Technical Note 32 - March Issued: July 2011 March Use of nuclear gauges for testing soils and asphalt

Transcription

1 Technical Note 32 - March 2013 Issued: July 2011 March 2013 Use of nuclear gauges for testing soils and asphalt

2 Copyright National Association of Testing Authorities, Australia 2013 This publication is protected by copyright under the Commonwealth of Australia Copyright Act NATA s accredited facilities or facilities seeking accreditation may use or copy this publication or print or this publication internally for accreditation purposes. Individuals may store a copy of this publication for private non-commercial use or copy a reasonable portion of this publication in accordance with the fair dealing provisions in Part III Division 3 of the Copyright Act You must include this copyright notice in its complete form if you make a copy of this publication. Apart from these permitted uses, you must not modify, copy, reproduce, republish, frame, upload to a third party, store in a retrieval system, post, transmit or distribute this content in any way or any form or by any means without express written authority from NATA.

3 Contents 1. Introduction Test Methods Principles of Operation Measurement Modes Direct Transmission Mode Backscatter Mode Moisture Measurement Mode Calibration of Gauges Nuclear Gauge Checks in the Laboratory Standard Count Check (Form 1a Troxler and Humboldt, Form 1b CPN) Gauge Function Checks Drift Test Consistency Check (Form 2) Initial Check Monthly Check Leak and Radiation Level Tests Use of Gauges Maximum Particle Size of Material to be Tested Density Range to be Tested Density/Moisture Offsets Checking of Services Location of Test Sites Surface Preparation Initial Preparation Source Rod Hole Use of Sand/Fines from Tested Material Roller Marks in Asphalt Depth of Testing General Client Specified Depth Unspecified Layer Thicknesses Asphalt Thickness Testing Over Pipes Importance of Locking Handle into Place Placement of the Probe in the Hole Counts Standard Counts Density and Moisture Counts Testing in Trenches Radiation Safety National Codes of Practice State and Territory Radiation Safety Acts and Regulations References Notes Density Moisture Location of Secondary Blocks Counts Asphalt Layers...19 Appendix A: Standards Australia Test Methods...20 Appendix B: Calibration Relationships...21 Appendix C: Worksheets...24 March 2013 Page 3 of 30

4 1. Introduction Nuclear surface-moisture density gauges (nuclear gauges) have been used for the testing of compaction of soils and asphalt for over twenty five years in Australia. In more recent times, these gauges have also been used to test the compaction of concrete. Thin-layer density gauges were developed for the compaction control testing of thin asphalt layers (see Note 5) and were introduced in Australia over ten years ago. 2. Test Methods There is a number of test methods covering the use and calibration of nuclear gauges. These are listed in Appendix A of this technical note. A number of state road authorities have also issued test methods. This technical note covers the Standards Australia methods only. The common brands on the Australian market are Campbell-Pacific (CPN), Humboldt and Troxler. 3. Principles of Operation Nuclear gauges contain a source of gamma rays (Note 1) for density measurement and, when a moisture measurement is required, a source of neutrons (Note 2). Density measurement is based on the scattering and absorption of gamma radiation which in turn can be related to the density of the material being tested. Moisture measurement is based on the slowing down (thermalisation) of fast neutrons, which is a function of the hydrogen content of the material being tested. The measurements are made by detectors built into the gauges which are displayed as counts. The counts are taken over at least one minute, but additional counting time will improve the accuracy of the measurement (see Note 4). Each nuclear gauge is provided with a standard reference block which needs to be kept with the gauge, and is used for determining standard counts both in the laboratory and in the field. Use of a standard reference block from another nuclear gauge is not technically valid. As background radiation may affect the readings, standard counts on a standard reference block provided by the gauge manufacturer are made at the site where the gauge is used. The actual counts measured are normalised against these standard counts to provide count ratios. Calibration equations provided by the calibrating authority are used to convert count ratios to density and water/moisture content values. The activity of the radioactive source decreases with time due to radioactive decay. The decrease is about 2% per year for the gamma source and 0.15% for the neutron source. Hence, standard counts are made and are used to normalise the raw count to provide a count ratio (raw count/standard count). March 2013 Page 4 of 30

5 Some nuclear gauges contain electronic circuitry and firmware which convert the detected counts into measures of density/moisture content respectively using the calibration constants. The form of the calibration equations is shown in the Standards Australia test methods AS , AS and AS and is also shown on the calibration authority s certificate (refer Appendix B). 4. Measurement Modes Nuclear gauges are designed to use the emission and detection of gamma radiation for determining density in two measurement modes- direct transmission and backscatter. The measurement of density by the nuclear gauge provides a wet density result. If suitable calibration for moisture and material dependent moisture offsets have been determined, dry density results can also be calculated using the nuclear gauge electronics. Nuclear gauges can generally be operated in the following modes. 4.1 Direct Transmission Mode The direct transmission method involves placing the detector on the surface and the source within the material (see fig.1 and note 1). 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 under test in order to position the source. It provides a measure of the average density of the material between the source and the detector. Measurement positions are normally provided to a depth of 300 mm in increments of 25 mm. March 2013 Page 5 of 30

