EXPERIMENTAL STUDY OF STRENGTH OF POLYPROPYLENE FIBER- REINFORCED MORTAR BY VARIABLE VOLUME PERCENTAGE OF FIBERS WITH MARBLE AGGREGATES

Transcription

1 EXPERIMENTAL STUDY OF STRENGTH OF POLYPROPYLENE FIBER- REINFORCED MORTAR BY VARIABLE VOLUME PERCENTAGE OF FIBERS WITH MARBLE AGGREGATES KANELLOPOULOU VASSO MSc STUCTURAL DESIDN & CONSTRUCTION MANAGEMENT THESIS FACULTY OF ENGINEERING 250 THIVON & P. RALLI St, AIGALEO, ATHENS-GREECE TEL.: , FAX:

2 EXPERIMENTAL STUDY OF STRENGTH OF POLYPROPYLENE FIBER- 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 KANELLOPOULOU VASSO SUPERVISOR SOTIROPOULOU ANASTASIA TEI PIREAUS KINGSTON UNIVERSITY DEPARTMENT OF CIVIL ENGINEERING SEPTEMBER

3 ACKNOWLEDGEMENTS This experimental study has been successful thanks to my supervisor, Mrs Anastasia Sotiropoulou, Dr Civil Engineer. I am grateful for her assistance and support to present thesis fulfillment. Also, I would like to thank Mr Pandermarakis Zacharias for his precious help during the testing process and preparation of this research. Finally, I deeply appreciate the contribution of Mrs Mpaka Aggeliki for the aid she offered me when necessary. 3

4 ABSTRACT The restraint for repairing mortars development leads to further investigation and new experimental results. The present study has to do with the behaviour of mortar consisted of marble aggregates and reinforced by polypropylene fibers. The composition of the mixture remains the same but the volume of fibers varies from 0% to 0.26%. Specimens had specific dimensions 160 mm x 40 mm x 40 mm and tested in compression and bending. The results arisen will be compared with corresponding glass fiber reinforced mortar. Key words: fiber reinforced mortar, marble aggregates, polypropylene fibers. 4

5 CONTENTS INTRODUCTION 1 AIM. 1 PROPERTIES OF FIBER REINFORCED CONCRETE. 2 Discrete fibers... 3 Continuous fibers.. 10 Advantages and Disadvantages of Fiber Reinforced. 12 POLYPROPYLENE. 14 Polypropylene Fibers.. 18 Application of Polypropylene Fibers in Concrete.. 19 MORTARS. 22 MARBLE AGGREGATES.. 32 RESEARCH METHODOLOGY 34 RESULTS & DISCUSSION CONCLUSIONS.. 47 FURTHER INVESTIGATION BIBLIOGRAPHY. 48 TABLE OF FIGURES Figure 1: (Polypropylene fibers) Figure 2: (Quarry process of marble).. 32 Figure 3: (Bending testing machine).. 36 Figure 4: (Compression testing machine) Figure 5: (Metal moulds) Figure 6: (Cast specimens). 37 Figure 7: (Maintenance in water). 37 Figure 8: (Vertical and Transverse Compression). 38 Figure 9: (Prismatic specimen 160mmx40mmx40mm with strain gauges). 38 Figure 10: (Change of flexural strength accordingly to fibers ratio) 42 Figure 11: (Stress deflection diagram in bending). 42 Figure 12: (Flexural Modulus of Elasticity).. 43 Figure 13: (Specimen tested in bending characterised by ductile behaviour.). 44 Figure 14: (Change of compressive strength accordingly to fibers ratio) Figure 15: (Diagram of stress deflection in compression) 45 5

6 Figure 16: (Characteristic type of failure in compression, Sotiropoulou 2004).. 45 Figure 17: (Specimen tested in vertical compression).. 46 Figure 18: (Specimen tested in vertical compression).. 46 TABLES Table 1: (Markantonatos and Demartinos 2003, p.10-9). 2 Table 2: (Koronaios and Poulakos 2006, p. 85 conformed to Hellenic Standards) 25 Table 3: (Compositions). 35 Table 4: (Results). 40 Table 5: (Results) 41 6

7 INTRODUCTION In our country there are often intense seismic phenomena that consequently cause extensive damages to structures. Also, many deteriorations and decays are observed to larger or smaller-scale works because of aging. Of course all the above-mentioned problems demand their direct restoration. For low scale decays for instance small cracks on load bearing structures it is possible to use suitable repairing mortars. There are a vast number of studies on common repairing mortars with limestone as aggregates but almost none of them regard the replacement of limestone aggregates by others, as happens here with marbles ones. Commercially available mortars with marble aggregates have already been available in construction industry markets but without a thorough out investigation. This study makes use of marbles aggregates with maximum grain size 4mm. These aggregates come directly from marble industry, which dispose it as waste. By this way, not only do we save raw materials but also lower its environmental impacts. One of the main features of this study will be the addition of polypropylene fibers to the investigated mortars. In general, fibers affect positively mortar's mechanical response, mainly by increasing its toughness. Consequently, the fiber volume percentage will be varied in order to investigate their influence and efficiency on mortars strength. The most common material contained in mortar and concrete is limestone aggregates. It is regarded useful with their replacement by marble aggregates and the observation of mortar s behaviour. As mortar, the maximum grain used is 4 mm. It is important to be mentioned the addition of polypropylene fibers in order to enhance the mechanical properties of the mortar and particularly the toughness. Moreover, the influence of different fiber volume percentage on mortar s behaviour is examined. The use of marble aggregates and fiber reinforcement are expected to demonstrate different mechanical behaviour and improved properties. Finally, the results of polypropylene reinforced mortar of this experimental investigation should be compared with the corresponding fiber glass mortar one. AIM The aim of this study is the experimental investigation of compressive and flexural strength of repairing fiber-reinforced and un-reinforced mortars with marble aggregates by various polypropylene fibers volume percentage and the comparison with corresponding of fiber-glass reinforced mortar ones. PROPERTIES OF FIBER REINFORCED CONCRETE. Fiber reinforced concrete is called the cement based matrix in which fibers are added either short and discrete or continuous and long during mixing. At early stages, the concept concerned the addition of short discrete fibers in order to improve its mechanical properties. Fibers are dispersed uniformly so this dispersion results to an almost homogenous material. Subsequent developments concern the addition of continuous long fibers to concrete. Fiber reinforced concrete becomes more and more useful in structures because of the improved properties that appear in comparison with the 7

8 conventional concrete. By using fibers, the concrete from a brittle material converts to a more plastic one because of fibers activation. Their addition plays an important role to the increase of strains during the failure and the limitations of cracks. Increasing the applied load stresses are shared to fibers and matrix until the latter cracks. After cracking stresses are transferred entirely to fibers till they are pulled out or broken. (Mullick et al. 2006). In some cases a trivial increase in strength is observed. Fiber reinforced concrete appears increased flexural strength, toughness and ductility which allow the application at many structures such as highway pavements, overlays, mortars, decks etc. The fibers indicated to each occasion are presented below. Type Application Glass Plastering of walls, pipes, shells, mortars, frames of sandwich type, wire fencing Steel Cellular roofs, pavements, decks, pipes, airport pavement, structure resistant to wind, tunnels. Polypropylene Foundation piles, pre stressed piles, plastering of frames, cover of underwater pipes Mantle Grids, pipes, insulting materials, fire resistant materials, roof panels, wall covers Carbon Corrugated roofs, membranous structures of single or double curvature, planks Natural fibers At low cost constructions (used at non-developed countries), separative walls Table 1 (Markantonatos and Demartinos 2003, p.10-9) The properties of fiber reinforced concrete differentiate at some points according to the type of fibers. Zia et al. (1994) have concentrated the results of many researches on fiber reinforced concrete and have composed a report on the mechanical properties of it, which are described below. Discrete fibers Compressive Strength In general, the addition of fibers slightly influences the compressive strength. In past researches an increase of about 20 % to mortar mixes is proved with straight steel fibers used. Only hooked steel fibers seem to effect on strength because of better anchorage into the matrix. Synthetic fibers such as those of polypropylene or polyethylene don t influence compressive strength but just increase the strains at peak stress. Finally, in experimental studies on carbon fibers used, it is noticed that the increase of volume of fibers indicates a decrease of compressive strength. Flexural Strength Flexural strength is influenced by many factors related to the fibers such as the type, geometrical characteristics, aspect ratio hence the fraction L/d f where L: fiber s length and d f : fiber s diameter, volume (V f ) that occupy in the matrix and orientation. Other factors such as ratio W/C, 8

