An attributional and consequential life cycle assessment of substituting concrete with bricks

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Journal of Cleaner Production xxx (2014) 1e11

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An attributional and consequential life cycle assessment ofsubstituting concrete with bricks

Harn Wei Kua*, Susmita KamathDepartment of Building, School of Design and Environment, National University of Singapore, 4 Architecture Drive, Singapore S117566, Singapore

a r t i c l e i n f o

Article history:Received 22 November 2013Received in revised form27 May 2014Accepted 2 June 2014Available online xxx

Keywords:Attributional life cycle assessmentConsequential life cycle assessmentBrickConcreteIntegrated policiesGreen building

* Corresponding author.E-mail addresses: [email protected] (H.W. K

com (S. Kamath).

http://dx.doi.org/10.1016/j.jclepro.2014.06.0060959-6526/© 2014 Published by Elsevier Ltd.

Please cite this article in press as: Kua, H.W.,bricks, Journal of Cleaner Production (2014)

a b s t r a c t

Singapore introduced the Concrete Utilization Index to promote the substitution of concrete productswith alternate building materials. This study examined the environmental impacts of replacing concretewith bricks. Using an attributional life cycle approach, it was found that replacing concrete with bricksmay actually increase the net environmental impacts. In the first ever consequential life cycle assessmentdone for bricks in the literature, we found that replacing concrete with bricks may result in smallreduction in global warming potential, provided there is no change to the amounts of bricks and concreteconstituents being imported into Singapore. Considering there are changes to the import quantities, wederived a mathematical relation that enables us to know how much the import of concrete constituentsmust decrease in order to nullify the increased global warming potential resulted from the increase inimport of bricks. In all these assessments, we found that the environmental impacts (including globalwarming potential) of the manufacturing stage of bricks need to be reduced. To achieve this, wereviewed a few new brick-making approaches that can produce more sustainable bricks; we also pro-posed a way of creating a “green demand” for these bricks and utilizing policies such as Singapore'sBusiness Angel Scheme to finance the upgrading of brick-making technologies through internationalpartnership.

© 2014 Published by Elsevier Ltd.

1. Introduction

Singapore's Green Mark Scheme (GMS) e the green buildingstandard created and implemented by the Building and Construc-tion Authority (BCA) e plays an important role in promoting sus-tainable design and construction in the building industry. In thelatest version of the GMS, a Concrete Utilization Index (CUI) isprescribed; it is defined as the total volume of concrete used in abuilding per unit gross floor area. If a design has a CUI of less than0.3, it will be awarded with the maximum of 5 points under theGMS for this criterion. The CUI was proposed to encourage the in-dustry to reduce the reliance on concrete, which will in turn reducethe dependence on its constituents, such as sand and granite. It alsoaims to promote the replacement of concrete with other structuralmaterials. For structural purposes, concrete can be replaced withwood, steel or bricks. Traditionally, wood is not widely used forconstruction in Singapore. While steel can be used to replaceconcrete columns, beams and, less commonly, slabs, it is not used to

ua), susmita.kamath@gmail.

Kamath, S., An attributional, http://dx.doi.org/10.1016/j.jc

replace concrete in shear walls. Replacing concrete entirely withsteel will decrease the walls' thermal resistance and increase thecost of construction. By contrast, bricks have similar thermalresistance as concrete blocks and have been widely used inSingapore in shear walls and internal light structural walls. In otherwords, there are more possibilities to replace concrete with bricksin Singapore.

Since its inception, there has not been a systematic and rigorousway of assessing the effectiveness of CUI in promoting sustainableconstruction, particularly as a result of substituting away concrete.The aim of this study is to apply the concept of life cycle assessment(LCA) to evaluate the resultant environmental impacts of replacingconcrete with masonry (bricks, specifically), which is becoming acommon strategy to achieve a lower CUI.

Concrete is arguably the most important and versatile materialin construction today. It is composed primarily of cement, aggre-gates and water. Each year, more than 10 billion tonnes of concreteare produced globally for use in construction projects (Thi Do,2011). It is estimated that the amount of concrete used in theconstruction industry is almost twice that of all other buildingmaterials put together (UNEP, 2003). Owing to its strength, dura-bility and ease of casting, concrete is used in a variety of

and consequential life cycle assessment of substituting concrete withlepro.2014.06.006

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H.W. Kua, S. Kamath / Journal of Cleaner Production xxx (2014) 1e112

applications in the construction industry. Cement, the main con-stituent of concrete, is a major source of greenhouse gases (GHGs).It is estimated that the cement industry contributes about 5e7% ofthe global anthropogenic CO2 emissions (UNEP, 2003). The pro-duction of concrete also causes extensive quarrying for sand, graveland stones for use as aggregates in the concrete mixture. Theconstruction industry is by far the only consumer of bricks (Roseet al., 1978). Bricks are one of the oldest and most popular build-ing materials, owing to their low price, durability and ease ofhandling. Bricks are known to retain their colour much longer thanconcrete blocks. Furthermore, concrete absorbs water at a ratehigher than bricks, thus causing larger changes in the dimensions ofconcrete blocks when they are being used. The thermal resistanceof bricks and concrete blocks are similar and so replacement withbricks is unlikely to change the energy consumption of the buildingduring the use phase. However, it is well known that brick makingis an energy intensive process. In 2008, the Asian brick makingindustry consumed about 110 million tons of coal and the dieselused for transportation produced approximately 180million tons ofcarbon dioxide (CO2) (Heierli and Maithel, 2008).

LCA is a popular and rigorous method for assessing the totalenvironmental impact of building materials. While applying LCA toassess the environmental impacts of bricks, we need to take intoaccount the net environmental impacts caused by the replacementof concrete by bricks. This study analysed the net impacts of such areplacement, using both an attributional LCA (ALCA) and conse-quential LCA (CLCA).