6 DETECTOR SOURCE Figure 1: Direct Transmission Mode GAMMA RADIATION PATHS 4.2 Backscatter Mode The backscatter mode enables the test to be performed rapidly as a non-destructive method. The gauge is placed above the material to be tested (i.e. on the surface see fig 2 and note 2). The gamma radiation emitted from the source is scattered back towards the detector to be measured. The backscatter method commonly utilises one measurement position (e.g. BS (backscatter) in Troxler and Humbolt gauges) or two measurement positions (e.g. BS and AC (asphaltic concrete) in CPN gauges). Backscatter mode has a restricted measurement depth and the accuracy of its measurements are biased toward the surface of the material. For the BS measurement position, about 80 to 90 percent of the measurement is made in the top 50 mm of the material. It therefore does not provide a measure of the average density of the material. Also, as it is very sensitive to surface roughness, the backscatter method is less precise than the direct transmission method and is not used for the measurement of soil density. Backscatter mode has been retained for the density measurement of asphalt where problems associated with surface roughness and measurement depth are reduced and where its rapid and non-destructive nature make it more attractive despite slightly reduced accuracy. March 2013 Page 6 of 30

7 The nuclear thin-layer density gauge uses two backscatter geometries to provide independent measures of material density at two depths. Mathematical computation of responses from the two geometries reduce the influence of the underlying layer on density measurement. The use of this type of gauge is restricted to asphalt having a nominal maximum particle size not greater than 40 mm and a nominal layer thickness between 25 and 100 mm. This gauge does not have a moisture mode, hence moisture measurements are not possible. DETECTOR GAMMA RADIATION PATH SOURCE Figure 2: Backscatter Mode 4.3 Moisture Measurement Mode The emission of neutron radiation and detection of slow neutron radiation for the determination of moisture content is not appropriate for direct transmission measurement. If moisture is to be determined it is conducted only in the "backscatter" mode with the source and detector positioned close together to provide a linear relationship between detected radiation and moisture content. March 2013 Page 7 of 30

8 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/m 3, 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 adversely affect the accuracy of moisture content measurement, provided that the water within the material is evenly distributed. As a consequence, reliable measurements of moisture can only be made to a depth of about 150 mm (see fig 3). MOISTURE DETECTION SOURCE DETECTOR Figure 3: Moisture Measurement Mode 5. Calibration of Gauges The Standards Australia test methods require that nuclear gauges be calibrated to establish the relationships between the count ratios and density and moisture values. The procedure for calibration of nuclear gauges is detailed in the Australian Standards: AS for gauges used for testing of soils, and AS and AS detail the calibration procedures for gauges used for testing asphalt. Calibrations are performed against standard blocks of known density or moisture content, as relevant. Nuclear gauges used in direct transmission mode need to be calibrated at each nominal depth at which they are to be used. Arising from the calibration is a set of coefficients, for each depth calibrated, for use in the density equation, and a single set of coefficients for use in the moisture equation (see Appendix B). March 2013 Page 8 of 30

9 Modern gauges have the facility to have these coefficients programmed into the gauge so that direct readings of wet density and moisture can be made. The direct reading of wet density is verified by the calibrator to ensure that the correct constants have been programmed into the gauge. As Troxler and Humboldt gauges take into account the effect of water on the gamma mass attenuation coefficient of the material under test when calculating the wet density, these gauges need to be calibrated in the moisture mode when direct reading of wet density is required. The field moisture content and field dry density can be determined directly using a nuclear gauge when the gauge is calibrated in the moisture mode and the moisture intercept for the materials being tested has been determined. The moisture readings and direct dry density readings from the gauge shall not be used. The moisture offset is the difference between the moisture content determined by oven drying (AS ) and the moisture content determined by the nuclear gauge moisture content (see AS Appendix A). 6. Nuclear Gauge Checks in the Laboratory Examples of worksheets are shown in Appendix C of this technical note. 6.1 Standard Count Check (Form 1a Troxler and Humboldt, Form 1b CPN) The Standards Australia test methods require that a standard count check be made on each day of use for both density and moisture modes. This is required to ensure correct operation of the gauge and that there is no drift in the response of the gauge. The check is to be made at the same location in the laboratory each day to ensure that the background radiation is generally the same. The check location must be at least two metres away from any other building walls or large structure and at least ten metres from any other radioactive source, including other gauges. The laboratory standard count check for both density and moisture is made on the standard reference block supplied by the manufacturer. The check is performed in accordance with the manufacturer s instructions over a counting period of at least four minutes. Records of the standard counts obtained during the standard count check must be maintained as well as the mean value of the previous four standard count checks. This provides the lower and upper limits against which the current check is being compared, as detailed in AS , Appendix B. The pre-scale factor, which should be obtained from the manufacturer, must be taken into account when checking the lower and upper limits. For the purpose of the equations shown in AS , this value is 64 for Humboldt and most Troxler gauges and 4 for Campbell Pacific gauges for 4 minute counts. (See Table 1). If a gauge fails the standard count check, the check needs to be repeated once. If it fails again, the gauge shall be removed from service and repaired. In this case, the previous working day s field density and/or moisture test results need to be reviewed to ascertain if they have been affected. March 2013 Page 9 of 30

