Masonry Magazine April 1993 Page. 30

Masonry Magazine April 1993 Page. 30

Masonry Magazine April 1993 Page. 30


Bond coats may be used between the concrete slab and mortar setting bed. Bond coats consist of portland cement mixed to a creamy consistency with water or a latex additive. The bond coat is used to create improved bond between the concrete slab and the mortar setting bed. It is installed as the setting bed and pavers are laid, and should not exceed in. (2 mm).

Latex-portland cement mortars improve bond strength, reduce water absorption and provide greater durability than conventional mortars. These mortars should be used in applications such as heavy vehicular traffic pavements or pavements where proper drainage is not possible. Latex-portland cement mortars are also useful in mortared brick paving over a suspended diaphragm and are typically used in thin-set mortar applications. Latex additives are water emulsions which are added to and may replace all or part of the mixing water. It is advisable to check latex-modified mortar and brick compatibility with respect to bond strength by preconstruction testing.

Jointing Materials

Materials used between brick pavers may be mortar or sand. Mortared brick paving uses mortar between the pavers. This mortar should be the same as the mortar used for the setting bed. In mortarless brick paving, the sand which is placed between the pavers should conform to ASTM C 144 (mason's sand). However, the maximum particle size should not be larger than the joint size. Typically, % in. (3 mm) joints are used in mortarless brick paving. The sand should be clean and washed with no deleterious materials. When mortarless brick paving is used on slopes or in areas where jointing sand may be washed out, a portland cement-sand mixture can be used. This mixture should be used with caution as it often stains pavers during installation and makes their reuse difficult. If a sand-cement mixture is necessary, it should consist of 1 part portland cement and 6 parts sand.

Base and Subbase Materials

Base and subbase materials consist of crushed aggregate, gravel, sand, asphalt or concrete. Suspended diaphragms are usually made of concrete, steel or wood. Asphalt and concrete bases often require an aggregate subbase. Some flexible bases may require a subbase because of heavy traffic loads or poor subgrade conditions.

Aggregate Bases and Subbases

Crushed, quarry-processed aggregate is often used as a base material because of its availability, ease of use in construction and good performance. Naturally-occurring gravel may also be used if it meets proper gradation requirements. The maximum size of aggregate used in construction depends upon the size of the project and the size of the compaction equipment being used. Proper gradation of materials is required to achieve adequate compaction. Gradation should conform to ASTM D 2940 for heavy traffic applications, while smaller projects can simply require aggregate graded down from in. (19 mm) in size. Aggregates are produced from different raw materials and are called different names in different parts of the country. Therefore, aggregate should be specified by gradation rather than by name.

Either dense graded or open graded aggregate may be used, although dense graded crushed aggregate develops a stronger, more impervious base. Open graded aggregate is often used in areas of poor drainage or in areas subjected to frost heave. If an open graded aggregate base is used beneath a sand setting bed, a geotextile must be used to prevent sand from filtering into the base.

In residential pedestrian applications, sand bases can be used when the subgrade is compacted or bearing on undisturbed earth, and in areas where frost heave is not a consideration. Sand should conform to ASTM C 33 (concrete sand) and be clean and free of deleterious materials. Salts in the sand will often wick up through the brick, showing efflorescence on the surface.

Asphalt Bases

New or existing asphalt bases may be used to support brick paving. Major defects such as cracks or holes in existing asphalt bases should be repaired prior to installation of brick. A membrane can be placed over an existing asphalt base to strengthen the pavement and prevent the sand setting bed from sifting through cracks in the asphalt. The specification of asphalt for bases is beyond the scope of this Technical Notes, but the asphalt should conform to ASTM D 3515 (hot-mixed asphalt), ASTM D 4215 (cold-mixed asphalt) or local codes.

Concrete Bases

New and existing concrete bases may be used for brick paving. New concrete should be installed following recommended concrete practices. Where a mortar setting bed is bonded to a new concrete slab, a rough textured finish should be used such as that produced by a screed or wood float. Concrete bases should be properly cured before the brick pavers are installed. If brick paving is placed over existing concrete, the concrete should be sound, with major cracks properly repaired. A geotextile can be used to bridge cracks when using a sand setting bed to prevent sand from sifting into the cracks. The specification of concrete for bases is beyond the scope of this Technical Notes, but should conform to local codes.

Membranes

Membranes are used in brick paving applications to separate layers in a paving system, accommodate differential movement or serve as a waterproofing element. Membrane materials include geotextiles, sheet membranes and liquid membranes.

Geotextiles or geosynthetics are used to separate pavement layers while still allowing drainage. They are composed of various types of fibers that are either woven or nonwoven. Thickness, permeability, elongation, grab strength, burst pressure and durability are properties of geotextiles which should be examined for


Masonry Magazine December 2012 Page. 45
December 2012

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Masonry Magazine December 2012 Page. 46
December 2012

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Masonry Magazine December 2012 Page. 47
December 2012

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Masonry Magazine December 2012 Page. 48
December 2012

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