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Technical Guide / Overview

Overview | Color Charts | Drawings | Specifications

Concrete block wall systems are unsurpassed in functioning as a barrier to contain the spread of fire. These systems effectively resist transmission of intense heat through the wall while also preventing the passage of flames and hot gases. The fire resistance rating period of concrete masonry elements is determined by testing, by calculation methods or through a listing service.

Testing of representative elements of the wall construction in accordance with standard fire test methods is usually measured by ASTM E 119, Standard Test Methods for Fire Tests of Building Construction and Materials.

Calculation methods determine fire resistance ratings based on physical and material properties of the concrete masonry unit, such as the equivalent thickness and aggregate types used in the manufacture of the concrete masonry units.

These calculation methods are based on extensive research which has established a relationship between physical properties of materials and the fire resistance rating. The rating is a function of the aggregate used in the manufacturing of the units and the equivalent thickness of the unit.

Private listing services allow a designer to specify a fire rated assembly which has been previously classified. The listing service monitors materials and production to verify that the concrete masonry units are in compliance with appropriate standards.

The equivalent thickness of a unit is the solid thickness that would be obtained if the same amount of masonry contained in a hollow unit were recast without core holes. The equivalent thickness of a hollow unit is equal to the percentage solid times the actual thickness of the unit. The equivalent thickness of a 100% solid unit or a solid grouted unit is equal to the actual thickness.

If the cells of hollow unit masonry are filled with approved material, the equivalent thickness of the assembly can be considered the same as actual thickness. The list of approved materials includes: sand, pea gravel, crushed stone, or slag that meets ASTM C33 requirements; pumice, scoria, expanded shale, expanded clay, expanded slate, expanded slag, expanded flyash, or cinders that comply with ASTM C331 or C332, or perlite or vermiculate meeting the requirements of ASTM C549 and C516 respectively.

The fire resistance rating of units manufactured with a combination of aggregate types is determined by linear interpolation based on the percent, by volume, of each aggregate used in the manufacture. This may be expressed by the following equation:

Tr = (T1 x V1) + (T2 X V2)

Where: Tr = required equivalent thickness for a specific fire resistance rating of an assembly constructed of units with combined aggregates. (Value may be inches or mm.)

T1, T2 = required equivalent thickness for a specific fire resistance rating of a wall constructed of units with aggregate types 1 and 2, respectively. (Value may be inches or mm.)

V1, V2 = fractional volume of aggregate types 1 and 2, respectively, used in the manufacture of the unit. (Value is expressed in % volume of aggregate type.)

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Sound absorption involves reducing the sound emanating from a source within a room by diminishing the sound level and changing its characteristics. Sound is absorbed through dissipation of the sound wave energy. The effectiveness of the absorption method is dependent on the ability of the room surfaces to absorb the noise rather than reflect it. Sound Absorption Coefficient (SAC) is an indication of the sound absorbing efficiency of a surface. The Noise Reduction Coefficient (NRC) is the average SAC taken at different frequencies.

NRC values depend on the porosity of the material and the surface. An open rough textured surface will have a higher NRC value. This means that a more porous block such as a Splitface or Fluted block will have a higher NRC rating. Also a medium weight block, because of its porosity will perform better from an absorption point of view, than a normal weight block. If the NRC = 1, then no sound is reflected back. The percentage that is reflected back is fractionalized, subtracted from 1 and this figure is the NRC value.

Sound transmission is concerned with sound traveling through barriers from one space into another. To prevent transmission the walls just have enough density to stop the energy waves. Sound Transmission Loss is the total amount of airborne sound lost at a given frequency, as it travels through a partition. The STL, which is measured in decibels, is measured at 16 frequencies and the loss at these frequencies is used to plot a curve, which is used to determine the Sound Transmission Class (STC). The STC of a wall is determined by comparing its sound transmission loss curve with a set of standard curves or contours. There is a definite correlation between Sound Transmission and the weight of the wall. If a wall is heavier and more dense then the Sound Transmission Coefficient will increase. For concrete masonry units this means that a Normal Weight Block would have a higher STC rating because of the mass of that block. Porosity of the units is also an important aspect, as the tighter a texture on the surface, the greater the resistance to sound penetration. Therefore a painted surface will increase the STC, but will decrease the NRC. If a sound of 100 decibels is generated on one side of a wall and 40 decibels is measured on the other side, then the reduction in sound intensity is 60 decibels. The wall then has a 60 decibel rating.
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Control joints are vertical separations built into a concrete masonry wall at locations where stress concentrations may occur. They are one method used to relieve horizontal tensile stresses due to shrinkage of the concrete masonry units, mortar, and when used, grout. Control joints reduce restraint and permit longitudinal movement.

Control joints should be located where volume changes in the masonry due to drying shrinkage, carbonation, or temperature changes are likely to create tension in the masonry that will exceed its capacity. Care should be taken to provide joints at locations of stress concentrations such as:

1. at changes in wall height,
2. at changes in wall thickness,
3. at movement joints in foundations and floors,
4. at movement joints in roofs and floors that bear on a wall,
5. near one or both sides of door or window openings,
6. adjacent to corners of walls or intersections within a distance equal to half the control joint spacing.

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Structural performance of masonry is based on the physical characteristics of its components, and on the construction methods used in assembling these components. The strength of masonry is influenced by the structural properties of units, grout, mortar and reinforcement. In engineered masonry structures, the required strength of structural elements is determined by distributing design loads to the various resisting elements in accordance with a structural analysis. After the required strength is determined, the designer uses it as a basis for specifying f'm, which is defined as the "specified compressive strength of masonry". This property is noted in the project documents and is used in accordance with masonry design codes to establish allowable stresses for masonry elements.
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Concrete block has three classifications according to weight. Lightweight units weigh less than 105 pounds per cubic foot. Medium Weight units weigh between 105 and less than 125 pounds per cubic foot, while Normal Weight units weigh 125 pounds per cubic foot or more. Oldcastle adams manufactures all three weight classifications. Lightweight block is the lightest, has the highest fire rating, the highest R value and will be more effective for sound absorption (NRC rating). Normal Weight block will have a tighter texture and will be more effective for sound transmission (STC rating). All weight classifications meet or exceed ASTM C90 Standard Specification for Loadbearing Concrete Masonry Units.
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Economy, superior design and function, and appealing aesthetics are readily achieved in projects constructed with integrally colored concrete masonry units.

It is important to note that minor variations in tone and texture are inherent in all masonry products. Factors influencing these variations in C.M.U. include: color variation in pigments, aggregates, cement, water content, degree of compaction achieved during manufacture, kiln conditions, and atmospheric conditions including temperature and humidity.

If properly dispersed throughout the wall these variations can enhance rather than detract from the appearance of a project. There are several steps that can be taken to ensure that the product performs as intended:

1. The architect should request samples for verification purposes showing the full range of exposed color and texture to be expected in completed construction.
2. A sample panel should be built on the jobsite. This sample panel should be used as a reference for the color of the CMU, the texture of the CMU and the workmanship. In case of disputes over these issues on the project, the sample panel should be referred to.
3. The mason should pull product to be placed in the wall from opposite corners of three randomly selected pallets to ensure dispersion of variability.
4. The initial order should be as accurate as possible, as Betco Supreme cannot guarantee an exact match from subsequent production runs.
5. Following construction the concrete masonry units should be cleaned using well-established and specified techniques.

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