H-2795_man_1109
product manual
H-2795
Roll-a-Meter
Directions
The Solution
The accuracy of Roll-a-Meter results is not dependent on the correctness of all
these factors, but gives directly the percent air in the sample. It is unnecessary
to know anything about the weight or physical characteristics of the ingredients
which are supposed to be in the mix.
In contrast to other methods commonly used to determine the percentage
of entrained air, this method is unaffected by changes in water cement ratio,
sand cement ratio, sand to gravel ratios, inaccuracies of specific gravity
determinations, and uncertainties as to absorbed or free water content of
the aggregates used in the mix.
The use of the Roll-a-Meter has eliminated practically all of the above listed
work, together with the arduous computations and uncertainties Involved.
Even the extremely accurate measurement of the sample to be tested is
not as important with this new meter, as the resulting error would be only about
1/20 as great in using the meter as the same error would be when
using other methods or meters. Only a small percentage of the original error
is involved in the air-meter result.
Used as a pycnometer, the Roll-a-Meter has been found to be excellent for
other tests, such as determination of specific gravities of cement, sand, gravel
and admixtures, and for quickly obtaining the percentage of free water in damp
sand and gravel.
Practical Control of Entrained Air
Held within well-established limits, air entrainment is highly beneficial In many
ways. With ordinary highway or building construction using 1-1/2" to 2"
maximum aggregate, a maximum of about 4% air is usually desirable.
Consequently, it is fundamentally important that an accurate method of
determining the percentage of air be available. Having this, the amount of
air entraining agent to be used, under any of the infinitely variable mix
combinations and placing conditions can be quickly determined and
effectively controlled.
Why the unit weight or gravimetric
method is unsatisfactory
The unit weight method of determining the volume of entrained air is tedious
and often impractical and unreliable. It involves technical manipulations and
computations, which can readily lead to serious errors.
General information
The accuracy of the unit weight method is dependent on extreme accuracy of
several Coronary technical determinations. Among these are:
• specic gravity of cement.
• specic gravity of sand and graver.
• absorption of sand and gravel.
• average free moisture in sand and gravel.
• there must also be accurate batching and accurate recording of all
ingredients (including water) in the batch.
• thorough mixing of all ingredients.
• accurate measurement of the sample taken for an entrained air test
How reliable is the unit weight method? It is possible for two well-qualified
laboratory technicians to run parallel tests on all the above details and to come
out with results differing materially in apparent entrained air. Here is some
convenient information in regard to the extreme accuracy required in
determination of percent of air by other methods. Slightly incorrect factors
may make errors as great or greater than listed below:
An error of: in Material= % Air Error
.03 Specific Gravity Sand .3%
.03 Specific Gravity Gravel .7%
.1 Specific Gravity Cement .6%
2% Free Water Sand .5%
1% Free Water Gravel .5%
1% Absorption Sand & Gravel .7%
Cement brands may differ .10 to .15 in specific gravity, or using kerosene instead
of water for obtaining specific gravity of cement may cause .6%. A sample taken
from a poorly mixed batch may weigh as much as 3 lbs. per cubic foot more or
less than average. This would lead to an error of 2% or so in apparent air
entrainment. Thus, accuracy by other meters or methods are dependent on:
• highly rened accuracy in determining all of the factors listed above;
• on getting truly average representative samples of all materials used
for making the above determinations;
• on getting all materials uniformly mixed;
• on getting a sample for air content test, which has all the ingredients
contained in the main batch, in practically the same proportions as
the main batch.
Satisfactory accuracy of all of these operations is very difficult to obtain
in the field.
Specifications
Total weight. Including accessories and carton: 22Ibs.
Height: 22 Inches
Outside diameter at center: 8 Inches
Volume of base: 130 Cu. In.
Important
Care should be taken to have approximately the same proportions of mortar and
course aggregate as are used in the mix. Larger than 2-inch aggregate should be
discarded and air determinations made on the balance. After proper agitation, the
air, accompanied by some foam, rises to the top. This should be allowed to stand,
with occasional light agitation until the bubbles practically cease rising. This may
take 3 to 5 minutes, although an immediate reading will tell whether there is any
material excess or deficiency of air. Following this, far closer results if desired,
two general steps are possible:
Method A
The foam may be dispelled by adding 23ml. of IsoPropyl alcohol (rubbing alcohol)
in a special brass cup provided with each meter. This 23ml. is sufficient to reduce
the air reading 1% (decreased air due to the added alcohol) will be the correct
percentage of the air in the test batch.
Method B
Numerous tests made by Method A indicate that usually the true reading should
be 85 to 90 percent of the primary reading before defoaming. This is often
sufficiently accurate for routine control purposes, but may be confirmed or
modified by a few (A) tests. The water, the kind of air entraining agent used,
as well as the brand of cement and the type of sand, gravel or admixture, may
alter the above factor.
Value of Entrainment
This is probably the greatest new development in concrete in this generation.
Tests indicate that correctly controlled air entrainment will increase the durability
of concrete under severe exposure several hundred percent. The careful control
of the air to about 4% of the volume is considered ideal for average 1-1/2" to 2"
maximum concrete. Beyond this point the concrete strength is rapidly reduced.
Air entrainment increases the placability of concrete, and aids in preventing
segregation. When air is entrained, the water may be reduced, which aids in
keeping the strength high.
