Chap. 18 (2010).

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CHAPTER 18
Test Methods

Quality control and acceptance testing are indispensable cyclic freezing and thawing, harmful materials by petro-
parts of the construction process. Test results provide graphic examination, and potential alkali-aggregate reac-
important feedback on compliance with project specifica- tivity), and to assure uniformity (such as tests for moisture
tions and also may be used to base decisions regarding control, (relative density or specific gravity), and grada-
any necessary adjustments to the concrete mixture. Past tion). Some tests are used for both purposes.
experience and sound judgment must be relied on in
evaluating test results. Fresh concrete is tested to evaluate the performance of
available materials, establish mixture proportions, and
Most specifications today are still a combination of pre- control concrete quality during construction. ASTM C94,
scriptive and performance requirements (Parry 2000). Standard Specification for Ready-Mixed Concrete (or AASHTO
Specifiers are, however, moving toward performance- M 157), specifies that slump, air-content, density, and tem-
based specifications (also called end-result or end-prop- perature tests be performed when strength test specimens
erty specifications) that are concerned with the final are made. Following is a discussion of frequency of testing
performance of concrete rather than the process used to and descriptions of the major control tests to ensure uni-
achieve the performance (Hover, Bickley, and Hooton formity of materials, desired properties of freshly mixed
2008). Such specifications may not have acceptance limits concrete, and required strength of hardened concrete.
for process control tests (such as slump or limits on the Special test methods are also described.
quantities of concrete ingredients) as with prescriptive
specifications. Instead, physical tests are used to measure ASTM (2009) and Lamond and Pielert (2006) provide
in-place performance. These tests then become the basis extensive discussions of test methods for concrete and
for acceptance. Of course, even though process control concrete ingredients.
tests may not be specified, a producer may use them to
Computational Software: to provide an easier method
guide the product to a successful end result.
for recording test data and calculating test results,
NRMCA (2001) provides a CD with spread sheets for a
Classes of Tests variety of concrete and aggregate tests.

Project specifications may require specific characteristics Frequency of Testing

of the concrete mixture (such as maximum size of aggre-
gate, aggregate proportions, and minimum amount of
The frequency of testing is a significant factor in the effec-
cementitous materials) and certain properties of the
tiveness of quality control of concrete. Specified testing
freshly mixed and hardened concrete (such as tempera-
frequencies are intended for acceptance of concrete or its
ture, slump, density, air content, and compressive or
components. Tests should be conducted at random loca-
flexural strength).
tions within the quantity or time period represented by
Cementitious materials are tested for their compliance the test. Occasionally, specified testing frequencies may be
with ASTM or AASHTO standard specifications to avoid insufficient to effectively control materials within speci-
abnormal performance such as early stiffening, delayed fied limits during production. Therefore, process control
setting, or low strength in concrete. tests (nonrandom tests) are often performed in addition to
acceptance tests to document trends so that adjustments
Aggregate are tested to determine their suitability for use can be made to the concrete mixture before performing
in concrete (including tests for abrasion, resistance to the required acceptance tests.

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Design and Control of Concrete Mixtures ◆ EB001

The frequency of testing aggregates and concrete for Strength of standard-cured specimens should not be used
typical batch-plant procedures depends largely upon the as an indication of in-place concrete strengths (ACI 318).
uniformity of materials, including the moisture content
of aggregates, and the production process. Initially, it is In-place concrete strengths are typically estimated by
advisable to make process control tests several times a testing specimens that have been field-cured in the same
day, but as work progresses and materials become more manner (as nearly as practical) as concrete in the structure.
predictable, the testing frequency often can be reduced. ASTM C31/C31M (or AASHTO T 23) provides require-
ASTM C1451, Standard Practice for Determining Uniformity ments for the handling and testing of field-cured speci-
of Ingredients of Concrete From a Single Source, provides mens. Tests of field-cured specimens are commonly used
a standard practice for determining the uniformity of to decide when forms and shores under a structural slab
cementitious materials, aggregates, and chemical ad- might be removed or to determine when traffic will be
allowed on new pavement. Although field-cured speci-
mixtures used in concrete.
mens may be tested at any age, 7-day tests are often made
Usually, aggregate moisture tests are made once or twice for comparison with tests of standard-cured specimens
a day. The first batch of fine aggregate in the morning is at the same age. These are useful to judge if curing and
often overly wet because moisture will migrate overnight protection during cold weather concreting is adequate.
to the bottom of the storage bin. As fine aggregate is drawn
from the bottom of the bin and additional aggregate is Testing Aggregates
added, the moisture content should stabilize at a lower
level and the first moisture test can be conducted. It is Sampling Aggregates
important to obtain moisture samples representative of Methods for obtaining representative samples of aggre-
the aggregates being batched; a 1% change in moisture gates are given in ASTM D75, Standard Practice for Sam-
content of fine aggregate corresponds to approximately pling Aggregates (or AASHTO T 2). Accurate sampling is
8 kg/m3 (13 lb/yd3) of mix water. important. The location in the production process where
samples will be obtained must be carefully planned. Sam-
Slump, air content, density (unit weight), and temperature
pling from a conveyor belt, stockpile, or aggregate bin
tests should be made for the first batch of concrete each may require special sampling equipment; caution must
day, whenever consistency of concrete appears to vary, be exercised to obtain a sample free from segregation of
and whenever strength-test specimens are made at the different particle sizes. The sample must be large enough
jobsite. Air-content tests should be made often enough at to meet ASTM minimum sample size requirements.
the point of delivery to ensure proper air content, parti- Samples obtained for moisture content testing should
cularly if temperature and aggregate grading change. be placed in a sealed container or plastic bag as soon as
possible to retain moisture until testing.
The number of strength tests will depend on the job speci-
fications and the occurrence of variations in the concrete Reducing large field samples to small quantities for indi-
mixture. The ACI 318 building code and ASTM C94 re- vidual tests must be done in accordance with ASTM C702,
quire that strength tests for each class of concrete placed Standard Practice for Reducing Samples of Aggregate to Test-
each day be made at least once a day, at least once for each ing Size (or AASHTO T 248) so that the final samples will
115 m3 (150 yd3) of concrete, and if applicable, at least be truly representative. For coarse aggregate, this is done
once for each 500 m2 (5000 ft2) of surface area for slabs or by the quartering method. The sample is thoroughly
walls. In ACI 318, a strength test is defined as the average mixed and formed into a conical pile. The pile is flattened
strength of two 150-mm x 300-mm (6-in. x 12-in.) or three into a layer of uniform thickness and diameter (four to
100-mm x 200-mm (4-in. x 8-in.) cylinders tested at 28- eight times the thickness). The flattened mass is divided
days or other age designated for ˘. A 7-day test cylinder, into four equal parts, and two opposite quarters are
along with the two or three 28-day test cylinders, is often discarded. This process is repeated until the desired size
made and tested to provide an early indication of strength of sample remains. A similar procedure is sometimes used
development. As a rule of thumb, the 7-day strength is for moist, fine aggregate. Sample splitters are desirable for
about 60% to 75% of the 28-day compressive strength, de- dry aggregate (Figure 18-1) but should not be used for
pending upon the type and amount of cementitious mate- samples that are more moist than saturated surface dry. A
rials, water-cement ratio, initial curing temperature, and sample splitter comprises of chutes that empty into alter-
other variables. Additional specimens may be required nating directions so that one-half of the sample introduced
when high-strength concrete is involved or where struc- into a hopper is diverted into one receptacle and the other
tural requirements are critical. Specimens for strength half into another receptacle. The sample from one recep-
tests are subjected to standard curing as defined in ASTM tacle is reintroduced into the splitter as many times as
C31/C31M, Standard Practice for Making and Curing Con- necessary to obtain the required sample size.
crete Test Specimens in the Field, (or AASHTO T23).

