Six Sigma Approach to Real Time Cast In-Situ Slab Concreting
Process Improvement
Seyed Ali Mousavi Niaraki
A PROJECT REPORT SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR
THE AWARD OF THE DEGREE OF MASTER OF SCIENCE (CONSTRUCTION MANAGEMENT)
FACULTY OF CIVIL ENGINEERING
UNIVERSITI TEKNOLOGI MALAYSIA
April, 2010
To My Lovely Father & Mother…
ACKNOWLEDGEMENT
I would like to give my sincere appreciation to my project supervisor Assoc. Prof.
Dr. Abdul Kadir Bin Marsono for being patience with me, and his friendly guidance,
critic advices, motivation and last not least the valuable encouragement.
While preparing this project, I was in contact with many academicians’ student and
lecturers from Faculty of Civil Engineering, Built Environment, Geo-technique, besides
construction professionals in construction firm, consultants. They have contributed
towards my understanding and thoughts. In particular, I am also very thankful to all of
them for their willingness to share their valuable knowledge, expertise and technical
know-how which assist me a lot in preparing this project. Without their continued
support and interest, this project would not have been the same as presented here.
I am also would like to thank all the lecturers who have conducted the course from
the beginning of this master program and not hesitating to share their knowledge with
us. My fellow postgraduate students should also be recognized for their support. My
sincere appreciation also extends to all my classmates Ali, Mohsen, Farahbod, Niloofar,
Hamed, Masoud and others which unfortunately, it is not possible to list all of them in
this limited space, which have provided individually and sometime group assistance at
various occasions.
Finally, I want to give my special thanks to my panels Dr. Aminah, Dr. Shaiful, Mr.
Bachan Singh, for their kindly advises.
ABSTRACT
The best way of construction processes improvement is by problem solving
approaches. Before problems start to emerge in construction phases. In accordance to
experiencing in real time problem solving approaches in other industries processes this
study suggest that its time to go toward other industries experiences in real time
problem solving. Proposing check sheet for real time problem solving within Six Sigma
by; Identifying problem’s root causes and taking preventive actions before facing
problem during construction phase, is main target of this study. This study were
conducted as project experience and data gathering from interview with related experts.
For achieving this goal, study adopting cast in-situ slab concreting quality
improvement. Finding root causes of plastic crack in cast in-situ slab concreting and
eliminating them in first place by applying Six Sigma tools and techniques.
ABSTRAK
Cara terbaik proses perbaikan pembinaan adalah dengan pendekatan penyelesian
masalah.Sebelum masalah mulai muncul dalam fasa pembinaan, Sesuai untuk yang
mengalami masalah pendekatan penyelesaian real time dalam industri lain proses kajian
ini menunjukkan bahawa masa untuk pergi ke arah pengalaman industri lain dalam
penyelesaian masalah real time. Mengajukan helai semak untuk menyelesaikan masalah
real time dalam Six Sigma oleh; Mengidentifikasi akar penyebab masalah dan
mengambil tindakan preventif sebelum menghadapi masalah selama fasa pembinaan,
merupakan target utama dari kajian ini. Studi ini dilakukan sebagai pengalaman projek
dan pengumpulan data dari wawancara dengan para ahli berkaitan. Untuk mencapai
matlamat ini, kajian mengadopsi cor concreting peningkatan high in-situ slab. Mencari
akar penyebab retak plastik di cor concreting slab-situ dan menghilangkan mereka di
tempat pertama dengan menerapkan Six Sigma dan alat teknik.
CONTENTS
CHAPTER
DESCRIPTION
PAGE
TITLE
DECLARATION
DEDICATION
ACKNOWLEDGEMENT
ABSTRACT
ABSTRAK
CONTENTS
LIST OF TABLES
LIST OF FIGURES
LIST OF APPENDICES
CHAPTER 1
INTRODUCTION
1.1
Introduction
1
1.2
Problem statement
2
1.3
Objectives of the Research
3
1.4
Scope of the Study
3
CHAPTER 2
LITERETURE REVIEW
2.1
2.2
Construction Process
4
2.1.1 Background of CPI
4
2.1.2 CPI Tools & Techniques
5
Six Sigma
8
2.2.1 Historical Background of Six Sigma
8
2.2.2 What is Six Sigma?
12
2.2.2.1 Why Six Sigma?
14
2.2.3 Six Sigma Problem Solving Process
20
2.2.4 DMAIC
21
2.2.5 Six Sigma Champion
21
2.2.5.1 Master Black Belt
22
2.2.5.2 Black Belt
23
2.2.5.3 Green Belt
23
2.2.5.4 Yellow Belt
24
2.2.6 Six Sigma Principles & Metrics
24
2.2.7 Six Sigma as a Quality Movement
28
2.2.7.1 (1.5 Sigma)
29
2.2.7.2 (3 Sigma (TQM))
29
2.2.7.3 (3 Sigma with 1.5 Sigma Shift) 31
2.2.7.4 (4.5 Sigma)
32
2.2.7.5 (4.5 Sigma with 1.5
Sigma Shift)
32
2.2.7.6 (6 Sigma)
33
2.2.8 Six Sigma in Construction
35
2.2.8.1 Pervious Application of
Six Sigma in Construction
2.3 Cast-In-Situ Concreting Process
37
37
2.3.1 Design of Mix & Reinforcing
38
2.3.2 Ready-Mix & Hand-Mix
38
2.3.3 Workability of Concrete
39
2.3.4 Access to Site
40
2.3.5 Formwork
40
2.3.6 Placement
41
2.3.7 Curing
42
2.4 Reinforced Concrete Cracks
45
2.4.1 Structural Cracks
45
2.4.2 Application Based Cracks
45
2.4.2.1 Fresh Concrete Cracks
45
2.4.2.2 Settlement Cracks
46
2.4.2.3 Plastic Shrinkage Cracks
46
2.4.2.4 Over Aged Concrete Cracks
48
CHAPTER 3
CHAPTER 4
RESEARCH METHODOLOGY
3.1 Introduction
50
3.2 Method of Data Collection
50
3.3 Data Collection
50
DATA ANALYSIS
4.1 Introduction
53
4.2 DPMO Calculation of Current
Cast-In-Situ Slab Concreting Process
54
4.3 Identify Causes & Root Causes of
Plastic Crack in Cast-In-Situ Slab
Concreting Process
61
4.4 Identify Potentials Level of
Each Root Causes
68
4.5 Identify Frequency Level of
Each Root Causes
69
4.6 Proposed Check Sheet for Real Time
Improving Cast-In-Situ Slab
Concreting Process
70
4.7 Explanation of Items of Proposed
Check Sheet
4.8 Explanation of Proposed Check Sheet
CHAPTER 5
74
75
CONCLUSION AND RECOMMENDATION
5.1 Conclusion
77
5.4 Recommendation
77
REFERENCES
79
APPENDICES
81
LIST OF TABLE
TABLE NO.
TITLE
PAGE
Table 2.1
Contrasting Six Sigma and Total Quality Management
17
Table 2.2
Simplified Sigma Conversion Table
27
Table 4.1
Root Causes of Plastic Crack in Cast-In-Situ Slab
Concreting Process
Table 4.2
66
Percentage of each category in each potential level
according to number of root causes in each category
which is placed in each potential level
Table 4.3
68
Percentage of each category in each frequency level
by considering number of root causes which is placed
in each frequency level
69
LIST OF FIGURE
FIGURE NO.
TITLE
PAGE
Figure 2.1
Traditional bell curve of normal distribution of data
14
Figure 2.2
3.4 deviate from either side of the average
15
Figure 2.3
Process of introducing Six Sigma
18
Figure 2.4
Systematic and scientific approach of Six Sigma
18
Figure 2.5
1.5 Sigma
29
Figure 2.6
3 Sigma (TQM)
30
Figure 2.7
3 Sigma with 1.5 Sigma Shift
31
Figure 2.8
4.5 Sigma
32
Figure 2.9
4.5 Sigma with 1.5 Sigma Shift
33
Figure 2.10
6 Sigma
34
Figure 2.11
Six Sigma’s Structured Methodology (DMAIC)
35
Figure 2.12
Operations involved in traditional concrete
Construction (schematic)
44
Figure 2.13
Classifications of Cracks in Reinforced Concrete
49
Figure 3.1
Methodology Flow
52
Figure 4.1
Concerting process
55
Figure 4.4
Cracks which is investigated from the site
58
Figure 4.5
Fish Bone Diagram
62
Figure 4.6
Pareto Chart
67
Figure 4.7
Proposed Check Sheet
71
LIST OF APPENDICES
APPENDICES
TITLE
PAGE
A
Questionnaire Form A
82
A
Questionnaire Form B
89
B
Six Sigma Conversion Table
96
1
CHAPTER 1
INTRODUCTION
1.1 Introduction
In the recent years, construction projects have turned into a more complicated,
dynamic and interactive scenario. Project managers are constantly required to speed-up
reflective decision-makings on time. Construction is an experience-based discipline,
knowledge or experience accumulated from pervious projects, plays very important role
in successful performance of new works. If experience and knowledge are shared, then
the same problems in construction projects will not be repeated.
Several enabling activities should be considered to help to achieve the ultimate goal
of efficient experience and knowledge reuse; experience and knowledge should be
preserved and managed; that is, they should be captured, modeled, stored, retrieved,
adapted, evaluated and maintained and updated (Bergmann, Ralph (2002). The reuse of
information and knowledge minimizes the need to refer explicitly to past projects;
reduces the time and cost of solving problems, and improves the quality of solutions
during the construction phase of a construction project. The knowledge can be reused
and shared among the involved engineers and experts to improve the construction
process and reduce the time and cost of solving problems.
Only in recent years has sparing the six-sigma method been utilized by some of the
major players in the construction sector. While traditional quality programs have
2
focused on detecting and correcting mistakes, six-sigma encompasses something
broader: it provides specific methods to re-create the process itself so that the defects
are never produced in the first place. The concept seeks to continually reduce variation
in processes with the aim of eliminating defects from every transaction (Hahn et al.,
1999; Tennant, 2001). The main advantage of the six-sigma method is that it shares
much of the same values and uses similar tools to TQM. The tools are nothing new, but
the strategic way that the six-sigma programme proactively uses them, within its
structured framework, is what generates improved results. (Hagemeyer, C; Gershenson,
J.K; Johnson D.M, 2006).
By considering previous project experiences we can find problematic element of
defects in previous project learn it, and find the defect’s root causes by eliminating root
causes in current project systematically. For achieving this goal this study has choose
Six Sigma problem solving approach.
1.2 Problem Statement
In accordance real time delay and defect problem. Approaches of “quality record and
document” and “corrective and preventive actions” with different objectives, major
process, information requirements industries processes is use in the project. The study
suggest that several amount of defect and late delivery of project in times need to be
learned.
3
1.3 Objectives
1- To identify and analyze the root causes of plastic crack to Six Sigma problem solving
approach.
