Estimating Carbon Dioxide emission reduction by waste minimization in civil construction through the use of BIM

methodology.

Hans Peter van Putten

Marco Antonio Rocha

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Table of Contents

1 Introduction ____________________________________________________3

2 Research Questions _____________________________________________5

3 Background ____________________________________________________6

3.1 Carbon dioxide emissions in C&D Industry ____________________________6

3.2 Building Information Modeling (BIM) ________________________________11

3.3 Information Delivery Manuals (IDM) ________________________________14

4 Thoughts and Ideas for Problem Solving _____________________________16

5 Research Development __________________________________________19

6 Conclusion ____________________________________________________34

7 Bibliography ___________________________________________________35

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Figures List

Figure 01 – Clinkering process in a rotary kiln

Figure 02 – Production of lime in a rotary kiln

Figure 03 – The phases to produce clay bricks

Figure 04 – Quarried aggregates production

Figure 05 – Mechanism of the steelmaking in a blast oven

Figure 06 – Steelmaking processes

Figure 07 – Building Information Modelling (BIM)

Figure 08 – The ICC BIM platform for managing sustainable construction

Figure 09 – IDM support for business processes

Figure 10 – BIM methodology including a Virtual Waste Generation Stage, in an attempt

to reduce waste

Figure 11 - BIM based clash detection chart for preconstruction and construction

phases.

Figure 12 – Comparison of compositions of construction materials and construction

waste prevented by BIM in the two cases

Figure 13 – Carbon dioxide prevented by BIM-based design validation example

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1. Introduction

In the last decades we have seen, on scientific publications, on TV and other

media, a big concern in the increasing of Greenhouse Gases (GHG) in Earth’s

atmosphere. By the definition in the Kyoto Protocol to the United Nations

Framework Convention on Climate Change (UNFCCC), GHG is a group that

includes six types of gas: carbon dioxide (CO2), methane (CH4), nitrous oxide

(N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulphur

hexafluoride (SF6). (1)

These gases retain part of the sun’s heat, by trapping infra-red and other long

wave radiation that is otherwise reflected back into space, what is called the

Greenhouse Effect. The scientific debate now is about the increasing on Earth’s

temperatures, or Global Warming, probably caused by the high degrees in GHG’s

emissions by human activity. The main gas in these concerns is carbon dioxide.

(2)

The great concern in Global Warming comes from its many possible negative

effects to mankind: reduce the food offer in many countries, increasing the

number of hungry people all around the world; increase in global temperatures

between 1,8 and 4 celsius degrees; increase in the sea levels up to 58

centimeters, generating heat waves and dry weathers; extinction of some animal

species; and the emigration of around 200 million climate refugees until the end

of this century. (3)

One of the main human activity sectors that emits GHG’s is the civil construction

one, or the Construction and Demolition sector (C&D), representing one third of

the GHG’s emitted by mankind. Its emissions are associated: to raw material

extraction used in building materials; to the fabrication processes of these

materials; to the energy spent during the lifecycle of the constructions; to the

operation and maintenance of the constructions; and to the materials transport

and waste disposal. (4)

The waste generation is an important factor in research today, not only because

its reduction brings lower costs, but it may help in the reduction of GHG’s emitted

during the lifecycle of these disposable materials. The amount of waste generated

in C&D processes is enormous. This waste represented 26% of the solid waste

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in the United States in 2007 and 48% of the solid waste in South Korea in 2013.

And these numbers still growing in most of the countries in the world, usually

because of design errors, commonly detected in the construction industry. (5)

Buildings most commonly consist of elements which are designed by different

project participants and companies, and its corrections are made only after the

construction work has already begun on-site. This leads to rework and tons of

construction waste. Improper design and unexpected changes in the project were

identified, by many researchers, as major causes of construction waste

generation, with the possibility of a 33% increase in the volume of waste. (5) This

roughly means that with the waste of three buildings, you could build a new one.

A solution for this waste generation caused by rework would be an integrated

building design, avoiding design problems and changes. For many years,

researchers had studied one tool and methodology that facilitates building design,

the Building Information Modeling (BIM).(5)

BIM is a methodology which uses intelligent graphic and data modeling software

to create optimized and integrated building design solutions, to produce,

communicate and analyse building models. This tool includes the use of three-

dimensional, real-time, intelligent and dynamic modeling, facilitating successful

coordination and collaboration in the construction process. This technology is

already used to reduce cost and time, improving productivity in construction

industry. The use of BIM is already reported as well to reduce rework in

construction industry, reducing waste generation as a consequence.(5,6) But

what about the reduction in emissions of GHG’s, or in the case of this study, the

reduction in weight of carbon dioxide emissions to the atmosphere?

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2. Research Questions

How much waste is generated in common building projects?

How much of this waste can be reduced with the same results in C&D industry by applying a specific methodology in integrated building design?

How much carbon dioxide is emitted in the life-cycle of this waste?

How much would this reduction be beneficial to the environment?

