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Technical Notes 8 - Mortars for
Brick Masonry
Abstract: This Technical Notes addresses mortars for brick masonry. The major ingredients of mortar are identified. Means of specifying mortar are covered. Mortar properties are described as well as their effect on brick masonry. Information is provided for selection of the appropriate materials for mortar and properties of mortars. Key Words: hardened mortar properties, mortar, plastic mortar properties, specifications, types of mortar.
INTRODUCTION Mortar is the bonding agent that integrates brick into a masonry assembly. Mortar must be strong, durable, capable of keeping the masonry intact, and it must help to create a water resistant barrier. It must accommodate dimensional variations and physical properties of the brick when laid. These requirements are influenced by the composition, proportions and properties of mortar. Because concrete and mortar contain the same principal ingredients, it is often erroneously assumed that good concrete practice is also good mortar practice. In reality, mortar differs from concrete in working consistencies, methods of placement, and structural performance. Mortar is used to bind masonry units into a single element, developing a complete, strong and durable bond. Concrete, however, is usually a structural element in itself. Mortar is usually placed between absorbent masonry units, and loses water upon contact with the units. Concrete is usually placed in non-absorbent metal or wooden forms which absorb little if any water. The importance of the water cement ratio for concrete is significant, whereas for mortar it is less important. Mortars have 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. This Technical Notes addresses the materials, means of specifying and properties of mortars. Other Technical Notes in this series include a standard specification for portland cement-lime mortars (BIA M1-88 in Technical Notes 8A) and the selection and control of mortars.
MATERIALS Historically, mortars have been made from a variety of materials. Burned gypsum and sand were used to make mortar in ancient Egypt, while lime and sand were used extensively in this country before the 1900's. Currently, the basic dry ingredients for mortar include portland cement, mortar cement, masonry cement, hydrated lime, and sand. Each of these materials makes a definite contribution to mortar performance. Portland and Other Hydraulic Cements Portland cement, a hydraulic cement, is the principal cementitious ingredient for mortars. It contributes to durability, high strength, and early setting of the mortar. Portland cement used in masonry mortars should conform to ASTM C 150, Specification for Portland Cement. Of the eight types covered by ASTM C 150, only three are recommended for use in masonry mortars: Type I - For general use when the special properties of Types II and III are not required. Type II - For use when moderate sulfate resistance or moderate heat of hydration is desired. Type III - For use when high early strength is desired. ASTM C 270, Specification for Mortar for Unit Masonry, permits the use of other hydraulic cements in mortar. Some of these materials may slow down the strength gain or may affect the color of mortar. The material standards for these cements are ASTM C 595, Specification for Blended Hydraulic Cements, such as portland blast-furnace slag cement, portland-pozzolan cement, and slag cement; and ASTM C 1157, Standard Performance Specification for Hydraulic Cement. The use of blended hydraulic cements is not recommended unless the mortar containing such cements meets the property specification of ASTM C 270. Because high air entrainment can significantly reduce the bond between the mortar and masonry units or reinforcement, the use of air-entrained portland, blended hydraulic or hydraulic cements is not recommended. Most building codes have lower allowable flexural tensile stress values for mortars made with air-entrained portland cement. Mortar Cements Mortar cements are hydraulic cements, consisting of a mixture of portland cement, plasticizing materials such as limestone or hydrated or hydraulic lime, and other materials intended to enhance one or more of the properties of mortar. In this respect, mortar cement is similar to masonry cement. However ASTM C 1329, Specification for Mortar Cement, includes requirements for maximum air content and minimum flexural bond strength that are not found in the masonry cement specification. Because of the strict controls on air content and the minimum strength requirement, mortar cement and portland cement mortars are treated similarly in the Masonry Standards Joint Committee (MSJC) Code and Specification. Three types of mortar cements are specified in ASTM C 1329: Types M, S and N. Physical requirements vary depending upon mortar cement Type. Air content for all three Types must be a minimum of 8 percent. The maximum air content for Types M and S is 14 percent and 16 percent for Type N. Flexural bond strength, as measured by ASTM Test Method C 1072, is also specified. The minimum flexural bond strength for Types M, S and N mortar cements is 115 psi (0.8 MPa), 100 psi (0.7 MPa) and 70 psi (0.5 MPa), respectively. Masonry Cements Masonry cements are proprietary cementitious materials for