ALCA calculates the environmental burdens resulting from agiven product, whereas CLCA considers higher order effects,including the net environmental impacts due tomarket response tomaterial substitution (Earles and Halog, 2011). In other words, CLCAextends the system boundary beyond what the conventional ALCAconsiders. Most of the available literature on LCA for bricks is ALCAin nature. For example, a detailed ALCA was carried out for themanufacturing of clay bricks, with respect to energy consumptionand CO2 emissions, by Koroneos and Dompros (2007). It was acradle-to-gate study that studied the life cycle stages of raw ma-terial extraction, brick manufacturing, packaging and trans-portation. Owing to the difference in processes employed formanufacturing and the difference in composition of clay from re-gion to region, a large variation is obtained in embodied energy ofbricks. It varies from 2200 MJ/tonne (Ashby, 2009) to 5909 MJ/tonne (Utama and Gheewala, 2008). In comparing brick and con-crete, Venta (1998) conducted a cradle-to-gate study in Canada toanalyse the inputs and outputs from brick production; it was foundthat the embodied energy and the emissions due to themanufacturing and transportation were substantially higher forclay bricks than concrete (for a functional unit of one cubic metre ofbricks). Utama et al. (2012) studied the embodied energy of housesin Indonesia that might use either clay bricks or concrete blocks fortheir envelopes. The embodied energy of clay bricks was found tobe half of that of concrete blocks, due to the manufacturing processemployed and the tropical weather in the country. The resultsindicated that clay bricks perform better in global warming po-tential (GWP) and human toxicity potential (HTP), whereas con-crete blocks fare better in acidification potential (AP),eutrophication potential (EP) and photochemical oxidation poten-tial (PCOP). The AP impacts in clay bricks were mainly due topresence of hydrogen fluoride and chloride in the clay. The usage ofhigher amount of mortar for clay bricks and its replacement alsocontributed to the AP.

In comparison, CLCA for buildingsmaterials has been rare. In thefirst CLCA study in the Singapore context, the effects of substitutionof cement with copper slag were analysed (Kua, 2012). The resultsof ALCA suggested that the substitution is desirable; however, the

Please cite this article in press as: Kua, H.W., Kamath, S., An attributionalbricks, Journal of Cleaner Production (2014), http://dx.doi.org/10.1016/j.jc

CLCA indicated a reduction in the benefits of such a substitution.Presently, there has not been any CLCA on the replacement ofconcrete products with bricks anywhere in the world. The need toassess possible consequences of the CUI in Singapore provides uswith the motivation to conduct such a CLCA, in order to fill thisimportant knowledge gap in the literature.

2. Materials and methods

2.1. System boundary of brick

The assessments carried out in this study were for a functionalunit of 1 kg of clay bricks. Data for this paper was acquired mainlythrough literature review, questionnaires, telephone interviewsand emails correspondence with relevant stakeholders in the in-dustry. When necessary, the information gathered was furthermodified to suit the Singapore context, for example by applyinglocal electricity fuel mix and the estimation of transport emissionsspecific to the specific cases being studied. The results of bothmaterials were then analysed from an ALCA and CLCA perspective.

The characterization factors for various inputs were taken fromthe ECOINVENT database (ECOINVENT, 2010). For the ALCA, thefocus was put on five impact categories, namely GWP, AP, EP, HTPand Cumulative Energy Demand (CED).

The inputs considered for all life cycle stages are primarilyelectricity, diesel and water. In the literature, it was noted that theliquid and solid wastes generated during brick life cycle are negli-gible (Koroneos and Dompros, 2007; Venta, 1998). Hence, our studyfocused only on gaseous emissions.

The major suppliers of bricks for Singapore are located inMalaysia (specifically in the state of Johor). Bricks fromMalaysia areusually manufactured in large automated plants. Hence, wemodelled the life cycle of bricks according to the processes in such aplant. In calculating the impacts due to transportation, we firstcalculate the “tonne-kilometer” (measured in tkm) of the materialsinvolved. Tonne-kilometre is the unit of measurement for thetransportation of 1 tonne of a material by a given transport modeover a distance of 1 km. The CO2 emission due to transportation isthen computed by multiplying the value of tonne-kilometer by theemission factor (in kgCO2

/tkm) and the total mass of materialtransported (Cefic-ECTA, 2011).

Fig. 1 illustrates the processes that are within and beyond thescope of study. Each of these life cycle stages are described asfollow:

2.1.1. Raw material extraction

The raw material used is clay from two quarries near themanufacturing unit (Worrell et al., 1994). The equipment usedfor this operation is digging and excavation equipment that runson diesel. We considered themanufacturing unit (in Johor) to belocated within a 5e10 km radius around the quarries (Utamaet al., 2012). For 1 kg of clay bricks, 1.11 kg of clay is required.The average distance between the quarry and themanufacturing plant is 15 km. Hence, the tonne-kilometer is

15� 1:111000

¼ 0:017 tkm (1)

Bymultiplying this value to the emission factor (in kgCO2/tkm) of

the 40-tonne truck, the CO2 emission can be found (Cefic-ECTA,2011). The other outputs and environmental impacts due totransportation were found by estimating the total amount offuel used for the transportation and multiplying it by the factors


Table 1Sources of data for life cycle stages of bricks.

Life cycle sages Data sources

Raw material preparation Main data was taken from surveys andinterviews. Other sources include:Bovea et al., 2007; Ib�a~nez-For�eset al., 2011; Koroneos and Dompros, 2007.

Body preparation Rose et al., 1978; Koroneos and Dompros,2007; Venta, 1998.

Shaping Rose et al., 1978.Drying and firing Rose et al., 1978.Unloading and packaging Koroneos and Dompros, 2007.Construction Data taken from surveys and interviews.Demolition ECOINVENT (2010)Sorting and storage at

disposal plantECOINVENT (2010)

Fig. 1. System boundary for ALCA of bricks. The “use” phase of bricks is not included inthis study.

H.W. Kua, S. Kamath / Journal of Cleaner Production xxx (2014) 1e11 3

in ECOINVENT (2010). This method was also employed by Kua(2012).

