Tuesday, August 30, 2011


Concrete is a rock like material, which is made by mixing cement, coarse aggregate and fine aggregate with water.

Thursday, August 18, 2011

Endogeneous or endogen timber

This kind of trees increase both longitudinally and diametrically.Its diameter increase by the addition of new fibre with the old. Endogens are mostly plants like paddy, sugarcane, jute etc.

Exogeneous or exogen timber

This kind of trees increase diametrically by annual formation of layer new wood between old wood and bark of the wood which consists all the living portion of the tree.

Types of Timber

Timber is of mainly two types.
1.Exogeneous or exogen
2.Endogeneous or endogen

Relation between water cement ratio to the strength of concrete

Water has three functions in concrete

1.Wets aggregate surface
2.Imparts workability
3.Binds aggregate with cement chemically by hydration

For a given degree of compaction with the increase
of percentage of water, percentage of hydration increases.
So sufficient amount of water is necessary for hydration as well
as for increase in strength.Water also imparts workability to
concrete.but excess water cause concrete to be porous.
Hence for a certain limit strength increase with the increase of
water cement ratio.But after that strength decreases with the
increase of water cement ratio.

Why fineness of cement is necessary for rapid development of strength

The surface area of cement particles increases with the increase of fineness modulus. Hydration takes place on the surface area of cement particles.For rapid hydration surface area of cement particles should be high.Strength develops on the concrete as hydration takes place. This is why for rapid development of strength high fineness of cement is necessary.

Placing concrete underwater

Sometimes concrete needs to be placed underwater.In this case bottom dump bucket or tremie pipe is used. In this case concrete is carried through the water in water tight box by bottom dump bucket and reaching the final position there is a mechanism to open the bottom of the bucket and dispose the concrete. This will not give satisfactory result as some concrete get washed away.

Sometimes dry cement and dry coars aggregate and fine aggregate are mixed in a cement bag and disposed under water. This also do not give satisfactory result as cement bag make voids in concrete.

Among the two tremie pipe method is preferable.

Process of determining the opening area and opening length of seive

Let us consider we have to determine the opening area and opening length of #100 sieve.
#100 sieve means 100*100 openings are present in 1 square inch or 25.4*25.4= 645.16 square mm.

Hence 1 opening is present in =645.16/(100*100)
                                           =0.065 square mm
sieve openings are surrounded by threads which take some areas.Hence sieves actually get areas of around 36 to 40 percent(can vary) of its opening.
Let us assume sieve opening is 36 percentage.
Then the actual are of sieve opening is =0.065*(36/100)
                                                        =0.0234 square mm
As sieve openings are square size
Then length of the each sieve opening =square root of 0.0234
                                                       =0.153 mm

Advantages of Timber

1.Timber can be easily worked with tools of any size and can take a good polish.
2.It is comparatively stronger than any other materials in proportion to weight. That is other materials of such light weight as timber are not stronger than timber.
3.It is economic in the sense that any small piece of timber can be utilized.
4.Its use for making furniture, sports goods and decorative articles of artistic design are accepted universally without doubt.
5.Its low thermal conductivity, high resistance(electricity) and sound proofing property make it as an important building material.
6.timber structures are comparatively durable if properly treated and carefully protected from direct contact with weather and alternate change in wetting and drying.
7.Various types of timber products such as plywood, laminated board. hard board etc are nowadays used because of low weight and beauty.
8.It can be used both load bearing and non-load bearing members in structures and structural connections.
9.Its another importance is great resale value. The discard timber can be used as fuel.Even saw dust can be used by reconstructing partex board, hard boards, laminated boards etc.

Definition of Timber

Any wood which is used in engineering works is termed as timber.Although some of its usages are given up to steel, concrete and other products its usages in construction and other commercial purposes are still of great importance.