using the enzymatic product depends directly on the construction strategy. It leads to a reduction in the environmental impact when used as a substitute of soil wetting and compaction at standard Proctor energy. For the LCIA of the lignosulfonate treatment (strategy 2), a large increase in the environmental impact of the embankment construction can be seen compared with the reference strategy (number 3). For example, the energy consumption is
estimated to be 927 × 10 3 MJ instead of 18.8 × 10 3 MJ (Fig. 5). Despite the savings in water during the construction stage, the quantity of water consumed during the whole life cycle is significantly higher for the lignosulfonate treatment strategy. A study on the contribution of each stage of the life cycle to the global environmental impact was conducted for both treatments. For the ES treatment, the production of the additive contributed especially to the solid waste production (88 % of the global impact of the system), the stratospheric ozone depletion (84 %) and the terrestrial acidification (49 %). The impact of this stage is less than 10 % for the seven other categories (Fig. 6). The transportation stage contributes less than 2 % to all impact categories except for terrestrial acidification (6 %) owing to the contribution of the marine transportation, which uses sulphur-rich heavy fuel. The global low contribution of the transportation phase is explained by the small quantities of additives to be transported. For lignosulfonates (Fig. 7), the water consumption during the whole cycle is estimated to be 460 × 104 L instead of 9.1 × 104 L for the reference strategy (number 3). This is mainly related to the water consumption during the processing of the lignosulfonate, which represents approximately 99 % of the global impact. A comparison of the two construction strategies using non-traditional products demonstrates that despite the technical benefits obtained from lignosulfonate, their use leads to a dramatic increase in the environmental impact owing to the important contribution of the production stage, which represents at least 90 % of the global environmental impact.
5 Sensitivity analysis A sensitivity analysis is a compulsory step in any LCA study. Its aim is to test the influence of a change in the inputs characteristics or hypothesis used for the
Int J Life Cycle Assess
a 20
18.8
Untreated (strategy 3)
18 16
Enzymatic treatment (strategy 1) 15.3
14.5
14
Im pact value
Fig. 4 LCIA results for the use of the enzymatic solution. a Comparison between construction strategies 1 and 3. b Comparison between construction strategies 1 and 4
12
10.7
10
9.1
8.9
9.0
8.4
8 5.1
6
4.6
4.4
3.6
4
2.3
2
0.7 0.9
0.8
0.7
2.0
2.5 1.1
Water pollution (x 102 m3)
Air pollution (x 104 m3)
Photochemical oxidant formation (kg eq. ethylene)
Stratospheric ozone depletion (x 10-5 kg eq. CFC-11)
Terrestrial acidification (kg eq. SO2)
Climate change (x 102 kg eq. CO 2)
Solid wastes production (kg)
Water depletion (x 104 L)
Energy consumption (x 103 MJ)
Mineral ressources depletion (kg eq. Sb)
0
b 20 Untreated (strategy 4)
18
Enzymatic treatment (strategy 1)
16
Im pact value
14 12 10.8 10.7
10
8.8 9.0
8.3 8.4
8 5.1 5.1
6
4.6 4.6 3.6
4
2.5 2.5
2.3
2
0.4 0.9
0.4
0.4
1.1 1.1
environmental impact calculation. The analysis of the relative contribution of each stage of the life cycle (Fig. 6) show that the major contribution to the environmental impact is the construction stage and production of the additive for three specific categories. Because the LCI of the additive is not well defined, the emphasis must be put on the uncertainties linked with this stage. For the construction stage, the impact is especially linked with the fuel consumption of the machines, which is quite well defined by the constructors and the field experience of DTP. Another point to be discussed in the sensitivity analysis is the choice made in the initial approach to exclude the impacts during the life stage and the end of life stages. Another strong hypothesis was to exclude the