2.1.2. Manufacturing of bricks

2.1.2.1. Preparation. Clay that arrives at the plant is stored in pilesand allowed toweather for a few days. The clay that is most suitablefor common brick manufacturing is “sandy clay loam”, which isfound abundantly in Malaysia (Ahmed et al., 2009; Johari et al.,2011; Kheiralla et al., 2004). This type of clay does not require theaddition of any additives. Instead, clay from the two different lo-cations stated above is mixed in the proportion of 60% and 40%. Themixture is then ground to required size in crushers. Water is addedto the clay and the mixture is then tempered to the required con-sistency. Electricity in Malaysia is derived from natural gas (52.2%),coal (39.5%), hydroelectric (5.1%), diesel and oil (2%), biomass andothers (1.2%) (Loo, 2012).

2.1.2.2. Forming, drying and firing. Clay is then passed through anextruder and cut into blocks by a wire cutter. These wet bricks arethen dried in a drier, which utilizes the heat from exhaust of thekilns (Rose et al., 1978). The dried bricks are then transferred to atunnel kiln where they are fired at high temperatures. An averagefuel mixture of Malaysia was considered: sawdust (70%), naturalgas (20%) and diesel oil (10%). The sawdust has been assumed to becomposed of 50% rubber wood and 50% general timber.

2.1.2.3. Packaging and storage of bricks. The finished bricks areunloaded from the kilns using diesel powered equipment and thencarried to the storage area. The packaging is carried out manually,as indicated by a vendor during a telephone interview. When thebricks are ready for dispatch, the packaged units are transferred totrucks by diesel powered loaders.

The electricity, water and fuel required for these processes werefound directly from the vendors or estimations from the length of


operation times of the machineries. This approach was similarlytaken by Kua (2012) in his LCA of copper slag.

2.1.2.4. Distribution to and within Singapore. We have consideredthe Singapore brick dealer to be located in Senoko e about 48.5 kmaway from the factory in Johor. Hence, the tonne-kilometer oftransporting 1 kg of brick is

48:5� 11000

¼ 0:049tkm (2)


the 40-tonne truck, the CO2 emission can be found (Cefic-ECTA,2011). The distance between dealer's storage yard and the con-struction site has been estimated as 15 km; the method by Kua(2012) was adopted to calculate the environmental impacts dueto the transportation between Senoko and construction site.

2.1.2.5. Use of bricks in construction. Assembly of bricks is carriedout manually. The emissions due to the use of mortar were alsoconsidered in this stage, and the method used was adopted fromKua (2012).

2.1.2.6. Demolition and end-of-life use. Buildings are demolishedusing equipment that is powered by diesel. The equipment con-sumes 0.0359 MJ of diesel per kg of brick. The construction anddemolition (C&D) waste is transferred to a waste processing plantin a place known as Sarimbun, which is located in Lim Chu Kang.The average distance between Sarimbun and the average con-struction site is around 6.3 km. Hence, the tonne-kilometer fortransporting 1 kg of brick waste is

6:3� 11000

¼ 0:0063tkm (3)


the 25-tonne truck, the CO2 emission can be found (Cefic-ECTA,2011). At the recycling plant, the C&D waste is sorted and stored.Brick waste is usually down-cycled and used as “hard core” in thesub-base layer of roads. In our study, we considered the life cycleonly up to storage of brick wastes at the recycling plant.

In summary, the data sources for the different life cycle stagesare shown in Table 1 and the detailed information for calculatingthe transportation stage of bricks are presented in Table 2.

2.2. LCA of concrete

Concrete is produced bymixing coarse and fine aggregates (suchas gravel and sand) with cement, water and admixtures. Ready-mixconcrete is manufactured bymixing the rawmaterials at a concrete


Table 2Transportation distances and tonnage of vehicle.

Transportation stages Distance(km)

Tonnageof truck(tonne, t)

Source of tonnage

Transportation of clay fromquarry to plant

15 40 Kua, 2012

Transportation of brick fromJohor to Senoko

48.5 40 Derived frominterviews withvendors

Transportation of brick fromSenoko to an averageconstruction site

15 25 JPPL, 2010

Transportation of demolishedbrick from an averageconstruction site to Sarimbunrecycling plant (near LimChu Kang)

6.3 25 JPPL, 2010


batching plant and then transferred it to the construction site in atruck mounted mixer.

The life cycle inventory (LCI) of cement is taken from a study of aTaiwan based cement manufacturing company (Teo et al., 2010). In2007, Singapore imported 678,298 metric tons of cement fromTaiwan. The manufacturing plant under study is located in Hualiancounty of Taiwan. Lime and clay are the two main materialsinvolved in the production of cement. The process ofmanufacturing cement can be divided into three broad processes,namely, raw meal production, clinker formation and cement pro-duction. The transport of cement to Singapore port is included inthe LCI for concrete production. The distance between Hualian portand Singapore port is taken as 3,178 km and the weight of cementrequired for 1 kg of concrete is 0.154 kg. The impacts due totransportation of cement within Singapore were taken from Kua(2012).

The LCI data for concrete aggregates was obtained from a studyby Thi Do (2011) on the carbon emissions of concrete aggregatesused in Singapore. Malaysia and Indonesia are the two countriesfrom which Singapore imports most of its aggregates. These ag-gregates typically consist of sand and gravel. Granite is the mostwidely used gravel in Singapore. The production of gravel involvestwo kinds of crushers, namely jaw crushers and impact crushersthat break the gravel up into pieces of required size. The electricityrequirement for these crushers for production of 1 kg of gravel is0.1152 MJ and 0.094 MJ for jaw crusher and impact crusherrespectively.

The distance between granite mine and the plant and seaport istaken to be 30 km (Thi Do, 2011). For every 1 kg of concrete pro-duced, 0.770 kg of aggregate (0.462 kg gravel and 0.308 kg sand) isrequired. 770 g (0.00077 tonnes) of aggregate is required for 1 kg ofconcrete production. Hence, 0.00077 tonnes of aggregate is locallytransported over 30 km. The tonne-kilometer of the gravel (to thepoint of the Indonesian port) is thus

0:00077� 30 ¼ 0:023tkm (4)

Based on the study by Kua (2012), we assume that the localtransportation is carried out by means of 5-tonne truck that carriesamaximum load of up to 20 tonnes. The resultant CO2 emissionwasthen calculated by multiplying this value of tkm by the emissionfactor of an average 20-tonne truck (which has a unit of kgCO2

pertkm).

