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Last edited 09 Sep 2016

Quality control for construction works

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[edit] Introduction

Quality control is the part of quality management that ensures products and service comply with requirements. It is a work method that facilitates the measurement of the quality characteristics of a unit, compares them with the established standards, and analyses the differences between the results obtained and the desired results in order to make decisions which will correct any differences.

Technical specifications define the type of controls that must be carried out to ensure the construction works are carried out correctly. They include not only products materials, but also the execution and completion of the works.

One way of controlling quality is based on the inspection or verification of finished products. The aim is to filter the products before they reach the client, so that products that do not comply with requirements are discarded or repaired. This reception control is usually carried out by people who were not involved in the production activities, which means that costs can be high, and preventative activities and improvement plans may not be effective. It is a final control, located between producer and client, and although it has the advantage of being impartial, it has a large number of drawbacks, such as slow information flows, and that the inspectors are not familiar with the circumstances of production and are not responsible for the production quality.

When tests are destructive, the decision to accept or reject a full batch must be made on the basis of the quality of a random sample. This type of statistical control provides less information and contains sampling risks. However, it is more economical, requires fewer inspectors, and speeds up decision-making, while the rejection of the whole batch encourages suppliers to improve their quality. This type of control can also identify the causes of variations and, so establish procedures for their systematic elimination.

Statistical control can be applied to the final product (acceptance control) or during the production process (process control). Statistical controls at reception establish sampling plans with clearly-defined acceptance or rejection criteria, and complete batches are tested by means of random sampling. The sampling control can be based on inspection by attributes in line with the ISO 2859 standard (Sampling procedures for inspection by attributes), or on inspection by variables in line with the ISO 3951 standard (Sampling procedures for inspection by variables).

A construction company should reduce the costs of bad quality as much as possible, and ensure that the result of its processes comply with the client's requirements. Both internal and external controls can be carried out. For example, the control of concrete received by the contractor can be carried out by an independent entity; the execution of steelworks can be controlled by the project manager (on behalf of the client), or the construction company can establish an internal control for the execution of the building work.

[edit] Quality assurance in accordance with ISO 9001

Quality assurance is a set of planned and systematic actions to ensure that products and services comply with specified requirements. It not only involves checking the final quality of products to avoid defects, as is the case in quality control, but also checking product quality in a planned way in all the production stages. It is the development of work and product design procedures to prevent errors from occurring in the first place, based on planning backed up by quality manuals and tools.

When a consensus has been reached on the requirements of a quality management system, it is possible to define a series of generic standards applicable to any type of organisation. The international standards, generically called ISO 9000, are the most widespread and generally accepted in developed countries. The ISO 9000 standards consists of four basic interdependent standards supported by guides, technical reports and technical specifications:

Companies can only be certified under the requirements of the ISO 9001 standard. It is a standard that can be used to certify the efficiency of a quality management system. Nevertheless, if the aim is to improve efficiency, the objectives of the ISO 9004 standard are broader in scope. The principles that underlie the management of quality in these standards are the following: customer focus, leadership, involvement of people, process approach, system approach to management, continual improvement, factual approach to decision making and mutually beneficial supplier relationships.

The ISO 9001 standard specifies requirements for a quality management system where an organisation needs to demonstrate its ability to consistently provide products that meet the requirements of clients and applicable regulations requirements. Regulatory requirements focus on the quality management system, management responsibility, resources management, product realisation and measurement, analysis and improvement.

When a quality system is applied to a product as complex and unique as construction, a specific quality plan must be drafted by applying the company's global system to the specific project. The plan must be drafted by the contractor before the start of the construction works and will be reviewed throughout its execution. The quality plan is applicable to the materials, work units and services that have been specifically chosen by the construction company in order to comply with the quality requirements stipulated in the contract. The quality plan is drafted for the construction works when a preventive strategy is needed to guarantee the construction quality, even though there might also be a quality manual, in compliance with the ISO 9001 standard requirements.

The construction company determines the need to prepare execution documents, work instructions, inspection regimes, process files, action plans, etc. for the execution and control of processes, depending on the complexity of the activity, the qualifications of the personnel and the experience of the team. The plan establishes the resources required and associated documents (lists, purchasing documentation, machinery, equipment, etc.). The control activities (verification of compliance with specifications, validation of specific processes, monitoring of activities, inspections and tests), which the units, materials or services undergo must also be established. These activities can be defined through inspection, testing plans, action plans and where applicable specific tests (for example, load tests for structures).