Water pollution (x 102 m3)
Air pollution (x 104 m3)
Photochemical oxidant formation (kg eq. ethylene)
Stratospheric ozone depletion (x 10-5 kg eq. CFC-11)
Terrestrial acidification (kg eq. SO2)
Climate change (x 102 kg eq. CO 2)
Solid wastes production (kg)
Water depletion (x 104 L)
Mineral ressources depletion (kg eq. Sb)
Energy consumption (x 103 MJ)
0
impact of the water production even if its contribution is very low. All impacts of a change in these inputs and in the boundaries of the system must be studied in a sensitivity analysis. The aim of this analysis is to characterise the influence of these hypotheses on the global environmental impact and the final choice of the construction strategy. Because the study compares different construction strategies, the potential impact of errors due to inherent uncertainties and variability of LCI data could have an effect on the result only if the nature or quantity of an input is different between two strategies. This is why, in this study, the major source of variability in the LCIA is directly linked with LCI data of a specific input such as non-traditional additives or linked
Int J Life Cycle Assess
with the definition of the system boundary. Thus, in the sensitivity analysis, the emphasis was placed both of these topics. 5.1 Influence of system boundaries For all treatments, the use stage and end of life stage were excluded from the system. The LCIA results showed that for the enzymatic treatment, the principal benefit of the product is to make the compaction easier. It was also shown in a specific study that the product is totally biodegraded a few days after
382
31
2.0 0.7
15
Photochemical oxidant formation (kg eq. ethylene)
0.7
Stratospheric ozone depletion (x 10-5 kg eq. CFC-11)
15
373
10,400
4.4
Water pollution (x 102 m3)
273
Terrestrial acidification (kg eq. SO 2)
0.8
434
mixing with the soil (Blanck et al. 2014). Because the product is used in very small quantities (0.002 % by dry weight of soil) and mainly enhanced with renewable raw materials, the impact of its degradation is considered to be negligible. Moreover, after degradation, the soil could be used and recycled in the same conditions as untreated soil. In conclusion, for ES treatment, the initial boundary definition has no impact on the comparison between untreated strategies. For LS treatment, as demonstrated in the LCIA, the environmental impact of the production step of lignosulfonates contributed to a huge part of the total impact. The technical Construction
Transportation
Manufacturing
100% 90% 80% 70% 60% 50% 40% 30% 20%
Water pollution (x 102 m3)
Air pollution (x 104 m3)
Photochemical oxidant formation (kg eq. ethylene)
Stratospheric ozone depletion (x 10-5 kg eq. CFC-11)
Climate change (x 102 kg eq. CO2)
Solid wastes production (kg)
Water depletion (x 104 L)
Mineral ressources depletion (kg eq. Sb)
0%
Terrestrial acidification (kg eq. SO2)
10% Energy consumption (x 103 MJ)
Relative contribution
Fig. 6 Relative contribution of the different life cycle stages of the enzymatic treatment solution (strategy 1) to the global environmental impact
9.1
Lignosulfonate treatment (strategy 2)
1,460
Climate change (x 102 kg eq. CO2)
Energy consumption (x 103 MJ)
Mineral ressources depletion (kg eq. Sb)
8.9
19
460
Solid wastes production (kg)
230
Water depletion (x 104 L)
927
Air pollution (x 104 m3)
Untreated (strategy 3)
Fig. 5 LCIA results for the use of lignosulfonate: comparison between construction strategies 2 and 3
Int J Life Cycle Assess Construction
Transportation
Manufacturing
100% 90%
80%
Relative contribution
Fig. 7 Relative contribution of the different life cycle stages of the lignosulfonate treatment solution (strategy 2) to the global environmental impact
70% 60%
50% 40% 30%
20%
benefits of lignosulfonates are not associated to an environmental benefit. This product will thus not be used in the field, and there is no reason to continue technical and environmental investigations. For the same reason, the sensitivity analysis is unnecessary.
