Statistical Process Control in the
Construction Industry
Dr Mohamed AICHOUNI
m.aichouni@uoh.edu.sa
www.uoh.edu.sa/dept/qicrc/
Monday, November, 21st , 2011
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
Quality Definition and Characteristics
Quality is defined by the totality of features
and characteristics that satisfy customers
needs” (ASQ)
Quality Characteristics
Variables
Can be measured or expressed with some
unit, such as height, length (m), mass
(kg), cycle time (s), concrete strength
(MPA) etc..
Attributes
Can be counted such as number of defects,
errors, accidents etc ..
Process
Variations
Process Variations and Quality
• Quality is inversely proportional to variability
(Variability & Quality are enemies).
• The more variation in product characteristics, in
delivery times, in work practices: the more waste,
higher costs and poor quality, is delivered to our
customers.
(Out of the Crisis, 1982)
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
Process Variations Causes
1. Common causes are ever-present in the process;
========= Natural Variations
2. Special causes are intermittent effects that must be
investigated immediately.
========= Assignable Causes Variations
• Management should help people identify and remove
special causes and reduce the occurrence of common
causes in the process.
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
Process Improvement
• Process Improvement is basically about
the reduction of variability in processes,
products and services.
• It results in waste reduction, quality
improvement, Customer Satisfaction and
more importantly to Business
Excellence.
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
How to Improve Processes and Quality ?
 Study and Understand Process Variation.
 Use Appropriate Quality Tools (The 7 Basic
tools (Statistical Process Control), the 7 New
Tools for Management and Planning etc..
 Set Process improvement teams
 Use Employee suggestions
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
Seven Basic Quality Tools
Kaoru Ishikawa (1972)
 Called the Magnificent Seven
 They are simple visual tools
based on the use of data to study
and understand the things we do
(Process) so that we can improve
the quality of products and
services .
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
Seven Basic Quality Control Tools
Magnificent Seven
Process
1
2
3
4
5
 Flow Chart
 Check Sheet
 Pareto Analysis
 Histogram – Process Capability
 Cause-and-Effect Diagram
 Scatter Diagram
 Control Charts (SPC) – Process Stability
1 2 3 4
Dirt
Old
Temp
Fault
x xx
x
x x xx x
x x x
xx
x
x
UCL
LCL
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
Control Chart (SPC Chart)
What is it?
Special Cause Variation
Variable Y
• Quality Management tool, showing
whether a process is working
predictably and smoothly.
Out of Statistical Control Situation
Upper limit
Average/Spec
What is its use?
• To monitor, control and improve
process performance overtime by
studying variation and its source.
Common Causes Variation
Lower limit
X (Time)
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
What Does a Control Chart Do ?
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
Out of Statistical Control Situation
Special Cause Variation
Variable Y
 Focuses attention on detecting and
monitoring process variation over
time;
 Distinguishes special from common
causes of variation, as a guide to
local or management action;
 Serves as a tool for ongoing control
of a process;
 Helps improve a process to perform
consistently and predictably for
higher quality, lower cost, and
higher effective capacity;
 Provides a common language for
discussing process performance.
Upper limit
Average/Spec
Common Causes Variation
Lower limit
X (Time)
Control Charts Interpretation
• Stable process: one which performs
with a high degree of consistency at
an essentially constant level for an
extended period of time
– “In-control”
• A process that is not stable is
referred to as being in an out-ofcontrol state.
This is due to the existence of Special causes in the
process, It requires immediate cause-effect analysis to
eliminate the special cause of variation.
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
Histograms
What is it?
What is its use?
• Histogram provides an easy way to evaluate
the distribution of the process and to have a
precise look at process variations.
frequency
• A Histogram is a bar graph used to present
frequency data.
USL
LSL
• How the process distribution with respect to
Customer Specifications (USL, LSL)
Category
• Is the Process Capable to meet our customer
requirements ?
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
Applications of SPC tools in the
Construction Industry
BinLaden Research Chair on Quality in the
Construction Industry (QICRC)
www.uoh.edu.sa/dept/qicrc/
Statistical Process Control (SPC)
in the Construction Industry
World Class
Research
Other Projects (TQM,
zero energy
buildings,
Constructions
Materials, etc…)
(1) Concrete
Production
(2) Concrete
Production,
Montgomery et al.
Arizona State
University, 2010
Aichouni, 2011
Asphalt Quality
Characteristics,
UoH Projects ;ReadyMixed Concrete
Divinsky, Haifa Inst of
Technology, ASTM, 2003
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
(3) Optimization of
Applications in Concrete
Production Processes
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
Applications in Concrete Production
Processes
• Concrete is the most widely used material in
construction industries. Therefore, it is necessary to
understand and improve the efficiency of a concrete
production process.
• Producers of concrete can use control charts to
determine if the concrete production process is
out-of-control and subsequently attempt to identify
the root causes for the out-of-control situation.
• By identifying assignable causes of the out-ofcontrol process, the producer can then improve the
process by reducing product variation, unnecessary
waste, or over-designed concrete
mixtures.
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
Applications in Concrete Production
Processes
Historical Data of Concrete (Arizona
Department of Transportation) were
analyzed using SPC techniques.
For the majority of concrete delivered to
customers, the strength far
exceeded that required for a
particular project.
