GURU NANAK DEV ENGINEERING COLLEGE, LUDHIANA Submitted to RESPECTED.C.S. SINGLA SIR (GNDEC) Submitted by Submitted by: Salman Khan Univ. Roll No

What is time of set or setting time of concrete? Time of set is defined as the point in the time at which penetration resistance reaches a specific values.

Initial and final setting time IS:4031-PART INITIAL SETTING is the time period between the time water is added To the cement and time at which 1mm square section needle fails to Penetrate the cement paste, placed in the vicat’s mould 5 to 7mm From the bottom of the mould. INITIAL SETTING TIME

FINAL SETTING TIME It is that time period between the time water is added to the cement and the time at which 1 mm needle makes an impressionon the paste in the mould but 5mm attachment does not make any impression

Why is the time of set significant? These are important because they give an indication of when the concrete can be properly placed, consolidated and finished.

What influences the time of set ? Initial and final time of set influenced by – 1.Cementitious material chemistry 2.Cementitious material fineness 3.Cementitious material content 4.Water ratio 5.Temperature 6.Admixture types 7.Fly ash and pozolan properties

Procedure- Test block preparation- 1.Before comencing the setting time test, do the consistency test to obtain the water required to give the paste normal consistency 2.Take 400g of cement and prepare a neat cement paste with 0.85P of water by weight of water 3.Gauge time is between 3 to 5 min. start the stop watch at the instant when the water is added to the cement and record the time. 4.Fill the vicat mould,resting on the glass plate, with the cement paste as gauged as above.fill the mould completely and smooth off the surface of the paste makiing it level with the top of the mould.the cement block thus prepared is called test block

Initial setting time - 1.Place the test block confined in the mould and resting on the non porous plate, under the rod bearing the needle. 2.Lower the needle gently until it come in contact with the surface of test block and quick release,allowing it to penetrate into the test block 3.In the beginning the needle completely pierce the test block. Repeat this procedure i.e. quickly releasing the needle after every 2 min till the needle fails to pierced the block for about 5 mm measured from the bottom of the mould.

Final setting time - 1.Replace the needle of the vicate’s apparatus by the needle with an annular attachment. 2.The cement is considered finally set when upon applying the final setting needle gently to the surface of the test block. The needle makes an impression there on, while the attachment fails to do so… notes the readings

11 WORKABILITY OF CONCRETE workability is an important property of concrete in its stage. workability in simple terms can be defined as “the ease with which the concrete can be mixed, transported, placed and compacted”. The workability of concrete has also been defined as the amount of work required to place concrete and to compact it thoroughly The workability is associated with the following four concepts: 1.Ease of flow (internal friction) 2.Prevention of segregation 3.Prevention of harshness 4.Prevention of bleeding PAGE=2

12 FACTORS AFFECTING WORKABILITY The factors which effect the workability of concrete are: 1. Water content 2. Size of aggregate 3. Shape of aggregate 4. Grading of aggregate 5. Porosity and absorption of aggregate 6. Admixtures 7. Mixing time 8. Temperature PAGE=11

Effect of time on workability When fresh concrete is laid at the site then proper curing of concrete is required, because structures are exposed to the environment and in these conditions if there is no such an arrangement against the environment, then there are many factors that affect the workability of concrete and temperature is One of them. Temperature, almost in every aspect has negative effects on the properties of concrete and same is the case with the workability of fresh concrete. When temperature increases, then in the same proportion workability of fresh concrete decreases. The reason that stands behind is “ when temperature increases then evaporation rate also increases due to that hydration rate decreases and hence, concrete will gain strength earlier “. Due to fast hydration of concrete, a hardening comes in concrete and that decreases the workability of fresh concrete. Therefore, In return manipulation of concrete become very difficult.

When temperature increases then fluid viscosity increases too and that phenomenon affects the flow ability of fresh concrete. Flow ability of concrete starts reducing and hence, as a result concrete workability decrease. And when workability of concrete decreases, then due to the less flow ability of a fluid, voids within the mass of concrete develops more. This is because deeper air voids in concrete only fill, if freshly mixed fluid has the ability to move deeper inside the small opening in the concrete. As in the present case due to higher temperature, viscosity of fluid increases and that viscous of fluid resists the movement of fluid. Now In case when empty voids left in the concrete, then number of weak points rise in concrete and that became the reason of a reduction in the strength of concrete. EFFECT ON FLOWABILITY OF CONCRETE

it indicates that the temperature has a negative effect on the workability of concrete as well as strength up to some extent. Temperature decreases the setting time by increasing hydration rate and that increase the early age strength of the concrete. This is an advantage that less time will be required before removing of form works on site, but this decrease the use of proper placement of concrete in the initial stages. And if concrete is not properly laid, then strength distribution will not remain the same throughout the cross-section. conclusion

With the passage of time after mixing ingredients of concrete with water, workability of concrete starts shrinking. This happens because of fluidity loss from the concrete. Fluidity is the amount of available water in concrete that is being utilized in hydration of cement compounds for the sake of bonding. When hydration of cement compounds C 3 S and C 3 A occurs than water within a concrete gets absorbed by these compounds and now the least amount of water will remain for workable concrete. If the temperature at the site varies, then some amount of water also lost due to evaporation Effect of time on workability

As the time further proceeds, loss in slump value of concrete becomes effective. Slump indicates how much concrete is workable? And hence slump value is almost directly related to the time passes. When time further proceeds slump loss will show almost linear behavior. Slump loss increases likewise with the increase of temperature and it also start reducing if increasing any ingredient in concrete more than the required amount. Generally with the increase in cement contents then, then there is a decrease in the required amount of water and hence again it effects workability of freshly laid concrete. If there is an extra addition i.e. Chemical admixtures that has some distinct functions. For example admixtures that are mostly used are set accelerators, set retarders, water reducing admixtures, etc. Then every isolated admixture has its own effect on the properties of concrete. Effect on slump

Workability of concrete is almost dependent on the amount extra available water in the concrete. For good workable concrete, calculate the concrete mix proportion and add that much amount of water in the concrete during batching. So that after every loss, there is still enough water available within concrete that will be enough for hydration and workability of concrete. So if the least amount of extra water is available, then in the same manner available mixing time will be less and vice versa. conclusion

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