Project Goals

The main goal is to research the amount of CO2 emitted in the lifecycle of the

materials that become waste in civil construction, and through this data, calculate

the reduction of these emissions in constructions built using BIM methodology.

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3. Background

3.1. Carbon dioxide emissions in C&D industry

The industries, the forest burnings and the fossil fuel utilization in transport and

in the generation of energy are the main emitters of GHG’s to the atmosphere.

Despite the 'in development' classified countries’ need to adhere to Kyoto

Protocol’s principles in 2012, the five biggest emerging markets, Brazil, China,

India, Mexico and South Africa, will increase their emissions of greenhouse gases

as their economies grow, according to the NGO Fund World for Nature– WWF.(3)

The C&D industry emits large amounts of greenhouse gases. According to

studies, carbon dioxide emissions from the construction industry account for

approximately 30% of total emissions in European cities. Only the cement

industry accounts for 7% of CO2 emissions. The production of the materials used

in constructions have a big participation in these carbon emissions. So the next

topics will discuss about the part of the main construction materials in the carbon

emissions to Earth’s atmosphere.(3)

3.1.1. Cement

The cement industry is responsible for around 5% of the global carbon

dioxide emissions. Cement is the main ingredient in concrete, the second

most consumed substance on the planet, water being the first one.

Cement’s main component is limestone, which is heated in a kiln at

1400ºC and then ground to form the clinker, as seen in Figure 01.

Combining clinker with gypsum results in cement.

Figure 01 – Clinkering process in a rotary kiln

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In the whole process, greenhouse gases are emitted both directly and

indirectly. The direct emissions come from the limestone heating, in a

process called calcination. Limestone is made mainly of calcium carbonate

(CaCO3) which, when heated, is decomposed in carbon dioxide, and

calcium oxide (CaO), as seen in Equation 01. The indirect emissions are

produced when heating the kiln, as this energy is provided by the burning

of fossil fuels, lke coal, natural gas, or oil, as seen in Equation 01.(10)

Equation 01 – CO2 emissions during the production of cement clinker and lime originate from either combustion or process CO2. CaCO3 is the main mineral in both cement

clinker and lime production.(11)

If following exactly the stoichiometry of this reaction, for each 1 ton of

cement produced, about 0,6 ton of carbon dioxide is emitted to the

atmosphere. It is not difficult to see how important it is to study ways to

minimize the use of this material.(3)

3.1.2. Lime

Lime, also known as calcium oxide, is a white powder, usually applied for

the preparation of mortars used in buildings, or even in painting

arrangements. It is obtained from the calcination of limestone in a rotary

kiln, as in Figure 02, and following Equation 01. This means that it emits

carbon dioxide in its lifecycle by the same mechanisms as in the

manufacturing of cement.3

Figure 02 – Production of lime in a rotary kiln

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3.1.3. Clay Bricks

Clay bricks are made by a process that includes: excavating the soil for

raw material, treatment of this brick earth or brick clay; hand or machine

molding of the bricks, with the treated and watered brick earth; air drying

of the bricks; burning in a clamp or in a flame kiln (Figure 02). (12)

Most of the red ceramic industry uses biomass as its source of energy in

the burning phase, like firewood, or sawdust. This means that it emits

amounts of CO2, although the energy source usually is more “green” than

the fossil fuels. But the use of fossil fuels, like coal, is still present in this

industry in the burning phase. (3)

Figure 03 – The phases to produce clay bricks (12)

3.1.4. Aggregates: sand and gravel

Aggregates are vastly used around the world, as they are part of the

concrete. They usually consist of crushed stone, gravel and sand, and are

mainly used in the construction of roads, rail track beds, the manufacturing

of concrete, concrete products, and asphalt. The sand and gravel used in

many building processes is natural, extracted directly from riverbeds and

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fluvial deposits, using dredges moved by diesel. But the use of aggregates

quarried from hard rock is very usual.

The aggregates extracted from quarries, follow through steps like: drilling

of the rock; blasting of the rock with explosives; extraction of the material;

processing of the same by crushing, shaping, screening; washing when

required; and the transport to the construction place.(13)

Figure 04 – Quarried aggregates production (13)

The main environmental impacts in this process are still the degradation

of the blasted areas for the extraction of raw material, the exhaustion of

non-renewable resources, and the contamination of watercourses. But

most of the equipment used for extraction and crushing run on diesel,

which is responsible for not only carbon dioxide emissions, but some

nitrogen and sulphur oxides as well.