Water pollution (x 102 m3)
Air pollution (x 104 m3)
Photochemical oxidant formation (kg eq. ethylene)
Stratospheric ozone depletion (x 10-5 kg eq. CFC-11)
Climate change (x 102 kg eq. CO2)
Solid wastes production (kg)
enzymatic solution was regarded as equivalent to the LCI of a classical surfactant based on geotechnical observations. An alternative hypothesis could also be considered. For example, the LCI of the enzymatic product can be regarded as equivalent to those of alcohol ethoxylate (strategy 1 LCI = AE), another kind of surfactant derived from the transformation of oil (LCI in Stalmans et al. 1995). The enzymatic treatment can also be considered as a waste production of the sugar beet industry. This last hypothesis leads to every field of the LCI being set equal to zero (strategy 1 LCI = 0), because the environmental impact of the factory is assumed to be supported by the produced goods. These two hypotheses are tested in the
5.2 Influence of LCI of enzymatic product The potential impact of uncertainties linked with the LCI data of the enzymatic treatment must be studied because the LCI of the non-traditional product was unavailable. In the approach adopted for life cycle impact assessment, the LCI of the
20
Fig. 8 Sensitivity analysis on the origin of the enzymatic product
Water depletion (x 104 L)
Mineral ressources depletion (kg eq. Sb)
Energy consumption (x 103 MJ)
0%
Terrestrial acidification (kg eq. SO2)
10%
18
Untreated (strategy 3)
Strategy 1 - LCI = 0
Strategy 1 - LCI = AE
Strategy 1 - LCI = AE
16
12
10 8
6 4
2 Water pollution (x 102 m3)
Air pollution (x 104 m3)
Photochemical oxidant formation (kg eq. ethylene)
Stratospheric ozone depletion (x 10-5 kg eq. CFC-11)
Terrestrial acidification (kg eq. SO2)
Climate change (x 102 kg eq. CO 2)
Solid wastes production (kg)
Water depletion (x 104 L)
Mineral ressources depletion (kg eq. Sb)
0
Energy consumption (x 103 MJ)
Impact value
14
Int J Life Cycle Assess
sensitivity analysis. The calculated environmental impact is presented in Fig. 8, which compares strategies 1 (untreated) and 3. Figure 8 shows that the hypothesis considering the enzymatic solution as an alcohol ethoxylate instead of an alcohol sulphates (strategy 3 LCI = AE) induced roughly the same environmental impact. Considering the enzymatic solution as waste induced, a maximal reduction of approximately 10 % for eight impact categories compared with the other hypothesis tested for strategy 3. Only the solid waste production and terrestrial acidification categories are strongly reduced because these impacts are mainly generated by the production step of the product. 5.3 Influence of water supply The diversity in possibilities and the lack of statistical data on the water supply at the construction site lead to the exclusion of the water supply in the analysis of the first approach to avoid large uncertainties in the study. This hypothesis is discussed in this part. The input data (Table 5) show that the water consumption for the construction step is the same among the different treatment strategies (strategies 1, 2 and 4) with a consumption of approximately 44,500 L. Only strategy number 3 required a higher quantity of water with 89,000 L. Therefore, the environmental impact induced by the water supply and transportation will always be the same for strategies 1, 2 and 4 and will be doubled for strategy 3. Therefore, an increase in the impact of the water supply or transportation will always lead to a twofold increase in the environmental impact of the untreated strategy. This analysis shows that the LCI of water and the hypothesis regarding its transportation is unlikely to change the selection of the best strategy based on environmental and technical aspects. Therefore, the result of this study is insensitive to the environmental impact of the water supply even if the differential impact between strategy 3 and the other one will increase with increasing difficulty of the water supply.
embankment construction is in a dry state compared with its optimal moisture content. In this case, they induce significant water savings. For the selected construction strategies, the life cycle assessment showed that treatment with the enzymatic product induces a relative reduction of the environmental impact for most impact categories compared with untreated strategies. For these construction strategies, treatment with nontraditional products combines technical and environmental interest. In contrast, the lignosulfonate treatment generates a significant increase in the impact for all categories, which limits the usefulness of this non-traditional product. Therefore, this study shows that even if the lignosulfonate and the enzymatic products have similar effects in terms of geotechnical properties and lead to similar construction strategies, they are far from equivalent from an environmental point of view. This study also demonstrates that detailed knowledge of the conditions of use of a given nontraditional stabiliser for a given soil is required to perform a relevant LCA and that performing an LCA before actual implementation is useful in the selection of non-traditional products from a sustainability perspective. As an avenue of constant research on the reduction of environmental impacts without reducing the performance of the construction, the comparative process-LCA appears to be an accurate methodology. As shown in this study, the evaluation of non-traditional treatments requires a coupled technical and environmental analysis. To be performed, LCA requires a precise definition of the studied system and can be simplified in a comparative approach by considering only the modified input among the different construction strategies. For nontraditional treatments, an important limit in LCA analysis is the LCI data on the products. These data are not always available as they are for enzymatic treatment. In this situation, hypotheses regarding LCI must be defined, and their impact on the LCIA result must be evaluated by a sensitivity analysis. A specific technique of uncertainty evaluation such as stochastic modelling should be used in the sensitivity analysis (for example, Kucukvar et al. 2014; Noori et al. 2014) could be undertaken in specific contexts to complement the analysis.
