Bridge collapse due to poor quality of cement used
Bridges are designed for vehicles to pass through, they are supposed to support high traffic flow and maintain their quality and purpose. However, the poor quality of bridge construction causes the defects, deterioration, and distress of these bridges. The failure and collapse of these bridges might endanger the user and even involve in human lives lost as well.
Newly constructed RCC structures sometime fall in a fraction of its design life span. Therefore, the causes of premature deterioration in relatively new bridges are different as compared to those for old bridges. Generally, the main reason is poor or improper construction and/or poor or incorrect design [1]. Poor construction includes the following A. Poor workmanship B. Inadequate cement quantity C. Excessive water cement ratio D. Inadequate concrete cover E. Honeycombed or Un-vibrated concrete F. Cold joints or bad construction joints G. Initially rust steel bars H. Congested reinforcement bars I. Porous cover blocks amongst others.
Another key reason for such collapses is the usage of poor quality of cement or cement which may be expired beyond usage date or its improper storage. The binding property and strength of cement depend upon its capacity for chemical reaction, which can take place in the presence of water. Cement if not stored properly can absorb moisture from the atmospheric air or any other source and react with it chemically. The strength of such type of cement when used would be adversely affected to the extent such reaction would have taken place.
For prevention of cement against deterioration and retaining its freshness its storage should be such that no dampness or moisture is allowed to reach cement either from the ground, walls or from the environment. This becomes particularly important during the humid season and in coastal regions when atmospheric air contains higher amount of moisture in it.
Impact on strength of cement due to storage
The cement when stored for longer period of time loses its strength characteristics. The strength of cement when used after one year of its production loses its strength by about 40–50% on application as compared to that of freshly produced cement. The loss of strength characteristic of cement at different interval of times is as given below in the table.
Age of Cement% Reduction in its Strength
3Months — — — — — — 20–30
6Months — — — — — — 30–40
12 Months — — — — — — 40–50
In order, to ensure quality of cement, the Bureau of Indian Standards has notified quality and marking parameters as highlighted below. In case procedures are not followed, the marking and sale of such cement is prohibited.
STANDARD MARK The Standard Mark, as given in Column (1) of the First Schedule of the licence, shall be printed or stenciled on each bag or drum of Ordinary Portland Cement or on the label applied to it, provided the material in each bag or package to which the mark thus applied conforms to the specification. The size of the Standard Mark shall be either 60
X 90 mm or 120 X 180 mm.
5.1 MARKING — In addition the following information should be given on each cement bag or package or on the label applied to it. Same information shall be provided in the delivery advices accompanying the shipment of packed or bulk cement and on cement drums. The ISI Mark and the following details shall be applied on each bag or package in BLACK COLOUR.
Key Marking requirements:
Name of the manufacturer and its registered trade mark, if any;
Name and Designation of cement;
Net quantity, in Kg.;
Batch/control unit number in terms of week, month and year of packing;
Best before date (that is, 3 months/12 weeks from date of packing);
Licence Number (CM/L — — — — — — );
Address of the manufacturer;
Type and percentage of performance improver(s) added, in case of addition of performance improver and
Any other marking required under current Legal Metrology Act and Rules framed there under.
PACKING
The packing of Ordinary Portland Cement shall be in conformance to clause -10 of IS 269: 2015. A test certificate either from the manufacturer or from any BIS recognized testing laboratory shall be received along with each consignment. Alternatively the sample of bag from each consignment shall be tested by the cement manufacturer either in his own laboratory or any other BIS recognized laboratory before they are used for packing cement. No testing would be required if bags carry BIS Certification Mark. The cement shall be in good condition at the time of packing.
10.1 Colour of bags: Any colour except red can be used. However, the colour of bags shall be in contrast to the colour of marking so that marking on the bags is clear and legible.
STORAGE: Storage shall conform to clause -8 of IS 269: 2015
STOP MARKING The marking of the product shall be stopped under intimation to the Bureau if, at any time, there is any difficulty in maintaining the conformity of their product to the specification, or the testing equipment goes out of order. The marking may be resumed as soon as the defects are removed under intimation to Bureau.