The distance between Indonesian seaport and Singaporeseaport is about 77 km. Transporting 0.00077 tonnes of aggregatesover 77 km in ocean liners yields a tonne-kilometre of

0:00077� 77 ¼ 0:059tkm (5)



an average ocean liner, the CO2 emission can be found (Cefic-ECTA,2011). Characterization factors for assessing the life cycle impacts ofthe inputs of sand and gravel, electricity and transport have beenutilized from the ECOINVENT database (ECOINVENT, 2010). Forgranite, the data for transport and electricity data were adoptedfrom Thi Do (2011).

In this study, we considered ready mix cement produced by thewet process. At the batching plant, the sand, gravel, cement andwater are mixed together and then loaded on to mixer trucks fortransportation to various locations. The concrete maybe cast intoblocks at the construction site 12) or at a separate casting location.The concrete may also be cast into wall panels at a casting yard. Weassessed that the manufacture of 1 kg of ready mix concrete at thebatching plant would need 0.00183 kWh of electricity. Within thebatching plant, we assumed that loaders and unloaders were usedfor internal transportation of materials. The diesel fuel consump-tion of these vehicles for 1 kg of concrete is estimated to be about0.010MJ (Thi Do, 2011). This readymix concrete is transported fromthe batching plant to a construction site by means of a concretemixer truck, with an average tonnage of 17.6 tonnes. The impactsdue to all the transportation stage was calculated using the meth-odology introduced by Kua (2012).

Demolition is done using equipment fuelled by diesel. Theequipment consumes 0.036 MJ of diesel per kg of concrete. InSingapore, it is forbidden to landfill salvaged concrete; after de-molition, the concrete will either be used as recycled concreteaggregate in structural members of new buildings or down-cycledas sub-base for new roads. Hence, we have not considered land-filling for the concrete from C&D waste. The tonne-kilometre oftransporting the concrete wastes is the same as that for the brickwaste. The inventory for crushing and sorting of concrete wastewas taken from Thi Do (2011). In summary, the disposal stage isfound to consume about 0.006 kWh of electricity and 0.109 MJ ofdiesel.

In this study, the life cycle impacts of concrete products madefrom recycled concrete aggregates (RCA) were also compared tothose made from virgin coarse aggregates (gravel). In Singapore,1 kg of RCA is derived from 2.5 kg of waste concrete. The systemboundary of RCA was adopted from Thi Do (2011). In this study, weconsidered that 30% of the aggregates in the concrete mixture werereplaced with RCA (BCA, 2012).

2.3. CLCA of replacing concrete with bricks

2.3.1. Scenarios for CLCA and sensitivity analysisWe focused only on assessing the GWP (measured in kg CO2-eq)

for the CLCA because GHG emissions of cement production havealways been a major concern in the building industry. Using theGWP values of clay bricks and concrete derived from the stepsdescribed above, the likely consequential changes in GHG emis-sions from replacing concrete with brick can be estimated. A fewlikely scenarios were considered. The baseline scenario of substi-tution (concrete for bricks) assumes that we aim to reduce the CUIof a building from 0.9 (which is the average value in the industry) to0.7 (which will earn 1 point under the GMS); doing so requiresreducing the total volume/mass of concrete by about 22%. In otherwords, the baseline scenario considers replacing 22% of the con-crete with bricks. In our sensitivity analysis, we considered varia-tions to the following replacement scenarios:

� Replacement scenario 1: 10% of the concrete is replaced bybricks, and

� Replacement scenario 2: 30% of the concrete is replaced bybricks.


Table 3Different scenarios arising from replacing concrete with bricks. For both scenarios, the net changes in quantities are multiplied by their respective global warming potentials eGWPBrick, GWPBricknot used

, GWPConcreteiðnot usedÞ and GWPConcretei e and summed up to yield the net changes in global warming potential for the scenarios. For scenario 1 and 2, thismethod results in Equations (8) and (9) respectively.

Baselinequantities of thetwo materials

Quantities of the two materials underconsequence scenario 1 (assuming nochange in export and import of eithermaterial)

Quantities of the two materials under consequence scenario 2(assuming that in the long term, concrete import is reducedwhereas the import of bricks increases)

Brick Concrete Brick Concrete Brick Concrete

Quantities used for buildingconstruction

A C A þ X C � Y A þ X C � Y

Net change in quantities requiredfor building construction

0 0 (A þ X) � A ¼ X (C � Y) � C ¼ �Y (A þ X) � A ¼ X (CeY) � C ¼ �Y

Quantities present in nationalstockpile/reserve

RB RC RB � X RC þ Y RB � X þ (f.X) RC þ Y � (e.Y)

Net change in quantities innational stockpile/reserve

0 0 (RB � X) � RB ¼ �X (RC þ Y) � RC ¼ Y RB � X þ (f.X) � RB ¼ (f � 1).X RC þ Y � (e.Y) � RC ¼ (1 � e).Y


When concrete is replaced by bricks in the industry, two likelyconsequence scenarios may occur (these are summarized inTable 3):

� Consequence scenario 1: The total consumption of concrete forbuilding construction reduces by a quantity Y and that of bricksincreases by a quantity X; these changes in consumptions ofboth materials in buildings neither change the consumption forother purposes nor change their international trade (import andexport). However, this means that additional X of bricks is takenfrom the national stockpile and Y of concrete is saved from thenational stockpile. Overall, the total quantities of brick andconcrete in the whole of Singapore are the same.

