Quality in construction is defined as ‘meeting or exceeding the requirement of client/owners. In construction industry, quality is used in different every than the product industry. In the product industry, quality of some product is better than the other, but we can not say that one grade of concrete. Quality in construction is employed with conformity with which specifications are met.
Designer specifies the grade of concrete to be used and contractor has to use the in gradients of concrete such that desired grade of concrete is obtained.
Quality in construction is related to
- satisfying the specification mentioned in the contract
- completing the project time.
- Fulfilling the owner’s requirement within budget
- Avoiding disputes claims and
- Ensuring the faculties performs its intended purpose.
We use certain product in the construction industry such as tiles, brick. Quality of these products can be partially related with the general connotation of quality. Other aspect in quality has slightly different meaning at various stages of life cycle of product such as at design stage or construction stage.
Quality schemes involve economic studies of selection of types of material and methods to be included in design , ensuring that this design is in accordance with all applicable codes and regulation and controlling the construction on the project to be sure that the work is performed according to the standards specified in the contract documents . Method to be adopted may vary from the automated documented through computer to statistical quality control in the field.
Quality assurance is referred as a scheme adopted by a construction company to maintain the standard or quality consistent. It is primarily an internal management system of a construction company. Generally a company maintains a quality assurance chart by specify various checks at different levels as well as constantly improving its attributes. A quality assurance program may include
- Arranging periodical training for its worker
- a good safety Programme
- a sound procurement system to get best quality material and suppliers
- A reward scheme for innovative work and competitive career progress scheme
If a company is involved in repetitive work, then implementations of statistical control of the process. Such as in concreting, regular sampling scheme control the production of concrete. Similarly in asphalt work , regular satisfied quality control is carried out.
Quality control is the periodic inspection to ensure that the constructed facilities meet the standard specified in the contract. It is usually carried by team of owners engineers or its morning. As for example, in a high way project, engineers check that compaction of soil is carried out properly by measuring its density; workability of concrete is checked by employing slump test etc. or checking compressive strength of concrete at periodical level.
Quality assurance is good management scheme whereas quality control is an inspection or sampling process.
Government works is generally carried out using lowest bid system. In lowest bid system, high quality work carried out by contractor does not play a major role rather price quoted by them is an important criteria.
The procedure for selection of contractor affects the quality control in the construction. Low bid system hardly provides any incentive to high quality work carried out by the contractor. Government organizations are highly their hard to improve the low bid system.
Quality control includes
- Setting up specific standard for construction
- Checking the deviation from the standard
- Taking action to correct or minimize the variation
- Improvement of the standard.
ISO 9000 standards fix the standard for quality. ISO stands for International organization for standardization. This organization founded in Switzerland in 1947. Similar standards for Indian context are IS 14000 – 04.
ISO 9000 series of standard are quality assurance standard that assures client that the organization having obtained the certification works according to specified requirement.
It stands for system standardization and certification. Emphasis is given to defining and laying down the procedure, process etc in the form of documents.
ISO is important because it offers an internationally recognized systematic approach, coupled with institutionalization of the institutes, policies, procedures, record keeping, technologies and resources for managing quality work.
Basic principles advocated by ISO are -
- Focus on customer
- Provide leadership
- Involve your people
- Use a process approach
- Take a systematic approach
- Encourage continual improvement
- Get the facts before you decide
- Work with your supplier
ISO 9000 series standards are –
- ISO 9000
- ISO 9001
- ISO 9002
- ISO 9003
- ISO 9004
Elements of Quality
The basic element of quality in construction is
- Quality characteristics
- Quality of design
- Quality of conformance
A quality characteristic is related to the parameters with respect to which quality – control processes are judged. Quality characteristic includes strength, colors, texture, dimension, height etc. Example in compressive strength of concrete, usability of concrete in slump, etc.
Quality of design:- It refers to the quality with which the design is carried out. It primarily related to meeting the requirement of the standard, functionally efficient system and economical maintainable system.
Quality of conformance:- It is referred to the degree to which the constructed facility conformed the design and specification. Quality of conformance is affected by-
- field construction methodology
Economics of Quality of design
|Quality of design is generally evaluated based on economics of quality. There are two aspects of economics of quality design|
With the increase of quality of design, dost increase is exponential but value addition initially increases, but starts saturating at of some point. Hence the optimum cost is arrived when slope of both the curves is same.
The economics of quality conformance is shown in the figure. One can note that with the increase of quality of construction, cost of quality control gets saturated. Thus we can arrive at optimum quality for minimum cost from total cost of the construction. This has been shown in the figure.