9 density, air content etc, which influence the workability of reinforced concrete, can effect on the flexural strength indirectly. Considering all factors above, it s obvious that the ultimate strength is different from the first cracking strength. A general model that can describe approximately the behaviour of the matrix under flexural loading is presented above. Firstly, there is a linear branch from 0 to point A, which represents that the matrix has elastic behaviour. Stresses are transferred from matrix to fibers by interfacial shear until the matrix cracks. The corresponding strength is called first cracking strength. To be continued, there is a non linear branch from point A to B where the fibers take over all the stresses transferred by matrix after first crack. The load increases till point B termed as peak strength and the fibers tend to gradually pulled out from the matrix leading to high deformation. Finally, it is observed a descending branch after peak strength which represents the energy that the fiber reinforced concrete can absorb before its complete failure. In other words, this branch indicates the increased toughness that characterise the fiber reinforced concrete. For low volume of fibers (V f < 0,5%), point A is identical with point B which means that the strains take place immediately after the first cracking load. In experimental studies occurred, it is concluded that steel fibers increase the flexural strength and toughness of the matrix. Factors that influence flexural strength are the fiber content, aspect ratio and fiber surface deformation. Fiber content is of great importance factor in determining the maximum rate of strength. The other two factors effect on the fraction w/c which influences the demand in water and the workability of mix. Also, geometry such as hooked ends influence positively flexural strength because of better adhesion in the matrix which results to a higher resistance of pulling out of the matrix. So as concern fibers by polypropylene or polyethylene there isn t consistent alteration in flexural strength although the increase in toughness and post peak resistance of the matrix is obvious. The most important characteristic for polymer fibers is the flexural resistance that the matrix indicates after peak strength. A comparative study between steel and polymer fibers indicates that the descending branch of matrix with polymer fibers is steeper than this with steel fibers. This is explained by the low modulus of elasticity the polymers have. Carbon fibers have also the same behaviour than the fibers above, such as the increase of flexural strength and ductility. It is necessary to mention the significant increase of the later properties almost up to 90% compared to the unreinforced concrete. Tensile and Splitting Tensile Strength Generally, the addition of fibers improves tensile properties corresponding with the conventional concrete. There are difficulties in interpreting the results from direct tensile test as tensile and splitting tensile strength derive from indirect methods. The differences in specimens, shape, production and methods of measurement explain why direct tests aren t indicated. Also, investigators find difficulties in determining the post cracking behaviour which is characterized by a 9

10 single crack. The volume of fibers influences the correlation between stress and strain or load and elongation. The diagram of stress strain is separated into three stages. At first stage, before cracking the material presents elastic behaviour and seems like the un reinforced concrete. At second stage, after cracking the fibers pull out and tends to bridge the crack surface. At this point, the elongation curve joins the cracking stress rate to post cracking stress rate. If post cracking stress is higher than cracking stress, then a third stage exists beyond peak point. Therefore a descending branch is presented which indicates that the fibers pull out until they fail. Descending branch can be steep or moderate depending on the fiber rate and type of failure (brittle or ductile). Finally, post cracking strength depends on aspect ratio, volume of fibers and bond strength between the later and matrix. Splitting tensile strength is influenced by the same factors already mentioned. In addition to these factors hooked and deformed fibers present better splitting tensile strength than straight and non deformed. Also, the amount of fibers does not substantially enhance the first cracking strength but large volumes increase significantly the tensile load that matrix can carry. This behaviour is explained by the fact that fibers control the appearance of micro cracks and allow the creation of macro cracks. The remarks above are proved by same researches occurred on using different type of fibers with the view to determine the tensile strength. Shear strength The use of fibers is expected to improve shear strength as it happened with the others. As there are not many researches on this field, the conclusions derived are limited. Methods, by which shear strength is determined, are the direct shear tests and tests on beams and corbels. Generally, an increase of shear strength and ductility is observed. Also, steel fibers can be used as shear reinforcement in place of stirrups. The fibers can affect more on characteristics using high strength concrete than plain one. Therefore, fibers performance is enhanced in high strength concrete which is attributed to the improved bonding between them. In a comparative study, it is indicated that steel and polypropylene fibers increase ultimate load and ductility but steel fibers affect more ultimate load than polypropylene fibers do, while the later influences more on ductility. Finally, fibers are compared to conventional stirrups and the improvement in ductility is obvious but not in ultimate strength. Modulus of elasticity Modulus of elasticity is a characteristic element for each material. It expresses the dynamic energy that can be stored in the material without causing permanent deformations. It is important to be determined this property in order to choose the most appropriate material for each structure. Modulus of elasticity is affected by distribution of fibers in the matrix, their orientation and the aspect of ratio. Experimental studies indicate that steel fibers improve the modulus of elasticity of the composite compared with glass fibers. On the contrary, polypropylene fibers having low modulus of elasticity cause a decrease of modulus of elasticity of the composite. 10

11 So as far as the modulus of elasticity under compression is concerned, the addition of steel fibers seems to influence it slightly. On the other hand, studies realized using different fibers tensile modulus of elasticity increases with the increase of volume of fibers in the matrix. Creep In recent studies conducted to reinforced concrete with steel and polypropylene fibers, it is noted that their presence increases the creep strains in comparison with plain conventional concrete. In some cases a decrease of creep strains is observed due to reduced interfacial bond characteristics. Shrinkage As to plain concrete so as to reinforced one the factors that influence the shrinkage are the temperature, humidity, duration of curing and materials properties. The addition of fibers improves the affect of shrinkage. Fibers balance the movements which arise from volume alteration and stabilize them earlier than plain concrete. However, fibers slightly effect on free drying shrinkage strains but reduce the adverse width of cracks. It is observed that short and discrete fibers are more favourable than long ones due to higher volume occupied in concrete. So as cracks concern, steel fibers delay the formation of first crack and reduce significantly crack width. On the contrary, polypropylene fibers are less useful in reducing crack width than steel fibers. Finally, for high strength concretes the addition of fibers doesn t improve autogenous shrinkage in comparison with conventional concrete but concrete can undertake cracking at later age. Strain Capacity The essential property that distinguishes the fiber reinforced concrete is the ability of undergoing larger deformations before failure. Also, it limits cracks propagation and presents increased ductility. All these elements termed as toughness is the primary reason that fiber reinforced is used for many structures. In order to calculate the toughness the indexes I 5, I 10, I 20 are used according to ASTM Standards. The indexes depend on the aspect ratio, volume fraction, orientation and type of fibers. Generally, the addition of fibers results to an increase of bonding characteristics, creation of more deformations and elongation of post cracking, descending branch. These elements are explained by the large bending energy that the fibers develop during the pullout process and the presence of cracks after peak load. Steel fibers increase ductility, toughness and deformations after peak stress. By adding steel fibers the strain capacity under compression loads is improved. Moreover, steel fibers are useful in preventing sudden and explosive type of failure under static loading and in absorbing energy under dynamic loading. Other fibers used for reinforcement such as glass, polyester and polypropylene increase toughness and post peak deformations but not as much as steel fibers. This difference attributes to the low performance of these fibers which cause difficulty in mixing and higher porosity of concrete. 11

12 Coefficient of Thermal Expansion No change of coefficient of thermal expansion is notified due to the presence of fibers. The coefficient of thermal expansion of steel is the same to plain concrete and the same behaviour to fiber reinforced is expected. Furthermore, for low volume of glass and polypropylene fibers there is no alteration of coefficient as well. However, for high volume of fibers the use of simple rule of mixtures is suggested so as to determine the coefficient of thermal expansion and to conclude on the affect that the temperature has on properties of fibers and their bonding characteristics. Poisson s Ratio There are a few experimental studies concerned with the determination of Poisson s ratio. Till now, Poisson s ratio of fiber reinforced concrete is considered the similar to that of conventional concrete. It is attributed to the fact that composite remains in the elastic area but in the same time fibers tend to bridge the cracks, so the deformation can influence the value of Poisson s ratio. Fracture Toughness Toughness is expressed as the area under the load deflection curve. In general, reinforcement by fibers contributes significantly to the fracture toughness of the composite. Essential is the increase of crack growth resistance which appears as a stable process of crack growth and extension of cracks before failure. Factors that affect fracture toughness are the type of fibers, their length, shape of the edges, volume that the fibers occupy in concrete and pretreatment. The most important of them is fiber s length and type. Also, pretreatment contributes to improvement of toughness by means of controlled damage of fibers during pullout process or effective irregularities. In order to improve toughness the effect of workability to high fiber volume composites must be taken into consideration, as well as the reduction of compressive strength and the properties of fibers. Researches on concrete reinforced by steel, polypropylene and glass fibers indicate that the increase of volume fraction leads to an increase of post cracking toughness. Impact Resistance It is postulated that the impact resistance is improved by using fibers. There are multiple studies on determining impact resistance. Also, the increase of impact resistance, that steel fibers indicate, is of great importance. Polypropylene and polyester fibers increase the impact resistance too, but not as much as steel ones. Fatigue There are difficulties in determining the fatigue strength as there aren t any postulated tests for these reasons. There are two methods to approach the later term by measuring the maximum fatigue stress at which the composite material can resist to certain number of fatigue cycles before it fails. The second method is to measure the endurance limit of fiber reinforced concrete in flexural 12

