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..

AttributesCan 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

Flow Chart Check Sheet Pareto AnalysisHistogram – Process CapabilityCause-and-Effect Diagram Scatter DiagramControl Charts (SPC) – Process Stability

Seven Basic Quality Control Tools Magnificent Seven

1 2 3 4Dirt

Old

Temp

Fault

xx x

xx

x xx

x

x x xx

xx

x

UCL

LCL

12345

Process

© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA

Control Chart (SPC Chart)

What is it? • Quality Management tool, showing

whether a process is working predictably and smoothly.

What is its use?• To monitor, control and improve

process performance overtime by studying variation and its source.

Varia

ble

Y X (Time)

Upper limit

Lower limit

Average/Spec

Common Causes Variation

Special Cause Variation

Out of Statistical Control Situation

© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA

What Does a Control Chart Do ?

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.

Varia

ble

Y

X (Time)

Upper limit

Lower limit

Average/Spec

Common Causes Variation

Special Cause Variation

Out of Statistical Control Situation

© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA

Control Charts Interpretation

© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA

• 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-of-control 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.

HistogramsWhat is it?

• A Histogram is a bar graph used to present frequency data.

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.

• How the process distribution with respect to Customer Specifications (USL, LSL)

• Is the Process Capable to meet our customer requirements ?

LSL USL

© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA

freq

uenc

y

Category

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

(1 )Concrete Production

Montgomery et al. Arizona State University,

2010

(2 )Concrete Production ,

Aichouni, 2011 UoH Projects ;Ready-

Mixed Concrete

Other Projects (TQM, zero energy buildings,

Constructions Materials, etc…)

(3 )Optimization of Asphalt Quality Characteristics,

Divinsky, Haifa Inst of Technology, ASTM, 2003

World Class Research

© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA

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-of-control 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

Hybrid Control Charts for Active Control and Monitoring of Concrete Strength, B. Laungrungrong; B. Mobasher; D. Montgomery; and C. Borror, Arizona State UniversityJOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / JANUARY 2010 / 77

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.

Applications in Concrete Production Processes

Hybrid Control Charts for Active Control and Monitoring of Concrete Strength, B. Laungrungrong; B. Mobasher; D. Montgomery; and C. Borror, Arizona State UniversityJOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / JANUARY 2010 / 77

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

Applications in Concrete Production Processes

Hybrid Control Charts for Active Control and Monitoring of Concrete Strength, B. Laungrungrong; B. Mobasher; D. Montgomery; and C. Borror, Arizona State UniversityJOURNAL OF MATERIALS IN CIVIL ENGINEERING © ASCE / JANUARY 2010 / 77

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.

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:

Production Process Variability Required Strength = 35 Mpa Delivered Mean = 46 Mpa Std Dev = 5.8 MPa Min = 35.77 M Max = 63.20 MPa

Delivered Mpa

Frequency

666054484236

70

60

50

40

30

20

10

0

Mean 46.24StDev 6.230N 524

Frequency Distribution for RMC-35 ProcessNormal

© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA

Applications in Concrete Process Hail University Projects RMC 35

1. Out of Control Situation and big variability in the concrete.2. Management Decision to set up Quality Control Department led to

improved process;3. However, still some opportunity for Improvement exist.

Applications in Concrete Process Hail University Projects RMC 21

Fully Satisfied Customer (Delivered Strength varies from 137 to 207 % of Required )

Production Process Variability 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

Delivered Mpa

Frequency

5045403530

20

15

10

5

0

Mean 36.27StDev 4.211N 75

Frequency Distribution for RMC-21 ProcessNormal

© 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. ?????

• For Process Improvement, reasons need to be investigated using appropriate quality tools

7 basic toolbox

© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA

LSL Target USL

Product not meeting

specifications

UCL

LCL

UCL

LCLTarget

• Histogram = Product (18.75 %) lower than specifications limit (LSL) required by customer.

Process Capability ?

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

© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA

Applications in Asphalt ProductionComparison of # Processes

CP ≥ 1 Process Capability is acceptable ; CP ≥ 1.3 Process Capability excellent. Expected level of quality : highCP < 1 : Big problem with the process and the product quality . Process Not Capable to meet Customer Specifications

ConclusionsStatistical 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 WordQuality Control begins with education and ends with education,

Dr Kaoru Ishikawa

© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA

BinLaden QICRC team will be happy to provide the training according to the construction industry needs.www.uoh.edu.sa/dept/qicrc/

Thank you

http://www.uoh.edu.sa/dept/qicrc/

Dr Mohamed AICHOUNIEmail : m.aichouni@uoh.edu.sa

© Copyright : Dr Mohamed AICHOUNI, PhD, SQC, KAQA