Nuclear Gauge Testing Manual Edition 3, Amendment 7

Nuclear Gauge Testing Manual Edition 3, Amendment 7
May 2022

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© The State of Queensland (Department of Transport and Main Roads) 2022.
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List of contents: Edition 3, Amendment 7

Section 1
Section 2
Section 3 N01 N02 N03 N04 N05 N06 N07 Section 4 N101 N102 N103 N104 N107 N108 N113 N114 N119 N120 N121 N122 N123 N124 N127 N128 N131 N132 Section 4 N201 N202 N203 N204

Introduction Introduction Calibration Calibration Test methods Compacted Density of Soil and Crushed Rock (Nuclear Gauge) Material Bias – Soil Moisture Content Material Bias – Soil Wet Density Compacted Density of Asphalt (Nuclear Gauge) Asphalt Density Bias Compacted Density of Concrete (Nuclear Gauge) Concrete Density Bias Operating instructions – Operational checks Standard Count – Troxler 3440 Statistical Count – Troxler 3440 Standard Count – Troxler 3430 Statistical Count – Troxler 3430 Standard Count – Troxler 4640B Statistical Count – Troxler 4640B Standard Count – Humboldt 5001EZ Statistical Count – Humboldt 5001EZ Standard Count – Xplorer 3500 Statistical Count – Xplorer 3500 Standard Count – Troxler 3440P Statistical Count – Troxler 3440P Standard Count – Troxler 3430P Statistical Count – Troxler 3430P Standard Count – CPN MC3 Elite and CPN MC1 Elite Statistical Count – CPN MC3 Elite and CPN MC1 Elite Standard Count – Instrotek Xplorer 2 3500 Statistic Count – Instrotek Xplorer 2 3500 Operating instructions – Testing soils Test Parameters (Soils) – Troxler 3440 Measurement (Soils) – Troxler 3440 Test Parameters (Soils) – Troxler 3430 Measurement (Soils) – Troxler 3430

May 2022
May 2022
April 2021 July 2019 July 2019 July 2019 February 2021 February 2021 February 2021
April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 May 2022 May 2022
April 2016 April 2016 April 2016 April 2016

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List of contents: Edition 3, Amendment 6

N211 N212 N217 N218 N219 N220 N221 N222 N225 N226 N229 N230 Section 4 N301 N302 N303 N304 N307 N308 N313 N314 N319 N320 N321 N322 N323 N324 N327 N328 N331 N332

Test Parameters (Soils) – Humboldt 5001EZ Measurement (Soils) – Humboldt 5001EZ Test Parameters (Soils) – Xplorer 3500 Measurement (Soils) – Xplorer 3500 Test Parameters (Soils) – Troxler 3440P Measurement (Soils) – Troxler 3440P Test Parameters (Soils) – Troxler 3430P Measurement (Soils) – Troxler 3430P Test Parameters (Soils) – CPN MC3 Elite and CPN MC1 Elite Measurement (Soils) – CPN MC3 Elite and CPN MC1 Elite Test Parameters (Soils) – Instrotek Xplorer 2 3500 Measurement (Soils) – Instrotek Xplorer 2 3500 Operating instructions – Testing asphalt Test Parameters (Asphalt) – Troxler 3440 Measurement (Asphalt) – Troxler 3440 Test Parameters (Asphalt) – Troxler 3430 Measurement (Asphalt) – Troxler 3430 Test Parameters (Asphalt) – Troxler 4640B Measurement (Asphalt) – Troxler 4640B Test Parameters (Asphalt) – Humboldt 5001EZ Measurement (Asphalt) – Humboldt 5001EZ Test Parameters (Asphalt) – Xplorer 3500 Measurement (Asphalt) – Xplorer 3500 Test Parameters (Asphalt) – Troxler 3440P Measurement (Asphalt) – Troxler 3440P Test Parameters (Asphalt) – Troxler 3430P Measurement (Asphalt) – Troxler 3430P Test Parameters (Asphalt) – CPN MC3 Elite and CPN MC1 Elite Measurement (Asphalt) – CPN MC3 Elite and CPN MC1 Elite Test Parameters (Asphalt) – Instrotek Xplorer 2 3500 Measurement (Asphalt) – Instrotek Xplorer 2 3500

April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 May 2022 May 2022
April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 April 2016 May 2022 May 2022

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1

Scope

This manual is applicable to the use of both the nuclear surface moisture-density gauge and the nuclear thin-layer density gauge.

