Lab 1- Normal Consistency and Setting Time

 Jordan University University of Science Science and Technology Technology  Department of Civil Civil Engineering  Materials of Construction Laboratory (CE 326)

Experiment 1:  Time of Setting of Hydraulic cement   By:  Eng. Zain Ghazi AL-Kofahi

Cement Tests  Number of tests are performed in the cement plant laboratory to ensure that the cement is of the desired quality and that it conforms c onforms to the requirements of the relevant national standards.

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Objectives  1.

To determine the amount of water required to  prepare cement paste for testing.

2.

To determine the time of setting of hydraulic cement by means of the Vicat needle.

 Apparatus  1.

 Mixer.

2.

Vicat apparatus.

3.

Conical ring.

4.

Glass plate.

5. 6.

 Balance. Timer.

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Materials   

 Hydraulic cement 650g. Water (23oC)

Normal consistency test (ASTM 187 - 86 Re approved 1991)  In the acceptance tests for cement, the water content is regulated by bringing the paste to a standard condition of wetness. This is called “Normal Consistency” - Cement of normal consistency is required to measure setting time.  Definition of terms - Normal consistency: A standard measure of plasticity of a cement paste. A paste has normal consistency when a Vicat plunger (10 mm in diameter) penetrates 10 ± 1 mm in 30 sec under its own weight. The required water/cement ratio is determined by trial and error.

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The quantity of mixing water to form a standard paste  for setting and soundness test .  It depends upon the compound composition and  fineness of cement.  About 24%~30% ( by weight) for Portland cement.

Normal consistency test  

 Mixing of Cement Paste :

- place all the mixing water in the bowl. -Add the cement to the water and allow 30s for the absorption of the water. - Mix at slow speed (140 ± 5 r/min.) for 30s. - Stop the mixer and wait for 15s, during this time scrap down into batch any  paste that may have collected on sides of the bowl. -Mix at medium speed (285 ± 10 r/min.)  for 1minute.

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Normal consistency test  

 Molding Test Specimen:

- Mold cement paste into shape of a ball. With gloved hands, toss ball six times through a free  path of about six inches from one hand to another. - Press ball into larger end of Vicat ring and completely fill ring with paste. - Remove excessive paste without compressing samples and locate ring under plunger of Vicat apparatus.

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Consistency Determination:

- Place plunger in contact with top of  paste and lock. Set indicator on the scale to zero. - Release plunger and record settlement of plunger in mm after 30 seconds. - Repeat process with trial paste with varying percentages of water until normal consistency is observed.

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Report   Record the weight of water added to 650g of cement, when the plunger penetrates 10mm (9mm to 11mm) in 30 seconds. W =--------------- g of water. w/c = --------------% 

 Discussion Question: With finer cement particle size, would more or less water be required to achieve the normal consistency? Briefly explain.

Set Time Test (ASTM C 191 - 92) 

Setting time is the term used to describe the stiffening of the cement paste, and it refers to a change from a fluid state to a rigid state.

 Definition of terms: - Time of initial set: The time at which the concrete can no longer be  properly mixed, finished or compacted. (Represented by a Vicat needle ( 1mm in diameter) penetration of 25 mm or less). ASTM C150 prescribes a minimum initial setting time of 60 minute for Portland cement. (45 minutes (BS12:1978)) - Time of final set: The time required for the cement to harden to a  point where it can sustain some load. (Represented by no  penetration of Vicat needle, the needle makes an impression and the cutting edge fails). ASTM C150 prescribes a maximum final setting time of 10-12 hours for Portland cement. 

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Set Time Test  Factors affecting setting time:   

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Temperature and humidity.  Amount of water (w/c) Chemical composition of cement. Fineness of cement ( finer cement →  faster setting).

Set Time Test  Procedures - Mix 650 g of cement with the percentage of water required for normal consistency as described  previous. - After molding cement paste into the test ring,  place specimen in moist room for 30 minutes. - Place specimen ring under Vicat apparatus and lock needle on surface of paste. Set indicator scale to zero. - Release weighted needles and record the  penetration in mm after 30 seconds. - Repeat process every fifteen minutes until initial set is achieved. - Repeat processes every hour until final set is achieved. 

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Report  Calculation Calculate the time to the nearest minute required for the paste of normal consistency to achieve initial and final sets. 

The setting time for the given cement sample are found to be :   Initial setting (Represented by a Vicat needle penetration of 25 mm) =……………………………….minutes Final setting time =………………………….minutes 

 Discussion Questions: (1) Does the initial setting time satisfy the requirements of the British Standards? (2) Discuss briefly the significance of determining the initial and final setting times. (3)If the initial setting time is not qualified, can we use the cement in engineering?

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Conclusions:  

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The amount of water required to prepare cement  paste for testing is ………………… The setting times for the given cement sample are  found…………………………..(within/ not within) the standards.

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