MECHANICAL BEHAVIOR OF ALUMINA

Mechanical behaviour of alumina

Mechanical behaviour of alumina

Abstract

The origin and use of cementations materials dates from the origin of civilization. Egyptians were the ?rst people that used hydraulic materials as gypsum; Romans and Greeks used volcanic ashes mixed with lime that produced a much better material than gypsum. However, Romans were the ?rst to use cementations mixes in common buildings. As is well known cementations mixes are brittle and have a high compressive strength.

Introduction

To get a material with better mechanical properties reinforced concrete was developed; it is a compound of steel bars inside a concrete bulk. However, corrosion in steel bars appear due the chemical attack from the environment, and to avoid this phenomenon steels bars should have a few centimeters of concrete covering them. By doing so, elements of great mechanical properties are obtained but these elements are also very heavy. To solve this problem glass fiber reinforced cement (GRC) was developed based in the previous works done with glass fibers and polymeric matrices. GRC has the great compressive strength of cement mortars and the tensile strength of the glass fibers.

Description and manufacture of GRC

The GRC is a composite material that is formed by a matrix of cement mortar and glass short fibers. It was devised around 1950 due to the success of polymer matrix composite materials reinforced with glass fibers. We attempted to replace the steel reinforcement in concrete construction elements, other materials, but this was achieved using glass fibers as its modulus of elasticity is approximately three times less than that of steel, making the deformations the structures were too large. However, began developing applications in which the glass fibers were introduced into the mesh shaped material and part of the reinforcement bars of the concrete. In these first tests were reached volume fractions of fibers of 50%. In 1960 he saw the need to replace, component due to carcinogenic asbestos fibers that were used in the industry Construction by another type of fibers, thereby idea indorse the GRC. The first types of GRC were formed by the binding of E-glass fibers and made with Portland cement matrix. The fibers were introduced in various ways and found in all improved properties produced in the cement mortar. However young material properties disappeared with the passage of time.



E fibers

AR fibers

25th modulus C (GPa)

75.5

70

Tensile strength of a fiber (MPa)

3600

3600

Tensile strength of a fiber bundle (MPa)

1700-2700

1450-1900

Break strain

2%

2%

Table 1.1

This was attributed to corrosion suffered by glass fibers by the matrix cement. In order to expand the use and study of this material is worked in the development of glass fibers to alkaline environments. The base element is varied chemical formulation of the glass fibers that have passed a siliceous base having as a base element zirconium. These fibers are called alkali resistant fibers or AR. The most important mechanical properties of the glass fibers were not affected, as shown in Table 1.1. With changing the formulation varied somewhat modulus of elasticity of the ...