In Ghana, road works whether new development or maintenance, are generally executed by contracting.
Hence, quality control of road works in Ghana is very crucial.
A contract is a legal agreement between two parties where one party agrees to carry out certain works in return for a reward (or in legal terms a consideration usually of money) to be given by the other party in the contract.
The party which agrees to do the work is called the Contractor whilst the other that pays for the work or the owner is referred to as the Employer or Client.
Prior to any construction of works, the Employer or Client employs an engineer to design the solution scheme and to prepare contract documents comprising drawings, specifications, bills of quantities and others.
These documents are then sent to contractors to tender for the work. The Contractor who wins the contract for the road works and the Employer then sign and go into a contract for the execution of work.
During work execution, the works must be monitored and controlled to ensure that a high quality product is achieved and within budgetary allocations and that the finished product is indeed what was specified.
Monitoring or quality control is the joint responsibility of the Contractor and the Client and it must be a continuous effort throughout the construction process.
Three important questions to pose and answer in order to ensure the quality of the construction works are:
- What are the items and areas to control?
- What guides the control process?
- What is to be done in the case of substandard works?
These and many more are questions that border on real situations that characterize contracts in road works.
A contract and the accompanying conditions must endeavour to address all these problems to the extent humanely possible so that the road works do not suffer any major setbacks in quality and budget.
Quality control in road works can’t be emphasized more.
Quality control and assurance procedures
These procedures are to guide resident site staff who are directly involved in the supervision of the works in carrying out their work so that the desired level of quality can be achieved.
Quality control and assurance are achieved in three separate but related areas:
- Materials control
- Work control
- Quantity control
For each of the above control areas, the activities and procedures required may comprise one or more of the following:
- Checking that appropriate instruction is given and any information required by the Contractor is supplied in a good time.
- Checking that materials and workmanship are satisfactory and as specified, and where necessary, issuing instructions for remedying faulty works or replacing substandard materials.
- Checking lines, levels, layout, etc. of the works to ensure conformity with the drawings.
- Issuing further instructions, drawing, and clarifications of details as are necessary to ensure satisfactory construction of the works.
- Measuring the volume of work done
- Undertaking all tests required and keeping records thereof
- Reporting on all the foregoing to the Engineer/Consultant in the form he requires.
Reference for quality control
The conditions of contract define the terms under which the work is to be undertaken, the relationship between the Employer, the Engineer and the Contractor, the powers of the Engineer and the terms of payment.
Plans are approved drawings and reproductions pertaining to the work covered by the contract such as the plan of a road, vertical and horizontal alignment, sections of cut and fill, and cross-section of road.
The specifications are the written instructions that accompany and supplement the plans and form a guide for the standards required in the execution of the work.
These standard specifications, which are the results of the experience and knowledge acquired over a period of years include:
- All the general requirements and
- The quality of workmanship and material required.
The materials to be used must be controlled in quality to ensure that substandard materials are not used to compromise the quality of the work being executed.
All index properties and strength characteristics as required of the material by the specification must be met. This requires that representative samples are taken occasionally from a batch and tested for quality.
In addition, any time a new supply is made, the necessary quality tests must be undertaken on representative samples.
For example, soils for use in building the pavement structure must be checked to see if they meet the requirements in terms of
- Atterberg Limits
- Strength characteristics (measured by California Bearing Ratio- CBR)
Aggregates for Portland cement concrete works (such as bridge and drains and culvert construction, retaining walls), asphalt concrete formulation, surface dressings, etc, must be checked to see that they conform to the specification requirements for such works.
The properties to check will include;
- Abrasion resistance
- Affinity for bitumen
In the case of bitumen, it must be ascertained that the material is of the right grade or consistency (hardness if solid or viscosity if liquefied).
In asphalt overlay construction, material control will involve
- Gradation of the aggregates for the mix
- Asphalt content of the mix
- Stability of the mix
- Density and voids of the compacted overlay
For any of the above and other road building materials, samples that fail to meet specification requirements must not be allowed for use. Where substandard materials have been used, the contractor must be ordered to remove them and replace with approved material meeting the quality requirements contained in the specifications
The right sequence of the construction process must be followed and the manner of construction must be such as would achieve the desired quality of the end product.
In building the pavement layers, items to control include
- Materials for each layer
- Thickness of layers
- Compaction and densities
In controlling compaction especially soils placed behind bridge abutments or used for embankments where the total thickness of soil to place is large, the total thickness must be placed in smaller lifts (layers of materials) and compacted.
Large lifts will not achieve adequate compaction and will lead to further compaction by traffic and differential settlement after the road has been opened to traffic.
In surface dressings, work control must be exercised in respect of
- Primer application
- Blinding of the primed surface
- Tack coat application
- Chippings application
- Rolling of spread chippings
In asphalt overlay construction, items to control include
- Gradation of plant mix
- Asphalt content
- Production temperature of mix
- Temperature of laid mat prior to compaction
- Compaction characteristics
Quality control also requires that quantity is controlled in accordance with design and drawings. Quantity items to control include
- Depth or thickness
- No. of culverts, etc.
To be sure that quality has not been compromised but has been assured, it is necessary to conduct tests to satisfy one’s self that indeed what was specified is what has been produced.
This is done by conducting on-site observations of the work in progress and of the finished road. Areas of the construction that appear to be defective must be tested to see whether indeed there is a construction defect or not. In addition, random testing may be carried out for the same purpose. Such tests may include density tests, depth of pavement tests, asphalt content test, gradation tests, etc.
Good record keeping and documentation are essential to the Resident Engineer’s ability to monitor and control the project and to deal with substandard work. Records should be kept of
- mistakes made by the Contractor,
- defective construction and their location
- quality test results
- field inspections
- field tests and results
- items supplied for construction
- sections of the roads for which certain items were used
- instructions given to the Contractor and verbal agreements reached with the Contractor.
Where possible photographic documentation may be employed to supplement the record keeping.
Each photograph is dated and location, subject and photographer noted. These photographs are kept in a central album to be used in case of any litigation.