EXPERIMENTAL STUDY OF FIBER GLASS REINFORCED MORTAR BY VARIABLE VOLUME PERCENTAGE OF FIBERS WITH MARBLE AGGREGATES SKOULIKARI MALAMATENIA

Transcription

1 EXPERIMENTAL STUDY OF FIBER GLASS REINFORCED MORTAR BY VARIABLE VOLUME PERCENTAGE OF FIBERS WITH MARBLE AGGREGATES SKOULIKARI MALAMATENIA MSc Structural Design and Construction Management THESIS 1

2 EXPERIMENTAL STUDY OF FIBER GLASS REINFORCED MORTAR BY VARIABLE VOLUME PERCENTAGE OF FIBERS WITH MARBLE AGGREGATES Dissertation submitted as part requirement for the Degree of Master of Structural Design and Construction Management By SKOULIKARI MALAMATENIA SUPERVISOR SOTIROPOULOU ANASTASIA TEI PIREAUS KINGSTON UNIVERSITY DEPARTMENT OF CIVIL ENGINEERING SEPTEMBER

3 Acknowledgments I would like to express my acknowledgments to my supervisor Mrs Sotiropoulou Anastasia, Dr Civil Engineer for her precious assistance and guidance during this thesis. Also I would like to thank Mr Pandermarakis Zaxarias for his help for the implementation of this project. Finally I would like to thank my parents for their guideless, their undivided sympathy and their tolerance all these years. 3

4 ABSTRACT In the present study the properties of unreinforced mortar to glass - fiber reinforced one is determined and compared. Fibers content in the mixture varies. Mechanical properties of the mortar are influenced depending on the change of fiber volume. The objective of this research it is the measurement of the improved properties of the mortar. The fibers used are 6mm long and their content in the mixture increased gradually from 0 to 0.26%. The mortar examined is tested in bending and compression. Glass - fiber reinforced mortar is also compared to mortar reinforced by polypropylene fibers. 4

5 TABLE OF CONTENT 1. INTRODUCTION 1 2. AIM 1 3. MORTARS Introduction Mortars attributes Categories of mortars Materials of Mortars Physical properties of mortar Premix Mortars FIBER REINFORCED CONCRETE Introduction Factors Affecting Properties Applications of fiber reinforced concrete MARBLE AGGREGATES GLASS FIBERS Introduction Physical and Technical requirements from Fibers Glass Fiber Oxide Compositions Glass Fiber Properties Physical Properties Chemical Resistance Electrical Properties Thermal Properties Radiation Properties METHODOLOGY Materials Experimental Procedure RESULTS DISCUSSION CONCLUSIONS FURTHER DISCUSSION ENGLISH BIBLIOGRAPHY GREEK BIBLIOGRAPHY 47 5

6 TABLE OF FIGURES Figure 1: Load - Deflection Curve 17 Figure 2: Quarrying of marble 26 Figure 3: Glass fibers 27 Figure 4: Orientation of fibers in the mixture 31 Figure 5: Prismatic specimens 40 x 40 x 160mm 31 Figure 6: Specimens immersed in water 33 Figure 7: Bending machine 33 Figure 8: Load direction in flrexural test 33 Figure 9: Compression machine 34 Figure 10: Load parallel with layering 35 Figure 11: Load perpendicular to layering 35 Figure 12: Metal Mould 36 Figure 13: Load - Deflection Diagram 38 Figure 14: Variation of Flexural Strength via Volume Percentage of Fibers 38 Figure 15: Specimen after bending test 39 Figure 16: Flexural stress-strain diagram 40 Figure 17: Modulus of Elasticity via Volume Percentage of Fibers 40 Figure 18: Compressive strength with the different percentage of glass fibers and with different solutions investigated 42 Figure 19: Specimen after Compression test 42 Figure 20: Characteristic fracture of specimen after compression test 42 Figure 21: Compressive stress strain for unreinforced specimen 43 Figure 22: Compressive stress strain for reinforced specimen by 0.07% glass fibers by volume 44 6

7 TABLES Table 1: Compression strength according to time 6 Table 1: Limits of mid-grained sand 8 Table 3: Quantities of Constituent Materials and Mix Percentage of Fiber Reinforced High-Performance Mortar 32 Table 4: Results from Compression and Flexural Tests 37 Table 5: Value of compressive strength according to the volume of fibers in the mixture with the different solutions investigated. 4 7

8 1. INTRODUCTION Mortars have been extensively used in order to repair damage components in various structures. Our country is located in a region with intensive seismic activity. In past, many earthquakes with various sizes were noticed. One of the higher was occurred recently, in September of 1999, and then serious damage on load bearing structures was caused. So, a quick repair and reinforcement of all these constructions were necessary. For this reason, high toughness mortars are needed for the above repairs. Mortars have already been investigated extensively for years but there are still many points about fiberreinforced mortars that must be cleared. Especially those with marbles aggregates that come by marble industry which handling them until now as waste. The mortar that we will study consists of high-strength cement, marble aggregates with sizes between 0-4mm and glass fibers. The selection of marble by-products as aggregate is based on two criteria: a) this type of mortars that are already now sold in markets it has not been yet checked and b) a lot of tons of these marbles by-products are disposed as waste in our country and more useful ways of their handling it is necessary to be found. Parallel with the investigation of applicability of marble grains as aggregates, we want to evaluate the influence of glass fibers and their cooperative influence with marbles aggregates on mortars strength and toughness. At this study the behavior of fiber reinforced mortars will be examined according to fiber volume percentage. 2. AIM The aim of the present study will be to determine experimentally the influence on the compressive and flexural strength of the addition of glass fibers in mortars at three different fiber volume percentage and to compare fiber-reinforced mortars with unreinforced one. Also we will compare the above results with corresponding results of polypropylene fiber- reinforced mortars and the results that come by fiber reinforced sprayed mortar. Furthermore, we want to see the influence of marble aggregates in mechanical response of repairing mortars. 8

9 3. MORTARS 3.1 Introduction Mortars are called the mixes of one or more cements with inactive materials of small granulometric gradation and with treatment liquid, which is usually water. The basic institution of resistance of mortar is aggregate, while cement constitutes the adhesive material. Used aggregates are usually sand with biggest diameter of grain 4 mm. Their content in thin grains with diameter d < 0,2 mm should be 20% - 25% in weight and the dimensions of biggest grain should be smaller than the 1/3 of thickness of coat. For mortar preparation should be used the minimal possible quantity of cement should be used, so the aggregate materials can have such granulometric gradation, in order the volume of voids, which takes shape between their grains, to be as smaller as possible.the water that is used for manufacture of mortar should be clean, non-alkali and potable. It should not contain any deteriorative admixtures, as free organic or inorganic acids, plant and more generally organic substances, soluble salts, mainly sulphate or even chloride. The use of water that has been used previously for the cleaning of tools and containers is not allowed. Also, a great deal of the success of mortar lies in the temperature of water. The tepid water helps in the better hardening of mortars. The use of water that is found close to its temperature of thickening is prohibited. 3.2 Mortars attributes The mortar should be homogeneous and have satisfactory workability. When transported the layering should not presents segregation of its components. Also, it should have very good plasticity, in order to be formed without loosing its cohesiveness and not leak from the joint of stonework. Moreover, the mortar should have stability of volume and very good faculty of accretion and elasticity to avoid cracks, retain the small structural elements and ensure leak-tightness, as well as suitable time of coagulation, so that mortar can bear the structural charges with safety. Finally, the mortar should have such composition, in order to satisfy all requirements of structural manufacture. 9

10 The attributes of mortars depend on the following factors: a. the type of cement b. the type of aggregates, c. the proportion of mixture of their components at volume, d. the way of mixture of their components, e. the type of additives and f. the way of treatment and condensation of mortar. 3.3 Categories of mortars The mortars are classified in the following categories depending on their way of discrimination: 1. According to the type of binder The mortars depending on cement that it used for their preparation are distinguished on: a) Leam Mortar In leam mortar clay is used as cement, which is a mixture of clay with sandy components small and intermediate granulometric gradation. It presents good accretion; insulation attributes and provides fire safety. When the mixture permeated it returns from the dry situation to plastic. Leam mortar is used for the preparation of tile and brick. b) Lime Mortars In lime mortars structural lime is used as binder, which should have suffered good staking, in order plastering does not present efflorescence. Ordinary lime formats mortars, present very good plasticity and workability. Lime stone mortars are durable in usual strain and are used in masonry, as well as plastering. The mortars, which contain hydraulic lime, harden faster and have higher resistances than those of ordinary lime. c) Lime Plaster of Paris Mortars Lime Plaster of Paris Mortars are lime mortars in which gypsum has been added. These mortars are used as plastering of internal spaces because they do not present micro cracks and create smooth surfaces. 10

