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TRANSPORT and ROAD RESEARCH LABORATORY
Department of the Environment
SUPPLEMENTARY REPORT 56 UC
PROBLEMS IN THE ANALYSIS OF DENSE SLAG-TARMACADAM
by.
S.G. Bond and I.H. Czarnecki
Any views expressed in this Report are not necessarily those of the Department of the Environment
Construction Methods Division Highways Department
Transport and Road Research Laboratory Crowthorne, Berkshire
1974
CONTENTS
Page
Abstract
1. Introduction
2. Objects of the investigation
3. Experimental work
4.
5.
3.1 Preparation of the vehicle.to receive the tarmacadam 3.2 Preparation of sampling tools and containers 3.3 Sampling procedu.re
3.3.1 Supplementary samples
Methods of analysis
Discussion of the analysis results
5.1 Relationship between binder content and the percentage of aggregate passing the 3.2 mm BS sieve
5.2
5.1.1 Relationship between tar content and 'fineness' for the mixture under study.
Comparison of results obtained-by the hot-extractor and sieving-extractor methods of analysis. "
5.2.i
5.2.2
5.2.3
Comparison of results for the percentage of aggregate passing the 3.2 mm BS sieve Comparison of results for the percentage of aggregate passing the 75 micron BS sieve Comparison of tar contents
1
2
2 2 2
3
3
4
4
4
5.3 Comparison of results obtained on samples taken before and after the simulated haul
5.3.1
5.3.2
Comparison of results for the percentage of aggregate passing the 3.2 mm BS sieve. Comparison of tar contents
5.4 Variability o f the analysis methods
6. Conclusions 7
7. Acknowledgements
8. References
7
10
9 Appendix 1 Detailed analysis results
© CROWN COPYRIGHT 1974
Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.
10
Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on 1 st April 1996.
This report has been reproduced by permission of the Controller of HMSO. Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.
PROBLEMS IN THE ANALYSIS OF DENSE SLAG- -TARMACADAM
ABSTRACT
This report describes an experiment to determine whether there was any basis for the reported differences in tar content obtained when dense slag-tarmacadam is analysed by the hot-extractor and sieving-extractor methods of analysis.
The results obtained showed that there was a small ~uantitativ~erdifference of about 0.1 per cent in tar content between the two me~'laoOs ot analysis, the hot-extractor results being the greater.
There were significant differences between the gradi~ngs ob ta~ed by the two methods, caused by difficulty in completing the grading-following hot-extraction.
1. INTRODUCTION
In recent years, there have been occasional reports of difficulties in the accurate determination of the com- position of dense tarmacadam, especially when it contained slag aggregate and high-viscosity coke-oven tar binder. In some cases dispute between producer and customer has resulted when different methods of analysis have been used by the parties concerned. Some test results have been quoted in which the binder contents have differed by as much as one per cent."
In all early comments on the matter there had been an absence of factual data but, more recently, a fairly detailed examination of the problem was undertaken by a coated-macadam manufacturer and a county authority, and from the findings of these investigators there appears to be some justification for the concern expressed. It appeared probable that there were differences in the quantity of aggregate passing the 3.2 mm BS sieve, as determined on the aggregate recovered after extraction b y the hot-extractor and by sieving-extractor methods. The results also indicated that the real differences in binder content were only small when an appropriate allowance was made for the difference in grading. Differences in binder content and grading were also detected between samples taken at the plant and those taken at the laying site originating from the same loads of material. In every case samples taken on site had shown slightly lower binder contents. Both the hot-extractor and sieving-extractor methods of analysis gave the same relative differences. With this more positive indication of a testing problem, affecting the judgement of compliance with specification of the considerable quantities o f dense slag-tarmacadam being produced, it was decided that a more detailed independent investigation to resolve the uncertainties was necessary.
2. OBJECTS OF THE INVESTIGATION
The objects of the investigation were:
(i) To compare the results of analyses of two equivalent sets of samples taken from a single batch of dense slag-tarmacadam prepared with aggregate of 40 mm maximum size, one set being analysed by the hot- extractor method and the other by the sieving-extractor method.
(ti) To compare the composition of samples of the same material taken just after manufacture with samples taken in a similar manner from the same batch but after a haul lasting 1½ hours.