13 bending, which is termed as the maximum flexural stress to resist after certain number of fatigue cycles expressed as a percentage. The addition of fibers increased the fatigue life of fiber reinforced concrete and the ductility. However, the type of failure remains the same. More specifically, the increase of volume of steel fibers results in an increase of flexural fatigue strength and endurance limit. Moreover, the durability of reinforced concrete is enhanced. Finally, it is proved that steel fibers indicate better behaviour on fatigue than that of synthetic fibers which is similar to plain concrete. Abrasion Resistance Erosion of concrete surface can be arisen from two reasons by wearing gradually because of debris rolling over the surface at low velocities or by high velocity flow and impact of large debris. In the first occasion abrasion resistance is not affected, while in the second one there is a substantial contribution to abrasion resistance by steel fibers. Steel fibers increase the compressive strength which leads to an increase of abrasion resistance. The main factor that influences abrasion resistance is the content of fibers. Freezing and Thawing Conventional concrete itself does not present resistance to freezing and thawing. The same phenomenon is observed by adding fibers. In other words fiber reinforced concrete has not improved its resistance to freezing and thawing. Only by entraining air in the matrix the resistance can be improved. Investigations notice that concrete reinforced by polypropylene fibers indicates improved resistance to freezing and thawing only by air entrainment. Wet Dry Exposure The studies, focused on the exposure of fiber reinforced concrete to wet or dry environment, are referred to the use of polypropylene fibers. The conclusions indicate that polypropylene fibers retard the deterioration process of the surface significantly. Alkaline Environment For the durability of concrete in alkaline environment to be estimated non metallic fibers are used such as nylon 6, polypropylene and polyester. Specimens are saturated in lime water under standard temperature for specific period. All types of fibers present post cracking resistance. Nylon 6 and polypropylene fibers provide durability in alkaline environment on the contrary to polyester ones. [Zia et al. 1994] Continuous fibers Continuous fibers are added in concrete as reinforcement in order to improve the behaviour of the composite material. This type of fibers is considered as an alternative for steel reinforcement for 13

14 prestressed and non stressed concrete applications. The addition of continuous fibers enhances the properties of the composite. Concrete reinforced with continuous fibers called Fiber-Reinforced Composite because it behaves as a materials system, as mentioned in work of Zia et al. (1994). Composite consists of any combination of two or more separate materials and an interface between them. This interface determines the adhesion of two faces. In order to enhance the adhesion surface treatment with appropriate components is necessary. The composite s performance depends on the materials used, the interaction between them and the fiber portion of the composite. Parameters that also influence the performance of the fiber matrix composite are fiber orientation, length, shape and composition of the fibers, the adhesion or bond between the fibers and the matrix. The fibers used widely in civil engineer application, are made by glass, carbon and aramid. Glass fibers offer improved strength properties with economical profit. The most common type is E- Glass which is commercially available and provides greater alkali resistance. Fibers by carbon or aramid are considerably more expensive than glass fibers and are used either for their strength and modulus properties or as hybrids with glass. Physical and Mechanical Properties Physical and mechanical properties are determined by testing Fiber Reinforced Polymers (FRP) bars or tendons. The FRP bars are anisotropic and the longitudinal axis is the strong axis. Mechanical properties of FRP differentiate accordingly to volume and type of fiber, fiber orientation and quality control during manufacture. Moreover, loading history and duration, temperature and moisture affect them. Specific Gravity FRP products weight about ¼ of the weight of steel, factor that offers lower costs of transportation and storage, less handling on job site and reduced time of installation. Thermal Expansion FRP is a composite material, so the different constituents behave as similar as the deformations of concrete and reinforcement are lower. The linear coefficient of thermal expansion varies depending on the mix proportions. Tensile Strength FRP bars and tendons do not exhibit the yielding strength of the materials while they reach their ultimate tensile strength. It must be noted that the measurements are taken by the longitudinal direction which is the strong axis of the composite. 14

15 Furthermore Glass-Fiber Reinforced Polymers provides higher tensile modulus of elasticity than that of steel. Carbon Fiber Reinforced Polymers has almost the same value of tensile modulus of elasticity to that of glass. Compressive Strength FRP bars are not as predominant in compression as in tension. Bars with higher tensile strength are expected to show higher compressive strength. Moreover, the compressive strength depends on whether the bar is smooth or ribbed. In general, the compressive modulus of elasticity is lower than the tensile modulus of elasticity for the same material. Compressive modulus of elasticity depends on bar size, type, quality control in manufacturing and the length to diameter ratio of the specimens. Shear Strength FRPs present low shear strength and fail easily in the direction perpendicular to the longitudinal axis. In order to overcome this weakness, the orientation of the bars such that they resist the applied loads of axial tension is suggested. Creep and Creep rupture Creep resistance differentiates for variable materials. It is influenced considerably by the orientation and the volume of fibers. Creep rupture, described as a permanent, adverse loading applied on FRP bars which fail suddenly after the endurance time, exists for all the materials used in structure. Fatigue Bars made by carbon and glass exhibit good resistance in fatigue. In general, the higher fatigue resistance is provided by graphite-epoxy bars, steel bars follow and glass bars indicate the lower resistance. Durability Durability is a characteristic property of FRPs. As concerns as glass and aramid fibers, researches have shown that they are deteriorated in alkaline environment and are degraded in case of exposure to UV rays. Especially for glass fibers, their load carrying capacity losses when are exposed to salt solution. Aramid fibers are degraded by strong acids and bases, even though they do not loose strength capacity. Finally, carbon fibers are chemical resistant and present excellent durability characteristics. [Zia et al. 1994] Advantages and Disadvantages of Fiber Reinforced 15

16 Fiber reinforced concrete is useful to many applications of civil engineering because of the improved properties that provides. It is recommended to structures where increased durability is restrained. Fiber reinforced concrete decrease damages from erosion or cavitation fact that is effective in structures such as navigational locks and bridge piers in terms of high velocity flow. It applies in thin layers which provide equivalent strength to thicker sections of conventional concrete. As a result the reduced weight of the structure. Also, fiber reinforced concrete is helpful to avoid harmful failures when is applied to bridges. Last but not least, fibers develop internal forces which prevent from forming microcracks into the concrete. On the other hand, the process of incorporating fibers into the matrix is more expensive and less time consuming than plain concrete. Despite of the cost in money and time, fiber reinforced concrete provide such advantages that override disadvantages. (Brown et al. 2002) The present experimental study examines the affect of polypropylene fibers into the mortar. The physical and mechanical properties of polypropylene are presented in the following chapter. The reasons why polypropylene fibers are advantageous for mortar are also explained. POLYPROPYLENE 16

17 Polypropylene has induced in market and been used widely even in applications of civil engineering. Due to good mechanical properties and low cost, polypropylene becomes more and more common in various applications. (Material property data 2007) Polypropylene is produced by means of polymerization of monomer units of propylene molecules into a long chain under certain conditions of pressure and temperature. Propylene is an unsaturated hydrocarbon and is consisted merely by carbon and hydrogen atoms. The structure of Propylene is presented below: Polymerisation is achieved by many ways. Propylene molecules are added to the main chain in a specific orientation as a result of increasing the chain length. The structure of polypropylene chain is shown below: (Brown et al. 2002) Over the past few years, the production of polypropylene is increased and exceeded by polyvinyl chloride and polyethylene from all thermoplastics. The low cost, low density, favourable characteristics and ease of manufacturing contribute to its wide use in many applications. The produced forms of polypropylene are a semi crystalline solid and its by product in lower volume. The semi crystalline solid termed as isotactic polypropylene provides worthy physical, mechanical and thermal properties while the by product termed as atactic indicates insignificant mechanical and thermal properties. The good properties of isotactic polypropylene are presented due to high crystallinity. On the contrary, atactic has a random orientation relating to the polymer backbone. Another form produced is the syndiotactic polypropylene in which methyl groups are on the opposite sides of the polypropylene chain. The form, that polypropylene has, depends on the catalyst used and polymerisation conditions. Polypropylene is a semi crystalline with various types of crystal structures and degrees of crystallinity. Crystal types are influenced by the rate and manner in which the crystals have been formed. Crystal types determine physical properties and processing characteristics of the polymer. The regularity of molecular structure determines the crystallinity. Occasional irregularities in molecular structure limit the extent of crystallization. In general, atactic polymers are amorphous and have random, irregular molecular structure. They are more transparent and indicate greater toughness and ductility. Isotactic polymers provide high strength, stiffness, density, sharp melting point and can be used at higher temperatures. 17

