Various Factors Affect workability cement concrete
Workability of concrete:-
The term workability indicated the ease or difficulty with which the concrete is handled, transported and place. The amount of water present in the concrete should be in the proper ratio. If water is much more than required, it will result in a non-uniform composition of concrete. If water is less than required it will result in difficulty to handle and place it in the position. The concrete should enable to be fully compacted with given efforts at the site.
Generally, a higher water-cement ratio is required for good workability. IN actual, function of water is to lubricate the concrete. The concrete which is easy for handling and placing is a workable concrete. The lubricant should be in such a manner so it produces concrete without aggregation, without loss of homogeneity and to finish it sufficiently easily.
The water should be added to applicable to appreciable quantity. If more water is added it will result in the concrete of low strength and poor durability and quality. The workability of concrete is affected by concrete is also affected by the shape, grading, texture and maximum size of the coarse aggregate.
There are many tests to measure the workability of the concrete mixture. The tests such as flow test, compacting test and slump test are done to determine the workability of the concrete mixture.
Various Factors Affect workability cement concrete
- Influence of mix proportions
- Influence of aggregate properties
- Influence of admixtures
- Effect Of Environmental conditions
- Effect Of Time
Influence of mix proportion
The maximum area in concrete is covered by aggregate, so as well graded aggregates with different size fractions should be chosen to minimize the void contents. An increase of water content results in an increase in workability but segregation and bleeding occur due to excess amount of water. The water content is limited to some maximum value given by the water-cement ratio. The proportion of coarse aggregate, fine aggregates, cement, and water should be as per design requirements.Influence of aggregate properties
For the same value of aggregate in concrete, the use of a coarse aggregate of large size or rounded aggregates gives the higher workability. The use of angular, elongated or flaky aggregates results into two workabilities. For the same water content, the use of finer aggregated decreases the workability. The grading of fine aggregate is more critical than the grading of coarse aggregate due to greate contribution to the total specific surface area. An unsuitable choice of overall grading can produce honeycombing or segregation. Generally, the mixes with higher water-cement ratio would require finer grading can for mixes with the low water-cement ratio a coarser grading is preferable. The workability is aslo affected by the physical and chemical properties of cement but to a much lesser than that the aggregate properties.
Influence of admixtures
Use of air-entraining agents which are normally surface-active reduces the internal friction between the particles. The air bubbles may be considered as an artificial fine aggregate of a very smooth surface. Similarly, The fine glassy pozzolanic materials, in spite of increasing the surface area, offer better lubricating effects for giving better workability.
Effect Of Environmental Conditions-
The workability of a concrete mix is also affected by the temperature of concrete and, therefore, by the ambient temperature. On a hot day, it becomes necessary to increase the water content of the concrete mix in order to maintain the desired workability. The amount of mixing water required to bring about a certain change in workability also increases with temperature.
Effect of time
The fresh concrete losses workability with time mainly because of the loss of moisture due to evaporation. A part of mixing water is absorbed by aggregate or lost by evaporation in the presence of sun and wind and part of it is utilized in the chemical reaction of hydration of cement.The loss of workability varies with the type of cement, the concrete mix proportions, the initial workability in terms of compacting factor decrease by about 0.10 during the period of one hour from the time of mixing. The decreases in workability with time after mixing may be more pronounced in concrete with admixtures like plasticizers.
