ACI 216.1 (Standard Method for Determining Fire Ratings of Concrete and Masonry Assemblies), has been adopted by the new International Building Code (IBC) that will go into effect in early 2000 A.D. Chapter 3 of ACI 216.1 provides a chart (see Pages 2.5 and 2.6) identifying the types of aggregates used to manufacture CMU's and the fire ratings for each of the aggregates. The blending of aggregates is acceptable (and common), however, the fire ratings will need to be established using the calculation method.

EXAMPLE AND CAUTIONS:

Example: An 8"x8"x16" CMU is used in a construction project and the specifications require a two hour fire rating for the block. The manufacturer should be required to submit a test report establishing the equivalent thickness of the 8 inch unit being supplied. Most 8"x8"x16" CMU's will have an equivalent thickness of 3.8 inches to 4.0 inches.

Cautions:

• If the block is made with calcareous sands and gravels (normal weight block),

an 8 inch CMU will not meet a two hour requirement unless the equivalent thickness is

4.2 inches or greater.

• If the block is made with a blend of limestone screens and sand, the equivalent thickness will need to exceed 4.1 inches depending on the ratios of limestone and sand.
• As a general rule, an 8 inch block will need some lightweight aggregate in the mix design in order to meet a two hour rating if the equivalent thickness is 4.1 inches or less.

Listed below is a suggested specification language designed to put the responsibility to accurately comply with fire rating requirements on the block manufacturer. It is an example of a section that can be added to a firm's standard specifications to assure compliance with required fire ratings. The section numbers may vary according to each firm's numbering format.

04200 UNIT MASONRY

04204 Fire Rated Concrete Masonry Units

4.01 Fire ratings for concrete masonry units will be considered being in compliance when:

4.01.1 The CMU has been certified through ASTM E-119 testing, or

4.01.2 The CMU has been certified through the equivalent thickness method contained in Chapter 3 of ACI 216.1 or NCMA TEK 7-1A. (These requirements apply to blended and single aggregate CMU's).

4.01.2.1 For fire rated CMU's that are manufactured with blending two or more aggregates under the requirements of 2.01.2, blending percentages must be established by determining the dry-rodded weights of the aggregates rather than the damp-loose weights (as weighed in the batching process).

4.01.2.2 The percentage of each aggregate (dry-rodded weight) will be reported in the concrete masonry submittal.

4.02 The equivalent thickness of each fire rated block will be established by ASTM C-140. Verification of the equivalent thickness of fire rated CMU's will be supplied by an independent testing laboratory and submitted in the concrete masonry submittal.

Concrete Masonry Units Equivalent

Thickness Requirements

For Fire Ratings When Blending Primary Aggregates With Sand As Per ACI 216.1

 

50/50% Blending*

Minimum Equivalent Thickness (Inches) Required

Aggregate Plus 50% Sand

4 hr

3.5 hr

3hr

2.5 hr

2 hr

1.5 hr

1hr

0.5 hr

Pumice or Expanded Slag Expanded Clay, Shale, Slate Limestone or Cinders or Slag Calcareous or Siliceous Gravel

5.45 5.65 6.05 6.20

5.10 5.30 5.65 5.80

4.65 4.85 5.15 5.30

4.20 4.40 4.65 4.80

3.70 3.90 4.10 4.20

3.15 3.45 3.50 3.60

2.45 2.70 2.75 2.80

1.75 1.90 1.95 2.00

40/60% Blending*

Minimum Equivalent Thickness (Inches) Required

Aggregate Plus 60% Sand

4 hr

3.5 hr

3hr

2.5 hr

2 hr

1.5 hr

1hr

0.5 hr

Pumice or Expanded Slag Expanded Clay, Shale, Slate Limestone or Cinders or Slag Calcareous or Siliceous Gravel

5.60 5.76 6.06 6.20

5.24 5.40 5.68 5.80

4.78 4.94 5.18 5.30

4.32 4.48 4.68 4.80

3.80 3.96 4.12 4.20

3.24 3.48 3.52 3.60

2.52 2.72 2.78 2.80

1.80 1.92 1.96 2.00

Determining The Fire Resistance Of

Concrete Masonry Assemblies

FIRE RESISTANCE RATINGS

The fire resistance rating of concrete masonry elements can be determined by two methods:

• Testing using Test Method ASTM E-119, or
• Calculation Method based on the equivalent thickness of the concrete masonry unit and the type(s) of aggregate used.

ASTM E-119 tests full walls under fire conditions. It is an expensive procedure that is generally used as a research tool rather than a compliance test. Because of the vast number of ASTM E-119 testing programs using a variety of aggregates, there is sufficient data available to support an accurate calculation method for determining the fire resistance ratings of concrete masonry wall systems.

CALCULATING FIRE RESISTANCE

Extensive testing has established a relationship between fire resistance and the physical properties of concrete masonry units. This relationship provides the basis for calculating fire ratings based on the equivalent thickness of the masonry unit and the types of aggregates used in the production of the unit. This calculation can even be made when the different aggregates are blended together.

