Compression test is done for knowing the compressive strength of hardened concrete. For this purpose, concrete cube test or concrete cylinder test is done in laboratory. But, concrete cylinder or cube for testing is made on site.
Apparatus for making concrete cylinder:
- Cylinder mould (100mm X 200mm or 150mm X 300mm or 300mm X 600mm)
- Bulled-nosed rod (16mm dia & 600mm long)
- Steel float
Procedures of making concrete cylinder:
Step-1: Clean the Cylinder mould properly and apply a coat of form oil on the inner surface of mould. But no excess oil should be visible on inner surface.
Step-2: Fix the nuts & bolts tightly with base plate and no gaps should be within the parts of cylinder mould.
Step-3: It is necessary that the cylinder mould should be placed on a clean, level & firm surface.
Step-4: Concrete for specimen should be collected from three or four random mixes.
Step-5: Place concrete into the mould in each layer of maximum 50 mm thick & compact each layer at least 30 blows of 16 mm rod.
Step-6: Level off the top with the steel float & clean any concrete from around the mould and leave the mould undisturbed for 24 hours.
Step-7: Give number & casting date of the specimens on the top surface after 90 minutes.
Step-8: After 8–10 hours the mould should be covered with damp hessain cloth (jute cloth) but no water should fall on the surface of the specimen. Surface can be covered with polythene.
Step-9: After 24±½ hours the specimen should be uncovered & removed from the mould. The concrete is still weak at this stage. So, should be handled carefully.
Step-10: To remove specimen from mould - loosen all bolts & nuts, side off the base plate & then top the mould gently to free the specimen.
Step-11: Just after removal from mould the specimen should be put straight into a tank of clean water. The specimen should be fully submerged under water.
Step-12: After 28 days, send the specimen to the testing laboratory to determine the compressive strength of concrete.
Minimum three specimens are made at a time on site. The average test result is taken to determine the compressive strength of concrete.
Which size of “Cylinder mould” do you use for making concrete specimen? Please share in comments.