2- To propose check sheet for real time problem solving cast in situ slab concreting
process from the outputs of pervious problem and solutions.
1.4 Scope of Study
In this research cause of different nature of construction projects like dam, road, air
port, high rise building, office buildings project and further; researcher has selected
office building construction. With focusing on cast in situ slab concreting process. In
this research, researcher has concentrated on DMAIC methodology of Six Sigma
problem solving approach. The study conducting site survey on construction project in
Universiti Teknologi Malaysia (UTM).
4
CHAPTER 2
LITERATURE REVIEW
2.1 Construction Process
2.1.1 Background of Construction Processes Improvement
The aim of process improvement in construction is to produce something of equal or
better worth, at a lower cost. Brown and Adams (2000) reported that in the procurement
of projects, leading clients are increasingly demanding a high quality product at a low
cost, which is also reliable and delivered on the date required. The major feature of
construction processes is that they are notorious for their complexity and changes
during the construction process (Van der Aalst et al., 2002). The construction industry
has few structured frameworks on which to based on process improvement initiatives
and achieving total quality. The absence of clear guidelines has meant that
improvements are often isolated and benefits cannot be coordinated or repeated.
The construction industry is a business sector that plays a substantial role in many
economies. However, the attainment of acceptable levels of quality in the construction
industry has long been a problem. Significant quantities of resources, both human and
material, are wasted each year as a result of inefficient or non-existent quality
5
management procedures (Arditi and Gunaydin, 1997). There exists great potential for
quality improvements in the construction industry; its importance cannot be
understated, regardless of a nation’s primary business, and organizations will always
require interaction with the construction industry to source physical assets to house
operations (Cox and Ireland, 2002). In recent years, globalization and deregulation of
markets has led to increased foreign participation in domestic construction, placing
further pressure on local leading firms for major reforms. The cause of many problems
lies in the organization of the industry and associated processes. Firms need to build on
their competitive strengths through a deliberate and managed process to improve the
capacity and effectiveness of the industry and to support sustained national economic
and social objectives.
2.1.2 Construction Processes Improvement Tools & Techniques
A number of techniques and tools can be found under the TQM/Continuous Process
Improvement (CPI) umbrella, including the process cost model, standardized process
improvement for construction organizations, the balanced scorecard, Kaizen and
statistical process control. Traditionally, businesses have tended to measure
performance using only financial measures. As a result, organizations adopted
techniques similar to the process cost model (PCM). This concept was developed in
manufacturing industry and has been moulded into a workable strategy suitable to
construction applications (Aoieong et al., 2001). The PCM is a process-orientated
approach that values client satisfaction and continuous process improvement. PCM uses
financial theory to analyse and direct efforts for improvement; which has its advantages
and disadvantages. The use of a single measure clearly illustrates the tangible benefits
in a compatible format that is easy to interpret (Arditi and Gunaydin, 1997; Moen,
1998). However, the weakness of financial metrics stems from their failure to measure
and monitor multiple dimensions of performance. Additionally, financial measures used
in isolation create problems in that they are characterized as lagging measures, i.e. they
are the result of past events. Consequently, PCM is a reactive approach, because waste
and associated non-value adding activities have already transpired. For construction
6
firms to succeed in the future they need to implement a more proactive approach to
improving processes (Moen, 1998). To look beyond financial measures, Sarshar et al.
(2000) developed the standardized process improvement for construction enterprises
(SPICE) framework. This framework was founded on the principles of the capability
maturity model (CMM) and argues that the outcome of a process is a function of the
maturity of the organization and its associated processes (Hutchinson and Finnemore,
1999; Sarshar et al., 2000). The philosophy of this framework is that a process becomes
more predictable and reliable as the organization and its processes simultaneously
mature. SPICE provides a structured framework with a definite starting point that
assists the process improvement teams to prioritize areas for improvement. The SPICE
framework provides a good process diagnostics tool with a strong process focus.
Sarshar et al. (2000) demonstrated the application of the SPICE framework in two case
studies aimed at improving construction processes. An interesting outcome of these
studies was that an organization does not have the capability to capture best practices
until ‘level 3 (defined)’ of the framework.
In light of this, the SPICE framework has many similarities with six-sigma,
particularly in its ability to address priority processes. Although the two previous
techniques provide an indication as to the success or failure of a project, they do not
provide a balanced view of a project’s performance. Kaplan and Norton (1992)
developed the balanced scorecard (BSC) to capture both the tangible and intangible
perspectives of performance. The BSC provides information on four perspectives,
including customer perspective, internal business perspective, learning and growth
perspective and financial perspective. However, this approach is far from simple and
requires a comprehensive understanding of the fundamental characteristics of
performance measurement as well as a significant commitment from top management
and employees (Chan et al., 2002). Moreover, construction firms may find
implementation difficult due to the diversity of their projects (Sommerville and
Robertson, 2000). Hubbard (2000) also felt that the BSC was too generic in design and
7
did not consider a specific industry’s needs or the strategic desires of individual
organizations.
Another process improvement technique that was developed by the Japanese and
was a contributor to their economy’s rapid growth in the second half of the twentieth
century was Kaizen. This technique was formed from a quality culture that emphasizes
continuous process improvement through standardization – i.e. establish a standard,
maintain it and then improve it (McGeorge and Palmer, 2002). However, the technique
tends to be difficult to adopt for firms that have already implemented the TQM culture.
In view of this, the authors do not believe that Kaizen can offer the construction
industry substantial benefits since it merely promotes similar ideals already created
through TQM. What the industry needs is a structured datadriven approach to direct its
efforts. A more data-driven technique is statistical process control (SPC), which has an
emphasis on numbers, fact-based analysis and tangible decision-making. Consequently,
due to its technical nature, it has never been fully embraced (Dale et al., 2000). With
managements becoming more interested in performance and profitability, they are
beginning to divert attention back to the analysis of process variation and elimination
through root cause analysis and problem solving. Use of SPC identifies overall process
capabilities and areas that need improvement. Although SPC equips the users with an
extensive array of measurement techniques it appears to lack a strong organizational
supportive framework. The tools employed by SPC have, to a large extent, fuelled the
development of the latest addition to the TQM/CPI umbrella that is Six-Sigma.
8
2.2 Six Sigma
2.2.1 Historical Background of Six Sigma
Sigma is a letter in the Greek alphabet that has become the statistical symbol and
metric of process variation. The sigma scale of measure is perfectly correlated to such
characteristics as defects-per-unit, parts-per million defective, and the probability of a
failure. Six is the number of sigma measured in a process, when the variation around the
target is such that only 3.4 outputs out of one million are defects under the assumption
that the process average may drift over the long term by as much as 1.5 standard
deviations. Six Sigma may be defined in several ways. Tomkins(1997) defines that Six
Sigma is "a programme aimed at the near-elimination of defects from every product,
process and transaction". Harry(1998) defines that Six Sigma is "a strategic initiative to
boost profitability, increase market share and improve customer satisfaction through
statistical tools that can lead to breakthrough quantum gains in quality". Six Sigma was
launched by Motorola in 1987. It was the result of a series of changes in the quality area
starting in the late 1970s, with ambitious ten-fold improvement drives. The top
management with CEO Robert Galvin developed a concept named Six Sigma. After
some internal pilot implementations, Galvin, in 1987, formulated the goal of "achieving
Six-Sigma capability by 1992" in a memo to all Motorola employees (Bhote, 1989).
The results in terms of reduction in process variation were on-track and cost savings
totalled US$13 billion and improvement of labor productivity became 204% increase
during 1987-1997 (Losianowycz, 1999).
In the wake of successes at Motorola, some leading electronic companies such as
IBM, DEC, Texas Instruments launched Six Sigma initiatives in early 1990s. However,
it was not until 1995 when GE and Allied Sigma launched Six Sigma as strategic
initiatives that a rapid dissemination took place in non-electronic industries all over the
9
world(Hendricks and Kelbaugh, 1998). In early 1997, Samsung and LG groups in
Korea began to introduce Six Sigma under their companies. The results were amazingly
good in those companies. For instance, Samsung SDI, which is a company under
Samsung group, reported that the cost savings by Six Sigma projects totalled US$150
million (Samsung SDI, 2000). At the present time, the numbers of big companies
applying Six Sigma in Korea are exponentially growing, with a strong vertical
deployment into many small and medium sized enterprises as well. Through the
consulting experiences of Six Sigma in Korea, the author believes that Six Sigma is a
new strategic paradigm of management innovation for a company to survive in this 21st
century(Park et. al, 2000).
Six Sigma implies three things; statistical measurement, management strategy and
quality culture. It tells us how good our products, services and processes really are
through statistical measuring of quality level. It is a new management strategy under
leadership of the top management to create quality innovation and total customer
satisfaction. It is also a quality culture. It provides the way to do things right the first
time and to work smarter by using data information. It also provides an atmosphere to
solve many CTQ (critical-to-quality) problems through team efforts.
Motorola, Inc. invented Six Sigma, and we have learned a great deal about it over
the last 18 years. During that time, Six Sigma has evolved from its roots as a measure of
quality to an overall business improvement methodology and to what it is today at
Motorola – a fully integrated management system.
In 1986, Bill Smith, a senior
engineer and scientist within Motorola’s Communications Division, introduced the
concept of Six Sigma in response to increasing complaints from the field sales force
about warranty claims. It was a new method for standardizing the way defects are
counted, with Six Sigma being near perfection. Smith crafted the original analysis and
tools that were the beginnings of Motorola’s Six Sigma methodology. He took his ideas
to CEO Bob Galvin, who was struck by Smith’s passion and came to recognize the
10
approach as key to addressing quality concerns. Six Sigma became central to
Motorola’s strategy of delivering products that met the high quality standards our
customers deserved. Following a common Six Sigma methodology, Motorola began its
journey of documenting key processes, aligning these processes to critical customer
requirements and installing measurement and analysis systems to continuously improve
the process.
Past definitions of quality were found to have focused on ‘‘conformance to
standards’’ where companies strived to create products and services that fell within
certain specification limits. In Six Sigma, the definition of quality is broadened to
include economic value and practical utility to both the company and the customer. Six
Sigma recognizes that business quality is the highest when costs of delivering products
and services to meet customer requirements are at the absolute lowest for both the
producer and the consumer. Six Sigma is therefore developed as a business strategy and
philosophy built around the concept that companies can gain a competitive edge and
stay ahead of the competition by reducing defects in their industrial and commercial
processes (Harry and Schroeder 2000). Various authors have defined Six Sigma in the
following ways.
Harry and Schroeder 2000, who are the key developers and proponents of the Six
Sigma program at Motorola, defined SixSigma as ‘‘a disciplined method of using
extremely rigorous data gathering and statistical analysis to pinpoint sources of errors
and ways of eliminating them.’’ Snee 2000, indicated that ‘‘Six Sigma should be a
strategic approach that works across all processes, products, company functions and
industries.’’