mortar. They are widely used because of their convenience and good workability. ASTM C 91, Specification for Masonry Cement, defines masonry cement as “a hydraulic cement, primarily used in masonry and plastering construction, consisting of a mixture of portland or blended hydraulic cement and plasticizing materials (such as limestone, hydrated or hydraulic lime) together with other materials introduced to enhance one or more properties such as setting time, workability, water retention, and durability”. ASTM C 91 provides specific criteria for physical requirements and performance properties of masonry cements. The constituents of masonry cement may vary depending on the manufacturer, local construction practices and climatic conditions. Masonry cements are classified into three types by ASTM C 91: Types M, S and N. The current edition of ASTM C 91 requires a minimum air content of 8 percent (by volume) and limits the maximum air content to 21 percent for Type N masonry cement and 19 percent for Types S and M masonry cements. Mortar prepared in the field will typically have an air content 2 to 3 percent lower than that when tested under laboratory conditions. In the model building codes, allowable flexural tensile stress values for masonry built with masonry cement mortars are lower than those for masonry built with non air-entrained portland cement-lime mortars. Therefore, the use of masonry cement should be based on the requirements of the specific application. Hydrated Lime and Lime Putty Hydrated lime is a derivative of limestone which has been through two chemical reactions to produce calcium hydroxide Ca(OH)2. Lime, which sets only upon contact with carbon dioxide in the air, contributes to bond, workability, water retention and elasticity. Hydrated lime in ASTM C 207, Specification for Hydrated Lime for Masonry Purposes, is available in four types. Only Type S hydrated lime should be used in mortar. Type N hydrated lime contains no limits on the quantity of unhydrated oxides. Types NA and SA lime contain air entraining additives which reduce the extent of bond between the mortar and masonry units or reinforcement, and are therefore not recommended for mortar. ASTM C 1489 Lime Putty for Structural Purposes is prepared from hydrated lime and is often used in restoration projects. Because lime hardens only upon contact with carbon dioxide in the air, hardening occurs slowly over a long period of time. However, if small hairline cracks develop, water and carbon dioxide which penetrate the joint will react with calcium hydroxide from the mortar and form calcium carbonate. The newly developed calcium carbonate will seal the cracks from further water penetration. This process is known as autogenous healing. Aggregates Sand acts as a filler, providing for an economical mix and controlling shrinkage. Either natural sand or manufactured sand may be used. Gradation limits are given in ASTM C 144, Specification for Aggregates for Masonry Mortar. Gradation can be easily and inexpensively altered by adding fine or coarse sands. Sometimes the most feasible method requires proportioning the mortar mix to suit the available sand, rather than requiring sand to meet a particular gradation. However, if the sand does not meet the grading requirement of ASTM C 144, it can only be used provided the mortar meets the property specifications of ASTM C 270 or BIA M1, Specification for Portland Cement-Lime Mortar for Brick Masonry. Water If water is clean, potable, and free of deleterious acids, alkalies or organic materials, it is suitable for masonry mortars. Admixtures Admixtures are sometimes used in mortar to increase workability, decrease setting time and to retard freezing. Admixtures to achieve a desired color of the mortar are the most widely used. These should conform to ASTM C 979, Standard Specification for Pigments for Integrally Colored Concrete. Although some admixtures are harmless, some are detrimental to mortar and the resulting brickwork. Since the properties of both plastic and hardened mortars depend so largely upon mortar ingredients, the use of admixtures should not be considered unless their effect on the mortar is known. The use of admixtures should also be examined for their effect on the masonry, masonry units and items embedded in the brickwork. ASTM C 1384, Standard Specification for Admixtures for Masonry Mortars, provides methods to evaluate the effect of admixtures on mortar properties.
SPECIFYING MORTAR Masonry mortars are classified into four types: M, S, N and O. Each mortar type consists of aggregate, water, and one or more of the four cementitious materials (portland cement, mortar cement, masonry cement and lime) listed in the previous section. There are two methods of specifying mortar by type in ASTM C 270 and BIA M1: proportions or properties. Proportion Specifications The proportion specifications require that mortar materials be mixed according to given volumetric proportions. If mortar is specified by this method, no laboratory testing is required for the mortar. Table 1 lists proportion requirements of the various mortar types. Note that masonry cement and mortar cement may be used alone to produce Type M, S, N, or O mortars. Additionally, Type N mortar cement or masonry cement may be combined with portland cement to produce a Type M or Type S mortar.