To meet these objectives a sampling plan was designed in which two sets of 32 samples each were taken from a single batch of the tarmacadam; the first set was taken immediately after mixing.and the second after a simulated haul lasting 1½ hours.
To ensure the equivalence of the two sets of samples to be used in the comparison of the analysis methods, the samples were consecutively numbered so that Samples 1 and 2, 3 and 4, 5 and 6, etc were taken from adjacent sampling positions. From each pair of side-by-side samples one was then selected at random for analysis by one of the test methods, the remaining sample of the pair being analysed by the other test method.
The relative positions from which the samples were taken and the test method used when analysing the samples are shown in Fig. 1. The test method used on each sample is indicated by an H for the hot- extractor method and an S for the sieving-extractor method.
For this investigation the samples were divided into 4 groups as indicated below:
Group A Immediately after mixing
Group B Immediately after mixing
Group C After simulated haul
Group D After simulated haul
and the following groups used for the necessary comparisons:
Hot-Extractor Method
Sieving-Extractor Method
Hot-Extractor Method
Sieving-Extractor Method
(i) Analysis methods - GROUPS A and C with GROUPS B and D
(ii) Before and after simulated haul - (a)
(b) GROUP A with GROUP C GROUP B with GROUP D
3. EXPERIMENTAL WORK
3.1 Preparation of the vehicle to receive the tarmacadam
The interior of the rear of a 4 m s lorry was divided into three compa.rtments by partitioning across the full width of the lorry so that sampling operations in the central compartment could be undertaken easily and safely by staff standing in the end compartments. A plan of the partitioned lorry body is shown in Fig. 2. The centre section was constructed so that a layer of hot tarmacadam about 200 mm deep could be placed into the section to provide an insulating layer in the bot tom of the lorry. After covering this layer with a separating membrane there was just sufficient space to accomodate a 2 Mg batch of the normal production from the mixing plant. Insulation was added to the outside of the wooden partitions to reduce the loss of heat from the abnormally small load when taken for the simulated haul.
3.2 Preparation of sampling tools and containers
As one of the objectives of the investigation required the comparison of two equivalent sets o f samples it was particularly important to adopt a consistent sampling system. Sample reduction, which can introduce additional variability, was avoided by taking samples of the size required for analysis. These requirements, o f consistent operation and appropriate sample size (3½ kg), were met by employing only two samplers each equipped with a long-handled scoop of the required size, 180 mm x 130 mm x 75 mm deep.
To prevent the tarmacadam from cooling excessively before being dispatched on its simulated haul, speed was essential in collecting the abnormally large number of samples required. All sample containers were therefore code-marked and carefully stacked to avoid any possible errors and uncertainty during the
sampling operations.
3.3 Sampling procedure
Sampling commenced almost immediately after the test-batch of tarmacadam had been dropped into the prepared bay of the lorry. All samples were taken in pairs, side by side, for the reasons stated earlier, each sample being obtained by inserting a scoop into the material in a pre-determined position and transferring the 3½ kg of material so collected to its appropriate container. Sampling positions are
shown in Fig. I A.
2
At the completion of this initial phase of sampling the temperature of the tarmacadam was 78°C.
The remaining material was then levelled off, carefully covered with tarpaulin sheets and the lorry dispatched for a journey lasting approximately 1½ hours during which 56 km were covered.
On the return of the lorry the tarmacadam was uncovered and the temperature checked and found to be 74°C.
A further 16 samples were taken by each of the samplers following the plan shown in Fig. lB. Sampling after the simulated haul was physically more difficult to carry out because of the formation of a hard crust on top of the tarmacadam; nevertheless the samples followed as closely as possible the sampling technique as that previously used.
3.3.1 Supplementary samples
After the main sampling programme had been completed extra samples of the tarmacadam were collected to provide material for any additional tests that might be required. For similar reasons samples of the slag aggregate were obtained. Also a sample Of the tar used was. taken for the estimation of the proportion insoluble in the solvents to be employed in the analysis procedures.
4. METHODS OF ANALYSIS
The two methods of analysis, compared in this exercise, have both been in use for many years, the hot-extractor method having been developed first. Both methods are in British Standard 598:1958 but fine descriptive detail in the Standard is somewhat inadequate and this has led to the use of a variety of procedures in different laboratories. In some cases, the differences in technique have been found to cause significant differences in the estimates of composition of the material subjected to analysis. For this investigation a very rigid and thorough procedure:was therefore adopted throughout. Important procedural points are outlined below:
(a) Hot-extractor method
(i) Extra care was taken to ensure that the solvent and apparatus were dry before use.