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Chapter 18 ◆ Test Methods

Objectionable Fine Material

Large amounts of clay and silt in aggregates can adversely
affect durability, increase water requirements, and increase
shrinkage. ASTM C33 (AASHTO M 6/M 80) limits the
amount of material passing the 75 µm (No. 200) sieve to
3% (abrasion exposure) or 5% in fine aggregate and to 1%
or less in coarse aggregate. Testing for material finer than
the 75-µm (No.-200) sieve should be done in accordance
with ASTM C117, Standard Test Method for Materials Finer
than 75-µm (No. 200) Sieve in Mineral Aggregates by Wash-
ing (AASHTO T 11). Testing for clay lumps should be
performed in accordance with ASTM C142, Standard Test
Method for Clay Lumps and Friable Particles in Aggregates
(AASHTO T 112).
Figure 18-1. Sample splitter commonly used to reduce coarse
aggregate samples.
Grading
The particle size distribution, or grading, of an aggregate
Organic Impurities
significantly affects concrete mixture proportioning and
Organic impurities in fine aggregate should be deter- workability and are an important element in the assur-
mined in accordance with ASTM C40, Standard Test ance of concrete quality. The grading of an aggregate is
Method for Organic Impurities in Fine Aggregates for Con- determined by a sieve analysis in which the particles are
crete (or AASHTO T 21). A sample of fine aggregate is divided into their various sizes as the sample passes
placed in a sodium hydroxide solution in a colorless glass through a stack of standard sieves. The sieve analysis
bottle and shaken. The next day the color of the sodium should be made in accordance with ASTM C136, Standard
hydroxide solution is compared with a glass color stan- Test Method for Sieve Analysis of Fine and Coarse Aggregates
dard or standard color solution. If the color of the solu- (AASHTO T 27).
tion containing the sample is darker than the standard
color solution or Organic Glass Plate No. 3, the fine aggre- Results of sieve analyses are used: (1) to determine whether
gate should not be used without further investigation. or not the materials meet specifications; (2) to select the
most suitable material if several aggregates are available;
Some fine aggregates contain small quantities of coal or and (3) to detect variations in grading that are sufficient
lignite that give the solution a dark color. The quantity to warrant blending selected sizes or an adjustment of
may be insufficient to reduce the strength of the concrete concrete mixture proportions.
appreciably. If surface appearance of the concrete is not
important, ASTM C33, Standard Specification for Concrete The grading requirements for concrete aggregate are
Aggregates (AASHTO M 6), states that fine aggregate is shown in Chapter 6 and ASTM C33 (AASHTO M 6/M
acceptable if the amount of coal and lignite does not 80). Materials containing too much or too little of any one
exceed 1.0% of the total fine aggregate mass. A fine aggre- size should be avoided. Some specifications require that
gate failing this ASTM C33 (AASHTO M 6) limit may be mixture proportions be adjusted if the average fineness
used if, when tested in accordance with ASTM C87, Stan- modulus of fine aggregate changes by more than 0.20.
dard Test Method for Effect of Organic Impurities in Fine Other specifications require an adjustment in mixture
Aggregate on Strength of Mortar (or AASHTO T 71), the proportions if the amount retained on any two consecu-
7-day strengths of mortar cubes made with the fine ag- tive sieves changes by more than 10% by mass of the total
gregate following ASTM C109, Standard Test Method for fine-aggregate sample. A small quantity of clean particles
Compressive Strength of Hydraulic Cement Mortars (Using that pass a 150-µm (No.-100) sieve but are retained on a
2-in. or [50-mm] Cube Specimens) (or AASHTO T 106), are 75-µm (No.-200) sieve is desirable for workability. Most
at least 95% of the 7-day strengths of mortar made with specifications permit up to 10% of this finely divided
the same fine aggregate, but washed in a 3% solution of material in fine aggregate.
sodium hydroxide and then thoroughly rinsed in water.
It should be realized that appreciable quantities of coal Well-graded (uniform) aggregates contain particles on
or lignite in aggregates can cause popouts and staining each sieve size. Well-graded aggregates enhance numerous
of the concrete and can reduce durability when concrete characteristics and result in greater workability and dura-
is exposed to weathering. Local experience is often the bility. The more well-graded an aggregate is, the more it
best indication of the potential durability of concrete will pack together efficiently, thus reducing the volume
made with such aggregates. between aggregate particles that must be filled by paste.
On the other hand, gap-graded aggregates – those having
either a large quantity or a deficiency of one or more sieve

