Effects of too much water in concrete

If additional water is present in concrete mix, the concrete can be set easily but the strength & quality of the concrete is reduced significantly. Due to additional water, the damage to concrete structures occurs in the following was :-

1. Strength Reduction 2. Drying shrinkage 3. Loss of abrasive resistance 4. Rise in permeability 5. Dusting and scaling 6. Reduced durability

1. Strength Reduction: Compressive strength is a vital characteristic of solidified concrete and it is decreased due to redundant quantity of water in concrete. The additional water will not engage in the hydration process and contain in concrete even after being solidified.

When the water is vulnerable to atmosphere, it vaporizes and produces voids in the concrete and these voids will decrease the compressive strength of concrete.

2. Drying Shrinkage: If water-cement ratio is raised, the drying shrinkage is also raised and concrete become poor in tensile strength and consequently, cracks build up on the concrete surface.

3. Loss of Abrasive Resistance: Abrasive resistance of concrete is related to its strength directly. With the rise in additional water quantity in concrete, the strength of the concrete is reduced and as a result, the abrasive resistance is also decreased.

4. Permeability: The concrete gets permeable once the additional water in solidified concrete is evaporated. The voids created due to evaporation, will consume water and transform the concrete structure permeable.

5. Dusting: The additional water in concrete mix fetches the fine aggregate to the top, therefore, after getting solidified, a fine loose powder will be arranged on the top of the concrete surface. This method is known as dusting.

6. Scaling: Because of additional water content in concrete, scaling of concrete happens. Under this situation, the top layer of the solidified concrete surface is detached. It is caused by the reaction of water with freeze and thaw effects./p>

7. Reduced durability: The above-explained effects finally result in decreasing the stability of concrete. So, it is necessary to maintain the exact water cement ration for the development of long-lasting concrete. Low water-cement ratio facilitates to produce more long-lasting concrete. By including air entraining admixtures, the longevity is enhanced with low water content.



Read more
~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~

Details about bond failure in reinforced concrete beams

To operate as reinforced concrete member, the strain of steel should be equivalent as that of concrete; with the existence of any slip, the composite action of concrete and steel will become invalid. Reinforcing bars in concrete beams undergo two types of failure under bond stress like Direct pullout and Splitting.

Direct pullout failure:

This type of failure happens to those beams where there is adequate confinement in adjacent concrete for reinforcing bars. Direct pullout failure occurs under the following conditions :-

• Considerably small diameter of bars
• Adequate confinement with large concrete cover

Confined bars in adjacent concrete, when exposed to tensile force, adhesive bond other than friction among two materials turns out to be mobilized. When both obstructions are suppressed, adjacent concrete is crushed ultimately prior to deformations on the bar surface and this local crushing leads to detachment of bars.

Adjacent concrete, except for that has been crushed prior to ribs just nearby interface of bars, persists intact. For deformed bars, mechanical interlock with adjoining concrete arranged by deformations is more crucial as compared to adhesive force and friction.

Splitting failure: Under this type of failure, concrete is broken along specific length of bars. When a beam or any flexure member deflects, a wedging action is formed owning to deformation of bars that results in generating lateral tension on concrete. This failure becomes evident when bar spacing, concrete cover or confinement is inadequate.

Splitting type failure of concrete beam is mostly found in general as compared to bond failure because of splitting. As a result of wedging action, ribs on bars tolerate against surrounding concrete.
Splitting happens in two directions. It may form in vertical plane or developed horizontally along the plane of reinforcing bars. Horizontal splitting is found extensively at a diagonal crack. Dowel action often enhances the possibility of splitting.

Hence, shear failure (diagonal cracking) and bond failures are interconnected but this relation is very complicated to explain.

To get more detail, go through the following link civil-engg-world.blogspot.com



~~~~~~~~~~~~~~~~~~~~~~~~
Published By
Rajib Dey
www.constructioncost.co
~~~~~~~~~~~~~~~~~~~~~~~~