Mild Steel Bars in Cement Concrete

Cement concrete is strong in compressive strength but weak in tensile strength. To increase tensile strength we use mild steel bars in cement concrete. Steel bars used in cement concrete provide good strength to the structure. A strong building structure is what all need for their homes, offices and steel is the best option used with cement concrete.

1) Overlapping in Steel Bars in Reinforced Cement Concrete

There should be no joints in steel bars used for RCC work. If it is necessary to use small length steel bars, proper overlap should be given. The joints of bars should be welded in case the diameter of bars is more than 36 mm. Overlapping of bars should not touch each other and they should be kept apart. Where it is not possible, overlapping bars should be bound together at intervals not exceeding twice the diameter of such bars with two strands of steel wires trusted tight. The overlap should be staggered for different bars. The length of overlap should not be less than 50 times the diameter of steel bar.

• Steel bars are clear, free from loose mil scales, dust, loose rust and any oily materials.
• The bars used at site are manufactured from reputed brand and have a full length.
• Use full length steel bars in beams, slabs etc if not possible, proper overlap should be given in steel bar and overlap should be staggered.
• Tor, ribbed and twisted steel bars are used as they have more tensile stress. Also they are economical and have more strength in cement concrete.
• The bars must be in full length according to the design.
• Proper sizes/ height of crank bars are given in slab and beams etc.
• Proper support under crank bars of beams and slabs must be given.
• Steel bars are not disturbed while lying cement concrete.
• If steel bars are more in number in beams, the bars are placed in two layers by giving spacer between the layers.

3) Checklist/Points before Laying Cement Concrete

• Form work /shuttering should be checked for line, level and its strength.
• Steel bars and their placing should be checked.
• Proper cover to steel bars and adequate numbers of sports/chairs under crank bars must be checked.
• Proper planks or plates provided for walking over reinforcement are not disturbed during working.
• Raw materials should be proper and sufficient in quantity.
• Electrical pipes, fan box etc. should be laid before lying cement concrete.
• Gap in shuttering plates is sealed properly by jute bags /mortar /rubber etc.
• Shuttering plates are properly oiled.
• Curing arrangement must be checked in advance for smooth curing after laying RCC slab.
• Precautionary arrangements are taken in case of rains etc.

Mass Concrete
Mass concrete means cement concrete used for constructions of dams, massive structures, raft slabs and heavy structure beam foundation. There should be rigid/strict control on concrete work with view to ensure durability, strength, and uniformity. In big projects detailed specification is issued separately for individual project according to site requirement and other situation at site of work. Mass concrete is used in important project having heavy load and different types of stresses. Any small deviation in specifications or any irregularity omitted or committed may cause failure of the structure.

Precautions for mass concrete

• Cement used in the project is Portland cement of 43 grade IS No. 8112 or 53 grade IS No. 12269 and it is from fresh supply not from the old stock.
• Storage of cement is in weather proof store.
• The cement should be used within 30 days from the supply taken from factory.
• For increasing strength of the concrete at early stage use accelerators.
• Air entry agent is used to improve the quality and workability of the concrete.
• The water used confirms specification as per IS 3025.
• Coarse aggregate consisting of natural occurring stones gravel without being broken is from 6 inch to ¾ inch grading size.
• The test for soundness, strength, resistance to abrasion, volume change, particle shape specific, gravity, gradation and contaminating substances are investigated in lab before use.
• Fine aggregate confirms test requirement such as soundness, organic impurities etc and having fineness modulus 3.5 to 4.2.
• Weight batching equipment is used for mixing concrete mix.
• All mix is mechanical mix using concrete mixer, truck mixer, agitators, charging operations, maxing operation, discharging operation machinery etc.
• At the end of each mix/run and before placing new mix again all hardened concrete is removed.
• Consolidate cement concrete by vibrators and slump for mass concrete should be low having value 25-75 mm.
• Construction joints are given in concrete work after each stoppage of work. The joints are given where required according to the need of structure.
• Concrete works are suspended during excessive hot, cold or rainy weather.
• Finishing of concrete surface is done as desired for mass concrete.
• Curing of all concrete is done at least for 28 days.