11 d) Lime Marble Mortars Lime marble mortars are lime mortars in which the sand has been replaced from marble sand. They are used as plastering and they give surfaces that can be grated until become completely smooth. The last layer plastering is usually manufactured by lime marble mortar for economical reason. e) Lime Pozzuolanic Mortars Lime Pozzuolanic Mortars are lime mortars in which the sand has been replaced partially or totally with pozzuolana. They are prepared with proportions 1:3 paste of lime: pozzuolana and 1:2:1 paste of lime: pozzuolana: sand. They are hydraulic mortars with small resistance and used in humid and underground spaces. f) Lime Cement Mortar In lime cement mortar lime and cement are used as binder. They present hydraulic faculties and decrease impermeability. Also, they are more durably and present bigger resistance in the strains from clean lime mortars. g) Cement Mortars Cement mortars are mortars in which various types and quantities of cement are used as binder. They present intense hydraulic attributes and increased resistances. They are used for the structural elements that are submitted in powerful strains as well as for plastering. Their attributes depend mainly on the type and quantity of cement and water-cement ratio as well. Cement mortars should have increased plasticity and elasticity, so that their adhesion must be powerful, not to present cracks and ensure complete leaktightness. This is achieved by the addition of small quantity of hydrate lime with the form of paste or dust, in cement mortar without decreasing cement content. 2. Proportionally by the quantity of bender The mortars depending on the quantity of binder that is used for the preparing of mortars are classified in the following categories: a) Regular mortar As regular mortar is characterized the one, in which the quantity of binder is just the necessary one to fill the voids among the grains. 11

12 b) Thick mortar As thick mortar is characterized the one in which more binder quantity than necessary for preparation of regular mortar is used. c) Lean mortar As lean mortar is characterized the one in which the prepared paste does not fill completely the voids within the grains of sand. 3. Proportionally with their way of hardening The mortars depending on their way of hardening are distinguished in: a) Air Hardening Mortar Air hardening mortars are the ones which harden in air. The hardening becomes with the effect of carbon dioxide of atmosphere in hydrate lime of mortar, while the water is removed. b) Hydraulic mortars Hydraulic are the mortars which both freeze and hardened in air and then mature in water or freeze and hardened directly in water. The hardening is owed to the hydraulic factors, which are contained in these binders. 4. Proportionally with their mechanic The mortars depending on their mechanic resistance are distinguished in: a) Mortars of low resistance Mortars of low resistance are leam mortar as well as clean lime mortars. b) Mortars of medium resistance Mortars of medium resistance are lime Pozzuolanic mortars as well as lime cement mortar. c) Mortars of high resistance Mortars of high resistance are the cement mortar and organic mortars. 5. Proportionally with their use The mortars depending on their use are distinguished in: a) Mortars for masonry The mortars of masonry are used in the structure of masonry, as binding material of structural elements, which are natural or artificial stones. They are interfered between the structural elements and fill the created joints. 12

13 Also, they are layered in horizontal surfaces and abetted the placement of other structural elements. Consequently, they should have good workability and plasticity, in order to cover all the irregularities of structural elements. Moreover they must have good faculty of bonding of water retention, sufficient resistance and good accretion, so that the masonry becomes compact and constant. Furthermore, these mortars should have increased elasticity; in order to follow the changes of stonework without is creating leakage of joints. In Table 1 the variance of compression strength according to time for the three categories of mortar is shown Category I II III Type of Cement Proportion of mixture lime: cement: sand Average strength of hardened mortar in (Kg/dm³) Average compressive strength in Mpa Paste of Air Hardening Lime 1 : 0 : 3,5 1,70 1,85 0,4 0,6 Powder of Air Hardening Lime 1 : 0 : 3 1,75 1,90 0,5 0,8 Hydraulic Lime 1 : 0 : 3 1,85 2,00 0,5 1,5 Very Hydraulic Lime 1 : 0 : 3 1,90 2,05 1 2,0 Super Hydraulic Lime 1,5 : 1 : 8 1,90 2,10 2,5 5 Lime paste + Cement 2 : 1 : 8 1,80 2,00 2,5 4 Lime Powder + Cement 1 : 1 : 6 1,95 2,10 3,5 8 Lime Powder + Cement 1 : 0 : 3 2,00 2, Cement 0 : 1 : 4 2,00 2, Cement + Lime Powder 0,2 : 1 : 4 1,95 2, Table 1: Compression strength according to time b) Mortars for plastering The mortars for plastering are used for the cover, grading and better appearance of exterior and interior surfaces. Also, the usually contribute to the increase of thermal and sound protection. The mortars of plastering should have good accretion, on layering surface as well as among their layers. 13

14 Each layer should have uniform structure. Also, mortars should present stability of volume, in order to avoid micro cracks. Their resistance, as well as the type of surface should correspond to the aim of work. The mortars used as plaster in exterior surfaces should present increased strength and resistance to the effect of weather changes (temperature, rain, humidity, frost, solar radiation etc). Those used in internal spaces should form smooth and levelled surfaces, so to be easily painted and covered. c) Mortars under pressure The mortars under pressure are cement pastes or cement mortars and they are used in the technology of pre-stressed concrete for the filling of covering pipes and pre-stressed shroud. Also, they are used in the manufacture of tunnels and dams, where the resistance of soil with concrete injection is increased. 3.4 Materials of Mortars a) Sand The sand should emanate from fragment of quarry and it must be suitable depending on the use of mortar. For cement mortars it is preferable to use the sand that come from hailstone or at least hard limestone. Also the sand must have sufficient mechanic resistance. Natural sand (pit sand, marine sand and sea sand) is used for work with bigger accuracy (thin layers and joints) it is not suitable for plastering because it contains salts which they cause sulphate efflorescence. Harmful substances such as clay, organic components, talc and mica should be removed from the sand and the maximum contents by weight must be: 4% for clay, 1% for organic components and 1% for talc and mica. The quality and the appearance of the mortar depend on the sand gradation. The better the gradation is, the better the quality of mortar becomes. According to general specifications for the granulometric gradation, the granulometric line must be continuous. This means that the sand must contain all sizes of grains and in percentages as much as possible nearest to the ideal granulometric curve. In masonry or pavings mortars where the thickness of mortar is bigger than 15 mm, coarse-grained sand (0/7) is used. When the thickness of joint or layer is 8 15mm the mid-grained 14

15 sand (0/3) is used. Finally, for cases with smaller thickness than 8mm the sand should be fine-grained (0/1). The mid-grained sand is determined by the following limits: American Standard Specification A. A. S. H. : M 92 Number of screen Screen [ m ] Passing percentage % by weight # No 8 2, No 50 0, No 100 0, No 200 0, Table 2: Limits of mid-grained sand b) Lime The lime must be of very good quality. It must contain calcium oxide and magnesium at 95% percentage. The pulp that comes from slaking of lime should not contain coagulum or solid material and it must constitute at higher percentage from colloid form of lime. The utilisation of lime pulp which has been changed in carbonic calcium is prohibited. In order to used lime hydrate dust, all its grains must pass from screen with hole 0,25 mm and have a uniform colour. The mortars that have resulted from hydrate limes should be used within 2-4 h afterwards their preparation. Particular attention should be given to the directives of brick factory production with regard to the proportion of lime in the mortar (many times they recommend the abstraction of lime from the mortar). c) Cement The cement must comply with the national specifications, be recent production, Portland and clean. After the period of 3 months from its production, it is not suitable for any usage. The cement must be of the same quality throughout the duration of the project. d) Water For the manufacture of mortars the water should not contain any deteriorative admixtures, as free organic or no organic acids, plant and in general, soluble salts, mainly sulphate or even chloride. The use of water that has been used 15

16 previously for the cleaning of tools and containers is not allowed. Also, a great deal of the success of mortar lies in the temperature of water. The tepid water helps in the better hardening of mortars. 3.5 Physical properties of mortar Mortars have two important sets of properties: a) those in the plastic state which include workability, water retention, initial flow and flow after suction and b) those in the hardened state which include bond strength, extensibility, durability and compressive strength. The plastic properties help to determine whether the mortar is suitable for the construction or not. On the other hand, properties of hardened mortars concern the determination of the performance of the finished masonry. Bond strength In bond strength the extend as well as the strength of bond are major importance. Many factors can have effect on this physical property of hardened mortar. These are: texture of the brick, suction of the brick, air content of the mortar, water retention of the mortar, pressure applied to the joint during forming, mortar proportions and methods of curing. Effect of Brick Texture. Brick texture can provide a mechanical bond between the brick and the mortar. Mortar bond is greater in roughned than in smooth surfaces. The bond strength change in sanded and coated surfaces proportionally to the amount and type of material on the surface and its adherence to the surface. Effect of Brick Suction. The laboratory measured initial rate of absorption of brick and indicates the brick s suction and whether it should be wetted prior to use. The magnitude of strength bond depends on the actual section of brick by the time of layering. The most suitable value of section must be less than 30g/min/30in 2, if this value exceeds then the brick should be wetted three to twenty-four hours prior to laying. The surface of wetted brick must be dry before the laying of mortar. Finally several researches have shown that the initial rate of absorption have got not a significant importance on bond strength. Effect of Air Content. An increase of air content in the mortar causes reduction in bond strength and compressive strength, while workability and resistance to freezethaw deterioration are increased. 16

