What Is Bleeding And Segregation In Concrete?
What Is Bleeding And Segregation In Concrete?
Bleeding and segregation in concrete are issues that arise due to the inconsistency of water content in mixed concrete.
Bleeding occurs when the top layer of concrete loses excess water during the curing process, which causes a reduction of cohesion between particles and increases porosity.
Segregation is caused by improper mixing, resulting in uneven distribution of cement, aggregates, and water throughout a batch or pour.
It leads to weaker points or voids that can compromise the strength and integrity of the structure.
Bleeding and segregation in concrete are two common issues which may occur when concrete is poured or placed into forms.
Bleeding occurs when excess water rises to the surface of freshly placed concrete due to separation of the mix ingredients. This process can reduce the strength of the finished product and result in other detrimental effects.
Segregation occurs when heavier materials such as sand, aggregate and cement separate from each other due to excessive slump (workability) causing a reduction in quality.
Both bleeding and segregation can be avoided by controlling the amount of water used during mixing, increasing the slump of fresh concrete and properly compaction during placement.
What Are The Effects Of Segregation In Concrete?
Segregation in concrete occurs when the components of concrete, such as coarse aggregate, sand, and cement are not uniformly blended or thoroughly mixed during the batching process.
It can cause a decrease in compressive strength because it affects the quality of bond between the cement paste and aggregate.
Moreover, segregation can also lead to an uneven distribution of load on the structure leading to possible damage or failure.
Poor mix consistency due to segregation can result in honeycomb formation and voids in the concrete, making it more susceptible to water infiltration which in turn may trigger corrosion of steel reinforcement and other damage over time.
Additionally, segregation can reduce workability, resulting in a reduction of both air entrainment and homogeneity necessary for good consolidation.
Thus, segregation has a detrimental effect on the performance of concrete both structurally and durability-wise.
How Can We Prevent Bleeding And Segregation In Concrete?
To prevent concrete segregation, it is important to add admixtures, air entraining agents and supplementary cementitious materials to the mix.
Furthermore, it is recommended to pour the concrete using a chute or boom placer rather than dropping it from a height of more than 1.5 meters.
When using a chute, the angle of inclination should be between 1:3 and 1:2 so that the concrete flows smoothly from the top to bottom; adding a small amount of free water at intervals can also help lubricate this path.
Proportioning the mix correctly and using an appropriate diameter needle for vibration are additional ways to reduce segregation.
What Is The Relation Between Cohesiveness And Segregation In Concrete?
Cohesiveness and segregation in concrete are two terms used to describe how the mixture of concrete components interact with each other.
Cohesiveness refers to the way all the particles in the concrete stick together; this is usually due to the presence of cement, which acts as a glue, binding all parts of the mix.
Segregation occurs when there are differences in particle size, composition or density between various parts of the mix.
This often leads to cracking and reduced durability of concrete structures. Good cohesiveness ensures that concrete is durable while excessive segregation can lead to lower strength and greater porosity.
It is therefore important that measures are taken to ensure good cohesiveness and minimal segregation when mixing and placing concrete.
What Are The Types Of Segregation In Concrete?
Segregation in concrete is the separation of aggregates and the cement paste. This can be caused by improper batching, inadequate mixing, insufficient vibration, or improper curing.
There are three main types of segregation: mortar drop out, sand streaks, and honeycombing.
- Mortar drop out occurs when there is excessive water in the mix, causing the heavier cement particles to settle down while leaving the lighter aggregate particles above them. This can create an uneven surface texture on the hardened concrete.
- Sand streaks appear when larger pieces of aggregate are not distributed evenly throughout the mix and cause a ‘streaking effect’ on its surface due to their presence in certain parts of the mix over others.
- Honeycombing is created by large voids occurring in between surrounding particles that become exposed on the hardened surface.
All these issues are avoidable if concrete is mixed properly with adequate water content at a consistent speed for a uniform blend.
How Is Segregation Treated In Concrete?
Segregation in concrete is treated mainly through careful mixture of the ingredients. The mixture needs to be carefully balanced so that a smaller ratio of cement compared to other materials such as fine aggregate, coarse aggregate and water can help form a homogeneous mix that will be durable over time.
It is also important to use a vibrator at various stages of pouring and curing so that the concrete can reach its maximum density, eliminating unwanted gaps or voids and preventing segregation.
Additionally, proper consolidation techniques need to be employed when placing and finishing the concrete, which will help eliminate air pockets trapped inside the mix as well as boost strength characteristics.
Segregation should also be avoided by avoiding excessively dry or wet mixtures with excessive water-cement ratios should generally be avoided.
