Normal Consistency Of Cement 3hw5n

Normal Consistency of Cement The standard consistency is that consistency, which will permit the Vicat plunger to penetrate to a point 5 to 7mm from the bottom of the Vicat mould when tested. VICAT APPARATUS The vicat apparatus consists of a frame having a movable rod with a cap at one end and at the other end any one of the following attachment, which are interchangeable. i) Needle for determining the initial setting time ii) Needle for determining the final setting time iii) Plunger for determining the standard consistency The Vicat frame consists essentially of a metal stand with a sliding rod. An adjustable indicator moves over a graduated scale. The needle or plunger is attached to the bottom end of the rod to make up the test weight of 300 g. The frame 63-L0028/1 is supplied without accessories, which have to be ordered separately depending on the requirement. It is also proposed with basic EN accessories (63-L028) or ASTM/AASHTO accessories (63-L0028/A). Weight approx.: 4 kg This test helps to determine water content for other tests like initial and final setting time, soundness & compressive strength. NAME OF TEST

AMOUNT OF WATER REQUIRED

Soundness (Le-chatelier method) cement paste)

0.78 P (P=Consistency of standard

Setting time cement paste)

0.85 P (P=Consistency of standard

Compressive strength

cement consistency of combined mass of cement and sand.

Consistency refers to the relative mobility of a freshly mixed cement paste or mortar or its ability to flow. The thickness or the viscosity of the cement paste is called consistency. For a mortar the standard consistency is measured by flow table test. It is the amount of water needed to prepare a plastic mix. It is the thickness or the viscosity of the standard paste and is expressed as the percentage of weight of water.

Generally the normal consistency for OPC ranges from 26 to 33% but is generally less than 30% Consistency test is used to find the amount of water to be mixed with cement. It is necessary to find the consistency because amount of water present in the cement paste may affect the setting time.standard consistency is indicated by the vicat plunger reading (5 to 7) from the bottom of mould. To determine initial and final setting time, the amount of water needed to make standard paste is required. So the significance of consistency test comes into play as it helps to determine the amount of water used to make standard paste. Cement consistency also affects workability of concrete (slump) and the workability of cement is affected by cement paste. Also strength of cement classes (32.5/42.5/52.5) and other properties of cement are measured at specified consistency rather than at specified watercement ratio. Factors affecting consistency of cement 1. Fineness of cement 2. Temperature 3. Method of mixing water 4. % of ixtures in cement (flyash in case of PPC) 5. Water - cement ratio Cement Paste The viscous mass obtained by mixing cement with water is known as cement paste. Standard Cement Paste. It is the cement paste for which the 10mm diameter plunger in a standard VICAT test penetrates to such an extent that its distance from the bottom is 5-7mm. Workability It is one of the physical parameters of concrete which affects the strength and durability as well as the cost of labor and appearance of the finished product. Concrete is said to be workable when it is easily placed and compacted homogeneously i.e without bleeding or Segregation. Unworkable concrete needs more work or effort to be compacted in place, also honeycombs &/or pockets may also be visible in finished concrete. Definition of Workability

The property of fresh concrete which is indicated by the amount of useful internal work required to fully compact the concrete without bleeding or segregation in the finished product.

Factors affecting workability:         

Water content in the concrete mix Amount of cement & its Properties Aggregate Grading (Size Distribution) Nature of Aggregate Particles (Shape, Surface Texture, Porosity etc.) Temperature of the concrete mix Humidity of the environment Mode of compaction Method of placement of concrete Method of transmission of concrete

How To improve the workability of concrete       

Increase water/cement ratio Increase size of aggregate Use well-rounded and smooth aggregate instead of irregular shape Increase the mixing time Increase the mixing temperature Use non-porous and saturated aggregate With addition of air-entraining mixtures

Sources: http://civilblog.org/2013/05/04/consistency-of-standard-cement-paste-is4031-part4-1988/ http://www.aboutcivil.org/concrete-workability-factors.html http://civilengineerspk.com/plain-reinforced-concrete-experiments/exp-1consistency-of-cement/

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1. Take 400 g of cement and place it in the enameled tray. 2. Mix about 25% water by weight of dry cement thoroughly to get a cement paste. Total time taken to obtain thoroughly mixed water cement paste i.e. “Gauging time” should not be more than 3 to 5 minutes. 3. Fill the vicat mould, resting upon a glass plate, with this cement paste. 4. After filling the mould completely, smoothen the surface of the paste, making it level with top of the mould. 5. Place the whole assembly(i.e. mould + cement paste + glass plate) under the rod bearing plunger.

6. Lower the plunger gently so as to touch the surface of the test block and quickly release the plunger allowing it to sink into the paste. 7. Measure the depth of penetration and record it.