17 Effect of Flow. An increase in the flow of mortar when used is beneficial because it helps the bricklayer to work more easily and satisfy the suction of the brick. The increas of flow helps to increase the bond strength but too much water leads to the reduction in workability and bond strength. Also the bond strength depends on the time lapse between spreading mortar and placing brick. When the brick has high suction or the construction takes place during hot weather then the mortar will have less flow and the bond strength will be reduced. For highest bond strength, this time interval must be reduced to a minimum. There are several times that mortar is not used immediately after mixing. During this time some of its water may evaporate. The combination of an addition of water to mortar and retempering will cause the reduction of compressive strength and mortar color lightened. For that reason mortar should be used within 2 ½ hours after sixing sine the mortar will begin to set. Effect of Movement. Once mortar has begun to harden any movement to the brick can cause serious problem to the bond between brickand mortars. The partially dried mortar will not have sufficient plasticity to adhere well to the masonry units. Effect of Proportions. There is no suitable combination of material in order to produce the bond with the desirable strength. Effect of Curing. The way of curing the masonry influences the magnitude of bond strength. Wet curing of masonry leads to higher bond strength then dry curing but eventually mortar materials will influence the result. Test Methods. There are many factors that affect bond so the test methods in labotory must be done according to specifications in order to evaluate rightfully the flexural bond strength. Finally, in order to increase the flexural bond strength: 1. bond mortar must be laid in wire cut and roughened surface, 2. check the brick suction and control it according to the specifications 3. select the appropriate mortar with the minimum air content 4. produce a mix mortar with maximum flow by using a maximum mixing water and permit retempering Water Content Concrete and mortar are very similar materials. Many time the designers base mortar specifications on the assumption that the requirements for concrete and 17

18 mortar are the same especially with regard to the water-cement ratio. Mortars with the minimum quantity of water and with prohibited retempering will have higher compressive strengths comparatively with mortars with maximum quantity of water and retempering. The bond strength increases with the increase of water. Retempering is permitted only for replacement of water loss by evaporation. Mortars must be used within 2 ½ hours otherwise retempering is necessary. Workability A mortar is workable when it can be spread without difficulty and adhere easily to vertical masonry surfaces. Workability of the mortar is also influenced by the components of the mixture. Also the quantity of water contributes in workability: when the quantity of water is more the mixture will have higher flow. Till now several researches in regard with the requirements for water retention and aggregate gradation do not exist and each time the quantities that are judge as suitable to ensure satisfactory workability are used. Initial Flow and Water Retention Extensibility is another term for maximum tensile strain at failure. It reflects the maximum elongation possible under tensile forces. High lime mortars exhibit grater plastic flow than low lime mortars. Plastic flow, or creep, acting with extensibility will impart some flexibility to the masonry, permitting slight movement. Where greater resiliency for movement is desirable, increase the lime content while still satisfying other requirements. (Technical Notes 8) Durability The durability of mortar is shown in masonry structures that haven t been in serviced for many years. Usually the air content helps to increase the durability of mortar, but leads to the decreasion of bond strength and other desirable properties. So it is better not to use air-aintraining admixtures to increase air content. Compressive Strength The compressive strength of mortar depends primarily on the cement content and water cement ratio. If the cement content of mortar increases then the compressive strength will increase, but if the water content or lime content increases then the compressive strength will decrease. Another factor that influences the compressive strength is retempering. Retempering must occur within 2 ½ hours 18

19 because then the mortar starts to stiffen. If the retempering occurs within that time the reduction of compressive strength will be noticeably less but if not then the compressive strength will lessen more. It is frequently desirable to sacrifice some compressive strength in favor of improved bond strength by permitting retempering. Volume Change Volume change in mortars can result from four significant factors: chemical reaction in hardening, temperature changes, wetting and drying, and unsound ingredients with chemical expansion. Volume change caused by hardening and cements hydration, is often termed shrinkage and depends on curing condition, mix proportions and water content. The magnitude of shrinkage depends on where the mortar hardened. If the mortar hardened in absorbent moulds or in contact with brick the shrinkage would be less than those hardened in non-absorbent molds. Change in the temperature leads to expansion and contraction of mortar. Moisture content increase and decrease depends on the circumstances. When the mortar wets, moisture increases and the mortar swells, but when it dries out, moisture decreases and the mortar shrinks. Unsound ingredients or impurities can cause mortar to expand. Efflorescence Efflorescence is a crystalline deposit of water-soluble salts on the surface of masonry. Mortar is a primary source of calcium hydroxide. This chemical can produce efflorescence on its own. Also it can react with carbon dioxide in the air or solutions from the brick and it forms insoluble compounds. Until now there is no standard test method to determine the efflorescence of mortar but scientists consider that mortars will effloresce under any standard test. Colour The color of the mortars depends on the aggregates and pigments that it is used. Coloured aggregates are most suitable for the manufacture of colour mortars. In order to produce white joints the better aggregates are: white sand, ground limestone or ground marble with white Portland cement and lime. The requirements for the pigments of mortars are: they must be fine to disperse throughout the mix, they must be capable to form the desirable color and finally they must not react with the other ingredients to the detriment of mortar. Metallic oxide pigments meet all these requirements, but also carbon black and ultramarine blue have been used as 19

20 mortar colors. It is better not to use paint pigments, organic colors and those containing Prussian blue, cadmium lithopone, zinc and lead chromates. The maximum permissible quantity of most metallic oxide pigments is 10 percent of the cement content by weight and for carbon black to 2 percent no the cement content by weight. Using greater proportions of pigments will cause reduction in mortar strength. For more uniform color there must be premix large and controlled quantities of cement and coloring agents. Colour consistency in smaller batches can be achieved by consistent sequence mixing. It is better to use the same source of mortar materials. Whether the color is uniform or not depends on the amount of mixing water, moisture content of the brick when laid and if the mortar is retempered. Also the time and degree of tooling and cleaning techniques will influence final mortar colour. Colour permanence depends upon quality of pigments, weathering and efflorescing qualities of the mortar. 3.6 Premix Mortars The premix mortars depending on the kind of binder that is used for their preparing are classified in: cement mortars, acrylic mortars, mortars with hardener resigns and gypsum mortars. Depending on their attributes are distinguished in: soundproof, heat-insulating and decorative and finally depending on their use are distinguished in: mortars for masonry, first layer plastering, internal plastering for final layer and external plastering for final layer. Concisely the characteristics of cement mortars are the followings: - Specific weight of dry material: 1600 kg / m kg / m 3 - Temperature resistance from: 30 C to + 70 C - Tensile strength: 18 kg / cm 2 20 kg / cm 2 - Temperature of application: 5 C - 40 C - Flexural strength: 40 kg / cm 2 - Compression strength: 90 kg / cm 2 Cement mortars that are used for the first and second layer do not contain lime. They are usually used for external and internal surfaces. They can ensure high resistances and protection from erosion. In their formation apart from cement and mid-grained lime sand, specific additives are contained. Their characteristics are: 20

21 - Detention of water 18% - 19% - Compression strength (after 28 days) 120 kg / cm 2 - Flexural strength (after 28 days) 30 kg / cm 2 The waterproof marble mortars are used for the final layer of plastering. They are prepared with white fine-grained stucco and white cement which contains specific additives suitable for the final layer of plastering. The ready-made heat-insulating mortars are cement mortars with inactive sand, small grains of pearlite or resembling heat-insulating materials and with additives that ensure the accretion. Their technical characteristics are: - Specific weight of binder: 400 kg / m kg / m 3 - Modulus of thermal conduction: 0,075 kcal / mh C 0,085 kcal / mh C - Resistance in the diffusion of water vapours Compression strength (after 28 days) 10 kg / cm 2 15 kg / cm 2 - Flexural strength (after 28 days) 4 kg / cm 2 6 kg / cm 2 The mortars with hydrate lime and gypsum are produced with hydrate lime, anhydrite gypsum and traces of marble. Moreover chemical additives are put in order to ensure elasticity, plasticity and accretion on the surfaces which they are placed. They are applied in 2 layers. The first layer is the prime with thickness 6 7mm and the second is the filling with thickness 1, 8-2mm. Their technical characteristics are: - Specific weight of dry material: 1250 kg / m 3 - Modulus of thermal conduction: 0,40 kcal / mh C - Compression strength: 32 kg / cm 2 - Tensile strength 14 kg / cm 2 21