Chowdhury 2001, explained that Six Sigma represents a statistical
measure and a management philosophy that teaches employees how to improve the way
they do business, scientifically and fundamentally, and how to maintain their new
performance level. It gives discipline, structure, and a foundation for solid decisionmaking based on simple statistics. Pande et al. 2000, defined Six Sigma as a way of
11
measuring processes, a goal of near perfection represented by 3.4 defects per million
opportunities (DPMO); and more accurately, a comprehensive and flexible system for
achieving, sustaining, and maximizing business success. It is uniquely driven by a close
understanding of customer needs, disciplined use of facts, data, and statistical analysis,
and diligent attention to managing, improving, and reinventing business processes.
Pande and Holpp 2002, defined Six Sigma as a statistical measure of the performance of
a process or a product; A goal that reaches near perfection for performance
improvement; and a system of management to achieve lasting business leadership and
world-class performance. In general, the above definitions of Six Sigma may be
summarized into the following two aspects: Six Sigma is a statistical measure used to
measure the performance of processes or products against customer requirements. This
is known as the ‘‘technical’’ definition of Six Sigma; and Six Sigma is a ‘‘cultural and
belief’’ system and a ‘‘management philosophy’’ that guide the organization in
repositioning itself towards world-class business performance by increasing customer
satisfaction considerably and enhancing bottom lines based on factual decision making.
In the last 10 years, Six Sigma has risen to the top as one of the most talked about
process improvement and quality management programs available. It rivals ISO 9001
and CMMI in interest and adoption. But of the three, it is often the least understood.
There are a couple of reasons for this. The first is that compared to ISO and CMMI, Six
Sigma has the potential to be imminently more complex. By moving seriously into its
statistical and quantitative aspects, it can be both powerful (to the informed) and
powerfully daunting (to the uninformed).
12
2.2.2 What is Six Sigma?
Six Sigma is different from ISO 9001 and CMMI in that its focus is on measuring
existing processes with a view to making them more efficient and effective. Six Sigma
assumes there are processes in place. Maybe they are formal, maybe they are informal,
but they are definitely doing something to produce something. At its core, Six Sigma is
a way to measure processes and then modify them to reduce the number of defects
found in what you produce. With this program, they study the sources of defects and
then analyze ways to make the processes more resilient, so that defects are not
introduced or have fewer opportunities to creep in.
Many people think that the idea behind Six Sigma is to have a system that produces
zero defects. That's not really true. But, statistically, the rote measure of "six sigma"
means that your system will turn out only 3.4 defects per million opportunities for
defects.
The real idea behind Six Sigma is to manage process improvement quantitatively. It
seeks to put measures and controls in place so that you can readily and regularly
monitor the performance of your processes and, using performance data, adjust them to
maximize their ability to produce predictable, quality results. They can think of Six
Sigma as the evaluation side to a process improvement program. That's why many
organizations pair Six Sigma with programs like ISO 9001, CMMI, or LEAN. Six
Sigma gives you the tools you can use to rate how well these programs are performing
for you. And this rating is not qualitative. It is not instinctive or intuitive. It is a rating
based on hard data, on fact.
By looks at the high-level focus of Six Sigma, that it is a cycle of seven general steps:
1. Look at the product. Put a critical eye on what is producing. Continually
examine what it is making and how is made it so that you can always seek ways
to make it better. There are few sacred big issues Six Sigma.
13
2. Identify defects. Examine the
product and identify defects. Count them.
Measure them. Know what is mean by the term "defect." a defect can be as
anything that holds the product back from being the best and it can be in the
minds of customers.
3. Look to the process. If the product is not all it can be, then chances are the
processes could be improved. Examine the processes. What's happening with the
current processes that might be letting defects in? What opportunities might see
to keep defects out?
4. Determine sources of defects. Analyze how the process works. Study its flows
and structure to determine where in its operations defects are seeping in.
5. Improve the process. Based on the analysis of process performance and
understanding of the process structure, now adjust the process with the intention
of improving its performance. The goal is to lock defects out.
6. Use the new process. Now that the processes have improved, put it to work. Set
it into the production environment and let the improvements make their mark.
7. Look at the product. Take a fresh look at the product. Did the improvement
make a difference? Is the product better? If it is, look for new improvement
opportunities and the cycle continues.
The philosophy behind Six Sigma could be summarized as "Deliver Quality." That
capital Q in Quality is important. It implies a certain kind of quality, and that is what
Six Sigma drives at, a very special definition of quality. Quality is not whatever
happens to be the biggest, the strongest, the prettiest, the best, or the coolest. It is not
what organization says it is. It is not what competition thinks it is. In the world of Six
Sigma, quality is what the customer wants. That is all it is. The meaning of the word
quality comes from that source and that source only. Nothing else matters. Everything
else is irrelevant. GE calls this the Voice of the Customer (VOC).
14
2.2.2.1 Why Six Sigma?
Six Sigma is all about the spread of variation in a set of measured data. In a normal
distribution, data tends to spread out in a very predictable pattern. Most of the values
fall around the middle. Some fall more or less to either side. By plotting the result, the
figure will look like a bell. As shown in Figure 2.1.
Figure 2.1
The traditional bell curve shows a normal distribution of data. The "average" values
fall in the middle and the less common values fall to either side of the center. A chart
such as that illustrated in Figure 2.1 is called a normal distribution. It has the general
shape of a bell, and known from statistics that's a normal way that data like that should
fall.
Six Sigma predicts that when a process run, the way the performance varies over
time will dance up and down around the center line, the average line just like the range
of heights in nature. But here is the key with Six Sigma: it wants to put techniques in
place to control what numbers (what data points) are going to most influence the
average. The common understanding of achieving Six Sigma performance is that for
every 1,000,000 data points, only 3.4 will deviate from either side of the average. In a
grossly exaggerated example, that might look more like Figure 2.2.
15
Figure 2.2
In Figure 2.2, shows the hardly any variation. Everything is grouped right at the
middle. In general, that's not a bad understanding. But the technical explanation is
better, and it sheds more light on the purpose and design of Six Sigma. Let's get at this
by looking at the name Six Sigma.
Sigma means the same thing as standard deviation. Standard deviation (SD) is a
well-founded measure of the range of variation from the average for a group of
measurements. In any set of data, 68 percent of all the measurements will fall within
one standard deviation of the average. 95 percent of all the measurements will fall
within two standard deviations of the average. By the time you're out to six standard
deviations six sigma you've accounted for 99.9997 percent of the data. Practically
nothing is out of those bounds.
Six Sigma is about process control. The more to able to control a process, the better
will be able to make it hit the performance numbers wanted. Six Sigma is a program
that works best when it uses hard data as the foundation for process improvement.
That's why one of the general interpretations of this program is that it is heavy on
statistics. So far, we've looked at a few common Six Sigma concepts: Voice of the
Customer and X=f (Y). Here's another one: DPMO.
DPMO is Defects Per Million Opportunities for defects. When they are building a
product, they want their production processes to be predictable. They want to know how
many microns of carbon coating they are going to lay onto a filament. No process is
16
perfect. No process operates without variance. One of the things they need to establish
with Six Sigma is the number of process variations.
To get a valid statistical indicator of the reliability of this process (the talent of the
catcher), we have to repeat the transaction over and over. Measure and measure. When
we have a process that achieves statistical six sigma, we can pretty much guarantee that
we'll have only 3.4 defects for every million transactions. That's 3.4 misses for every
million throws. Whatever we are doing, it is so controlled, so streamlined, so proven
that the outcome is a safe bet.
The Six Sigma methodology is an alternative to TQM for obtaining: manufacturing
defect reduction, cycle time reduction, cost reduction, inventory reduction, product
development and launching, labor reduction, increased usage of resources, product sales
improvement, capacity improvements, and delivery improvements. Six Sigma is based
on a measurement strategy focused on customer satisfaction & financial benefits
through variance reduction and continuous process improvement. Six Sigma uses two
methodologies named ‘DMAIC’ (Define, Measure, Analyze, Improve, Control) and
‘DFSS’ (Design For Six Sigma).
While Six Sigma was originally created as a continuous quality improvement
technique, today it is significantly different than the total quality management (TQM)
approach of the 1980s. Table 1 shows the key differences between Six Sigma and TQM.
17
Table 2.1
Six Sigma is very popular in Korean industry. There are several reasons for this
popularity. First, it is regarded as a fresh quality management strategy which can
replace TQC, TQM and others. In a sense, it view the development process of Six
Sigma as shown in Figure 1. Many companies which were not quite successful in
implementing the previous management strategies such as TQC and TQM, are eager to
introduce Six Sigma.
18
Figure 2.3
QC: quality control
SQC: statistical quality control
TQC: total quality control
TQM: total quality management
ISO: International Organization for Standardization
SPC: statistical process control
TPM: total productive maintenance
QE: quality engineering
TCS: total customer satisfaction
Six Sigma is viewed as a systematic and scientific approach for management
innovation by the integration of four elements; customer, process, manpower and
strategy as shown in Figure 2.
Figure 2.4
19
Second, Six Sigma provides a scientific and statistical basis for quality assessment
for all processes through measurement of quality level. The Six Sigma method allows to
draw comparisons among all processes, and tells how good a process is. By this
information, the top management knows what to do for process innovation and
accordingly for customer satisfaction. Third, Six Sigma provides an efficient manpower
cultivation and utilization. It has a belt system in which there are green belt, black belt,
master black belt and champion. As a person in a company gets some education, he
belongs to a belt. Usually, a black belt is the leader of a project team and several green
belts work together for the project team. Lastly, there are many successful stories of Six
Sigma in well known world-class companies. Besides Motorola, GE, Allied Signal,
IBM, DEC and Texas Instruments as mentioned above, Sony, Kodak, Nokia, Philips
Electronics, Samsung Electronics, LG Electronics among others have been quite
successful in Six Sigma.
Six Sigma is a long-term, forward-thinking initiative designed to fundamentally
change the way corporations do business. It is first and foremost “a business process
that enables companies to increase profits dramatically by streamlining operations,
improving quality, and eliminating defects or mistakes in everything a company does.
While traditional quality programmes have focused on detecting and correcting defects,
Six Sigma encompasses something broader: it provides specific methods to re-create the
process itself so that defects are never produced in the first place”. [“Management
Processes for Quality Operations”, Richard S. Johnson, 2002.]
While Six Sigma is a long-term strategy, it is designed to generate immediate
improvements to profit margins too. Compared to traditional quality management
programmes, such as TQM, that project three or more years into the future, Six Sigma
focuses on achieving financial targets in twelve-month increments. The Six Sigma
breakthrough strategy is a disciplined method of using extremely rigorous data-
20
gathering and statistical analysis to pinpoint sources of errors and find ways of
eliminating them.
