More C Aggregate for use in masonry mortar shall consist of natural sand or manufactured sand. Manufactured sand is the product obtained by crushing stone, gravel, or air-cooled iron blast-furnace slag specially processed to ensure suitable gradation. Aggregate for use in masonry mortar shall be graded within the limits prescribed.
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Mortar serves many important functions: it bonds units together into an integral structural assembly, seals joints against penetration by air and moisture, accommodates small movements within a wall, accommodates slight differences between unit sizes, and bonds to joint reinforcement, ties and anchors so that all elements perform as an assembly. In addition, Type N masonry cement can be combined with portland cement or blended hydraulic cement to produce Type S or M mortars.
Quicklime must be slaked combined chemically with water prior to use. The resultant lime putty must be stored and allowed to hydrate for at least 24 hours before use. Consequently, quicklime is rarely used in mortar. Slaking of hydrated lime is not required, thus hydrated lime is immediately usable and much more convenient than quicklime. Types N or NA lime are not typically used in mortar; however, they are permitted if shown by test or performance record to not be detrimental to the soundness of the mortar.
Air-entrained limes are only permitted in mortars containing nonair-entrained cement. Manufactured sand is the product obtained by crushing stone, gravel, or air cooled blast furnace slag. It is characterized by sharp, angular shaped particles. Aggregates which fail these gradation limits may be used, as long as the resulting mortar complies with the property specification requirements of ASTM C, as shown in Table 2.
Potability of water is not in itself a consideration, but the water obtained from drinking supply sources is considered suitable for use. Admixtures are functionally classified as bond enhancers, workability enhancers, set accelerators, set retarders, and water repellents. Since chlorides accelerate the corrosion of steel reinforcement and accessories ASTM C stipulates that admixtures add not more than 65 ppm 0.
Similarly, the Specifications for Masonry Structures ref. Effect of Materials on Mortar With the diversity of materials available, masonry mortars can be formulated to produce the desired properties for most specific job requirements. Each of the individual ingredients cement, lime, sand, water, and any modifiers present contributes to the performance of the mortar.
Portland cement provides strength and durability. Lime imparts workability, water retention, as well as some limited cementitious and autogenous healing properties. Sand acts as a filler and provides body to the mortar while helping to reduce shrinkage and control cracking. Water acts as a mixing agent, a lubricant, and is also needed for hydration of the portland cement.
The various material options alter the characteristics of the mortar in a predictable manner. Changes in cement type promote slight changes in setting characteristics, workability, color, and strength development.
Use of air-entrained cement or lime generally results in decreased water demand, improved workability, increased freeze-thaw resistance, and decreased bond strength. Masonry cements, used singly or in combination with portland cement, provide mortars with excellent workability and freeze-thaw durability; however, bond strengths may be reduced. Consequently, design allowable flexural tension values vary based on mortar type and cementitious materials or lime used for unreinforced masonry ref.
Changes in sand type and gradation affect mortar properties. Natural sand gives improved workability at a lower water demand because of the spherical particle shape, while manufactured sands require additional water due to their angular shape. In general, well graded aggregates reduce segregation in a plastic mortar, which in turn inhibits bleeding and improves workability. Sands deficient in fines generally produce harsh mortars, while sands with excessive fines typically result in mortars with lower compressive strengths.
Four mortar types, M, S, N and O are included in this standard. However, Types M, S, and N are typically required by building codes. Building codes also may restrict the use of some mortars for particular applications.
For example, empirical design of foundation walls requires Type M or S mortar and glass unit masonry requires Type N or S mortar ref.
Only one of the specifications should be called for in the project documents, not both. The proportion specification Table 1 prescribes the parts by volume of each ingredient required to provide a specific mortar type.
A combination of portland cement and lime may be used as the cementing agent in each type of mortar. Also, masonry cements ref. As an alternative, approved materials may be mixed in controlled percentages as long as the resultant mortar meets the physical requirements designated in ASTM C, as shown in Table 2. The aggregate ratio noted in Table 2 must be followed. Conformance to the property specification of ASTM C is established by testing laboratory prepared mortar during a pre-construction evaluation of the mortar proposed for the project.