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3.1.5. Steel

Steel is a common material in the C&D industry. Every construction will

have its presence, usually in the shape of bars or wires, used to provide

tensile resistance in concrete structures. It is obtained by steelmaking

processes, with the addition of carbon to iron ore in a blast furnace (Figure

05), followed by passage in other furnaces for the purification of the steel,

and then shaping of the final product (Figure 06). (3)

The extraction of the iron is basically a fusion of magnetite (Fe3O4) and

hematite (Fe2O3), contained in the iron ore, in the blast furnaces. The

carbon from the coke, together with the carbon dioxide emitted from the

heating of the limestone and the burning from the own coke, react,

resulting in carbon monoxide (CO). This carbon monoxide becomes a

reduction agent to the iron oxides present in the furnace, generating

molten iron, as seen by the mechanism shown in Figure 05. The process

generates high amounts of carbon dioxide and carbon monoxide.

Figure 05 – Mechanism of the steelmaking in a blast oven

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Figure 06 – Steelmaking processes

3.2. Building Information Modelling (BIM)

Building Information Modelling (BIM) is an approach to describe and

display the information required to a construction process, including the

design, the construction itself and the operation of the constructed facility.

In a single operating environment, it can join the many threads of different

information used in the building process. BIM is a methodology which uses

intelligent graphic and data modeling software, with integrated information

in computer aided design (CAD) form from all areas of a project, to create

optimized and integrated building design solutions, to produce,

communicate and analyse building models. This tool includes the use of

three-dimensional, real-time, intelligent and dynamic modeling, facilitating

successful coordination and collaboration in the construction process, as

seen in Figure 07. This results in a 3D digital representation in real time

of the physical and functional characteristics of the asset, as contractors

are no longer reliant only in 2D paper models and worried if all of their staff

is working in the same data after a change has been made. (5,6,16)

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Efficiency in this methodology depends on the quality of communication

between different participants in the construction process. The information

required has to be available when it is needed, and its quality needs to be

satisfactory. To build a BIM 3D model, all of the technical teams (e.g.

electrical, structural, hydraulic, fire prevention, and architects) have to be

working in the same model, so they necessarily have to be putting the

same type of information in this model, having the same standards in order

to do so. This means a common understanding about the building

processes, the information that is needed to each of them, and the results

from their execution. (16)

Figure 07 – Building Information Modelling (BIM)

Using BIM in the form of an integrated information, communication, and

collaboration (IICC) platform, staff and every component of project

concerned will have opportunity to contribute in managing a sustainable

construction as a whole. Figure 07 shows the IICC BIM platform for

managing sustainable construction, with each component contributing in

the net’s flow of information. (17)

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Figure 08 – The ICC BIM platform for managing sustainable construction

BIM applications are used to make contributions in (17):

• lower net information costs and risks;

• quick first response in early stage of design to make building safer;

• efficient monitoring, lower operation cost;

• better views of facilities for better decision making;

• reduced project cost and risks;

• better building environmental performance.

The Industry Foundation Classes (IFC) are the open and neutral data

format for BIM. It provides a good reference to all the information within

the lifecycle of a building, created as an integrated whole in response to

business needs identified by the international building construction

community. Still, it does not incorporate a comprehensive reference to the

individual processes within building construction. That’s why it is seen the

need to formulate Information Delivery Manuals (IDM).

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3.3. Information Delivery Manuals (IDM)

The C&D industry is known by joining many different companies and

authorities together in a specific project. To have a good level of efficiency

in this kind of work, it is necessary for all integrants in the organisation to

know which and when different kind of information has to be

communicated. The IDM standard was developed by buildingSMART, with

the aim in having a methodology to capture and specify processes and

information flow during the lifecycle of a facility. It is a methodology that

captures and integrates, progressively, business process while at the

same time provides detailed user defined specifications of the information

that needs to be exchanged at particular points within a project. (16,18)

The Information Delivery Manual (IDM) aims to provide the integrated

reference for process and data required by BIM by identifying the

discrete processes undertaken within building construction, the

information required for their execution and the results of that activity.

(16)

IDM is a proposal focused on improving the communication for BIM users

through better information quality. It not only tries to make standards for

the information flows, but to identify the relevance of the processes

involved, the relevant staff in creation, consuming and benefitting from it,

and how it should be supported by software solutions. In order to make it

operational, it has to be supported by software, as its main purpose is to

be sure that the important data is communicated in such ways that it can

be read by the software that receives this data. (16,18)

The IDM benefits BIM users with a plain language description of building

construction processes, requirements of information to be provided to

enable them to be fulfilled successfully, and their expected outputs, at the

same time that it benefits software developers, with the identification and

description of the processes and the IFC capabilities needing to be

supported for each functional part in terms. (16)

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Usually, information is exchanged about a particular topic and the level of

detail provided is driven by the project stage. The need is to support one

business requirement over one or more project stages, what means

deciding which IFC components need to be used to meet requirements. It

is not just a case of selecting one of the development schemas since these

are formed to help the task of distributing development between the model

authors (Figure 09). (16)

Figure 09 – IDM support for business processes (16)

IDM can unite the description of business processes with the specification

of information within the C&D project lifecycle, to enable realization of the

full benefits of process improvement and information sharing. This is

achieved by providing comprehensive reference to information

requirements for the C&D industry, by identifying the processes that

require the exchange or sharing of information between project

participants, the information required for and resulting from the execution

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of these processes, a basis for the consistent development of project

specific process models, and a common basis for agreement between

project participants about the information that can reasonably be expected

to support a project specific process. A proposal for development of IDM

is presented in section 5. (16)

4. Thoughts and Ideas for Problem Solving Methodology The methodology to this research project is based on finding relevant articles

containing value data about:

a) Carbon dioxide emissions in the lifecycle of construction

materials.