Over-designed concrete mixtures : The
amount of cement that could be
saved by reducing the total cement
content in the mixture is significant.
Savings can be huge.
Hybrid Control Charts for Active Control and Monitoring of Concrete Strength,
B. Laungrungrong; B. Mobasher; D. Montgomery; and C. Borror, Arizona State University
JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / JANUARY 2010 / 77
Applications in Concrete Production Processes
Project (1)
 EWMA and CUSUM Control Charts were used to analyze concrete data
 This case represents an in-control stable and capable process.
 The process is stable under the acceptable level of concrete strength (greater
than the fc`) .
No action is required on the process
Hybrid Control Charts for Active Control and Monitoring of Concrete Strength,
B. Laungrungrong; B. Mobasher; D. Montgomery; and C. Borror, Arizona State University
JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / JANUARY 2010 / 77
Applications in Concrete Production Processes
Project (2)
Out of Control Process (points outside Control Limits)
Unstable Process
Poor Process capability : unacceptable level of concrete strength lower than the fc
It is important to investigate the process and reduce variation with the goal being
to bring the process back into statistical control and make it capable.
Hybrid Control Charts for Active Control and Monitoring of Concrete Strength,
B. Laungrungrong; B. Mobasher; D. Montgomery; and C. Borror, Arizona State University
JOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / JANUARY 2010 / 77
Applications in Concrete Process
Hail University Projects
Customer : UoH, Engineering College Building
Producer : XXX Ready-Mix Concrete Co (Hail)
Concrete Types : RMC 21 and
RMC 35
Quality Characteristic: Concrete Compressive
Strength (MPa) at 28 Days;
Tests Data were taken from Third party
laboratory (Period : March – October 2011)
Data Analysis using Minitab Quality Software
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
Applications in Concrete Process
Hail University Projects RMC 35
Fully Satisfied Customer (Delivered
Strength varies : 102 – 181 % of
Required )
BUT Overdesigned Concrete
Producer Perspective:
Frequency Distribution for RMC-35 Process
Normal
70
Mean
StDev
N
60
46.24
6.230
524
Frequency
50
40
30
20
10
0
36
42
48
54
Delivered Mpa
60
66
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
Production Process Variability
Required Strength = 35 Mpa
Delivered Mean = 46 Mpa
Std Dev = 5.8 MPa
Min = 35.77 M
Max = 63.20 MPa
Applications in Concrete Process
Hail University Projects RMC 35
1.
2.
3.
Out of Control Situation and big variability in the concrete.
Management Decision to set up Quality Control Department led to
improved process;
However, still some opportunity for Improvement exist.
Applications in Concrete Process
Hail University Projects RMC 21
Frequency Distribution for RMC-21 Process
Normal
20
Mean
StDev
N
36.27
4.211
75
Frequency
15
10
5
0
Fully Satisfied Customer (Delivered
Strength varies from 137 to 207 %
of Required )
Production Process Variability
30
35
40
Delivered Mpa
45
50
Required Strength = 21 Mpa
Delivered Mean = 36.2 Mpa
Std Dev = 4.2 Mpa
Min = 28.7 Mpa
Max = 43.8 Mpa
Out of Control Process
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
Applications in Asphalt Production
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
Applications in Asphalt Production
(a) Process with Problem / Without Problem
•
•
Production Plant 24
IR-R charts indicate
clearly process out of
control = Lower
Quality level of
Asphalt. ?????
UC
L
Target
LCL
UC
L
•
Histogram = Product
(18.75 %) lower than
specifications limit (LSL)
required by customer.
Process
Capability ?
LCL
For Process
Improvement, reasons
need to be
investigated using
appropriate quality
tools
7 basic toolbox
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
LSL
Product not
meeting
specificatio
ns
Target
USL
Applications in Asphalt Production
(b) Process with Problem / Without Problem
• Production Plant
22
• IR-R control charts
indicate clearly in
control process
• = Quality level
high
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
UCL
LCL
UCL
LCL
LSL
Target
USL
Applications in Asphalt Production
Comparison of # Processes
CP ≥ 1 Process Capability is acceptable ;
CP ≥ 1.3 Process Capability excellent.
Expected level of quality : high
CP < 1 : Big problem with the process and the product quality .
Process Not Capable to meet Customer Specifications
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
Conclusions
Statistical Process Control (SPC) help construction industry to
understand the process and to improve its efficiency and
capability to meet customer specifications and requirements.
When historical data are available on projects, better insight
into operational procedures can be obtained through the use
of control charts.
Construction Companies can use SPC to reduce their cycle
times and defect rates as well as their operational and
administrative costs and, simultaneously, increase their
products quality and their returns on investment.
SPC allow construction companies to work leaner
and faster, with greater quality and customer
satisfaction levels, and lower costs and accident
rates.
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
A Final Word
Quality Control begins with education and ends with education,
Dr Kaoru Ishikawa
BinLaden QICRC team will be happy to provide the training according to the
construction industry needs.
www.uoh.edu.sa/dept/qicrc/
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA
Thank you
http://www.uoh.edu.sa/dept/qicrc/
Dr Mohamed AICHOUNI
Email : m.aichouni@uoh.edu.sa
© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA