Water Cement Ratio and workability
A cement of average composition requires about 25% water by mass for chemical composition. In addition, a quantity of water is required to fill the gel pores. About 100 years ago, Duff Abrams discovered a direct relationship between water-to-cement ratio and strength, that is, less water used more concrete strength, because too much water led to too many holes in the cement's past. Go. According to Aubram's law, the strength of a fully compacted concrete at a certain age and normal temperature is inversely proportional to water. Here the water-cement ratio is the relative weight of the cement water in the mixture. For most applications, the water-to-cement ratio should be between 0.4 to 0.5 for low permeability and high strength. In concrete, the trade-off is, of course, with practicality, as the very low water content results in very hard mixtures that are difficult to place. Water-to-cement ratio is a factor selected by the civil engineer.
workability
Practicality is one of the physical parameters of concrete that affects strength and durability as well as the cost of labor and the appearance of the finished product. Concrete is said to be practical when it is easily laid and compacted symmetrically i.e. without bleeding or separation. Concrete concrete for work requires more work or effort, finished concrete may also show hives and / or pockets. Stability of Functionality.
Factors affecting practicality:
The amount of water in the concrete mixture
• Quantity of cement and its properties
• Gross grading (size distribution)
• Concrete mixing temperature
• Environmental humidity
• Method of compaction
• Method of Concrete
• Method of transmission of concrete
How to improve the performance of concrete
• Increase water / cement ratio
• increase in overall size
• Use well-rounded and smooth aggregates instead of irregular shapes
• Increase mixing time
• Increase the mixing temperature
• Use non-porous and saturated aggregates
• With air-inlet mixture
Practicality test:
There are 4 types of tests for workability. They are slump test, compacting factor test, flow test and wave bee test
slump test
The slum test result is a deceleration of the behavior of an inverted cone of concrete under the action of gravity. It measures stability or wetness of concrete. The metal mold, in the shape of a cone frame, is open at both ends, and is provided with handles, the top inner diameter 4 in (102 mm), and the lower inner diameter 8 in. (203 mm) height 1. Ft (305 mm). Bullet nosed metal rod, 2 ft (610 mm) long, (16 mm) in diameter. Required Equipment: Compacting Factor Equipment, Travels, Graduated Cylinder, Balance and Temp Rod and Iron Bucket
The test is performed using what is known as a slope cone or abram cone. The cone is placed on a hard non-absorbent surface. This cone is filled with fresh concrete in three stages, each time it is tapped using a rod of standard dimensions. At the end of the third stage, the concrete is struck by a flush on top of the mold. The molice carefully lifted vertically upward, so as not to disturb the concrete cone. Solid subside. This subsection is called the slope, and is measured to the nearest 5 mm if the deceleration is <100 mm and to the nearest 10 mm when the deceleration occurs.
Molded concrete takes various shapes, and according to the profile of lumped concrete, deceleration is called true deceleration, shear deceleration or slope deceleration. If a shear or steep slope is obtained, a fresh sample should be taken and the test repeated. A collapse slope is an indication of very wet mixing. Only a true recession is of any use in testing. A sloping slope will usually mean that the mixture is too wet or is a high practicality mixture, for which the deceleration test is not appropriate. Very dry mixture; Deceleration 0 - 25 mm is used in road making, low practicality mixes; Dull 10 - 40 mm is used for mixing light reinforcement, medium working capacity; 50 - 90 vibration for normal reinforced concrete, paired with high practicality concrete; > 100 mm.
This test is usually performed in the laboratory and determines the workability of fresh concrete at a maximum of about 40 mm in size. The test is carried out according to the specification of IS: 1199-1959.
0 Comments