The laboratory then establishes proportions for mortar, based on successful tests. These proportions are then followed when preparing field mortar. For example, mortars can be rated on the basis of obtaining visually satisfactory mortar joints. Depending on the particular circumstances for a given project, the criteria for mortar selection are based on design considerations, mortar properties in the plastic state or mortar properties in a hardened state.
Consideration of each is necessary to achieve a desired result. Properties of Plastic Mortar Workability is the property of mortar characterized by the smooth plastic consistency which makes it easy to spread. This is the property of most importance to the mason. A workable mortar spreads easily under the trowel; adheres to vertical surfaces during unit handling, placement, and bedding; maintains alignment as other units are positioned; and provides a watertight, closed joint when tooled.
Once mix proportions have been established, the addition of water should be consistent with that required to improve mortar placement without sacrificing the ability to support the masonry unit. Adequate water content promotes intimate contact between the unit and mortar, which is essential for satisfactory bond.
While water content has the greatest influence on the workability of a mortar, cementitious materials, aggregate gradation, and air-entrainment also contribute to a lesser degree. Mortars with low water retention stiffen more quickly, making it difficult for the mason to bed and adjust the masonry unit during placement.
Mortars with desired water retention characteristics allow the mason to lay a mortar bed two or three units ahead before placing subsequent units. Water retentivity is dependent on properties of the cementitious materials, sand gradation, and mortar proportions. The time lapse between spreading a mortar bed and placing block should be kept to a minimum, because the workability will be reduced as water is absorbed into the block. If too much time elapses before a block is placed on a fresh mortar bed, units are less easily positioned and the bond will be reduced.
Evaporation of the mixing water from mortar may require retempering mixing in additional water. This generally is not harmful as long as it is done prior to hydration of the mortar. Properties of Hardened Mortar Properties of hardened mortar that affect the performance of the finished concrete masonry include bond, compressive strength, and durability.
These properties are difficult to measure other than in laboratory or field specimens prepared under controlled conditions. When obtaining the sample, however, it is important to ensure that the sample is representative of the mortar in question, i. Bond is a term used to describe both the extent of contact between mortar and unit and the strength of adhesion. Bond is a function of several factors including mortar properties, unit surface characteristics, workmanship, and curing.
Other factors being equal, bond strength will increase as the compressive strength of the mortar increases, although not in direct proportion. Bond may also be effectively increased through the use of properly designed mortars having water contents which provide good workability. Compressive strength is perhaps the most commonly measured property of mortar but is perhaps the most misunderstood.
Whenever compressive strength results are intended to be used to determine conformance of a mortar to the property specifications of ASTM C, compressive strength tests must be conducted in accordance with the laboratory procedures required by ASTM C ASTM C contains no requirement for minimum compressive strength of field mortar.
The mortar strength in the wall will be much higher than the field test because of the reduced water cement ratio due absorption of mix water into the masonry units and a greatly reduced shape factor in the mortar joint versus the mortar test cube. ASTM C recognizes this and states that the strength should not be construed as being representative of the actual strength of the mortar.
Durability of mortar also is an important consideration for parapets or other walls with an extreme exposure to the weather. Oversanding or overtempering can decrease durability. High strength mortars and air entrained mortars provide increased durability. Reported by the Masonry Standards Joint Committee, NCMA, Ca, Standard Specification for Masonry Cement. C, Standard Specification for Portland Cement.
C, Standard Specification for Mortar Cement. NCMA and the companies disseminating this technical information disclaim any and all responsibility and liability for the accuracy and the application of the information contained in this publication.
Mortar serves many important functions: it bonds units together into an integral structural assembly, seals joints against penetration by air and moisture, accommodates small movements within a wall, accommodates slight differences between unit sizes, and bonds to joint reinforcement, ties and anchors so that all elements perform as an assembly. In addition, Type N masonry cement can be combined with portland cement or blended hydraulic cement to produce Type S or M mortars. Quicklime must be slaked combined chemically with water prior to use. The resultant lime putty must be stored and allowed to hydrate for at least 24 hours before use. Consequently, quicklime is rarely used in mortar.
ASTM C 144
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ASTM C144 PDF
ASTM C144 - 11