6 Conclusions Public works companies are facing issues regarding sustainable development. They must comply with the technical, economic and environmental aspects of projects. In the area of earthworks, the challenges to reduce the environmental impact require optimization regarding the use of materials extracted within the construction site. The present study addressed nontraditional methods of treatment both in terms of geotechnical aspects and environmental issues with a life cycle assessment. The geotechnical tests permitted the determination of construction strategies that could benefit from the use of nontraditional products. The results showed that the products are particularly of interest when the soil to be used for the
Acknowledgments The research presented in this paper was funded by the French Environment and Energy Management Agency (ADEME), Egis Géotechnique and DTP.
References AFNOR NF EN ISO 14040 (2006) Management environnemental Analyse du cycle de vie – Principes et cadre. 25 p AFNOR NF EN ISO 14044 (2006) Management environnemental – Analyse du cycle de vie – Exigences et lignes directrices AFNOR NF P01-010 (2004) Qualité environnementale des produits de construction - Déclaration environnementale et sanitaire des produits de construction
Int J Life Cycle Assess AFNOR NF P94-078 (1997) Sols : Reconnaissance et essais - Indice CBR après immersion - Indice CBR immédiat - Indice Portant Immédiat AFNOR, Fascicule de documentation FD P01-015 (2006) Qualité environnementale des produits de construction – Fascicule de données énergie et transport Berney ES IV, Peters JF, Newman JK, Smith DM (2003) Effect of surfactant on the dry-side compaction of silty sand. Transp Res Rec 1819:57–62 Blanck G, Cuisinier O, Masrouri F (2014) Soil treatment with organic non-traditional additives for the improvement of earthworks. Acta Geotech 9:1111–1122 Chowdhury R, Apul D, Fry T (2010) A life cycle based environmental impacts assessment of construction materials used in road construction resources. Conserv Recycl 54:250–255 Corté, JF, Havard, H (2003) Practical manual for the use of soils and rocky materials in embankment construction. Technical Guide Edited by LCPC and SETRA (Paris, France) 60 p Erlandsson M, Borg M (2003) Generic LCA-methodology applicable for buildings, constructions and operation services—today practice and development needs. Build Environ 38:919–938 Eurostat (2015) Generation of waste, last update http://ec.europa.eu/ eurostat/data/database v3.1.6-20150904-5608-PROD_ EUROBASE, last update 23-07-2015 Fevre-Gautier A-L, Vaxelaire S, Beylot A, Michel P, Brullot S, Lannou G, Stoos M (2012) Construction projects using alternative materials: a framework to assess their sustainability. In: Arm M, Vandecasteele C, Heynen J, Suer P, Lind B (eds.) Wascon 2012 Conference Proceedings; Gothenburg Gow AJ, Davidson DT, Sheeler JB (1961) Relative effects of chlorides, lignosulfonates and molasses on properties of a soil-aggregate mix. Highw Res Board Bull 282:66–83 Guinée JB, Gorée M, Heijungs R, Huppes G, Kleijn R, de Koning A, v Oers L, Wegener Sleeswijk A, Suh S, Udo de Haes HA, de Bruijn H, v Duin R, Huijbregts MAJ (2002) Handbook on life cycle assessment: operational guide to the ISO standards serie: eco-efficiency in industry and science. Kluwer Academic Publishers, Berlin Hendrickson CT, Lave LB, Matthews S (2006) Environmental life cycle assessment of goods and services: an input–output approach, 1st