Determination of tensile strength of hydraulic cement mortar using briquette samples.
Tools and Materials
- 2 kg scale precision 0.1 g
- Briquette Molds
- small steel trowels
- Clips for holding test samples
- Testing machine capable of applying load at a rate of 2.67 ± 11 (600 ± 25 lb/ft.)2)/Minute
- At least 85% of Ottawa sand passed through an 850-micron (No. 20) sieve and no more than 5% passed through a 600-micron (No. 30) sieve
- Portland cement
Normal room temperature shall be assumed for the laboratory, treatment facility and the water used. Samples will be produced in briquette gang molds in multiples of three.
- The ratio of standard mortar will be 1 part cement (300 grams of Type I, IA, II, or III) to 3 parts Ottawa sand (900 grams) or 400 grams of cement for 6 samples and 1200 grams of Ottawa sand for 9 samples. samples. The amount of water required after achieving normal consistency of clean cement as per ASTM-C-187 shall be determined with reference to the following table.
|Percentage of water required for a neat cement paste of normal consistency||Percentage of water required for standard mortar, one part cement to three parts sand|
- Weigh dry ingredients on a smooth non-absorbent surface and mix well and make a crate. Add appropriate amount of clean water to the crater and mix thoroughly with a steel trowel for 30 seconds. Allow the material to absorb the water for an additional 30 seconds, during which the drying material at the edges is turned into a mortar mass to reduce evaporation and promote absorption. For the next 90 seconds, vigorously mix the mortar with hands fitted with snug-fitting rubber gloves.
- Coat the briquettes with a thin film of mineral oil and place them on a piece of clean glass or metal.
- The briquettes should now be filled with mortar. Fill the pile molds without condensation. Press the mortar firmly into the molds with the gloved hand, applying twelve bars of thumb pressure to each mold. Again, pile excess mortar on each sample and strike off the excess with a steel trowel. Cover the specimens with a similar piece of glass or metal and turn the assembly over, reversing the top and bottom. Repeat the process of stacking, thumping, and troweling the excess mortar that was done on the opposite surface.
- Place the specimens in a treatment chamber with the top surface facing up, but do not subject to dripping water for between 20 and 24 hours. Then separate the samples from the molds and place them in saturated lime water until ready for testing. Lime water should be changed from time to time to keep it clean.
- All samples must be tested within a given time period.
|test age||permissible time tolerance|
|twenty four hours||± hour|
|3 days||± 1 hour|
|7 Days||± 3 hours|
|28 days||± 12 hours|
Before testing, the samples should be cleaned and dried on the surface. Any loose grains of sand or other extraneous material should be removed from surfaces in contact with the testing machine. The specimen should be centered in the clip and pressure should be applied at a rate of 2.67 ± 0.11 kN (600 ± 25 lb)/min.
Record the breaking load for each sample and calculate the kilopascal or pound/inch. Calculate the tensile stress in2 In the following data sheet. The tensile stresses of all allowable samples made from the same mortar should be calculated and averaged to the nearest 34.5 kPa (5 psi) strength.
|sample number||Max Weight, Newton or Pound||cross section, cm cm or inch inches||kPa or psi. tensile stress in|
|Date Samples Prepared:|
|Date samples tested:|
|Average tensile strength of mortar:|