Question

I mention everything in detail (Concrete mix design)

INTRODUCTION TO REINFORCED CONCRETE

Answer 1

Introduction to Reinforced Concrete

• It is the concrete with reinforcement embeded in it. As we kmow, concrete is strong in compression and weak in tension. The embeded reinforcement makes it capable of resisting tension also.
• Steel bars embeded in the tension zone of concrete., relieves concrete of any tension and takes all tension without sperating from concrete.
• The bond between steel and concrete ensures strain compactibility i.e. strain in any point of steel is equal to strain in adjoining concrete.
• Reinforcing bar imparts ductility to concrete which is other wise brittle material.
• Here ductility means large deflection owing to yeildingof steel, there by giving ample warning of collapse.
• Tensile stresses arises due to direct tension, flexural tension, diagonal tension (due to shear), temprature and shrinkage effect, restraint to deformation.

Concrete Mix Design.

• The most common method used for concrete mix design is established by ACI.
• Design of concrete mix involves economic selection of relative properties various ingredients in concrete.
• Apart from meeting criteria for characteristic strength, the concrete must be workable in fresh state and impermeable and durable in hardened state.
• Following steps are used for mix design.

1. Determine the job parameters. :- Aggregate properties, maximum aggregate size, slump, water-cement ratio (w/c ration), admixtures, etc.
2. Calculation of batch weight.
3. adjustments to batch weights based on trial mix.

Basic considerations duering mix design.

• Water-Cement Ratio: Strength of concrete at given age is depends on w/c ratio. The lower water cement ratio higher is the strength.
• Strenght and Durability : Minimum compressive strength and range of w/c ratio are mentioned for given mix design. Also, possible chemical and termite attack attack must be considered during mix design.
• Economy : The material cost is most important in determining the relative costs of different mixes. Since cement is more expensive than aggegate, it is important to minimize cement content in mix. ( can be achived by low slump, using admixtures)
• Workability: A good mix design must be capable of being placed and compacted, with minimum bleed and segregation and be easily workable or handled. can be improved by adjusting water content.
• Maximum aggregate size : Maximum sixe should not be larger than,

A) 1/5 the minimum dimensions of structural members.

B) 1/3 the thockness of slab.

C) 3/4 clear distance between reinforcing bars and forms.

This limits maximum aggregate size to 1.5 inches except in mass concrete applications.

• Cement Content : Once watercontent and water cement ratio determined, then the amount of cement content per unit volume of the concrete is found by dividing the estimated water content by w/c ration.

  

Here, minimum cement content is required to ensure strength and workability.