Some vital short notes for civil engineering students

Least Cover for several RCC members

Slab = 20 mm
Beam = 25 mm 
Column = 40 mm
Footing = 50 mm

Exact unit weight of steel

The unit weight concerning steel should be 78.5 KN/m3

Proportion of cement, sand and aggregate for different types of concrete mix grades

M10 = 1:3:6
M15 = 1:2:4
M20 = 1:1.5:3
M25 = 1:1:2
M30 = 1:1:1

Exact unit weight of concrete

It is based on the type of aggregates as well as the amount of voids. With adherence to IS : 456-2000, the unit weight of PCC is 24KN/m3 and RCC is 25KN/m3.

Crank Length In Slab

The crank length should be 0.42D. Here, D denotes depth of slab. It is obtained by deducting bottom cover from top cover i.e. Top Cover – Bottom Cover.

Initial & final setting time of standard cement mix

Initial setting time for standard cement mix should remain approx 30 minutes for different types of cements. For masonry cement it should be 90 minutes. Final setting time of standard cement mix should be 10 hours maximum. For masonry cement, it should not go beyond 24 hours.

Compressive Strength Of Brick

For first class brick, the strength should be 105 kg/cm2
For second class brick, the strength should be 70 kg/cm2
For fire brick, the strength should be 125 kg/cm2

The weight of steel bar in reinforcement

The weight of bar should be kg/m = D2/162.2, here dia means diameter of bar in mm.

Steps for design mix concrete according to IS10262

Target denotes strength fm = fck+1.65 σ, σ = standard deviation
Grade of concrete = N/mm2
Standard deviation for M10, M15 = 3.5
Standard deviation for M20, M25 = 4
Standard deviation for M30 to M50 = 5

Strength of concrete

Flexural strength of concrete (modulus of rupture) fcr = .7√fck

Split tensile strength of concrete (fct) fct = 66fcr

Minimum size of column footing

Minimum size of footing for 9” x 9” column should not be under 1.5 x 1.5 feet

Minimum size of footing for 1’ x 1’ RCC column should not be under 2’ x 2’

Standard Height Of Building Floor

The height should be 11 feet but should not be under 10 feet.

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Published By

Rajib Dey

www.constructioncost.co

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Benefits of compressive strength of concrete & factors impacting compressive strength

Concrete becomes leading usable material as soon as water is added to it. The strength of concrete is mainly dependent on aggregates, while cement and sand are responsible for the characteristic of binding and workability together with flowability to concrete.

Compressive strength means the capability of the material or structure to provide resistance against compression. The Compressive strength of a material is based on the capability of the material to withstand failure that appears as cracks and fissure.

With compressive test, the push force enforced on the both faces of concrete specimen and the maximum compression borne by concrete devoid of failure is recorded.

The purpose of concrete testing is to deal with the Compressive strength of concrete as it facilitates to measure the concrete strength to protect gainst Compressive stresses among structures while other stresses like axial stresses and tensile stresses are developed with reinforcement and other means.

In technical term, Compressive Strength of concrete is explained as the Characteristic strength of 150mm size concrete cubes @28 days.

Compressive strength of Concrete and its advantages:-

Concrete is formed by mixing sand, cement, and aggregate. The strength of the concrete is based on several factors which range from individual compressive strength of its materials (Cement, Sand, aggregate), quality of materials applied, air entrainment mix proportions, water-cement ratio, curing methods and temperature effects.

With Compressive strength, the entire strength of the concrete as well as information on the above mentioned factors can be obtained. By initiating this test, it is possible to analyze the concrete strength psi and quality of concrete formed.

The compressive strength of concrete is influenced by the factors given below:-

Coarse aggregate: Concrete becomes uniform by blending aggregates, cement, sand, water and different other admixtures. In spite of perfect mixing, some micro cracks may occur because of variations in thermal and mechanical properties of coarse aggregates and cement matrix, which results in collapsing of concrete structures.

In concrete, the size of aggregate is a key factor for compressive strength. When the size of aggregate is raised, then the compressive strength will also be increased.

But later on, it is discovered that bigger size of aggregates can raise strength in preliminary stage but the strength is decreased greatly. It happens because of the abridged surface area for bond strength among cement matrix and aggregates and lower transition zone.

Air-entrainment: Air entrainment in concrete is a useful feature to avoid damages because of freezing and thawing. Later on, multidimensional benefits of air entrainment lead to improve the workability of concrete at lower water/cement ratio.

When the required workability is attained at lower water content, the concrete contains superior compressive strength which consecutively results in creating light concrete with superior compressive strength.

Water/Cement ratio: Excessive water is injurious to the strength of concrete. Cement is considered as the major binding material in concrete that requires water for hydration process, but the water quantity is constrained to about (0.20 to 0.25) % of cement content. The excess water is useful in case of workability and finishing of concrete.

When the water in the concrete matrix gets dried, it departs large interstitial spaces between aggregate and cement grains. This interstitial space in turn creates primary cracks throughout compressive strength testing of concrete.

Go through the following article, to get more details civilread.com



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Published By
Rajib Dey
www.constructioncost.co
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Definition and categorisation of Pre-Stressed Concrete

Normal concrete structure contains greater compressive strength and very weak tension strength. For the purpose of removing the weakness of concrete in tension, pre-tensioning method is applied. Pre-stressed concrete belongs to the autonomous formation of permanent compressive stresses in a structure to enhance its behavior and strength toward different service situations.

Categorization of Pre-stressed concrete

Pre stressed concrete structure is categorized on the basis of their features of design and construction. The are categorized into the following three groups.

1. Location of construction
2. Level of construction
3. Method of pre-stressing

LOCATION OF CONSTRUCTION
Here, the pre-stressed structure may come as precast cast, cast in situ, composite constrictions.

PRE CAST
Precast pre-stressed components are fabricated in a plant or adjacent to the working site. Then they are conveyed to construction site and then they are constructed and set to its position.

CAST IN SITU
The cast-in-situ concrete is standard concrete that is poured into the exact formwork on the site and cured to attain the strength of RCC elements. So, the transportation and erection process are not necessary in this method.

COMPOSITE CONSTRUCTION
Composite construction is done by integrating both prestressed and cast in situ methods. As for instance, in a beam in a building structure is built up by pre-stressed concrete and the top roof slab is built up by the cast in situ method.

LEVEL OF PRE-STRESSING
Level of pre-stressing is categorized as completely pre-stressed, limited pre-stressed, partially pre-stressed.

FULLY PRE-STRESSED
In fully pre-stressed concrete members, there is not any tensile stress under the operation of working or service loads.

LIMITED PRE-STRESS
Members are pre-stressed to a limited extent in order that members may create some tensile stress under working loads but the magnitude is below the tensile strength of concrete. These members function as a completely pre-stressed member and remain uncracked under working loads.

PARTIALLY PRE-STRESSED
Partially pre-stressed structure contains both pre-stressing steel and reinforcing steel to withstand working load.

Partial pre-stressing is useful for both pre-stressed concrete and reinforced concrete. The tensile stress remains within the limit.

To get more detail, go through the following link learntocivilfield.com



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Published By
Rajib Dey
www.constructioncost.co
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