22 4. FIBER REINFORCED CONCRETE 4.1 Introduction Portland cement concrete is considered to be a relatively brittle material with high strength in compression but low in tension. Since the mid 1800 s steel reinforcing has been used to overcome this problem. As a composite material, the reinforcing steel is assumed to carry out all tensile loads. When fibers are added to the concrete mix, they increase more the tensile loading capacity of the composite and also improve the ductility. The random distribution of fibers in the concrete withstands higher homogeneity and more isotropic behaviour. Fibers used in mixture are consisted of materials such as steel, glass and polypropylene. Cracks aren t avoided by the addition of fibers; in case of creation they undertake all the tensile strengths and provide ductile behaviour in the concrete. 4.2 Factors Affecting Properties The principal factors affecting properties of glass fiber reinforced concrete are fiber content, water cement ratio, porosity, composite density, inert filler ratio, fiber orientation, fiber length, and type of cure. Density and porosity are also functions of the degree of compaction. Fiber content, length, and orientation primarily affect early tensile ultimate strength, early flexural ultimate strength, and impact strength. A minimum fiber content of 4 percent by weight is recommended to ensure adequate ultimate strengths, unless test data shows that reduced fiber contents are adequate for the application. Fiber length also plays a role in composite ultimate strengths. Shorter lengths, although easier to spray, will not give maximum reinforcement efficiency, and longer lengths may interfere with fiber/slurry lay down and lead to problems similar to those encountered with high fiber contents. The orientation of reinforcing fibers affects performance. Most glass fiber reinforced concrete spray-up composites which have a two-dimensional random fiber orientation, but if care is not taken during production, fibers can be parallel oriented and the composite material will exhibit different properties when tested along with different axes. 22

23 Composite density affects matrix dependent properties; flexural and tensile strength and modulus of elasticity vary directly with density. Low density reduces ultimate strengths because at lower densities entrapped air reduces the bond between the fibers and concrete. Therefore, proper compaction of the composite is very important. Fiber content has little effect on the modulus of elasticity. Adequate curing results in substantial hydration of the cement leads to good bonding between fibers and the matrix which improves both fiber and matrix dependent properties. The initial portion of the flexural curve apears straight, indicating that the glass fiber reinforced concrete behaves elastically in this region. In reality, micro cracking takes place within the matrix and the curve is not linear. The presence of the fibers restricts the growth of micro cracks, inhibiting matrix failure and increasing average matrix strength. The point at which the stress-strain curve appears to deviate from linearity is called the yield point. This is the point at which the first major crack has been formed. A substantial amount of energy is required to propagate the crack through the interfaces and the bundles of fibers which lie at the tip of the crack. The energy required is greater than that to initiate a new crack in the matrix. As a result, instead of cracking all the way through and breaking, a new crack is formed some distance away from the first one. As more cracks develop in the surface, the stress-strain curve gradually flattens, indicating a decrease in stiffness. Further bending or extension of the specimen now brings on a ductileappearing region in the curve due to the multiple cracking. At the end of this procedure, the development of the crack system is complete and the entire length of the specimen is covered with fine transverse cracks. The load is finally transferred to the fiber reinforcement system, and the specimen cracks open as fibers fracture or pull out. The specimen fails when the reinforcement system can no longer accept an increase in load. Compression The compressive properties of fiber-reinforced concrete (FRC) are relatively less affected by the presence of fibers as compared to the properties under tension and bending. Studies have shown that the stress-strain curve of glass reinforced 23

24 concrete, when tested in compression, is linear up to high stresses and similar to the curve which will be obtained from testing the matrix without any fiber. The effect of fibers depends on the orientation of the fibers relative to the direction of the compressive stress; fibers running parallel to the direction of compression create fracture planes which can reduce the compressive strength to about 70% of values obtained in testing across the plane of fibers Flexure There are a number of factors that influence the behavior and strength of fiber reinforced mortar in flexure. These include: type of fiber, fiber length (L), aspect ratio (L/d f ) where df is the diameter of the fiber, the volume fraction of the fiber (V f ), fiber orientation and fiber shape, fiber bond characteristics (fiber deformation). Also, factors that influence the workability of fiber reinforced mortar such as W/C ratio, density, air content and the like could also influence its strength. The ultimate strength in flexure could vary considerably depending upon the volume fraction of fibers, length and bond characteristics of the fibers and the ultimate strength of the fibers. Depending upon the contribution of these influencing factors, the ultimate strength of fiber reinforced concrete could be either smaller or larger than its first cracking strength. Generally, there are three regions of the load-deflection response of fiber reinforced concrete specimens tested in flexure and schematically shown in Fig. 1. Fig. 1: Load - Deflection Curve In Region 1 (O-A), the matrix and fibers act together behaving essentially elastically. At this stage, there are no visible cracks in the matrix. At the end of 24

25 region 1, the matrix cracks and the load at the cracked surface is transferred to the glass fibers. This is called the "First Crack" point. The process continious through out region 2 ( A-B) and very fine, almost faintly visible cracks appear on the tension face. As more cracking occurs, it reaches a point when it is no longer possible to transfer sufficient load back into the matrix. This is the end of Region 2. In Region 3 (B- End), the loading is carried only by the glass fibers, and continues so until failure. The non-linear portion between A and B exists, only if a sufficient volume fraction of fibers is present. For low volume fraction of fibers (V f < 0.5%), the ultimate flexural strength coincides with the first cracking strength and the load deflection curve descends immediately after the cracking load. [High Performance Concrete] Tensile and Splitting Tensile In cement-based matrices the associated strains are relatively small in magnitude and the failure in tension is rather brittle. The addition of fibers to such matrices improves the tensile properties of the fiber reinforced concrete in comparison with the unreinforced matrix. In the most investigations in the field of fiber reinforced concrete it is very difficult to interpretate the results from direct tension tests so the results come indirectly from flexural tests or split cylinder tests. The difficulties are due to differences in specimen sizes, specimen shapes, instrumentation and methods of measurement. Till now no standard specimen test has been available for direct tension strength. The size of the specimen, stiffness of the testing machine, gauge length, which is used to calculate strains, and the number of cracks developed within the gauge length are the factors in which we have the appearance of different stress-strain or force-elongation curves. The volume fraction of fibers determines the stress-strain or load-elongation response of fiber composites in tension. This response can be divided into two stages for fiber reinforced concrete. In the first stage, before cracking, the composite can be described as an elastic material with a stress-strain response very similar to that with the un-reinforced matrix. After cracking the fibers tend to pull out under loading resulting in a sudden change in the load-elongation or stress-strain curve. In the second stage the curve 25

26 drops very suddenly in the load-elongation curve joining the cracking to the post cracking load. There are many factors that influence splitting tensile mode; namely, the volume fraction, the aspect ratio, and the bond characteristics of fibers. In addition to these factors, hooked and deformed fibers are expected to increase the splitting tensile resistance compared to straight or non-deformed fibers. Finally the type and the amount of fibers do not significantly enhance the first-cracking stress or the fiber reinforced composite. Shear Strength Shear failure can be sudden and catastrophic. The use of fibers helps to improve the shear behavior of concrete. The methods that shear behavior of fiber reinforced concrete can be checked are mainly two: a) direct shear test and b) tests on beams and corbels. The direct shear tests are required so to understand the basic transfer behavior of concrete, while the test on beams and corbels are necessary to understand the behavior of structural members reinforced with fibers. The results of the investigations on the above tests have shown that the addition of fibers improves the shear strength and the ductility of concrete. The fibers are more effective in high strength concrete than in normal strength concrete due to the improved bond characteristics associated with the use of fibers in conjunction with high strength concrete. Modulus of Elasticity The modulus of elasticity of a material is a property needed for modelling mechanical behavior in various structural applications. It expresses the dynamic energy that can be stored in the body, without causing permanent deformations. Many tests have been performed to measure the moduli of elasticity for fiber reinforced concrete composites. The simplest model for composites made out of two different materials, the upper- and lower-bound solutions or a combination of them only depend on the volume fraction and the modulus of each material. More advanced models for fiber reinforced composites include, in addition, the properties of the interface between the two materials, whether the fibers are discontinuous or not, the distribution and orientation of the fibers, the aspect ratio (length and diameter) of the fiber, and the like. For the GRC the flexural stress-strain curves are used to determine values of modulus of elasticity for design purpose. Values of 26

