Consistency of Standard Cement Paste

CONSISTENCY OF STANDARD CEMENT PASTE

INTRODUCTION

Cement paste of standard consistency is to be used for the determination of cement initial and final setting times; soundness; and tensile and compressive tests. This experiment can be performed according to MS 522.1977, BS 4550: Part 3 and EN 1063:1987. The following experiment will be performed according to MS 522.1977. OBJECTIVE

The objective of this experiment is to determine the required amount of water to be added to a certain amount of cement to achieve a cement paste of normal or standard consistency. APPARATUS

1. 2. 3. 4. 5. 6.

Vicat apparatus Measuring cylinder Balance Mixing apparatus: glass plate, spatula and trowel Stopwatch Thermometer

MATERIALS

1. Ordinary Portland Cement 2. Fly-ash 3. Clean water

PROCEDURE

Introduction: Cement paste of standard consistency would have a penetration of about 33 to 35 mm under this experiment. Precaution:

The following procedures require a close monitoring of time.

1. Three samples of 500g of Ordinary Portland Cement were prepared on three glass plates. 2. Three samples of clean water were prepared and each sample has a mass of 25%, 30% and 35% of the cement samples. Precaution:

the following steps 3 to 7 must be performed within 4±¼ minutes.

3. One sample of cement was mixed on the glass plate with the trowel until there is no presence of any cement lumps. 4. The sample of cement was mixed with the sample of water having a mass of 25% of the cement sample on the glass plate using spatula for about 30 seconds. 5. The cement paste was mixed thoroughly with hand for about 1 minute. 6. The kneaded cement paste was tossed 6 times from one hand to another that is at about 150mm apart. 7. The Vicat mould that is resting on a non-porous was filled with the cement paste in one layer. The paste was pressed and the surface at the top of the mould was smoothen-off  using hand and trowel. Precaution:

The following steps 8 to 10 must be performed immediately after the filling of  cement paste into the mould.

8. The test block was placed under the rod-bearing plunger. The plunger was lowered gently into contact with the surface of the test block. 9. The rod was released quickly and allows it to sink into the test block and the penetration of the rod was recorded in Table 6.1. 10. The rod was raise after the penetration has been recorded in Tale 6.1. Attention:

Repeat steps 3 to 10 for the other two samples of cement paste that has water of  30% and 35% of the cement mass respectively.

11. A graph of penetration vs. percentage of water was plotted. 12. From the graph, the percentage of water that corresponds to a penetration of about 33 to 35 mm was determined. 13. Step (1) to (12) was repeated for fly-ash.

INITIAL SETTING AND FINAL SETTING TIMES OF CEMENT

INTRODUCTION

Setting of cement is the stiffening of cement paste or the change of cement paste and cement mix from fluid to rigid state. The terms initial and final set are used in practice to describe arbitrarily chosen stages of setting. It can be described that initial setting of cement is that stage in the process of hydration after which any cracks that may appear do not reunite. At the final setting of  cement, noticeable stiffening of cement paste is complete and the final hardening process responsible for its strength commences. False setting refers to the premature stiffening of cement within a few minutes of mixing with water. However remixing the cement paste without any addition of water restores the plasticity of the paste until it sets in the normal manner and without any loss of strength. The setting time of cement decreases with a rise in temperature but above about 30°C, a reverse effect may be observed. OBJECTIVE

The objective of this experiment is to determine the time that initial and final setting of cement has occurred. The experiment is prescribed by EN 196-3: 1987, ASTM C 15094, ASTM C 19192, ASTM C 266-89 and BS 915: 1972. APPARATUS

1. 2. 3. 4. 5.

Vicat apparatus Mixing apparatus: glass plate, spatula and trowel Measuring cylinder Balance stopwatch

MATERIALS

1. Ordinary Portland Cement 2. Clean water

PROCEDURE

Introduction: This experiment makes use of the result of Laboratory Experiment No. 6: Consistency of Standard Cement Paste. The test result shall be recorded in Table 7.1. Two different types of needles are used to determine the initial and final setting of cement paste. The round needle with a diameter of 1.13 ± 0.05 mm is used for determination of initial set. To determine the final set, use a similar needle fitted with a metal attachment hollowed out so as to leave a circular cutting edge 5 mm in diameter and set 0.5 mm behind the tip of the needle. Initial set is said to have taken place when the needle does not penetrate to a depth of  approximately 5±1 mm from the bottom of the mould. Final set is said to have taken place when the needle penetrates to a depth of approximately 0.5 mm but the circular cutting edge fails to make an impression on the surface of the paste. Precaution:

The following procedures require a monitoring of time.

1. One sample of 500g of Ordinary Portland Cement was prepared on one glass plate. 2. One sample of clean water that has the mass for achieving a cement paste of standard consistency based on the Laboratory Experiment No. 6: consistency of standard cement Paste was prepared. Precaution:

The following steps 3 to 8 must be performed within 4±¼ minutes.

3. One sample of cement was mixed on the glass plate with a trowel until there is no presence of any cement lumps. 4. The sample of cement was mixed with the sample of water on the glass plate using the spatula for about 30 seconds. 5. The cement paste was mixed thoroughly with hand for about 1 minute. 6. The kneaded cement paste was tossed 6 times from one hand to another that is at about 150 mm apart. 7. The Vicat mould that is resting on a non-porous plate was filled with the cement paste in one layer. The paste was pressed and the surface at the top of the mould was smoothenoff using hand and trowel. 8. The test block was placed under the rod-bearing plunger. Precaution:

The following steps 9 to 11 must be performed immediately after the filling of  cement paste into the mould. Use the right needle for initial and final set.

Attention:

Repeat steps 9 to 11 every 5 minutes for the determination of initial set and every 30 minutes for the determination of final set. For steps 9 to 11, use a different location for different penetration of the needle into the sample. For steps 9 to 11,

when the needle for the determination of initial set does not penetrate beyond a point approximately 5 ±1 mm from the bottom of the mould, change the needle to continue the test using the same sample for the determination of final set. For steps 9 to 11, stop the test to determine the final set when the needle penetrates to a depth of approximately 0.5 mm but the circular cutting edge fails to make an impression on the surface of the sample. 9. The plunger was gently lowered into contact with the surface of the test block. 10. The rod was released quickly and allows it to sink into the test block and the penetration of the rod was recorded. 11. The rod was raised after the penetration has been recorded in Table 7.1. 12. A graph of penetration vs. time was plotted. Plot only one graph using the data for both determination of initial and final set. 13. From the graph, the time for the initial and final setting of the cement paste was determined.