• Nuclear surface moisture-density gauges have been designed specifically to measure the density and/or moisture content of earthen materials (for example, soil or crushed rock), asphalt and concrete. These earthen materials may be unbound or treated with stabilising agents such as cement, foamed bitumen or lime.

• Nuclear thin-layer density gauges have been designed specifically for the density measurement of thin layers of asphalt.

Within this manual, both gauge types, or combinations of these gauge types, are referred to as nuclear gauges.

2

Content

The manual contains four sections as follows:

a) Section 1 Introduction

b) Section 2 Calibration

c) Section 3 Test methods, and

d) Section 4 Operating instructions.

3

Definitions

3.1 Standard definitions

The standard definitions listed in Table 3.1 shall apply to the Nuclear Gauge Testing Manual.

Table 3.1 – Standard definitions

Term Plant-mixed stabilisation
Sample
Test location Unbound materials

Definition
Involves the stationary pug mill mixing of a stabilisation agent with an unbound granular material sourced from a quarry or reclaimed construction and demolition waste (usually concrete). The quality of unbound granular pavement material used in plant mixing must conform to an unbound pavement specification.
The material to be forwarded for examination and/or testing which is representative of a lot. A sample is either a single entity (a spot sample) or, more usually, a representative sample, and derived by combining sample increments of approximately equal quantities from a lot, and thoroughly mixing to provide a single uniform sample and then dividing the sample into a suitable quantity for examination and/or testing.
The location, described in terms of longitudinal, lateral and, if required, vertical distance from where a single insitu test is performed.
Quarry materials, natural gravels or recycled materials produced for base and sub-base pavement construction.

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Section 1: Introduction

3.2 Definitions in other publications

Further relevant definitions are contained in the following Austroads publication and Transport and Main Roads Technical Specifications:

a) Austroads Glossary of Terms

b) MRTS01 – Introduction to Technical Specifications

c) MRTS04 – General Earthworks

d) MRTS05 – Unbound Pavements

e) MRTS06 – Reinforced Soil Structures

f) MRTS07A – Insitu Stabilised Subgrades using Quicklime or Hydrated Lime

g) MRTS07B – Insitu Stabilised Pavements using Cement or Cementitious Blends

h) MRTS07C – Insitu Stabilised Pavements using Foamed Bitumen

i) MRTS08 – Plant-Mixed Heavily Bound (Cemented) Pavements

j) MRTS09 – Plant-Mixed Foamed Bitumen Stabilised Pavements

k) MRTS10 – Plant-Mixed Lightly Bound Pavements

l) MRTS30 – Asphalt Pavements

3.3 Standard abbreviations

The standard abbreviations listed in Table 3.3 shall apply to the Materials Testing Manual.

Table 3.3 – Standard abbreviations

Abbreviation BS CPN MRTS

Definition Backscatter Campbell Pacific Nuclear Main Roads Technical Specification

3.4 Abbreviations in other publications Further relevant abbreviations are contained in the Austroads Glossary of Terms.

4

Referenced documents

4.1 Australian Standards

Table 4.1 lists the Australian Standards including Austroads Test Methods referenced in the Materials Testing Manual.

Table 4.1 – Referenced Australian Standards

Reference AS 1012.14
AS 1289.2.1.1

Title
Methods of testing concrete, Method 14: Method for securing and testing cores from hardened concrete for compressive strength and mass per unit volume
Methods of testing soils for engineering purposes, Method 2.1.1: Soil moisture content tests – Determination of the moisture content of a soil – Oven drying method (standard method)

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Section 1: Introduction

Reference AS 1289.2.1.2 AS 1289.2.1.4 AS 1289.2.1.5 AS 1289.2.1.6 AS 1289.2.3.1 AS 1289.5.8.4 AS 2891.1.2 AS/NZS 2891.9.2 AS/NZS 2891.14.3 AS/NZS 2891.14.4