27 flexural modulus of elasticity are normally in the 1.5 to 2.9 x 106 psi range, and will vary in accordance with water to cement ratio, sand content, cure, density and degree of micro cracking. Experimental studies have shown that the addition of fibers have only a slight effect on the ascending branch of the stress-strain curve of the composite. Creep and Shrinkage Glass fiber reinforced concrete is capable of sustaining load over prolonged periods. Creep behaviour is similar to that of other cement-based materials. Initial elastic deformation is followed by a slow creep deformation under sustained load. The creep rate decreases with time on a logarithmic basis. An exception to this general rule is found when load is applied to a saturated glass fiber reinforced concrete specimen. Higher creep deformation is observed in the first hour of loading of saturated specimens than in subsequent logarithmic increments. After this time the creep rate parallels to that of materials loaded in other environments. Creep strain is proportional to the initial strain, and creep data may be expressed as the ratio of creep strain to initial strain. In general, creep strains are smaller than expansion/contraction strains due to moisture changes. Creep studies with composites indicate that these properties are controlled largely by the matrix. This is expected because of the small proportions (typically 5 percent by weight) of the fiber in the composite. There has been no indication of any adverse creep effects in the composite resulting from the interaction between the matrix and the fiber. The factors that influence the shrinkage strain in fiber reinforced concrete are: temperature and relative humidity, material properties, the duration of curing and the size of structure accordingly. The addition of fibers to concrete helps in counterbalancing the movement arising from volume changes taking place in concrete, and tends to stabilize the movement earlier when compared to plain concrete.[ High Performance concrete] The results from the experimental studies have shown that the fibers can not restrain the free drying shrinkage strains or cause a slightly smaller shrinkage than that of plain concrete. If the purpose of fibers is only to restrain the free drying shrinkage strain then it is recommended to use short and randomly distributed fibers 27

28 because they have larger number of fibers available in a given volume of concrete. Proportionally with the type of fibers that is used in relation to shrinkage they affect more or less reduction on the average crack widths. Polypropylene fibers are much less affective in reducing cracks than steel fibers. Finally randomly distributed fibers could enhance the mechanical properties of shrinkage-compensating concrete by restraining the composite uniformly in all directions without adversely affecting the mechanical properties of such composites. Strain Capacity Fiber-reinforced concrete is distinguished for its toughness. This means that it has the ability to withstand relatively large strains before failure and large deformations and ductility. The fibers impart considerable energy to stretch and depond the fibers before complete fracture of the material occurs. In order to evaluate the toughness of fiber reinforced concrete three toughness indexes (I5, I10, I20 according to ASTM specifications) are used. These toughness indexes are calculated as the area under the load-deflection curve up to the prescribed service deflection divided by the area under the load-deflection curve up to the first cracking deflection. The factors that influence the flexural toughness are the type of fibers, volume fraction of fiber, aspect ratio, fiber s surface deformation, bond characteristics and orientation. Tests conducted on polypropylene, glass and steel fiber-reinforced concrete showed that glass and polypropylene fibers lead to low toughness values compared to steel fibers. This attributes partly to the high aspect ratio of the fibers used which lead to difficult mixing and possibly higher porosity. Coefficient of Thermal Expansion Till now there has been no experimental investigation dealing with the thermal expansion of fiber reinforced concrete. Since the coefficient of thermal expansion of glass is of the same order as that of concrete, the coefficient of thermal expansion of glass fiber reinforced concrete is expected to be the same with the plain concrete. For large volume fraction of fibers the simple rule of mixtures is used in order to determine the coefficient of thermal expansion providing that the properties of fibers and their interfacial bond with the matrix are not affected from the temperature of composite. 28

29 Poisson s Ratio Minimum elements are known for the Poisson s ratio of fiber reinforced concrete. Usually the Poisson s ratio assumed to be the same to that of concrete. This may be a reasonable assumption provided that the composite remains in the elastic range of behavior, after cracking the confining effects of the fibers bridging the cracks will have a significant effect on the lateral deformation, when measured according to the Poisson s ratio. Fracture Toughness Mortars as well as concrete are rather brittle materials. They have low tensile strength relative to their compressive strength. Randomly distributed fibers are putted in the mixtures in order to improve their fracture properties. For many years it has been attempted to characterize them by their fracture properties. Both linear-elastic and elastic-plastic fracture mechanics techniques have been applied. The crack growth mechanism in this material is described in terms of three different zones: a stress-free zone, a pseudo-plastic zone, and a process zone. The stress-free zone is the zone where the fibers have either completely pulled out or failed, the pseudoplastic zone is the zone where the matrix has cracked but the fibers bridging the crack provide some resistance to pull out, and the process zone is the distributed region in front of an advancing crack due to the stress concentration field. The psuedo-plastic zone provides the main contribution to the fracture energy of fiber reinforced cement composites. [High Performance Concrete] The factors that affect fracture energy of fiber reinforced concrete are: the fiber type, volume fraction and fiber lengths, the particular fiber finish and pretreatment. The composite toughness depends mainly from the fiber length and less from the fiber type and further improvement can achieve by means of fiber pretreatment to affect local crimp or irregularities or to induce controlled damage of fiber during the pullout process. In high strength concretes can be achieved high toughness when issues such as workability with higher fiber volume fractions, compressive strength reduction problems and also when using high performance fibers which have high modulus; high tensile strength and; high bond strength with the matrix can be solved. 29

30 Impact Resistance A number of studies have been conducted in order to check the influence of fibers to concrete in impact resistance. The result that was derived from those studies has shown that fibers enhance the impact resistance. The impact resistance of glass fiber reinforced concrete is influenced strongly by the reinforcing fibers. Increasing fiber length from, for example, 1 to 2 in. or using glass fibers with improved sizing, increases impact strength. Cured glass fiber reinforced concrete at 28 days has higher impact strengths than either unreinforced cement paste or asbestos cement. Impact properties relate to the area under the tensile or flexural stress-strain curve as these curves alter with time, the impact properties are reduced. Normally, impact strength is not a design parameter. In addition to its higher impact resistance, glass fiber reinforced concretes failure characteristics are different from those of asbestos cement or plain concrete. They exhibits pseudo ductile behaviour for several years and damage due to impact is usually confined to the area of impact without evidence of cracks propagating beyond this area. Upon prolonged aging glass fiber reinforced concrete can be expected to become less ductile, consequently diminishing impact resistance. Fatigue Fatigue strength can be described as the maximum flexural fatigue stress at which fiber reinforced concrete composites can withstand a prescribed number of fatigue cycles before failure. The fatigue strength can de calculated through endurance limit which is expressed as a percentage of either: a) its virgin static flexural strength, or b) the maximum static flexural strength of similar plain unreinforced matrix. The fatigue strength and the endurance limit increase with addition of fibers and increasing volume fraction of fibers. Also the improved bond characteristic of fibers improves the fatigue strength of fiber composite. Hooked-end steel fibers cause the highest increasing in fatigue strength. On the other hand the lowest increase was with straight steel fibers and polypropylene fibers. Abrasion Resistance Erosion in the surface of concrete can be caused due to a gradual wearing as a result of small particles or debris rolling over the surface at low velocities or due to abrasion resulting high velocity flow and impact of large debris. Fibers have 30

31 significant erosion resistance only in second occasion and mainly steel fibers. Abrasion tests in accordance with ASTM specifications showed almost any difference between the abrasion resistance of plain concrete and fiber reinforced concrete. Freezing and Thawing The fibers themselves do not cause increase in the resistance of concrete on freezing and thawing. That is, the addition of fibers in concrete with no resistance to freezing and thawing will not contribute in any further improvement. Many studies in the past have shown that «the addition of entrained air improves the freeze/thaw durability of fiber reinforced concrete in a manner similar to that of plain concrete».[high Performance Concrete] Wet Dry Exposure Experimental tests on concrete specimens, with and without polypropylene fibers, have shown that the addition of fibers retard the deterioration process on the surface skin of the concrete specimens. Tests have been conducted in hot weather environment. Alkaline Environment In order to investigate the durability of fibers in alkaline environment an accelerated aging process was used. The investigation was conducted with synthetic fibers made of nylon 6, polypropylene, and polyester. The specimens were stored in lime saturated water at certain temperature. Then the specimens tested under four point loading and the integrity and effectiveness of fibers was tested. The results have shown that all three types of fibers provided post cracking resistance. Finally, as we have seen, the change of reinforced mortar behaviour with regard to the ductility and absorption energy is essential. This is influenced from: the quantity of fibers, the geometry of fibers and finally from the adhesiveness of fibres with the cement paste. Fire Endurance Glass fiber reinforced concrete made of cement, glass fibers, sand, and water is non-combustible and meets the requirements of ASTM. When used as a surface material, its flame spread index is zero. 31