TABLE 1 Proportion Specification Requirements
Property Specifications The property specifications require a mortar mix to meet the specified properties under laboratory testing conditions. If mortar is specified by the property specifications, compressive strength, water retention, and air content tests must be performed on mortar mixed in the laboratory with a controlled amount of water. The material quantities determined from the laboratory testing are then used in the field with the amount of water determined by the mason. Table 2 lists property requirements of the various mortar types. Properties of field mixed mortar cannot be compared to the requirements of the property specifications because of the different amounts of water used in the mortars, the use of different mixers, and different curing conditions. TABLE 2 Property Specification Requirements1
1Laboratory prepared mortar only 2When structural reinforcement is incorporated in cement-lime or mortar cement mortar, the maximum air content shall be 12%. 3When structural reinforcement is incorporated in masonry cement mortar, the maximum air content shall be 18%.
Proportion vs. Property Specifications The specifier should indicate in the project specifications whether the proportion or the property specifications govern. If the specifier does not, then the proportion specifications govern by default. The specifier should also confirm that the mortar types selected and the materials indicated in the project specifications are consistent with the structural design requirements of the masonry. Mortar prepared by the proportion specifications should not be compared to mortar prepared by the property specifications. A mortar that is mixed according to the proportion specification will have higher laboratory compressive strengths than that of the corresponding mortar type under the property specification. The volumetric proportions given in Table 1 or as determined by laboratory tests can be converted to weight proportions. The assumed weights per cubic foot for the materials are: Portland and other cements 94 lb (42.6 kg) Masonry and mortar cements Varies, use weight printed on bag Hydrated lime 40 lb (18.1 kg) Sand, damp and loose 80 lb (36.3 kg) of dry sand
PHYSICAL PROPERTIES OF MORTAR Mortars have two distinct, important sets of properties; those in the plastic state and those in the hardened state. The plastic properties help to determine the mortar's compatibility with brick and its construction suitability. Properties of plastic mortars include workability, water retention, initial flow and flow after suction. Properties of hardened mortars help determine the performance of the finished masonry. Hardened properties include bond strength, durability, extensibility and compressive strength. Properties of plastic mortar are more important to the mason. Properties of hardened mortar are of more importance to the designer and owner Bond Strength Bond strength is perhaps the most important single physical property of hardened mortar. Both the strength and the extent of bond are important. Variables which affect the bond strength include 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 mortar. Mortar bond is greater to roughened surfaces, such as wire cut surfaces, than to smooth surfaces, such as die skin surfaces. Sanded and coated surfaces can reduce the bond strength depending upon 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 (IRA) of brick indicates the brick's suction and whether it should be wetted prior to use. However, it is the actual suction at the time of laying which influences bond strength. In practically all cases, mortar bonds best to brick whose suctions are less than 30 g/min/30 in.2 (1.55 kg/m2/min) at the time of laying. If the brick's suction exceeds this value then the brick should be wetted three to twenty-four hours prior to laying. Wetted brick should be surface dry before they are laid in mortar. Several researchers have shown that IRA appears to have little influence on bond strength. Effect of Air Content. Available information indicates a definite relationship exists between air content and bond strength of mortar. Provided other parameters are held constant, as air content is increased, compressive strength and bond strength are reduced, while workability and resistance to freeze-thaw deterioration are increased. Effect of Flow. An increase in the flow of mortar at the time of use is beneficial because it can satisfy the suction of the brick and can allow greater control of the mortar for the bricklayer. For all mortars, and with minor exceptions for all brick suctions, bond strength increases as flow increases. However, too much water can reduce both workability and bond strength. The time lapse between spreading mortar and placing brick will affect mortar flow, particularly when mortar is spread on high suction brick or when construction takes place during hot, dry weather. In such cases, mortar will have less flow by the time brick are placed than when it was first spread. Conceivably, bond to brick placed on this mortar could be materially reduced. For highest bond strength, reduce this time interval to a minimum. Because all mortar is not used immediately after mixing, some of its water may evaporate while it is on the mortar board. The addition of water to mortar (retempering) to replace water lost by evaporation should be encouraged. Although compressive strength may be slightly reduced and mortar color lightened if mortar is retempered, bond strength may be lowered if it is not. All mortar should be used within 2 1/2 hours after mixing since the mortar will begin to set. Effect of Movement. Once mortar has begun to harden, tapping or attempting to otherwise move brick can be detrimental to bond. Movement at this time will break the bond between the brick and mortar. The partially dried mortar will not have sufficient plasticity to adhere well to the masonry units. Effect of Proportions. There is no precise combination of materials that will always produce optimum bond. Type S mortar will typically develop the highest flexural bond strength of all the mortar types, if all other variables are held constant. Effect of Curing. Wet curing of masonry generally produces higher bond strength than dry curing, but mortar materials will influence the result. Bond strength design values, however, are based on dry curing. Test Methods. Because many variables affect bond, it may be desirable to achieve reproducible results from a small scale laboratory test. The bond wrench test, ASTM C 1072, Standard Test Method for Measurement of Masonry Flexural Bond Strength, appears to fulfill this need. It evaluates the flexural bond strength of each joint in a masonry prism. The bond wrench test has replaced various tests such as ASTM E 518 and E 72. The apparatus as shown in Figure 1 consists of a stack bonded prism clamped in a stationary frame. A cantilevered arm is clamped to the top brick over the joint to be tested. The free end of the cantilever arm is loaded until failure, which occurs when the clamped brick is “wrenched” off.
