ARTICLES & FEATURES
THE DIFFERENCE BETWEEN
Quality Assurance & Quality Control
ON CONSTRUCTION PROJECTS
Mr. Bandoo – MSc, BSc, NEBOSH – is a Civil Engineer at Coosal’s whose professional background includes over 10 years of civil engineering and project management experience, in both the public and private sectors of the Trinidad and Tobago construction industry.
One of the key components that contributes to the success of construction projects is the management of its quality from start to finish. This can be achieved by using a Quality Management System which include principles of both Quality Assurance and Quality Control. However, in the Trinidad and Tobago construction industry, Quality Assurance and Quality Control tend to be used interchangeably when in fact, they define different processes in the quality management of construction projects.
Defining Quality Assurance and Quality Control
Quality Assurance on construction projects can be defined as a part of a quality management system that is focused on providing confidence that quality requirements will be fulfilled. It is the development of procedures and standards commonly in the form of contractual documents, which aim to ensure construction projects achieve a required level of quality. It is also important to understand that these Quality Assurance documents are typically developed by the Client and done prior to the commencement of the construction phase of a project.
Quality Control on construction projects on the other hand, can be defined as a part of a quality management system that is focused on fulfilling the quality requirements set by the Quality Assurance procedures and standards. It is the practical implementation of these procedures and standards to achieve the required level of quality on construction projects. Quality Control methods are typically implemented by the Contractor and done throughout the construction phase of a project when applicable.
An example of Quality Assurance and Quality Control
Here, the simple construction stages of a strip footing foundation project will be used to further explain the difference between Quality Assurance and Quality Control. The Quality Assurance documents used for this example will be the Construction Drawings and the Technical Specifications whilst the Quality Control methods will aim to fulfill the quality requirements of these documents.
Stage 1: Surveying and Excavation Works
Quality Assurance – The Construction Drawings will show the setting out information and the depth of the foundation. The Technical Specifications will require the Contractor provide insurances for the equipment to be used and assurance of competent personnel to undertake the works.
Quality Control – The Contractor will include the services of a competent Engineering Surveyor to set out the foundation as shown on the construction drawings. Also, suitable equipment will be used for the works, for example an excavator, and operated by a certified operator to excavate to the required limits of the foundation. Personnel resumes and equipment third party certificates can be used as documentation to show that the Quality Assurance standards have been met.
Stage 2: Steel Work and Formwork
Quality Assurance – The construction drawings will show the sizes, shapes, dimensions, spacings etc. of the steel rebar to be used. It will also show the dimensions of the foundation, which will guide the Contractor’s formwork requirements. The Technical Specifications will state the grade of steel rebar required for the foundation i.e., ASTM Grade 40, ASTM Grade 60 or ASTM Grade 80 etc. It may also require the Contractor provide a formwork system designed to a recognized standard such as ACI 347.
Quality Control – The Contractor will select a competent supplier that can provide the steel rebar to meet the Quality Assurance standards. The supplier will produce mill test certificates to be used as documentation to show that the Quality Assurance standards were met. The Contractor will also include a formwork system designed in accordance with the Quality Assurance standards and it shall be constructed accordingly. Inspection of the works will also be conducted to ensure the steel rebar and formwork are installed per the construction drawings prior to concreting.
Stage 3: Concrete Works
Quality Assurance – The construction drawings will show the minimum required compressive strength of the concrete for the foundation. The Technical Specifications will state the workability of the concrete i.e., a slump ranging from 2 inches to 4 inches, as well as the sampling and testing requirements done to recognized standards such as ASTM C31 and ASTM C39. It may also require the Contractor provide concrete mix designs for the different strengths of concrete required, also designed to a recognized standard such as ACI 318.
Quality Control – The Contractor shall select a competent supplier and independent testing agency that can provide and test concrete respectively, to meet the Quality Assurance standards. The supplier and the testing agency will produce concrete mix designs, compressive strength test reports, slump test reports and sampling reports etc. to be used as documentation to show that the Quality Assurance standards were met.
Stage 4: Backfilling Works
Quality Assurance – The construction drawings will show the backfill materials required for the works whilst the Technical Specifications will show the testing and compaction requirements for the materials. It may also require the Contractor provide test reports and compaction reports for the materials, done to a recognized standard such as ASTM or AASHTO.
Quality Control – The Contractor shall select a competent supplier and independent testing agency that can provide and test backfill materials respectively, to meet the Quality Assurance standards. The test reports and compaction reports for the materials can be used as documentation to show that the Quality Assurance standards were met.
Conclusion
Whilst Quality Assurance and Quality Control are both important in successfully managing quality on construction projects, it must be understood that they are independent terms and cannot be used interchangeably. Quality Assurance is a preventive process that aims at establishing procedures and standards to provide a quality conducive environment for construction projects. Quality Control is a verification process that ensures compliance with the Quality Assurance procedures and standards established.
Understanding the difference between Quality Assurance and Quality Control makes the project team more efficient in achieving the quality goals on construction projects. Conversely, a lack understanding can increase the risk of defects which can lead to rework and associated incurred costs.