edn. Resources for the Future, Washington DC Katz LE, Rauch AF, Liljestrand HM, Harmon JS, Shaw KS, Albers H (2001) Mechanisms of soil stabilization with liquid ionic stabilizer. Transp Res Rec 1757:50–57 Klöpfer W (2008) Life cycle sustainability assessment of products. Int J Life Cycle Assess 13:89–95 Kucukvar M, Noori M, Egilmez G, Tatari O (2014) Stochastic decision modeling for sustainable pavement designs. Int J Life Cycle Assess 19:11185–11199 Li X, Zhu Y, Zhang Z (2010) An LCA-based environmental impact assessment model for construction processes. Build Environ 45:766–775
Modahl IS, Vold BI (2011) The 2010 LCA of cellulose, ethanol, lignin and vanillin from Borregaard Sarpsborg. Ostfold Research, Norway, p 78 Mroueh U-M, Eskola P, Laine-Ylijoki J (2001) Life-cycle impacts of the use of industrial by-products in road and earth construction. Waste Manage 21:271–277 Muench ST (2010) Roadway construction sustainability impacts: review of life cycle assessment. Transp Res Rec 251:36–45 Noori M, Tatari O, Nam BH, Golestani B, Greene J (2014) A stochastic optimization approach for the selection of reflective cracking mitigation techniques. Transp Res Part A 69:367–378 Park J, Vipulanandan C, Kim J, Myoung Hak O (2006) Effects of surfactants and electrolyte solutions on the properties of soil. Environ Geol 49(7):213–220 Peck GM (1963) Discussion to session 11, 4th Australian N.Z. conferenceon soil mechanics. Soil mechanics, edited by Lee IK Pittinger CA, Sellers JS, Janzen DC, Koch DG, Rothgeb TM, Hunnicutt ML (1993) Environmental life-cycle inventory of detergent-grade surfactant sourcing and production. J Am Oil Chem Soc 70:1–15 Rajendran D, Lytton RL (1997) Reduction of sulfate swell in expansive clay subgrade in the Dallas district. Texas Transportation Institute, College Station, Research Report TX-98/3929-1 Rauch AF, Katz LE, Liljestrand HM (2003) An analysis of the mechanisms and efficacy of three liquid chemical soil stabilizers. Center for transportation research, University of Texas, Austin, Report FHWA/TX-03/1993-1 Santoni RL, Tingle JS, Webster SL (2002) Stabilization of silty sand with nontraditional additives. Transp Res Rec 1787:61–70 Scholen DE (1995) Stabilizer mechanisms in nonstandard stabilizers, vol 2. TRB Natl Res Council, Washington, DC, pp 252–260, 6th Int Conf on Low-Volume Roads Stalmans M, Berenbold H, Berna JL, Cavalli L, Dillarstone A, Franke M, Hirsinger F, Janzen D, Kosswig K, Postlethwaite D, Rappert T, Renta C, Scharer D, Schick K-P, Schul W, Thomas H, Van Sloten R (1995) European life-cycle inventory for detergent surfactants production. Tenside Surfactants Deterg 32(2):84–109 Steen B (1999) A systematic approach to environmental priority strategies in product development (EPS) version 2000-general system characteristics / models and data of the default method CPM Report 1999, Gothenburg Surdahl RW, Woll JH, Marquez HR (2007) Stabilization and dust control at the Buenos Aires national wildlife refuge, Arizona. Transp Res Rec 1989:312–321 Tingle JS, Santoni RL (2003) Stabilization of clay soils with nontraditional additives. Transp Res Record J Transp Res Board 1819:72–84 Tingle JS, Newman JK, Larson SL, Weiss CA, Rushing JF (2007) Stabilization mechanisms of nontraditional additives. Transp Res Rec 1989:59–67 Velasquez RA, Marasteanu MO, Holzalski RM (2006) Investigation of the effectiveness and mechanisms of enzyme products for subgrade stabilization. Int J Pavement Eng 7:213–220