Many researches have already been done in the study of carbon

dioxide emissions related to the lifecycle of building materials. These

research papers make available average values of mass of CO2

emitted per mass of building material. The next table is an example of

information generated by this area of research:

Table 1 - Non-energetic CO2 generated in fabrication processes of some building materials (7)

Building Material t CO2/t

Aluminium 1,600

Lime 0,760

Cement 0,375

Concrete 0,045

Many other building information like this is at hand, like the Inventory of

Carbon & Energy (ICE), made available by the University of Bath. This

database is based on more than 1700 records of embodied energy in

construction materials, and has been structured into 34 main building

material groups, containing over 200 materials. (8)

This material information can be used to estimate the carbon cost to build

some projects, having in hand the volume or mass quantities of the

materials used in the building. This means that BIM designs, as they make

available all these volume and mass information, would be ideal to be used

with these data. Some researchers have already used this information to

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give even more complete estimations of carbon dioxide emitted by

constructions, as seen in Table 2.

Table 2 – Comparative results of Energy and CO2 embodied in the model (7)

Results New Zealand

Japan Denmark Brazil

t CO2/m2 0,35 0,40 0,40 0,37

GJ/m2 5,60 4,50 4,50 4,46

Results like the one shown above, despite the fact of being really averages

of individual kinds of buildings, can be a better and more accessible source

of information, if you are studying the same type of construction as the

ones worked with in these calculations.

b) Waste generation in construction processes of residential

buildings.

In scientific literature, is possible to find researches focused on

quantifying material waste in construction processes. The results of

these works give us some data as the ones shown in Table 3.

Table 3 – Waste generation rates and material loss rates according to different materials (9)

Materials Waste generation rate (kg/m2)

Mid-value of WGR (kg/m2)

Material loss rate (percentage of purchased)

Concrete 0,357 – 2,387 1,372 1,33

Timber (from formwork and falsework)

1,678 – 1,905 1,796 5

Metal (including reinforcement bar and fixing wire)

0,014 – 0,073 0,044 2,88

Bricks and blocks

0,037 – 0,821 0,429 7

Mortar 0,368 0,368 3,95

PVC pipes 0,035 0,035 1,05

Miscellaneous waste

0,786-3,202 1,994 -

Total 3,275-8,791 -

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c) Waste reduction in buildings that apply BIM methodology in their construction process. BIM has already been studied not only as a tool to reduce costs or get higher efficiency in the construction process. It has been studied as a methodology to minimize waste in construction due to design errors and consequent rework. Table 4 shows some results of an example of research done in this area. Table 4 – Volume of construction waste prevented by BIM-based design validation by materials (case 1) (5)

Case 1

Material Material type

Volume of prevented

waste (without likelihood)

Vow

Volume of prevented

waste (with likelihood)