� Consequence scenario 2: The total consumption of concrete forbuilding construction reduces by a quantity Y and that of bricksincreases by a quantity X; although these changes in con-sumptions of both materials in buildings do not change theconsumption for other purposes, over time it results in an in-crease in import of bricks and a decrease in import of materialsfor producing concrete. That is, although there are no changes tothe demand for bricks and concrete (just like in consequencescenario 1), the total quantities of bricks entering Singaporeincreases and quantities of concrete constituents decrease. Thiscan be explained as the market adjusting to the increase indemand for bricks and hence importers start to purchase morebricks in anticipation of future spur in brick demand for con-struction projects.

Fig. 2. Summary of the research meth


Expressed as a fraction of the quantity Y, “e” (shown in Table 3) isrelated to the amount of imported concrete that is avoided due to adecrease in the requirement for concrete. “f” is the fraction of thequantity X and it accounts for an increase in the requirement forbricks. Both coefficients “e” and “f”e ranging from 0 to 1e describehow the market responds to changes in consumptions of bricks andconcrete by changing the international import of these materials.

However, brick do not replace concrete in a one-to-one massproportion, due to different densities of both materials and thedesign of the components. Thus, for analysing the sensitivity of theresults, we consider a functional unit of one square metre (m2) ofwall. Typically when concrete is used for walls, it is in the form ofconcrete blocks or precast hollow concrete panels. The weights ofthese various components have been worked out in appendix A.The ratio of replacement (denoted by R) for one square metre ofwall can have the following three possibilities:

� Clay brick: Concrete blocks is 1:0.81 (R ¼ 0.81),� Clay brick: Precast concrete wall panel (90 mm thick) is 1:0.92(R ¼ 0.92),

� Clay brick: Precast concrete wall panel (100 mm thick) is 1:1.07(R ¼ 1.07).

Therefore, the relationship between X and Y (shown in Table 3)is

X ¼ YR

(6)

odology employed for this study.


Table 4Primary inputs required for 1 kg of finished bricks.

Input materials quantities

Clay (kg) 1.109Water (kg) 0.131Diesel (litre) 0.010Electricity (kWh) 0.154Gas (kg) 0.009Sawdust (kg) 0.100

Table 6Inputs for manufacturing of 1 kg of cement derived from (Teo et al., 2010).

Inputs Quantity Unit

Limestone 0.975 kgClay 0.024 kgElectricity 0.014 kWhInputs for 1 kg of clinkerRaw Meal 2.070 kgCoal 0.180 kgElectricity 0.052 kWhInputs for 1 kg of cementClinker 0.820 kgGypsum 0.230 kgElectricity 0.043 kWh

Table 7Inputs for different functional units of concrete in Singapore.

Inputs Quantity(for 1 m3 ofconcrete)

Quantity(for 1 kgof concrete)

Data source

Gravel 1108 g 462 g Kua and Wong, 2012Sand 740 g 308 gOrdinary

PortlandCement

370 g 154.17 g

Water 183 g 76.25 gElectricity 4.36 kWh 1.83 kwh Kellenberger et al., 2007Diesel 22.7 MJ 0.00953 MJ


To facilitate analysis, C (in Table 3) is taken as 10 kg. The values ofY can then be deduced as

Y ¼8<:

2:2 kg; for baseline replacement scenario1:0 kg; for replacement scenario13:0 kg; for replacement scenario2

9=; (7)

These values of Y follow from the definitions of baselinereplacement scenario and replacement scenarios 1 and 2, asdescribed in Section 2.3.1. The corresponding values of X can thenbe calculated using Equation (6).

Fig. 2 summarizes the research methodology for both the ALCAand CLCA, with respect to how the three replacement scenarios andtwo consequence scenarios are considered in each of theseassessment methods.

3. Results and discussions

3.1. Life cycle inventories (LCIs) of bricks and concrete

The main primary inputs for the manufacturing of bricks areclay, water, diesel fuel, electricity, gas and sawdust. A summary ofthe total inputs required is presented in Table 4.

It was found that the cradle-to-grave energy requirement for1 kg clay bricks in Singapore is about 2.89 MJ. The drying and firingprocess accounts for 87% of total energy requirement. This is fol-lowed by clay mixing and forming, which consumes around 8% ofthe total energy requirement. The raw material extraction, trans-portation and end of life processes altogether contribute only to theremaining 5%. The calculated impacts for 1 kg of bricks are shown inTable 5.

When the result for GWP was compared to that from the studyby Koroneos and Dompros (2007), it was found to be 7% lower. Thisvariation may be attributed to factors such as differences in fuelused, distances covered for transportation andmethods of disposal.Furthermore, the GWP for only the raw material extraction,manufacture and transportation of bricks was found to be 0.188 kgCO2-eq, which is 6% less than the range of 0.200e0.230 kg asmentioned by Ashby (2009).

The main inputs for the manufacturing of cement and concreteare shown in Tables 6 and 7 respectively. The impacts of 1 kg ofconcrete are shown in Table 8.

The contributions of various life cycle stages of concrete to theenvironmental impacts were analysed. We observed that theextraction and production of raw materials are the biggest

Table 5Calculated life cycle impacts for 1 kg of finished bricks.

Impact category Quantity Unit

Global warming potential 0.207 kg CO2-eqAcidification potential 0.002 kg SO2-eqEutrophication potential 0.000 kg PO4-eqHuman toxicity 0.080 kg 1,4 DB-eqCumulative energy demand 4.897 MJ-eq


contributors of environmental impacts e constitutes 65e80% ofthese impacts (Fig. 3 and 4). Cement production alone contributesto about 30e40% of all impacts; this is most likely caused by the useof coal for calcination of limestone in clinker making and theelectricity utilised in production of cement. The electricity requiredfor production of cement constitutes 37% and gravel crushingcontributes another 60% of the life cycle electricity involved in themanufacturing of concrete. The disposal stage contributes 33.67% tothe impact category of human toxicity, due to consumption ofdiesel oil in the wheel loader at the recycling plant.

However, if we considered the use of RCA to replace 30% of thecoarse aggregates in the concrete mixture, then the overall impactswill be reduced; results are shown in Table 9.

3.2. Comparison of ALCA results of brick and concrete

After considering the different replacement scenarios (R) asshown in Section 2.3.1, it was found that irrespective of the types ofconcrete products used, the impacts of concrete are actually lessthan those of brick (see Fig. 5). However, concrete in the form ofconcrete block has least impacts from an ALCA perspective.

