Main topic information
- Practical exercise No.1 Test on the initial and final setting time of gypsum
- Practical exercise No. 2 Vicat apparatus
- Laboratory Practical No. 3 Standard consistency test of cement slurry
- Practical exercise No. 4 Determination of cement setting time
- Practical exercise No. 5 Informative tests on water
Definition: Standard consistency is characterized by the penetration weight of a standard plunger. The quantity of water needed to reach standard consisteny is determined by several experiments of cement slurry with varying percentages of water. The standard cement paste consistency servres as a starting point for all cement tests ensuring compatability of results.
Materials: Worksheet Task No 3.
Results: Measured values of penetration width in millimetres
The quantity of water of the cement slurry is expressed as percentage by weight of the dry cement. The percentages of water, rounded to 0.5%, represent the quantity of water required for Standard Consistency of cement paste.
STN EN 196-3: Methods of testing cement. Part 3: Determination of setting times and soundness
STN EN 197-1: Cement. Part 1: Composition, specifications and conformity criteria for common cements
STN EN 196-7: Methods of testing cement. Part 7: Methods of taking and preparing samples of cement
Tools and equipment:
- Scales: accurate to ± 1g
- Measuring cylinder with an accuracy of ± 1ml
- Bowl and trowel
- Stopwatch with an accuracy of ± 1s
- Vicat apparatus with densitometer roller: the roller is made from corrosion-resistant metal in the form of a precise circular cylinder with an effective length of at least 45 mm and a diameter of 10,00 ± 0,05 mm. The total mass of the moving part should be 300 g ± 1 g and should move without significant friction
- Vicat ring (mould): it is filled with the tested slurry, it must be made from hardened rubber, plastic or brass. The ring has a conical shape, a depth of 40.0 mm ± 0.2 mm and an internal diameter of 75 mm ± 10 mm
- Washer (slide): is larger than the mould, with a thickness of 2.5 mm
- Test specimen prepared and tested in a laboratory with a constant temperature of 20° C ± 2° C and a relative humidity of at least 50%
Preparation of cement paste with standard consistency:
- 400 grams cement CEM II 32.5 (accurate to 1g)
- 120 milliliters of distilled water (accuracy up to 1 ml)
Carefully fill the mixing bowl so that no water or cement is lost. Addition time shall not exceed 10 seconds. Stir the mixture gently while pouring the cement. Immediately after that, stir the mixture vigorously and take this time as the starting time of the mixing process.
This given time is exactly 1 minute. After 90 s, stop stirring for 30 s. The cement paste, glued to the walls and bottom of the mixing bowl, is scraped with a suitable trowel and placed in the center of the bowl. Then mix for another 90s. The total mixing time is 3 minutes.
The Vicat ring is filled with cement paste. Both the mould and the washer are previously oiled with a separating agent. Air bubbles in the cement paste are removed by manually tapping the pad. The excess paste is carefully removed and aligned with the top edge of the ring.
Determination of standard consistensy
Vicat apparatus indicator scale shall be accurately set to the zero before the test. Then the roller is raised to the upper starting position. The filled Vicat ring is placed on the glass plate under the plunger. The plunger is gently lowered to touch the surface of the cement paste. The movable bearing rod is released so that the plunger penetrates vertically into the centre of the cement paste. The standard consistency test shall be performed 4min ± 10s after the end of the addition of cement to the water (zero time). The penetration depth is read on the scale when the plunger no longer penetrates deeper into the cement paste, but not before 5 s and at the latest than 30 s.
The test is repeated with a cement paste containing different pertentages of water until a distance of 6 mm ± 2 mm is reached between the bottom surface of the plunger and the glass plate. The plunger is cleaned after each standard consistency test.
|№||CEMENT (g)||WATER (ml)||Vicat apparatus (mm)|
w = (v / c) * 100 (%) = ………………………
in ……….. final quantity of water (g)
c ……….. final quantity of cement (g)