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Design and Control of Concrete Mixtures ◆ EB001

sizes – can result in reduced workability during mixing, using methods outlined in ASTM C127, Standard Test
pumping, placing, consolidation and finishing. Durability Method for Density, Relative Density (Specific Gravity), and
can suffer too as a result of using more fine aggregate and Absorption of Coarse Aggregate (AASHTO T 85), for coarse
water to produce a workable mixture. See Chapter 6 and aggregate and ASTM C128, Standard Test Method for Den-
Graves (2006) for additional information on aggregate sity, Relative Density (Specific Gravity), and Absorption of
grading. Fine Aggregate (AASHTO T 84) for fine aggregate.

Moisture Content of Aggregates Only the surface moisture, not the absorbed moisture,
Several methods are used for determining the amount of becomes part of the mixing water in concrete. Surface
moisture in aggregate samples. The total moisture content moisture percentages are used to calculate the amount of
for fine or coarse aggregate can be measured in accordance water in the aggregates to reduce the amount of mix water
with ASTM C566, Standard Test Method for Total Evaporable added to the batch as discussed in Chapter 12. In addition,
Moisture Content of Aggregate by Drying, (AASHTO T 255). the batch weight of aggregates should be increased by the
In this method a measured sample of damp aggregate is percentage of surface moisture present in each type of
dried either in a ventilated conventional oven, microwave aggregate. If adjustments are not made during batching,
oven, or over an electric or gas hotplate. Using the mass surface water will replace a portion of the aggregate mass
measured before and after drying, the total moisture con- and the batch will not have the correct yield. Table 18-1
tent can be calculated as follows: illustrates a method of adjusting batch weights for mois-
ture in aggregates.
P = 100(M – D)/D
Where: When drying equipment is not available a field or plant
determination of surface (free) moisture in fine aggregate
P = moisture content of sample, percent can be made in accordance with ASTM C70, Standard Test
M = mass of original sample Method for Surface Moisture in Fine Aggregate. The same
D = mass of dried sample procedure can be used for coarse aggregate with appro-
priate changes in the size of sample and dimensions of
The surface (free) moisture can be calculated if the aggre- the container. This test depends on displacement of water
gate absorption is known. Absorption refers to the increase by a known mass of moist aggregate. Therefore, the rela-
in aggregate mass due to filling of permeable pores follow- tive density (specific gravity) of the aggregate must be
ing a standard procedure. It is expressed as a percentage known accurately.
of the dry mass. The surface moisture content is equal to
the total moisture content minus the absorbed moisture. Electrical moisture meters are used in many concrete
Historic information for an aggregate source can be used batching plants primarily to monitor the moisture content
to obtain absorption data if the mineral composition of the of fine aggregates, but some plants also use them to check
pit or quarry has not changed significantly. However, if coarse aggregates. They operate on the principle that the
recent data are not available, they can be determined electrical resistance of damp aggregate decreases as

Table 18-1. Example of Adjustment in Batch Weights for Moisture in Aggregates

Aggregate data Absorption, % Moisture content, %

Fine aggregate 1.2 5.8
Coarse aggregate 0.4 0.8

Aggregate mass Aggregate mass Mix water correction for

Mix design mass (SSD condition),** (in moist condition), surface moisture in
(aggregates in dry kg/m3 (lb/yd3) kg/m3 (lb/yd3) aggregates, kg/m3 (lb/yd3) Adjusted
Concrete BOD condition),* (Absorbed %) (Moisture %) (Moist%-Absorb%) batch weight,
BOD • BOD • BOD •
ingredients kg/m3 (lb/yd3) 100 100 100 kg/m3 (lb/yd3)
Cement 355 (598) 355 (598)
Fine aggregate 695 (1171) 703 (1185) 735 (1239) 32 (54) 735 (1239)
Coarse aggregate 1060 (1787) 1064 (1793) 1068 (1800) 4 (7) 1068 (1800)
Water 200 (337) 164 (276)
Total 2310 (3893) 36 (61) 2322 (3913)†
* An aggregate in a bulk-oven dry (BOD) condition is one with its permeable voids completely dry so that it is fully absorbent.
** An aggregate in a saturated, surface-dry (SSD) condition is one with its permeable voids filled with water and with no surface moisture on it.

† Total adjusted batch weight is higher than total mix design weight by the amount of water absorbed in the aggregate.
Concrete suppliers often request mix design proportions on a SSD basis because of batching software requirements.

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Chapter 18 ◆ Test Methods

moisture content increases, within the range of dampness Consistency

normally encountered. The meters measure the electrical The slump test described by ASTM C143, Standard Test
resistance of the aggregate between electrodes protruding Method for Slump of Hydraulic-Cement Concrete (AASHTO
into the batch hopper or bin. Moisture meters based on T 119), is the most generally accepted method used to
the microwave-absorption method are gaining popularity measure the consistency of concrete (Figure 18-2). In this
because they are more accurate than the electrical resist- context, the term consistency refers to the relative fluidity
ance meters. However, both methods measure moisture of fresh concrete. The test equipment consists of a slump
contents accurately and rapidly, but only at the level of cone (a metal conical mold 300 mm [12 in.] high, with a
the probes. These meters require frequent calibration and 200-mm [8-in.] diameter base and 100-mm [4-in.] diam-
must be properly maintained. The variable nature of mois- eter top) and a steel rod 16 mm (5⁄8 in.) in diameter and
ture contents in aggregates cause difficulty in obtaining 600 mm (24 in.) long with hemispherically shaped tips.
representative samples for comparison with moisture The dampened slump cone, placed upright on a flat, non-
meter readings. Several oven-dried moisture content tests absorbent rigid surface, should be filled in three layers of
should be performed to verify the calibration of these approximately equal volume. Therefore, the cone should
meters before trends in accuracy can be established. be filled to a depth of about 70 mm (2.5 in.) for the first
layer, a depth of about 160 mm (6 in.) for the second layer,
and overfilled for the third layer. Each layer is rodded 25
Testing Freshly Mixed Concrete times. Following rodding, the last layer is struck off and
Sampling Freshly Mixed Concrete the cone is slowly raised vertically 300 mm (12 in.) in 5 ± 2
seconds. As the concrete subsides or settles to a new height,
The importance of obtaining truly representative samples the empty slump cone is then inverted and gently placed
of freshly mixed concrete for control tests is critical. Unless next to the settled concrete. The tamping rod is placed on
the sample is representative, test results will be misleading. the inverted cone to provide a reference for the original
Samples should be obtained and handled in accordance height. The slump is the vertical distance the concrete
with ASTM C172, Standard Practice for Sampling Freshly settles, measured to the nearest 5 mm (1⁄4 in.); a ruler is
Mixed Concrete (AASHTO T 141). Except for routine slump used to measure from the top of the slump cone (mold)
and air-content tests performed for process control, ASTM to the displaced original center of the subsided concrete
C172 (AASHTO T 141) requires that sample size used for (see Figure 18-2).
acceptance purposes be at least 28 L (1 ft3) and be obtained
within 15 minutes between the first and final portions of A higher slump value is indicative of a more fluid con-
the sample. The composite sample, made of two or more crete. The entire test through removal of the cone should
portions, should not be taken from the very first or last be completed in 21⁄2 minutes, as concrete will lose slump
portion of the batch discharge. The sample should be pro- with time. If a portion of the concrete falls away or shears
tected from sunlight, wind, contamination, and other off while performing the slump test, another test should
sources of rapid evaporation during sampling and testing. be run on a different portion of the sample. Shearing
of the concrete mass may indicate that the mixture
lacks cohesion.

A B

Figure 18-2. Slump test for consistency of concrete. Figure A illustrates lower slump, Figure B a higher slump.

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Design and Control of Concrete Mixtures ◆ EB001

Another test method for flow of fresh concrete involves

the use of the K-Slump Tester (ASTM C1362, Standard Test
Method for Flow of Freshly Mixed Hydraulic Cement Con-
crete). This is a probe-type instrument that is inserted
into the fresh concrete in any location where there is a
minimum depth of 175 mm (7 in.) of concrete and a
75-mm (3-in.) radius of concrete around the tester. The
height of the mortar that has flowed through the open-
ings into the tester provides a measure of fluidity.

Additional consistency tests include: the FHWA vibrating

slope apparatus (Wong and others 2001 and Saucier 1966);
British compacting factor test (BS 1881); Powers remold-
ing test (Powers 1932); German flow table test (Mor and
Ravina 1986); ASTM C1170, Standard Test Method for
Determining Consistency and Density of Roller-Compacted
Concrete Using a Vibrating Table; Kelly ball penetration test
Figure 18-3. A thermometer is used to take the temperature of fresh
(ASTM C360-92 withdrawn) (Daniel 2006); Thaulow concrete.
tester; Powers and Wiler plastometer (Powers and Wiler
1941); Tattersall (1971) workability device; Colebrand test;
Density and Yield
BML viscometer (Wallevik 1996); BTRHEOM rheometer
for fluid concrete (de Larrard and others 1993); ICAR The density (unit weight) and yield of freshly mixed
rheometer (Koehler and Fowler 2004); free-orifice rhe- concrete (Figure 18-4) are determined in accordance with
ometer (Bartos 1978); delivery chute torque meter (US ASTM C138, Standard Test Method for Density (Unit
patent 4,332,158 [1982]); delivery-chute vane (US patent Weight), Yield, and Air Content (Gravimetric) of Concrete
4,578,989 [1986]); Angles flow box (Angles 1974); ring pen- (AASHTO T 121). The results may be used to determine
etration test (Teranishs and others 1994); and the Wigmore the volumetric quantity (yield) of concrete produced per
consistometer(1948). The Vebe test and the Thaulow test batch (see Chapter 12). The test also can give indications of
are especially applicable to stiff and extremely dry mixes air content provided the relative densities of the ingredi-
while the flow table is especially applicable to flowing ents are known. A balance or scale sensitive to 0.3% of the
concrete (Daniel 2006). anticipated mass of the sample and container is required.
For example, a 7-L (0.25-ft3) density container requires a
For self-consolidating concrete, ASTM C1611/C1611M, scale sensitive to 50 g (0.1 lb). The size of the container
Standard Test Method for Flow of Self-Consolidating Concrete, used to determine density and yield varies with the size of
can be used to evaluate consistency. The slump cone mold aggregate; the 7-L (0.25-ft3) air meter container is commonly
is filled with fresh concrete without rodding. The mold is used with aggregates up to 25 mm (1 in.); a14-L (0.5-ft3)
raised and the concrete is allowed to spread. After spread-
ing has ceased, the average diameter of the concrete mass
is measured and reported as the slump flow.

Temperature Measurement

Concrete temperature is measured in accordance with

ASTM C1064, Standard Test Method for Temperature of
Freshly Mixed Hydraulic-Cement Concrete (AASHTO T
309). Because of the important influence concrete tempera-
ture has on the properties of freshly mixed and hardened
concrete, many specifications place limits on the tempera-
ture of fresh concrete. Glass or armored thermometers are
available (Figure 18-3). The thermometer should be accu-
rate to plus or minus 0.5°C (±1°F) and should remain in
a representative sample of concrete for a minimum of
2 minutes or until the reading stabilizes. At least 75 mm
(3 in.) of concrete should surround the sensing portion
of the thermometer. Electronic temperature meters with Figure 18-4. Fresh concrete is measured in a container of known
precise digital readouts are also available. The tempera- volume to determine density (unit weight).
ture test should be completed within 5 minutes after
obtaining the sample.

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Chapter 18 ◆ Test Methods

container is used with aggregates up to 50 mm (2 in.). The

volume of the container should be determined at least
annually in accordance with ASTM C29/29M, Test Method
for Bulk Density ("Unit Weight") and Voids in Aggregate.
Care is needed to consolidate the concrete adequately by
either rodding or internal vibration. Strike off the top
surface using a flat plate so that the container is filled to a
flat smooth finish. The density is expressed in kilograms
per cubic meter (pounds per cubic foot) and the yield in
cubic meters (cubic feet). Yield is determined by dividing
the total batch weight by the density.

The density of unhardened as well as hardened concrete

can also be determined by nuclear methods as described
in ASTM C1040/C1040M, Standard Test Methods for
In-Place Density of Unhardened and Hardened Concrete,
Including Roller Compacted Concrete, By Nuclear Methods
(AASHTO T 271).
Figure 18-5. Pressure-type meter for determining air content.
Air Content
A number of methods for measuring air content of freshly
The volumetric method (Figure 18-6) described in ASTM
mixed concrete can be used. ASTM test methods include:
C173/C173M (AASHTO T 196) is based on the removal of
ASTM C231/C231M, Standard Test Method for Air Content
air from a known volume of concrete by agitating the
of Freshly Mixed Concrete by the Pressure Method (AASHTO
concrete in a fixed volume of water-isopropyl alcohol
T 152); ASTM C173/173M, Standard Test Method for Air
mixture. This method can be used for concrete containing
Content of Freshly Mixed Concrete by the Volumetric Method
any type of aggregate, including lightweight or porous
(AASHTO T 196); and ASTM C138/138M (AASHTO T
materials. An aggregate correction factor is not necessary
121). Although they measure only total air volume and not
with this test. The volumetric test is not affected by atmos-
air-void characteristics, laboratory tests have demonstrated
pheric pressure, and the specific gravity of the concrete
that total air content is indicative of the adequacy of the
ingredients need not be known. Care must be taken to
air-void system. With any of the above methods, air-
agitate the sample sufficiently to remove all air. The addi-
content tests should be started within 5 minutes after the
tion of 500 mL (1 pt) or more of alcohol accelerates the
final portion of the composite sample has been obtained.
removal of air, thus shortening test times; it also dispels
The pressure method, ACTM C231 (AASHTO T 152), is most of the foam and increases the accuracy of the test,
based on Boyle’s law, which relates pressure to volume. including tests performed on high-air-content or high-
Many commercial air meters of this type are calibrated to cement-content concretes.
read air content directly when a predetermined pressure is
applied (Figure 18-5). The applied pressure compresses the
air within the concrete sample, including the air in the
pores of aggregates. For this reason, the pressure method
is not suitable for determining the air content of concretes
made with some lightweight aggregates or other very
porous materials. Aggregate correction factors that com-
pensate for air trapped in normal-weight aggregates are
relatively constant and, though small, should be subtracted
from the pressure meter gauge reading to obtain the cor-
rect air content. The instrument should be calibrated for
various elevations above sea level if it is to be used in local-
ities having considerable differences in elevation. Some
meters are based on the change in pressure of a known
volume of air and are not affected by changes in elevation.
Pressure meters are widely used because the mixture pro-
portions and specific gravities of the concrete ingredients
need not be known. Also, a test can be conducted in less
time than is required for other methods. Figure 18-6. Volumetric air meter.

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Design and Control of Concrete Mixtures ◆ EB001

The gravimetric method, ASTM C138/C138M or AASHTO Air-Void Analysis of Fresh Concrete
T 121, uses the same test equipment used that is for deter- The conventional methods for analyzing air in fresh
mining the density (unit weight) of fresh concrete. The concrete, such as the pressure method noted above, only
measured density of concrete is subtracted from the theo- measure the total air content; consequently, they provide
retical density as determined from the absolute volumes no information about the parameters that determine the
of the ingredients, assuming no air is present. This differ- quality of the air-void system. These parameters – the size
ence, expressed as a percentage of the theoretical density, and number of voids and spacing between them – can be
is the air content. Mixture proportions and specific gravi- measured on polished specimens of hardened concrete
ties of the ingredients must be accurately known; other- (see Testing Hardened Concrete, Air Content); but the
wise results may be in error. Consequently, this method is result of such analysis will only be available several days
suitable only where laboratory-type control is exercised. after the concrete has hardened. A test method has been
Significant changes in density can be a convenient way developed to determine the key air-void parameters in
to detect variability in air content. samples of fresh air-entrained concrete. The method uses
an apparatus known as an air-void analyzer (AVA) (Figure
AASHTO T 199, Standard Method of Test for Air Content of
18-8). The test apparatus determines the volume and size
Freshly Mixed Concrete by the Chace Indicator, can be used
distributions of entrained air bubbles. The measured data
as a quick check for the presence of low, medium, or high
are used to estimate the spacing factor, specific surface,
levels of air in concrete. It is not a substitute for the other
and total volume of entrained air.
more accurate methods. A representative sample of
mortar from the concrete is placed in a cup and intro-
duced into a graduated glass container (Figure 18-7). The
container is then filled with alcohol to the zero mark on
the stem. A thumb is placed over the stem opening and
the container is rotated repeatedly from vertical to hori-
zontal end to remove the air from the mortar. The drop in
the alcohol level and the mortar content are used to esti-
mate the air content of concrete.

Figure 18-8. Equipment for the air-void analyzer.

In this test method, air bubbles from a sample of fresh

Figure 18-7. Chace air indicator (AASHTO T 199).
concrete rise through a viscous liquid, enter a column of
water above it, then rise through the water and collect
Studies into the effect of fly ash on the air-void stability under a submerged pan that is attached to a sensitive
of concrete resulted in the development of the foam-index balance (Figure 18-9). The viscous liquid retains the orig-
test. The test can be used to measure the relative air- inal bubble sizes. Large bubbles rise faster than small ones
entraining admixture requirements for concrete mixtures through the liquids. As air bubbles accumulate under the
containing fly ash. The fly ash is placed in a wide mouth pan, the buoyancy of the pan increases. The balance meas-
jar along with the air-entraining admixture and shaken ures this change in buoyancy, which is recorded as a func-
vigorously. Following a waiting period of 45 seconds, a tion of time and can be related to the number of bubbles
visual determination of the stability of the foam or bubbles of different size.
is made (Gebler and Klieger 1983).

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Chapter 18 ◆ Test Methods

nominal maximum size of aggregate and the height should

be twice the diameter. Alternatively, it is permitted to wet-
sieve fresh concrete with large aggregate using a 50 mm
(2 in.) sieve in accordance with ASTM C172. While rigid
metal molds are preferred, paraffin-coated cardboard,
plastic, or other types of single-use molds conforming to
ASTM C470, Standard Specification for Molds for Forming
Concrete Test Cylinders Vertically, can be used. They should
be placed on a smooth, level, rigid surface and filled care-
fully to avoid distortion of their shape.

Figure 18-9. Air bubbles rising through liquids in column.

Fresh concrete samples can be taken at the ready mix

plant and on the jobsite. Testing concrete before and after
placement into forms can verify how the applied methods
of transporting, placing, and consolidation affect the
airvoid system. Because the samples are taken on fresh
concrete, the air content and air-void system can be
adjusted during production.
Figure 18-10. Preparing standard test specimens for compressive
strength of concrete.
In 2008, AASHTO adopted a provisional test method for
the AVA (AASHTO TP 75-08, Method of Test for Air-Void
The smaller 100-mm (4-in.) diameter by 200-mm (8-in.)
Characteristics of Freshly Mixed Concrete by Buoyancy
high cylinders have been commonly used with high
Change). The AVA was not developed for measuring the strength concrete containing up to 19 mm (3⁄4 in.) maxi-
total air-content of concrete, and because of the small mum nominal size aggregate (Burg and Ost 1994, Forstie
sample size, may not give accurate results for this quan- and Schnormeier 1981, and Date and Schnormeier 1984).
tity. However, this method may be useful in assessing the The 100-mm x 200-mm (4-in. x 8-in.) cylinders are easier to
quality of the air-void system; it gives good results in cast, requires less material, weigh considerably less than
conjunction with traditional methods for measuring air 150-mm x 300-mm (6-in. x 12-in.) cylinders and requires
content (Aarre 1998, Distlehorst and Kurgan 2007, and less storage space for curing. In addition, the smaller cross-
Peterson 2009). sectional area allows the use of smaller capacity testing
machines to test high-strength concrete cylinders. The
Strength Specimens
difference in indicated strength between the two cylinder
Specimens molded for strength tests should be made and sizes is insignificant as illustrated in Figure 18-11. The
cured in accordance with ASTM C31/C31M or AASHTO standard deviation and coefficient of variation of 100-mm
T 23, and laboratory-molded specimens according to (4-in.) cylinders is slightly higher or similar to that for
ASTM C192/C192M, Standard Practice for Making and 150-mm (6-in.) cylinders (Detwiler and others 2001, Burg
Curing Concrete Test Specimens in the Laboratory (or and others 1999, Pistilli and Willems 1993, and Carino and
AASHTO R39). Molding of strength specimens should others 2004). The predominant size used in Canada is the
be started within 15 minutes after the composite sample 100-mm (4-in.) diameter cylinder (CSA A23.1). Consult job
is obtained. specifications for allowable cylinder sizes.

Traditionally, the standard test specimen for compressive Beams for the flexural strength test should be 150 mm
strength of concrete with a nominal maximum aggregate x 150 mm (6 in. x 6 in.) in cross section for nominal maxi-
size of 50 mm (2 in.) or smaller was a cylinder 150 mm mum size of aggregates up to 50 mm (2 in.). For larger ag-
(6 in.) in diameter by 300 mm (12 in.) high (Figure 18-10). gregates, the minimum cross-sectional dimension should
In 2008, ACI 318 was revised to permit 100 mm (4 in.) in be at least three times the nominal maximum size of ag-
diameter by 200 mm (8 in.) high cylinders. The smaller gregate. The length of beams should be at least three times
cylinders can only be used for nominal maximum aggre- the depth of the beam plus 50 mm (2 in.), or a total length
gate size of 25 mm (1 in.) or less. For larger aggregates, the of at least 500 mm (20 in.) for a 150-mm x 150-mm (6-in.
diameter of the cylinder should be at least three times the x 6-in.) beam.

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Design and Control of Concrete Mixtures ◆ EB001

6x12-in. cylinder strength, psi exterior of the mold to prevent confusion and errors in
0 5,000 10,000 15,000 20,000 25,000
25,000
reporting.
160
Standard testing procedures require that specimens be
100x200-mm cylinder strength, MPa

20,000 cured under controlled conditions, either in the laboratory

4x8-in. cylinder strength, psi

120 (Figure 18-12) or in the field. Standard curing gives an
15,000 accurate indication of the quality of the concrete as deliv-
ered. After specimens are molded in the field, they are
80
10,000
subjected to initial curing for up to 48 h in accordance
Moist cured
Air cured with ASTM C31/C31M. The temperature surrounding the
Best fit line
40 specimens should be between 16 and 27°C (60 and 80°F)
5,000
and moisture loss should be prevented. For concrete with
a specified strength greater than 40 MPa (6000 psi), the
0 0 storage temperature should be between 20 and 26°C (68
0 40 80 120 160
150x300 mm cylinder strength, MPa and 78°F). After initial curing and mold removal, speci-
Figure 18-11. Comparison of 100 x 200-mm (4 x 8-in.) and 150 x mens are subjected to final curing with free water main-
300-mm (6 x 12-in.) cylinder strengths (Burg and Ost 1994). tained on their surfaces and at a temperature of 23.0±
2.0°C (73.5 ± 3.5°F). Specimens can be submerged in lime-
water or stored in a moist room. To prevent leaching of
ASTM C31/C31M prescribes the method of consolidation
calcium hydroxide from concrete specimens, limewater
and the number of layers to be used in making test spe-
must be saturated with hydrated lime, not agricultural
cimens. For concrete with slump less than 25 mm (1 in.), lime (limestone), in accordance with ASTM C511, Standard
consolidation is by vibration. For slump of at least 25 mm Specification for Mixing Rooms, Moist Cabinets, Moist Rooms,
(1 in.), consolidation is by vibration or rodding. For cylin- and Water Storage Tanks Used in the Testing of Hydraulic
ders to be consolidated by rodding, the molds are filled in Cements and Concretes (AASHTO M 201).
two layers for 100-mm (4-in.) diameter cylinders and three
layers for 150-mm (6-in.) diameter cylinders. Each layer is
rodded 25 times and a smaller diameter rod is used for the
smaller cylinders. If the rodding leaves holes, the sides of
the mold should be lightly tapped with a mallet or open
hand. Cylinders to be vibrated should be filled in two
layers with one insertion per layer for 100-mm (4-in.) di-
ameter cylinders and two insertions per layer for 150-mm
(6-in.) cylinders. Care should be used to avoid over-vibra-
tion. Usually vibration is sufficient when the top surface
becomes relatively smooth and large air bubbles no longer
break through the surface.

Beams up to 200 mm (8 in.) deep are molded using two

layers if consolidated by rodding and using one layer if
consolidated by vibration. Each layer is rodded once for
each 1400 mm2 (2 in.2) of top surface area. If vibration is
used, the vibrator should be inserted at intervals less than
150 mm (6 in.) along the center of the beam. For beams
wider than 150 mm (6 in.), alternate insertions of the
vibrator should be along two lines. Internal vibrators
should have a maximum width not more than 1⁄3 the
width of beams or 1⁄4 the diameter of cylinders. Imme- Figure 18-12. Controlled moist curing in the laboratory for standard
test specimens at a relative humidity of 95% to 100% and tempera-
diately after casting, the tops of the specimens should be ture of 23±2°C (73.5±3.5°F) (ASTM C511 or AASHTO M 201).
sealed with plastic caps or plastic bags or covered with
an oiled glass or steel plates.
Specimens cured in the field in the same manner as the
The strength of a test specimen can be greatly affected by structure more closely represent the actual strength of
jostling, changes in temperature, and exposure to drying, concrete in the structure at the time of testing. However,
particularly within the first 24 hours after casting. Thus, they give little indication of whether a low strength test
test specimens should be cast in locations where subse- result is due to the quality of the concrete as delivered or
quent movement is unnecessary and where protection is to improper handling and curing. On some projects, field-
available. Cylinders and test beams should be protected cured specimens are made in addition to those destined
from rough handling at all ages. Identify specimens on the for standard curing; these are especially useful during

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Chapter 18 ◆ Test Methods

cold weather, to determine when forms can be removed, Accelerated Compression Tests to Project
or to determine when the structure can be put into use. Later-Age Strength
For more information see Strength Tests of Hardened ASTM C684, Standard Test Method for Making, Accelerated
Concrete and ASTM (2009). Curing, and Testing Concrete Compression Test Specimens,
In-place concrete strength development can also be evalu- uses accelerated strength tests to expedite quality control
ated by maturity testing (ACI Committee 228 [2003] and of concrete. Strength development of test specimens is
ASTM C1074, Standard Practice for Estimating Concrete accelerated using one of four curing procedures: warm
Strength by the Maturity Method), which is discussed in water at 35°C ± 3°C (95°F ± 5°F), in boiling water for 3.5 h,
Chapter 17. autogenous curing in an insulated container, or 5 hours
at a high temperature of 150°C ± 3°C (300°F ± 5°F) and a
Time of Setting pressure of 10.3 ± 0.02 MPa (1500 ± 25 psi). Accelerated
ASTM C403/C403M, Standard Test Method for Time of strength tests are performed at ages ranging between
Setting of Concrete Mixtures by Penetration Resistance 5 and 49 hours, depending on the curing procedure used.
(AASHTO T 197), is used to determine the time of setting Later-age strengths are estimated using previously estab-
of concrete by means of penetration resistance measure- lished relationships between accelerated strength and
ments made at regular time intervals on mortar sieved standard 28-day compressive strength tests (Carino 2006).
from the concrete mixture (Figure 18-13). The initial and
final time of setting are determined as the times when the ASTM C918/C918M, Standard Test Method for Measuring
penetration resistance equals 3.4 MPa (500 psi) and 27.6 Early-Age Compressive Strength and Projecting Later-Age
MPa (4000 psi). Typically, initial setting occurs between Strength, uses the maturity method of monitoring temper-
2 and 6 hours after batching and final setting occurs ature of cylinders cured in accordance with ASTM C31/
between 4 and 12 hours. Temperature, water cementitious C31M (AASHTO T 23). Cylinders are tested at early ages
materials ratio, and admixtures all affect setting time. beyond 24 hours, and the concrete temperature history is
used to compute the maturity index at the time of test.
To use this method, a prediction equation relating strength
to maturity index, is developed from laboratory or field
data in accordance with ASTM C918/C918M. The predic-
tion equation is used to project the strength at later ages
based on the maturity index and measured strength of the
specimens tested at early-age. See Carino (2006).

Chloride Content
The chloride content of fresh concrete should be checked
to make sure it is below the specified limits, such as those
given in ACI 318, to avoid corrosion of reinforcing steel.
An approximation of the water-soluble chloride content of
aggregates, admixtures, and freshly mixed concrete can be
made using a method developed by the National Ready
Mixed Concrete Association (NRMCA 1986). The total
35 5
chloride content of freshly mixed concrete may be esti-
mated by summing up the chloride contents of all of the
Final setting individual constituents of the mixture. The NRMCA
28 4
method provides only a quick approximation and should
Penetration resistance, 1000 psi

not be used to determine compliance.

Penetration resistance, MPa

21 3
The water extractable chloride content of aggregate may
be determined using ASTM C1524, Standard Test Method
for Water-Extractable Chloride in Aggregate (Soxhlet Method).
14 2
In this method, the aggregate is not pulverized so that
chloride ions within the aggregate particles are not ex-
7
tracted. These chlorides would not be available to initiate
1
or contribute toward steel corrosion (ACI 222R). See also
Initial setting
Testing Hardened Concrete, Chloride Content.
0 0
180 210 240 270 300 330 360 390 420
Elapsed time, min.

Figure 18-13. (top) Time of setting equipment. (bottom) Plot of

test results.

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Design and Control of Concrete Mixtures ◆ EB001

Portland Cement Content, Water Content, and Water-

Cement Ratio
Test methods have been developed for estimating the
portland cement and water content of freshly mixed
concrete. Due to their complexity, however, they are used
rarely for routine quality control. Nevertheless, results
of these tests can assist in determining the strength and
durability potential of concrete prior to setting and hard-
ening and can indicate whether or not the desired cement
and water contents were obtained. While not currently
in issue, ASTM C1078, Test Methods for Determining the
Cement Content of Freshly Mixed Concrete (Withdrawn
1998), and ASTM C1079, Test Methods for Determining the
Water Content of Freshly Mixed Concrete (Withdrawn 1998),
based on the Kelly-Vail method, can be used to determine Figure 18-14. Fly ash particles retained on a 45µm sieve after
cement content and water content. Experimental methods washing, as viewed through a microscope at 200x.
using microwave absorption have also been developed
to estimate the water-cement ratio. The disadvantage of Bleeding of Concrete
these test methods is that they require sophisticated The bleeding tendency of fresh concrete can be deter-
equipment and special operator skills, which may not mined by two methods described in ASTM C232, Standard
be readily available. Test Methods for Bleeding of Concrete (or AASHTO T 158).
Other tests for determining cement or water contents One method consolidates the specimen by tamping with-
can be classified into four categories: chemical determi- out further disturbance; the other method consolidates
nation, separation by settling and decanting, nuclear the specimen by vibration after which the specimen is
methods, and electrical methods. The Rapid Analysis vibrated intermittently throughout the test. The bleeding
Machine (RAM) and nuclear cement gage have been tendency is expressed as the volume of bleed water at the
used to measure cement contents (Forester, Black, and surface per unit area of exposed concrete, or as a percent-
Lees 1974 and PCA 1983). The microwave oven drying age of the net mixing water in the test specimen. Typical
method (AASHTO T 318, Standard Method of Test for values range from 0.01 to 0.08 mL/cm2 or 0.1% to 2.5% of
Water Content of Freshly Mixed Concrete Using Microwave mixing water. The bleeding test is rarely used in the field,
Oven) and neutron-scattering methods have been used but it is useful for evaluating alternative mixtures in the
to measure water contents. For an overview of these and laboratory (Figure 18-15).
other tests from all four categories, see Hime (2006). A
combination of these tests can be run independently to
determine either cement content or water content to cal-
culate the water-cement ratio. None of these test methods,
however, have the level of reliability required for use as
acceptance tests.

Supplementary Cementitious Materials Content

Standard test methods are not available for determining
the supplementary cementitious materials content of
freshly mixed concrete. However, the presence of certain
supplementary cementitious materials, such as fly ash,
can be determined by washing a sample of the concrete’s
mortar over a 45 µm (No. 325) sieve and using a stereo
microscope (150 to 250 X) to view the residue retained
(Figure 18-14). Fly ash particles appear as spheres of
various colors. Sieving the mortar through a 150- or 75-µm
(No. 100 or 200) sieve is helpful in removing sand grains. Figure 18-15. ASTM C232 (AASHTO T 158) test for bleeding of
concrete; Method A without vibration. The container has an inside
diameter of about 255 mm (10 in.) and a height of about 280 mm
(11 in.). The container is filled to a height of about 255 mm (10 in.).
Bleed water is drawn off the concrete surface and recorded in regular
intervals until cessation of bleeding. Inset: The container needs to be
covered during the test to prevent evaporation.

356