In summary, the highly energy intensive process of brickmanufacturing e in particular, the firing of bricks e leads to greaterlife cycle environmental impacts of bricks when compared toconcrete products. This result serves as a precaution against any

Table 8Summary of impacts for 1 kg of concrete.

Impact category Quantity Unit

Global warming potential 0.107 kg CO2-eqAcidification potential 0.001 kg SO2-eqEutrophication potential 0.000 kg PO-eqHuman toxicity potential 0.026 Kg 1,4 DB-eqCumulative energy demand 1.668 MJ-eq


Fig. 3. Contributions by various life cycle stages of brick to environmental impacts.


assumption that reducing the use of concrete products willnecessarily lead to a net reduction in environmental impacts.

3.3. CLCA of net GWP of replacing concrete with brick

The 3 replacement scenarios and, for each of them, 2 conse-quence scenarios were analysed and the results are shown inTable 10. These were conducted for various forms of concrete(block, precast (PC) wall) composed of conventional concrete and30% RCA concrete. The net GWP of these difference scenarios were

Fig. 4. Contributions to environmental impact


calculated using the following formulae, which was derived fromthe relationships described in Table 3:

3.3.1. Consequence scenario 1

Net GWP ¼�YR

��GWPBrick � GWPBricknot used

�þ Y

hGWPConcreteiðnot usedÞ � GWPConcretei

i(8)

s by various life cycle stages of concrete.


Table 9Summary of impacts for 1 kg of concrete with 30% recycled concrete aggregate.

Impact category Quantity Units

Global warming potential 0.092 kg CO2-eqAcidification potential 0.001 kg SO2-eqEutrophication potential 0.000 kg PO4-eqHuman Toxicity potential 0.025 Kg 1,4 DB-eqCumulative energy demand 1.538 MJ-eq


3.3.2. Consequence scenario 2

NetGWP ¼�YR

��GWPBrick þ ðf � 1Þ$GWPBricknot used

�� Y

hGWPConcretei þ ðe� 1Þ$GWPConcreteiðnot usedÞ

i(9)

where GWPBrick and GWPConcrete i refer to the GWP of bricks andtype i of concrete elements respectively. GWPBricknot used

andGWPConcreteiðnot usedÞ refer to the GWP due to the bricks and concretein the national material stockpile; these materials are not used inconstruction sites and so the values do not include the GWP due totransportation to construction sites, deployment, demolition andrecycling.

As shown in Table 10, from the perspective of the entireSingapore market, the higher the replacement rate, the higher thenet reduction in GWP. Having 30% RCA in the concrete mixturereduces its overall GWP; therefore, replacing this type of concretewith bricks results in the lowest net reduction in GWP. In otherwords, replacing concrete containing 30% of RCA reduces theoverall benefit of substituting concrete with bricks. Finally,replacement of 1 kg of 100 mm-thick precast concretewall requiresthe most amount of bricks; this explains why such a replacementproduces the most reduction in GWP. Nonetheless, values inTable 10 clearly show that there are only slight reductions in GWP

Fig. 5. Impacts of concrete expressed as a perce


for all the replacement scenarios (for consequence scenario 1)considered. In other words, replacing concrete products with bricksis likely to yield small GWP reductions, from the perspective of theentire Singapore market. However, it is worth noting that thisconclusion may be different for other countries that employdifferent methods of cement production, concrete manufacturingand brick production. As shown in Figs. 3 and 4, these life cyclestages play the most important roles in deciding the net GWP ofconsequence scenario 1.

With respect to consequence scenario 2 and Equation (9) above,to ensure that replacing concrete with bricks does not result in anychange in GWP (that is, set Equation (9) to zero), and after somealgebraic manoeuvres, the following condition must be satisfied:

e ¼ 1þ"�

GWPBrick þ ðf � 1Þ$GWPBricknot used

�R$GWPConcretei ðnot usedÞ

� GWPConcreteiGWPConcreteiðnot usedÞ

#(10)

In other words, if the increase in domestic consumption ofbricks causes an increase in import of bricks by a fraction “f”, then toensure that this does not result in a net increase in GWP, the frac-tional decrease in import of constituents of concrete “e” must be ofa magnitude defined by the relation in Equation (10).

Fig. 6 shows how the values of “e” changewith “f” for each of the6 types of concrete products. It shows the required decrease inimport of concrete constituents to nullify the increase in GWP dueto increase in brick import is the highest when bricks are requiredto replace concrete blocks (with 30% RCA content) and lowest whenprecast wall of thickness 100 mm are to be replaced. For example, ifthe import of bricks is increased by 1.5 times (that is, f ¼ 1.5), thenthe resultant increase in GWP can be nullified by decreasing theimport of concrete constituents by around 4 times (that is, g ¼ 4),provided the concrete is to be used to make concrete blocks.

ntage of impacts of bricks for 1 m2 of wall.


Table 10Net Global Warm Potential (GWP) of different replacement scenarios due to theconsequence scenario 1 for all the 6 types of concrete products. A negative valueindicates a net decrease in GWP.

Form of concrete Baselinescenario(22%replacement)

Replacementscenario 1(10% replacement)

Replacementscenario 2(30% replacement)

Concrete block �0.018 �0.008 �0.025PC wall (90 mm

thick)�0.020 �0.009 �0.028

PC wall (100 mmthick)

�0.022 �0.010 �0.031

30% RCA Concreteblock

�0.013 �0.006 �0.018

30% RCA PC wall(90 mm thick)

�0.016 �0.007 �0.021

30% RCA PC wall(100 mm thick)

�0.018 �0.008 �0.024


Furthermore, we found that the required decrease in concreteconstituent imports are the same for precast concrete wall ofthickness 90 mm and wall of thickness 100 mm with 30% RCA.

