Types of Quality Control
One of the most important tasks of the supervision during the execution of a road contract is technical quality control, i.e. control as to whether the materials and work supplied by the Contractor meet the technical requirements in the contract specifications. There are two types of quality control, which are described below:
1.Control of Methods
Method control is usually carried out by the Consultant`s field staff whose job it is to be on the site and supervise the Contractor during the execution of the works. At the same time the field staff will perform simple measurements, such as the recording of the thickness of fill layers, the temperature of asphalt material, and the slump of cement concrete.
Method control is carried out according to the type of work. Where the work method is of considerable importance and requires constant supervision to achieve the quality, or where in some case, the quality is difficult to improve on, there should always be a field engineer on the site. Examples are the ramming of piles, the laying of asphalt, and concreting etc. Where work methods are of less importance or quality is constantly being achieved by the contractor, there may be no need for continuous surveillance.
Examples are excavation and compaction of soil.
2.Control of End-Results
End-result control includes field tests e.g. control of the evenness of completed pavement layers and laboratory tests, e.g. Marshall tests on asphalt materials. Other tests are a combination of field and laboratory tests. An example of this is the compaction control of earthworks where the achieved density is determined by means of a field test, and where the IS/ AASHTO density with which the result should be compared is found by means of a laboratory test. End results control is carried out by laboratory technicians, and most of the work consists of laboratory tests.
The frequency of end-result control depends on the quality parameters that are to be checked. Parameters which can vary considerably are continuously controlled. Examples are the composition of asphalt materials and the compaction of asphalt courses. As regards regulating laboratory tests the specification usually determines the number of tests. When the works are started and in cases where difficulties as regards compliance with quality requirements are encountered, laboratory testing will normally be intensified.