Vow

Increased volume factor

Fvol

Demolished volume of prevented

waste

Vdw

Density values

ρ

Demolished weight of

prevented waste

Wdw

Concrete Concrete – cast-in-place

2071,1 94,81 1002,2 94,37 1,10 1102,4 94,36 2,4 2645,8 94,33

Concrete - plain

84,0 3,85 42,0 3,95 1,10 46,2 3,95 2,4 110,9 3,95

Total 2155,1 98,65 1044,2 98,32 1148,6 98,31 2756,7 98,29

Metal Metal - Aluminum

0,1 0,00 0,0 0,00 1,02 0,0 0,00 2,7 0,1 0,00

Metal – Copper

0,0 0,00 0,0 0,00 1,02 0,0 0,00 9,0 0,1 0,00

Metal – Stainless

0,1 0,01 0,1 0,01 1,02 0,1 0,01 7,9 0,9 0,03

Metal - Steel

0,1 0,01 0,1 0,01 1,02 0,1 0,01 7,2 0,5 0,02

Metal - Tin

0,1 0,00 0,0 0,00 1,02 0,0 0,00 7,1 0,3 0,01

Total 0,4 0,02 0,3 0,03 0,3 0,03 1,9 0,07

Finishes Plaster board

8,0 0,37 2,0 0,19 1,10 2,2 0,19 1,1 2,4 0,09

Total 8,0 0,37 2,0 0,19 2,2 0,19 1,1 2,4 0,09

Plastic Plastic – CPVC

0,1 0,00 0,0 0,00 2,00 0,1 0,01 1,5 0,1 0,00

Plastic – PVC

0,2 0,01 0,1 0,01 2,00 0,3 0,03 1,7 0,5 0,02

Total 0,3 0,01 0,2 0,02 0,4 0,03 0,6 0,02

Stone Stone – Granite

1,1 0,05 0,6 0,05 1,10 0,6 0,05 2,6 1,6 0,06

Stone - Marble

18,8 0,86 14,1 1,33 1,10 15,5 1,33 2,6 40,3 1,44

Stone – Mock marble

0,9 0,04 0,7 0,06 1,10 0,7 0,06 1,8 1,3 0,05

Total 20,8 0,95 15,3 1,44 16,8 1,44 43,2 1,54

Grand Total

2184,6 100,00 1062,0 100,00 - 1168,3 100,00 - 2804,8 100,00

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Quality Control

As this project is based on publications of other scientists, the quality control will be based on the relevance of these publications, consequently showing the confidence in the values and data used in this work.

5. Research Development

Construction waste origins are usually related to design changes, leftover

material scraps, non-recyclable/re-useable packaging waste, design/detailing

errors, and poor weather. A study indicated that construction waste is related to

design, site operation, procurement routes, material handling and sub-

contractor’s practices, and went further to compile and group the main sources

of waste factors in terms of construction lifecycle stages, comprising contractual,

design, procurement, transportation, on-site management and planning, material

storage, material handling, site operation, residual, and other. (17)

There is a consensus in literature that a significant portion of waste is caused by

problems which occur in stages that precede production, and design stage is

one of the major construction waste sources. (17)

All construction stages directly or indirectly contribute to on-site waste generation.

However, the level and severity of waste production varied from stage to stages

depending on a number of variables that include type of procurement, project

brief, stakeholders’ engagement and commitment, etc. It is widely argued that

waste reduction intervention should focus on pre-construction stages, particularly

design, where simulated waste generation during design stages, as opposed to

physical on-site waste, could be effectively identified, evaluated and reduced. It

would be an interesting idea to design out waste, since 33% of construction waste

might be directly influenced by inappropriate design decision making and design

changes, which contribute to more than 50% of the total on-site waste production

in construction projects. (17)

In a waste management context, BIM is a real-time interactive and collaborative

communication system that can help project stakeholders to collaboratively attain

construction waste minimisation throughout the lifecycle stages of a building,

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improving building construction performance. BIM enhanced communication and

collaboration are important facets of managing successful sustainable

construction. It has been argued that BIM could enhance communication and

collaboration; increase efficiency; and reduces errors, which in turn would reduce

resources, energy, materials and waste. Furthermore, BIM provides the

opportunity of testing, revising, rejecting and accepting design ideas in real-time,

such as the case for collaborative design methods. (5)

BIM tools may bring the possibility of reduction of construction waste, by making

easier the identification of design errors, and this way minimizing the possible

rework generated by it. A virtual waste generation phase could be studied during

the design phase, by identifying the mistakes and the conflicts between designs

from different parts involved in the construction process. This Virtual Waste

Generation stage would be fit in the BIM methodology as seen in Figure 10.

Figure 10 – BIM methodology including a Virtual Waste Generation Stage, in an attempt to

reduce waste (17)

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Various BIM uses like design validation, quantity take off, and prefabrication were

proposed for minimization of construction waste. Especially, they have claimed

that clash detection and design review have high potential to reduce construction

waste generated on-site by virtually identifying during design phase those

constructability issues that can be resolved ahead of time. (5)

Detecting building-element clashes and other causes of rework were chosen as

the most beneficial way of using BIM by owners, now becoming a common BIM

practice called the BIM-based design validation process. BIM-based design

validation can improve design quality by reducing the number of design errors,

change orders, and rework in the planning, design, preconstruction, and

construction phases. (5)

To the present work, the data was obtained from a research in two case studies

carried out in South Korea, based on qualitative and quantitative information from

construction waste generated on-site and prevented by BIM-based design

validation. A lot of practitioners say that most design errors can be found by

skilled and experienced building engineers without using BIM. A proposal was a

BIM Return of Investment analysis method in design error detection that

considers the likelihood of identifying an error without the aid of BIM.

The first case consists of two residential buildings (reinforced concrete structures),

with a total floor area of 120,000 m2 and the contractor decided to adopt BIM to

effectively manage such a complex project. 381 design errors were found by

practitioners by conducting a BIM-based design validation.

The second case is a sports complex composed of a baseball training facility and

a clubhouse, with a total floor area of 9995 m2. The contractor adopted BIM in

this case for error reduction as well as improved execution flow. This time,

practitioners found 136 design errors through BIM-based design validation. The

likelihood based BIM return of investment analysis method was the base to

categorizing these design errors (Figure 11). (5)

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Figure 11 - BIM based clash detection chart for preconstruction and construction phases (5)

The data about the construction waste in the two cases were estimated based on

the amount of rework caused by each error detected. They were classified and

analysed in accordance to level of impact. These levels of impact were

subcategorized into the cause and the likelihood of identifying an error before

construction using the traditional drawing based approach. Six project

participants in case 1 and three in case 2 classified the errors following the

author’s guidance, and estimated the likelihood of identifying each design error

without using BIM before construction based on their experiences and BIM issue

reports with screen shots and short descriptions of each error. In case 1 all the

participants had more than 15-year work experience in general contractors and

in case 2 the average was 10-year work experience.