3.4. Integrated sustainability policies to improve the CUI

Our results showed that the recent strategy to reduce CUI andpromote the replacement of concrete with other types of buildingmaterials may not be as effective in reducing GHG emissions asexpected. From an ALCA perspective, replacing concretewith brickswill bring about a net increase in all the environmental impactsconsidered (including GWP). If changes to the national stockpilesfor brick and concrete constituents were considered, our CLCAindicated that there will be small changes to the GWP. Finally, if thedomestic changes in demands for concrete and bricks triggered achange in the imports of these materials, we derived a mathe-matical relation allowing us to know how much the import ofconcrete constituents must decrease in order to nullify theincreased GWP resulted from the increase in import of bricks.

While the CUI can still be implemented, results from this studysuggest that we can use integrated sustainability policies (ISPs) tosupplement CUI, and ensure that the CUI successfully promotes thereduction of GWP. ISPs are policies that, wherever possible, exploresocial, environmental and economic solutions to a certain problem.That said, an extensive discussion of all possible policies that can beemployed to improve CUI is beyond the scope of this paper.Nevertheless, innovations in kiln technology and financing policiesare two important aspects of ISP solutions. In particular, we focused

Fig. 6. Fractional decrease in import of concrete constituents required to nullify in-crease in global warming potential due to fractional increase in import of bricks.


our argument on the 1) reduction of environmental impacts ofbricks' life cycle through technology diffusion, and 2) innovativefinancing the upgrading of brick kilns.

3.4.1. Reducing impacts of bricks' life cycleAs mentioned above, the manufacturing phase of bricks

disproportionately contributes the most environmental impacts. Toreduce these impacts, one can increase the energy efficiency of themanufacturing process. Sun-drying wet cast bricks before firingthem is documented to be effective in reducing the overall energyand fuel demand of the firing process. Accurate control of kilntemperature is known to help increase kiln efficiency too. Morespecifically, the temperature should rise gradually and constantly,otherwise not only heat can be wasted, the bricks may also bedamaged. However, the temperature should not fluctuate untilfiring is complete. For example, researchers at Schilderman (2010)suggested that as a rough guide, a 40,000 brick kiln fired externallyshould be slowly heated over a period of 2 or 3 days until no moresteam emerges from the kiln, before being fired for another 4e6days until the bricks at the top are getting red hot. The kiln is thensealed at the top, and the firesmaintained for about a day. Similarly,the flow of air through a kiln should be controlled - too much airflowwill result inwastage of the heat energy, whereas too little willretard the combustion of the fuel. Protecting the fires from windsby means of wind breaks will also promote economy and help thekiln burn evenly throughout. The higher AP and EP impacts of brickcan also be attributed to incomplete combustion of biomass(sawdust, in our study) in the brick kiln. While it is desirable fromthe GHG abatement perspective that many brick manufacturers inSoutheast Asian countries (such as Vietnam, Thailand andIndonesia) are already using waste fuels (such as sawdust and ricehusk) as alternate fuels implies that similar problems withincomplete combustion of this biomass may occur. Hence, ensuringsufficient air flow in the kiln is very important.

To a large extent, these energy (and money) wastage andpollution issues can adequately be addressed by technologicalinnovation in kiln design and construction. A popular example ofsuch an innovation is known as the vertical shaft brick kiln (VSBK),which was devised in the early 1970s for burnt-clay brick manu-facturers in rural China and was later developed by several coun-tries in South Asia and Southeast Asia, most notably Vietnam andIndia. VSBK is about 40e50% more energy efficient than conven-tional kilns. If coal is used in the kilns, the CO2 emission from VSBKis estimated to be about 0.175 kgCO2

per brick, whereas conven-tional kiln (such as the fixed chimney type) produces about 0.345kgCO2

per brick (Tuladhar et al., 2006).The Energy and Resources Institute (TERI) in India is an example

of an organization that transferred VSBK technology to the Indianbrick industry (TERI, 2013). The Swiss Agency for Development andCooperation, in conjunctionwith TERI and other agencies proposeda systematic programme to augment brick production with theadoption and diffusion of this technology. Similarly, 166 brick kilnsin the Kathmandu Valley, Nepal, had been the target for introduc-tion of the VSBK technology (Tuladhar et al., 2006). In short, VSBK isa relatively well-known technology in Asia.

However, widespread adoption and diffusion of such a tech-nology requires a rigorous and yet effective financing mechanism.In the following section, two of the commonly utilized mechanismsare described. A new financing mechanism based on “green de-mand” was also proposed.

3.4.2. Financing the upgrading of brick kilns and the concept of“green demand” financing3.4.2.1. Conventional financing mechanism. Financing mechanismsfor the VSBK has taken several forms. The two most common forms



are direct financing by banks and utilizing the Clean DevelopmentMechanism (CDM). An example of the former is the World Bank'sfinancing of USD3.86 million for building 126 brick kilns in thestates of Chattisgarh, Rajasthan, Jharkhand, Madhya Pradesh, andOrissa in India. The funds came from the Community DevelopmentCarbon Fund (CDCF) managed by the World Bank (2006). On theother hand, CDM is one of the mechanisms under the Kyoto Pro-tocol with an objective to allow Annex I countries to meet part oftheir emission reduction commitments under the Kyoto Protocol bybuying Certified Emission Reduction units from CDM emissionreduction projects situated elsewhere, but mostly in developingcountries (Carbon Trust, 2009). As long as the conditions requiredby CDM are met, kiln upgrading can be (and has been) financed byCDM. For example, 8 brick kilns in Bangladesh, with a daily pro-duction rate of 500,000 bricks per day, had been upgraded underCDM; this project involved funders and participants from 13different countries, including the Ministry of Sustainable Devel-opment and Infrastructure of Luxembourg and 4 different organi-zations from Japan (including Fujifilm Corporation, Idemitsu KosanCo. Ltd., JX Nippon Oil & Energy Corporation, and Okinawa ElectricPower Corporation Incorporated) (UNFCCC, 2012).

