Ensuring quality in construction
Ensuring quality in construction
There is a construction boom going on in the country at the moment. Residential houses are being built, office and factory buildings are being built, shopping malls are being built and bridges are also being built, both in public and private sector. With such spur of activities, there comes the question of quality of the materials that are being used for construction. Along with this also come the questions of architectural design, construction time supervision by experts and finally maintenance. What is the standard of cement, steel rods, sand, bricks, bricks chips, stone chips etc. that are going into these structures? In our quest for finding answers we talked to some experts on the subject.
While talking to Dr. A.F.M. Saiful Amin, Professor of Civil Engineering Department, BUET (Bangladesh University of Engineering and Technology), we put forward the following questions. In reply to our question whether the standard of construction materials produced by various companies is maintained properly and whether these materials contribute to resisting earthquake or minimizing losses due to earthquake or any other disaster, Dr. Amin said that any engineered construction must use materials meeting a specified quality or strength. When an earthquake hits, it is important that a building or a bridge shows its performance as was anticipated in the design. Here, there is a definite role of material quality. However, earthquake is not the only leading factor considered in an engineered design process. First a designer considers the general stability of the structural system. Let us take the example of the disaster that happened due to Rana Plaza collapse. It was not the result of any earthquake. A building, at first and foremost, must be capable of carrying the gravity load and then also the load of other things that we put on it i.e. the loads coming from its usage type. Next, the designer emphasizes on its resistance against natural calamities like earthquake and severe storm that a building or bridge 'may' experience during its life cycle. Use of materials of better quality may offer additional safety margins against earthquake or other unforeseen natural calamities. Magnitudes of loads coming on the structure from such calamities are often quite unpredictable. Many of the existing old buildings in Bangladesh are not fit to face a big earthquake, if it really hits. It will cost a lot on life and property. Now we cannot even handle a small disaster. We do not have enough equipment or rescue plan. Existing noncompliant buildings must be strengthened. We need a strong enforcement effort from the government in this regard. Many of our construction industries still do not have enough know-how on the materials and techniques used worldwide for strengthening structures. These are imported from abroad. We also need to customize those materials and technologies for use in our local context.
He further added, 'like as a human being, buildings also have a life cycle. If not properly used or maintained, today's buildings cannot bear their loads of tomorrow. So the point of maintenance, repair and strengthening comes into picture. We have to build our constructions with products that are economic. In this regard, we have to consider two things: is it economic for now? Or is it economic for a longer life time with minimum maintenance cost to yield the lowest life cycle cost?
On the question of using steel or concrete, Dr. Amin mentioned that the Hardinge Bridge, made about 100 years ago, was built by British engineers with steel. We are going to celebrate 100 years of Hardinge Bridge next year. British India could afford to build it with steel for the intended economic needs of that time. There was no other alternate material available either during that time to go for longer spans to bear heavy rail loads. The popularity of using prestressed concrete for bridge construction in Europe increased significantly around the 1950s and 60s. However, a history of problems has encountered that cast doubt over the long-term durability of such structures. Due to poor workmanship or quality control during construction of prestressed concrete, sometimes the ducts containing the prestressing tendons are not fully filled, leaving voids in the grout where the steel is not protected from corrosion and reduces durability. Bangabandhu Bridge, a prestressed concrete box girder bridge was opened to traffic in 1998. We are now going to build Padma Bridge with steel sections. So which material will be used in construction depends on our affordability. The life cycle cost of materials depends on that choice. Life cycle cost of concrete is often costlier than that of steel. We could not afford to build any remarkable long bridge with steel in the last 50 years in the country.
We wanted to know from him whether cement and steel manufactured in Bangladesh are of high standard. Dr. Amin said that most of the companies maintain international standard. BSTI is the regulatory body in Bangladesh to specify and enforce the quality. But proper use of a material through a good construction practice is important. Good cement does not mean good concrete. For it you will need good stone; good sand and good workmanship. Most of our cement companies import clinker from abroad. Steel billets/steel ore is also imported. In Bangabandhu Bridge construction, stone was imported. For Padma Bridge, we also face similar challenge. Perhaps, we can only have sand from our river beds.
There is a problem of salinity in some areas. What should be done to tackle this problem? In reply Dr. Amin said, “Salinity promotes in an acidic environment. Salinity and reinforcement steel has an inter relation. Acidic environment promotes corrosion. So we need additional protection in this regard. Concrete gives steel an alkaline environment which is opposite to acidic environment. Moisture cannot reach steel in a less permeable concrete. In case of saline environment, clear cover (gap of concrete and steel) should be enhanced. This will require larger concrete sections. Concrete should be dense as well.
On the question of quality of bricks, he said that bricks are used in two ways, making walls and also making concretes by crushing bricks to produce aggregates. We have not enough stones in Bangladesh. Standard of bricks depends on soil or clay that we use to produce the brick. This reduces our quality of our agricultural land from where we harvest clay. Cement based bricks from recycled concrete or sand is an option to explore. 'We build so many walls but not enough bridges'-Sir Isaac Newton. It is one of the favorite quotations.
Dr. Amin offered the following suggestions. 'All should be conscious of proper engineered supervision during construction of a building or bridge. If people take advices from any professional engineer, they can minimize cost in many ways. They can have a safe accommodation as well. A building or bridge when in use shall also be maintained properly. Repair works shall have to be carried out in a time efficient manner. Only professional engineers know the proper use of construction materials to get maximum benefits out of it. Columns and foundations should be constructed with care because these elements carry the total load. These are the most critical structural elements. We had a finding during investigation of 'Spectrum Sweater Factory collapse'. It had flat plate structure/beamless slabs. Risk of disaster was high in such structural system. But the failure triggered due to weakness in construction supervision. Inadequate design and use of materials of not so good quality increased the risk, leading to a catastrophe. All should consult with the experts before construction of a building. We have ignorance in many works. We take much care in casting a roof and cure it with water but we have carelessness with the construction of columns. Supervision from experts is important. Media can spread our message to all. I have not learnt formally how I should cross a road before studying Traffic Engineering at BUET. But the syllabus of primary and secondary education should include the basic steps for constructing a safe building where we will work for the whole day or sleep in the house at night. Everyone does not need to be an engineer but we have to have basic knowledge of following good construction steps. The definition of literacy should be redefined.'