32 Density The dry density of spray-up glass fiber reinforced concrete depends primarily on fiber content, water-cement ratio, polymer content, sand addition, compaction, and spray techniques. These factors also influence porosity. Effects of Orientation of Glass Fibers The fibers are only able to provide strength and stiffness in their direction. Fibers which are not aligned with the direction of stress act in a less efficient manner that those that are. Hence, a composite with the fibers all aligned in one direction will provide maximum resistance to stress in that direction. Apart from some specialist process, it is not practically feasible to make use of this orientation property to its maximum effect. In thin section products, the major stresses are normally in the plane of the section and advantage can be taken by using sprayed glass reinforced concrete which lays down the fibre in a random 2-dimersion array in the plane of the material. The use of Chopped Strand Mats in premix glass reinforced concrete enables the properties to approximate to those of sprayed one as long as there is sufficient glass fiber present. A further effect of orientation is on the quantity of fibers that can be incorporated into the matrix. The packing density of the glass fibers stands is higher if there is some degree of alignment and this is shown in the manufacture of glass reinforced concrete, where 5% by weight is commonly used in sprayed one, but only 3.5% by weight is used in premix. The effect of orientation also needs to be considered in a negative sense. If the fibers are assumed to be randomly orientated, they may give rise to plane of weakness. This can arise in the manufacture of premix glass reinforced concrete if the mix is badly placed. 4.3 Applications of fiber reinforced concrete Because the advantages of fibres are presented in advanced stage of deformities (afterwards the fracture) and with datum the restriction from workability and financial, the application of fibres cannot replace the reinforcement in fiber reinforced concrete. The application becomes where important deformation and 32

33 ductility is required or where reinforcement is difficult to placement due to its figure or shape. Such cases are: tunnels reinforcement, the enhancement of concrete from the erosion on its surface due to abrasion, fire, seismic stresses etc. Mortar and concrete are very similar materials with similar ingredients. Till now little information is given on reinforced mortars specifications and that s the reason why many designers consider that mortar properties are the same to concrete ones. 5. MARBLE AGGREGATES In international bibliography the majority studies concern mortars with limestone aggregates. But today tones of mortar with marble aggregates have been started to be sold. As aggregate called the materials that derives from nature (quarries, mines) and they do not react chemically with the other binding materials and the other auxiliary matters. Those materials are crashed and categorized in various categories according to their granulometric gradation. Limestone is the most popular aggregate for the mortar preparation. It derives from lime rocks and is presented either like clean limestone (CaCO 3 ) or like Dolomite (limestone with carbonate magnesium MgCO 3 ). The clean limestone has got an open gray or white color. But when it has got a green color existence of iron may be included therefore the specific limestone must be avoided in the production of mortar. The limestone, before its use for the mortar preparation, the constitution of the rock that it comes from, its toughness, absorbency in water and color must be checked. Finally it should be free from any foreigner corpuscle and admixtures. Marble aggregates are used in the present study. Marble derives from the recrystallisation of limestone. It is commercially disposed mainly for sculptures. In order to be used in construction it is cut, chopped and smoothed. The characteristics of marble aggregates which are going to be used for Fig. 2: Quarrying of marble the production of dry mortars depend on their chemical and mineralogical gradation, on their color, on their strength and toughness and finally on their absorbency. These 33

34 marble aggregates come from waste of curries. A voluminosity of this waste is inadequate for cutting and further use and disposal as marble. These volumes of marble are discarded and called "stem". These fracture in smaller pieces and then they are rubbed dried, and graded in granulometrics. According to the purpose of the study the marble with the suitable gradation is selected. In the present study the granulometric gradation of marble aggregate is 0-4mm. 6. GLASS FIBERS 6.1 Introduction Fibrous materials have been used for many thousands of years to stabilize materials that are inherently unreliable. Straw in mud bricks and horse hairs plaster are two examples. Now, there are numerous fiber types available for commercial use, the basic type being steel, glass, synthetic materials Fig. 3: Glass fibers (polypropylene, carbon, nylon etc.). Of these, glass and steel fibers have received the most attention. Ancient Egyptian made containers of coarse fibers drawn from heat softened glass. Then at 18 th century, the French scientist, Reaumur, considered the potential of forming fine glass for woven glass articles. Today glass fibers are among the most versatile industrial material. They can be incorporated into a matrix either in continuous lengths or in discontinuous (chopped) lengths. There are five categories of glass fibers: E glass, C glass, S-2 glass, M glass, AR glass and D glass. Each category is distinguished according to its property or characteristics. Our study refers to E-glass fibers. They have a good strength and stiffness, a high strength to weight ratio and good resistance to corrosion in various environments. Also, they are characterized by either low electrical conductivity and for that reason they are used where strength and high electrical resistivity is required. The main role of fibres is to include regions of high strength material which control the propagation of cracks from voids in the matrix 34

35 and hence give a reliable tensile strength to an otherwise brittle material with unreliable strength and poor impact characteristics. 6.2 Physical and Technical requirements from Fibers The ideal fiber needs to be economical, easy to use and meet a demanding technical specification. Physical and technical requirements for fiber reinforced mortar include the following: Disperse uniformly without segregation Do not protrude from the surface They are invisible when the mortar surface weathers Have a high tensile strength to withstand stresses during shrinkage Have a high modulus of elasticity to absorb shrinkage stresses before the mortar cracks Have a superior bond with the mortar They are chemically resistant to the alkalinity of the mortar Present no health hazards. Have sufficient length Have high aspect ratio, they must be long relative to their diameter. 6.3 Glass Fiber Oxide Compositions E-glasses fibers are general purpose fibers because they offer useful strength at low cost. Their oxide components are the followings: silica content (SiO 2 ) 54.0% by weight, aluminium content (Al 2 O 3 ) 15.0 % by weight, calcia content (CaO) 22.0% by weight, magnesium content (MgO) 0.5% by weight, boron oxide (B 2 O 3 ) 7.0% by weight, iron oxide (Fe 2 O 3 ) 0.3% by weight and K 2 O 0.8% by weight. 6.4 Glass Fiber Properties Glass fiber properties, such as tensile strength, Young s modulus, and chemical durability, are directly measured on the fibers. Other properties, such as dielectric constant, dissipation factor, dielectric strength, volume/surface resistivities, and thermal expansion, are measured on glass that has been formed into a bulk 35

36 sample and annealed (heat treated) to relieve forming stresses. Properties such as density and refractive index are measured on both fibers and bulk samples, in annealed or unannealed form Physical Properties Density of glass fibres is measured and reported either as shaped or as bulk annealed samples. Tensile strength of glass fibers is usually reported as the pristine single-filament or multifilament strand measured in air at room temperatures. Moisture has a detrimental effect on the pristine strength of glass. This is best illustrated by measuring the pristine single-filament at liquid nitrogen temperature the influence of humidity is minimised. The result is an increase of % in strength over a measurement at room temperature in 50% relative humidity. E-Glass fibers properties are the following: Fracture Deformation, %: 4.8 Young s Modulus: 71.7 GPa Flexural Strength: 3447 MPa Specific Weight: 2.54 gr/cm Chemical Resistance The chemical resistance of glass fibers to the corrosive and leaching actions of acids, bases, and water is expressed as a percent weight loss. The lower this value, the more resistant the glass is to the corrosive solution. It should be noted that glass corrosion in acidic environments is a complex process beginning with an initial fast corrosion rate. With further time, an effective barrier of leached glass is established on the surface of the fiber and the corrosion rate of the remaining unleached fiber slows, being controlled by the diffusion of compounds through the leached layer. Later, the corrosion rate slows to nearly zero as the non-silica compounds of the fiber are depleted. For a given glass composition, the corrosion rate may be influenced by the acid concentration (Figure 3), temperature, fiber diameter, and the solution volume to glass mass ratio. In alkaline environments weight loss measurements are more subjective as the alkali affects the network and reprecipitates the metal oxides. 36