(ii) Extraction and drying times were always more than adeuqate.
(iii) The whole of the solution in the extractor pot after extraction was filtered through a No. 5 Whatman filter paper to ensure 100 per cent recovery of any insoluble material.
(iv) The insoluble-content of the actual tar used in the manufacture of the tarmacadam was determined in the solvent used foi; the hot extraction. This insoluble-content was allowed for in the determination of the total tar content o f the samples analysed.
(v) The aggregate was graded in two stages: the aggregate retained or~ a 3.2 mm sieve was first graded and the material passing the 3.2 mm sieve then sub-divided using a sample divider. Only a portion of the fine material was graded to prevent overloading of the fine- mesh sieves.
(vi) Adjustments were made to the material passing the 75 micron BS sieve to allow for the tar insoluble as well as for the aggregate retained on the filter paper and the insoluble in the solution from the pot. It was assumed that the tar insoluble was all to be found in the material passing the 75 micron BS sieve. This is clearly a source of inaccuracy but is generally accepted as the best compromise.
3
Co) Sieving-extractor method
(i) The procedure described in the second edition of Road Note 102 was followed very closely.
(ii) The sample was shaken in the sieving extractor with dichloromethane for 20 minutes in order to dissolve the soluble tar. \ (iii) The insoluble-content o f the tar, in dichlororr)ethane, was allowed for in the determination o f the total tar content. /
7 J - / " .
(iv) The aggregate was t h o r ~ y ~ " ~ s h e d before removal from the extractor. This required up to 6 litres of~clean dichloromethane. After drying the aggregate the efficiency of theJ 'me~rading was quickly checked by further hand sieving before being recorded. JTl~e aggregate retained on the 3.2 mm sieve was graded separately.
(v) "The_aggregate passing the 75 micron sieve was calculated by difference. It is given by- Wt of sample - wt of recovered aggregate - wt of total tar - wt of water. The weight o f the water is calculated from the hot-extractor figures (as recommended in the British Standard).
5. DISCUSSION OF THE ANALYSIS RESULTS
Full details of the results of analyses are given in the appendix.
Before discussing the results it should be emphasised that dense macadam prepared with slag aggregate and high-viscosity coke-oven tar is one of the most difficult materials to analyse accurately and particular care is therefore required in the analysis procedure.
5.1 Relationship between binder content and the percentage of aggregate passing the 3.2 mm BS Sieve
In a bituminous mixture that has been throughly mixed the binder content of a sample taken from that mixture will increase with increasing 'fineness' o f the actual sample analysed; this is because the binder content is a function of the surface area of the aggregate in the sample. This basic property of bituminous mixtures must be taken into account if meaningful comparisons of test results on a bituminous mixture are to be ob- tained and it is particularly relevant when several samples are taken from a single batch of material. In such a case, provided the material is thoroughly mixed, any distortion in the composition of the mixture indicated by the analysis results is due almost entirely to the method of obtaining the samples, with an insignificant contribution arising from the analysis method. Thus, when the fineness of each sample of a set, represented by the percentage of aggregate passing the 3.2 mm BS sieve, is plotted against its corresponding binder content the points will be found to lie close to a straight line. The slope of this line gives an accurate indiciation of dependence of the binder content on the 'ffmeness'.
5.1.1 Relationship between tar content and 'fineness' for the mixture under study
A plot of each tar content against its corresponding percentage of aggregate passing the 3.2 mm BS sieve (fmeness) for all of the analyses of samples taken during this investigation is given in Fig. 3. From the plot it can be seen that the points form two separate groups centred about two parallel lines; one of the groups representing the results of the sieve-extractor method of analysis and the other group the hot-extractor method. The slopes of both lines show that for the particular mixture under examination the tar content changes by 0.09 per cent for each one-per-cent change in the quantity of aggregate passing the 3.2 mm BS sieve.
4
5.2
Also plotted on Fig. 3 are four analysis results obtained by the bottle-extraction method (Method C of BS 598:19581) on some of the extra material taken after the main sampling programme had been completed. A line drawn through these points confirms the relationship found for the other two methods.