Bond Wrench Test Apparatus FIG.1
In general, to increase the flexural bond strength: 1. Bond mortar to a wirecut or roughened surface rather than a die skin surface. 2. Use brick with suction less than 30 grams/min/30 in.2 (1.55 kg/m2/min) when laid. Control high suction by wetting brick prior to laying. 3. Use Type S portland cement-lime mortar, Type S mortar cement mortar or Type S masonry cement mortar with air content in the low to mid-range of ASTM C 91 limits. 4. Mix mortar to the maximum flow compatible with workmanship. Use maximum mixing water and permit retempering.
Water Content Water content is possibly the most misunderstood aspect of masonry mortar, probably due to the similarity between mortar and concrete materials. Many designers mistakenly base mortar specifications on the assumption that mortar requirements are similar to concrete requirements, especially with regard to the water-cement ratio. Many specifications incorrectly require mortar to be mixed with the minimum amount of water consistent with workability. Often, retempering of the mortar is prohibited. These provisions result in mortars which have higher compressive strengths but lower bond strengths. Mixing mortar with the maximum amount of water consistent with workability will provide maximum bond strength within the capacity of the mortar. Retempering is permitted, but only to replace water lost by evaporation. This can usually be controlled satisfactorily by requiring that all mortar be used within 2 1/2 hours after initial mixing. Workability A mortar is workable if its consistency allows it to be spread with little effort and if it will readily adhere to vertical masonry surfaces. Although experienced masons are good judges of the workability of the mortars, there is no standard laboratory test for measuring this property. Water retention, flow and resistance to segregation affect workability. In turn, these are affected by properties of the mortar ingredients. Because of this complex relationship, quantitative estimates of workability are difficult to obtain. Until a test is developed, the requirements for water retention and aggregate gradation must be relied upon to ensure satisfactory workability. Initial Flow and Water Retention Initial flow is essentially a measure of the mortar's water content. It can be measured by either of two methods: 1) ASTM C 109, Standard Test Method for Compressive Strength of Hydraulic Cement Mortars or 2) ASTM C 780, Standard Test Method for Preconstruction and Construction Evaluation of Mortars for Plain and Reinforced Unit Masonry. In ASTM C 109, a truncated cone of mortar is formed on a flow table, which is then mechanically raised one inch (25 mm) and dropped 25 times in 15 seconds. During this test, the mortar will flow increasing the diameter of the mortar specimen. The initial flow is the ratio of the increase in diameter from the initial four inch (100 mm) cone base diameter, expressed in percent. In ASTM C 780, a 3 1/2 in. (89 mm) high hollow cylinder is filled with mortar, and a cone shaped plunger, whose point is placed at the top of the cylinder, is dropped into the mortar. The depth of the cone penetration into the mortar is measured in millimeters. The greater the penetration of the cone into the mortar, the greater its flow or water content. Water retention is the ability of a mortar to hold water when placed in contact with absorbent masonry units. The laboratory value of water retention is the ratio of flow after suction to the initial flow, expressed in percent. Flow after suction, as described in ASTM C 91, is determined by subjecting the mortar to a vacuum and re-measuring the flow of the mortar. A mortar which has low water retention will lose moisture more rapidly. The IRA of the brick is considered in order to determine if this is detrimental to bond. Laboratory mortars are based on an initial flow of only 105 to 115 percent. Construction mortars normally have initial flows in the range of 130 to 150 percent to produce a level of workability satisfactory to the mason. Requirements for laboratory prepared mortar should not be applied to field prepared mortar. Further, test results of laboratory prepared mortar should not be compared to test results of field prepared mortar without considering the initial flow of each. The lower initial flow requirements for laboratory mortars were set to allow for more consistent test results on most available laboratory equipment and to compensate for water absorbed by the units. In general, the following will increase water retention: 1. Addition of sand fines within allowable gradation limits. 2. Use of highly plastic lime (Type S lime). 3. Increase air content. Extensibility and Plastic Flow Extensibility is another term for maximum tensile strain at failure. It reflects the maximum elongation possible under tensile forces. High lime mortars exhibit greater 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. Compressive Strength As with concrete, the compressive strength of mortar primarily depends upon the cement content and the water cement ratio. However, because compressive strength of masonry mortar is less important than bond strength, workability and water retention, the latter properties should be given principal consideration in mortar selection. Effect of Proportions. Compressive strength increases with an increase in cement content of mortar and decreases with an increase in water content, lime content or over-sanding. Sometimes air entrainment is introduced to obtain higher flows with lower water content. The reasoning here is that lower water cement ratios will provide higher compressive strengths. However, this generally proves futile since compressive strength