880 Materials and Structures(2008)41: 879-890 Fiber reinforced Polymers or abbreviated FRP. Due temperature boundary between the areas of different to their properties, small mass, and high tensile mechanical properties of the same polymer. At this ally used in military and temperature, fibers will not be damaged, but the bond aviation industries. The manufactures were seeking strength between the matrix and fibers will decrease, new applications for their FRP product and the as well as the bond between the matrix and the possibility of massive use in civil engineering surrounding material. The most commonly used industry appeared. The basic idea was to produce a coating is epoxy resin. The usual properties of the material that would satisfy the growing needs for cold curing epoxy adhesive, concrete and steel used strengthening of structural elements and replace the in civil engineering, are shown, for comparison, in steel reinforcement of concrete and/or masonry Table 1 [1]. structures in aggressive environment. It is well known that aggressive environment can accelerate the corrosion of steel that was placed as reinforce 2.2 Fibers ment in concrete or masonry elements. Polymer composites are used in civil engineering and are Polymer composites have acronyms depending on the made of Aramid Fibers(AF), Carbon Fibers(CF)and fibers they are reinforced with: GFRP(glass fibers), Glass Fibers(GF). All these fibers possess high AFRP(aramid fibers), or CFRP(carbon fibers). The tensile strength. Polymer glue bounds fibers and such fibers increase the strength and stiffness of the com posite are shaped in moulds, applying pressure, composites. In order to create composites, one of which results in: AFRP, CFRP, and GFRP products. three types of fibers can be used: (1) short fibers There are two basic components of FRP products: (50 mm), oriented in all directions;(2) longitudinally fibers and polymer matrix. In polymer composite oriented, interwoven, straps of long fibers; and (3) fiber content is between 35 and 70 vol%o long fibers in bundles or fabric woven from bundles. The fibers are 5-20 um (10 m) thick and thei physical and mechanical properties vary depending 2 Components of polymer composites on fiber's type, [1, 2]. Carbon fibers are manufactured by controlled oxidation, carbonization, and graphiti- 2.1 Polymer matrix zation comparison with the other types of The matrix is made of different polymer resins, fibers have a higher strength and modulus of elastic selection of which depends on the type of fiber that ity, as well as better corrosion, fatigue, and creep should be bounded. Polymer matrix bounds fibers resistance Glass fibers are produced by protrusion of into composites and ensures the right position and a mixture of melted quartz sand, china clay, lime direction of fibers. At the same time the matrix stone, and colemanite, through small apertures at the protects fibers from environmental damage and mixture temperature of 1, 600oC. Th partially also from the mechanical damage. The later cooled. Different types of glass fibers are hatrix is also responsible for the transfer of load manufactured. Most often used glass fibers in com- between fibers, which implies a need for a good bond posites are: A-glasses (alkaline), E-glasse between fibers and the matrix. Strength and defor- (electrical), and C-glasses (chemical) fibers. The mation of composites are determined by the content A-glass fibers contain high proportion of boric acid of fibers and polymer matrix in the composites and and aluminates, thus, they are sensitive to alkaline he quality of bond between the matrix and the fibers. corrosion. E-glasses are more resistant to alkaline An important property of a synthetic resin is water agents and are significantly stronger and stiffer resistance, especially in extremely damp environ- C-glasses are highly resistant to alkaline agents ments. Thermal properties of the matrix determine E-glass fibers are most commonly used fibers due to he resistance of the composite, because the matrix their acceptable price and good technical properties has got much smaller thermal resistance and stability Composites with the glass fibers are heavier and of than fibers. The main property of the matrix is smaller strength and modulus of elasticity, but they Tg.the glass transition temperature, i.e., the are several times less expensive than the compositesFiber Reinforced Polymers or abbreviated FRP. Due to their properties, small mass, and high tensile strength, they were initially used in military and aviation industries. The manufactures were seeking new applications for their FRP product and the possibility of massive use in civil engineering industry appeared. The basic idea was to produce a material that would satisfy the growing needs for strengthening of structural elements and replace the steel reinforcement of concrete and/or masonry structures in aggressive environment. It is well known that aggressive environment can accelerate the corrosion of steel that was placed as reinforce￾ment in concrete or masonry elements. Polymer composites are used in civil engineering and are made of Aramid Fibers (AF), Carbon Fibers (CF) and Glass Fibers (GF). All these fibers possess high tensile strength. Polymer glue bounds fibers and such composite are shaped in moulds, applying pressure, which results in: AFRP, CFRP, and GFRP products. There are two basic components of FRP products: fibers and polymer matrix. In polymer composites, fiber content is between 35 and 70 vol%. 2 Components of polymer composites 2.1 Polymer matrix The matrix is made of different polymer resins, selection of which depends on the type of fiber that should be bounded. Polymer matrix bounds fibers into composites and ensures the right position and direction of fibers. At the same time the matrix protects fibers from environmental damage and partially also from the mechanical damage. The matrix is also responsible for the transfer of load between fibers, which implies a need for a good bond between fibers and the matrix. Strength and defor￾mation of composites are determined by the content of fibers and polymer matrix in the composites and the quality of bond between the matrix and the fibers. An important property of a synthetic resin is water resistance, especially in extremely damp environ￾ments. Thermal properties of the matrix determine the resistance of the composite, because the matrix has got much smaller thermal resistance and stability than fibers. The main property of the matrix is Tg, ‘‘the glass transition temperature,’’ i.e., the temperature boundary between the areas of different mechanical properties of the same polymer. At this temperature, fibers will not be damaged, but the bond strength between the matrix and fibers will decrease, as well as the bond between the matrix and the surrounding material. The most commonly used coating is epoxy resin. The usual properties of the cold curing epoxy adhesive, concrete and steel used in civil engineering, are shown, for comparison, in Table 1 [1]. 2.2 Fibers Polymer composites have acronyms depending on the fibers they are reinforced with: GFRP (glass fibers), AFRP (aramid fibers), or CFRP (carbon fibers). The fibers increase the strength and stiffness of the composites. In order to create composites, one of three types of fibers can be used: (1) short fibers (50 mm), oriented in all directions; (2) longitudinally oriented, interwoven, straps of long fibers; and (3) long fibers in bundles or fabric woven from bundles. The fibers are 5–20 lm (106 m) thick and their physical and mechanical properties vary depending on fiber’s type, [1, 2]. Carbon fibers are manufactured by controlled oxidation, carbonization, and graphiti￾zation of organic materials rich in carbon. In comparison with the other types of fibers, carbon fibers have a higher strength and modulus of elastic￾ity, as well as better corrosion, fatigue, and creep resistance. Glass fibers are produced by protrusion of a mixture of melted quartz sand, china clay, lime￾stone, and colemanite, through small apertures at the mixture temperature of 1,600C. Those fibers are later cooled. Different types of glass fibers are manufactured. Most often used glass fibers in com￾posites are: A-glasses (alkaline), E-glasses (electrical), and C-glasses (chemical) fibers. The A-glass fibers contain high proportion of boric acid and aluminates, thus, they are sensitive to alkaline corrosion. E-glasses are more resistant to alkaline agents and are significantly stronger and stiffer. C-glasses are highly resistant to alkaline agents. E-glass fibers are most commonly used fibers due to their acceptable price and good technical properties. Composites with the glass fibers are heavier and of smaller strength and modulus of elasticity, but they are several times less expensive than the composites 880 Materials and Structures (2008) 41:879–890