Comparison of results obtained by the sieving-extractor and hot-extractor methods of analysis
5.2.1 Comparison of results for the percentage of aggregate passingtl~e :3.2 mm BS Sieve. i
The mean results of the four groups of samples, A, B, C and D (see Section 2) are given in Table I. The means for the percentages of aggregate passing the 3.2 mm BS sieve obtained by the sieving-extractor method, groups B and D, are greater than for the corresponding groups, A and C, obtained by the hot-extractor method. The actual differences were 4.4 per cent on samples taken before the haul and 4.0 per cent after the haul. These differences were broadly in agreement with the differences reported by the two laboratories previously metnioned and are judged to be large considering that:
(i) the size of sample taken avoided any sub-sampling errors
(ii) the same sampling technique was followed throughout
(iii) the samples were from a single batch of material
(iv) the samples were carefully analysed.
Thus, under these ideal conditions, a difference was found that could easily be of major importance when assessing the quality of the macadam (especially if the supplier was unaware of the method of analysis being used by the customer). The difference found between the gradings could not possibly represent a real difference in the fineness of the two sets of samples and must be a consequence of the different methods of analysis only.
The explanation of this difference in grading is not quite as simple as it would at first
appear. It has commonly been assumed that shaking in the sieving-extractor degrades the aggregate; this has rarely been found to have been established for materials that are suitable for road construction
and where the method has been sensibly used. More frequently, incomplete grading of the aggregate re- covered after extraction by the alternative methods has been found to be the major cause of the difference.
Nevertheless, it was evident that with this particular slag aggregate there was some slight degradation in the sieving extractor during the extraction and subsequent washing procedures.
As is usual when using the hot-extractor method for dense tar-coated materials, it was not found possible to separate completely the particles of aggregate even with a great deal more effort than is commonly used, the process of separation being seriously affected by the presence of the insoluble matter derived from the tar. By washing the graded aggregate with dichloromethane with the mildest of rinsing processes, an increase in the proportion of aggregate passing the 3.2 mm BS sieve resulted. It is of interest to note that the aggregate passing the 3.2 mm BS sieve deter- mined on the aggregate recovered after extraction by the bottle method using a roller shaker was closer to the sieving-extractor value.
5.2.2 Comparison of results for the percentage of aggregate passing the 75 micron BS sieve
There was a difference of 2.1 per cent between the means of the percentages of aggregate passing the 75 micron BS sieve determined by the two methods of analysis. This was primarily due
5
to the inefficient separation of the aggregate particles after hot extraction. Support for this assessment o f the cause is provided by comparison with the figure obtained by the bottle method with separation of the fine material by the decantation method described in BS 812:19673.
5.2.3 Comparison of tar contents
When comparing binder contents of samples taken from the same material it is normally sound practice, for the reasons discussed in 5.1, to adjust the values obtained to allow for differences in the finenesses of the samples, thereby reducing the distortion in the composition analysis caused by sampling errors. For this investigation it has been shown that the estimates of the percentage of aggregate passing the 3.2 mm BS sieve were dependent upon the method of analysis employed; there- fore, any adjustment of tar content for grading where different methods of analysis were involved would be misleading but where the'same method is used adjustments would be in order.
Table 1 gives the mean values for the determined tar contents obtained by the two analytical methods on samples taken before and after the simulated haul. The mean tar content obtained on samples taken before the haul and analysed by the hot-extractor method was 0.08 per cent greater than the mean for the sieve-extractor method on similar samples. For the two groups of samples, C and D, taken after the haul, the difference was 0.18 per cent, with the tar content obtained by the hot-extractor method again being the greater.
These differences, although small, were considered important enough to warrant further inves- tigation. It was shown that:
(i) there was some soluble tar left in the pores of the slag after cold extraction in the sieving extractor; the quantity of undissolved tar was smaller on samples taken immediately after mixing.
(ii) the slag aggregate was slightly soluble in the hot trichloroethylene used for the hot-extraction process when refluxed for the time required for complete solution of the soluble tar.