The errors were categorized in three types: illogical design (eg. Clashes between

different building elements and drafting errors), discrepancies between drawings

(eg. A wall represented as a solid wall in an architectural drawing while it is

represented as steel beams in a structural drawing), and omission (eg. Missing

identifier numbers, lines or symbols for stepped floors, schedules, dimensions).

The likelihood considered here is the probability to identify each design error,

which was identified through BIM based design validation, without using BIM

(using drawing-based design review). For the likelihood applied to each error, for

example, 100% likelihood does not mean a chance to identify all errors but a

100% chance to find a specific error. The method used categorized the

likelihoods into three groups: 25% (unlikely), 50% and 75% (likely to be identified

without using BIM). The values of actual construction waste in both cases were

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also collected for a final comparison. Since obvious mistakes can also be missed,

0% or 100% likelihood were not considered.

Table 5 - Errors categorized by cause and likelihood of identification without BIM

Not every design error causes rework or additional work, so the ones that do

cause it should be identified to measure the prevented total amount of waste

using this methodology. 6 project participants identified that 108 (28%) out of 381

total errors had a potential impact on rework in the first case and in the second

case 21 (15%), based on their experience to resolve each of these errors. The

estimations were made with only the errors that generate waste. This can be seen

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in Table 6. The amount of construction waste prevented by

BIM-based design validation was analysed in two ways

according to building elements and material types: without

considering the likelihood of detecting each error, and

applying the likelihood (25, 50 and 75%). Quantity

information extracted from BIM models and separate

spreadsheets were used to calculate the volume of

prevented construction waste. Building elements were

categorized in 14 types (beam, cable tray, catwalk, ceiling,

column, duct, foundation, frame, pipe, ramp, slab, stairs,

truss and wall).

The total volume of construction waste prevented by BIM-

based design validation in cases 1 and 2 considering the

likelihood of detecting design errors without BIM were 1062

m3 and 79.5 m3, respectively. Without considering the

likelihood, the volumes of waste prevented were 2184.6 m3

and 270.2 m3. The reduction rate considering the likelihood

of identifying those design errors were 51.4% and 70.6%,

respectively.

In the second case, the amount of design errors that can be

easily detected without BIM design validation is greater

because the project is smaller and simpler than the first one.

The formula adopted to calculate waste prevention in these

cases was:

Vdw = Vow x P x Fvol

Where Vdw is the volume of construction waste prevented by

BIM-based design validation; Vow is the volume of prevented

waste without considering the likelihood (m3); P is the

likelihood of not being able to identify the error in the

traditional drawing based approach; and Fvol is the

increased volume factor, that could transform the amount of

construction waste into apparent volume.

Tab

le 6

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But since many waste management planning processes calculations are based

on weight, not volume, density information is needed (Tables 7 and 8). Then, the

following equation for unit conversion factor was formulated:

Wdw = Vdw x ρ

Where Wdw is the weight of prevented construction waste (ton); and ρ is the

default density of the waste material (ton/m3).

These cases compared the volume of construction waste reduction and

construction materials (Figure 12). Both volumes of construction materials used

were extracted from the BIM models used. The avoided construction waste was

Table 7

Table 8

26

estimated based on the volume of construction waste by considering the

likelihood of identifying errors without using BIM. The volume of waste avoided

by BIM-based design validation in the first case was 0.9% of the total value of

construction materials.

Concrete was the main material used in both cases (67% and 80%, respectively)

and was also the main material that was saved by BIM-based design validation

(98.3% and 95.7% of the materials that would become waste).

These case studies used the demolished volumes of avoided construction waste

(1168.3 m3 and 87.3 m3) by considering the likelihood of detecting errors without

using BIM to compare the disposed and avoided construction waste because the

waste disposed on construction sites are usually demolished before being

delivered.

In the end, the volume of construction waste avoided by using BIM-based design

validation were 15.2% in case 1 and 4.3% in case 2 of the sum of the volumes of

construction waste disposed. The discrepancy in these two values is given mainly

because of the difference in the nature and complexity of the projects, which

Figure 12

27

affect directly the likelihood of detecting errors in them, either by BIM or drawings

based design validation. (Table 9)

With the data obtained from Tables 7 and 8, and relating it to factors obtained in

the ICE database, it is possible to obtain CO2 mass values related to the life cycle

of the materials that had their waste volume reduced, as made in Table 10. This

was made following the equation:

WCO2 = Wdw x EC

Where Wdw is the weight of the waste of the material, prevented by BIM-based

design validation; EC is the embodied carbon in the material per mass unit; and

WCO2 is the weight of carbon prevented to be emitted to the atmosphere.

