07-03-2012, 01:35 PM
FERROCEMENT
INTRODUCTION.docx (Size: 477.38 KB / Downloads: 325)
. INTRODUCTION
The term ferrocement is most commonly applied to a mixture of Portland cement and sand reinforced with layers of woven or expanded steel mesh and closely-spaced small-diameter steel rods rebar. It can be used to form relatively thin, compound curved sheets to make hulls for boats, shell roofs, water tanks, etc. It has been used in a wide range of other applications including sculpture and prefabricated building components. The term has been applied by extension to other composite materials including some containing no cement and no ferrous material. These are better referred to by terms describing their actual contents.
CONSTRUCTION
The desired shape may be built from a multi-layered construction of mesh, supported by an armature or grid, built with rebar and tied with wire. For optimum performance, steel should be rust-treated, (galvanized) or stainless steel. (In early practice, in the desert, or for exterior scenery construction, "sound building practice" was not considered or perhaps unknown as it grew in some cases, from a folk craft tradition of masons collaborating with blacksmiths.) Over this finished framework, an appropriate mixture (grout or mortar) of Portland cement, sand and water and/or admixtures is applied to penetrate the mesh. During hardening, the assembly may be kept moist, to ensure that the concrete is able to set and harden slowly and to avoid developing cracks that can weaken the system. Steps should be taken to avoid trapped air in the internal structure during the wet stage of construction as this can also create cracks that will form as it dries. Trapped air will leave voids that allow water to collect and degrade (rust) the steel. Modern practice often includes spraying the mixture at pressure, (a technique called Shotcrete,) or some other method of driving out trapped air.
ECONOMICS
The economic advantage of Ferro concrete structures is that they are stronger and more durable than some traditional building methods Depending on the quality of construction and the climate of its location, houses may pay for themselves with almost zero maintenance and lower insurance requirements. Water tanks could pay for themselves by not needing periodic replacement, if properly constructed of Reinforced concrete.
ADVANTAGES
The advantages of a well built Ferro concrete construction are the low weight, maintenance costs and long lifetime in comparison with purely steel constructions. However, meticulous building precision is considered crucial here. Especially with respect to the cementitious composition and the way in which it is applied in and on the framework, and how or if the framework has been treated to resist corrosion.
When a Ferro concrete sheet is mechanically overloaded, it will tend to fold instead of break or crumble like stone or pottery. So it is not brittle. As a container, it may fail and leak but possibly hold together. Much depends on techniques used in the construction.
1.4 DISADVANTAGES
The disadvantage of Ferro concrete construction is the labor intensive nature of it, which makes it expensive for industrial application in the western world. In addition, threats to degradation (rust) of the steel components is a possibility if air voids are left in the original construction, due to too dry a mixture of the concrete being applied, or not forcing the air out of the structure while it is in its wet stage of construction, through vibration, pressurized spraying techniques, or other means. These air voids can turn to pools of water as the cured material absorbs moisture. If the voids occur where there is untreated steel, the steel will rust and expand, causing the system to fail.
INTRODUCTION.docx (Size: 477.38 KB / Downloads: 325)
. INTRODUCTION
The term ferrocement is most commonly applied to a mixture of Portland cement and sand reinforced with layers of woven or expanded steel mesh and closely-spaced small-diameter steel rods rebar. It can be used to form relatively thin, compound curved sheets to make hulls for boats, shell roofs, water tanks, etc. It has been used in a wide range of other applications including sculpture and prefabricated building components. The term has been applied by extension to other composite materials including some containing no cement and no ferrous material. These are better referred to by terms describing their actual contents.
CONSTRUCTION
The desired shape may be built from a multi-layered construction of mesh, supported by an armature or grid, built with rebar and tied with wire. For optimum performance, steel should be rust-treated, (galvanized) or stainless steel. (In early practice, in the desert, or for exterior scenery construction, "sound building practice" was not considered or perhaps unknown as it grew in some cases, from a folk craft tradition of masons collaborating with blacksmiths.) Over this finished framework, an appropriate mixture (grout or mortar) of Portland cement, sand and water and/or admixtures is applied to penetrate the mesh. During hardening, the assembly may be kept moist, to ensure that the concrete is able to set and harden slowly and to avoid developing cracks that can weaken the system. Steps should be taken to avoid trapped air in the internal structure during the wet stage of construction as this can also create cracks that will form as it dries. Trapped air will leave voids that allow water to collect and degrade (rust) the steel. Modern practice often includes spraying the mixture at pressure, (a technique called Shotcrete,) or some other method of driving out trapped air.
ECONOMICS
The economic advantage of Ferro concrete structures is that they are stronger and more durable than some traditional building methods Depending on the quality of construction and the climate of its location, houses may pay for themselves with almost zero maintenance and lower insurance requirements. Water tanks could pay for themselves by not needing periodic replacement, if properly constructed of Reinforced concrete.
ADVANTAGES
The advantages of a well built Ferro concrete construction are the low weight, maintenance costs and long lifetime in comparison with purely steel constructions. However, meticulous building precision is considered crucial here. Especially with respect to the cementitious composition and the way in which it is applied in and on the framework, and how or if the framework has been treated to resist corrosion.
When a Ferro concrete sheet is mechanically overloaded, it will tend to fold instead of break or crumble like stone or pottery. So it is not brittle. As a container, it may fail and leak but possibly hold together. Much depends on techniques used in the construction.
1.4 DISADVANTAGES
The disadvantage of Ferro concrete construction is the labor intensive nature of it, which makes it expensive for industrial application in the western world. In addition, threats to degradation (rust) of the steel components is a possibility if air voids are left in the original construction, due to too dry a mixture of the concrete being applied, or not forcing the air out of the structure while it is in its wet stage of construction, through vibration, pressurized spraying techniques, or other means. These air voids can turn to pools of water as the cured material absorbs moisture. If the voids occur where there is untreated steel, the steel will rust and expand, causing the system to fail.