10 The standard count check is quite separate from and additional to the standard counts measured at the work site during daily operations. TABLE 1 PRE-SCALE FACTORS (AS Appendix A) Nuclear Gauge Type Pre-scale Factor CPN 4 Troxler- except Models and 4640B Troxler Models and 4640B Humboldt Gauge Function Checks Monthly gauge function checks are performed to ensure that the nuclear sources are stable. There are two main function checks performed: Stability Test, also known as the Statistical Stability or Stat Test; Drift Test. (CPN - Form 3a, Humboldt - Form 3b, Troxler - Form 3c) A suitable location for the function checks needs to be selected, preferably at the same location as that used for the standard count check. The same site is used each time these checks are made. The site location should at least two metres away from any building walls or large structure and at least ten metres from any other radioactive source (i.e. other gauges). The stability test procedure is detailed in the manufacturer s handbook Drift Test On completion of the stability test the gauge needs to remain on for three hours then five sets of standard density and moisture counts need to be obtained immediately. The mean of the five standard density counts and the mean of the five moisture standard counts is then calculated. For Troxler gauges, the density drift and moisture drift are calculated as detailed in the manufacturer s handbook. Density drift should not exceed 0.5% and moisture drift should not exceed 1.0%. A drift test is not specified for Humboldt gauges by the manufacturer, however, there are no technical issues preventing a facility from performing a drift test and applying the same acceptance criteria. CPN gauges automatically turn the power off after 60 minutes if keyboard functions are not used, therefore a drift test cannot be performed. March 2013 Page 10 of 30

11 6.3 Consistency Check (Form 2) A consistency check is performed to ensure that the mechanical parts of the gauge used for locating and locking the source rod have not worn and that the electronics within the nuclear gauge are operating consistently. The density system consistency check is performed at least monthly to confirm the calibration for each source rod position. Such checks are performed on a standard density block as defined in AS , or a dry secondary block of naturally occurring stone (see Note 3). The block must be stored in the laboratory or covered and protected from the rain and moisture ingress Initial Check Following the return of a nuclear gauge from calibration, the facility must immediately (i.e. prior to operational use and preferably within one month of calibration) check wet density readings at each calibrated source rod position on the secondary block to confirm that consistent density readings are being obtained (see Note 3). The height of secondary block is required to be at least 50 mm greater than the greatest source rod depth for which the gauge is calibrated. The results of these checks should be compared to the last consistency density readings taken prior to calibration. If these results differ by more than 0.04 t/m 3, checks should be made with the calibration authority. The facility should also review test results obtained immediately after recalibration to ensure that no sudden change in density results has occurred which may be attributed to the recalibration. If a nuclear gauge is moved to another location where a different secondary block is used then the following needs to be performed. A further consistency check is made at each calibrated source rod position on the secondary block which was used for the initial check after calibration. These checks should meet the requirements in AS , i.e. within 0.02 t/m 3 of the initial reading after calibration. The difference (ρ s ) between the density measured at the initial check (ρ i ) and the density measured at this check is calculated. Consistency checks shall be made on the secondary block used at the location to where the gauge has been moved. This value must then be used as the initial value for consistency checks at that particular location. The difference between the values obtained in subsequent monthly consistency checks (see below) should not exceed (0.02 ρ s ) t/m Monthly Check For each calibrated source rod position, further density measurements on the secondary block using the nuclear gauge are made at intervals not exceeding one month, or sooner if it is suspected that the gauge is malfunctioning. March 2013 Page 11 of 30