IS Code provision for quality control of concrete
IS 456 provides the schemes for quality control and quality assurance of concrete, we have reproduced the clauses –
Clause 10.1 Quality Assurance Measures
Clause 10.1.1 In order that the properties of the completed structure be consistent with the requirements and the assumptions made during the planning and the design, adequate quality assurance measures shall be taken. The construction should result in satisfactory strength, serviceability and long term durability so as to lower the overall life-cycle cost. Quality assurance in construction activity relates to proper design, use of adequate materials and components to be supplied by the producers, proper workmanship in the execution of works by the contractor and ultimately proper care during the use of structure including timely maintenance and repair by the owner.
Clause 10.1.2 Quality assurance measures are both technical and organizational. Some common cases should be specified in a general Quality Assurance Plan which shall identify the key elements necessary to provide fitness of the structure and the means by which they are to be provided and measured with the overall purpose to provide confidence that the realized project will work satisfactorily in service fulfilling intended needs. The job of quality control and quality assurance would involve quality audit of both the inputs as well as the outputs. Inputs are in the form of materials for concrete; workmanship in all stages of batching, mixing, transportation, placing, compaction and curing; and the related plant, machinery and equipments ; resulting in the output in the form of concrete in place. To ensure proper performance, it is necessary that each step in concreting, which will be covered, by the next step is inspected as the work proceeds (see also 17).
15 SAMPLING AND STRENGTH OF DESIGNED CONCRETE MIX
Samples from fresh concrete shall be taken as per IS 1199 and cubes shall be made, cured and tested at 28 days in accordance with IS 516.
15.1.1 In order to get a relatively quicker idea of the quality of concrete, optional tests on beams for modulus of rupture at 72 + 2 h or at 7 days, or compressive strength tests at 7 days may be carried out in addition to 28 days compressive strength test.
For this purpose the values should be arrived at based on actual testing. In all cases, the 28 days compressive strength specified in Table 2 shall alone be the criterion for acceptance or rejection of the concrete.
15.2 Frequency of Sampling
15.2.1 Sampling Procedure
A random sampling procedure shall be adopted to ensure that each concrete batch shall have a reasonable chance of being tested that is, the sampling should be spread over the entire period of concreting and cover all mixing units.
The minimum frequency of sampling of concrete of each grade shall be in accordance with the following:
Quantity of Concrete in the Number of Samples
Quantity of Concrete in the work , m 3
|No of samples|
51 and above
|4 plus one additional sample for each additional 50 m 3 or part thereof|
|NOTE – At least one sample shall be taken from each shift where concrete is produced at continuous production unit, such as ready-mixed concrete plant, suppliers and purchasers may agree upon frequency of sampling mutually by suppliers and purchasers.|
15.3 Test Specimen
Three test specimens shall be made for each sample
IS 456 : 2000
for testing at 28 days. Additional samples may be required for various purposes such as to determine the strength of concrete at 7 days or at the time of striking the formwork, or to determine the duration of curing, or to check the testing error. Additional samples may also be required for testing samples cured by accelerated methods as described in IS 9103. The specimen shall be tested as described in IS 516.
15.4 Test Results of Sample
The test results of the sample shall be the average of the strength of three specimens. The individual variation should not be more than +15 percent of the average. If more, the test results of the sample are invalid.
Total Quality Management ( TQM )
Total quality management (TQM) is a system of continuously improving goods or services. The philosophy was promoted by W. Edwards Deming. A TQM approach is considered as essential to long term survival of the business, such as construction. In the TQM philosophy, everyone in the company should feel involved and committed for quality of products, from top to bottom of the organization. Total quality management provides principles, tools and techniques for cultural changes and continuous improvement. Quality assurance can be considered as part of Total Quality Management. Basically quality assurance is a system of approach which is related to attitudes and working environment of the company. Deming has suggested 14 points for total quality management which are –
- create constant commitment to the employee for aim and purpose of the company and improvement .
- Adopt new philosophy to avoid defects.
- Use statistical quality control and understand purpose of inspection.
- Practice of business should be based on statistical evidence rather than price tag alone.
- Improve constantly and forever production and services.
- Employee training.
- Teach and institute leadership.
- Encourage communication and productivity.
- Encourage teamwork, to work in group.
- Eliminate posters or slogans with specific improvement methods.
- Use statistical methods to continuously improve quality and productivity.
- Remove barriers that rob people of pride of workmanship.
- Provide education and self improvement for everybody.
- Define top management commitment for quality.
The basic foundation for total quality management is –
- Everyone in the company should understand the mission and vision of the business.
- Total management should be highly committed to quality.
- Continuous training is required.