2.2.3 Six Sigma Problem Solving Process
The original problem-solving process for Six Sigma developed from Motorola is
MAIC which means measurement, analysis, improvement and control. Later, DMAIC
instead of MAIC is advocated from GE where D stands for definition. MAIC or
DMAIC is mostly used as the unique problem-solving process for manufacturing areas.
However, for DFSS there are multiple proposed processes. They are as follows.
1) DMADV (Define - Measure - Analyse - Design - Verify). MADV was suggested by
Motorola for DFSS, and D was added to it for definition. DMADV is similar to
DMAIC.
2) IDOV (Identify - Design - Optimize - Validate). This was suggested by GE and has
been used most frequently in practice.
3) DIDES (Define - Initiate - Design - Execute - Sustain). This was suggested by
Qualtec Consulting Company.
It seems that the above problem-solving processes for manufacturing and R&D areas
are not quite suitable for service areas. The author believes that DMARI (Define Measure - Analyze - Redesign - Implement) is an excellent problem-solving process for
non-manufacturing service areas. Here, the phase 'redesign' means that the system for
service works should be redesigned in order to improve the service function.
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2.2.4 DMAIC
Six Sigma employs two basic methodologies to problem solving. The first is termed
DMAIC. DMAIC is used to improve existing processes in an organization. The other
methodology is DFSS. It is used when you want to design a new process and introduce
it into an organization in a way that supports Six Sigma management techniques.
DMAIC is the one that gets the most press. There are five basic steps in the
methodology: define, measure, analyze, improve, control. DMAIC is used to improve
and increase the efficiency and reliability of processes that exist in an organization. It is
a process improvement methodology that employs incremental process improvement
using Six Sigma techniques.
DFSS stands for Design for Six Sigma. It is also sometimes referred to as DMADV.
This methodology also has five steps: define, measure, analyze, design, verify. DFSS is
used when an organization wants to design and produce new products in a timely, costeffective manner to meet exact customer needs. It is a business development
methodology. The core steps, DMADV, are used to create reliable processes in an
organization that does not have processes, or when an organization must discard a
deeply faulted process. DFSS is a process design approach.
2.2.5 Six Sigma Champion
The Six Sigma Champion is usually an executive or high-level manager in the
organization with the ability to promote and sponsor the use of Six Sigma. Champions
may manage a series of Six Sigma teams, or they may simply fund and support Six
Sigma projects. Champions should have a pretty good working knowledge of Six
Sigma, but more than that, they should share an enthusiasm for the promise and
approach of Six Sigma, believing in the Six Sigma vision of improvement through data
22
management and quantitative analysis. Well-positioned Champions will possess
authority to:
•
Control resources
•
Allocate budgets
•
Assign responsibility
•
Set strategic direction
Champions are the executive sponsors of the Six Sigma world, and they usually direct
and develop the organization's Six Sigma programs.
2.2.5.1 Master Black Belt
Master Black Belt is the highest level of Six Sigma certification. This is an
individual who has not only had extensive training in the methodology and techniques
of Six Sigma, but who has also had extensive experience designing and implementing
Six Sigma projects in a variety of organizations. Master Black Belts possess a deep
understanding of DMAIC, as well as Design for Six Sigma and the Design Measure
Analyze Validate Deploy methodologies. They are considered experts at applying
statistical measurements to diverse and heterogeneous data sets, and they have a solid
grasp of the use and application of quantitative techniques to understand process
performance and derive empirical process improvements.
Master Black Belts have the ability to manage Six Sigma programs as well as
program teams. The tradition with Master Black Belts is that they can empirically
demonstrate that their projects designed and managed by them have saved companies
hundreds of thousands of dollars. The term "hundreds of thousands" is not used here for
dramatic purposes. It's to be taken literally. In the true Six Sigma culture, no one will
call herself a Master Black Belt if she is not able to put that data in front of a client.
23
2.2.5.2 Black Belt
Black Belts typically lead Six Sigma projects. They may design the project with the
help of a Master Black Belt, or they may design it on their own. They are usually highly
trained in Six Sigma methods, with solid experience in DMAIC, DFSS, and DMAVD.
Like Masters, they should have sound knowledge in applying statistical measurements
to diverse and heterogeneous data sets. And they should have broad experience
applying Six Sigma methods to a number of process improvement projects. They should
be able to demonstrate very strong statistical and quantitative analysis skills, effective
project management skills, strong interpersonal and communication skills, and strong
writing and organizational skills. Like Masters, Black Belts should also be able to show
empirical cost savings or ROIs as a result of their Six Sigma project work. Most
reputable Six Sigma Black Belt courses require that the candidate design, plan, and
execute a real-world project with the potential to save an organization at least $100,000.
2.2.5.3 Green Belt
Six Sigma teams are usually mostly composed of Green Belts. These are people with
at least one pretty in-depth course in Six Sigma applications and the interest (and
opportunity) to work on a Six Sigma project. They have a beginning ability to produce
statistical control charts, calculate percent noncompliance, plot histograms and Pareto
charts, identify common-cause and special-cause variation, and calculate process
sigmas. They have a good working knowledge of DMAIC, DSFF, and DMAVD and are
positioned to participate in Six Sigma projects of varying complexity, size, and
duration. They are the field soldiers in the world of Six Sigma.
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2.2.5.4 Yellow Belt
Green Belt, Black Belt, and Master Black Belt are well-accepted Six Sigma
designations. Yellow Belt is less so. Many people think there should be no such things
as a Yellow Belt. I tend to agree. Because when you think about it, under a Green Belt,
a Yellow Belt can only be a Six Sigma team contributor. And if someone is on a Six
Sigma team but is not really trained in any of the methodologies, design considerations,
or statistical techniques, they can't really be expected to contribute a lot. I guess he
could perform measurements and collect data; those are valuable activities, but they
probably don't warrant a belt of distinction on their own. What does it take to be
recognized as a Yellow Belt? If you read this chapter, twice, slowly, you might be able
to qualify.
2.2.6 Six Sigma Principles and Metrics
The principles of Six Sigma can be distilled into the following six themes (Pande et
al. 2000; Pande and Holpp, 2002):
1. Genuine focus on the customer. While profits and statistical tools seem to get the
most publicity, the emphasis on customers is the most remarkable element of Six
Sigma.
2. Data and fact-driven management or metrics for decision making. Six Sigma takes
the concept of ‘‘management by facts’’ to a new and more powerful level. Instead of
basing business decisions on opinions and assumptions, Six Sigma builds the
foundation of decision making by using metrics in building up key measures that
represent and calculate the success of everything an organization does.
3. Process focus, management, and improvement. Six Sigma positions the process as the
key vehicle of success, be it in design of products and services, measuring performance,
improving efficiency and customer satisfaction, etc.
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4. Proactive management. Proactive means action in advance of events rather than
reacting to them. An example of proactive management in Six Sigma is the focus on
eliminating defects at the source instead of trying to manage the defect or problem after
it has occurred. It tries to solve why the bad results are occurring.
5. Boundless collaboration. Boundless means working to break down corporate barriers
and to improve teamwork up, down, and across organizational lines.
6. Drive for perfection, tolerate failure. Although these two ideas sound contradictory,
they are actually complementary. The bottom line is that any company that makes Six
Sigma its goal will have to keep pushing to be more perfect while being willing to
accept and manage occasional setbacks.
There are several models that can be used in the implementation of Six Sigma in an
organization, for example, the five-phase improvement cycle that has become
increasingly common in Six Sigma organizations: define, measure, analyze, improve,
and control (DMAIC). The steps involved are:
•
Define. Define the customers, their requirements, the team charter, and the
key processes that affect the customers. Goals and/or objectives of a certain
process are then set based on the customer’s requirements.
•
Measure. Identify the key measures, the data collection plan or the plan for
measurement for the process in question, and execute the plan for data
collection.
•
Analyze. Analyze the data collected as well as the process to determine the
root causes of the problem that need improvement.
•
Improve. Generate and determine the potential solutions and plot them on a
small scale to determine if they positively improve the process performance.
Successful improvement methods are then implemented on a wider scale.
•
Control. Develop, document, and implement a plan to ensure that
performance improvement remains at the desired level (Pande et al. 2000;
Eckes 2001).
26
The sigma concept of measuring defects was started by Motorola in the early 1980s
as a way to develop a universal quality metric that applied regardless of product
complexity or dissimilarities between different products or processes. Higher sigma
values indicate better products or processes with fewer numbers of defects per unit of
product or service. Products produced at a Six Sigma level of quality operate virtually
defect-free by definition, with only 3.4 defects per million opportunities (DPMO) as
shown in Table 2. Through Six Sigma, every measurable can be compared on the same
platform ~through converting yields or DPMO to sigma level!, no matter how different
they may be. All the organization needs to do is to set out guidelines in determining
measurable during implementation. From Table 2, at 3.8 sigma, companies would be
getting it right 99% of the time. This may seem very good, but this 1% margin of error
can add up to a lot of mistakes. Chowdhury, 2001 estimates it to be approximately
20,000 lost articles of mail every hour, 5,000 botched surgical procedures every week,
and four accidents per day at major airports. Hence six is the sigma level of perfection
that companies should be aiming for. The statistical theory of variation for Six Sigma is
based on the supposition that all things, when measured fine enough, vary and this is
called ‘‘natural variation.’’ Assuming this is true, anything that can be measured on a
continuous scale, such as height, length, and weight would follow a bell-shaped curve.
Theoretically, this bell-shaped curve also called the ‘‘standard normal distribution’’ or
the ‘‘Gaussian Curve’’ after the German mathematician who empirically determined its
characteristics! Has been extensively studied and has been proven very useful as
numerous natural continuous phenomena seem to follow it or can be approximated by
it.
The standard normal distribution curve has the following characteristics:
• It is bell-shaped and is symmetrical in appearance;
• It represents virtually 100% of whatever is being measured, referred to as
‘‘population’’ in statistical terms;
• The peak of the curve represents the most commonly occurring value, and
27
• The curve can be divided into a series of segments. Each segment represents a certain
percentage of what is being measured. For example, the area under the curve from the
center line to the first segment line to the left or right represents approximately 34% of
what is being measured, the area of the curve from the first to second segment line
represents approximately 14% and so on. The technical name for each segment is the
standard deviation from the mean, represented by the lower case Greek letter, sigma.
Although the distribution extends to infinity in both directions, usual drawings of the
distribution frequently only show the area from 23 standard deviations to 13 standard
deviations because this range includes 99.73% of the data.
The technical concept of Six Sigma is to measure current performance and to
determine how many sigma exists is measured from the current average before
customer dissatisfaction occurs. When customer dissatisfaction occurs, a defect (defined
as any event that does not meet the requirements) occurs.(Eckes,2001).