12 These readings are compared to the relevant initial reading. If the difference between the initial reading and the monthly reading is greater than 0.02 t/m 3, the gauge needs to be put out of service and repaired. Each monthly check is recorded. 6.4 Leak and Radiation Level Tests State/Territory regulations require leak tests which check the integrity and the shielding of the source to be performed annually or more often if required. Annex 3, ISO 9978 Radiation protection Sealed radioactive sources Leakage test methods describe how leak tests are performed. These are generally arranged through the state authority which regulates the operation of radioactive devices. Facilities possessing equipment for checking gamma and neutron radiation levels must ensure that this apparatus is recalibrated regularly in keeping with the requirements of the appropriate State/Territory regulatory body (see Table 2). 7. Use of Gauges The Standards Australia and State Road Authority test methods describe how nuclear gauge testing is to be performed. The test methods describe the minimum requirements for the tests. This section of the technical note sets down some practical aspects of testing and provides more detail than described in some test methods. Facilities should look at the risk management issues related to each test instance and in areas of medium to high technical risk, consideration should be given to exceeding the minimum requirements, e.g. count time, multiple readings or rotation of the gauge (see Note 4). If the minimum requirements are exceeded this is to be recorded. All checks and testing involving a nuclear gauge must be performed by, or in the presence of a licensed operator. All operators are required to wear personal radiation monitoring badges (refer Section 8 on Radiation Safety). 7.1 Maximum Particle Size of Material to be Tested The Standards Australia test method for testing soils using a nuclear gauge limits the maximum particle size of material to be tested to not more than 20% by mass of particles retained on a 37.5 mm sieve. In earthworks, the size of the particles in the material as placed often exceeds these requirements. However, the field compaction of the material may break down the particles to meet the standard. Tests should be made to ensure that oversize does not exceed the requirement of 20% by mass of particles retained on a 37.5 mm sieve. In cases where the amount of oversize is greater than 20%, the field density result using the nuclear gauge is not a valid test result and should not be reported. 7.2 Density Range to be Tested The Standards Australia Standard test methods for Calibration of Nuclear Gauges, AS , AS and AS , require that the calibration certificate includes the wet density range for which the density calibration is valid. March 2013 Page 12 of 30

13 If a nuclear gauge measures wet density values outside the calibrated range, the result must not be reported under the scope of accreditation of NATA accreditation. 7.3 Density/Moisture Offsets It is essential that moisture offsets be determined in accordance with AS , Appendix A (or State Road Authority method), for each type of material whenever soil moisture content is to be determined using the nuclear gauge. Similarly, it has been found that, with asphalt testing in the backscatter mode or with the thin layer asphalt gauge, density offsets may need to be determined. Density offsets may be positive or negative, or sometimes zero. The method for determining these offsets is detailed in the appropriate test methods. AS neither requires nor provides for wet density offsets. It has been found that with soils that contain certain minerals, e.g. blast furnace slag and ironstone, density offsets may be needed. In such cases the test results cannot be reported as complying with AS Checking of Services When operating nuclear gauges in direct transmission mode, the location of services such as water, and gas pipes under the surface being tested should be known, prior to drilling/driving the hole for the source rod. 7.5 Location of Test Sites The test methods do not detail the criteria for selection of test sites. These are usually specified in the overall contract documents or by the client. In the event of no specification requirements, the selection of sites should be made using the random stratified method described in AS If a test site has been selected using a random number method, the location should not be changed as this will bias the selection procedure. If problems are encountered on earthworks sites caused by site preparation or the use of earthmoving equipment, the test site may be moved within a 500 mm radius of the site selected and the location of the new site recorded. The presence of a harsh or coarse looking asphalt surface is not sufficient reason for moving a gauge from the randomly selected site. 7.6 Surface Preparation Initial Preparation Generally roller finished surfaces of road pavements, carparks, etc. and asphalts do not require surface preparation other than sweeping the surface free from loose particles. However, the scraper plate may be used to scrape earthen surfaces to ensure that the gauge sits flat on the surface and is free of any rocking movement. Earthworks require a flat surface to be prepared by a grader or other similar item of equipment prior to any additional preparation by the tester. The surface then needs to be March 2013 Page 13 of 30

14 scraped flat using the scraper plate which must allow the gauge to sit on the surface without rocking movement Source Rod Hole The hole for the source rod is to be drilled to the required depth (see Section 7.7 below) plus at least 25 mm. It has been found that drilling using an appropriate power drill is effective in most materials and essential for asphalt, hardened stabilized materials and hardened concrete. The spiking or drilling equipment used must be relocated at least two metres from the test site prior to testing with the nuclear gauge. When a source rod hole is driven by the hammering of a spiking tool, cracking in the surface of the soil may occur but this generally does not affect the test result provided the crack does not extend from the source rod to the detectors and the soil has broken up. Occasionally, a small hump (less than 5 mm) occurs when the driven rod is removed. This may be flattened by placing the scraper plate over the hump and gently tapping it with a mallet or hammer. If a larger hump or cracks wider than 1 mm appear, another site should be selected and a new hole formed Use of Sand/Fines from Tested Material While not all test methods specify that sand or fines from the parent material must be used, fines will minimise the possibility of an air gap between the gauge and the surface of the material being tested. Air gaps will significantly reduce the measured density. The fines are required to have 100% passing a mm sieve and should not form a separate layer (i.e. less than 0.5 mm thick). The amount of fines should be just sufficient to enable the nuclear gauge to sit on the surface without rocking. Sand or fines must be used when testing dense graded asphalt. Fines from the asphalt need to be obtained from the asphalt plant raw materials or from the hot bins Roller Marks in Asphalt Occasionally roller patterns or marks occur in asphalt. Operators should ensure that this does not cause the rocking of the gauge or air gaps to occur under the gauge. The use of sand flattened with a straight edge will indicate the amount and extent of any patterns. It may be possible to move the gauge within a 500 mm radius to avoid the roller marks. The reason and the new location are to be recorded on the test worksheet. 7.7 Depth of Testing General The Standards Australia test methods define the test depth as the maximum depth that allows the probe to be located in the testing position, and the probe to remain in the layer being tested, i.e. the full depth of the layer. It is therefore important to obtain the correct layer thickness. A number of gauges have 50 mm depth increments for the source rod probe. This often restricts the depth which can be tested, e.g. for a layer depth of 240 mm, the bottom 40 mm of the material cannot be tested. This is often the area where the lower compaction March 2013 Page 14 of 30