decreases with an increase in air content. Effect of Retempering. Retempering will decrease mortar compressive strength, the amount of decrease increasing with time after mixing. Mortar will begin to stiffen about 2 1/2 hours after initial mixing. Since mixing after initial set lowers compressive strength more, reduction in strength will be noticeably less if retempering occurs within that time. It is frequently desirable to sacrifice some compressive strength in favor of improved bond strength by permitting retempering. Test Methods. Compressive strength is measured by testing 2 in. (50 mm) mortar cubes or 2 in. (50 mm) and 3 in. (75 mm) diameter cylinders. Procedures for molding and testing cubes and cylinders appear in ASTM C 109 and ASTM C 780, respectively. Because the tests are relatively simple and because they give consistent, reproducible results, compressive strength is considered one basis for comparing mortars. Durability The durability of mortar in unsaturated masonry is not a serious problem. The durability of mortar is shown in the number of masonry structures that have been in service for many years. Although an increase in air content may increase the durability of masonry mortar, it will decrease bond strength and other desirable properties. For this reason, and because mortar is normally quite durable without air entrainment, the use of air-entraining admixtures to increase air content is not recommended. Volume Change Volume changes in mortars can result from four causes: chemical reactions in hardening, temperature changes, wetting and drying, and unsound ingredients which chemically expand. Differential volume change between brick and mortar in a given wythe has no important effect on performance. However, total volume change can be significant. Volume change caused by hardening, cement hydration, is often termed shrinkage and depends upon curing conditions, mix proportions and water content. Mortars hardened in absorbent molds or in contact with brick exhibit considerably less shrinkage than those hardened in non-absorbent molds. An increase in water content will cause an increase in shrinkage during hardening of mortar if the excess water is not removed. Change in temperature will lead to expansion and contraction of mortar. Thermal expansion and contraction of masonry and means to accommodate the expected movement are discussed in Technical Notes 18 Series. Mortar swells and shrinks as its moisture content increases and decreases, respectively. Moisture content changes with normal cycles of wetting and drying. The magnitude of volume change due to this effect is smaller than that from shrinkage. Unsound ingredients or impurities can cause mortar to expand. Unhydrated lime oxides or gypsum are examples of these, and can cause significant volume change. Efflorescence Efflorescence is a crystalline deposit of water-soluble salts on the surface of masonry. Mortar may be a major contributor to efflorescence since it is a primary source of calcium hydroxide. This chemical can produce efflorescence on its own and can react with carbon dioxide in the air or solutions from the brick to form insoluble compounds. Mortar can contain other soluble constituents, including alkalies, sulfates and magnesium hydroxide. Currently there is no standard test method to determine the efflorescence potential of mortar or of a brick/mortar combination. Scientists conclude that mortars will effloresce under any standard test. Color Colored mortars may be obtained through the use of colored aggregates or suitable pigments. The use of colored aggregates is preferable when the desired mortar color can be obtained. White sand, ground granite, marble or stone, usually have permanent color and do not weaken the mortar. For white joints, use white sand, ground limestone or ground marble with white portland cement and lime. Mortar pigments must be sufficiently fine to disperse throughout the mix, must be capable of imparting the desired color when used in permissible quantities and must not react with other ingredients to the detriment of the mortar. These requirements are generally met by metallic oxide pigments. Carbon black and ultramarine blue have also been used successfully as mortar colors. Avoid using organic colors and, in particular, those colors containing Prussian blue, cadmium lithopone, and zinc and lead chromates. Paint pigments may not be suitable for mortars. Most pigments which conform to ASTM C 979, Standard Specification for Pigments for Integrally Colored Concrete, are suitable for mortar. Use the minimum quantity of pigments that will produce the desired results; an excess may seriously impair strength and durability. The maximum permissible quantity of most metallic oxide pigments is 10 percent of the cement content by weight. Although carbon black is a very effective coloring agent, it will greatly reduce mortar strength when used in greater proportions. Therefore, limit carbon black to 2 percent of the cement content by weight. For best results, use cement and coloring agents premixed in large, controlled quantities. Premixing large quantities will assure more uniform color than can be obtained by mixing smaller batches at the job. A consistent mixing sequence is essential for color consistency when mixing smaller batches at the job. Further, use the same source of mortar materials throughout the project. Color uniformity varies with the amount of mixing water, moisture content of the brick when laid and if the mortar is retempered. The time and degree of tooling and cleaning techniques will also influence final mortar color. Color permanence depends upon quality of pigments and weathering and efflorescing qualities of the mortar.