18 Polypropylene provides hard, stiff and brittle behaviour at low temperature. Increasing temperature, polypropylene becomes more flexible, softer and tougher. Polypropylene s stiffness varies significantly with temperature. This transition is relevant to melting point temperature (Tm) and glass transition temperature (Tg) The crystalline structure of the semi-crystalline polymer causes a major change at melting point Tm. At Tm, physical properties of the PP change abruptly, as the material becomes more viscous, simultaneously Tm varies with the amount of crystallinity. Under normal processing conditions, the theoretically maximum Tm value expected for a semi-crystalline isotactic polypropylene resin is 176 o C. Melting points of commercial isotactic polypropylene resins normally range from 160 to 166 o C due to the presence of atactic material and non-crystalline regions. Low crystallinity regions decrease the melting point at great degree. Also, polypropylene has high melting point which attributes to its resistance in softening at elevated temperatures. Amorphous regions of the PP undergo a transition, named glass transition (Tg) at a temperature between -35 and 26 o C. This transition depends on various parameters, such as the heating rate, polymer s thermal history and microstructure. Above glass transition temperature, molecules and segments of polymer chains vibrate and move in non-crystalline regions. At the glass transition temperature, free volume is restricted and only low amplitude vibrations occur. This movement continues during cooling to absolute zero temperature (-273K), at which point all movement ceases. PP is most commonly used in a temperature range limited by the glass transition temperature Tg on the lower side and by the crystalline melting point Tm on the higher side. Mechanical Properties Opposite to traditional materials, which are not greatly affected by time and temperature, thermoplastics exhibit a time-dependent behaviour. Stresses and strains that a thermoplastic can withstand, when slowly applied, may cause its shattering when applied rapidly. For instance, a stress that creates no problem to polymer for a short period may make the material to deform or creep over a longer period of application. The mechanical properties of polypropylene are strongly dependent on time, temperature and stress. Furthermore, it is a semi-crystalline material, so the degree of crystallinity and chain orientation affects the mechanical properties, but at the same time these are dependent on the amount of stress imposed, the duration of stress application and the temperature of test environment. Mechanical properties are also influenced by the presence of fillers, reinforcements and modifiers used in the material in order to create homopolymers, block copolymers or random copolymers. Thermal properties Polypropylene as a thermoplastic softens when heated and hardens when cooled. Melting point and the glass transition temperature determine the operating range. A wide temperature working range provides a significant co-efficient of linear expansion to the material. The polypropylene s coefficient of linear expansion is higher than most commodity plastics but is lower than that of 18

19 polyethylenes. Unlike the metal s co-efficient of linear expansion, polypropylene s one varies with temperature. During exposure to high temperatures within its maximum operating rates, polypropylene deteriorates gradually. This effect is known as thermal ageing. In fact, it is about an oxidation process which is related to weathering. At elevated temperatures polypropylene is more susceptible to oxidation by oxidizing agents and by air. Normally all polypropylenes are stabilized against oxidation by adding stabilizers. Substances like copper, manganese, cobalt and carbon black additives decrease resistance of polypropylene to heat ageing. Thermal ageing resistance is measured by using an "induction" technique. In this method samples are held at a particular temperature for some days to degrade to a particular extent. Ageing temperature varies from 70 o C to 135 o C depending upon the degree of stability of the polymer and the expediency of the test. A loss of 50% in strength and elongation or the toughness factor shows generally the end of the induction period and is considered as a relative measure of polymer stability at test temperature. The resulting data make an approximate estimation of the service life of polypropylene at elevated temperatures possible. For example, an induction period of 20 days would imply a service life of about 6 years at 80 o C, while one of 10 days at the same temperature would make polypropylene have a service life of about 1,000 days. Chemical resistance Chemical resistance is regarded as the polypropylene s inertness and compatibility with other ingredients, as well as its resistance to external environment. It is often related with polymer s heat stability because most reactions take place during high temperature processing. Due to its non-polar nature polypropylene presents a high resistance to chemical attack. The term non-polar refers to the bond between atoms; these atoms have specific electro-negativity values. If this electro-negativity value is great, the polarity of the bond will be higher, so it would be a polar atom. On the contrary, when this difference is small the material is said to be non-polar. In other words, bond s polarity determines polymer s solubility, one measure for this solubility consists solubility parameter. When the solubility parameter of the polymer and this one of the solvent are similar, vulnerability occurs. It is understood that lower the value of the solubility parameter, the more resistant to solution will be the polymer. Because of its non-polar nature, polypropylene presents low water absorption and solubility. Normally polymers are not dissolved in chemical solutions but soften and also may swell. These changes can be reversible when the chemical is removed, but changes caused by chemical reaction are irreversible. At higher temperatures and at higher concentrations of the chemical reagent, many chemical attacks are more severe and destructive. Generally, polypropylene is resistant to alcohols, organic acids, esters and ketones. It is swollen when come in contact with aliphatic and aromatic hydrocarbons, and by halogenated hydrocarbons but is highly resistant to most inorganic acids and alkalis. However, its resistance to oxidizing acids and halogens is readily low. Particularly in the presence of fillers and reinforcements, its contact with copper and copper alloys accelerates oxidation. (Brown et al. 2002) 19

20 Polypropylene Fibers Polypropylene compared to other polymers, can be formated in fibers much more easily due to its melt flow properties and its low density. Melt spinning, spun-bonded and melt blown process consist the most common techniques for fiber fabrication. In case of polypropylene, melt spinning is the widely used technique, where fibers are drawn by heating to a temperature close to Figure 1 Polypropylene fibers melting point and then stretched. This process reduces significantly the cross section between macromolecular chains, causes great orientation, resulting in high tensile strength in final product. The properties of these polypropylene fibers are determined by the mode of polymerization, polymer s molecular weight and molecular orientation and manufacturing technique. In the absence of external forces, during crystallization process the polymer chains are arranged randomly with no preferred direction. Subjecting an external stress, usually a uniaxial one, immediately after crystallization the polymer chains get aligned in stress direction. This process is known as orientation and it is necessary for producing polypropylene fibers. Polypropylene fibers are usually commercially available in two different forms: mono-filaments and multi-filaments. Monofilaments are ribbons of a single extruded polypropylene filament produced by melt spinning followed by water quenching. Monofilaments are used for producing stiff products such as ropes. These ropes have high wear resistance, do not absorb water, float due to the low density and they retain their high strength even when they are wet. Generally, monofilament fibers are characterized by highly reflective and translucent surface, limited water absorption capacity, high stiffness and tensile strength. Individual monofilaments grouped into a single continuous bundle produce multifilaments. Most of these filaments are air quenched, so slow air cooling results in highly ordered crystal structure and hence high thermal stability and low creep of the fibers. Some larger multifilaments cool more slowly and air quenching is not economically appropriate method, hence water quenching is used instead. Due to its rapid cooling, water quenching does not provide enough time to fibers to form crystalline structures, so water quenched fibers are tough with high tenacity. Consequently, multifilament fibers are characterized by toughness, lightweight and hydrophobic nature. (Brown et al. 2002) Properties of Polypropylene Fibers Polypropylene fibers are composed of crystalline and non-crystalline regions. The crystalline parts, known as spherulites develop from a nucleus and appear in a wide range of size from fractions of micrometer to centimeters in diameter. Each one of spherulites is surrounded by amorphous regions. During fiber spinning and drawing both crystalline and non-crystalline regions get oriented to draw direction. If polymer is extended less than 0.5%, the spherulite deforms in elastic way and as a result no disruption of the structure occurs, otherwise spherulites are highly oriented in the direction 20

21 of the force and are finally converted to microfibrils. These microfibrillar structures are very anisotropic and lead to anisotropic fiber properties. Concluding polypropylene fibers are characterized by lightweight, good resilience, good thermal stability, high strength, and favourable elongation properties. (Brown et al. 2002) Application of Polypropylene Fibers in Concrete Over the past decades, polypropylene fibers have been used as reinforcement in concrete as they have many properties which make them adaptable for application in concrete. The real and most important advantage of adding these fibers in concrete is that, after its cracking, fibres manage to bridge the gaps caused by the cracking and restrain them. By this process the concrete remain integral even after cracking and the capacity of load carrying improves. (Sukontasukkul 2004) The incorporation of polypropylene fibers improves considerably flexural strength and load carrying capacity after cracking. Moreover, fibers enhance toughness, ductility and impact resistance. Researches have proved the increase of splitting tensile strength and shrinkage. On the contrary, they affect slightly compressive strength. In addition to these properties, it is important to mention that the fiber reinforced concrete provide the same behaviour in all directions because of the uniform dispersion of fibers in the matrix. (Brown et al. 2002) Factors that mainly influence the mechanical properties of fiber reinforced concrete are the type of fibers, their orientation in the matrix, the volume fraction of fiber and aspect ratio. Other parameters which control the composite s performance are the physical properties of the fiber reinforced concrete and matrix, the bonding strength between fibers and matrix and the chemical properties of the fibers (such as inertness, reactivity with the environment). Change in properties of polypropylene fibers during certain time period leads to different bonding characteristics. (Brown et al. 2002) Compared to most polymers, polypropylene has high melting point (165 o C) and is chemically inert. Its chemical inertness makes the fibers resistant to almost all chemicals. Any chemical, that cannot attack the concrete, will have no effect on the fiber either. Polypropylene cannot be wetted by the cement paste due to its hydrophobic surface. Since the bundles of polypropylene fibers are non-polar, they do not cling together. However, the hydrophobic nature of the polypropylene fiber does not affect the water mixing requirements of the concrete. While manufacturing the orientation makes the fibers weak in the lateral direction, which facilitates fibrillation. The cement matrix penetrates in the mesh structure between the fibrils and creates a mechanical bond between fiber and matrix. Polypropylene fibers are characterized by low modulus of elasticity and poor physiochemical bonding, as mentioned in study of Brown et al. (2002), with concrete, even though the load carrying capacity under bending increased significantly. They seem to contribute inconsiderably to the peak load in contrast to the ductility at large deformation after peak. (Sukontasukkul 2004) Although, polypropylene fibers used in low volumes increase slightly the peak 21