[edit] Standards and procedures

When the aim is to guarantee the uniformity of a system, process or product, reference patterns are established in documents called standards or norms. The general objectives of standards are simplification, communication between the parties involved, production economy, safety and health, protection of consumer interests and the removal of trade barriers.

In any type of company, the set of tasks carried out is so complex that they have to be written down to ensure internal consistency, to preserve them and to make sure they are methodically applied. These documents are called procedures, and describe the way in which an activity or process must be carried out.

Therefore, standards establish the requirements of products or processes. Procedures are documents drawn up by the company itself and take into account the requirements established in the standards. These documents must include the purpose of the procedure, references to other documents, scope, method and sequence of tests, acceptance and rejection criteria, key control points and time of inspection. In all cases the control of a procedure should be documented in the quality records and filed in the quality log at the construction site.

Technical or administrative procedures can also be part of a quality management system. In this case, the manual provides a generic description of the company's quality system, while procedures, whether general or specific, establish what is required to attain the objectives listed in the manual. Procedures must link the ISO standards' requirements and the activities of the company. They should include the people involved, information about materials and equipment and a description of key activities. Each organisation should decide which processes should be documented on the basis of client and regulatory requirements, the nature of its activities, and its corporate strategy.

[edit] Certificates and technical approvals

The quality control of a product or process can sometimes be replaced with certification of the quality characteristics by third parties. Products that have received officially recognised quality marks may be exempt from controls and reception tests, increasing batch size and improving safety systems.

However, the scope and aim of these quality marks are variable and an in-depth understanding is required to know what they mean. Below are different types of quality certificates, starting with the least reliable:

  • Certificate of origin: in this case the manufacturer states that the product complies with some specifications. Although the certificate might not be very reliable, failure to comply with the specifications can be legally actionable.
  • Accredited laboratory test certificate: the test is performed on a small sample, and therefore cannot guarantee all production. These certificates should be used with caution due to their limited scope.
  • Product type approval certificate: this approves a prototype and therefore does not guarantee the quality of the subsequent manufacturing process.
  • Standard compliance seal or mark: its scope includes continual production and therefore it is more reliable than other certificates. When the product is very new and there is no specific standard to regulate it, the certificate is issued in the form of technical suitability documentation.

Directive 89/196/EEC of the European Union establishes the laws, regulations and administrative provisions of the member countries to construction products. The purpose of the directive is to guarantee the free movement of all construction products throughout the Union by harmonisation of national laws which regulate the health, safety and welfare requirements. These requirements can take the form of harmonised European standards adopted by European standardisation bodies (CEN or CENELEC) or European technical suitability documents if there is no harmonised norm, national norm or European norm mandate. Under this Directive, construction products must have the CE mark, whereby the manufacturer declares that the product complies with the provisions of Community Directives. This mark indicates that the product complies with the essential requirements of harmonised norms (EN) and the Guides for European Technical Approval.

(See also Energy related products regulations and Construction Products Regulation)

Nevertheless, all the countries within the Union have their own particular set of conditions that have a direct impact on construction (weather, local construction procedures, etc.) and which are not included in the CE mark guidelines. So although the mark facilitates the movement of construction materials between countries, it does not mean that the quality controls established for particular conditions are abolished. This could be solved by the adoption of voluntary norm conformity certificates for each specific case.

When the construction materials and systems are very new (not traditional), the European Organisation for Technical Approvals, an umbrella organisation for national authorisation bodies, may draft European technical suitability document guides for a construction product or family of products, acting on a mandate from the Commission. When there is no European standard or European technical suitability document available, products can be assessed and marketed in accordance with existing national provisions and in conformity with essential requirements.


The text in this article is based on an extract from CONSTRUCTION MANAGEMENT, by Eugenio Pellicer, Víctor Yepes, José M.C. Teixeira, Helder Moura and Joaquín Catala. Valencia, Porto, 2008. The original manual is part of the Construction Managers' Library – created within the Leonardo da Vinci (LdV) project No: PL/06/B/F/PP/174014, entitled: “COMMON LEARNING OUTCOME FOR EUROPEAN MANAGERS IN CONSTRUCTION”. It is reproduced here in a modified form with the kind permission of the Chartered Institute of Building.

--CIOB

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