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....INSTRUCTIONS FOR TESTING CONCRETE CYLINDERS USING A COMPRESSION TESTING MACHINE WITH GAUGES AND A GREENLEE HYDRAULIC PUMP....



1. Sample Preparation

Prepare the concrete sample in accordance with ASTM C-39.
Use the capping method of choice. If using pad caps, be sure to have the appropriate durometer pads in the bases.

Be sure to thoroughly clean the bases on a regular basis both inside and out.
Concrete debris will build up on the inside of the steel bases. This will cause excessive corner breaks on damples if the debris is allowed to build up. Use a blunt instrument to remove the debris and reinstall fresh pads.

When using pad caps, the rule of thumb is to break 100 cylinders, flip the pads over test 100 cylinders and throw the pads away. Typical life expectancy of pads is 200 breaks. Over usage of pads will cause unacceptable test resulsts.

When installing pad caps on the specimen, always put the bottom of the specimen in the bottom pad cap base. The bottom of the specimen is the side which sits in the bottom of the cylinder mold.

2. Preparing for application of load to the sample

Take your capped specimen and insert it into the testing machine.
Center the specimen in the upper and lower pad bases.
Center the specimen in the testing machine.
If you have a machine with a piston on the top of the loading frame, center the specimen on the top platen.
If you have a machine with a piston on the bottom of the loading frame, center the specimen on the bottom platen.

This is very important if you want accurate testing results!!!
Your testing machine will have hydraulic gauges for load indication. These gauges will contain a zero adjustment (on 12"diameter models) which is located at the bottom of the gauge. The gauges will also have a red pointer or maximum load of the test. These pointers should be free moving and have minimal friction. If the pointer is not free moving, Contact CSI at 724-867-6664 to recieve instruction of service of the max needle.

Your machine may have one or two gauges, depending of the model of machine. Machines with one gauge are primarily used for cylinder testing of concrete samples 4 X 8 or 6 X 12. The rule of thumb states that a bourdon tube gauge is accurate from 10% of the gauge capacity to full scale. If your gauge reads 0 to 250,000 lbs. the gauge will be accurate from 25,000 to 250,000 lbs. You should not use the gauge below 25,000 lbs.

If tests are required below the 25,000 lbs. level on a 250,000 lb gauge, then a low range gauge must be used for these tests.

Most low range gauges on these machines have a capacity of 30,000 lbs. These would be used for cube, beam, or specialty lightweight cylinders. The rule of 10% to full scale applies to these low range gauges also.

3. Application of Load

Before applying load to the specimen, it is very important to understand the operation of the control valve on the pump.

The machine in this example has a Greenlee Hydraulic Pump with a Greenlee flow control valve.

The Pump
The pump uses Dextron III ATF as the fluid of choice.
The reservoir should be 3/4 full of fluid.
The vent, located on the back of the reservoir, should be open prior to testing.

The Valve
The valve contains 2 levers and 1 stem.
The lever on the right side of the valve is the pressure/release lever.
In the upright position (with the knob against the motor) the pump will build pressure.
In the down position (with the knob against the reservoir) the pump will release pressure and allow the piston to retract.

The lever on the left is the rapid advance/controlled rate lever. With the knob pull toward the operator, and the release lever in the pressure position, the pump is in rapid advance.

This means the piston will move rapidly. Care must be taken when using the rapid advance function. The piston only has 2 1/2 inches of stroke. If left in the rapid advance position for too long, the piston will overextend causing a release in oil from the piston area. Immediately shut off the pump and Call CSI at 724-867-6664 for proper instruction of how to eliminate this problem.

The rapid advance lever is used only to position the piston close to the sample for zeroing purposes, or to preload the sample once zeroing has been performed. Never use the rapid travel position to test the cylinder to total failure. This will provide inaccurate test results.

With the knob pushed back toward the pump motor (all the way back) the pump will be in the controlled rate position.

All the fluid will be sent through the stem located in the center of the valve. This stem will allow you to set the rate of loading for the machine.

ASTM C-39, for a 6 X 12 concrete cylinder, requires th rate of loading to be 35 psi/sec +/- 7 psi. Calculated in lbs, this comes out to 990 lbs per second. +/- 200 lbs.

The stem in the center acts like a water spigot. Counter-clockwise increases the rate of force application per second. Clockwise decreases the rate.

Once the proper rate is achieved, you can leave the stem at that setting at that setting and the machine will continue to load at the proper rate.

You are now ready to test your specimen.

Select the appropriate gauge for your test using the criteria listed above in section two of this document.
Turn on the pump and move the release lever up to the loading position.
(This is the lever on the right.)

Pull the knob on the left toward you and move the piston close to the top of the sample.

Push the knob back toward the motor when you have achieved 1/4 inch of daylight space.

Tap on the gauge and turn the zero adjustment until the needle is on the zero line of the gauge. THIS IS CALLED FRICTION ZEROING.

Move the red needle to 10% of the gauge capacity.
Check centering of the specimen on the cylinder and close the fragment guard (if so equipped).

Pull the knob on the left side of the valve toward the operator and preload the specimen to the point where the red needle is set (at 10% of the gauge capacity). Push the knob back toward the motor in a swift action.

Adjust the stem in the center of the valve until you have the loading rate at approximately 1000 lbs/sec. You can time the needle motion by determining the 5000 lb intervals on the gauge and setting the valve so that the needle passes 5000 lb intervals in 5 seconds.

Continue loading the sample, adjusting the stem slightly if necessary, until the specimen breaks.

Once you have achieved a load of more than 1/2 of the specimen's strength, do not continue to adjust the stem. The specimen testing rate will slow automatically when the specimen reaches yeild point.

Be sure that the specimen has fully broken. Small corner breaks are common with pad caps. These corner breaks are not considered ultimate failure breaks. Continue to run the machine until you achieve a total failure of the sample.

Move the knob on the left to the down position.
Shut off the pump.
Record the position of the red pointer on the gauge as your maximum force value.
Reposition the red pointer to 10% of the gauge capacity.
Remove all debris and wipe down cap bases.

You are now ready to test your next specimen.

Special Note: Tests made on the low gauge require extra special attention to the zeroing procedure. Failure to carry out the procedure effectively will cause great differences in ultimate load. This gauge is much more sensitive. Friction zeroing of this gauge is very important. Please follow the instructions carefully.

 



CALIBRATION SERVICES, INC.

 


300 Buttertown Road
Emlenton, PA 16373
(724) 867-6664 or (800) 793-1870
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