Table 10 – CO2 emission prevented with BIM-based design validation

Material Specification Case 1

Wdw Case 2

Wdw EC –

KgCO2/Ton WCO2 Case

1 WCO2 Case

2

Concrete Cast-in-place 2645.8 200.6 130 343954 26078

Plain 110.9 0 130 14417 0

Metal

Aluminum 0.1 0.4 8240 824 3296

Copper 0.1 0 3830 383 0

Carbon steel 0 1.0 2700 0 2700

Stainless 0.9 4.1 6150 5535 25215

Steel 0.5 14.1 2750 1375 38775

Tin 0.3 4.5 13700 4110 61650

Plastic PVC 0.5 0.7 2410 1205 1687

CPVC 0.1 0 2410 241 0

Finishes Plaster Board 2.4 0 380 912 0

Stone

Granite 1.6 0 781 1249,6 0

Marble 40.3 0 112 4513,6 0

Mock Marble 1.3 0 460 598 0

Total (Kg) 379317.2 159401

Total sum (Kg) 538718.2

Table 8

28

In Table 8, we can see that concrete was the biggest responsible for the carbon

emissions in case 1, and tin in case 2. The amount of concrete saved in the first

case is higher, as the quantities used were higher. In Table 9, we see the results

obtained per area unit of the constructions.

Table 9 – CO2 emission prevented with BIM-based design validation per area unit

Case 1 Case 2

Total area (m2) 120,000 9,995

Σ CO2 prevented (Kg) 379317.2 159401

Σ CO2 prevented/m2

(Kg) 3.160977 15.94807

As can be seen, the bigger saving in CO2 was possible in the project that was not

residential. Almost 16 kg of carbon dioxide per square meter built. This happened

because the materials used were different, including metals with high GHG’s

emissions known. One fact that has to be taken in consideration is that the

relative amount of concrete is considerably higher in the second case, in which

the concrete saving were higher than in the first one. The first case is more

relevant in this study, as this type of project is far more common that the other

one.

Comparing the value of case 1 with the previous results obtained for residential

constructions, as seen in Table 2, it can be observed that the amount of carbon

dioxide prevented corresponds to almost 1% of the total that would be emitted by

the construction. This is considerably high, as we are analysing only one of the

tools that the BIM methodology can provide, the BIM-based design validation.

And if taken in consideration the amount of residential buildings that are

constructed around the world every year, it is visible that this is a considerable

reduction, not only in carbon dioxide emissions, but in costs. Cement is the

second most used material by humankind, behind water. This reduction would be

important to reduce the demand for cement, maintaining the same final

construction results.

29

The information needed to prevent this carbon emissions were the required ones

in the design and preconstruction phases. The creation of a Virtual Waste Stage

in the BIM methodology was essential to reduce rework and real waste

generation.

This research project was based on a construction where BIM was applied only

after the designs were done, in preconstruction phase. In an ideal model, where

the designs would be made aided by IDM standardized information, the BIM tools

would be applied even before the preconstruction. The waste could be almost

totally virtual waste, before this stage.

As we can see in the research done, the information necessary for this were the

2D drawings, so they could be put together in a BIM model, analysed by

specialists and have their conflicts checked. This step generates information that

would go to the Virtual Waste Generation Stage, which is one of the sources of

necessary data to change the BIM model. The process to detect and resolve

design errors involves more than one sector in the building process. It can be

organized into an IDM flow chart, showing the flow of information needed to get

the expected results.

The designs used for the studied example came from many companies, and put

together in a BIM model. In this IDM flow, the responsibility for this is shown as

the Design Sector. The professionals who make the BIM-based design review

are put together in the Clash Detection Sector, detecting Illogical design,

discrepancies and omissions. This information is sent back to the Design sector,

as the Virtual Waste, so the BIM model can be modified if necessary, solving the

collisions. This cycle is done until no more collisions are found and the BIM model

can finally be sent to the Building Process sector, which generates the real waste.

The real waste can be quantified for further analysis by the Design and Clash

Detection sectors for the next building processes, as this information could

complement the Virtual Waste data, knowing that some methods inside the

building process will always need to generate waste to be completed. This Virtual

Waste generation can be finally combined with the information provided by the

ICE Database, to estimate the carbon dioxide generation embodied in the

lifecycle of its waste (Figure 13).

30

Figure 12 – Flow Chart for the information flow necessary for the estimation of the embodied

carbon in the waste generated in a building process

31

If a BIM model had been applied since the beginning, the time and costs would

be lower than the ones spent in the researched process, and the same probably

for the generated waste and, consequently, the carbon dioxide emissions. The

efficiency of the process shown in Figure 12 could be even higher by the

application of IDM and IFC standards in the transmitted information. This flow

chart is named process map in the IDM standard. (18,25) As IDM is to be applied

to software applications, an information output format could be configured for

each of these steps.

