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.
ACI 318 Table 19.3.3.1 gives F1 its own column and lumps F2 and F3 together in a second, higher column. Do not read one for the other. For 1 inch nominal aggregate, F1 is 4.5 percent and F2/F3 is 6.0 percent. For 3/4 inch, F1 is 5.0 percent and F2/F3 is 6.0 percent. For 3/8 inch aggregate (small slabs, decorative work), F1 is 6.0 percent and F2/F3 is 7.5 percent. The placement tolerance on the specified value is plus/minus 1.5 percentage points per ACI 117 and ASTM C94.
When Fritz-Pak is the right tool
Fritz-Pak Air Plus and similar field-dosable powdered AEAs are appropriate when:
- 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).
- The job is a small-yardage owner-mixed pour where buying a 5 gallon pail of liquid AEA is overkill.
- The crew is doing a hot-weather retrofit on the truck where air loss in transit has dropped the target below tolerance.
- The crew is correcting a load that pressure-tested low at the site.
Fritz-Pak is not appropriate when:
- 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.
- The truck is non-air mix design intended for interior slabs where freeze-thaw is not in the exposure class.
- 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.
Air content verification is the contractor's call before the truck leaves. Once the load is placed and finished, there is no field remediation for an out-of-tolerance air content. A load that pressure-tests below the lower tolerance bound (4.5 percent where the specified value is 6 percent) is a rejected load. Document the test result, document the rejection, and call dispatch for a replacement load. Pouring it anyway and hoping shifts the liability to the contractor.
What Fritz-Pak does not fix
A bag of air-entraining admixture solves exactly one problem: total air content in a load that is short of target. Crews reach for it to solve several others, and it does not touch any of them.
It does not fix added water. A load that has been watered down at the site is weaker and more shrinkage-prone regardless of what the air meter reads afterward. Air entrainment protects the paste from freeze-thaw; it does nothing about a water-cement ratio the contractor blew out with a hose.
It does not fix finishing. Most surface scaling blamed on air content is actually a finishing failure: bleed water worked back into the surface, the slab sealed before it stopped bleeding, or a hard steel trowel run over air-entrained exterior concrete. That last one is worth repeating, because entrained air makes delamination more likely, not less, when the surface is closed up too tight. Correct air plus wrong finish still equals a slab that flakes.
It does not fix a bad air-void system. The pressure meter reads how much air is present, not how well distributed it is. Durability depends on bubble size and the spacing between bubbles, and a late field redose, aggressive pumping, over-vibration, or a long haul at agitation speed can leave you a perfect number on the meter and a poor void system in the slab. Only petrographic examination of hardened concrete reads spacing. Treat a redose as a recovery, not as equivalent to properly batched air at the plant.
It does not survive placement on its own. Air is lost through a pump line and under heavy vibration. If the load is pumped, verify at the point of placement, not just at the truck, or the number you certified is not the number in the slab.
It does not fix the curing. An uncured slab has a weak, porous top layer that scales in its first hard winter no matter what the air content was.
It does not fix salt on a young slab. Deicing chemicals on first-winter concrete cause scaling at correct air content. That is a customer-education problem, and it belongs in the handoff conversation.
It does not fix bad aggregate or bad drainage. Freeze-thaw failure driven by unsound coarse aggregate, or by a slab that sits saturated because water ponds against it, is a mix design and a site problem. Air buys margin, it does not overcome standing water.
It does not buy back strength. Every point of air above target costs strength, so an over-corrected load is a different kind of failure with no field remedy.
And it does not fix concrete already on the ground. Once the load is placed and finished, air content is what it is. Everything above has to happen while the truck is still turning.
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.