How to check the Concrete Quality at Construction Project Site


Sep 7, 2017
How to check the Concrete Quality at Construction Project Site

Workablity of Fresh Concrete
  • Ensure the standard Slump Cone and associated equipment are clean before test and free from hardened concrete.
  • Wet the Slump Cone and drain away the superfluous water.
  • Request the mixer or concrete truck to well mix the concrete for additional 5 minutes.
  • Place the Slump Cone on one side ( i.e. not in middle ) of the base plate on leveled ground and stand with feet on the foot-pieces of cone .
  • Using a scoop and fill the cone with sampled concrete in 3 equal layers, each of about 100mm thick.
  • Compact each layer of concrete in turn exactly 25 times with a Slump Rod, allowing the rod just passes into the underlying layer.
  • While tamping the top layer, top up the cone with a slight surcharge of concrete after the tamping operation.
  • Level the top by a “sawing and rolling” motion of the Slump Rod across the cone.
  • With feet are still firmly on the foot-pieces, wipe the cone and base plate clean and remove any leaked concrete from bottom edge of the Slump Cone.
  • Leave the foot-pieces and lift the cone carefully in a vertical up motion in a few seconds time.
  • Invert the cone on other side and next to the mound of concrete.
  • Lay the Slump Rod across the inverted cone such that it passes above the slumped concrete at its highest point.
  • Measure the distance between the underside of rod and the highest point of concrete to the nearest 5mm.
  • This reading is the amount that the sampled concrete has slumped.
  • If the concrete does not show an acceptable slump, repeat the test with another sample.
  • If the repeated test still does not show an acceptable slump, record this fact in the report, or reject that load of concrete.

Compression test
The Compression Test is a laboratory test to determine the characteristic strength of the concrete but the making of test cubes is sometimes carried out by the supervisor on site. This cube test result is very important to the acceptance of insitu concrete work since it demonstrates the strength of the design mix.

The procedure of making the test cubes is as follows: –
  1. 150 mm standard cube mold is to be used for concrete mix and 100 mm standard cube mold is to be used for grout mix.
  2. Arrange adequate numbers of required cube molds to site in respect with the sampling sequence for the proposed pour.
  3. Make sure the apparatus and associated equipment are clean before test and free from hardened concrete and superfluous water .
  4. Assemble the cube mold correctly and ensure all nuts are tightened.
  5. Apply a light coat of proprietary mold oil on the internal faces of the mold so that you can remove the concrete cubes from the mould with out breaking.
  6. Place the mold on level firm ground and fill with sampled concrete to a layer of about 50 mm thick.
  7. Compact the layer of concrete thoroughly by tamping the whole surface area with the Standard Tamping Bar. (Note that no less than 35 tamps / layer for 150 mm mold ).
  8. Repeat Steps 5 & 6 until the mold is all filled. (Note that 3 layers to be proceeded for 150 mm mold ).
  9. Remove the surplus concrete after the mold is fully filled and trowel the top surface flush with the mold.
  10. Mark the cube surface with an identification number (say simply 1, 2, 3, etc) with a nail or match stick and record these numbers in respect with the concrete truck and location of pour where the sampled concrete is obtained.
  11. Cover the cube surface with a piece of damp cloth or polythene sheeting and keep the cube in a place free from vibration for about 24 hours to allow initial set .
  12. Strip off the mold pieces in about 24 hours after the respective pour is cast. Press the concrete surface with the thumb to see any denting to ensure the concrete is sufficiently hardened, or otherwise de-molding has to be delayed for one more day and this occurrence should be stated clearly in the Test Report.
  13. Mark the test cube a reference number with waterproof felt pen on the molded side, in respect with the previous identification number.
  14. Place the cube and submerge in a clean water bath or preferably a thermostatically controlled curing tank until it is delivered to the accredited laboratory for testing.