Lacunae of R.C.C. - I
Cracking and Spalling |
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A heterogeneous material with voids and capillaries |
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Designed as cracked section |
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Density about 2500 Kgs/M3 |
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Vibration by needles leave some porosity between two pokes- means somewhat honeycombing |
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Voids and capillary formation is said to be normal in concrete. |
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Excess water than required for hydration cause void, capillaries |
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These voids and capillary filled with water cause spalling of concrete crack formations |
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Least energy absorbing material, easy collapse in earthquake |
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Carbonation phenomena cause spalling of concrete |
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Cracks wide and with large spacing and deep |
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If cracks are minute, then sealed by autogenous healing |
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It is easy for water moistures, air polluted gases to enter cracks and cause expansion and corrosion of reinforcement |
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Therefore RCC is never a waterproof material |
In spite of several types of preventive treatment defects development may be reduced but definitely
persists |
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Virtues of Ferrocement - I
No Cracking and Spalling |
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Ferrocement is isotropic material upto 40% of yield |
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Designed as isotropic material upto 40% of yield |
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Density about 2750 Kgs/M3 Therefore free of voids and capillary |
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Vibration on machinery set up- no honeycombing,no voids, no capillaries cast insitu vibrated,no possibility of honeycombing, voids, capillary since thin section |
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No Void and capillary in Ferrocement except human inadvertence |
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No / nominal excess water cause no voids and capillary being thoroughly vibrated |
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No voids, no capillary, no spalling wiremesh bind matrix very efficiently. |
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High energy absorbing – does not collapse in earthquake may deform, better than steel |
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No carbonation phenomena since W.C. ratio are 0.35-0.38 |
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Crack very minute/nil and at close spacing and shallow |
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Crack if at all are very minute in microns and autogenous healing most effective |
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No entry of water moisture, polluted gases since no void no capillary no cracks
Ferrocement is always waterproof material |
| There is no defect development for Ferrocement manufactured strictly as per specifications and workmanship except human inadvertence |
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Slip of cementing matrix on coarse aggregate is beginning of compression failure |
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When compression failure takes place rarely coarse aggregate is crushed |
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Much delayed slip of cementing paste over sand fine aggregate because of high specific surface and high bond strength– compression failure delayed. |
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Compression failure is delayed since cement matrix of high strength. No compression failure of sand particles |
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Lacunae of R.C.C. - II
Corrosion of reinforcement |
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Excess water in concrete around reinforcement cause of corrosion. The same excess water in concrete also causes spalling in due course of time. |
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Corrosion of reinforcement takes place due to access of water, gases, moisture etc. through cracks and porosity in concrete |
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During concreting the water starts corroding the reinforcement from the day one |
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Corrosion due to excess water around reinforcement cannot cause damage to concrete body behind the reinforcement |
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But the rust strong enough to cause cracks in the concrete cover which is 12mm to 30mm - 40 mm |
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Virtues of Ferrocement - II
No Corrosion of reinforcement |
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No/nominal excess water– no corrosion of wire reinforcement – no spalling |
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No corrosion of wire reinforcement; no cracks and porosity and no entry of water, gases etc. |
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During manufacture only nominal Layer of water film make brown coloration/ nil coloration since wires
galvanized. |
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Such thing does not happen with Ferrocement |
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No/negligible rust, no force to crack matrix cover about 5mm thk. However superficial surface crazing in
fractions of microns with no relation to crack formation due to rust from reinforcement |
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Water, gases, moisture enter cracks and cause further corrosion |
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This corrosion adds to widening of cracks and further deterioration all around reinforcement. |
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There is chain reaction leading to collapse if not attended |
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No entry of water, gases etc although superficial surface crazing |
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No such phenomena |
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No collapse phenomena but deformation under severe conditions such as earthquake phenomena higher than about 7.5 Richter scale |
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Lacunae of R.C.C. - III
Structural aspects |
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This will be covered LATER ON |
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Virtues of Ferrocement - III
Structural aspects |
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This will be covered LATER ON |
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| The Ferrocement plate arrangement on R.C.C. surfaces is a separate topic |
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