22 load, they appear a significant flexural resistance beyond peak load. On the other hand, for high volume polypropylene fiber reinforced concrete, a significant increase in post peak load and resilience beyond first crack are observed. (Mullick et al. 2006) Generally, increase of the fibers content seems to enhance toughness and ductility of the composite. Finally, polypropylene fibers are indicated for applications with large deformations because they can resist against them in comparison to other fibers such as steel ones. (Sukontasukkul 2004) Despite the fact that the research on fiber reinforced concrete began many years ago, there is still an expand field that hasn t been studied as far as the mortar is concerned. Concrete and mortar contain the same principal ingredients; as a result they often appear the same behaviour. The affect of polypropylene fibers on mortar with marble aggregates is examined in this research. Therefore, it is expected to have the same observations on concrete. MORTARS Mortar is a mixture of fine aggregates, a binder such as cement or lime, and water and is applied as a paste which then hardens. (wikipedia 2007) 22

23 Despite the fact that concrete and mortar are consisted of the same principal ingredients, they differ in methods of placement, working consistencies and structural performance. Concrete is used as a structural element in constructions. On the other hand, mortar is used to bind masonry units and create strong and durable bond between them. Concrete is placed in non adsorbent forms while mortar is applied on masonry, which absorbs water of mortar, when they are in contact. Water cement ratio plays a greatly important role to concrete, on the contrary for mortar is insignificant. Concrete of high value of water cement ratio is rejected but mortar demands high water cement ratio. (Brick Industry Association 2003) When mortar is fresh, mortar indicates significant fluidity and plasticity and when it hardens, mortar obtains mechanical strength. (wikipedia 2007) Mortars must be durable, strong, water resistant and capable of keeping the separate elements intact. (Brick Industry Association 2003) The properties of mortar depend on the type of principal ingredients, their proportion in the mixture, the mixing way and weather conditions of in situ manufacturing. (Patsaboudis 1991) Materials The principle factor that affects on mortar s strength is the aggregates used, like sand, with maximum grain 4 mm. The concentration of small grains, with diameter d < 0.2 mm, in the mixture must be lower than 20 % - 25 % by weight. The dimensions of maximum grain must be lower than the 1/3 of mortar s width. The grain distribution of aggregates must be that of minimum possible voids in order the later be fulfilled with binder. (Koronaios and Poulakos 2006) The type of used sand depends on the application. Hence, mortar for masonry and plaster of high width contains coarse sand but mortar for plaster of low width consists of fine sand or marble. (Patsaboudis 1991) The water used for mortar must be clean, potable, and free of deleterious acids, alkalies or organic materials, glycols and oils. Mortar has a high water cement ratio when mixed, but this ratio changes to a lower value when the mortar comes in contact with the absorbent units. (Brick Industry Association 2003) Portland and other hydraulic cements, lime or combination of them, marble, gypsum, pumice and clay are used as binder. The corresponding mortars are described below. 1. Cement based mortar Portland cement and hydraulic cement are the principal cementitious ingredients for mortars. Cement contributes to durability, high strength and early setting of the mortar and must be in accordance with Standards of each country. (Brick Industry Association 2003) It is usually applied to constructions which should undertake high strains and plastering. The properties of cement based on mortar mainly depend on type of cement and water cement ratio. This mortar must have increased plasticity and elasticity in order to indicate high adhesion, water resistance and prevent from cracking. This is achieved by adding a small fraction of lime in the mortar. (Koronaios and Poulakos 2006) Specifications permit the use of hydraulic cements in mortar but use is not recommended unless the 23

24 mortar contains cements conformed to corresponding Standards. In addition to using hydraulic cement, the use of air-entrained Portland, blended hydraulic or hydraulic cements is not recommended because of air entrainment, which reduces drastically the bond between the mortar and masonry units or reinforcement. In general, specifications permit lower flexural and tensile stress values for mortar which contains air-entrained Portland cement. (Brick Industry Association 2003) 2. Lime based mortar Lime derives from limestone which has undergone through two chemical reactions to produce calcium hydroxide Ca(OH) 2. Lime, which sets only in contact with carbon dioxide in the air, contributes to bond, workability, water retention and elasticity. Furthermore not all types of lime as recommended there are additives such as unhydrated oxides and air entrainment that deteriorate the mortar. (Brick Industry Association 2003) There are two types of lime that can be used, the air lime and the hydrated lime. The air lime provides important plasticity, workability and strength to mortar. Mortar consisted of air lime is applied to masonry and plastering. The use of hydrated lime provides earlier hardness and indicates higher strength than air lime. (Koronaios and Poulakos 2006) 3. Lime cement based mortar This type of mortar contains lime and cement as binder. Lime cement based mortar presents durability and increased strength to loadings than plain lime based mortar. Also, it provides resistance in water absorption and hydraulic attributes; hence it hardens in presence of water. (Koronaios and Poulakos 2006) 4. Lime marble based mortar In lime marble based mortar sand is replaced by marble aggregates. It is used for the final layer of plastering because it gives leveled surfaces after grating and it not so expensive. (Koronaios and Poulakos 2006) 5. Lime gypsum based mortar The addition of gypsum in lime based mortar results to the creation of lime gypsum based mortar. This mortar is used to plaster internal rooms because it does not present cracks and provides leveled surfaces. (Koronaios and Poulakos 2006) 6. Lime pumice based mortar In lime pumice based mortar; pumice replaces sand either partially or entirely. The proportions are given for each occasion by Standards of each country. Lime pumice based mortar is hydraulic mortar and is used in underground, wet places. (Koronaios and Poulakos 2006) 7. Clay based mortar This mortar contains clay which is a mixture of argil with sandy ingredients of low or mediate grain distribution. Clay based mortar offers good adhesion, insulting to warmth and safety in fire. In case of soak it returns from dry condition to plastic. Finally, it is used for manufacturing bricks and tiles. (Koronaios and Poulakos 2006) 24

25 Corresponding to what application is needed; specifications fix the proportions of principal ingredients. Mortars are classified according to their mechanical strength. Lean mortar is the mortar which contains a small quantity of binder and the later does not fill in the voids among the grains. Normal mortar is called the mortar that has the appropriate quantity of binder so as to fill in the volume of voids. Thick mortar is termed the mortar that includes more than the quantity needed for the normal mortar. (Koronaios and Poulakos 2006) Cate gory I II III Type of binder Average density Average Proportion of hardened compressive lime : cement : sand mortar (in Kg/dm 3 strength ) Paste of air lime 1 : 0 : Powder of air lime 1 : 0 : Hydraulic lime 1 : 0 : Super hydraulic lime 1 : 0 : Hyper hydrated lime 1 : 0 : Lime paste + cement 1.5 : 1 : Lime powder + cement 2 : 1 : Lime powder + cement 1 : 1 : Cement 0 : 1 : Cement + lime powder 0.2 : 1 : Table 2 (Koronaios and Poulakos 2006, p. 85 conformed to Hellenic Standards) Physical Properties of mortar Mortar must be homogenous, workable and not to have lumps, hence the ability to deforming and applying without segregation of its ingredients. Also, it must have satisfying plasticity, good adhesion and elasticity in order to be formed without losing its consistency and not to leak from masonry joints. Mortar has to keep its volume constant so as to avoid cracking on and ensure impermeability. The sufficient time of congelation is crucial in order to undertake loadings with safety. (Koronaios and Poulakos 2006) Mortar distinguishes into two states, plastic and hardened, and presents the corresponding properties. The properties of plastic mortar are workability, water retention, initial flow and flow after suction. They are noticed in order to determine mortar's compatibility with brick and its construction suitability. The properties of hardened mortar are bond strength, durability, extensibility, compressive strength and strength in ageing. They are observed so as to determine the performance of the finished masonry.(brick Industry Association 2003) The parameters that affect mortar s properties are: type of binder type of aggregates Proportions of ingredients by volume way of mixing ingredients 25

26 additives TECHNOLOGICAL EDUCATION INSTITUTE OF PIRAEUS way of applying and compacting of mortar. (Koronaios and Poulakos 2006) Bond Strength Hardened mortar bears two significant properties bond strength and extent of bond. Factors that influence bond strength are the following: texture and suction of the brick, air content and water retention of the mortar, pressure applied to the joint during forming, proportions of principal materials and methods of curing. The factors that influence bond strength are included in the text of Brick Industry Association (2003) and described below: Brick Texture. The texture of brick provides a mechanical bond between the brick and mortar. Roughened surfaces indicate greater bond of mortar than smoother ones. Also, sanded and coated surfaces prevent the creation of bond strength accordingly to the type of material, its proportion in the mixture and adherence to the surface. Brick Suction. Brick s suction at the time of layering has been proved to affect bond strength. Suction must be lower than a specific value so as brick and mortar have the best possible bond. In the opposite case, brick should be wetted prior to layering. There is a limit for suction in which mortar has the best bonding to the brick at the time of layering. Air Content. Air content in the mixture influences the bond strength of the mortar. Under constant conditions, the increase of air content cause reduction of compressive and bond strength but workability and resistance to freeze and thawing presents improvement. Flow. While layering, the increase of flow can effect positively on brick s suction and bond strength and permit greater control of the mortar for the bricklayer. On the other hand, excessive use of water may deteriorate workability and bond strength. Mortar flow is influenced by the time margin between spreading mortar and placing brick, mainly when mortar is layered on high suction brick or when the weather is hot or dry. The application of the mortar doesn t occur immediately after mixing, so as a result an amount of water evaporates. The addition of water is intentional in order to replace the lost amount of it. This procedure is termed as retempering. However retempering enhances bond strength; it causes harmful changes to mechanical properties of mortar, such as reduction of compressive strength and lightness of the color. Finally, the application of mortar is recommended within 2 1/2 hours after mixing. Movement. By the time mortar begins to harden, any attempt to move the mortar can be destructive to bond between brick and mortar. Moreover, a partially dry mortar has not got the adequate plasticity to adhere well to the masonry. Proportions. The composition of materials to produce the optimum bond is not indicated. The different demands for each construction determine the materials used. 26