37 Tensile strength after exposure is a better indicator of the residual glass fiber properties Electrical Properties The dielectric constant or relative permittivity is the ratio of the capacitance of a system with the specimen as the dielectric to the capacitance of the system with a vacuum as the dielectric. Capacitance is the ability of the material to store an electrical charge. Permittivity values are affected by test frequency, temperature, voltage, relative humidity, water immersion, and weathering Thermal Properties The viscosity of a glass decreases as the temperature increases. Also, the conductivity of glasses drops steadily with decreasing temperature and reaches very low values, near absolute zero. Thermal conductivity data for glass varies among investigators for materials which are normally identical. In general fused silica glass and the alkali and alkaline earth silicate glasses have relatively similar conductivities at room temperature, whereas conductivities of borosilicate and glass that contain lead and barium are somewhat lower. Near room temperature, the thermal conductivity for glasses ranges from 0.55 W/m K for lead silicate (80% lead oxide, 20% silicon dioxide) to 1.4 W/m K for fused silica glass. E. H. Ratcliffe developed property coefficients for predicting thermal conductivity from the percentage weight compositions of component oxides making up the glass. Using this calculation, it is found that the approximate thermal conductivity of C Glass is 1.1 W/mK, E Glass is 1.3 W/m K, and S-2 Glass fibers is 1.45 W/mK near room temperature Radiation Properties E Glass and S-2 Glass fibers have excellent resistance to all types of nuclear radiation. Alpha and beta radiation have almost no effect, while gamma radiation and neutron bombardment produce a 5 to 10% decrease in tensile strength, a less than 1% decrease in density, and a slight discoloration of fibers. Glass fibers resist radiation because the glass is amorphous, and the radiation does not distort the atomic ordering. Glass can also absorb a few percent of foreign material and maintain the 37

38 same properties to a reasonable degree. Also, because the individual fibers have a small diameter, the heat of atomic distortion is easily transferred to a surface for dispersion. E Glass and C Glass are not recommended for use inside atomic reactors because of their high boron content. S-2 Glass fibers are suitable for use inside atomic reactors. 7. METHODOLOGY 7.1 Materials Cement A high strength cement type CEM I52.5 was used with high C3S content (65%) and low C3A content (2%). A low C3S content guarantees a good durability against sulfate attack. A high C3S content speeds up the hardening. Aggregate Marble aggregate with maximum grain size of 4mm was used. Aggregate are premix with the cement at factory. Glass Fibers Glass fibers type E was used in three different volume percentage. The fibers were used for the increase of absorption of energy during the flexural test. The shape and the dimensions of the fibers affect on the rheological attributes of the fresh mortar Fig. 4: Orientation of fibers in the mixture and on the mechanical properties of hardened mortar. The orientation of the fibers in the mixture is presented in Fig.4 Specimens Prismatic specimens, 40 x 40 x 160 mm in size (Fig.5), were manufactured according to National Standards (ΕΛΟΤ EN ), for compression and bending tests. These specimens were cast in stainless steel moulds and wet carring at 20ºC until the time Fig. 5: Prismatic specimens 40 x 40 x 160mm 38

39 of test. The quantities of constituent materials and mix percentage of fiber reinforced High-Strength mortar are reported in table 3. Parameter Mix Designation GFRM I GFRM II GFRM III GFRM V Cement Content, gr Aggregate content, gr Fiber Content, gr Volume Fraction, Vf percentage (%) Water-Cement Ratio Table 3:Quantities of Constituent Materials and Mix Percentage of Fiber Reinforced High- Performance Mortar 7.2 Experimental Procedure It were prepared unreinforced and reinforced specimens in three different volume percentages. Their fabrication begins with mixing of cement, aggregates, and fibers without water for a few minute to obtain an optimise fiber dispersion in mortar. Then water is added and the blend is also mixed for few minutes. The mixure is vibrated by a vibrator and then the fresh mix is cast in specific moulds in two approximately equal layers vibrating them suitably in each layer. The moulds should be clean and their internal faces must be lubricated with a thin layer of mineral oil to prevent adhesion of the hardened mortar and steel moulds. The excess mortar is removed with a palette knife, leaving the mortar surface flat. After casting a wet blanket is laid on moulds in order to maintain the hardened material in the necessary saturated condition for cracking resistance. After 48h the specimens were removed from the moulds and they immersed in water for 26 days (Fig.6). The storage chamber had a controlling temperature of 20 C ± 2 C. In 28 th day mortar specimens are tested in compression and bending loading. 39

40 Fig. 6: Specimens immersed in water Accordingly to ΕLΟΤ ΕΝ for the bending tests three specimens shall be provided. These we fracture in two halves to provide totally six half specimens for the compressive strength tests. In our study, for each category, five specimens are provided for flexural strength and ten prisms for compressive strength. Determination of flexural strength The testing apparatus (Fig.7) shall be comply all the needed requirements ΕLΟΤ ΕΝ : According to this standard the testing apparatus shall have two steel supporting rollers of length between 45mm and 50mm with 10mm ± 0.5mm diameter, spaced 100,0mm ± 0.5mm apart. A third steel roller of the same length and diameter located above and centrally between the supports rollers for load impose. The three vertical planes through the axes of the three rollers shall be parallel and remain parallel, equidistant and normal to the direction of the prism under test. One of the support rollers and the loading roller shall be capable of tilting slightly to allow a uniform distribution of the load over the width of the prism without subjecting it to any torsional stresses. The load direction is presented in figure8. Fig. 7: Bending machine Fig 8: Load Direction in Flexural Test 40

41 The specimens after casting are wiped with a clean cloth to remove any loose grit or other material. Before testing the bearing surface of the rollers are cleaned and then the specimens are placed with one of its faces (which have been cast against the steel of the mould) on the supporting rollers. The load is applied without shock at a uniform rate and the maximum load applied is recorded. Then the broken specimens are return to the storage room and they kept there for the compressive strength measurements. The flexural strength is calculated using the follow equation: F = 1, 5 Pl 2 bd where: P = maximum flexural load l = length of specimen b and d = the base and light lengths of specimens Determination of compressive strength The testing machine (Fig.9) shall be comply all the above requirements according to ΕΛΟΤ ΕΝ : The upper machine platen shall be able to align freely as contact is made with the specimen, but the platen shall be restrained from the tilting with respect to another during loading. Two bearing plates made of tungsten carbide or of steel of surface hardness at least 600HV Vickers hardness value in accordance with EN ISO The plates shall be 40,0mm long x 40,0mm ± 0,1mm wide and 10mm thick. The Fig.9: Compression machine dimension tolerance for the width shall be based on the average of four symmetrically placed measurements. The flatness tolerance for the contract faces shall be 0.01mm. Compression jig used to facilitate the location of the bearing plates. The base plate of the jig shall be of hardened to steel and the faces shall have a fitness tolerance of 0,01mm. A device to provide 41

42 positive centring on the lower platen of the testing machine shall be provided. Hardened and tempered silver steel pillars shall be symmetrically placed about the centring device so that the gap in one direction is the normal width of the prism plus 0,3mm and in the other direction is the normal width of the prism plus 0,8mm. the top face of the base plate shall be marked with an arrow in the direction of the greater distance between the pillars to indicate of the long axis of the bearing structures. The load direction is shown is figure 10, 11. Fig. 10: Load Parallel with Layering Fig. 11: Load Perpendicular to Layering in The half specimens after the flexural strength test are wiped with a clean cloth and placed in the machine in such a manner that the load is applied to one of its faces (which has been cast against the steel of the mould). The rest of them are placed in the machine and the load is applied parallel with the steel of the mould. In both cases the load is being applied to the whole width of the faces in contact with the platens without shock and with continuously increasing rate. The maximum load applied is recorded and the compressive strength is calculated as the maximum load carried by the specimen divided by its cross-sectional area. [ΕΛΟΤ] For the determination of strain for bending and compression tests strain gauges were staked on the surface of one specimen from each category. Metal Moulds The assembled moulds (Fig.12) shall be conform all the following requirements according to ΕΛΟΤ ΕΝ : a) Dimensions. The internal depth and width of each compartment is 40mm ± 0,1mm, the length of each component is 160mm ± 0,4mm. 42

43 b) Flatness. The surface of each internal face lies between two parallel planes 0,03mm apart: The joints between the sections of the mould and between the bottom surface of the mould and the top surface of the base plate shall lie between two parallel planes 0,06mm apart. Fig. 12: Metal Mould c) Squareness. The surface of each internal face lies between two parallel planes 0,50mm apart, which are perpendicular to the bottom surface of the mould and also the adjacent internal faces. d) Parallelism. The top surface of the mould lies between two parallel planes 1,0mm apart and is parallel to the bottom surface. e) Surface Texture. The surface texture of each internal surface shall be not greater than 3.2mm R a measured in accordance with ISO RESULTS The results from unreinforced and reinforced specimens that have been tested in compression and flexural are presented on the above table. It is shown for each specimen: dimensions, mass, volume, density, bending, maximum load from compression and flexural test and the corresponding stresses 43

