This method of test covers the procedure for determining the reactivity of the pozzolanic material (such as fly ash) with hydrated lime, as represented by compressive strength of standard mortar test cubes prepared and tested under specific conditions.
Size and Number of Test Specimens
The tests specimen shall be 50 mm cubes. At least three specimens shall be made for each period of test specified.
Cube Moulds of 50 mm in size
Step – 1 (Preparation of Moulds)
The interior faces of the specimen moulds shall be thinly covered with mineral oil or light cup grease. After assembling the moulds, excessive oil or grease shall be removed from the interior faces and the top and bottom surfaces of each mould. Moulds shall then be set on plane, nonabsorbent base plates that have been thinly coated with mineral oil, or light cup grease.
Step – 2 (Preparation of Mortar)
Clean appliances shall be used for mixing. The temperature of the water and that of the test room at the time when the mixing operation is being performed shall be from 27°C ± 20C
The dry materials of the standard test mortar shall be lime : pozzolana : standard sand in proportion of 1 : 2M : 9 by weight blended intimately.
M = (Specific gravity of Pozzolana / Specific gravity of lime)
The amount of water for gauging shall be equal to that required to give a flow of 70 ± 5 percent with 10 drops in 6 sec (as explained in Step – 3 given below)
The following quantities of materials are suggested for preparation of mortar:
300 x M g
These quantities will suffice for preparing six test specimens.
Step – 3 (Determination of Flow)
Trial mixing – With dry material as given above, make mortars with different percentages of water until specified flow is obtained. Make each trial with fresh mortar. The mixing shall be done mechanically by means of mixing apparatus. Place the dry paddle and the dry bowl in the mixing position in the mixer.
Then introduce the materials for batch into the bowl and mix in the following, manner:
(a) Place all the mixing water in the bowl.
(b) Add the pozzolanic mixture to the water, then start the mixer and mix at the slow speed (140 ± 5 rev/min) for 30 sec.
(c) Add the entire quantity of sand slowly over a period of 30 sec, while mixing at slow speed.
(d) Stop the mixer, change to medium speed (285± 10 rev/min), and, mix for 30 sec.
(e) Stop the mixer, and let the mortar stand for one and a half min. During the first 15 sec of this interval, quickly scrape down into the batch any mortar that may have collected on the side of the bowl, then for the remainder of this interval, cover that bowl with the lid.
(f) Finish by mixing for one minute at medium speed (285 ± 10 rev/min).
(g) In any case requiring a remixing interval, any mortar adhering to the side of the bowl shall be quickly scraped down into a batch with the scraper prior to remixing.
Upon the completion of mixing, the mixing paddle shall be shaken to remove excess mortar into the mixing bowl.
Carefully wipe the flow-table top clean and dry and place the mould at the centre. Place a layer of mortar about 25 mm in thickness in the mould and tamp 20 times with the tamping rod. The tamping pressure shall be first sufficient to ensure uniform filling of the mould. Then fill the mould with mortar and tamp as specified for the first layer. Cut off the mortar to a plane surface flush with the top of the mould by drawing the straight edge of a trowel (held nearly perpendicular to the mould) with a sawing motion across the top of the mould. Wipe the table top clean and dry; particularly taking care to remove any water from around the edge of the flow mould. Lift the mould away from the mortar one minute after completing the mixing operation. Immediately drop the table through a height of 12.5 mm ten times in 6 sec.
The flow is the resulting increase in average base diameter of the mortar mass, measured on at least four diameters at approximately equispaced intervals expressed as a percentage of the original base diameter.
The materials for each batch of moulds shall be mixed separately using the quantities of dry materials, conforming to the proportions specified and the quantity of water as determined. Mixing of mortar shall be done mechanically as described.
Step – 4 (Moulding Test Specimen)
Immediately following the preparation of the mortar place the mortar in a 50 mm cube mould in a layer of about 25 mm thickness and tamp 25 times with the tamping rod. The tamping shall be just sufficient to ensure uniform filling of the mould. Then fill the mould to overflow and tamp as specified for the first layer. On the completion of the tamping, the tops of all cubes shall extend slightly above the tops of the moulds. Cut off the mortar to a plane surface flush with the top of the mould by drawing the straight edge of a trowel (held nearly perpendicular to the mould) with a sawing motion across the top of the mould.
Step – 5 (Storage and Curing of Specimens)
Cover the surface of the specimen in the mould with a smooth and greased glass plate. Keep the specimens with the moulds along with the cover plates under wet gunny bags for 48 hour. Then remove the specimens from the moulds and cure at 90 to 100 percent relative humidity at 500C + 20C for a period of eight days. Samples shall not be cured under water.
This may be achieved by keeping the specimens in a one liter capacity wide mouth jar with screwed lid over a galvanized iron sheet platform placed at bottom of the jar. The platform is covered with a piece of paper. Water is kept to a depth of about 10 mm at the bottom, below the level of the platform. After placing the specimen fitting the lid, the jar is sealed with insulation tape and kept in an incubator adjusted for 500 +20C for eight days.
Step – 6 (Perform Compression Test)
Remove the specimens after curing for eight days in the incubator as described above and test for compressive strength after, they reach the room temperature. Test not less than three cubes. The cubes shall be tested on their sides without any packing between the cube and steel platens on the testing machine. One of the platens shall be carried on a ball and shall be self-adjusting, and the load shall be steadily and uniformly applied, starting from zero and at a rate of 35 kg/cm2/min.
Step – 7 (Calculation)
Calculate the compressive strength from the crushing load and the average area over which the load is applied. Express the result nearest to 1 kg/cm2.
Faulty Cubes and Retests
Cubes that are manifestly faulty or that give strength differing by more than 15 percent from the average value of all test specimens, made from the same sample and tested at the same period shall not be considered in determining the compressive strength. After discarding such cubes, if less than two strength test values are left for determining the compressive strength at any given period, a retest shall be made.