Title
Methods of testing soils for engineering purposes, Method 2.1.2: Soil moisture content tests – Determination of the moisture content of a soil – Sand bath method (subsidiary method)
Methods of testing soils for engineering purposes, Method 2.1.4: Soil moisture content tests – Determination of the moisture content of a soil – Microwave-oven drying method (subsidiary method)
Methods of testing soils for engineering purposes, Method 2.1.5: Soil moisture content tests – Determination of the moisture content of a soil – Infrared lights method (subsidiary method)
Methods of testing soils for engineering purposes, Method 2.1.6: Soil moisture content tests – Determination of the moisture content of a soil – Hotplate drying method
Methods of testing soils for engineering purposes, Method 2.3.1: Soil moisture content tests – Establishment of correlation – Subsidiary method and the standard method
Methods of testing soils for engineering purposes, Method 5.8.4: Soil compaction and density tests – Nuclear surface moisture-density gauges – Calibration using standard blocks
Methods of sampling and testing asphalt, Method 1.2: Sampling – Coring method
Methods of sampling and testing asphalt, Method 9.2: Determination of bulk density of compacted asphalt – Presaturation method
Methods of sampling and testing asphalt, Method 14.3: Field density tests – Calibration of nuclear thin-layer density gauge using standard blocks
Methods of sampling and testing asphalt, Method 14.4: Field density tests – Calibration of nuclear surface moisture-density gauge – Backscatter mode

5

Principles of measurement

5.1 Nuclear gauge components

The essential components of a nuclear gauge comprise a source of gamma radiation for density measurement, a source of neutron radiation for moisture content measurement, detectors of gamma radiation and slow neutron radiation as appropriate, and electronics to convert the detected radiation into measures of density / moisture content.

5.2 Density measurement

Nuclear gauges utilise the emission and detection of gamma radiation for the measurement of the density of a material. Gamma radiation is a form of high energy radiation which readily penetrates most materials. In the transmission of gamma rays between a source and detector, a proportion of these rays will be absorbed and scattered in accordance with the density of the material between the source and detector. As the density of this material increases, the number of gamma rays absorbed and scattered increases and the number reaching the detector decreases.

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A relationship then exists between the detected gamma radiation and the density of the material. This relationship is commonly expressed in the following form:
D= CR AeBρ − C

where

DCR ρ
A, B, C

= density count ratio = density of the material = calibration constants for the nuclear gauge

The electronics of the gauges referenced in this manual use this exponential relationship to display density directly for a given value of count ratio.
An isotope of cesium (Cs - 137) is used as the source of gamma radiation in nuclear gauges for the measurement of density. The quantity of radioactive material used in the gamma source is usually either 0.296 or 0.37 GBq.
5.3 Moisture content measurement
Nuclear surface moisture-density gauges utilise the emission and detection of neutron radiation for the measurement of the moisture content of a material. Neutrons are emitted into a material and collisions occur between these neutrons and the nuclei of atoms within the material. These collisions will successively reduce the energy of these neutrons until they are slowed sufficiently to allow them to be detected by a 'slow neutron' detector.
The most effective collision by far in producing slow neutrons is that between a neutron and a nuclei of about the same mass (that is, hydrogen). The number of slow neutrons produced in a material is then proportional to the number of hydrogen atoms in the material. For most soil type materials where hydrogen is present only in the form of water, the number of slow neutrons detected is directly proportional to the moisture content of the material.
A relationship can then be established between the detected slow neutron radiation and the moisture content of the material. This relationship is commonly expressed in the following form:
M= CR F(W) + E

where

MCR W E, F

= moisture count ratio = moisture content of the material = calibration constants for the nuclear gauge

The electronics of the gauges referenced in this manual use this equation to display moisture content directly for a given value of count ratio.
An isotope of americium (Am - 241) in combination with beryllium (Be) is used as the source of neutrons for nuclear surface moisture-density gauges for the measurement of moisture content. The quantity of radioactive material used in the neutron source is usually either 1.48 or 1.85 GBq.
5.4 Density measurement modes
Nuclear surface moisture-density gauges are designed to use the emission and detection of gamma radiation for determining density in two measurement modes – direct transmission and backscatter.
The direct transmission method involves placing the source and detector on opposite sides of the material to be measured (that is, detector on the surface and source within the material). The gamma radiation emitted from the source then passes through the material to be measured before it is detected. This method is partially destructive in that it requires a hole to be formed in the material to