27 Curing. Curing is one of the main factors that affect mechanical strength. So as far as the masonry is concerned, curing in wet environment provides higher bond strength than curing in dry environment. Test methods in order to determine the bond strength are included in specifications. To sum up, the parameters that enhance flexural bond strength are the following: the wirecut or roughened surface of brick, the value of brick suction below maximum limit the minimum content of air in the mixture and the use maximum mixing water and permit retempering Water Content The determination of water cement ratio of mortar is of great importance because it has got direct relation to workability. Mixture with the minimum amount of water results in a mortar with low workability. In many cases, retempering of the mortar is forbidden by specifications thus a mortar with high compressive strength and low bond strength is arisen. On the other hand the use of high amount of water improves workability and provides higher bond strength. Retempering is allowed only to replace the evaporated water. Finally, mortar is recommended to be used within 2 1/2 hours after mixing. Workability There is no method to measure the workability; it is a property which can be determined qualitatively. Workability consists of other characteristics such as plasticity hence the ability of applying easily, fluidity and ability of adhesion to vertical masonry surfaces. The principal ingredients of the mortar influence water retention, flow and resistance to segregation which in turn affects workability. So there is difficulty in deciding on the composition in order to achieve the optimum workability. Despite the difficulty, water retention and aggregate gradation must be carefully selected. Compressive Strength Compressive strength is affected by the cement content and the water cement ratio such as concrete. For masonry mortar, compressive strength doesn t play a major role in contrast with bond strength, workability and water retention. So, the selection of mortar mainly depends on the latter three properties. The parameters that influence compressive strength are described below. 27

28 Proportions. An increase of cement content increases compressive strength while increase of water, lime or over sanding reduces it. In order to lower water content, air entrainment is introduced consequently so higher flows are achieved. In turn, compressive strength is increased but the excessive increase of air content leads to the opposite results. Retempering. Compressive strength is decreased after retempering. Retempering is enhanced by the pass of time after the first mixing. The reduction of compressive strength is not so obvious if retempering occurs in the 2 ½ hour margin. Although, retempering may decrease compressive strength, it is preferred so as to improve bond strength. Finally, tests methods are determined by international standards. Durability Durability is a property that can not be estimated. It is determined qualitatively by the time that masonry structures needn t be serviced. Durability is increased by an increase in air content but this affects negatively other required properties such as bond strength. That s the reason why air content is not suggested. Strength in Ageing The strength in ageing depends on the quality of aggregates, binder type, porosity and surface of the mortar. Compact mortar is more resistant because of preventing water penetration and air. Porosity is limited by using sand of good grain gradation and reducing water content. During manufacturing air entraining agents are used that decrease surface energy of water. As a result small bubbles are created which remain after hardening of the mortar. These bubbles improve workability and thawing resistance as ice find place to be dilated and avoid the creation of stresses. Increase of mortar strength is obtained by smoothing of the surface and limiting the creation of micro cracks after hardening. This phenomenon can be avoided by reducing binder and water. Volume Change The volume of mortar can be differentiated due to temperature changes, wetting, drying and chemical reactions in hardening and expansion of unsound ingredients. In general, volume change between brick and mortar has trivial effect on performance even though it can be significant. Change due to hardening, cement hydration, termed as shrinkage, and is influenced by curing conditions, mix proportions and water content. An increase in water content results to an increase of shrinkage. Also, hardening in absorbent moulds or in contact with masonry indicates less shrinkage than in a mortar hardened in non-absorbent moulds. Change due to temperature leads to expansion and contraction of mortar. Moisture content change owes to normal cycles of wetting and drying. When moisture increases mortar swells when moisture decreases mortar shrinks. Moreover, unsound ingredients and 28

29 impurities can cause chemical expansion of mortar. Gypsum or unhydrated lime oxides can cause important change of volume. Efflorescence On the surface of masonry a crystalline deposit of water-soluble salts can be created, termed as efflorescence. Mortar affects significantly efflorescence as contains calcium hydroxide which produces efflorescence itself and reacts with carbon dioxide in the air or solutions from the brick and forms insoluble compounds. Furthermore, mortar may consist of other soluble ingredients, including alkalis, sulfates and magnesium hydroxide. Till now, there is not any method for determining efflorescence. Colour The use of coloured aggregates or appropriate pigments achieves the colouring of the mortar. Materials such as white sand, ground granite, marble or stone have permanent colour and don t affect mortar negatively. White joints are obtained by using white sand, ground limestone or ground marble with white Portland cement and lime. Pigments dispersed in allowable limits into the mortar can obtain the demanded colour and they must not react with other ingredients to harm the mortar. Metallic oxide pigments, carbon black and ultramarine blue meet these requirements. The use of organic colours is not permitted and, especially, the ones containing Prussian blue, cadmium lithopone, and zinc. In general, pigments must conform to specifications when used. The excessive use of pigments can affect negatively on strength and durability. So they must be added in correct proportions. Addition of colouring agents before mixing ensures better results, so a more uniform colour of the mortar can be achieved than those of in situ mixing. The use of same materials is suggested throughout the project. Colour uniformity changes accordingly when mixing water, if there is any moisture content of brick during layering and retempering. Factors that may also affect colour are time and degree of tooling and cleaning techniques. Permanence of the colour is influenced by the quality of pigments, weather conditions and efflorescing qualities of the mortar. (Brick Industry Association 2003) Mortar for plastering Mortar used for plastering covers masonry and after grating, provides a leveled surface. Along with the good appearance, mortar has also practical properties such as warmth and sound insulation and impermeability. Mortar used for plastering must appear good adhesion either to masonry or between plastering layers. Each layer must have uniform and stable structure so as to avoid micro cracks. As far as external surfaces are concerns, mortars must indicate increased 29

30 strength, durability to weather conditions (temperature, rain, humidity, thaw, solar radiation etc). In general, mortar must be conformed to demands of the project. (Koronaios and Poulakos 2006) Mortar for masonry Mortar used in masonry operates as adhesive material between structural units such as rocks or bricks. Mortar is used in order to fill in the joints among masonry units. Also, it is layered in horizontal widths so as the setting of other structural units be possible. As a result, masonry mortar must provide workability and plasticity in order to cover the irregularities of masonry units. Moreover, it must indicate good water retention, sufficient strength and adhesion so as to create a compact and stable masonry. Finally, this kind of mortar must present increased elasticity in order to follow the changes of masonry without problem to joints impermeability. (Koronaios and Poulakos 2006) In the present investigation, the tested mortar can be used for restoring damages of either concrete framework or perhaps masonry. It isn t appropriate for plastering because it doesn t include hydrated lime. This mortar is reinforced by polypropylene fibers and is consisted of marble aggregates instead of limestone ones as usual. Even though, marble derives from limestone, it presents quite different properties which are analysed below. MARBLE AGGREGATES Till now, there has been a vast number of researches on the fiber reinforced, repairing mortars. In all the experimental studies mentioned above limestone aggregates are used. In the present study, limestone aggregates are replaced marble ones. This material is directly used after quarry process of marble and is considered as waste. The alternative exploitation of marble aggregates yields economic profit to quarry companies and lowers environmental impacts. Limestone is a sedimentary rock composed of the mineral calcite (calcium carbonate: CaCO 3 ) or dolomite (CaCO 3 + MgCO 3 ). Limestone often contains variable amounts of silica in the form of chert or flint, as well as varying amounts of clay, slit and sand as Figure 2 Quarry process of marble disseminations, nodules, or layers within the rock. (wikipedia 2007) It s highly important the purity of rock contained in repairing mortars. Limestone must have white or gray colour otherwise there are impurities in it, such as clay, sand, organic remains, iron oxide and other materials which aren t indicated in mortar s production as mentioned in wikipedia (2007). Limestone has to get rid of external mixtures, to be checked for hardness and water absorption in 30