Six Sigma describes a process that produces no more than 3.4 DPMO, which
represents near perfection. For reasons of brevity, this review of the technical concept
of Six Sigma has not covered other issues in the Six Sigma literature such as the singlestage process or multistage process. It also does not cover other more complex methods
of calculating sigma using the discrete method or the continuous method which involves
the capability ratio (CR), the capability index (Cp), and the ‘‘Capability Index
compared to some constant (Cpk).’’
Table 2.2 simplified Sigma Conversion
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2.2.7 Six Sigma as a Quality Movement
As a quality movement, Six Sigma is about process capability. It is about reducing
the variation in a process, and increasing our control over a process, so that we can
predict with considerable accuracy exactly how the process will behave. This level of
capability can be used to implement improvements in the process where we set targets
for future behaviors, and achieve those targets within the levels of quality control that
we choose to design into the improvements.
An understanding of Six Sigma Math requires a clarification of a few specific terms that
are used by quality professionals, the meanings of which are somewhat narrower than
might be expected by a novice:
•
Defective – Any product or service instance that fails to meet the requirements
of the customer, whether or not those requirements were clearly specified.
•
Defect – Any characteristic of a product or service instance that doesn’t conform
to its specification, whether such a specification was explicit or implied.
Typically, defective products or services are caused by one or more defects and are
referred to as defectives. Not all defects cause defectives. Defects in a product or service
that don’t result in the product or service being considered defective are often referred
to as latent defects. The distinction between defect and defective is very important in
Six Sigma. All processes exhibit some variability in their outcomes. Inevitably, some
portion of the output of a process will contain defects. If the variability of a process can
be reduced enough, these inevitable defects will be so close to specification that the
customer is unlikely to consider the resulting products or services defective.
Process variability can be seen by selecting one or more important measurable
characteristics from a process and then monitoring those characteristics over time. The
tool most likely to be used for such monitoring is the Statistical Process Control Chart,
or SPC. The basics of SPC can be used to review the history of thinking about defects
leading up to Six Sigma.
29
2.2.7.1. 1.5 Sigma
The early quality movement began in the face of very high rates of defectives. A
process with a very high defect rate is illustrated in Figure 3. The illustrated process has
a quality level of 1.5σ, meaning that the characteristic represented by the chart only falls
within the customer’s specification limits about 50% of the time.
Figure 2.5 Normal distribution of 1.5 Sigma
Because the chart’s control limits would be set at 3σ above and below the target, they
do not even appear on the scale of Figure 3. Organizations with defect rates this high
were unlikely to be using SPC effectively, but the figure illustrates the problems faced
by the early quality movement.
2.2.7.2. 3 Sigma (TQM)
With the advent of quality programs in the 1980s, including Total Quality
Management (TQM), the use of SPC to monitor and control processes became more
common. TQM programs worked to reduce process variation so that most of the
expected variability would fall with the customer’s requirements as represented by the
specification limits. Figure 4 illustrates a process that has been brought up to a quality
level of 3σ, meaning that the defect rate associated with the charted characteristics
could be expected to consistently fall below 10%.
30
Figure 2.6 Normal distribution of 3 Sigma
TQM thinking aligned defects and defectives. Defectives included any observation
outside of the specification limits. Defects included any observation outside of the more
restrictive of the control or specification limits. Because many TQM change initiatives
designed processes that would achieve customer tolerance, the target control limits
often ended up being roughly the same as the customer’s specification limits. The
relatively few defect observations that would fall outside of the control limits would be
defectives by definition, but the frequency of such observations was dramatically
improved compared to pre-TQM programs.
31
2.2.7.3. 3 Sigma with 1.5 Sigma shift
One problem with TQM-based alignment of defectives with defects was that
processes didn’t remain stable after they were improved. Processes tended to increase
their variability over time as a result of everyday deterioration of the conditions under
which those processes operated. Such deterioration might include a loss of calibration
of sensors, wear and tear on machinery, operator fatigue, supplier quality variation, etc.
Process characteristics were seen to wander from their original values by as much as
1.5σ in either direction. This wandering came to be known as the 1.5σ shift, and is
illustrated in Figure 5.
Figure 2.7 Normal distribution of 3 Sigma with 1.5 Sigma shift
This shift resulted in more defects occurring as the process wandered. Under a 1.5σ
shift, a process characteristic that had achieved 3σ performance would slip back to 1.5σ
performance. Without a proper recognition of the causes of the shift, or corrective
actions taken to avoid the shift, it was often perceived that the investment in improving
the process had been wasted. TQM programs often fell into disfavor as a result of this
fundamental misunderstanding of process behavior.
32
2.2.7.4. 4.5 Sigma
For organizations that recognized the problem of shift, the answer became to reduce
process variability further in order to allow for the naturally occurring shift. To achieve
the benefits of 3σ quality originally achieved by TQM programs, process variability had
to be reduced an additional 1.5σ. Figure 6 illustrates such a process characteristic at a
4.5σ quality level.
Figure 2.8 Normal distribution of 4.5 Sigma
Such low process variability was extremely difficult to achieve, but seemed to provide
extremely low defect levels, usually measured in fractions of a percent. In the
competitive environment of the late 1980s, such improvements were becoming
necessary to survive.
2.2.7.5. 4.5 Sigma with 1.5 Sigma shift
The reality of the 1.5σ shift gave rise to the concepts of short-term sigma, and longterm sigma. Short-term sigma was the quality level designed into a process and
typically achieved on process launch. Long-term sigma was the expected quality level
33
of the process over the time periods in which the 1.5σ shift could be expected to
materialize. Figure 7 illustrates the long term shift of a 4.5σ process back toward 3σ
performance.
Figure 2.9 Normal distribution of 4.5 Sigma with 1.5 Sigma shift
By taking into account the long-term shift associated with all processes, quality
improvement programs could provide the 3σ levels of quality originally targeted by the
earlier TQM programs. However, along with this realization came increasing pressure
to achieve even higher levels of quality in the late 1980s.
2.2.7.6 Six Sigma
The Six Sigma movement pushed these concepts to the extreme of targeting 6σ
quality levels in the short-term that would achieve 4.5σ quality levels in the long-term.
Defect rates at this quality level fall at about 3.4 defects per million opportunities. The
variability of a 6σ process relative to its specification limits is illustrated in Figure 8.
34
Figure 2.10 Normal distribution of Six Sigma
The quality movement toward Six Sigma effectively decoupled the definition of
defects from defectives. At Six Sigma, defectives are still any observation outside of the
customer’s specification limits, although such observations become exceedingly rare.
Defects remain however, as roughly 3-7% of all observations will continue to fall
outside of the control limits. With the control limits at 3σ, and the specification limits at
6σ, the vast majority of defects do not rise to a level close to resulting in a customer
defective. Each defect, though, remains an opportunity to continue to improve the
process and bring the expected process shift under control. By managing these defects
effectively, the process continuously improves without ever producing a defective for
the customer.
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2.2.8 Six Sigma in Construction
Six-sigma is a new way of managing business processes. Since its publicized
adoption at Motorola and General Electric in the early 1980s, six-sigma has evolved
into a leading method for managing process efficiency, not just in manufacturing
industry but increasingly in other areas close to project managements’ ‘heart’ such as
construction management. It is a formal and disciplined method for defining,
measuring, analysing, improving and controlling (DMAIC) processes (see Figure 9).
Figure 2.11 Six Sigma DMAIC Process
36
These five steps form the backbone of the six-sigma methodology and work on the
principle of a stage/gate process that requires certain deliverables to be met at the gate
before the firm can proceed to the next stage or phase (Marves, 2000).
Six-sigma has different interpretations and definitions for different applications; in
this case we refer to its proposed application to the construction/engineering sector. For
this sector, Six-Sigma improvement methods are not about being totally defect-free or
having all processes and products at six-sigma levels of performance – another
misconception of the six-sigma philosophy (Linderman et al., 2003). The appropriate
level will depend on the strategic importance of the process and the cost of its
improvement relative to the benefit (Brue, 2002). In the application of six-sigma there
are typically a number of common features, which include: it is a top-down rather than
bottom-up approach; it is a highly disciplined approach that typically includes five
stages (i.e. DMAIC); and it is a data-oriented approach using various statistical and
non-statistical decision tools (Klefsjo et al., 2001). This use of a structured approach to
improving processes in construction helps to reduce task complexity while increasing
performance and commitment from team members (Linderman et al., 2003). The
DMAIC methodology simplifies the process improvement project because it acts like a
road map for the improvement team. In the manufacturing industry, six-sigma has
typically been applied in an organization-wide manner, choosing macro opportunities as
Six-Sigma projects. Consequently, in manufacturing, we have tended to witness
revolutionary changes. These projects have tended to involve the design and
development of an entirely new product or service or the major redesign of an existing
one. Conversely, at this stage, the deployment of Six-Sigma in the construction industry
has been predominately aimed at micro-opportunities. This means that six-sigma
projects would be smaller in scope and likely to relate to a sub-task within a macro
opportunity. Keeping with the philosophy of CPI and TQM, the application of SixSigma at this early stage of its development is to argue enhancements for evolutionary
rather than revolutionary changes (Maleyeff and Kaminsky, 2002). Applying six-sigma
in construction typically involves breaking down large tasks into smaller ones that can
be re-engineered and improved.
37
2.2.8.1. Previous Application of Six Sigma In Construction
Despite the large number of studies having addressed the concept of quality in
construction, there is limited research into the use of Six Sigma as a strategy for process
improvement in construction. In 2002, Bechtel Corporation, one of the largest
engineering and construction companies in the world reported a savings of $200 million
with an investment of $30 million in its Six Sigma program to identify and prevent
rework and defects in everything from design to construction.( Eckhouse, 2003)
Rodney A. Stewart and Clinton A. Spencer 2006, described in their research study
the outcomes of a Six Sigma process improvement project (PIP) conducted for the
construction of concrete longitudinal beams on St Pancras raised railway station in
London, UK. The outcome of the Six Sigma PIP was the improved productivity of
beam construction, enhanced interaction between project teams and reduced project
delays. In summary, the Six Sigma approach provided the PIP team with a structured
process improvement strategy to reduce waste and other non-value adding activities
from the construction process.
2.3 Cast In-Situ Concreting Process
Successful concreting relies on two things; firstly the concrete has to be the right
specification for the job and secondly it has to be placed correctly. Handling concrete
effectively and safely requires careful planning, preparation. Concrete itself consists of
a mixture of cement, large fines (usually 20mm aggregate but this is dependent on the
application), small fines (usually building sand but this is also job specific) and water.
The mix may have other admixtures added for special reasons (waterproofing, frost
protection, colour, etc.).
38
2.3.1. Design of Mix & Reinforcing
A good design and specification of concrete structures should be followed and any
deviations should be fully discussed with the engineer beforehand. The overall job of
describing what sort of concrete want has been made easier by the introduction of
designated mixes into the British Standard for concrete (BS 5328). However, it is
important that a site leader can understand all the possible mixes he may be requested to
work with.