15 occurs. Where gauge rod allows 25 mm increments, only 15 mm of the layer would not be tested Client Specified Depth In some cases the client will specify a test depth which does not place the source at the depth required by the test method. Test reports must show the depth tested, the actual layer depth and that the test was performed at the depth shown as requested by the client Unspecified Layer Thicknesses In some cases the actual thickness of the layer is difficult to ascertain from the information supplied by the client. In such cases the layer thickness needs to be determined prior to field density testing at a site close to the test site. This requires a hole to be excavated at a distance, e.g. 1 metre, from the test site, which does not affect the gauge reading. As a guide, if the probe is placed 15 to 35 mm less than the actual layer thickness, adequate depth of material is tested. After the nuclear gauge readings have been taken and during the excavation of the soil, it is often necessary to obtain a moisture and/or reference density sample. If, when obtaining the reference sample, it becomes apparent that the source rod has been placed in a lower layer, the result from the test site is to be discarded and another site selected in accordance with Section 7.5 and tested Asphalt Thickness Generally the depth of asphalt is well known and most testing is carried out using backscatter mode (see Note 5). When a thin-layer gauge is used (AS ), the layer thickness is very important particularly when setting the design layer thickness value into the gauge and in the use of density offsets. If layer thickness is variable, as in, say, a regulation layer, an alternative method may be required to measure density, e.g. coring Testing Over Pipes When fill over pipes or the water table is being tested, the test probe should be between 35 and 55 mm above the top surface of the pipe or water table. Extreme care must be taken to ensure that preparation of the hole does not cause damage to the pipe. March 2013 Page 15 of 30

16 7.7.6 Importance of Locking Handle into Place Once the probe depth has been selected, the probe is lowered into the hole to that depth. It is extremely important to ensure that the test probe is set exactly to the depth and that the handle is locked into place at that depth. Operators should check the handle location each time a count is taken. A height error of only 3 mm will cause significant errors in density readings particularly at the shallower depths. 7.8 Placement of the Probe in the Hole Once the source rod is placed at the required depth, the gauge should be moved towards the detector end so that the probe is against the inner edge of the hole, thus avoiding air gaps. The placement of the probe needs to be checked each time a test is undertaken so that consistent readings are obtained. Prior to lifting the source rod from the hole, the nuclear gauge should be moved away from the edge of the hole to avoid wear of the source rod. 7.9 Counts In order to obtain density and moisture test results, the count ratios at each test site need to be recorded. Density Count Ratio = Density Count/ Site Density Standard Count Moisture Count Ratio = Moisture Count/Site Moisture Standard Count Standard Counts The Australian Standard test methods require that standard counts be made at the work site and not at every test site. Standard counts need to be taken at least every four hours and at sites more than 2 km from where the initial standard count for that work site was taken. Standard counts take into account variations in the natural radiation at the site. This radiation may vary over time and over long distances at the work site. In order to take into account these site variations, it is recommended that standard counts be taken for each lot or area being tested. The standard counts are obtained with the gauge placed on the reference block supplied with the nuclear gauge for a minimum of four minutes. It is important that the site where the counts are taken is clear from vertical projections and at least two metres from buildings or large structures and at least ten metres from any other nuclear gauges Density and Moisture Counts The Standards Australia test methods specify a minimum count time for the test of one minute for direct transmission and backscatter and four minutes for thin layer asphalt gauges. (See Note 4.) March 2013 Page 16 of 30

17 7.9.3 Testing in Trenches When testing in trenches where there is a vertical projection of the trench walls, or when vertical projections are within 1 metre of the test site, a standard count should be made at each test site and used in the calculation of the count ratio. See also Testing Over Pipes. 8. Radiation Safety 8.1 National Codes of Practice Code of Practice and Safety Guide for Portable Density/Moisture Gauges Containing Radioactive Sources (2004) Published by Australian Radiation Protection and Nuclear Safety Agency. Code of Practice - Safe Transport of Radioactive Materials Radiation Protection Series No. 2. Published by Australian Radiation Protection and Nuclear Safety Agency. 8.2 State and Territory Radiation Safety Acts and Regulations Each state and territory has legislation and regulations which cover the ownership, operation, storage and transport of nuclear gauges (see Table 2). Due to the potential risk of radiation to the public, it is essential that facilities meet all the requirements of the relevant state or territory. TABLE 2 STATE ACTS AND REGULATIONS State Act Regulations ACT Radiation Protection Act 2006 Radiation Protection Regulation 2007 NSW Radiation Control Act (1990) No 13 Radiation Control Regulation 2003 NT Radiation Protection Act (as in force at Radiation Protection Regulations (as in force at 5 5 October 2009) October 2009) Qld Radiation Safety Act 1999 Radiation Safety Regulation 2010 SA Radiation Protection and Control Act, 1982 Radiation Protection and Control (Transport of Radioactive Substances) Regulations 2003 Ionizing Radiation Regulations 2000 Tas Radiation Protection Act 2005 Radiation Protection Regulations 2006 Vic Radiation Act 2005 Radiation Regulations 2007 WA Radiation Safety Act 1975 Radiation Safety (General) Regulations 1983, (Qualifications) Regulations 1980, (Transport of Radioactive Substances) Regulations 2002 The contact addresses for the government organisation responsible for the administration of the regulations for each state is available at March 2013 Page 17 of 30

