Quality control of construction materials and product is an essential requirement for obtaining improved and uniform standard of road construction.
Quality Control is an essential part of any production process and highway constructions are no exception. The need for quality control on these specifications has increased considerably in recent times due to a significant increase in traffic intensities.
Improved level of service of roads & highways will result in considerable savings in vehicle operating cost and in favorable road user reaction and public opinion.
The extra cost of exercising quality control being only a fraction of the resulting benefits.
The cost of exercising quality control would be 1-2 percent of the total construction cost.
The direct and indirect economic return from quality control could be of the order of 5 to 10 percent of the total construction cost.
Pre requisite for Road Construction Quality Control
Mainly road construction specifications and estimates provide basis for effective quality control. In addition organizations setup quality management systems, adequately trained staff and good monitoring agency for exercising quality control.
Establish periodic appraisal of the quality control data not only for implementation during construction but also for effecting possible improvements in quality control and the construction techniques.
Another approach is updating of knowledge by improving the culture of on job training.
Types of Quality Control
Process Quality Control – the designer makes the decisions regarding the type of equipment, the procedure of construction and the amount of work required to obtain the desired result.
End quality control-In the end result type of quality control, the construction agency, which may be a private contractor, has a free hand in the selection of road construction methods and equipment to achieve the desired end product.
In the ‘End result’ type of specification, the field engineering personnel carry out tests on finished work at regular intervals to evaluate whether it meets the specification requirements or not whereas in the ‘Process type control’, the responsibility of field personnel is to make sure that the work is carried out as per laid down specifications.
Quality Control of Construction Materials
Quality controls tests on materials at project site are essential to ensure that the materials being incorporated in the construction are of specified quality.
All the materials brought to the site shall be stacked and stored as specified so as to prevent deterioration or intrusion by foreign matter and to ensure the preservation of their quality and fitness for work.
Materials which have been improperly stored or have been stored for long periods shall be re-tested where their suitability in the work is doubtful.
Testing Procedures
The procedure for testing of different materials and work shall be in accordance with the relevant standards and specifications. Where specific procedure of testing is not indicated the tests shall be carried out as per the prevalent practice to the direction of the Engineer-in-Charge.
Frequency & Extent of Site Testing
The frequency and extent of testing is the minimum considered necessary for normal conditions.
Carryout additional testing for abnormal conditions where variations may be excessive or where circumstances so warrant otherwise.
Site Acceptance Criteria
Acceptance criteria for different items of work may be based on minimum values or the statistical analysis as is considered judicious. For effective road construction quality control of materials and work, it will usually be necessary to lay down the acceptance criteria in the contract documents.
Quality Control Training
In order to bring awareness in the officers of department and to update their knowledge of methods of testing, regular workshops on quality control should be held.
To make the participants aware of basic necessities like specifications, required test acceptance criteria, frequency of testing and methodology of tests for understanding the quality control system and operation of regional/field laboratories.
The training could be imparted by known road research institutes or through on job training.
Project Site Testing Facilities
Testing facilities normally comprise laboratories at Central, Regional and Field levels.
The Regional laboratories are at circle level and headed by Executive Engineers (Quality Control)
In addition, they shall provide all facilities for training of all the Quality Control Staff in the Region.
Recording of Test Results
The tests shall be carried out in accordance with the standard procedures. It is desirable that of the total tests, 70 percent are carried on by the Junior Engineer, 20 percent by the Executive Engineer and the remaining 10 percent by the Executive Engineer.
The test result record registers shall be maintained regularly linked with the assured quality of work.
Critical Parameters for Road Construction Quality Control
The following points for construction in-process quality control shall be properly attended to:
- Gradation of combined aggregates and binder content shall satisfy the design criteria of the relevant IRC specifications.
- The design mix proportions arrived at in the laboratory shall be based on representative samples of materials actually available at the site.
- Prime coat where necessary shall be applied over the prepared base at the specified rate before laying the bituminous surfacing.
- Mixing plant shall be of adequate capacity to field a mixture of proper and uniform quality.
- Quantities of various sizes of aggregates shall be fed to the dryer in such proportions that the resulting combination complies with the job – mix formula.