31 order to be suitable for dry mortars. Under certain conditions of temperature and pressure, limestone recrystallizes into marble. Marble derives from the process of metamorphism of limestone or dolostone. In other words, marble originates from limestone but has different properties as far as a metamorphic rock. It is widely used for sculpture but also as structure material. In this study it is used as a component in the repairing mortar. Marble aggregates of grain distribution from 0 to 4 mm are used which are waste of the quarry process. By this way, it is expected to get the better possible development of this material. Properties of Marble Marble is a material applicable in furniture, sculpture and interior decoration. In constructions, it is widely used either as pure marble segments in covering floors and walls or as dust contained in plaster mixture. Marble indicates durability, water and frost resistance. Water resistance allows its use in finishes of bathrooms, pools and fountains. Frost resistance of marble is attributed to the minor water absorption which does not permit the creation of microcracks from freezing the liquid under low temperatures. Also, marble provides thermal stability which signifies that heat does not affect it. This characteristic permits its use in structures demanding exposure to high temperatures, such as fireplaces. (Akam encyclopedia 2007) On the other hand, marble is porous and can breathe but pittings and veins are often presented. It has hardness of 3 4 measured on Mohs scale. However, while marble polishes easily, it is scratched when subjected to abrasion. Finally, marble is susceptible to mild acids and as a result to corrods. (Patent htm) As stated in research of Corinaldesi et al. (2005), the addition of marble powder to mixture secures good cohesiveness of mortar and concrete. Even if water cement ratio is low and there is a superplasticizing admixture, the presence of marble powder increases its compressive strength at the same workability degree due to its high fineness. In the present experimental study, by products of quarry of marble replace limestone aggregates which have been conventionally used till now. Thus, the effect of marble aggregates on flexural and compressive strength of the mortar will be examined. 31

32 RESEARCH METHODOLOGY European Standard EN :1999 specifies the method for determining the strength in bending and compression of moulded mortar specimens. The flexural strength is specified by the three point loading method of hardened mortar prism specimen till failure. The compressive strength is determined by testing the two parts resulted from the flexural strength test. 1. Materials Marble aggregates The grains of marble aggregates range from 0 to 4 mm. The same fine aggregate gradation consists of all specimens. Aggregates consist the 75 % of the mortar. High strength cement High strength cement of type I52.5 is contained in the mix. This type of cement contains high quantity of C 3 S (65 %) and low of C 3 A (2 %). C 3 S accelerates hardening of cement and C 3 A assures a good durability against sulfate attack. Cement content is the 25 % of mortar solid component. Cement and aggregates are premixed and then packed for commercial use. (Schwartzentruber et al. 2004) Water For every 1000gr solid mortar components (where 750gr is aggregates, 250gr is cement) corresponds 125gr 125gr water. Water to cement ratio is calculated as: η = = gr Polypropylene fibers The characteristics of polypropylene fibers cited by the manufacturer are: Length 6 mm Diameter 40 µm Density 0,91 kg/lt Flexural strength 360 MPa Fracture strain of fiber 22% Modulus of elasticity 2500 MPa Swelling in liquids 0 % Solar radiation UV 200 kly 32

33 The volume percentage of polypropylene fibers added in the mixture is varied. Firstly, un reinforced mortar is manufactured (fiber content 0 % by volume) and then fibers are added. Four different mortars are manufactured. The components for 1 kg of mortar for each grade are presented below: Material Marble aggregates Cement Water Polypropylene fibers 1 st composition 750 gr 250 gr 125 gr 0 % by volume (unreinforced concrete) 2 nd composition 750 gr 250 gr 125 gr 0.07% by volume 3 rd composition 750 gr 250 gr 125 gr 0.13% by volume 4 th composition 750 gr 250 gr 125 gr 0.26% by volume Table 3 (Compositions) 2. Specimens Specimens are prismatic, with dimensions 160mm x 40mm x 40mm, according to National Standards ΕΛΟΤ ΕΝ (based on European ones). (Figure 9) 3. Apparatus For flexural strength test, as described in Hellenic Standard EN :1999 (1999, p.7) «a testing machine capable of applying the load at standard rate is used. The machine shall comply with the requirements. The machine shall have two steel supporting rollers of length between 45 mm and 50 mm and 10 mm ± 0.5 mm diameter, spaced mm ± 0.5 mm apart, and a third steel roller of the same length and diameter located centrally between the support rollers. The three vertical planes through the axes of the three rollers shall be parallel and remain parallel equidistant and normal to the directions of the prisms under test. One of the supporting 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.» As far as compression test is concerned, a testing machine capable of applying the load at standard rate is used. The machine shall comply with the requirements. The upper machine platen shall be able to align freely as contact is made with the specimen, but the platens shall be restrained from tilting with respect to one another during loading. Two bearing plates made of tungsten carbide or of steel of surface hardness at least 600 HV Vickers hardness value in accordance with EN ISO The plates shall be 40mm long x 40mm ± 0.1mm wide and 10mm thick. The dimensions of tolerance for the width shall be based on the average of four symmetrically plates measurements. The flatness tolerance for the contact 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 and tempered tool steel and the faces shall have a platness tolerance of 0.01mm. A device to provide 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 33

34 that the gap in one direction is the nominal width of the prism plus 0.3mm and in the other direction is the nominal 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 the direction of the long axis of the bearing plates. (Hellenic Standard 1999, p.8) Figure 3 Figure 4 (Bending testing machine) (Compression testing machine) Metal moulds The appropriate moulds for manufacturing mortar are metallic and consisted of a rigid base and compartment walls which are thick and rigid enough to avoid damaging the specimen during demoulding. Walls are assembled and attached to the rigid base by a screw or a clamp. This type of moulds provides: a. fixed dimensions to all specimens, b. flat surfaces of specimen as the internal faces of the mould are smooth, c. square sections as the internal dimensions of the mould are equal and d. parallel top and bottom surface. (Hellenic Standard 1999) 4. Preparation Figure 5 (Metal moulds) First of all, moulds must be assembled, cleaned and lubricated with mineral oil in order to prevent adhesion of the mortar. After mixing all the ingredients water, fibers, cement and aggregates according to specified proportions, the fresh mix is vibrated by a vibration rod. It is cast into moulds 34

35 which are settled on the vibrational table and then is again vibrated for a few minutes. Then, moulds are covered by a wet mat for 48 hours and maintain in a chamber in ambient temperature. The demoulding is taken place 2 days after casting and the specimens are immersed in water for 26 days at 23 o C. After 28 th day curing in all, specimens are tested in bending and compression. Figure 6 Figure 7 (Cast specimens) (Maintenance in water) Tested specimens are prisms with dimensions 160mm x 40mm x 40mm. Three specimens are provided for flexural strength test by each mould. These specimens break into two halves which are tested in compression. So, six prisms are provided for compressive strength test by each mould. (Figure 8) In this study, five (5) specimens are formed for each composition and tested in bending. So, there are ten (10) specimens that are tested in compression. Half of them are stressed by a load applied vertically to the layers of mortar. The rest specimens are stressed in the way that the load is applied transversely to the layers of the mix as shown in Figure 8. Half of the specimens are tested in order to examine the behaviour of the mortar in this direction. Mortars are usually stressed by different directions, so the study of unconventional compression is considered feasible in construction. In brief, five specimens are tested in bending; five specimens are tested in vertical compression and five in transverse compression. 35

36 Figure 8 (Vertical and Transverse Compression) Strain gauges are stuck on one specimen of each composition in order to measure the deflection in bending and compression. In the following chapter, testing results are presented and discussed. Figure 9 (Prismatic specimen 160mmx40mmx40mm with strain gauges) RESULTS & DISCUSSION The specimens are measured and the dimensions are written down. The volume and density are also calculated. After tests, the maximum values of both bending and compression load are recorded and the corresponding stresses are calculated. Flexural strength is determined by the equation: f = 1.5 Fl 2 bd where F : the maximum bending load l : the distance between the axes of the support rollers b : the width of the specimen d : the height of the specimen Compressive strength is calculated from the typical equation: F f = A where F : the maximum compressive load A : the area on which the load is applied 36

37 (The value of A is fixed for compression 40 mm x 40 mm as the load is applied by a plate of the same dimension.) Results are classified according to fiber ratio. Some values are rejected possibly because of malfunction during testing. The test results are presented at the following Table 4 (Results). 37