To arrive at a specification for concrete mix a decision first has to be made as to
which of the typical applications given matches with application and whether the
concrete will be reinforced or not. Consideration must also be given to the ground
conditions and the quality of the water the concrete will come into contact with. For
most applications Ordinary Portland Cement (OPC) will be used however other cements
exist for specialist applications such as high sulphate resistance (Sulfacrete), high initial
strength (Ferrocrete).
.
2.3.2 Ready-Mix And Hand Mix
Using concrete ready mixed is simpler, quicker and less wasteful. By using hand mix
concrete the people that mix the concrete is responsible for ordering and storing the
bulk ingredients and ensuring enough competent volunteers to mix and place the
concrete. By ordering from a ready mix company the responsibility for all these factors
rests with the company. There is an additional direct cost is that ready mix usually costs
about twice the price of the raw materials. If ready mix is the chosen technique then the
supplier should be given the mix designation, the required workability, the intended
placement method and finish required. To make sure that the quality of concrete is
going to be right, dealings should only be with suppliers who operate an independent
39
assessed quality system, or from producers who hold third party product conformity
certification.
2.3.3 Workability of Concrete
As soon as the concrete arrives on site, it needs to be inspected. Check the actual
delivery ticket to ensure what has arrived is actually what is ordered (volume, grade,
etc.). This is the only chance to get to send it back. Should be checked the workability
of the concrete to determine its suitability for placing. On an important job this would
be a full slump test (q.v.), however on most sites it usually takes the form of a token
load checked for “shovelability”. If testing indicates that the workability is below the
lower limit, it is fine for the driver to add water to the load to increase the workability
within specified tolerance, this is the usual case as the mix will leave the mixing plant a
little drier than specified and water will be added by the driver on delivery. However, if
the concrete arrives and find that its workability needs to be increased to assist placing
then must be asked for water to be added. But note that if this is done then all liability
for the properties of the concrete will be disclaimed by the producer. If the concrete
arrives and on site delays make it too stiff to use, then adding water is not the correct
solution. A plasticizer admixture should be added for the concrete to reach its lowest
possible water content, but still be suitable for placing. Concrete can also arrive too wet
due to excess water added at the mixing plant, though this is unusual. If this occurs, the
concrete should not be used until the supplier has been contacted and the concrete’s
suitability has been checked.
40
2.3.4 Access to Site
It is important to check the total weight and axle weight of the wagon. If concrete is
to be directly unloaded from the wagon then check the wagon can safely and easily get
into position. If it is to be transported by dumper then check the run is short enough to
ensure the vibration does not segregate the mix. Another option is the use of a concrete
pump. Pumping concrete is a very specialist technique that should be approved by the
design engineer and the manufacturer should be made aware of the intention to pump as
it will affect the mix required. Further, do not forget to finish off the surface.
2.3.5 Formwork
This is the item most often hurried on a concrete pour. The main failing (literally) of
concrete shuttering is not understanding how much force a concrete pour hits the
ground with or how much weight is associated with a mix (especially if it is being
vibrated). Remember that concrete weighs in at 2.4 tons per cubic meter and will be
ejected from the back of the wagon at a height of 3 meters so it should not be too much
of a shock that poorly erected shuttering often gets swept away. Another most common
mistake is that not enough thought has been given to the removal of the shuttering.
Another common mistake is designing shuttering with lips, projections or nails that are
then gripped by the concrete and become impossible to remove without damage to the
face of the pour. Nails should always be on the outside of shuttering and should not be
driven fully so that they can be removed easily.
Obviously the wood should be shuttering grade or better and it is strongly
recommended that the internal faces of the shuttering are coated with a proprietary
Mould Release Oil. Oiling the shuttering makes it easier to strike, produces a better
41
finish and allows the ply to be reused many times. Any joints in the shuttering should be
sealed otherwise the grout will leak out (especially if vibrated) leaving only the larger
fines around the joint producing a distinctive honeycomb effect.
The finishing of faces is often specified in the design. A smooth finish that is free of
voids and air bubbles and it applies to exposed faces. Other finishes are “brushed” and
“wet brushed”. The brush finish is used to provide a rough but regular surface whilst the
wet brushed is a refinement of the technique whereby once the surface has undergone
the first stages of curing a wet brush is used to wash away the surface grout leaving the
larger fines exposed. The common mistake made regarding shuttering is to strike it too
early, if this is done then damage may occur not only as the shuttering is removed but
also due to the concrete curing too quickly.
2.3.6 Placement
Generally any blinding should be good enough to walk on, if not then it is not up to
the job of supporting the pour. When preparing an excavation always ensure that all
edges and blanks are stable and will not collapse during the placement. Ensure all
organic matter is removed and any rubble, dust, etc. is removed. Concrete needs to be
placed so that it does not segregate and at a speed which allows it to be compacted
properly. This is achieved through placing it in a series of layers. Then the concrete is
vibrated to literally shake out the trapped air and encourage the mix to flow to all the
extents of the formwork. The layers of concrete should not be too deep otherwise the
weight of the material at the top makes it almost impossible to compact the bottom
layer. If this happens, air will be trapped in the mix leaving voids and blow-holes that
will result in surface blemishes and more importantly a loss of strength.
42
In all cases, a layer must be fully compacted before any more concrete is placed on top
of it as voids in the lower concrete cannot be removed once the next layer is placed on
top. However, the bottom layer still needs to be workable enough to respond to
vibration so that the two layers can knit together without any joints, which is another
reason for getting the material into position as quickly as possible.
The use of a vibrator will also allow the concrete to flow around coping stones or
similar when backfilling thus providing a far better job. Petrol driven vibrators are
undoubtedly the most popular but they are notoriously unreliable. Diesel models are
slightly heavier and harder to start but more robust. It is also possible to get electric
models which are much lighter but more susceptible to damage. Various support
systems exist for reinforcing and although they may seem more expensive than half
bricks they will remove a common weak point in concrete pours.
2.3.7 Curing
Curing is the last and one of the most important stages of concrete construction. The
“curing” problem is caused by the concrete giving off heat and shedding water too
quickly leading to cracking. If curing is not done properly, the concrete will not develop
its full strength. Properly cured concrete is stronger, more resistant to chemical attack
and erosion, and more watertight and frost proof. The surface of the concrete is worst
affected by poor curing, and it is this skin which gives concrete the ability to withstand
wear and that protects both the reinforcement and the ‘heart’ of concrete. Therefore, if
concrete is inadequately cured the effectiveness and the life-span of the concrete will be
reduced.
It is, therefore, important for curing to take the proper time and this can be achieved in
one of two ways:
43
•
The first involves keeping the concrete moist by the use of ponding,
spraying/sprinkling, damp sand or hessian.
•
The second method prevents the loss of moisture from the concrete by covering
it with polythene sheeting, spraying on a curing membrane or leaving the
formwork in place.
The first methods are undoubtedly the more correct. However, they are expensive,
labor intensive and time consuming. The second group of methods, while not so
efficient, are usually satisfactory for all except very special work and they can be
carried out more easily. Note that curing strengths given in specifications relate to the
strength of the concrete after 28 days.
44
Figure 2.12 Operations involved in traditional concrete construction
45
2.4 Reinforced Concrete Cracks
2.4.1. Structural Cracks
The structural crack results from the tensions that the structure must carry due to its
function. They take place in structures without projects, and when the ground problem
is not solved, and are very dangerous; they have nothing to do with the concreting and
the concreting conditions. In such cases we must certainly consult the relevant
authorities (engineering office, university etc.). No such problem is witnessed when the
structure is engineered properly and when there is no overloading. These types of cracks
occur vertically to the tensile strengths in reinforced concrete agents. Cracks occurring
in the middle of a simple girder interval or on a corbel bearing are of this type.
2.4.2 Application Based Cracks
This type of crack is seen in fresh concretes or over aged concretes.
2.4.2.1 Fresh Concrete Cracks
Fresh concrete cracks occur within the first 30 minutes to 5 hours following the
placement of the concrete to the formwork, generally in concretes with wide surfaces
such as floor concretes. The depth of these cracks can reach 10 cm and their length can
vary from a few centimeters to 2m. Deep and long cracks can be very harmful to the
concrete in terms of its strength and durability. The two most significant reasons for
fresh concrete cracks are settlement differences and plastic shrinkage.
46
2.4.2.2 Settlement Cracks
These cracks occur in newly poured concretes in which concrete cover is forgotten,
cure isn’t applied and excessive water is added, in reinforced concrete agents with
voids, in areas having too many reinforcements, on the reinforcements close to the
surface, and when the placement isn’t done properly. In fresh concrete, the water
containing cement particles rise up to the surface, while the big aggregate grains sink to
the bottom. The girders and floor reinforcements close to the surface resist this
replacement and the fresh concrete can not settle completely in these regions. The
unsettled concrete cracks throughout the steel. There is less settlement in flooring due to
its fineness and so cracks aren’t seen very often. There is more settlement in girders due
to their depth, and the map of the steel rods is seen on the concrete surface; the cracks
make the reinforcement places visible. As the water content of the concrete increases,
the amount of settlement increases. The settlement, and thus the cracks, increases unless
the concrete is placed, compacted and vibrated properly. The way to prevent these
cracks is to use concrete in normal consistency (- 12 cm slump), avoid concretes to a
high consistency with excessive water, and apply good vibration to the concrete.
2.4.2.3 Plastic Shrinkage Cracks
This type of crack, randomly spread in various sizes, may occur especially on
concretes (floor, ground, road, port etc.) poured on windy days, with low humidity, and
high temperature. The crack width is usually less than 1 mm and it is on the surface, not
deep. It is not dangerous in terms of the building’s safety. When floor concrete is
poured, the water in the upper surface starts to vaporize. It leaves the concrete and rises
into the air. In place of this water, the water inside the concrete comes up to the surface.
If the speed of vaporization is higher than that of the water coming up to the surface the
surface starts to dry, and therefore to shrink and crack. The same cracks may result from
the absorption of the concrete water by other materials such as briquettes in hollow-tile
floor slabs or moisturized concretes. Factors increasing the vaporization speed are:
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Air Temperature: The higher the temperature, the more the vaporization. The increase
of the temperature increases the vaporization approximately twofold. If the concrete is
hotter than the air, the vaporization speeds up.
The Humidity of the Air: The less the humidity in the air, the more and the easier the
vaporization. The vaporization increases fivefold when the relative humidity decreases
from 90% to 5%.
The Speed of the Wind: The more the wind, the faster the vaporization. The
vaporization increases fourfold when the wind speed increases from 0 to 20 km/h.
Sun Rays: If the concrete surface is open to direct sunlight, the temperature of the
concrete and therefore the speed of the vaporization increases. The two main factors
affecting the water desorption speed of the concrete are the compactness of the concrete
and the granulometry of the aggregates. The less voids in the aggregate granulometry,
the higher the strength in the concrete, however since there aren’t too many voids, it
gets harder for the desorption water to go up; it delays and the desorption speed
decreases. As long as the desorption water can’t replace the vaporization water, the
concrete surface dries and cracks. In ready-mixed concrete, there are more shrinkage
cracks because the granulometry is well adjusted so that desorption becomes difficult.