- The temperature of binder at the time of mixing shall be in the range of 1500C-1770C and of aggregates in the range of 1550C-1630C. Care should be taken so that the difference of temperature between the aggregates and the binder does not exceed 140C.
- Mixing time should be shortest possible to obtain uniform distribution of the binder and a homogeneous mix.
- Binder content with mix shall be checked periodically to ensure that the same conforms to the specifications.
- A variation in binder content of + 0.3 percent by weight of total mix shall, however, be permissible.
- The mix shall be carried to the site by tipper trucks and spread and compacted to obtain a carpet of required thickness. Spreading shall be done by self-propelled mechanical pavers provided with screeds for spreading tamping and finishing the mix true to grade line and cross-section. The temperature of the mix at the time of laying shall be in the range 1210C-1630C.
- Soon after laying of the mix, rolling shall be started with 8-10 tons vibratory rollers at a speed not more than 5 Km per hour. The final rolling shall continue till the mix is fully compacted and no roller marks are left on the surface. The density shall not be less than 95 percent of the laboratory density. During rolling the roller wheels shall be kept moist to prevent the mix from adhering to the roller wheels and being picked up.
- Traffic shall be allowed on the surface only when the carpet after final rolling has cooled down to the ambient temperature.
- The finished surface shall be checked in-process quality control for line, grade and regularity.
Concrete Pavement Quality Control
Construction of concrete pavements shall in general follow the guidelines given in IRC:15-2002.
“Standard Specifications and Code of practice for construction of concrete Roads”
For tools, equipments and appliances reference should be made to IRC:43-1972 “Recommended Practice for Tools, equipments and Appliances for Concrete Pavement Construction.
Mix proportions for concrete shall be pre-determined on strength basis as per guidelines IRC:44-1972 and IRC:59-1976 .
Quality Control Tests on Materials
| Cement | Physical & Chemical Tests | IS:269-1967 |
| Coarse and Fine
Aggregates |
Gradation | IS:2386 (Part – I, 1963) |
| Deleterious
Constituents |
IS:2386 (Part – II, 1963) | |
| Moisture Content | IS:2386 (Part – III, 1963) | |
| Bulking of fine Aggregate | IS:2386 (Part – II, 1963) | |
| Coarse Aggregate | Los Angeles Abrasion Value/ Aggregate Impact Value Test | IS:2386 (Part – IV: 1963) |
| Soundness | IS:2386 (Part – V, 1963) | |
| Alkali Aggregate Reactivity | IS:2386 (Part – V, 1963) | |
| Water | Chemical Tests | IS:425-1964 |
| Control Of Concrete Strength | |
| Test | Test Method |
| Workability of fresh concrete | IS:1199-1950 (One test per 10m3) |
| Concrete Strength | IS:516-1959 (3 cube/beam samples as specified for each age of 7 days and 28 days for every 30m3 of concrete) |
| Core strength on hardened concrete | IS: 516-1959 (2 cores for every 30m3 of concrete) |
Critical Factors in Quality of Concrete Design
Mostly the design is not the contractors responsibility. However, where the contractor is also to supply the design, the Quality Assurance Management (QAM)should include the agreed procedures for the items listed below to achieve QC/QA in design.
- Organization and Functional Responsibilities (including Personal Qualifications).
- Responsibilities for ensuring quality by persons in-charge of design and assuring that the stipulated quality of design indeed has been achieved (assurance function of QA team).
- Quality of Design basis Report for Development of Design:
– Requirements of Project/Client
– Preliminary drawings and data source, responsibility of supply and methods of verification.
– Design approach, applicable codes, special design specifications.
– Methods of analysis, calculation, checking and internal approvals.
– Contents of design reports detailed calculations)
– Final drawings
– Checking and approval by external approving authority if any
Preparation and approval of Quality design and approval of design
This includes:
– QA on software (Prior testing and Verification)
– Design preparation
– Design Verification (independent review, alternative analysis and quality control testing)
– Control of manufacturers/vendors design.
– Approval to design, distribution of design documents and document control.
– Design change requests
– Checking and approval by external approving authority, if any.
– Audit and Corrective Actions
– Design documentation records
– Proforma of Quality Design Records- Exhaustive & detailed proforma will have to be evolved and prescribed for the above purpose for each of the major highway to suit the special requirements, which form a part of the quality assurance manual for the project.