What equivalent thickness would be needed for an 8"x8"x16" block manufactured using Witelite pumice (50% by volume) and siliceous sand (50% by volume) to meet a tow hour fire-resistive rating?

Equivalent thickness of Witelite (2 hr) = 3.2 in.

Equivalent thickness of sand (2 hr) = 4.2 in.

Then: (3.2 x 0.50) + (4.2 x 0.50) = 3.7 in

NOTE:

Underwriter Laboratories tested a 50% Witelite pumice and sand blend 8 inch unit on July 17, 1998 using the E-119 test method. The test verified that it exceeded a two hour fire rating. Testing a total of six different walls with different blending ratios ratified the calculation method of determining fire ratings.

The equivalent thickness of a concrete masonry unit is determined through testing using ASTM C-140, Standard Methods of Sampling and Testing Concrete Masonry Units. For example, not all 8"x8"x16" concrete blocks have the same equivalent thickness. The equivalent thickness may vary depending on the core configuration, web thickness, and faced-shell thickness. Table 1 shows the equivalent thickness of typical concrete masonry units; however, for fire resistance ratings, it is important to know the precise equivalent thickness of a specified block. The concrete block supplier can be requested to submit test results that will establish the equivalent thickness of any CMU furnished for any job.

SOLID GROUTED CONSTRUCTION

The equivalent thickness of concrete masonry units which are solidly grouted will be considered the same as the actual measured width of the unit.

FILLING CELLS WITH LOOSE FILL MATERIAL

If the cells of hollow unit masonry are filled with approved materials, the equivalent thickness of the assembly can be considered the same as the actual thickness. Approved loose materials will be dry sand, pea gravel, crushed stone, pumice, scoria, expanded shale, clay, or slate, expanded flyash, perlite, and vermiculite.

REFERENCES:

NCMA TEK 7-1, ACI 216.1, ASTM E-119

Calculating Mix Designs For Fire

Rated Concrete Masonry Units

Using the calculation method for determining the fire resistance of concrete masonry units requires three things: (1) the exact equivalent thickness of the unit, (2) the type of aggregate(s) being used, and (3) the dry-rodded weight of the aggregate(s). Concrete masonry unit producers generally do not perform daily tests to determine the dry-rodded weight of the aggregates being used. Even weekly testing will not predict the amount of moisture present on the day the materials are being used. Dry spells and rain will affect the moisture daily. That being the case, estimating the moisture content of aggregates can be an acceptable practice only if the estimates are conservative.

Lightweight aggregates will generally hold more moisture than normal weight aggregates. A 20% moisture content is common if the lightweight aggregate is exposed to continued wet weather. This guide allows the block producer to assume the worst-case moisture content of aggregates based on conservative and safe aggregate blending ratios.

MIX DESIGN ASSUMPTIONS

1. Witelite aggregate - assume 54 pcf dry-rodded weight and 20% moisture content.

2. All limestone aggregates - assume 101 pcf dry-rodded weight and 12% moisture content.

3. All calcareous and siliceous aggregates - assume 103 pcf dry-rodded weight and 4% moisture content.

(Example: 50% Witelite and 50% sand CMU for a two hour fire rated block)

Cement - 750 lbs.

Witelite - 2,500 lbs. (w/moisture), moisture content - 20%

Sand - 4,100 lbs. (w/moisture), moisture content - 4%

To calculate dry weight of Witelite: 2,500 ÷÷÷÷ 1.20 = 2,080 lbs. dry-rodded weight

To calculate dry weight of sand: 4,100 ÷÷÷ 1.04 = 3,940 lbs. dry-rodded weight

Dry-rodded weight of Witelite - use 54 pcf

Dry-rodded weight of sand - use 103 pcf

Aggregate to Cement Ratio (Individual Aggregates)

750 lbs. cement ÷÷÷ 94 pcf = 7.98 cu. ft.

2,080 lbs. Witelite ÷÷ ÷ 54 pcf = 38.58 cu. ft.

4,100 lbs. sand ÷÷ ÷÷ 103 pcf= 38.27 cu. ft.

Ratio = 38.58 cu. ft. (Witelite) ÷ 7.98 cu. ft. cement = 4.84

38.27 cu. ft. (sand) ÷÷÷ ÷÷ 7.98 cu. ft. cement = 4.80

Proportions = 1: (4.84 + 4.80) = 9.63 4.84 ÷÷÷ ÷ 9.63 = 50.26% 4.80 ÷÷÷ ÷÷ 9.63 = 49.84%

Percentage of Aggregate (based on cu. ft. - dry-rodded weight)

Witelite - 50.26% (50%)

Sand - 49.84% (50%)

MIX DESIGN AS WEIGHED IN THE SCALE HOPPER

Witelite - 2,500 lbs.

Sand - 4,100 lbs.

Cement - 750 lbs.

Totals - 7,350 lbs.

PLANT MANAGERS WORKSHEET

This calculation can be performed automatically using a lotus or excel worksheet. Please refer to the front of this binder for the disk.

BASIC ASSUMPTIONS