Fritz-Pak Air-Entraining Admixture Dose Reference

Why this matters

Fritz-Pak Air Plus is one of the few field-dosable powdered air-entraining admixtures, distributed in pre-measured water-soluble bags so a small contractor on a ready-mix truck can hit a target air content without ordering a liquid AEA setup. Air entrainment is the line between a freeze-thaw-durable exterior slab and one that scales off in three winters. ACI 318 and ACI 301 specify air content by exposure class; the inspector measures air on the truck with a pressure meter per ASTM C231. Hit the spec or the load gets rejected. This article gives the dose framework: when Fritz-Pak is appropriate, what target air content to dial for, dose-per-yard math, and the field-test gotchas that send a load back to the plant.

Why air entrainment exists

Entrained air is a system of microscopic bubbles (10-1000 micrometers) distributed through the cement paste. When water in the paste freezes, it expands 9 percent. Without bubbles, the expansion has nowhere to go and the paste fractures. With a properly sized and spaced bubble network, the expansion is absorbed and the paste survives the freeze-thaw cycle. ACI 318 Table 19.3.3.1 specifies minimum air content for exposure class F1 (moderate freeze-thaw), F2 (severe), and F3 (de-icing chemical exposure). The targets are aggregate-size-dependent: smaller aggregate means higher paste fraction means higher required air.

For a typical 1 inch nominal aggregate exterior slab in F1 exposure, ACI 318 specifies 6.0 percent air, plus/minus 1.5 percent tolerance. F2 raises this to 6.0 percent and F3 maintains 6.0 percent for 1 inch aggregate. For 3/8 inch aggregate (small slabs, decorative work) the targets rise to 7.5 percent for F1/F2/F3.

When Fritz-Pak is the right tool

Fritz-Pak Air Plus and similar field-dosable powdered AEAs are appropriate when:

1. The ready-mix plant cannot batch the right air content (mix design is non-air, truck is loaded for a different job, plant AEA system is down).
2. The job is a small-yardage owner-mixed pour where buying a 5 gallon pail of liquid AEA is overkill.
3. The crew is doing a hot-weather retrofit on the truck where air loss in transit has dropped the target below tolerance.
4. The crew is correcting a load that pressure-tested low at the site.

Fritz-Pak is not appropriate when:

1. The mix design already includes a liquid AEA from the plant - double-dosing creates overair conditions (above 9 percent) that drop strength by roughly 5 percent per percentage point above target.
2. The truck is non-air mix design intended for interior slabs where freeze-thaw is not in the exposure class.
3. The crew does not have a working pressure meter on site to verify the result.

Dose-per-yard framework

Fritz-Pak publishes dose ranges on the bag. The standard dose for a 1 yard adjustment is one bag, intended to add roughly 1.5-2.5 percent air to a typical mix design. Actual addition depends on cement type, aggregate gradation, slump, ambient temperature, and how long the drum has been turning before the slug is added.

Practical field math:

• Truck arrives at 4.5 percent air, target 6.0 percent air, 8 yards in the load.
• Deficit: 1.5 percent across 8 yards.
• Conservative starting dose: 1 bag per 2 yards of deficit-correction. For 8 yards at 1.5 percent deficit, that's roughly 4 bags.
• Add bags to the drum hopper, run drum at mixing speed (12-15 RPM for typical transit mixers) for 70 revolutions per ASTM C94 redosing guidance.
• Pressure-test after the redose. If still low, add another bag per yard of remaining deficit. Do not exceed the published maximum dose; over-air shows up as low strength on the 28-day cylinder break and there is no field correction.

The 70-revolution rule

ASTM C94 specifies that after addition of admixture at the site, the mixer must run at mixing speed for a minimum of 30 revolutions, with 70 revolutions being a common contractor practice for thorough dispersion of powdered admixtures. A truck rolling at agitation speed (2-6 RPM) for 30 minutes does not satisfy this; the drum must be at mixing speed.

Field reality: the dispatcher dispatched the truck on a 90-minute round trip. The crew adds Fritz-Pak at minute 60. Running 70 revolutions at 12 RPM adds 6 minutes to the cycle. Build that into the load timing or the truck times out at the 90-minute ASTM C94 discharge limit (or 300 revolutions, whichever comes first).

Field test: pressure meter

Air content verification is by Type B pressure meter per ASTM C231. The meter is calibrated against a known volume, the chamber is filled with fresh concrete, the lid is sealed, and pressure is applied. The pressure drop reads air content directly.

Common errors:

• Meter not calibrated for the season. Calibrate per the manufacturer instructions at least monthly on heavy-use crews.
• Sample taken from the first 10 percent of the truck. ASTM C172 requires the sample from the middle of the load.
• Sample taken from a partially discharged truck after 30 minutes of waiting. Air migrates and the reading is no longer representative.

If the pressure meter reads 5.0 percent on a target of 6.0 percent, the load is within the 1.5 percent tolerance band of ACI 318 and should not be redosed.

Strength impact

Each 1 percent of air content beyond the target drops compressive strength by roughly 5 percent on a typical 4,000 psi mix design. A 4,000 psi mix dosed to 8 percent air when the target was 6 percent will break at roughly 3,600 psi at 28 days. ACI 318 and ACI 301 both allow strength acceptance based on f'cr (target average strength) which is set above f'c (specified) by a margin sized for the standard deviation of the plant. Overdosing eats the margin.

Underdosing is the opposite problem: a 4 percent air mix in F1 exposure that survives the first winter often scales by year 3-5 as the paste loses its freeze-thaw protection.

What Fritz-Pak does not fix

References

• ACI 318-19, Building Code Requirements for Structural Concrete, Table 19.3.3.1 Air Content Requirements.
• ACI 301-20, Specifications for Concrete Construction.
• ASTM C94/C94M, Standard Specification for Ready-Mixed Concrete.
• ASTM C231/C231M, Standard Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method.
• ASTM C172/C172M, Standard Practice for Sampling Freshly Mixed Concrete.
• Fritz-Pak Air Plus Product Data Sheet, current revision, fritzpak.com.