The following are the properties of concrete in its cured state, used by the designer during the reinforced concrete design process.

Table of Contents

## 1. Compressive strength

The characteristic strength is defined as the strength of concrete below which no more than 5% of the test results will fall. According to IS: 456 concrete mix always designed for the target strength calculated as,

target strength: **Strength properties + (1.65 x standard deviation)**

M20 is the minimum concrete grade for use in RCC work.

## 2. Tensile strength

Flexural strength is a measure of the tensile strength of concrete. In concrete structures, one set of visible cracks occurs under bending to calculate the load factor against cracks. According to IS: 456 the tensile strength of concrete can be calculated from the compressive strength using the empirical relationship given by:

bending strength: **f _{cream}=0.7**

**fck**N/mm

^{2}

## 3. Modulus Elasticity

Modulus of elasticity of concrete which is significantly affected by the following factors.

- Type of aggregates used,
- Type of cement and
- Mix proportions

This property is required for the calculations of deflections of structural concrete members that are an important limit state in the design of concrete members. In the absence of test data, the modulus of elasticity of concrete is normally related to the compressive strength and is calculated by the empirical relationship recommended by IS: 456-2000 code and is expressed as:

**E _{C}= 5000**

**fck**

where E_{C} is the short-term static modulus of elasticity of concrete expressed in N/mm^{2}

f_{ck} is the characteristic compressive strength of concrete expressed in N/mm^{2}.

## 4. Shrinkage of concrete

The ingredients of concrete and environmental factors such as temperature and humidity influence the total shrinkage of concrete. The water content in concrete has a major influence on shrinkage. The IS: 456-2000 recommends the total shrinkage stress as: **0.0003** in the absence of test data. Dry shrinkage in ordinary concrete can result in surface cracks. Concrete shrinkage also affects the deflections of reinforced concrete elements.

## 5. Creep of concrete

The inelastic time-varying stress that develops in a concrete ember under sustained load is called creep of concrete. Creep of concrete is affected by the following factors.

- cement content,
- W/C ratio,
- temperature and humidity,
- Size of structural element,
- Type of loading and period of loading.

In the absence of reliable experimental data, the creep coefficient is expressed as the ratio of ultimate creep strain/elastic strain at different loading ages, as recommended by IS: 456-2000 are given below.

Age at loading |
creep coefficient |

7 days | 2.2 |

28 days | 1.6 |

1 year | 1.1 |

Concrete creep has a significant influence on the deflections of reinforced concrete bending elements. Higher creep coefficient results in large deflections. The value of the creep coefficient is useful in the calculation of time-dependent deflections in reinforced concrete elements.

## 6. Expansion coefficient

The coefficient of thermal expansion of concrete, mainly influenced by the type of aggregate used in concrete, is required for the design of structures such as chimneys, water tanks, silos, etc. The values recommended in IS:456-2000 are compiled below.

Generator type |
Coefficient of Thermal Expansion for Concrete |

quartzite | 1.2 to 1.3 x 10^{-5} |

Sandstone | 0.9 to 1.2 x 10^{-5} |

Granite | 0.7 to 0.95 x 10^{-5} |

basalt | 0.8 to 0.95 x 10^{-5} |

Limestone | 0.6 to 0.9 x 10^{-5} |

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