These are the precautions to be taken in order to decrease shrinkage and the cracks
caused by shrinkage:
•
Avoid the formwork agents absorbing the concrete water and speed up
concrete’s desiccation by moisturizing the formwork and the reinforcement bar.
•
Protect the concrete from the sun (by pouring at night), and the wind (by means
of a wind screen).
48
•
Avoid water vaporization (by covering with wet burlaps, nylon blankets
 or by
sprinkling cure materials).
•
Pour concrete very quickly by using a sufficient number of quality workers,
apply surface finishing and start the cure as soon as possible, and continue the
cure for at least 3 days.
Plastic shrinkage cracks may occur in 30 - 45 minutes, which is even before the
concreting is completed. Therefore the desiccation precautions should be taken for the
poured parts while the concreting still goes on. These precautions can be taken step by
step as the surface finished pieces are covered with wet burlaps, nylon blankets and
sprinkled with cure materials. Otherwise, the concrete cracks in different amounts,
varying according to the temperature, humidity and wind conditions. It is in your power
to reduce and minimize these cracks.
2.4.2.4 Over Aged Concrete Cracks
This type of crack may be seen in concretes of different age groups (from few week
old concretes to 30 year-old concretes). The cracks are chemical or physical based.
These cracks seem like hairlines at the beginning but then they grow and combine.
Stripping, outpouring and bursting occur following the crack formation. If no
precautions are taken, the reinforced concrete agents fall completely into ruin as time
passes. Among the reasons of these types of cracking, freezing - thawing, alkali -active
silica reaction, carbonation, corrosion of the reinforcements and reactions caused by
harmful materials such as sulphate, acids and salts can be counted.
49
50
CHAPTER 3
Methodology
3.1 Introduction
There are various steps that can be adopted to fulfil the objectives of this study. Due
to the numbers of the objectives in this study these steps have been defined.
3.2 Method of Data Collection
Some of the data collected is form a literature review, which focused on Six Sigma
problem solving approach and methodology, tools and techniques, besides, factors
affecting to produce plastic crack. Further, some of data collected from questionnaire
through professionals to determine potential and frequency of root causes of plastic
crack in cast in-situ slab concreting process.
3.3 Data Collection
Data collection which have been done relatively under objectives of study are in
order as shown as below:
•
Conducting literature review on Six Sigma problem solving approach (DMAIC)
51
•
Conducting literature review for indentifying plastic crack root causes and close
group discussion through professionals.
•
Conducting multiple choice questionnaire for determining potential level of root
causes to produce plastic crack in cast in-situ slab concreting process besides
close group discussion.
•
Conducting multiple choice questionnaire to determine frequency of each root
causes in cast in-situ slab concreting process besides close group discussion.
52
53
CHAPTER IV
DATA ANALYSIS
4.1 Introduction
This chapter finding the objectives 1 and 2. The findings of objective 1 is made
through the study path to proposing one check sheet to fulfill the requirement of
objective 2.
Objective 1: To Identify and analyze of plastic crack root causes according to Six Sigma
problem solving approach
According to DMAIC methodology of Six Sigma problem solving study goes to
achieve result of each stage of DMAIC methodology by step by step validation through
close group discussion and questionnaire surveyor with related experts. At the first
stage of DMAIC methodology of Six Sigma methodology study was carried out to
define and identify problematic area and goal of application of Six Sigma problem
solving on it.
According to concept of define phase of DMAIC methodology with respect of scope
of this study, cast in-situ concreting process have been selected for applying Six Sigma
on it. Actually Quality of concrete depends on the constituent materials, their
proportions, mixing, transporting, placing, compaction and curing of concrete. By not
54
enough attention to those items, Sometimes, concrete does not perform satisfactorily in
the service life. One of the outcomes is fresh concrete cracks. The two most significant
reasons for fresh concrete cracks are plastic settlement and plastic shrinkage.
By above consideration this study define plastic crack as a problem which is
introduced after few hours finishing cast in-situ concreting process in slabs. And this
study tries to decrease or even eliminate the number of plastic cracks during this
specific times as a scope by applying DMAIC Six Sigma problem solving approach.
Actually this is the goal of this Six Sigma problem solving. Accordingly the number of
plastic crack after finishing cast in-situ slab concreting process is the problem which is
focused in this research study.
4.2 DPMO Calculation of Current Cast-In-Situ Slab Concreting Process
According to concept of measure phase of DMAIC problem solving methodology of
Six Sigma study was carried out to evaluate the sigma level of current cast in-situ slab
concreting process by respect of DPMO’s concept. For this achievement, study was
carried out to collect specific data from the current cast in-situ concreting process in
University Technology Malaysia (UTM) “Cadangan Membina dan Menyiapkan
Bangunan Tambahan Fakulti Alam Bina ( RMK9) di Universiti Teknologi Malaysia,
Skudai, Johor Bahru, Johor, 81310” by investigation during the process performance
and gather data during the process and also after finishing cast in-situ slab concreting
process to achieve total number of cracks which is appeared in slabs. For this
achievement researcher selected 5 slab as a focus. By two times checking each slab
during few hours (6 hours ) after finishing concreting process researcher found 8 crack
which is appeared during that time on slabs. Photos show below are the concreting
process and total number of crack which is investigated.
55
Figure 4.1 Concreting Process
56
57
Figure 4.3 Concreting Process
58
Figure 4.4 Cracks which is investigated from the site
59
Data gathered during site visit determine the sigma level of current cast in-situ slab
concreting process as below with respect of DPMO formula:
By putting relevant data which is gathered during site investigation the DPMO
(Defect Per Million Opportunity) has been calculated by using above actual formula.
And by refer to the Six Sigma table the sigma level of current cast in-situ concreting
process was achieved.
In order to calculate the DPMO, three distinct pieces of information are
required:
•
The number of units produced ( number of slabs unit which is checked ) = 5
slabs
•
The number of opportunities per unit ( number of checking which is checked for
per slab ) = 2 times
•
The number of defects ( number of cracks which is found after few hours after
process finished ) = 8 cracks
60
𝐒𝐒𝐒𝐒𝐒𝐒𝐒𝐒𝐒𝐒 𝐐𝐐𝐐𝐐𝐐𝐐𝐐𝐐𝐐𝐐𝐐𝐐𝐐𝐐 𝐋𝐋𝐋𝐋𝐋𝐋𝐋𝐋𝐋𝐋 = 𝟎𝟎. 𝟖𝟖𝟖𝟖𝟖𝟖𝟖𝟖 + �𝟐𝟐𝟐𝟐. 𝟑𝟑𝟑𝟑 − 𝟐𝟐. 𝟐𝟐𝟐𝟐 ∗ 𝐥𝐥𝐥𝐥(𝑫𝑫𝑫𝑫𝑫𝑫𝑫𝑫)
By above calculation the DPMO was calculated 160000 and by referring to Six
Sigma table the sigma level of current cast in-situ slab concreting process was achieved
as 2.5. From here, the approximate how much far from the Six Sigma level determine. It
then push the process to achieve better sigma level in comparison with pervious
process.
61
Identify Causes & Root Causes of Plastic Crack in Cast-In-Situ Slab Concreting
Process
After calculation of DPMO and sigma level of current cast in-situ slab concreting
process, study was carried out to on collected data and related information from related
professionals and review a literature to find which categories and factors involved to
produce plastic crack as a defect during cast in-situ slab concreting process. For this
achievement, this study used Fish Bone Diagram ( one of the Six Sigma problem
solving tools ) to determine causes and root causes of plastic crack defect during cast insitu concreting process.
62
63
64
65
After that, by close group discussion with 3 related experts the 44 root causes has been
found in 5 categories namely labour factor, materials factor, design & detailing factor,
equipment factor and environment factor. Table 4.1 shows the root causes in each
categories.
66
Table 4.1 Plastic Crack’s Root Causes
67
According to total number of root causes in each category, Pareto chart below shows
the total number of root causes in each category and cumulative percentage of each
category involved to produce plastic cracks in cast in-situ slab concreting process. The
Pareto chart shows the first 4 categories ( design & detailing, labor, environment and
materials) cover 89% of the total root causes which is involved to produce plastic crack
in cast in-situ concreting process.
Figure 4.6 Pareto Chart of Root Causes in Each Category
68
Identify Potentials Level of Each Root Causes
Because of the each root cause does not have the same potential to produce plastic
crack in cast in-situ slab concreting process, study was carried out to determine the
potential of each root causes for producing plastic crack in cast in-situ slab concreting
process with respect of pervious knowledge and experiences of related experts. For this
achievement study was carried out to conduct multiple choice questionnaire to 3
professionals and close group discussion with them to finding potential of each root
causes to produce plastic crack during cast in-situ slab concreting process. For this
achievement four potential level has been defined to the questionnaire namely very low
level potential, mean level potential, high level potential and very high level potential.
And table below shows the percentage of each category in each potential level
according to number of root causes in each category which is place in each potential
level.
Tbale 4.2 Percentage of each category in each potentia level according to number of
root causes in each category
As is mentioned in above table all professionals did not believe that any of these root
causes having very low potential level to produce plastic crack in cast in-situ slab
concreting process. And also that table shows that labor and design & detailing category
having more percentage according to number of root causes which is placed in all
potential levels.
69
Identify Frequency Level of Each Root Causes
Further, to achieve some additional useful data, study was carried out to determine
frequency of each root causes during cast in-situ slab concreting process with respect of
pervious experiences of related experts in this particular manner. For achieving this
specific information study was carried out to conduct multiple choice questionnaires
through 3 professionals by defining 3 frequency level in questionnaires ( frequency less
than 5 processes out of 10 processes, between 5 and 8 processes out of 10 processes and
more than 8 processes to 10 processes).
Below table shows the percentage of each category in each frequency level by
considering number of root causes which is placed in each frequency level.
Table 4.3 Percentage of each category in each frequency level according to number of
root causes in each category
According to above table, labor and design & detailing category having more
percentage according to number of root causes which is placed in all potential levels.
So, problem related to labor and design & detailing factors more occur during cast insitu slab concreting process in comparison with other categories.
70
Proposed Check Sheet for Real Time Improving Cast-In-Situ Slab Concreting
Process
Objective 2: To propose check sheet for real time problem solving cast in situ
slab concreting process from the outputs of pervious objective.
