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Buildex SmartWall Systems:
Built In Fire Safety...

The Buildex Expanded Shale Lightweight Aggregate used in SmartWall Systems is produced at 1000°C (2000°F) making it totally inorganic and thermally stable. Buildex aggregate is used in refractory grade structural / insulating concrete, where it achieves long service life under high temperature exposure. The strength, purity, thermal stability, and insulative qualities of Buildex aggregate make it an excellent performer in fire exposure, both in poured concrete and SmartWall masonry.

The model building codes recognize that the fire resistance rating of a concrete masonry unit (cmu) is based on it's equivalent thickness and type of aggregate, using linear interpolation if aggregates are blended in the cmu. See note 1.

A variety of aggregate combinations is possible. For this illustration, river sand is blended with Buildex Expanded Shale Lightweight Aggregate to produce a 93 pound per cubic foot concrete masonry unit, which is the specified maximum density for SmartWall Systems.

Table 1:
SmartWall Fire Resistance (see Note 2)

(oven dry)
8 Inch cmu
10 inch cmu
12 inch cmu
Buildex SmartWall Systems
93 pcf
2.1 hr
3.2 hr
4.1 hr
ASTM Lightweight
105 pcf
2.0 hr
3.1 hr
3.9 hr
135 pcf
2.0 hr
3.0 hr
3.8 hr
Sand & Gravel
135 pcf
1.8 hr
2.7 hr
3.4 hr

(SmartWall Systems and ASTM Lightweight units produced with Buildex and sand)

SmartWall has a clear advantage in fire endurance, exceeding code minimums with an extra margin of safety. Can you afford to specify anything less?

Note (1) Table 2 contains selected fire resistance rating periods for concrete masonry units recognized in the current Uniform Building Code (UBC), the BOCA National Building Code, and the new International Building Code (IBC). For masonry fire ratings the IBC directly references ACI 216.1 / TMS 0216 Standard Method for Determining Fire Resistance of Concrete and Masonry Construction Assemblies. The fire resistance rating is based on the equivalent thickness of the concrete masonry unit and the type of aggregate(s) used in its production.

Table 2:
Fire Resistance Ratings of CMU

Minimum Equivalent Thickness (inches) Required
To Achieve Listed Fire Resistance Rating


1 1/2 Hr.

2 Hr.

3 Hr.

4 Hr.

Expanded Shale, Clay
or Slate










Siliceous Gravel





The fire resistance rating of units made with blends of aggregates can be calculated using linear interpolation based on the volume percentage of each aggregate in the cmu. The ACI 216.1 / TMS 0216 Standard provides that if the cells of hollow units are filled with an approved lightweight or normal weight aggregate, or loose fill insulation, their equivalent thickness can be considered the same as the unit’s actual thickness. For example, an 8 inch hollow unit with cores filled would be considered as having a 7.6 inch equivalent thickness and thus a four hour fire rating.
Reference: NCMA Tek 7-1A (1999), ACI 216.1 / TMS 0216 (1997)

Note (2)
Fire Resistance Ratings are usually assigned by building codes in half hour or hourly increments based on the actual fire endurance of the assembly. The ratings are shown here in more detail to illustrate the difference in performance between different density units.

To calculate the fire resistance rating of a concrete masonry unit, its equivalent thickness and the proportion of aggregate(s) used in its production must be known. Table 3 lists the typical equivalent thickness for two-core concrete masonry units.

Table 3:
Equivalent Thickness
For Typical
Two Core Hollow Concrete Masonry Units

Nominal Width

Equivalent Thickness, inches

8 inch


10 inch


12 inch


Reference: NCMA Tek 7-1 (1999) Table 2

Calculation of the fire resistance rating for the 135 pcf normal weight units in Table 1 was performed using the appropriate values from Table 2 and Table 3, using linear interpolation between the hourly ratings for each material.

For the lightweight units (93 and 105 pcf density) the net volumes in Table 3 were reduced approximately 2.5 percent . This adjustment recognizes the fact that the ASTM C 140 test method for net volume of concrete masonry units typically results in slightly lower values for lightweight concrete masonry. This adjustment makes the calculations conservative, and they are expected to more closely match "real world" testing lab results, both for lightweight and heavy weight units.

The following proportions were used for blending Buildex and sand: For 105 pcf mixes, 52% sand, 49% Buildex by volume. For 93 pcf mixes, 33% sand, 67% Buildex by volume. The mixes used our Marquette, Kansas plant aggregate and assumed a typical 10:1 aggregate:cement ratio, by volume. If the mixes were made with a lightweight aggregate of different density from another source, the aggregate proportions and the resulting fire resistance ratings will vary from those shown in Table 1.

The fire resistance ratings for lightweight units were calculated by linear interpolation using two steps, as illustrated in Table 4 below. Fire resistance ratings greater than 4 hours are not listed in the building codes, so calculations of the rating for units with an equivalent thickness greater than that needed for a 4 hour rating was made by extrapolation, using the increase in equivalent thickness needed to raise the rating from 3 hours to 4 hours as the basis for the extrapolation. Table 4 contains sample calculations for the 93 pcf unit; calculations for the 105 pcf units use the same methods.

Table 4:
Calculation of Fire Resistance (FR)
for 90 pcf unit (67% Buildex: 33% sand).

Calulate the Equivalent Thickness (TE) Required For Each Fire Rating:

2 Hr: 67% x 3.6 + 33% x 4.2 = 3.80

3 Hr: 67% x 4.4 + 33% x 5.3 = 4.70

4 Hr: 67% x 5.1 + 33% x 6.2 = 5.46

8" cmu (Te=3.90"): Interpolate FR:

FR = 2 + [ 3.9–3.8] / [4.7–-3.8] = 2.11 Hours

10" cmu (Te=4.88"): Interpolate FR:

FR = 3 + [ 4.88–-4.70] / [5.46–4.70] = 3.24 Hours

12" cmu (Te=5.56"): Extrapolate FR:

FR = 4 + [ 5.56–5.46] / [5.46–-4.70] = 4.13 Hours