With air entrainment, coarser sand my be used or less of the regular sand, which
again helps to lower the water and maintain high strengths. Sand may be increased in coarseness from .3 to .5 above normal fineness. Modulus when proper
air entrainment is used. Tests indicate that the troubles caused by premature
stiffening of cement may be materially decreased by the use of the ideal amount
of air. Resistance to the deleterious action of sulphate waters may be increased
with air entrainment. Many contractors are voluntarily using air entraining agent
because of the great improvement in placability, prevention of bleeding, and
reduction in segregation accompanying its use, even where the extra durability is
not required.
Where is air entrainment desirable?
Any job where the concrete is to be exposed to weathering will benefit by the
use of an air entraining agent. To avoid loss in strength due to too much air, which
may be serious if over 5 or 6 percent, frequent routine tests of entrained air will
be invaluable. No change of mix can be made without a resulting change in the
percentage of air entrained with the same amount of air entraining agent being
used.
A prompt air meter measurement whenever a change occurs in temperature,
slump, time of mixing, richness of mix, or proportion of sand to gravel, will
usually reveal a corresponding change in
Use of roll-a-meter for specific gravity tests
To correctly Design mixes on technically controlled concrete work, accurate
specific gravity determinations are required. Using the Roll-a-Meter as a
pycnometer is one of the most convenient, accurate, and rapid methods of
testing for specific gravity (hereinafter referred to as S.G.).
Its use is based on the principle that any material immersed in a vessel full of
water will displace exactly its absolute volume of water (solid volume). S.G. is the
ratio of the weight of a unit volume of water to the same volume weight of the
material being tested. Displacing the water by a known weight of any material
and finding the loss in weight of the water displaced, compared to the weight of
the material immersed, gives the S.G.
In practice, three accurate gross weights are needed: the weight of the
Roll-a-Meter full of water (P), a known weight of gravel (B), and the weight
of the Roll-a-Meter refilled with water after gravel is added (Ps). The water
displaced is shown by the difference in the combined weight (Ps) from the sum
of the weights (P) and (B). Thus, if tile weight of water displaced is one-half of
the weight of gravel added, then the gravel must be twice as heavy for the same
volume as water. As the S.G. of water is 1.00, then the S.G. of the gravel must be
2.00. As the weight (P) is constant, the only weights necessary to be obtained for
the S.G. determination are weights (B) and (Ps). As the weight (P) is constant, the
only weights necessary to be obtained for the S.G. determination are weights (B)
and (Ps). The mathematics involved are very simple:
(B)
= Specific Gravity (S.G.)
(P) + (B) - (Ps)
Use a scale or balance with sensitivity of 114 ounce or less for weighing sand or
gravel. On fine materials such as cement, sensitivity should be .01 lb. or less.
Use about 10 Ibs. of sand or gravel and about 5 Ibs. of cement for a test. The
usual rolling of the Roll-a-Meter, to get all air released before final refilling and
weighing, will give very reliable accuracy. (The use of water instead of kerosene
for the determination of the S.G. of cement is more accurate for this purpose.)
The following example will illustrate the method:
(P) Weight of meter full of water (only) 30 1bs.
(B) Weight of sample of sand, gravel, or other material 10 Ibs .
(Ps) Weight of meter refilled with water (all air out) with sample of gravel. 37 Ibs.
(10 Ibs. immersed)
= Specific Gravity (S.G.)
10
30+ 10 - 37
2. Graduated Tube
3. Brass Cup
4. Gauge Tube
5. Glass Clamp Ring
6. Top Glass Gaskets
7. Bottom Glass Gaskets
8. Upper Chamber
9. Chamber Gasket
10. Adjusting Nuts
11. Brass Gasket Ring, Chamber
12. Base (Brass)
13. Guide Pin
14. Baffle Funnel Assemby
15. Toggle Pin
16. Toggle Lever
17. Spring Retainer
18. Jay Bolt
19. Jay Bolt Spring
23. Brass Plug for Cap
28. Clamp Assembly (15-19)
NOT Shown
20. Brass Measuring Cup
21. Strike-off Bar
22. Spanner Wrench
24. Tamping Rod
25. Syringe
26. Carrying Case
27. Gasket Kit Complete
Warranty
Humboldt Mfg. Co. warrants its products to be free from defects in material or
workmanship. The exclusive remedy for this warranty is Humboldt Mfg. Co.,
factory replacement of any part or parts of such product, for the warranty of this
product please refer to Humboldt Mfg. Co. catalog on Terms and Conditions
of Sale. The purchaser is responsible for the transportation charges. Humboldt
Mfg. Co. shall not be responsible under this warranty if the goods have been
improperly maintained, installed, operated or the goods have been altered or
modified so as to adversely affect the operation, use performance or durability
or so as to change their intended use. The Humboldt Mfg. Co. liability under
the warranty contained in this clause is limited to the repair or replacement of
defective goods and making good, defective workmanship.
Humboldt Mfg. Co.
875 Tollgate Road
Elgin, Illinois 60123 U.S.A.
Testing Equipment for
HUMBOLDT
www.humboldtmfg.com
U.S.A. Toll Free: 1.800.544.7220
Voice: 1.708.456.6300
Fax: 1.708.456.0137
Email: hmc@humboldtmfg.com
Construction Materials
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