However, financing by international financial institutions, suchas World Bank and Asia Development Bank, and CDM has itschallenges. For example, CDM projects of this nature tend to havehigh development and transaction costs. Besides, there may not bein-country expertise on applying for CDM andmanagement of CDMprojects. Verifying emission savings from kilns requires specialexpertise and this adds to the overall cost of the projects. CDMprojects also tend to demand considerable reductions of emissionsthat can only be achieved when a group of kilns participated in theprogram; however, engaging and committing a group of like-minded kiln owners can be challenging (Tuladhar et al., 2006).Hence, it is essential to create more options of possible fundingmechanisms for upgrading of brick kilns.

3.4.2.2. Financing from “green demand”. The GMS promotes theprocurement of sustainable building materials in that projects thatutilize stipulated materials are awarded different number of GreenMark rating points. Many of these materials are listed under theSingapore Green Label Scheme (SGLS) or certified under theSingapore Green Building Product list. Benefits of getting includedin these lists include companies enjoying greater market awarenessof their products and services, because certified products and ser-vices will be listed on Singapore Green Building Council's (SGBC)online certified products and services directory. This list enablesthose who are seeking green-differentiated products and servicesto access relevant information readily. Furthermore, certifiedproducts and services are entitled privileged entry to an exclusiveSGBC Export Grouping, which entitles participating companies toestablish valuable networks and participate in reputable local andoverseas tradeshows. In short, the GMS indirectly provides the“green demand” for sustainable building materials in the localindustry.

However, more can be done by applying this “green demand” topromote the “greening” of Singapore's sources of clay bricks.Recently, Singapore government (through an agency known asSPRING Singapore) has implemented many new policies and pro-grams to encourage entrepreneurship across all industries; forexample, under the Business Angel Scheme (BAS), with the goal toencourage experienced angel investing, SPRING Singapore workswith pre-approved private business angel investors to co-investand nurture innovative start-ups based in Singapore. While pro-moting the industry's uptake of sustainable building materials, theBCA may consider collaborating with SPRING Singapore to provideassistance to firms who are interested to either create, or partner


with existing building material producers to create, new sustain-able building materials.

That is, in our context, BCA may identify the need to have moreoptions of sustainable (or “green”) bricks for the local industry, andcollaborate with SPRING Singapore to proactively encourage en-trepreneurs in sustainable brick production to join the BAS.Singapore has been Malaysia's top trading partner; in 2013,Singapore market accounts for 50.1% of all exports by Malaysia(Department of Statistics Malaysia (2014)). It is also known that thelargest brick supplier in Malaysia exports 25% of its products toSingapore and Japan (Brick Dotcom, 2014) emaking Singapore oneof Malaysia's most important markets for bricks. If concrete blocksare replaced with bricks in Singapore, we expect even more bricksto be exported by Malaysia to Singapore. These entrepreneurs areencouraged to partner with incumbent brick producers inMalaysia.Investment from angels will be used to “green” the bricks' life cycle,possibly by upgrading existing brick kiln technologies. This is likelyto foster a multiple-win situation, in which the different partiesinvolved can benefit from the overall effort to provide more sus-tainable bricks to the local and international markets. This type ofmatch-made funding can be said to be based on “green demand”, ora form of “green demand” financing. Presently, there is only onetype of green brick that is listed under SGLS; this implies that thereis a potential for BCA to expand this list with a more innovativepolicy approach.

4. Conclusions

This study assesses the likely outcome of the CUI that isimplemented under the BCA GMS. Using an ALCA approach, wefound that the environmental impacts of replacing concrete withbricks may actually increase. Using a CLCA approach, we found thatreplacing concrete with bricks may result in GWP reductions butthese are small. Integrated technology and finance-related policyideas were proposed to address this likely problem. In our knowl-edge, this is the first ever CLCA conducted to compare environ-mental impacts of bricks and concrete. The methodology weapplied to identify and evaluate the consequence scenarios (shownin Table 3) is a new contribution to existing literature on conse-quences for CLCA. The ISPs proposed are new strategies that webelieve can help to improve the current CUI. Although our study hasfocused on Singapore, the methodology and policy ideas proposedcan be applied to evaluate any other building material and similarpolicies elsewhere in the world. From what we know, CUI is onlypracticed in Singapore. Themain reason is that Singapore is facing ashortage in sand supply, which is an important ingredient of con-crete. Hence, the results from this work serve as a precautionarynote for governments that plan to incentivize a reduction in the useof concrete due to possible shortages of sand in the future. This isthe international relevance of this study. Above all, at the morephilosophical level, this study reminds us that the net effects ofmaterial substitution must be studied cautiously and holistically,otherwise a strategy may not yield the results that we expect.

APPENDIX A. Calculations for functional unit of brick andconcrete in Singapore

a The bricks we have considered for our study are the mostcommonly used imperial bricks with dimension: 215 mm(length) � 70 mm (height) � 100 mm (thickness)The weight of each brick is 2.3 kg (from vendor's website).If we consider mortar thickness of 5 mm on each face, in onesquare meter of wall we have 55.5 units of bricks.Thus weight of brick per square meter of wall ¼ 55.5 X2.3 ¼ 127.65 kg



b From Vendor inputs we know, the dimensions of concrete blockused most commonly in Singapore ¼ 390 mm(length) � 190 mm (height) � 100 mm (thickness)The weight of each block ¼ 8.3 kg (from vendors' input)If we consider mortar thickness of 5 mm on each face, in onesquaremeter of wall we have 12.5 units of these concrete blocks.Thus weight of brick per square meter ofwall ¼ 12.5 � 8.3 ¼ 103.75 kgTherefore, replacement ratio of brick to concrete block ¼ 1: 0.81

c The weight of precast hollow concrete wall panel of 90 mmthickness ¼ 118 kgTherefore, replacement ratio of brick to precast concrete panel90 mm thickness ¼ 1: 0.92

d The weight of precast hollow concrete wall panel of 100 mmthickness ¼ 124e150 kgWe take an average of the above two values and arrive at 137 kg/m2 of wallTherefore, replacement ratio of brick to precast concrete panel100 mm thickness ¼ 1:1.07

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An attributional and consequential life cycle assessment of substituting concrete with bricks