ASTM C109 Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or [50-mm] Cube Specimens)

Scope:

The compressive strength of hydraulic cement and other mortars can be measured using the ASTM C109 test technique, and the findings can be used to assess whether or not the specifications have been satisfied. Numerous additional specifications and test methods also refer to this test procedure.

Test Procedure: 

Apparatus:

• Weights and Weighing Devices: Weights and weighing devices must meet the requirements of Specification C 1005, and they undergo a precision and bias evaluation of 2000 g for accurate measurements.
• Glass Graduates: Glass graduates are used to measure the water for mixing. To ensure precise measurements, they should have predetermined capacities, experience little fluctuation, and possess appropriate subdivisions.
• Specimen Molds: These molds are used to form cement mortar into 2-inch (50-mm) cubes for testing. To ensure that the cubes are the proper size and shape, they must fit very tightly. The molds must have only three cube sections and be capable of being divided into no more than two pieces.
• Mixer, Bowl, and Paddle: A mechanical mixer with an electrically operated paddle and mixing bowl that meets the requirements of Practice C 305 is used
• Flow Table and Flow Mold: These particular instruments are used to gauge how smoothly the cement mixture flows. Certain specifications outlined in Specification C 230 must be adhered to.
• Tamper: The tamper is used to compact the mortar in the molds. Strict size and material specifications must be adhered to to guarantee precise and constant compaction.
• Trowel: A straight-edged trowel with a steel blade that is between 4-6 in. [100-150 mm] long should be used.

• Moist Cabinet or Room: The moist cabinet or room should conform to the requirements specified in Specification C 511
• Testing Machine: Compressive loads are applied to the specimens by the testing machine, a critical component. Necessary components for exact testing that should be included are a dial scale or digital load indicator, maximum load indicator, zero adjustment, upper and lower bearing surfaces, and a loading range. It might be hydraulic or screw-type

Dial Scale: A graduated scale must be possessed by a dial scale that is utilized for accurate load measurements.

Digital Load Indication: When digital technology is used, the numerical display must be readable and accurate to within 1.0% of the validated loading range.

Both the upper and lower bearing surfaces should be made of hardened metal and should adhere to strict alignment and flexibility guidelines.

Procedure:

Mortar composition:

• The weight ratio of the components for the standard mortar is one part cement to 2.75 parts graded standard sand.
• A water-cement ratio of 0.460 should be used for all air-entraining Portland cement, and 0.485 should be used for all other types.
• For types of cement other than Portland and Portland cement with air-entraining, the amount of mixing water must be such that it creates a flow of 110 ± 5 and must be expressed as a percentage of the cement weight.

Mortar preparation:

• The steps outlined in Practice C 305 should be followed for the mechanical mixing process.

Flow determination:

• The method outlined in Test Method C 1437 should be used to determine the flow.
• The flow should simply be noted for Portland and air-entraining Portland cement.
• Test mortars with varied percentages of water for cement other than Portland or air-entraining Portland cement should be made until the desired flow is attained. Each test should be made with brand-new mortar.

Molding Test Specimens:

• After the flow test is completed, the mortar should be immediately placed back in the mixing bowl. The entire mixture should be stirred for 15 seconds at medium speed after the bowl sides are quickly scraped, and any mortar that may have accumulated there is added. After mixing is completed, the mixing paddle should be shaken to scrape any remaining mortar into the mixing bowl.
• The flow test may be omitted if a duplicate batch needs to be created immediately for more specimens, and the mortar can be left uncovered in the mixing bowl for 90 seconds instead. In the final 15 seconds of this time, the bowl’s sides should be quickly scraped, and any mortar that may have accumulated there should be added to the batch. Then, mix at medium speed for 15 seconds.
• As soon as the mortar batch has been thoroughly mixed, but no later than 2 minutes and 30 seconds, a layer of mortar measuring 1 in. or [25 mm] (about one-half the depth of the mold) should be added in each of the cube compartments by the specimens. Each round should be formed at a straight angle to the other and should consist of eight adjoining strokes over the specimen’s surface. The mortar in each cube compartment should be tamped 32 times in around 10 seconds throughout four rounds
• When the tamping is done, the tops of all the cubes should just barely rise beyond the rims of the molds. A trowel is used to smooth off the cubes after the mortar has been pressed into the tops of the molds by drawing across the tops of each cube once while keeping the trowel’s flat side at a right angle to the length of the mold. Then, softly draw the flat side of the trowel (with the leading edge slightly raised) once along the length of the mold to level the mortar and ensure that the mortar that extends past the top of the mold has a more consistent thickness.
• By sawing the straight edge of the trowel across the length of the mold while holding it almost perpendicular to it, we can trim the mortar to a smooth surface that is flush with the top of the mold.

Storage of Test Specimens:

• Immediately after molding is complete, the test specimens should be stored in a moist room or closet. All test specimens should be stored in wet closets or rooms from 20 to 72 hours after molding, with their upper surfaces exposed to moist air but shielded from dripping water. If the samples are withdrawn from the molds before 24 hours, they should be stored on the shelves of the damp closet or moist room until they have aged for 24 hours. Then, all of the samples, except those used for the 24-hour test, should be submerged in saturated lime water in storage tanks made of noncorroding materials. The water in the storage tanks should be changed as needed to keep them clean.

Determination of Compressive Strength:

• The samples should be tested right away after being removed from the wet closet for 24-hour specimens or from storage water for all other specimens to determine their compressive strength. For the 24-hour tests, if more than one specimen is taken out of the moist closet at once, these specimens should be kept covered with a damp towel until the testing period. If more than one specimen is taken out of the storage water at a time for testing, they should be maintained in water that is 73.5 ± 3.5°F or (23 ± 2°C) warm and deep enough to completely submerge each specimen until the time of testing.
• Loose sand or incrustations should be removed from the faces of each specimen that will come into contact with the testing machine’s bearing blocks after being wiped to a surface-dry condition. These faces should be inspected using a straightedge. If noticeable curvature is observed, either the item should be rejected, or the face or faces should be ground to achieve level surfaces. The cross-sectional area of the specimens should be periodically checked.
• A loading rate of 200 to 400 lbs/s [900 to 1800 N/s] should be applied to the specimen at a relative movement speed between the upper and lower platens. This predetermined rate should be maintained during the first half of the predicted maximum load, and it should not be altered during the second half of the loading, especially if the cube is yielding before failure.

Calculations:

To calculate the compressive strength

fm = P/A

where: 

fm = compressive strength in MPa or psi

P = maximum load total in lbf or [N]

A = area of loaded surface in [mm2] or in [in2].

Video 01: C109 – Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or [50-mm] Cube Specimens)

Preferred Test Sample Size: 

Number of test Specimen: 2-3 specimens per batch per age

Test Specimen Size: 2″ x 2″ x 2″

Keywords: Mortar, Compressive strength, Cubes

Conclusion:

The ASTM C109 compressive strength test determines if hydraulic cement mortar satisfies specified strength requirements, ensuring quality control in building materials. Non-compliance may highlight problems that require corrective action, whereas compliance validates the mortar’s appropriateness for its intended purpose.