The first essential information is, of course, the standardized BIM model of the

construction. The blocks that make the building need to be in IFC standards. One

example of information format for the BIM model is in Table 10, a proposal for

Exchange Requirements and Functional Parts. It shows the flow of information

and displays the information that underlies assessment, IFC standards 2x4 (ISO

16739:2013). This methodology for specification is based on the ISO 29481-

1:2016 standard. (18, 25)

Table 10 - Proposed structure of the IDM for use in calculation process used by QVILLER (20)

Exchange requirements

Functional Parts

Information IFC 2x4 standard XML Revit ArchiCAD

Beams ifcBeam xmlBeam - -

Columns ifcColumn xmlColumn - -

Slabs ifcSlab xmlSlab - -

Wall, equal sizes

ifcsWallStandardCase xmlWallStandardCase - -

A proposal for further use of this methodology would be to develop an “IDM for

Virtual Waste specification”. buildingSMART International (bSI) have a long list

of developed IDMs and the “IDM for Virtual Waste specification” could by this be

distributed through bSI. These specification of relevant information can be

extended with rules for calculation of waste related to type of building process,

and other constraints. This development, eg. as plug-in to Revit or other software,

can enable automatic calculation of waste based as part of the design process.

(18, 25)

32

A model for the collisions information was used in the case-study, as it was shown

in Table 6 before. This information is used to apply in the improvement of the BIM

project, at the same time it comes with number data about structural parts of the

project that would generate waste from these collisions. The numbers of

structural parts that would generate waste in the case of not fixing the collisions

is shown in data as the one in Table 11. With this amount of structural parts

affected, that follows the IFC standards, their volumes and percentages of

materials are directly extracted from the BIM model, obtaining the construction

materials waste as shown before in Table 7, Table 8 and Figure 12, as part of the

Virtual Waste Generation data.

With the materials volume obtained from the Virtual Waste Generation data, with

their previous conversion to weight through their average densities, these values

are combined with the Embodied Carbon values from the ICE database, having

the product between reduction of waste and the embodied carbon giving the

Carbon Dioxide Generation output, as shown in Table 10.

This process of calculation is show in Figure 13 with an example, considering the

extraction of columns and beams waste data, and concrete and steel as their

main components.

Table 11

33

Figure 13 – Carbon dioxide prevented by BIM-based design validation example

When thinking about saving money in a determined process in a company

nowadays, the first thought and option is usually to fire staff, to cut a process

short. Stakeholders are often more concerned on spending less money than

spending it smartly. Firing personnel is not only bad for an economy, it also makes

the company look bad, nobody wants to work where bosses fire staff before

looking at other options. When it comes to waste management, firms are worried

about options about what to do with the waste, it is often brought up the “5 R’s”

(Reduce, reuse, recycle, repair, reject) and others simply buy more eco-friendly

materials so the waste is less hazardous to the environment, but only a few think

about actually reducing the waste levels. With the methodology proposed in this

paper, the waste levels are reduced noticeably, while production stays the same.

With BIM-based design validation, project managers work harder in the planning

phase so they have a more controlled and error minimized execution, which

generates less rework and physical waste.

34

6. Conclusion

The present research work gathered information about carbon dioxide emissions

directly and indirectly related to building materials production, waste generation

on-site, BIM methodology and IDM standards to accomplish the objective of

calculating the reduction of carbon dioxide emissions to the atmosphere brought

by BIM-based design validation in building processes. The required data for the

calculation was extracted from two case-studies developed in South Korea, plus

the ICE database which provided values for carbon emissions in the lifecycle of

building materials.

The results obtained were savings of 379 tons of carbon dioxide for 120,000 m2

of two residential buildings, and 159 tons for 9.995 m2 of a baseball training facility.

This means savings of 3.2 kg CO2 / m2 in the first case and 15.9 kg CO2 / m2 for

the second one. In the two study cases from South Korea used in this paper, the

one which had a waste reduction rate of 15.2% is an extremely common project

(residential buildings with reinforced concrete structure), these 15.2% represent

around 1,200 m3 of waste, of which 98.3% is entirely concrete and represents

379 tons of CO2 as well. This waste prevented is 0.9% of the sum of the materials

used in the entire construction process, from beginning to the end, in only one

construction site. In 2011, South Korea emitted 610 million metric tons of CO2,

which 40% came only from the construction industry. If they had all saved 0.9%,

there would be 2.2 million metric tons less of carbon dioxide in the atmosphere in

that year, and South Korea is only the 8th country with most emissions. According

to the Environmental Protection Agency (EPA), this spared value is equivalent to

the annual GHG emissions of 406,761 passenger vehicles and it takes 15,490

acres of preserved forest to annually absorb these emissions. (21, 22, 23, 24)

The application of IFC and IDM standards were embedded in the BIM study, as

a way to enable high efficiency in the process of waste minimization,

quantification and carbon dioxide emission calculations. A model of information

necessary to get these results was proposed and it is open to be improved in

future studies.

35

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