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How large are spalls?
Up to 5 feet in diameter
What is the purpose for placing a orange cone in the spall areas?
helps to ensure all spalls
Explain solidification of molten metal in Electrical discharge machining process?
The electric current spalls metal into the machining liquid, and the metal cools to form metal "dust" that is carried away by the liquid.
What is the effect of a gunshot from 12-18 inches on a surface?
That will vary depending on the nature of the surface, and the type and caliber of the firearm. Concrete or cement or rock: projectiles at high velocity will cause pits to be chipped out of the concrete. This is known as "spalling", and is easily observed by looking at many of the military buildings around Hickam Air Force Base, Honolulu, Hawaii. Machine gun bullets knocked chips or "spalls" out of the concrete walls of many hangars and of the Base Operations building. Metal surfaces: depending on the metal and the type of projectile, the metal may be pierced with a ripped appearance, or the projectile may bounce off of the surface. For very hard surfaces with soft lead projectiles, the projectile may be "pancaked"as it deforms and slows down. Wood: depending on the thickness and hardness of the wood and the caliber of the projectile, the bullet may penetrate the wood completely or partially. The projectile may be caught by the wood. The surface may splinter, ejecting high-velocity wood splinters either back toward the shooter or forward through the wood. From a distance of 12-18 inches, ricochets back toward the shooter are highly likely.
Do all rocks react the same to freezing and thawing in water?
To give two examples: granite spalls off the outer layers in freeze thay cycles, like taking off the outer layers of an onion, forming rounded tors; shale tends to expand between the rock strata, causing much more erosion and breakage.
Why are some metals reactive?
Some metals are reactive because they have a tendency to lose electrons easily to form positive ions. This reactivity is influenced by the number of valence electrons they have and their position on the periodic table. Metals that are higher up in the reactivity series tend to be more reactive.
Why do rocks weahter rapidly in areas were freezing and thawing occur frequently?
The freeze thaw cycle of weathering is important in breaking up the crystal structures in the rock. [The rock itself is of course already frozen.] There are several mechanisms in action in the Freeze Thaw cycle.Water in the rock's crevices will expand when freezing, thus loosening the tiny crystals. This will allow a greater quantity of water to be held in the crack next wet period, and so on.The presence of water in the crack will be in contact with fresh minerals on the face of the rock's crystals, and this may dissolve some of the mineral, or it may add water of crystallization. In either case, the resultant product will be of greater volume than previously. Thus enlarging the cracks.In addition, some of the dissolved salts will dry out on the hanging surface of an rock, and will cause a cavity to develop. Commonly these tend towards hollow spheres, with an obvious salt crust.And there is a gross effect of spallation. This happens when the rock undergoes thermal expansion or shrinking due to temperature changes. The spalls will first fall off exposed corners of the rock, and in the long run, the rock may become quite rounded. On the ground around the rock mass, these fallen spalls will occur as plates of up to a metre in size, and of slightly curved or shell like form.
What is micro concrete?
Microconcrete is a dry ready mix Cementetious based composition formulated for use in repairs of areas where the concrete is damaged & the area is restricted in movement making the placement of conventional concrete difficult., It is supplied as a ready to use dry powder which requires only addition of clean water at site to produce a free flowing non shrink repair micro concrete. This is a cementitious material, with additives, which impart controlled expansion characteristics in the plastic state with reduced water demand.
What is praseodymium?
praseodymium is the 59th chemical on the periodic table of the elements. Praseodymium is a soft, silvery, malleable and ductile metal in the lanthanide group. it does develop a green oxide coating that spalls off when exposed to air, exposing more metal to oxidation --- a centimeter sized sample of Pr completely oxidizes within a year.
In which processes are rocks broken up and moved to different locations?