18 9. References 1. VicRoads Test Method RC (2002) 2. Code of Practice and Safety Guide for Portable Density/Moisture Gauges Containing Radioactive Sources (2004) Published by Australian Radiation Protection and Nuclear Safety Agency. 3. Code of Practice - Safe Transport of Radioactive Materials Radiation Protection Series No. 2. (2008) Published by Australian Radiation Protection and Nuclear Safety Agency. 10. Notes 10.1 Density An isotope of Cesium (Cs 137 ) is used as the source of gamma radiation used in nuclear gauges for the measurement of density. The quantity of radio-active material used in the gamma source is usually either 0.37 or GBq Moisture An isotope of Americium (Am 241 ) in combination with Beryllium 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 Location of Secondary Blocks The location of the secondary block when performing consistency checks is important. In particular, the block must be clear from vertical projections, be at least two metres from buildings and at least ten metres from any other nuclear gauges. The following are examples of interferences during consistency checks: Example 1- it was observed that the metal handles of a trolley used to move the block projected not only above the surface of the block but also above the gauge detectors. As the block could move on the trolley, inconsistent readings were being obtained due to the influence of the handles. Example 2- The block was relatively narrow, and the readings were altered by testers walking too close to the block during the counts. It is important to keep other staff away from the block during the counts as is normally required for safety. The presence of samples too close to the block during testing will also influence the consistency readings Counts Manufacturer s literature indicate that greater accuracy can be obtained using higher count times. Operators should consider this in relation to the risks associated with the job. March 2013 Page 18 of 30

19 If an anomalous result is obtained, the nuclear gauge may be rotated through 90 or 180 degrees after the initial count at the site and a second count be made. If the resultant density results from the two counts are not within t/m 3 both results should be discarded. Such variations may be due to an air gap or a large stone or voids in the path between the source and the detectors. The reason for the difference(s) should be checked by carefully excavating a hole in the area covered by the nuclear gauge measurement Asphalt Layers When asphalt is laid on a surface which is highly variable (e.g. the lower layers of a multilayer pavement) or where there is a crown in the surface, the asphalt layer depth may be different at each site. In such cases, the layer thickness may need to be determined using cores or probes. March 2013 Page 19 of 30

20 Appendix A: Standards Australia Test Methods The following Standards Australia test methods are required for the use and calibration of nuclear gauges in construction materials testing: AS (2007) AS (2009) Methods of testing soils for engineering purposes - Soil compaction and density tests - Determination of field density and field moisture content of a soil using a nuclear surface moisturedensity gauge - Direct transmission mode Methods of testing soils for engineering purposes - Soil compaction and density tests - Nuclear surface moisture-density gauges - Calibration using standard blocks AS (1996) Methods of sampling and testing asphalt - Field density tests - Determination of field density of compacted asphalt using a nuclear surface moisture-density gauge - Direct transmission mode AS (1999) Methods of sampling and testing asphalt - Field density tests - Determination of field density of compacted asphalt using a nuclear surface moisture-density gauge - Backscatter mode AS (1999) Methods of sampling and testing asphalt - Field density tests - Determination of field density of compacted asphalt using a nuclear thin-layer density gauge AS (1999) Methods of sampling and testing asphalt - Field density tests - Calibration of nuclear thin-layer density gauge using standard blocks AS (1999) Methods of sampling and testing asphalt - Field density tests - Calibration of nuclear surface moisture-density gauge - Backscatter mode March 2013 Page 20 of 30

21 Appendix B: Calibration Relationships 1. Density Measurement A relationship exists between the detected gamma radiation and the density of the material which depends on the type of calibration blocks used. When a nuclear gauge is calibrated in accordance with AS , AS and AS , the calibration report should provide the form of equation and the constants determined by calibration for field use. The equations take the form: AS and AS Type A and B Blocks: ln A ln ( DCR C) B B where ρ = wet density, in tonnes per cubic metre DCR = density count ratio A,B,C = calibration constants for the particular gauge Type C Blocks: P Q ln ( DCR) where ρ = wet density, in tonnes per cubic metre DCR = density count ratio P,Q = calibration constants for the particular gauge AS System 1 All blocks: 1 G H ( DCR1) where ρ 1 = density, in tonnes per cubic metre DCR 1 = density count ratio for System 1 G = intercept constant for System 1 H = slope constant for System 1 March 2013 Page 21 of 30