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Section 1: Introduction

locate the source. However, it does provide a measure of the average density of the material between the source and detector. Measurement positions are normally provided to 300 mm in increments of 25 mm.
The backscatter method commonly utilises one measurement position (for example, BS in Troxler, Humboldt and Instrotek gauges) or two measurement positions (for example, BS and AC in CPN gauges). It involves placing the source and detector on the same side of the material to be measured (that is, on the surface). The gamma radiation emitted from the source must then be scattered back towards the detector if it is to be detected. This method is performed rapidly and is truly nondestructive. However, it has restricted measurement depth and its measurements are biased toward the surface of the material with about 80 to 90 percent of its measurement coming from the top 50 mm of material for the BS measurement position. Hence, it does not provide a true measure of the average density of the material. The backscatter method is also very sensitive to surface roughness and is less precise than the direct transmission method.
Due to its sensitivity to surface roughness and inferior accuracy and precision, the backscatter method has been excluded from this manual as an option for the density measurement of soil type materials. However, it has been retained as the preferred option for the density measurement of asphalt and concrete where problems associated with surface roughness and measurement depth are reduced, and where its rapid and non-destructive nature compensate for its inferior accuracy and precision.
The nuclear thin-layer density gauge uses two backscatter geometries to provide independent measures of material density. Mathematical computation of responses from the two geometries, then allows a reduction in the influence from the underlying layer on density measurement. Use of this gauge is restricted to asphalt having a nominal maximum size not greater than 40 mm and a nominal layer thickness between 25 and 100 mm. This is the only nuclear gauge method allowed for the density measurement of compacted asphalt having a layer thickness between 25 and 50 mm.
For nuclear thin-layer density gauges a relationship has been developed to combine numerically the independent measures of material density to calculate the overlay density. This relationship is commonly expressed in the following form:
ρ = K2ρ1-K1ρ2 T K2 -K1

where

ρ T
ρ 1 ρ 2 K1, K2

= density of the overlay material
= system 1 density of the material
= system 2 density of the material
= values that quantify the influences of the density of the overlay material and of the underlying material on the density measured by the gauge.

The values of K1, K2 are calculated using the overlay thickness and depth factor calibration constants
determined for each density system in the gauge.
5.5 Moisture measurement mode
The emission of neutron radiation and detection of 'slow neutron' radiation for the determination of moisture content is not designed for direct transmission measurement. It is conducted only in a backscatter mode with the source and detector positioned close together to provide a linear relationship between detected radiation and moisture content.

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The effective measurement depth for moisture content varies according to the moisture content of the material and decreases with increasing moisture content. For a moisture content range of 0.1 to 0.3 t/m³, the measurement depth is about 250 to 200 mm respectively. However, detection of 'slow neutrons' relies on diffusion to the detector and, as such, moisture content measurements are biased towards the surface of the material. This bias will not affect the accuracy of moisture content measurement, provided that the water within the material is evenly distributed.

6

Calibration

6.1 Standard blocks calibration

Standard blocks calibration is a prerequisite for nuclear gauge measurement of both density and moisture content. It allows the conversion of nuclear gauge count data to measures of density and moisture content. Standard blocks calibration is described in Section 2 of this manual and is performed in accordance with the relevant Australian Standard as follows:

• Nuclear surface moisture-density gauge (direct transmission) AS 1289.5.8.4

• Nuclear thin-layer density gauge

AS 2891.14.3

• Nuclear surface moisture-density gauge (backscatter)

AS 2891.14.4.

The standard blocks calibration determined for a nuclear gauge will vary according to the particular type of standard blocks set chosen and the number, uniformity and composition of the standard blocks within the set. While standard blocks calibration methods allow the use of any one of two types of block sets, it places few conditions on the blocks selected for each set and makes no attempt to align the calibrations obtained from different block sets.

It is accepted that standard blocks calibration of nuclear gauges will not be undertaken by each user and will be restricted to those organisations and laboratories having the appropriate facilities. However, the user is required to arrange for standard blocks calibration and undertake calibration checks in accordance with the procedures and time frames specified in this manual.

6.2 Calibration adjustment – material bias

It is recognised that the density and moisture content results obtained from traditional tests (for example, sand replacement, core density) will differ from those results obtained from a nuclear gauge calibrated against standard blocks. The cause of this difference is due to a combination of factors relating to calibration (accuracy, precision), testing (test precision, commonality of tested material), material condition (surface roughness, density / moisture gradients, homogeneity) and material type (chemical composition). The contribution of each of these factors is not easily determined and will vary from job to job.

This difference (traditional test result - nuclear gauge test result) can be either positive or negative but tends to be positive for most materials (that is, nuclear gauge test tends to provide lower density results than those obtained using traditional tests). For many materials, this difference is small and can be ignored. However, for some materials it is substantial, and adjustment of the standard blocks calibration may be necessary.

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