44 d (mm) h (mm) l (mm) V (cm³) m (gr) ρ (gr/cm³) P (KN) Μ (KN*m) stress (MPa) P perpendicularly to layering (KN) stress perpendicularly to layering (MPa) P parallel with layering (KN) stress parallel with layering (MPa) Percentage of fiber by volume:0% A_N_1 40,55 40,30 160,00 261, ,23 3,07 0,08 6,99 66,19 41,37 89,91 56,19 A_N_2 40,28 40,35 160,00 260, ,24 3,45 0,09 7,89 64,54 40,34 94,88 59,30 A_N_3 40,23 40,60 160,00 261, ,21 3,05 0,08 6,90 62,88 39,30 87,70 54,81 A_N_4 39,97 40,35 160,00 258, ,25 2,69 0,09 Rejected 72,26 45,16 86,60 54,13 A_N_5 40,20 40,18 160,00 258, ,21 4,10 0,07 Rejected 70,61 44,13 89,91 56,20 Average Α_N: 7,26 42,06 56,13 Percentage of fiber by volume: 0,07% Υ600_1 40,32 40,50 160,00 261, ,16 3,24 0,08 7,35 55,16 Rejected 99,29 62,06 Υ600_2 40,45 40,70 160,00 263, ,18 3,90 0,10 8,73 77,22 48,26 100,40 62,75 Υ600_3 40,43 40,20 160,00 260, ,18 3,59 0,09 8,24 84,05 52,53 97,91 61,19 Υ600_4 40,27 41,07 160,00 264, ,20 3,41 0,09 7,53 65,08 40,68 100,94 63,09 Υ600_5 40,23 40,50 160,00 260, ,19 2,65 0,07 Rejected 71,71 44,82 101,22 63,26 Average Υ600: 7,96 46,57 62,47 Percentage of fibers by volume: 0,13% Υ1200_1 40,37 40,20 160,00 259, ,19 3,55 0,09 8,16 64,58 Rejected 104,25 65,16 Υ1200_2 40,20 40,72 160,00 261, ,21 3,62 0,09 8,15 81,36 50,85 98,74 61,71 Υ1200_3 40,22 40,33 160,00 259, ,23 3,62 0,09 8,30 75,84 47,40 102,60 64,13 Υ1200_4 40,15 40,37 160,00 259, ,21 4,11 0,10 Rejected 81,36 50,85 99,29 62,06 Υ1200_5 40,15 40,85 160,00 262, ,20 4,13 0,10 Rejected 70,05 43,78 107,02 66,89 Average Y1200: 8,20 48,22 63,99 Percentage of fibers by volyme: 0,26% Y2400_1 40,37 40,95 160,00 264, ,17 2,79 0,07 Rejected 75,29 47,06 0,00 0,00 Y2400_2 40,25 40,30 160,00 259, ,20 3,76 0,09 8,63 87,15 54,47 98,74 61,71 Y2400_3 40,17 41,42 160,00 266, ,16 2,07 0,05 Rejected 74,74 46,71 108,12 67,58 Y2400_4 40,53 41,10 160,00 266, ,16 3,62 0,09 7,93 79,43 49,64 97,67 61,04 Y2400_5 40,53 41,68 160,00 270, ,15 3,28 0,08 Rejected 62,33 Rejected 104,53 65,33 Average Y2400: 8,28 49,47 63,92 Table 4: Results from Compression and Flexural Tests 44

45 9. DISCUSSION The load deflection diagram is presented in figure 13. In this diagram are shown indicational curves for one specimen of each category (unreinforced, Y600, Y1200 and Y2400). 4 Load - Deflection P (kn) 3,5 3 2,5 2 1,5 1 0,5 0 P (kn) P (kn)-600 P (kn)-1200 P (kn)-2400 P(KN)_Unreinforced P(KN)_Y600 P(KN)_Y1200 P(KN)_Y ,001 0,002 0,003 0,004 0,005 δ (cm) Fig. 13: Load - Deflection Diagram By suitable calculations, the average flexural strength and modulus of elasticity are found and the variation of them is depicted in the Fig.14 and Fig.17. Flexural Strength Stress (Mpa) 9,00 8,00 7,00 6,00 5,00 4,00 3,00 2,00 1,00 0,00 Flexural Strength - V f (%) 0,26% 0,07% 0,13% 0% 0 0,05 0,1 0,15 0,2 0,25 0,3 V f (%) Fig. 14: Variation of Flexural Strength via Volume Percentage of Fibers

46 From the stress-percentage of fibers (%) diagram (Fig14) is noticed that the flexural strength is increases via volume percentage of fiber in the mixture. The unreinforced specimen has the minimum flexural strength (7.26 Mpa). The specimen with the minimum percentage of fiber indicates a high increase in flexural strength comparatively to the unreinforced one. A further increase is observed in strength of reinforced mortar with fiber percentage of 0.13%. Finally the strength seems to remain constant for higher fiber volume percentage. A characteristic shape of a specimen after bending test is presented bellow (Fig.15). The specimen has 0.13% fibers by volume. It is observed that the fracture was in the middle of the specimen. Fig.15: Specimen after bending test A stress strain diagram from the fracture of specimens in bending test is shown in Fig. 14. From the diagram is noticed that flexural stress of the specimen seems to increase for the specimen with the minimum percentage of fibers comparatively to the unreinforced one. The flexural stress seems to increase even more for the second ratio of fibers while for the third composition the flexural stress is slightly reduced. Also from the diagram is observed that the strain is increase for the specimen with 0.07% glass fibers while for the other two compositions (0.13% and 0.26%) the stress is decreased. The diagram in Fig.16 is not a representational stress-strain diagram for all the specimens because it has created from the values of one specimen from each category.

47 Flexural stress - strain stress (MPa) ε (10-6) unreinforced Y600 Y1200 Y2400 stress (Mpa)_Unreinforced stress (MPa)_Y600 stress (Mpa)_Y1200 stress (Mpa)_Y2400 Fig. 16:Flexural stress-strain diagram The change of modulus of elasticity via volume percentage is shown at the diagram (Fig.17). By the increase of fibers ratio is observed a slight enhancement of the modulus of elasticity. Between the second and the third composition of fibers it isn t noticed any further increase and the modulus of elasticity seems to remain constant. Modulus of Elasticity E (GPa) ,05 0,1 0,15 0,2 0,25 0,3 V f (%) Fig. 17: Modulus of Elasticity via Volume Percentage of Fibers

48 Compressive strength Compressive strengths (perpendicularly to layering and parallel to layering) of the unreinforced specimens and reinforced with three different volume percentage of fibers specimens are presented in table 5. From Figure18 it is observed an increasing in compressive strength comparatively with the volume ratio of fibers. It is noticed that the unreinforced specimen has the lower value of compressive strength (42.06 and respectively) and the specimen with the higher percentage of fiber has the maximum value (49.47 and respectively). Also, the values of compressive strength are higher for the specimens that are tested in compression parallel with the layering due to the different way of casting. Finally, it is not observed a significant variation in the value of compressive strength (separately for each category) among the unreinforced and reinforced specimens. This is predictable because when reinforced specimens tested in compression, the fibers that are parallel with the load slip in the mixture and voids are created, so the compressive strength is reduced. Compressive strength Percentage of fibers (%) stress perpendicular to layering (MPa) stress parallel with layering (MPa) Unreinforced 0 42,06 56,13 Υ600 0,07 46,57 62,47 Υ1200 0,13 48,22 63,99 Υ2400 0,26 49,47 63,92 Table 5: Value of compressive strength according to the volume of fibers in the mixture with the different solutions investigated.

49 Compressive Strength stress (MPa) 70,00 60,00 50,00 40,00 30,00 20,00 10,00 0,00 0,26% 0,13% 0,07% 0% 0,07% 0,13% 0,26% 0% stress perpendicular to layering stress parallel with layering 0 0,05 0,1 0,15 0,2 0,25 0,3 V f % Fig.18: Compressive strength with the different percentage of glass fibers and with different solutions investigated. A characteristic shape of a specimen after compression test is presented in Fig.19, 20. In Fig. 19 is shown the specimen in compression machine after compression test and in Fig. 18 is observed the characteristic shape of the specimen after fracture. Fig. 19: Specimen after Compression test Fig. 20: Characteristic fracture of specimen after compression tests The compressive stress-strain curve for the unreinforced specimen and reinforced with the minimum percentage of fibers specimen are presented in figures bellow (Fig.21, 22). From those diagrams is noticed that fibers have no significant affect on compression strengths. The compressive of strength of the unreinforced and reinforced specimen with 0.07% glass fibers do not modify significantly. The