RECOMMENDED MORTAR USES Selection of a particular mortar type is usually a function of the needs of the finished masonry element. Where high winds are expected, high lateral strength is required and, hence, mortar with high flexural bond strength should be chosen. For loadbearing walls and reinforced brick masonry, high compressive strength may be the governing factor. In some projects, considerations of durability, color and flexibility may be of utmost concern. Factors which improve one property of mortar often do so at the expense of others. For this reason, when selecting a mortar, evaluate properties of each type and choose that mortar which will best meet particular end-use requirements. No single type of mortar is best for all purposes. See Technical Notes 8B for selection of mortar types, and Technical Notes 19 for information on refractory mortar.
SUMMARY Mortar requirements differ from concrete requirements, principally because the primary function of mortar is to bond masonry units into an integral element. Properties of both plastic and hardened mortars are important. Plastic properties determine construction suitability; hardened properties determine performance of finished elements. No one combination of ingredients provides a mortar which is highest in all desirable properties. Factors that improve one property may do so at the expense of others. When selecting a mortar, evaluate all properties, and then select the mortar providing the best compromise for the particular requirements. The information and suggestions contained in this Technical Notes are based on the available data and the experience of the technical staff of the Brick Industry Association. The information and recommendations contained herein must be used in conjunction with good technical judgment and a basic understanding of the properties of brick masonry. Final decisions on the use of the information contained in this Technical Notes are not within the purview of the Brick Industry Association and must rest with the project architect, engineer and owner.
REFERENCES 1. ASTM C 270-02 Standard Specification for Mortar for Unit Masonry, Annual Book of ASTM Standards, Vol. 04.05, American Society for Testing and Materials, West Conshohocken, PA, 2003. 2. Borchelt, J. G., Melander, J. M. and Nelson, R. L., “Bond Strength and Water Penetration of High IRA Brick and Mortar”, Proceedings of the Eighth North American Masonry Conference, The Masonry Society, Boulder, CO, June 1999, pp. 304-315. 3. Borchelt, J. G. and Tann, J.A., “Bond Strength and Water Penetration of Low IRA Brick and Mortar”, Proceedings of the Seventh North American Masonry Conference, The Masonry Society, Boulder, CO, June 1996, pp.206-216. 4. Matthys, J.H., “Brick Masonry Flexural Bond Strength Using Conventional Masonry Mortar”, Proceedings of the Fifth Canadian Masonry Symposium, University of Vancouver, Vancouver, BC, 1992, pp. 745-756. 5. Melander, J.M. and Conway, J.T., “Compressive Strengths and Bond Strengths of Portland Cement-Lime Mortars”, Masonry, Design and Construction, Problems and Repair, ASTM STP 1180, American Society for Testing and Materials, Philadelphia, PA, 1993, pp. 105-120. 6. Ribar, J.W. and Dubovoy, V.S., “Investigation of Masonry Bond and Surface Profile of Brick”, Masonry: Materials, Design, Construction and Maintenance, ASTM STP 992, American Society for Testing and Materials, Philadelphia, PA, 1988, pp. 33-37. 7. Wood, S.L., “Flexural Bond Strength of Clay Brick Masonry”, The Masonry Society Journal, Vol. 13 #2, The Masonry Society, Boulder, CO, February 1995, pp. 45-55. 8. Wright, B.T., Wilkin, R.D. and John, G.W., “Variables Affecting the Strength of Masonry Mortars”, Masonry, Design and Construction, Problems and Repair, ASTM STP 1180, American Society for Testing and Materials, Philadelphia, PA, 1993, pp. 197-210.
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