Saturday 17 November, 2007

I WISH … I WERE

I WISH … I WERE

Every day when I go
to school, on a routine
I see that tree,
a very big tree.
Which spreads all over
to cover the earth and sky,

Even in the afternoon
when I return to home
with a new taught
so as to teach me
a new lesson of
Life, daily.

I wish I were a tree
who lonely helps
for the living strengthening
of the mankind and nobody
there in this universe
to stop me to do that

MEMOIRS

It was a splendid life. No responsibility, no tension, no fear, only play, play, and play, nothing else. But even in those free days, vacation holidays are the happiest movement on the earth to us.
To grab the every bit the holiday, we were planning it, two three months before its starting.

Thursday 15 November, 2007

CAUSES/REMEDIES OF CRACKS IN BUILDING


Introduction

C
racking of concrete is likely to impair the durability of concrete besides being unsightly. Aggressive elements find their way into concrete through cracks and accelerate corrosion of steel and deterioration of concrete. In addition cracking also affects water tightness of concrete, and may lead to leakages, damp patches and unsightly appearance.

Concrete cracks whenever tensile stress exceeds its tensile strength. Cracking may occur in green concrete (before hardening) due to plastic shrinkage, settlement of forms and support movements. After hardening concrete is prone to crack due to applied loading, drying ,shrinkage and chemical & thermal effects.

Remedies

The deleterious effects of cracking can be reduced significantly by correct detailing and construction practices. Reinforcement should be provided not only in the obvious locations of stresses but also at possible regions of cracking. Adequate archorage and lap lengths should be provided to restrict bond stresses and transverse strains.

Surface cracks are inevitable in reinforced concrete structures, but with proper design and detailing practices the width of cracks can be controlled and are barely perceptible to the naked eye. Stress induced cracks have their maximum width at the surfaces and narrow down towards the reinforcement, however, the difference in width may reduce with time. It should also be noted that greater the concrete cover the greater is the crack width. In the case of large concrete cover, more than about 40mm additional mesh reinforcement should be provided to avoid excessive surface crack width and possible spalling.

Repair of cracks and leakages

Several proprietary materials are available for repair of cracks. However, it is essential to determine the causes for cracks and ensure that they do not reappear a short while after expensive repairs. Often, fine cracks may disappear due to autogenous healing process.


The most common technique of repairing cracks is by grouting or injection. It is essential to select the materials judiciously depending upon the structure, its significance, location and size of cracks, and environmental conditions. Sometimes it may be necessary to widen the cracks by cutting deep grooves, and fill them with.

Some of the materials available commercially are as under:-

(a) Cement mortar
(b) Cement concrete,
(c) Polymer modified cement mortar
(d) Polymer modified cement concrete
(e) Polymer and fibre modified mortar
(f) Polymer and fibre modified concrete
(g) Resin fibre composite
(h) Resin mix and polymer mix.