REINFORCED COMPOSITE MATERIALS

The materials of this group are characterized by the presence of reinforcing component in their composition, which are mainly subjected to stretching and bending stresses, during the operation of the products. The reinforcing elements of materials are distinguished by their chemistry and substantial composition, form, sizes, and degree of orientation in the matrix phase.

Typical reinforced composite materials include: reinforced concrete, glass-cement and glass-fiber plastics. Fiber concrete and asbestos-cement can be related to the fiber-reinforced materials. Particle boards and fiberboards, other laminated plates and roll materials also belong to the fiber composites. They are considered in other chapters.

Composite materials, reinforced by continuous fibers, are characterized by the composite interaction of all the constituent elements. For a given orientation of the uniform continuous fiber rigidly coupled with the matrix in one direction, the relationship between the loads, perceived by both components of materials, will be determined by the ratio between their modules of elasticity and the volume content of fibers. The deformation behavior of composites, reinforced by discontinuous fibers, differs from those where unequal tensile stresses act in the segments of fibers along their length: at the ends of segments they are equal to zero, but achieve maximum values in their effective part.

Most building structures are subject to the action of compressive and/or tension stresses. Concrete has a relatively low tensile strength. For complex resistance of compressive and tensile stresses reinforced concrete constitute a composite material solution in which concrete and steel reinforcement are rationally combined and co-work. The combination of concrete and steel in one material is possible due to their high adhesion and similar values of thermal expansion coefficients. Furthermore, in the alkaline environment existing in hardened concrete, steel reinforcement is well protected against corrosion due to the formation of a dense protective concrete cover.

Reinforced concrete is the most commonly used construction material in the modern construction industry. This is due to its high mechanical strength properties, durability and availability of raw materials sources, possibility of production of structures of any forms, to meet various architectural and technological requirements.

Depending on the method of production, reinforced concrete structures are divided into monolithic (placed in the form directly at the construction site), precast (assembled from prefabricated elements) and precast-monolithic (combine precast reinforced concrete elements and monolithic concrete or reinforced concrete).

Precast reinforced concrete structures by comparison with monolithic have a number of advantages. These include: organization of works is simplified on site, the basic operations of reinforcing, placing and hardening of concrete mixture are performed at the plants, duration of construction is shortened and the labour productivity increases because the casting works are excluded, the output of large size elements with enhanceable manufacture readiness is possible.

However the use of precast reinforced concrete elements requires powerful and specialized lifting-transport equipment, using of cut charts of buildings and considerable financial expenses to achieve the desired joint arrangements, and does not always allow the desired architectural expressiveness of buildings and structures.

Experience of monolithic construction shows that it has technical and economic advantages over the precast ones in a number of cases. It allows reduction with respect to non-permanent charges on creation of production base, expense of steel, cement and energy. Monolithic structures allows a substantial promotion of the performance and reliability parameters of buildings. Monolithic construction plays a special role and effect in seismic areas where the metal saving reaches 20%.

The question of whether to apply precast or monolithic method in the construction of reinforced concrete is solved only by deciding which has the possibility of satisfying the project requirements of the structures and buildings with respect to time and cost.

Buildings with large length, in relation to their volumes and sizes (channels, dikes, sluices, underwater parts of hydroelectric power plants, retaining walls, etc.) are expedient to build as precast-monolithic process. The most labour consuming aspects are prefabricated in the plants or grounds whilst less labour intensive component elements and their junction are achieved by the in-situ monolithic constrcution.

Date: 2015-12-18; view: 662