Quality control

Defects and errors in construction projects have been subject to attention in the medias and debates through out the years. There exists a general consensus of a lack of quality on the construction sites, thus an increasing effort have been made to improve the quality of construction projects by a number of political initiatives . When managing quality in a project an important aspect is Quality Control, which is the topic of this article.

Definition of Quality Control

Quality Control (QC) is a part of quality management of construction projects, and to be more exact QC is at the heart of conformance management. The aim of QC in construction projects is to assure high quality of the construction being built and the individual processes in the project. In this content “high quality” means fulfilling standards and the established quality requirements of the specific project . It is important to investigate the causes of the arising problems, as well finding ways to eliminate unsatisfactory performance when performing QC, thus both corrective and preventive QC techniques are essensial.

Product Quality Control vs. Process Quality Control

Figure 1: Examples of input and output parameters in a process (Cite: hvor fuck fandt jeg den... Luuuurt)

QC deals with the specific products as well as the processes as mentioned. A certain understanding of the process or product is needed in order to perform QC of either part. A process is the transformation of a set of inputs into the desired output. Figure 1 shows the inputs can be materials, procedures and knowledge. Each process in a construction project can be analyzed by itself and afterwards actions can be determined in order to improve the process, thus the process QC become preventive .

Examples of process QC can for example by:

• Measuring the temperature of the concrete during casting and check if it fulfill specifications.
• Controlling the quality control process by checking if the quality control methods agreed upon are carried out .
• Checking if the pile movement during hammering process correspond to the predicted movement, when constructing the pile foundation.

QC of af product concerns instead the quality of the output/result of the a process in the construction project. It can be a product of a process in the design phase as well as in the construction phase. The output doesn't have be a physical product but can as well be a service, information or conducted paperwork as illustrated on Figure 1. Examples of defects that product QC deals with are:

• Missing information in drawing material
• Moisture damage of a construction element
• Cracking in a welding

Performing quality control

Table 1: Primary inputs and outputs when performing quality control

Primary inputs	Primary outputs
Progress data Deliverables Quality plan	Quality control measurements Verified deliverables Inspection reports Change requests Corretive actions

In order to perform QC, tools and inspection procedures are needed. These inspection procedures and QC tools are specified in the part of the quality management called Quality Assurance . The primary inputs and outputs of performing QC in construction project given by the standard DS/ISO 21500 are shown in Table 1. Here it can be seen that QC has a high dependency of good plan-ning, as the primary inputs are a result of planning the quality in the project. The primary outputs indicate, that QC is not only a checking if requirements are meet, but it also includes documenta-tion, communication and analysis. Further more it is seen that QC also have to prevent defects and non-conformance from taking place.

The standard DS/ISO 21500 states that QC should be performed during the whole project life cycle and that it includes following aspects:

• Monitoring the quality of the processes and detect defects.
• Analysis of the causes of defects and non-conforming performance.
• Eliminate unsatisfactory performance by identifying preventive actions and change requests.
• Communication of the changed requests and necessary corrective actions to project organization members.

Documentation is not mentioned directly by the standard, but it is implied in the last aspect "communication" as it is impossible to tell the craftsman which corrective actions that have to be fulfilled without. The documentation can made with control tables, but in large construction projects digital quality documentation is preferred as many parts perform quality control. By using digital documentation like "digitjek”, ”C-web” og ”Ajour” position and date of the defect can be noted on the layout drawing, so the craftsmen get a clear outline of defects .

Correct, prevent & predict

With the increased focus on minimizing non-conformance in construction projects the main goal of QC have shifted from a corrective to a predictive policy as illustrated on Figure 2. The intention of this shift is to predict the errors and defect, so they can be prevented. By achieving predictive and preventive QC the coast of the project will also be minimized as well as time will be saved. Noget med det er lettere sagt end gjort. In the following the three policies (corrective, preventive and predictive) of QC will be clarified.

Figure 2: Quality Control policies and associated actions

Corrective Quality Control

Figure 3: Corrective QC is performed after defects occur .

Corrective QC is necessary when non-conformance or a defect is found or a fatal event has occurred, thus corrective QC is defined as a reactive approach. This approach of QC is necessary because unexpected events and defect always will occur in construction projects. The ideal project where all problems are prevented is hard to establish, since many people, partners and processes are involved in the project. Questions like “have we met the requirements?” and “what went wrong?” are asked here. Corrective QC deals with critical defects and the less serious defects, which doesn't meet the requirements.

This type of quality control can be very expensive, due to the fact that rework can be very comprehensive . Correcting serious errors can also be very time consuming depending on how many parts that have to be involved, and new material deliveries can likewise result in delays.

