Ensuring quality of structures
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How engineers and workers can adhere to norms and procedures for upholding quality.
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Watchword: Quality should be focussed upon at every stage.
“Everyone lives by selling something,” said Robert Louis Stevenson. When there are too many sellers, competition becomes stiff, becoming a struggle for existence marked by the survival of the fittest.
An organisation must survive and grow. Essential for this customer confidence in the quality of its product or service. This applies to the construction industry also.
Quality in construction has a dimension different from that of the manufacturing industry. If a manufactured product, such as washing machine or refrigerator, turns out to be defective, the supplier or manufacturer can still win customer confidence by repairing or replacing it.
But the construction industry’s products, such as buildings, dams and bridges, are irreplaceable. Even if repairs can be done, the defect will mar the reputation of the contractor and the work will prove costly. Hence, quality should be ensured at every stage, from design to completion.
The role of design engineers in ensuring quality has not been understood in all its aspects. The structural engineer’s responsibility in ensuring strength of the structure is easily understood and acknowledged.
The design engineers need to pay adequate attention to detailing to make quality of construction possible. For example, presence of many reinforcement steel rods in column-beam junctions makes pouring of concrete and vibration difficult, resulting in hollow spaces in concrete and honeycombing. Architects, at times, come out with designs which make ensuring quality of construction difficult.
Elevation with complicated shapes and design does not always add beauty to the structure and can cause defects.
The next step in ensuring quality is selection of materials. This is done after conducting the prescribed tests in the laboratory and on the field.
Materials such as cement and steel, manufactured under controlled conditions, do not show significant variations in quality. The quality control laboratories of reputable manufacturers issue dependable test certificates. But there is the possibility of adulteration of materials such as cement during transit from manufacturing plant to the worksite. Transportation, handling and storage during transit with inadequate precautions can also affect quality.
Re-rolling mills, and not reputable manufacturers, supply a significant portion of the steel used.
The quality of steel from such sources has to be checked. So, even if manufacturers’ certificates are furnished, random samples of steel and cement should be tested in the laboratory and on the site.
Materials such as sand, metal, bricks and concrete blocks are not manufactured under strict control as in the case of steel or cement. In most cases, they are not tested at the manufacturers’ worksite. Hence, these materials have to be tested at site before use. Materials not meeting quality standards should be immediately discarded to prevent their use.
Ready-mixed concrete has appeared on the construction scene recently. It is manufactured under better-controlled conditions than concrete mixed on the site. But the selection of materials may not be controlled that strictly. Also, when the plants are located a long way from the site, the concrete may reach the latter late.
When the concrete remains in the rotating transit drums for long, its temperature rises, affecting the quality. Besides this, the concrete loses its workability by the time it is discharged into the pump, choking the pipes. To avoid this, the operators add extra water to easily pump the concrete. This reduces its strength. Hence, ready-mixed concrete should be tested at site, the sample taken from the end of the discharge pipe.
Laboratories
All materials must be tested as prescribed by the relevant Indian Standards. So, a fully equipped field laboratory, manned by qualified technicians, should be set up on the sites of major projects. The records of tests must be kept for reference.
Another aspect affecting quality of materials is storage. In most sites, cement is stored properly but not steel rods. Steel is mostly dumped on the ground. If the soil is wet, steel corrodes.
S.R.C. NAYAR
General Manager, Kunnel Engineers.
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