22 AS System 2 Type A and B Blocks: ln A ln ( DCR2 C) 2 B B where ρ 2 = density, in tonnes per cubic metre DCR 2 = density count ratio A,B,C =calibration constants for the particular gauge Type C Blocks: P Q ln ( DCR 2) 2 where ρ 2 = density, in tonnes per cubic metre DCR 2 = density count ratio P,Q =calibration constants for the particular gauge AS Depth factors Depth factor equations are expressed in the following form: K A12t A e A K A22t A e A where K 1 = depth factor for System 1 K 2 = depth factor for System 2 t = thickness, in metres A 12 = depth factor calibration constant for System 1 A 22 = depth factor calibration constant for System 2 A 11, A 21 = 1 A 13, A 23 = 0 Field density is calculated using the depth factors from the following equation: K 2 1 K 1 2 K 2 K1 where ρ = density, in tonnes per cubic metre ρ 1 = density measures by System 1, in tonnes per cubic metre ρ 2 = density measured by System 2, in tonnes per cubic metre K 1 = depth factor for System 1 K 2 = depth factor for System 2 March 2013 Page 22 of 30

23 2. Moisture Measurement A relationship exists between the detected slow neutron radiation and the water content of the material. This relationship is commonly expressed in the form: W d( MCR) c where MCR = moisture count ratio W = water content of the material d = moisture slope calibration constant c = moisture intercept for the particular material Nuclear gauges with more advanced electronics use this equation to display moisture content directly for a given value of count ratio. March 2013 Page 23 of 30

24 Appendix C: Worksheets 1. Standard Count Checks (a) Troxler and Humboldt (Form 1a) (b) Campbell Pacific (Form 1b) 1. Consistency Checks (Form 2) 2. Stability and Drift Checks (a) Campbell Pacific (Form 3a) (b) Humboldt (Form 3b) (c) Troxler (Form 3c) March 2013 Page 24 of 30

25 Form 581b1t&h June 2010 COMPANY AND LAB NAME Density :RD (U and NUCLEAR GAUGE STANDARD COUNT CHECK - TROXLER & HUMBOLDT (EXCEPT 3450 or 4640B models) TEST METHOD AS Appendix B1 L) = DS DS = DS PS DS 64 Limits for Troxler & Humboldt are then : MeanDS 0.5 MeanDS 4 4 Moisture: RM (U and L) = MS Limits for Troxler & Humboldt are then : MeanMS MS MS 8 = MS 8 NUCLEAR GAUGE PS 64 Serial No : MeanMS Make & Model : For this check, both DS (= Density Standard Count) and MS (= Moisture Standard Count), are taken at the same location (at the laboratory). PS = Prescale factor = 16 for Troxler & Humboldt, from the manufacturer s handbook, under stability test 1 Date 2 CurrentDS 3 Mean of previous 4 DS values (MeanDS) MeanDS 5 CurrentDS MeanDS modulus 6 Column 5 smaller than Column 4? yes/no 7 CurrentMS 8 Mean of previous 4 MS values (MeanMS) 9 MeanDS 10 CurrentMS MeanMS modulus 11 Column 10 smaller than Column 9? yes/no 12 Operator Initials & action March 2013 Page 25 of 30

26 Form 581b1cpn June 2010 COMPANY AND LAB NAME Density :RD (U and L) = DS DS = DS PS Limits for CPN gauges are then : MeanDS 2 MeanDS 4 NUCLEAR GAUGE STANDARD COUNT CHECK - CAMPBELL PACIFIC TEST METHOD AS Appendix B1 4 DS 4 Moisture: RM (U and L) = MS 8 MS = MS 8 PS Limits for CPN gauges are then : MeanMS 4 For this check, both DS (= Density Standard Count) and MS (= Moisture Standard Count), taken at same location (at the laboratory) MS 4 MeanMS NUCLEAR GAUGE Serial No : Make & Model : PS = Prescale factor = 1 for Campbell Pacific gauges 1 Date 2 CurrentDS 3 Mean of previous 4 DS values (MeanDS) 2 4 MeanDS 5 CurrentDS MeanDS modulus 6 Column5 smaller than Column 4?? yes/no 7 CurrentMS 8 Mean of previous 4 MS values (MeanMS) 4 9 MeanDS 10 CurrentMS MeanMS modulus 11 Column 10 smaller than Column 9?? yes/no 12 Operator Initials & action March 2013 Page 26 of 30