To achieve the purpose of last objective study was carried out to propose check sheet
by the outputs of pervious objective. And the check sheet has been proposed for real
time problem solving cast in situ slab concreting process by the result of pervious
objective. The proposed check sheet are as follows:
71
72
73
74
Explanation of Items of Proposed Check Sheet
•
By refer to the proposed check sheet all items which is placed in specific
check sheet are as follows:
•
Categories which is involved to produce plastic crack in cast in-situ slab
concreting process
•
Specific root causes in each category which is had more influence to
produce plastic crack in cast in-situ slab concreting process
•
Specific potential of each root causes to produce plastic crack in cast insitu slab concreting process by specific sign color which is defined for
each potential level
•
Specific frequency of each root causes with respect of pervious
experiences of related experts by specific sign color which is defined for
each frequency level
•
Specific slab concreting process by separation in each floor of
construction project
•
Specific area for mentioning “ √ “ or “ × “ to determine which root
causes has been eliminated or not. If one root cause has been eliminated
the “ √ “ sign has been mentioned in specific area and, if one root cause
has not been eliminated the “ × “ sign has been mentioned in specific
area.
•
Further, specific area for calculating the total number of the “ × “ sign
in each slab concreting process in each floor
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Explanation of Proposed Check Sheet
Actually all of those items which is mentioned earlier help us to achieve specific
results that is main reason for proposing check sheet. In fact, by using this specific
check sheet on site during the cast in-situ slab concreting process we can determine
which root causes exist in current cast in-situ concreting process before starting the
process. And by this consideration we can identify root causes which is introduced in
current process and we have excellence view about them for eliminating them before
starting the process so that they never occur at the first place. And by this root cause
elimination before starting concreting process we could decrease propensity to produce
plastic crack during cast in-situ slab concreting process.
And specific potential of each root causes in this check sheet help us to identify
which root cause which is introduced in current concreting process has most powerful
potential to produce plastic crack so that eliminate those at first and rapidly. And also
consideration of potential of each root causes help us to do not skip or ignore some root
causes which is had high potential level to produce plastic crack in cast in-situ
concreting process.
Further, frequency of each root causes in this check sheet help us to evaluate our
current cast in-situ slab concreting process which is placed in which frequency level in
comparison with current position of cast in-situ slab concreting process as a whole. And
also push us to improve our current process to decrease of root causes’ number which is
produced in current cast in-situ slab concreting process for future concreting process.
76
In fact, by using this check sheet on site during cast in-situ slab concreting process, if
specific root cause has been eliminated, so we must mention “√ “ sign and, if specific
root cause has been not eliminated, so we must mention “ × “ sign. After that, by
calculating total number of “ × “ we can evaluate how many root causes has been
eliminated in comparison with pervious slab concreting process and tries to decrease
number of “ × “ in next slab concreting process for achieving zero number of “ × “ in
slab concreting process. It means that we have eliminated all root causes, so concreting
process have a very low potential as whole to produce plastic crack. And also by crack
investigation after finishing slab concreting process we can determine the sigma level of
each slab concreting process. Therefore, we can compare every slab concreting process
with consideration of sigma level of each slab concreting process to determine how
much far from the six sigma level are we?. And this consideration of sigma level for
each slab concreting process or even each floor concreting process encourage us to
achieve better sigma level in next slab concreting process. And this consideration
encourage everyone which is involved the process to achieve best sigma level as a
target.
77
CHAPTER 5
CONCLUSION & RECOMMENDATION
5.1 Conclusion
Study was carried out step by step according to DMAIC methodology of Six Sigma
approach. First the problem and project’s goal is defined after that Sigma level of
current cast in-situ slab concreting process is calculated by gathering relevant data from
the site investigation. After that study was carried out to find root causes of plastic crack
in cast in-situ slab concreting process. For achieving useful information to propose
check sheet, study was carried out to determine potential and frequency level of each
root causes with respect of previous concreting process experiences from related
experts. And then, study carried out to propose check sheet for real time improving and
controlling the cast in-situ slab concreting process during process of work. Further,
DMAIC “ Define- Measure- Analysis- Improvement- Control” methodology of Six
Sigma problem solving has been adopted for cast in-situ slab concreting process
through step by step validation through professionals with conducting questionnaire and
close group discussion.
5.2 Recommendation
This methodology (DMAIC) can be suitable for other processes in construction
projects to identify defect and eliminating them in systematic and organized way.
Identifying more root causes by investigating on site during specific process and make
check sheet more updated. Implementing proposed check sheet in a case study to
capture results in real condition. For future study can be recommended that to conduct
research study to fine proper and more powerful methods for eliminating each root
78
causes during process of work. And also for future study can be recommended that to
have effective outcome it is better to prepare software which is consist of all check
sheets related to process that can be run on cell phone for using during process of work.
This consideration can be more useful to achieve the zero defect target as an outcome of
a specific process. And, go to granular level of defect of process and documenting
in the newly proposed check list.
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81
APENDICES
82
QUESTIONNAIRE FORM A
The purpose of this questionnaire is to get potential level of each root causes of plastic
crack in cast in-situ slab concreting process during process of work. Root causes
divided to five categories consist of Labor category, Design and Detailing category,
Environment condition category, Material category and Equipment category. Please
kindly answer the questions based on your experience and knowledge in cast in-situ
slab concreting process by tick … in the box as shown using the rating scale below.
Your co-operation is extremely appreciated. Thank you.
Rating Scale:
1.
2.
3.
4.
5.
=
=
=
=
=
Very Low Potential
Low Potential
Mean Potential
High Potential
Very High Potential
a) Root causes related to labor categories:
1. Rapid screeding
2. Late starting curing
3. Keeping surface wet lower than 3 days
4. Rapid trowelling
83
5. Improper placement of rebar;
6. Omitted rebar;
7. Insufficient vibration;
8. Excess vibration;
9. Improper reading design detail sheet;
10. Unwashed aggregate;
11. Rapid drying;
12. Incorrect using materials;
13. Reinforce moving;
84
14. Formwork moving;
b) Root causes related to Design and Detailing category
1. Inadequate thickness or thinner section
2. Inadequate reinforcing
3. Incorrect geometry
4. Incorrect detailing
5. Low water content
6. Low slump
7. Depth of cover to the reinforcement greater than one third of the section depth
85
8. Decreasing cover limited range
9. Abrupt changes in section depth
10. Increasing bar size
11. Improper selection of reinforcement
12. Improper detailing reinforcement
13. High water contents
14. Increasing slump
15. Mix proportion tendency to bleed
86
c) Root causes related to materials
1. Poor quality of materials
2. Poor quality of reinforcement
3. Use retarders which increased time that it remains in plastic state
4. High proportion of fine materials
5. Low pozzolanic additions
6. High sedimentation
87
d) Root causes related to equipment category
1. Use leaking forms
2. Highly flexible forms
3. Not adequate braced forms
4. Shortage of equipments
5. Broken equipment
e) Root causes related to environment conditions
1. Wind velocity excess of 5 mph
2. Low relative humidity
88
3. High ambient temperature
4. Large difference temperature between air and concrete
5. Large difference temperature between concrete and formwork
89
QUESTIONNAIRE FORM
The purpose of this questionnaire is to get frequency level of each root causes of plastic
crack in cast in-situ slab concreting process during process of work. Root causes
divided to five categories consist of Labor category, Design and Detailing category,
Environment condition category, Material category and Equipment category. Please
kindly answer the questions based on your experience and knowledge in cast in-situ
slab concreting process by tick … in the box as shown using the rating scale below.
Your co-operation is extremely appreciated. Thank you.
Rating Scale:
6.
7.
8.
=
=
=
Less than five out of ten cast in-situ concreting process
Between five and eight out of ten cast in-situ concreting process
More than eight to ten cast in-situ concreting process
f) Root causes related to labor categories:
15. Rapid screeding
16. Late starting curing
17. Keeping surface wet lower than 3 days
18. Rapid trowelling
90
19. Improper placement of rebar;
20. Omitted rebar;
21. Insufficient vibration;
22. Excess vibration;
23. Improper reading design detail sheet;
24. Unwashed aggregate;
25. Rapid drying;
26. Incorrect using materials;
27. Reinforce moving;
91
28. Formwork moving;
g) Root causes related to Design and Detailing category
16. Inadequate thickness or thinner section
17. Inadequate reinforcing
18. Incorrect geometry
19. Incorrect detailing
20. Low water content
21. Low slump
22. Depth of cover to the reinforcement greater than one third of the section depth
92
23. Decreasing cover limited range
24. Abrupt changes in section depth
25. Increasing bar size
26. Improper selection of reinforcement
27. Improper detailing reinforcement
28. High water contents
29. Increasing slump
30. Mix proportion tendency to bleed
93
h) Root causes related to materials
7. Poor quality of materials
8. Poor quality of reinforcement
9. Use retarders which increased time that it remains in plastic state
10. High proportion of fine materials
11. Low pozzolanic additions
12. High sedimentation
94
i) Root causes related to equipment category
6. Use leaking forms
7. Highly flexible forms
8. Not adequate braced forms
9. Shortage of equipments
10. Broken equipment
j) Root causes related to environment conditions
6. Wind velocity excess of 5 mph
7. Low relative humidity
95
8. High ambient temperature
9. Large difference temperature between air and concrete
10. Large difference temperature between concrete and formwork
96
Six Sigma Conversion Table
Yield %
Sigma
Defects Per Million Opportunities
99.9997
6.00
3.4
99.9995
5.92
5
99.9992
5.81
8
99.9990
5.76
10
99.9980
5.61
20
99.9970
5.51
30
99.9960
5.44
40
99.9930
5.31
70
99.9900
5.22
100
99.9850
5.12
150
99.9770
5.00
230
99.9670
4.91
330
99.9520
4.80
480
99.9320
4.70
680
99.9040
4.60
960
99.8650
4.50
1350
99.8140
4.40
1860
99.7450
4.30
2550
99.6540
4.20
3460
99.5340
4.10
4660
99.3790
4.00
6210
99.1810
3.90
8190
98.9300
3.80
10700
98.6100
3.70
13900
98.2200
3.60
17800
97.7300
3.50
22700
97.1300
3.40
28700
96.4100
3.30
35900
97
95.5400
3.20
44600
94.5200
3.10
54800
93.3200
3.00
66800
91.9200
2.90
80800
90.3200
2.80
96800
88.5000
2.70
115000
86.5000
2.60
135000
84.2000
2.50
158000
81.6000
2.40
184000
78.8000
2.30
212000
75.8000
2.20
242000
72.6000
2.10
274000
69.2000
2.00
308000
65.6000
1.90
344000
61.8000
1.80
382000
58.0000
1.70
420000
54.0000
1.60
460000
50.0000
1.50
500000
46.0000
1.40
540000
43.0000
1.32
570000
39.0000
1.22
610000
35.0000
1.11
650000
31.0000
1.00
690000
28.0000
0.92
720000
25.0000
0.83
750000
22.0000
0.73
780000
19.0000
0.62
810000
16.0000
0.51
840000
14.0000
0.42
860000
12.0000
0.33
880000
98
10.0000
0.22
900000
8.0000
0.09
920000