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What should be the standard Roof height?
CB Sowmya
The ceiling height of residential buildings is generally 3 m. However, the minimum height requirements as per the National Building Code are as follows You can find more about it in this link below: https://theconstructor.org/building/rooms-minimum-height-size-standards/5116/ The ceiling heigRead more
The ceiling height of residential buildings is generally 3 m. However, the minimum height requirements as per the National Building Code are as follows
You can find more about it in this link below:
https://theconstructor.org/building/rooms-minimum-height-size-standards/5116/
The ceiling height of public and industrial buildings are larger than residential buildings, due to various reasons like the people traffic, ventilation purposes and for easy operation in case of industries.
The minimum height of public buildings and industrial buildings is 3.6m.
See lessWhat is Soundness Property of Cement?
CB Sowmya
The soundness of a material is the ability of the material to retain its volume after hardening without excess expansion. Now coming to the soundness of concrete, Concrete is made up of cement, aggregates, water and admixtures. Of this, only cement has expansive properties. Therefore soundness of coRead more
The soundness of a material is the ability of the material to retain its volume after hardening without excess expansion.
Now coming to the soundness of concrete,
Concrete is made up of cement, aggregates, water and admixtures. Of this, only cement has expansive properties.
Therefore soundness of concrete is can be related to the soundness of cement. This expansive behavior is caused due to excess lime in the cement. The excess lime CaO hydrates very slowly to form slaked lime. This slaked lime is higher in volume than the initial lime. This causes volume changes and results in high volume.
The same phenomenon can be observed in the cement having high traces of the magnesium oxide.
The excess volume may also be caused by the sulfate attack where the sulfate components in the cement react with the environment to produce calcium sulphoaluminate, which is very high in volume.
The soundness of the cement can be improved if the above-mentioned mishaps are avoided. Soundness can be found using Le – Chatelier’s apparatus, where we subject the cement to an environment that challenges the soundness of the cement. A cement of 10 mm or less expansion is accepted.
The Soundness test by Le- Chatelier’s apparatus is explained in detail here TheConstructor.org
See lessWhat is the reason for micro cracks in concrete?
CB Sowmya
The reason why micro-cracks occur in concrete even before loading is because of the Interfacial Transition Zone. The interfacial transition zone is the weakest link in the concrete. It is caused by the formation of a water film around the aggregate surface. When concrete is mixed, the water forms aRead more
The reason why micro-cracks occur in concrete even before loading is because of the Interfacial Transition Zone.
The interfacial transition zone is the weakest link in the concrete. It is caused by the formation of a water film around the aggregate surface. When concrete is mixed, the water forms a film around the aggregate, and as a result, the water-cement ratio near that aggregate increases. A high water-cement ratio means less strength.
This water film hinders the hydration reaction and results in a porous network of hydrated products. This porous network is much weaker than the bulk mortar. Therefore, even small changes in temperature cause differential movement of the material in the concrete. Differential movement occurs due to the difference in the porosity of the hydrated products.
As a result, the micro-cracks are formed. They are formed even without the application of loads.
Thanks
See lessWhat is meant by Theoretical Thickness in Concrete?
CB Sowmya
Theoretical thickness = (C/S Area of the section ) / (Semi perimeter in contact with the atmosphere.) Where, semi perimeter = perimeter /2 For example, Consider a 150 mm side cube, and assume these three sides are exposed to the atmosphere Then, Thus the theoretical thickness for the given cube andRead more
Theoretical thickness = (C/S Area of the section ) / (Semi perimeter in contact with the atmosphere.)
Where, semi perimeter = perimeter /2
For example, Consider a 150 mm side cube, and assume these three sides are exposed to the atmosphere
Then,
Thus the theoretical thickness for the given cube and given exposure conditions is 100 mm.
Where is it used?
Theoretical thickness is generally used in the study of creep or drying shrinkage of a structure. During dry shrinkage, the water is expelled outside of the concrete. As a result, the water travels a path. This path is expressed in terms of theoretical thickness.
See lessWhat is the difference between fe 500 and fe 500D rebars?
CB Sowmya
Both Fe 500 and Fe 500D have the same yield strength. But, Fe 500D is more ductile than Fe 500. The 'D' in Fe 500D denotes Ductility. Ductility This ductile feature comes in as an advantage when the structure is subjected to sudden loads or vibration and makes them ideal for areas prone to earthquakRead more
Both Fe 500 and Fe 500D have the same yield strength. But, Fe 500D is more ductile than Fe 500. The ‘D’ in Fe 500D denotes Ductility.
Ductility
This ductile feature comes in as an advantage when the structure is subjected to sudden loads or vibration and makes them ideal for areas prone to earthquakes, cyclones, etc.
See lessWhy are 6 cubes cast for testing the Compressive Strength?
CB Sowmya
Generally, Three cubes are tested for seven days of strength. The cube should have achieved at least 70% of its strength on the 7th day. The other three cubes are tested for 28 days strength. The cube should have achieved at least 99% of its strength on the 28th day.
Generally,
Three cubes are tested for seven days of strength. The cube should have achieved at least 70% of its strength on the 7th day.
The other three cubes are tested for 28 days strength. The cube should have achieved at least 99% of its strength on the 28th day.
See lessWhat is meant by Dry Shrinkage?
CB Sowmya
Dry shrinkage or drying shrinkage occurs due to loss of moisture in the concrete. There are different types of water in a hydrated cement paste. Dry shrinkage occurs due to the loss of capillary water. This water can be found in voids of sizes ranging from 5 nm to 50 nm in the hydrated cement paste.Read more
Dry shrinkage or drying shrinkage occurs due to loss of moisture in the concrete. There are different types of water in a hydrated cement paste. Dry shrinkage occurs due to the loss of capillary water.
This water can be found in voids of sizes ranging from 5 nm to 50 nm in the hydrated cement paste. Due to the small size of the voids, the water is held inside by surface tension or capillary tension. Due to the bond created by the surface tension, evaporation, or any other form of removal of this water causes significant volume changes to the structure. This volume changes causes dry shrinkage to the structure.
Thanks!
See lessWhy is the characteristic compressive strength fck reduced to 0.67 fck?
CB Sowmya
The characteristic strength of concrete is the compressive strength below, in which not more than 5% of the test results should fall. It is generally represented as fck. But during analysis, we reduce the characteristic strength of concrete and include a factor of safety 0.67. As a result, fck becomRead more
The characteristic strength of concrete is the compressive strength below, in which not more than 5% of the test results should fall. It is generally represented as fck.
But during analysis, we reduce the characteristic strength of concrete and include a factor of safety 0.67. As a result, fck becomes 0.67fck.
In order to understand the reason, let us look into how concrete is tested for the characteristic strength in the first place.
A given concrete mix is prepared and cast into cube molds of side 150 mm. After sufficient curing, the cubes are tested for its compressive strength. In those test results, the compressive strength below which not more than 5% of the test results fell is taken as the characteristic strength. Let’s take that as fck.
If the same design mix was cast into a cylindrical mold of 150 mm diameter and 300 mm length and given the same curing, then it would have yielded only 80% of the compressive strength of that of the cubes, i.e., 0.8 fck. This because of the side effect due to the slenderness ratio in the cylinder.
There has been a 20% reduction in strength for a mere slenderness ratio, though both the specimens were monitored in the same laboratory conditions.
Answering your question, in reality, concrete is versatile. It can be cast into a number of shapes and sizes. In order to overcome the size effect on the concrete, in design, we assume that concrete can carry only 2/3rd of its characteristic strength. Thus we reduce fck to 0.67 fck.
Thank you!
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