In order to correct non-conformance, knowledge of the causes to the problem has to be obtained. Performing corrective QC can be accomplished with different techniques, and one technique “cause and effects diagrams” is elaborated in following.

Preventive Quality Control

Figure 4: Preventive QC alerts before errors occur.

By changing the strategy of QC from corrective to preventive the questions to be asked are changed to "Can we do the job correctly" and "Are we doing the job correctly" . In order to answer the questions a certain amount of knowledge and experience is required, and without this it isn't possible to prevent failures and non-conformance from happening. That people trying to control procedures doesn't have the competencies is a common problem, and for this reason the advice from W. Edwards Deming, a guru of quality management, was :

"Don't just do something, sit here and think"

A way to increase preventive QC in construction projects is to make specifications, recommendations and regulations of work procedures and construction products. By introducing these aspects the people involved in the project can get a clear overview of which aspects of the procedure that are important to focus on in order to prevent non-conformance. Examples of this.

Continous, delivery and start-up control

A qualitative analysis of processes and methods in flawless construction projects, that based on experience from project managers, showed that continous, delivery and start-up control was very import in order to prevent fatal errors :

A way to prevent expensive corrective actions to quality problems is to perform continuous QC. This can for example include thermo graphic measurements of the first rooms finished, and if non-conforming performance is found, then preventive actions can be made to assure the quality of the remaining rooms.

Control at delivery of for example reinforcement and concrete elements is very import, as these elements often are shot in and hidden, thus later control is impossible. Poor quality of these elements could be fatal as it can result in construction failure, which can be prevented by performing quality control at the delivery.

Start-up control at the shift between contractors can prevent fatal errors from occurring. This way the quality of the previous work is assured and the following work is not going to hide defects that potentially can result in critical errors, that will be very expensive and time consuming to correct. This concept is also called "stop the line" in lean construction, where the following work are set on hold until all errors from previous work are corrected : .

Predictive Quality Control

Figure 5: Predictive QC alerts at trends of possible failure .

In order to determine preventive actions predictions of possibles failures is necessary. The predictions should be based upon analysis of data well-founded arguments thus immaterial actions aren't initiated. Valuable predictions can be made by utilising modern technology, that makes it possible to collect large amounts of data from different systems. Problems can be detected before they happen by analyzing the collected data. The selection of the digital tool is very important, as an inaccurate selection of a system can lead to a failed outcome of collected data, which limits the performance of predictive QC. . Using this approach it is important that the problem leave digital footprints before it occurs, otherwise predictions can't be made.

Monitoring

Not written but is going to include:

Digital tools for inspections Sensor systems Radio Frequency Identification (RFID)

Quality control techniques

Write something about the 7 tools Ishikawa...

Cause and effect diagrams

Figure 6, structure of a cause effect diagram with six chosen categories of causes, which all have an influence on the overall problem. The secondary cause are attached to the primary causes by small arrows .

Cause and effect diagrams also go under the names “fishbone diagram” (due to their shape) and “Ishikawa diagram” (after the techniques inventor). The reason for the name “cause and effect diagram” is that the diagram is separates the problem (the effect of the causes) from the causes. The basic idea of the technique is to work back form the problem by asking: “why did it occur”, and in that way finding the different roots to the problem . Each cause is thereby found by using a form of brainstorm technique, and they are grouped under different categories. A cause can either be a primary cause or a secondary cause to the primary cause. When illustrating the causes this way, the diagram takes form as a fish skeleton as shown from Figure 6.

A cause effect diagram shows there often are several roots to non-conformance and defects, and that several corrective actions have to be performed. This allegation becomes clear by grouping the causes under different categories, because it illustrates the difficulties of complex processes. The categories often include people, process/methods, equipment/machines, material, environment and management, as these are some of the basic elements in construction projects .

This technique can also be used as a preventive QC tool. In this way the problem have to be predicted before it occurs and then the problem can be prevented by making qualified decisions for the actions and processes that have to take place. The difficulties will be to predict all the causes to a specific problem desired to be prevented.

Statistical process control

Text goes here

Performance measurements

Text goes here

Value stream mapping

Text goes here

Limitations

Not written but is going to include:

The requirements have to be clear (from the client to the designer, as well as to the entrepreneurs and craftsmen)

Operationally orientated and doesn't take factors as customer satisfaction into account

Project specific control

Not enough ressources from the designers

Time – there have to be time to do it.

Knowledge – people have to understand the process in order to control them. Problem is that managers are trying to controll processes they have no knowledge about. (Cite Oakland den mindre article)