Frost heave is an interesting process but acting in polar regions of course. The thermal expansion and contraction of the soil matrix is such that the component materials separate according to their size. So eventually, a Frost Polygon develops, in which the larger stones have migrated to the perimeter of the polygon, and the fine material concentrates in the interior. Slightly raised as well. These Polygons are irregular shapes, but with fairly straight sides. Quite striking to see. Freeze-Thaw cycles will act on massive rocks as well - rocks the size of houses. The temperature of the interior of such a rock does not change very much, because of the poor thermal conductivity, and the great thermal mass. But any surface irregularity may be subject to a daily freeze-thaw cycle, and this tends to spall off any irregularities, and the rock gradually becomes more round. The spalls may be several hundred mm in surface dimension, but only a few cm in thickness. Not uncommon to find in mountainous regions. The transport of rocks is a water process, either by glacier, or by a river. A glacier will actually pluck rocks from rock wall bounding the glacier, particularly in the upper reaches where schrunds develop. The glacier will freeze to the rock, but as the glacier is moving, particularly in the upper snowfields, it will pull away any rock that has a fracture line behind it. The collisions in a river will soon round the rock.
Why concrete cover is important?
The most important reason for "Depth of Cover" requirements, is to afford protection to the steel reinforcement embedded in the concrete. Certain tension, compression and bending moments also play a role, when the structural engineer designs for loads of the intended use, however the need to prevent corrosion [rust] from forming on the steel is the primary objective. New concrete has pH of 13-13.2 when placed. This high pH forms a "Passivating Layer" on the steel. The deeper placement of the steel [ Cover ] delays the degradation of the pH to a level that supports and fosters formation of corrosion cells. Chloride ions [Salts] are the most common contaminates in concrete that commence a corrosive environment. At a pH of 13.2, a chloride level of 8000 ppm are needed to begin rusting steel ! When that pH drops to a level of 11.5 the chloride threshold is lowered to 70 ppm ! Drastic difference ! Rusting Re-Bar expands in size as rust forms on it's surface. This expansion swells the re-bar size to the point that the concrete surrounding the steel cracks away [spalls] and the bond is lost, weakening the concrete in tension. Now cracked or spalled, these cracks allow a new path for contaminates and moisture to enter the matrix and speed the corrosion process up significantly. This corrosion leads to unsightly rust stains, loss of designed strength and very expensive repairs to the concrete. Left to continue a complete failure will occur. Although several other conditions may contribute to the corrosion cycle, by far, Depth of Cover is the most Important. Knowledgeable structural designers and contractors should also call for a specification to "Waterproof the Concrete". Doing so will slow the loss of pH and decrease the oxygen and moisture content at the level of the steel inside. Corrosion does not occur if moisture and oxygen are not present!
Why is cover important?
The most important reason for "Depth of Cover" requirements, is to afford protection to the steel reinforcement embedded in the concrete. Certain tension, compression and bending moments also play a role, when the structural engineer designs for loads of the intended use, however the need to prevent corrosion [rust] from forming on the steel is the primary objective. New concrete has pH of 13-13.2 when placed. This high pH forms a "Passivating Layer" on the steel. The deeper placement of the steel [ Cover ] delays the degradation of the pH to a level that supports and fosters formation of corrosion cells. Chloride ions [Salts] are the most common contaminates in concrete that commence a corrosive environment. At a pH of 13.2, a chloride level of 8000 ppm are needed to begin rusting steel ! When that pH drops to a level of 11.5 the chloride threshold is lowered to 70 ppm ! Drastic difference ! Rusting Re-Bar expands in size as rust forms on it's surface. This expansion swells the re-bar size to the point that the concrete surrounding the steel cracks away [spalls] and the bond is lost, weakening the concrete in tension. Now cracked or spalled, these cracks allow a new path for contaminates and moisture to enter the matrix and speed the corrosion process up significantly. This corrosion leads to unsightly rust stains, loss of designed strength and very expensive repairs to the concrete. Left to continue a complete failure will occur. Although several other conditions may contribute to the corrosion cycle, by far, Depth of Cover is the most Important. Knowledgeable structural designers and contractors should also call for a specification to "Waterproof the Concrete". Doing so will slow the loss of pH and decrease the oxygen and moisture content at the level of the steel inside. Corrosion does not occur if moisture and oxygen are not present!
