OBJECT: -To Take Out Concrete Core by Core Drilling Machine and Determining its Compressive Strength.
THEORY:
Core drilling is a type of service in which a drill is used to remove a cylinder of material, called a core. Usually diamond core drills are utilized in order to best cut through the concrete and additional material and ensure that the customer’s upmost satisfaction is met. This type of technique of concrete cutting is used in many cases such as but not limited to:
- Walls, floor slabs, and ceilings for electrical and communication services, cabling, plumbing, or HVAC
- Slab and roadway holes for doweling drilling, rebar tie-ins, or drainage
- Recessed lighting and fixtures
- Sample and analysis of material
The examination and compression testing of cores cut from hardened concrete is a well – established method, enabling visual inspection of the interior regions of a member to be coupled with strength estimation.
SAFTEY EQUIPMENT
- Wear nitrile gloves to reduce the incidence of skin contact with potentially contaminated
- Concrete and to reduce the risk of potential cross contamination.
- Wear goggles or a face shield to protect your eyes from air borne debris.
- The coring machine is a powerful tool that produces high torque, operators should be
- Experienced in concrete coring.
REQUIRED EQUIPMENT
- Coring machine with stand and 1” coring bit (or other bit, as appropriate)
- Extension cord
- Electric drill with masonry bit, anchor bolts, wrench to tighten bolts, and 4 ½ inch angle
- grinder with cutting wheel
- Water tank filled with water (and a water container filled with tap water, if there is not a nearby water tap)
- Hammer, screw driver, wire and other tools which can be used to retrieve the core sample from the core hole and/or coring bit
- Paper towels
- Tape measure
- Universal Testing Machine
- Vernier Caliper
PROCEDURE:
- Concrete Core Drilling
In terms of the procedure, the operator first uses a small threaded anchor to secure the drill post to the wall and then bolts the drill post, which will act as a guide for the core drill itself. This bolting of the drill post allows for the core drill to hit its mark straight on and make one smooth, consistent core – no matter what angle.
Once the drill post is securely fastened, the next step is for the drill bit to be mounted. This drill bit can be to whatever size the customer specifies.
After the drill is properly mounted, it is turned on while water is applied as coolant and pressure is placed on the crank. The hand crank on the core drill itself drives the drill to the surface and cuts through the concrete. Most drill cans are built to accommodate a depth of 12-14”, but can be any length if needed depending on the depth of the core. Also, if necessary, the core drill can cut through rebar steel. Once the surface and existing materials are penetrated, the core comes out with the bit, or the core can be pulled out manually if it is found in a slab. From there the coring of the hole is complete and additional hos can then be cored if need be.
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- Determination of Concrete Core Compressive Strength
- Measure the diameter and height of the core.
- Place the core in the UTM.
- Applied the load uniformly until the core starts to fail.
- Note down the load.
- Calculate the compressive strength using formula:
PRECAUTIONS:
A core to be tested for strength shall not be removed from structure until the concrete has become hard enough to permit its removal without disturbing the bond between the mortar and the coarse aggregate. Normally the concrete shall be 14 days old before the specimens are removed. It is preferred the concrete should be 28 days old for drilling cores.
f the ends of the cores do not conform to the perpendicularity and planeness requirements, they shall be sawed or ground to meet those requirements or capped as per standard procedure.
Safety must remain a top priority for anyone operating a concrete core drill. Key steps to take include:
- Wearing goggles at all times
- Wearing earplugs to prevent hearing damage
- Wearing gloves to prevent hand injuries
OBSERVATIONS AND CALCULATIONS:
Diameter of the concrete core =……….
Applied load =……………
Compressive Strength = _____________ =
RESULT:
The compressive strength of concrete core was found to be ……….