27 Form 581b3 June 2010 COMPANY AND LAB NAME NUCLEAR GAUGE DENSITY SYSTEM CONSISTENCY CHECK TEST METHOD AS , Appendix B3 Serial Number Make & Model Checked at completion: Report No: Initiating Date: Date of Calibration Date: Initiating Operator: Calibrat'n Report No Block Material & No DIRECT TRANSMISSION DEPTH mm Soon after calibration, record FOUR - MINUTE DENSITY READINGS (t/m3) (minimum of 8 minutes of readings, maximum of 20 minutes of readings) Four-min reading 1 Four-min reading 2 Four-min reading 3 Four-min reading 4 Four-min reading 5 STANDARD COUNT = INITIAL DENSITY ρi t/m3 (Average of readings above) ρi ρi t/m3 t/m3 At the required monthly interval DATE & Operator ----> Standard Count Record a single FOUR - MINUTE DENSITY READING (t/m 3 ) Current DENSITY ρc At the required monthly interval DATE & Operator ----> Standard Count Record a single FOUR MINUTE DENSITY READING (t/m 3 ) Current DENSITY ρc At the required monthly interval DATE & Operator ----> Standard Count Record a single FOUR MINUTE DENSITY READING (t/m 3 ) Current DENSITY ρc At the required monthly interval DATE & Operator ----> Standard Count Record a single FOUR MINUTE DENSITY READING (t/m 3 ) Current DENSITY ρc Criteria: Current Density ρc should always be within t/m3 of Initial Density ρi. If required, plot on graph paper, Initial Density ρi, and values of Current Density ρc, against date upon which the readings were recorded. March 2013 Page 27 of 30

28 COMPANY AND LAB NAME NUCLEAR GAUGE FUNCTION CHECK CAMPBELL PACIFIC TEST METHOD AS Appendix B2 Nuclear Gauge Checked Report No. Serial Number Date Make & Model Date Operator STABILITY CHECK MC-1, 2 STABILIY CHECK MC 3 Perform initial & final checks, 3 hour intervals Use standard count & Xi 15 sec INITIAL FINAL 4 min DENSITY MOISTURE Counts Density Moisture Density Moisture Std count 1 Time 2 Std 1 3 Xi 1 4 Result Pass/Fail Pass/Fail 5 Time 6 Std 2 7 Xi 2 8 Result Pass/Fail Pass/Fail 9 Time 10 Std 3 11 Xi 3 12 Result Pass/Fail Pass/Fail 13 Time 14 Std 4 15 Xi 4 16 Result Pass/Fail Pass/Fail 17 Time 18 Std 5 19 Xi 5 20 Result Pass/Fail Pass/Fail Mean Start Stability Initial SD Start Stability Final / M Stab Ratio Pass Yes/No Pass Yes/No Pass Yes/No Pass Yes/No FUNCTION CHECK Complies/ Does Not Comply STABILITY RATIO Query: & STABLE: Unstable: < 0.65 & > 1.35 March 2013 Page 28 of 30

29 COMPANY AND LAB NAME NUCLEAR GAUGE FUNCTION CHECK - HUMBOLDT TEST METHOD AS Appendix B2 Nuclear Gauge Checked Report No. Serial Number Date Make & Model Date Operator STABILITY CHECK Use shaded cells for autotest DRIFT CHECK Use shaded cells for autotest One min DENSITY MOISTURE Four min DENSITY COUNTS COUNTS COUNTS D Mean 7 a C D 8 b (C + D)/2 9 Drift 100*a/b 10 Limit Pass/Fail 11 No MOISTURE COUNTS Q Mean r P Q s (P + Q)/2 Drift 100 * r/s Mean C: P: Limit Pass/Fail < ± 1.0% SD C P Time 0:00 Start Stability 4 / M 4 C/ C 4 P/ P Time 3:00 Start Drift Stab Ratio PASS/FAIL PASS/FAIL FUNCTION CHECK COMPLIES-Yes/No STABILITY RATIO LIMITS Query: & Unstable: <0.50 & >1.50 March 2013 Page 29 of 30

30 COMPANY AND LAB NAME NUCLEAR GAUGE FUNCTION CHECK - TROXLER TEST METHOD AS Appendix B2 Nuclear Gauge Checked Report No. Serial Number Date Make & Model Date Operator 3411 Electronic TEST value /- 2 ( ) SLOW Density & Moist 4 min: NORMAL Density & Moist 1 min: FAST Density & Moist 15 sec: STABILITY CHECK 3401/3411B Use shaded cells for 3440 DRIFT CHECK 3401/3411B Use shaded cells for 3440 One min DENSITY MOISTURE Four min DENSITY COUNTS COUNTS COUNTS D Mean 7 a C D 8 b (C + D)/2 9 Drift 100*a/b 10 Limit Pass/Fail 11 No MOISTURE COUNTS Q Mean 18 r P Q 19 s (P + Q)/2 20 Drift 100 * r/s Mean C: P: Limit Pass/Fail SD C P Time 0:00 Start Stability < ± 1.0% 4 / M 4 C/ C 4 P/ P Time 3:00 Start Drift Stab Ratio PASS/FAIL PASS/FAIL FUNCTION CHECK COMPLIES Yes/No STABILITY RATIO LIMITS Query: & Unstable: <0.12 & > 0.40 March 2013 Page 30 of 30