38 specimen width b (mm) height d (mm) length l (mm) volume (cm3) mass (gr) density flexural load (KN) flexural stress (MPa) compressive load vertically (KN) compressive stress vertically (MPa) compressive load transversely (KN) compressive stress transversely (MPa) Fiber content: 0 % by volume A_N_1 40,55 40,30 160,00 261, ,23 3,07 6,99 66,19 41,37 89,91 56,19 A_N_2 40,28 40,35 160,00 260, ,24 3,45 7,89 64,54 40,34 94,88 59,30 A_N_3 40,23 40,60 160,00 261, ,21 3,05 6,90 62,88 39,30 87,70 54,81 A_N_4 39,97 40,35 160,00 258, ,25 2,69 6,20 72,26 45,16 86,60 54,13 A_N_5 40,20 40,18 160,00 258, ,21 4,10 rejected 70,61 44,13 89,91 56,20 AVERAGE (Α_N) 7,00 42,06 56,13 Fiber content: 0.07 % by volume Π600_1 40,30 40,45 160,00 260, ,18 rejected rejected 72,26 45,16 85,50 53,44 Π600_2 40,27 41,07 160,00 264, ,20 3,31 7,31 69,50 43,44 93,77 58,61 Π600_3 40,30 40,22 160,00 259, ,17 rejected rejected 70,60 44,13 81,08 50,68 Π600_4 40,17 41,22 160,00 264, ,18 3,31 7,28 59,02 rejected 87,15 54,47 Π600_5 40,30 41,02 160,00 264, ,20 3,31 7,32 71,71 44,82 87,15 54,47 AVERAGE (Π600) 7,30 44,39 54,33 Fiber content: 0.13 % by volume Π1200_1 40,25 41,58 160,00 267, ,20 rejected rejected 68,40 42,75 112,53 70,33 Π1200_2 40,17 41,40 160,00 266, ,19 3,31 7,21 76,12 47,58 113,08 70,68 Π1200_3 40,23 41,05 160,00 264, ,16 3,31 7,32 60,13 rejected 104,81 65,51 Π1200_4 40,18 40,88 160,00 262, ,16 3,31 7,39 75,02 46,89 113,63 71,02 Π1200_5 40,52 41,30 160,00 267, ,15 rejected rejected 64,54 40,34 100,39 62,74 AVERAGE (Π1200) 7,31 44,39 68,06 Fiber content: 0.26 % by volume Π2400_1 40,27 41,17 160,00 265, ,16 4,41 9,69 72,26 45,16 102,04 63,78 Π2400_2 40,50 41,08 160,00 266, ,16 3,31 7,26 70,05 43,78 97,64 61,03 Π2400_3 40,42 40,75 160,00 263, ,17 3,31 7,40 83,29 52,06 94,87 59,29 Π2400_4 40,25 41,02 160,00 264, ,18 2,76 6,11 66,19 41,37 111,42 69,64 Π2400_5 40,25 41,43 160,00 266, ,16 4,41 9,57 72,81 45,51 92,12 57,58 38

39 AVERAGE (Π2400) 8,01 45,58 62,26 39

40 Accordingly to fibers ratio, flexural and compressive strength are shown in the table below. Table 5 (Results) volume ratio of fibers flexural strength (MPa) flexural modulus of elasticity compressive stress vertically (MPa) compressive stress transversely (MPa) 1st composition nd composition rd composition th composition ratio of flexural to compressive strength = = = = A general observation is that flexural and compressive strength are improved as the volume of fibers increase. It is also noticed that the flexural strength increases 15% in comparison to plain mortar without fibers. Compressive strength is also increased. Compressive strength in vertical direction is increased by 8 % while in transverse direction by 10 % approximately. Bending By suitable calculations, it is observed that flexural strength is increased by the addition of fibers. The composition with the maximum ratio of fibers indicates an increase of 15 % in comparison to unreinforced mortar. The variation of flexural strength according to fibers volume ratio in the matrix is depicted in Figure 10. Flexural strength indicates a constant increase depending on fibers volume increase. In general, despite of strength increase, the addition of fibers improves mortar s behaviour in bending. Fiber reinforced specimens are expected to present more ductile behaviour comparatively to conventional mortar. According to stress strain diagram (Figure 11), it is noticed that the increase of fiber ratio doesn t actually leads to more ductile behaviour of the mortar. FACULTY OF ENGINEERING 250 THIVON & P. RALLI St, AIGALEO, ATHENS-GREECE TEL.: , FAX:

41 Change of flexural strength Stress (M Pa) 9,00 8,00 7,00 6,00 5,00 4,00 3,00 2,00 1,00 0, % by volume 0.07% by volume 0.13% by volume 0.26% by volume Fibers volume (Vf %) (Change of flexural strength accordingly to fibers ratio) Figure 10 Stress - Strain Diagram Stress (MPa) st composition (unreinforced) 2nd composition (fibers: 0.07% by volume) 3rd composition (fibers: 0.13% by volume) 4th composition (fibers: 0.26% by volume) 0 0,05 0,1 0,15 0,2 0,25 0,3 0,35 0,4 ε Figure 11 (Diagram of stress stain in bending) The increase of the volume of fibers in the mortar affords an increase and ductility as it is evident in case of the 2 nd and 3 rd composition. Strength and ductility are increased gradually for specimens of the 2 nd and 3 rd FACULTY OF ENGINEERING 250 THIVON & P. RALLI St, AIGALEO, ATHENS-GREECE TEL.: , FAX:

42 composition as expected. The specimens deformations after elastic area become more and more intense by the rise of fiber proportion in mortar. Mortars of the 2 nd and 3 rd composition are considered that act as a normally reinforced concrete beam. Hence, they present an ultimate load by which specimens being deformed till complete failure. On the contrary, mortar of the 4 th composition specimen is considered to act as a concrete beam with much steel reinforcement. However, when the flexural strength increases, the deformation decreases. According to reinforced concrete theory a highly reinforced beam indicates higher strength than a normal reinforced one without significant deformation after elastic area. First crack is appeared at a high load value and proceeds through the section of specimen. Specimen fails in brittle way without the steel reinforcement being deformed. In case of reinforced mortar with maximum fiber ratio, similar behaviour to reinforced concrete is noticed. Mortar indicates the highest strength with the lowest deformation compared with the other specimens. Consequently, flexural strength is increased by the addition of fibers unlike ductility which may be decreased. The best ratio to be added in mortar, stressed by bending seems to be the 0.13% by volume as it provides increased strength and ductility at the same time. Nevertheless, the curves mentioned above are indicative by one specimen of each composition they can t be verified because of lack of data. Flexural modulus of elasticity is calculated by the equation: E σ ε = where σ : maximum flexural stress ε : maximum strain The values are taken graphically from Stress Diagram. (Figure 10) It is also remarked that the flexural modulus of elasticity is increased by the addition of fibers. (Figure 12) The calculated are considered more reliable than those of E (GPa) Flexural Modulus of Elasticity ,00 0,07 0,13 0,20 0,26 Fibers volume (Vf %) Figure 12 (Flexural Modulus of Elasticity) and Strain values compressive modulus of elasticity which can t be calculated as there are not adequate measurements. Compression Figure 13 (Specimen tested in bending characterised by ductile behaviour.) Compressive strength shows trivial increase by the addition of fibers. From Figure 14, it is obvious that the compressive strength in transverse direction is higher than that in vertical direction. This higher value is explained because of the different load direction in relation to the layering of mortar. The compression of FACULTY OF ENGINEERING 250 THIVON & P. RALLI St, AIGALEO, ATHENS-GREECE TEL.: , FAX:

43 transverse layers indicates higher strength, a fact that it is beneficial to the application of mortar. This improvement is owed to the different load direction in relation to the layering of the mortar. The compressive strength of the mortar transversely to layers is increased slightly via fiber volume percentage as shown at Figure 15. Change of compressive strength 70,00 60,00 Stress (MPa) 50,00 40,00 30,00 20,00 10,00 Compressive strength vertically Compressive strength transversely 0, % by volume 0.07% by volume 0.13% by volume 0.26% by volume Fibers volume (Vf %) (Change of compressive strength accordingly to fibers ratio) Figure 14 The addition of fibers in the mortar doesn t affect significantly on compressive strength due to the smooth surface that fibers appear. As a result cement paste can t have good adhesion with them and may slip. In turn new voids can be created in the mass of mortar leading to a deterioration of compressive strength. (Mpaka 2004) FACULTY OF ENGINEERING 250 THIVON & P. RALLI St, AIGALEO, ATHENS-GREECE TEL.: , FAX:

44 Stress - Strain Diagram Stress (MP th composition (fibers: % by volume) 5 1st composition (unreinforced) 0 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 ε 15 (Diagram of stress strain in compression) Figure From Figure 15 it is remarked that fiber reinforced specimen presents more strains than unreinforced one as expected. There is no further data for the specimens of 2 nd and 3 rd composition because strain gauges broke during testing process. That s the reason why compressive modulus of elasticity can t be calculated. Failure of the tested mortar in compression is similar to reinforced concrete. The characteristic type of failure is depicted in Figure 16. A tested specimen in compression is shown in Figures 17 and 18. (Specimen tested in vertical compression) Figure 16 (Sotiropoulou 2004) (Characteristic type of failure in compression) FACULTY OF ENGINEERING 250 THIVON & P. RALLI St, AIGALEO, ATHENS-GREECE TEL.: , FAX:

45 Figure 17 Figure 18 Finally, the mean ratio of flexural to compressive strength for the tested mortar is calculated about 1 6. This value is between the ratios of mortar and concrete which are 1 4 and 1 8 respectively. According to Hellenic Standards concerned to concrete, the ratio of flexural to compressive strength with maximum grain 8 mm is equal to 1 8. [29] The corresponding ratio for mortar with maximum grain 4 mm equals to 1 4 according to several laboratory data. The ratio for the present mortar is acceptable because it is between the bounds mentioned above. FACULTY OF ENGINEERING 250 THIVON & P. RALLI St, AIGALEO, ATHENS-GREECE TEL.: , FAX: