AASHTO T 348-13

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Standard Test Method for

Air-Void Characteristics

of Freshly Mixed Concrete

by Buoyancy Change

AASHTO Designation: T 348-131

American Association of State Highway and Transportation Officials

444 North Capitol Street N.W., Suite 249

Washington, D.C. 20001

TS-3b T 348-1 AASHTO

Standard Test Method for

Air-Void Characteristics of Freshly Mixed

Concrete by Buoyancy Change

AASHTO Designation: T 348-131

1. SCOPE

1.1. This test method covers the determination of characteristics of the air-void system of fresh

concrete using a sample of mortar. Spacing factor, specific surface, and entrained air content are

determined by capturing air bubbles released from a mortar sample.

1.2. The sample will only be representative of the depth of the concrete within approximately 60 mm

(2.5 in.) below the level at which the sampling is begun. This method is applicable to fresh

concrete with a minimum slump of 10 mm (0.4 in.) and air content between 3.5 and 10 percent by

volume. Only air voids less than 3 mm (0.1 in.) in diameter are measured by this method.2 The test

must be performed in sheltered, stable conditions.

1.3. The values stated in SI units are to be regarded as the standard.

1.4. This standard does not purport to address all of the safety concerns, if any, associated with its use.

It is the responsibility of the user of this standard to establish appropriate safety and health

practices and determine the applicability of regulatory limitations prior to use.

2. REFERENCED DOCUMENTS

2.1. AASHTO Standards:

 M 231, Weighing Devices Used in the Testing of Materials

 T 119M/T 119, Slump of Hydraulic Cement Concrete

 T 121M/T 121, Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete

 T 152, Air Content of Freshly Mixed Concrete by the Pressure Method

 T 196M/T 196, Air Content of Freshly Mixed Concrete by the Volumetric Method

2.2. ASTM Standard:

 C457/C457M, Standard Test Method for Microscopical Determination of Parameters of the

Air-Void System in Hardened Concrete

3. SUMMARY OF TEST METHOD3

3.1. This method determines the air-void characteristics of fresh concrete by expelling all air bubbles

present in a given mortar sample, collecting the air bubbles and recording their quantities, and

calculating their size distribution. According to Stokes’ Law, larger bubbles rise faster than

smaller ones. Thus, for bubbles rising a known distance, the size of the bubbles can be determined

from the time of their arrival at the surface of the liquid. The air voids of a sample of fresh

concrete mortar are released as bubbles by mixing the mortar with a viscous liquid. The bubbles

then emerge from the viscous liquid, rise through an overlying column of water, and collect under

TS-3b T 348-2 AASHTO

a submerged dish. As the bubbles accumulate under the dish, the buoyancy of the dish changes.

The change in buoyancy of the dish, as measured by a change in weight and recorded as a function

of time, can be related to the number of bubbles of different sizes by an empirical correlation.

Specific surface, spacing factor, and air content as specified by ASTM C457/C457M may be

calculated from this data with the use of an algorithm.

4. SIGNIFICANCE AND USE

4.1. An adequate air-void system in hardened concrete protects the cement paste from damage during

freezing and thawing cycles under moist conditions. This air-void system can be characterized by

the volume of entrained air, spacing between air voids, specific surface, and void-size distribution.

4.2. This buoyancy change test method is capable of testing the air-void system of concrete in situ,

reflecting the history of the concrete as it is in place, not as it is prepared in a sample for testing.

4.3. The primary function of the buoyancy change method is to provide air-void size and distribution

information for concrete mixture designs. This test method could be used by the mix designer to

evaluate various mix proportion options during prequalification. The effect of admixture

combinations and admixture dosages on the air-void system can be evaluated. It can also be used

by the approving agency as a quick laboratory check on mixes offered to them for approval.

4.4. During production, the adequacy of the air-void system can be verified for acceptance and

feedback can be provided for manufacturing control. This method also allows rapid assessment of

the effect of production changes in the mixture or equipment or variations in placement conditions

such as temperature, slump, and pumping on the air-void system. Characterization of the air-void

system of the concrete shortly after production provides an assessment of the durability of the

cement paste. Results are usually obtained within 2 h, allowing adjustments in the subsequent

production.

4.5. This method yields results that generally correlate well with the results of a linear traverse

measurement on hardened concrete, as prescribed in ASTM C457/C457M for characteristics of

the air-void system. Discrepancies between the results of this method and the results of

ASTM C457/C457M may be due to coalescence of bubbles in the analysis liquid or due to errors

in the ASTM C457/C457M test. The buoyancy change method does not give a total air content

result that can be directly correlated with the results of T 152 and T 196M/T 196.

4.6. For further discussion of the significance of characteristics of the air-void system, see

ASTM C457, Section 5, Significance and Use.

5. APPARATUS4

5.1. Analysis and Data Collection Apparatus—This assembly, the sampling equipment, and materials

are designed and built to function as an integrated system that has been demonstrated by the

manufacturer to accurately measure and calculate air-void distribution in fresh air-entrained

concrete.

5.1.1. Riser Cylinder—A clear plastic cylinder with a base and a collar approximately as shown in

Figure 1. The base shall have an integral heating element capable of maintaining the analysis

liquid at 23 ± 2°C (73 ± 4°F) and entry holes for the plastic rod and the sample syringe with

gaskets to make a watertight seal.

5.1.2. Magnetic Stirrer—A magnetic stirrer capable of maintaining 300 rpm during mixing.

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摘要：

AASHTO T 348-13 是美国国家公路与运输官员协会（AASHTO）发布的一项标准测试方法，专门用于评估热拌沥青混合料（HMA）对水敏感性的抗剥落性能。该标准通过测量压实沥青混合料试件在经历冻融循环前后的间接拉伸强度比（TSR），来判断沥青混合料在潮湿环境下的耐久性和粘附性。AASHTO T 348-13 是公路工程与路面设计关键质量控制规范，广泛应用于实验室检测及施工现场材料验证，确保沥青路面能抵抗水分诱发剥离破坏，延长道路使用寿命。该规范为工程师、检测人员和施工承包商提供了统一、可靠

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