Basic civil engineering part 14

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What are the causes of building collapse?

Answer 1
The Passage of time is one reason. Buildings also collapse due to weak foundations. Earthquakes, hurricanes and other natural disasters can also damage the structure of the buildings and cause it to collapse. Bombings or demolition of buildings is also other reasons.

Answer 2
Foundation weakness and nature of soil.

What are the applications of modulus of elasticity?

Answer #1
As the term implies, "Modulus of Elasticity” relates to the elasticity or "flexibility" of a material. The value of modulus of elasticity is very much significant relating to deflection of certain materials used in the construction industry. Take for example the general E value of mild carbon steel is about 200 GPA comPAred to about 70 GPA for aluminum. This simply translate that aluminum is 3 times flexible than steel.

Answer #2
It indicates that how a material will behave under the application of load. An elactic material has more tensile strength and it can be stretched to a greater extent like steel. So basically good to resist tension at the time of bending. To BUY Our Basic Civil Engineering DVD - PLEASE CALL US AT 70 92 89 89 88

What is the difference between absorption & adsorption and sorption?

Absorption generally refers to two phenomena, which are largely unrelated. In one case, it refers to when atoms, molecules, or ions enter some bulk phase - gas, liquid or solid material. For instance, a sponge absorbs water when it is dry.

Absorption also refers to the process by which the energy of a photon is taken up by another entity, for example, by an atom whose valence electrons make transition between two electronic energy levels. The photon is destroyed in the process. The absorbed energy may be re-emitted as radiant energy or transformed into heat energy. The absorption of light during wave proPAgation is often called attenuation. The tools of spectroscopy in chemistry are based on the absorption of photons by atoms and molecules.

Adsorption is similar, but refers to a surface rather than a volume: adsorption is a process that occurs when a gas or liquid solute accumulates on the surface of a solid or, more rarely, a liquid (adsorbent), forming a molecular or atomic film (the adsorb-ate). It is different from absorption, in which a substance diffuses into a liquid or solid to form a solution.To BUY Our Basic Civil Engineering DVD - PLEASE CALL US AT 70 92 89 89 88
How do you measure concrete?

Cubic feet, Cubic yards, Cubic Meter

 

What is the meaning of soil reinforcement?

Soil reinforcement is the act of improving soil strength to enable it support or carry more load.

Two common examples are:

a) Mixing a soil amendment such as lime into weak clayey soil and re-comPActing to improve soil-bearing capacity (often done under the road base in highway construction)

b) Installing plastic or composite webbing layers (called geo-grid material) alternating with compacted soil to produce a stronger sloped soil structure (often done on steep roadway embankments to improve strength and stability)

Types of admixtures used in concrete as per IS 9103

IS 9103 define the admixture as a material other than water, aggregates, and hydraulic cement and additives like pozzolana or slag and fibre reinforcement used as an  ingredient of concrete or mortar and added to the batch immediately before or during its mixing to modify one or more of the properties of concrete in the plastic or hardened state.

The different types of admixture covered in IS 9103 are as per following

Accelerating Admixtures:

These admixtures when added to concrete, mortar or grout increases the rate of hydration of hydraulic cement, shortens the time of set, accelerates the hardening or development of strength of concrete/ mortar. These admixtures function by interaction with C3S (Tri-calcium
silicate) component of the cement thus increasing the reaction between cement and water.

Retarding Admixtures:

This type of chemical admixtures decreases the initial rate of reaction between cement and water and thereby retards the setting of concrete. It functions by coating the surface of C3S (Tri calcium silicate) components, thus, delaying this reaction with the water. Reaction products are slow to form as such the setting and hardening of concrete are delayed reducing early compressive strengths. Since the rate of stiffening of concrete can be too fast in our tropical climatic conditions, sufficient time for the concrete is required for transportation and placement before setting. In such conditions retarding admixtures can be very useful. Retardation in setting time up to 8-10 hours is possible by suitable use of retarders. The delay in hardening caused by the retarders can be exploited to obtain an architectural finish of exposed aggregate: the retarder is applied to the interior surface of the formwork so that the hardening of the adjacent cement is delayed. This cement can be brushed off after the formwork has been struck so that an exposed aggregate surface is obtained.

Plasticizer (Water Reducer) Admixtures:

A material, which either increases workability of freshly mixed concrete without increasing water cement ratio or maintains workability with a reduced amount of water, is termed as water reducing admixture. As their name implies, the function of water reducing admixture is to reduce the water content of the mix, usually by 5 to 10%, sometimes (in concrete of very high workability) upto 15%. Thus, the purpose of using a water reducing admixture in a concrete mix is to allow a reduction in the water cement ratio while retaining the desired workability or, alternatively, to improve its workability at a given water cement ratio. The actual reduction in water depends on dose of admixtures, cement content, type of aggregate used, ratio of cement, fine and coarse aggregate etc. Therefore, the trial mixes containing an actual material to be used on the job are essential to achieve optimum properties.

Superplasticizer Admixtures:

At a given water /cement ratio and water content in the mix, the dispersing action of superplasticizer increases the workability of concrete, typically by raising the slump from 75mm to 200 mm, the mix remaining cohesive. The resulting concrete can be placed with little or no  compaction and is not subject to excessive bleeding or segregation.

Air Entraining Admixture:

This is an admixture for concrete or mortar which causes air to be incorporated in the form of minute bubbles in the concrete or mortar during mixing, usually to increase workability and resistance to freezing and thawing. Air entrained also breaks the continuity of capillaries.

The dosages required are between 0.005 to 0.05% by mass of concrete and it is advisable to mix it with batching water for uniform dispersion. As per department of Atomic Energy Practice, the air content is controlled between 3 to 6%. Method of measuring air content is given in IS 1190.

SLUMP TEST to determine WORKABILITY of concrete