06 - Compressive Strength test

Engr. Erish V. De Guzman Youtube Channel https://www.youtube.com/channel/UCmMKE1meJNf-AHQto-Uo8AQ Compressive strength is the maximum compressive stress that, under a gradually applied load, a given solid material can sustain without fracture. The main purpose of Compressive strength test is to determine the compressive strength of a cast-in-place of cube/cylindrical concrete specimen and its suitability with accordance to 2013 DPWH Standard Specification and ASTM C39. This test is limited only in footing, column footing, column, reinforced slabs and any related concrete structure except to beam and diagonal structure (slope protection). The maximum application of load in specimen is strictly in a rate of 140kg./cm2/min. The equipment and apparatuses we need for this test are: 1. Universal Testing Machine, to test the compression 2. Concrete Cylinder/Cube Specimen (Cured) a. Fine and Coarse Aggregate b. Portland Cement c. Tampering Rod with hemispherical tip d. Concrete Cylinder/Cube Mold e. Bitumen Material/use oil/ 3. Digital Weighing Scale (10kg. capacity-sensitive to the extent of 0.1% of total sample) Before conducting test, use safety gloves, safety shoes & apron at the time of test; After the test, switch off the machine; Keep all the exposed metal parts greased; Equipment should be cleaned thoroughly before testing & after testing; And make sure that no one is around, we need a 1-meter radius distance from the testing machine. Now, let’s proceed to the testing procedure. The following procedure was adopted in ensuring that the data to be record from compressive strength test specimens was taken in an organized and consistent manner. 1. Prepare the cube/cylindrical concrete mold and clean the internal and outside surface of the mold; 2. Sample casting mold should be 15 cm x 15 cm x 15 cm cube mold or cylindrical specimens of 15 cm diameter x 30 cm long; 3. Apply some oil (bitumen material/motor oil/crude oil is highly recommended) in internal surface of the mold to avoid sticking of cement paste; 4. Randomly get fresh concrete at the first, middle and last discharge of the mixture; 5. Make sure to hold tight handle of the mold so that it will not move before and after pouring of concrete mixture; 6. Pour the fresh concrete in the mold in three equal layers; 7. Each layer should be tampered circularly 25 times using tampering rod. Take note, don’t let tampering rod to reach the bottom surface of each layer, it can cause segregation which may affect the output; 8. When the mold is completely filled with concrete (completed 3 layers), hold the tampering rod horizontally and roll it to the top surface of the mold to ensure that no excess of concrete will remain around it; 9. To prevent evaporation of sample, cover the upper surface with glass plate; 10. The specimen shall be stored at the laboratory (or in any room with same temperature) for 24hr and 30mins under curing (use matting method); 11. After that, demold the sample into the mold and submerge it into potable/clean water at 27ºC+2ºC until time of test; 12. Make sure that the head of the water surface and top surface of the mold should not be greater than 50mm; 13. Make sure that the Universal Testing Machine is clean before conducting test; 14. When the testing day comes, remove the specimen from the water and conduct testing while the specimen is in wet condition; 15. Specimen shall be free in any unnecessary loose material and be wiped clean. Follow the steel patter at the bottom of the machine and place the specimen at the center to ensure that the specimen is align with the axis; 16. In machine controller of the UTM, set it on stress-strain diagram and fill up the form as its stated in the window; 17. The load shall be applied slowly at a rate of 140kg./cm2/min until the specimen breaks (observe the line graph in the monitor); 18. When specimen breaks, stop the operation of the machine and remove the unnecessary debris under break specimen; 19. Take a photo on the break specimen and notice its type of fracture; and 20. Record and gather all the data in the monitor.