Cube Casting III Year

Segregation refers to the separation of the coarse aggregate from the mortar in concrete. This occurs when the concrete mix is not properly proportioned or when excessive water is added, causing the heavier aggregate particles to settle and separate from the mortar. Segregation can lead to a non-uniform distribution of aggregates, affecting the strength and durability of the concrete. Compaction, on the other hand, refers to the process of reducing the volume of air voids in the concrete mix to increase its density. Bleeding is the process in which water rises to the surface of freshly placed concrete.

Bleeding of concrete refers to the excess water rising to the surface of freshly placed concrete. This can occur due to two reasons mentioned in the answer: 1) excess of water, which means that too much water was added during the mixing process, and 2) too much finishing, which means that excessive troweling or smoothing of the concrete surface was done. The third option, coarse aggregates, is not a cause of bleeding as it refers to the size of the particles used in the concrete mixture. Therefore, the correct answer is 1 and 2 only.

According to IS 456:2000, the minimum slab thickness is 15mm. This means that any slab constructed must have a minimum thickness of 15mm to meet the standards set by the Indian Standard code for reinforced concrete design.

Segregation, which is the separation of coarse and fine particles in a mixture, can be prevented by properly grading the aggregate. This means ensuring that the different sizes of particles are distributed evenly. Controlling water content in a mix is also important as excessive water can cause the finer particles to separate from the coarser ones. Finally, using correct handling procedures, such as avoiding excessive dropping or sliding of the mixture, can also help prevent segregation. Therefore, all of the above options are correct ways to prevent segregation.

All the given options - controlling water content, using finely ground cement, and controlling compaction - can contribute to preventing bleeding in concrete. Controlling water content helps in achieving the desired consistency and reduces the risk of excessive bleeding. Using finely ground cement improves the particle packing and reduces water demand, which can also help in preventing bleeding. Controlling compaction ensures that the concrete is properly consolidated, reducing the chances of bleeding. Therefore, all the above options can play a role in preventing bleeding in concrete.

Workability refers to the ability of concrete to be easily mixed, placed, and compacted without any segregation. It is a measure of how easily the concrete can be worked with and manipulated. A concrete mix with good workability allows for proper placement and compaction, ensuring uniformity and strength in the final product. Bleeding refers to the separation of water from the concrete mix, while segregation refers to the separation of coarse aggregates from the mix. Therefore, the correct answer is workability.

Concrete is a material that continues to gain strength and durability over time. As it cures, the chemical reactions within the concrete cause it to harden and become stronger. This process, known as hydration, can continue for several years, resulting in concrete that is stronger and more resistant to damage as it ages. Therefore, the statement "Concrete grows with age" is true.

Increasing the depth of a slab helps to reduce shear stress because a deeper slab provides more resistance to shear forces. As the depth increases, the lever arm for the shear force also increases, resulting in a higher resisting moment. This increased resisting moment helps to distribute the shear stress over a larger area, reducing the overall shear stress in the slab. Therefore, increasing the depth is an effective way to reduce shear stress in a slab.

According to IS: 4561978, the column or the strut is the member whose effective length is greater than 3 times the least lateral dimension. This means that the effective length of a column or strut should be at least 3 times its smallest lateral dimension. This requirement is specified to ensure the stability and strength of the column or strut, as a longer effective length can lead to increased buckling or bending moments. Therefore, the answer "3 times the least lateral dimension" is the correct choice according to the given standard.

The correct answer is 4%. Bulking of sand refers to the increase in volume of sand when it is moistened. As the moisture content increases, the surface tension between the sand particles decreases, causing them to separate and occupy more space. However, there is a limit to this bulking effect. When the moisture content exceeds a certain point, the sand particles become too saturated and the bulking effect decreases. Therefore, the maximum bulking of sand occurs at a moisture content of around 4%.

Bleeding refers to the process of separation of cement paste from sand in the mortar, causing the water or cement paste to rise and appear on the surface. This occurs due to the settlement of solid particles in the mixture, leading to the upward movement of water. Bleeding can negatively affect the quality and strength of the concrete, as it can result in an uneven distribution of cement paste and reduce the bond between the concrete and reinforcement.

The correct answer is "Provided more on front face than on inner face". The reason for this is that the front face of the retaining wall is more exposed to external heat sources, such as sunlight, compared to the inner face. Therefore, the temperature reinforcement needs to be increased on the front face to compensate for the higher temperature gradient and prevent cracking or other thermal-related issues.

Concrete in a structural member goes through both the plastic stage and the hardened stage. In the plastic stage, the concrete is still malleable and can be molded into shape. It is during this stage that the concrete is poured and compacted into the formwork. Once the concrete starts to harden, it enters the hardened stage where it gains strength and becomes rigid. Both stages are crucial for the proper development and performance of the structural member.

Sand in mortar is needed for decreasing the quantity of cement, reducing shrinkage, and decreasing the surface area of the binding material. By adding sand to the mortar mixture, the amount of cement required can be reduced while still maintaining the desired strength. Sand also helps to reduce shrinkage by providing a filler material that can accommodate the drying and curing process of the mortar. Additionally, sand helps to decrease the surface area of the binding material, which can improve the workability and cohesion of the mortar mixture. Therefore, statements 1, 2, and 3 are correct.

The diagonal tension in a beam increases below the neutral axis because the beam is subjected to compressive forces in this region, which causes the tension to increase. On the other hand, the diagonal tension decreases above the neutral axis because the beam is subjected to tensile forces in this region, which causes the tension to decrease. This pattern of tension distribution is due to the bending moment acting on the beam, which causes varying stress and strain along its cross-section.