Chemistry Project To Study the Setting of Cement

Chemistry Project: To Study the Setting of Cement

Certificate

This is to certify that this project work is submitted by Rohit Gupta to the Chemistry department, Aditya Birla Public School, Kovaya, and was carried out by him under the guidance and supervision during academic year 2009-2010.

Principal: Raji Jayaprasad, Aditya Birla Public School, Kovaya

Head of Chemistry Department: Mr. B D Kotwani

Acknowledgement

I wish to express my deep gratitude and sincere thanks to Principal, Raji Jayaprasad, Aditya Birla Public School, Kovaya, for her encouragement and for all the facilities that she provided for this project work. I sincerely appreciate this magnanimity by taking me into her fold for which I shall remain indebted to her.

I extend my hearty thanks to Mr. B D Kotwani, Chemistry teacher, who guided me to the successful completion of this project. I take this opportunity to express my deep sense of gratitude for his invaluable guidance, constant encouragement, constructive comments, sympathetic attitude and immense motivation, which has sustained my efforts at all stages of this project work.

I can’t forget to offer my sincere thanks to my classmates who helped me to carry out this project work successfully and for their valuable advice and support, which I received from them time to time.

Rohit Gupta

Declaration

I do hereby declare that this project work has been originally carried out under the guidance and supervision of Mr. B D Kotwani, Head of Chemistry Department, Aditya Birla Public School, Kovaya.

Rohit Gupta

Experiment 1

Aim: To study the setting of mixtures of cement with lime, sand of different qualities, rice husk, fly ash, etc.

Requirements: Beakers, glass rod, weights, small wooden boxes or empty match boxes. Lime, pit sand, river sand, cement, fly ash, rice husk.

Introduction

Cement is essentially a finely ground mixture of calcium silicates (3CaO.SiO2) and aluminates (3CaO.Al2O3) which sets to a hard mass when treated with water. This property makes cement capable of joining rigid masses like bricks, stones, tiles etc. into coherent structures. The cements have the property of setting and hardening under water due to certain physicochemical processes and are, therefore, called hydraulic cements. During setting of cement, the physical changes taking place are gel formation and crystallization, and chemical changes are hydration and hydrolysis.

The process of solidification of cement paste involves:

1. Setting
2. Hardening

Setting is stiffening of the original plastic mass into initial gel formation. After setting, hardening starts due to gradual start of crystallization in the interior of the mass. The strength developed by cement at any time depends upon the amount of gel formed and the extent of crystallization. A mixture of cement, sand, small pieces of stone (gravel) and water is known as concrete and sets to an extremely hard structure.

When cement is used for construction purposes, it is always mixed with sand and little water to make a pasty material called mortar. Here cement or lime forms the binding material and the function of sand is to prevent shrinking and cracking and to increase the bulk, thereby reducing the cost of the mortar. When cement is used as the binding material it is called cement mortar and when lime is used as the binder it is called lime mortar. Sand in addition to its other functions also increases the adhesive qualities of the binding material.

Effect of Quality of Sand on Setting of Cement Mortar

Sand obtained from different sources has different qualities. For example, sea sand obtained from the sea contains some unwanted salts and retards the setting of cement, and is unsuitable for making mortar. On the other hand, pit sand obtained from pits in the soil and river sand obtained from river beds are considered excellent for preparing mortar and concrete.

Effect of Time on Setting of Cement Mortar

Time has an important role in the strength developed by cement mortar. When a cement-sand paste in the ratio 1:3 in water is allowed to dry, the strength of the solid mass keeps on increasing with increase in the time given for setting. It acquires nearly full strength in 28 days.

Procedure

1. Prepare the sets of mixtures of various compositions as given in the observation table.
2. Take each of the mixtures in different beakers and prepare their pastes by adding minimum quantity of water.
3. Take 10 empty match-box inner cases and mark them from 1 to 10.
4. Transfer the prepared pastes immediately into the match-boxes and compact them by pressing with hand.
5. Spray water from time to time over the pastes so that they are always moist.
6. Take out the slabs after three days and test for strength. Hold a weight of 10 g at a fixed height (say 50 cm above the ground) and drop the weight on the slab. See if the slab breaks or not. If it does not break, take 20 g weight and drop it from the same height. Keep on increasing the weight and note down the minimum weight required to break the slab.

Observations

Setting time allowed = 3 days

Sl. No.	Cement	River Sand	Pit Sand	Lime	Fly Ash	Rice Husk	Min. Weight to Break Slab
1	1	3	-	-	-	-	………… g
2	1	6	-	-	-	-	………… g
3	1	-	3	-	-	-	………… g
4	1	-	6	-	-	-	………… g
5	1	6	-	-	1	-	………… g
6	1	9	-	-	1	-	………… g
7	1	3	-	1	-	-	………… g
8	1	3	-	2	-	-	………… g
9	1	1	-	-	-	1	………… g
10	1	3	-	-	-	2	………… g

Experiment 2

Aim: To study the setting of mixtures of cement with sand, lime and fly ash with respect to time and strength.

Requirements: Beakers, glass rod, weights, small wooden boxes or empty match boxes. Lime, pit sand, river sand, cement, fly ash, rice husk.

Procedure

1. Prepare mixtures of the various compositions as given in the following observation table.
2. Take each of the mixtures in different beakers and prepare their pastes by adding minimum quantity of water.
3. Take 9 empty match-box inner cases and mark them from 1 to 9.
4. Fill three cases with paste of each composition.
5. Spray water from time to time over the pastes so that they remain moist all the time.
6. After three days take out one slab of each composition and test for their strength by the method described in the previous experiment.
7. Similarly, take out a set of three slabs after 7 days and then after 30 days and test for their strengths.

Observations

S. No.	Composition of Mixture	Min. Weight after 3 Days	Min. Weight after 7 Days	Min. Weight after 30 Days
1	Cement : River Sand (1:3)	………… gm	………… gm	………… gm
2	Cement : River Sand : Fly Ash (2:9:1)	………… gm	………… gm	………… gm
3	Cement : River Sand : Lime (1:3:1)	………… gm	………… gm	………… gm

Conclusions

The strength of the slab increases with increase in the setting time allowed.

Bibliography

1. Practical Manual
2. wikipedia.com
3. www.icbse.com