5.3 Comparison of results obtained on samples taken before and after the simulated haul
5.3.1 Comparison of results for the percentage of aggregate passing the 3.2 mm BS sieve
Before comparing the tar contents before and'after the haul it is important to consider the fineness of the groups of samples being examined. From Table 2 it can be seen that there is a difference of approximately 2 per cent in the percentage of aggregate passing the 3.2 mm BS sieve between the samples taken before and after the haul, irrespective of the method of analysis used. There is no certainty of the cause of the coarsening of the gradings after the haul but it is possible that some segre- gation occured during the removal o f the samples and the levelling-off of the tarmacadam before the simulated haul.
5.3.2
by:
Comparison of tar contents
The comparison of the tar contents of the samples taken before and after the haul was complicated
(i) the differences in the gradings obtained by the two analysis methods and
(ii) the apparent coarsening of the material sampled after the haul.
6
It was decided therefore to treat the results obtained by the two analysis methods separately, and then to make appropriate adjustments to the tar contents to allow for the coarsening of the samples.
Table 2 gives for each analytical method separately the determined mean tar contents and the mean percentages of aggregate passing the 3.2 mm BS sieve for the samples taken before and after the haul. The Table also gives the mean percentages of aggregate passing the 3.2 m m BS sieve for all samples analysed by each analytical method, together with the tar contents adjusted to correspond with the mean gradings. The resul-
ting differences in tar content on samples taken before and after the haul are negligible for the samples analysed by the hot-extractor method but may be of some importance for the samples analysed by the sieving-extractor
method. Clearly a major problem may arise when the supplier is sampling at the plant and analysing by the hot-extractor method and the customer is sampling at the laying site and analysing by the sieving-extractor method.
5.4 Variability of the analysis methods
The variabilities of the tar contents and the percentages o f aggregate passing the 3.2 mm BS sieve determined by the two analysis methods were very similar, but the variability of the aggregate passing the 75 micron BS sieve, determined on aggregate recovered from the hot-extraction process was appreciably greater than for the sieving-extractor method. Values of the standard deviations of the various parameters are given in Table 1.
6. CONCLUSIONS
The resuits obtained from this investigation showed that:
I. The difference in tar content due to the method of analysis was 0.08 per cent for samples taken before the haul and 0.18 per cent after the haul, the sieving- extractor method giving the lower result in each case.
. The difference in tar content found between samples taken immediately after mixing and after a simulated haul was negligible for samples analysed by the hot-extractor method but there was a difference of 0.1 per cent for the sieving-extractor method.
. There were significant differences in the percentage of aggregate passing the 3.2 mm and 75 micron BS sieves largely because of the inefficiency of the dry-grading process used after hot extraction.
. The percentage of aggregate passing the 75 micron BS sieve determined after hot extraction was more variable.
7. ACKNOWLEDGEMENTS
The work described in this report was carried out in the Construction Methods Division (Head of Division Mr. N.W. Lister) of the Highways Department of the Transport and Road Research Laboratory. The members of the research team who took part in the investigation were G.D. GoodsaU, I.H. Czarnecki, S.G. Bond, A.C. Edwards and R.J. Mead. The cooperation of Clugston Asphalt Limited is gratefully acknowledged.
7
TABLE 1
Comparison of results obtained by sieving-extractor and hot-extractor methods of analysis
Results from samples obtained before simulated haul
Mean tar content 'per cent
Standard deviation
Mean aggregate passing 3.2 mm BS sieve per cent
Standard deviation
Mean aggregate passing 75/am BS sieve per cent
Standard deviation
Hot extractor
Group A
5.44
0.29
42.1
3.07
2.98
0.37
Method of analysis
_Sieving extractor
Group B
5.36
0.28
46.5
2.95
4.98
0.26
Results from samples obtained after simulated haul
Mean tar content per cent
Standard deviation
Mean aggregate passing 3.2 mm BS sieve per cent
Standard deviation
Mean aggregate passing 75 pm BS sieve per cent
Standard deviation
Hot extractor
Group C
5.26
0.46
40.4
5.20
2.73
0.52
Method of analysis
Sieving extractor
Group D
5.08
0.3.9
44.4
3.85
4.96
0.25
Bottle extraction
(4 results)
5.31
45.3
5.0
8
/
TABLE 2
Comparison of results obtained from samples taken before and after simulated haul
Sieving-extractor method of analysis
Before haul
Group B
After haul
Group D
Tar content per cent 5.36 5.08
Aggregate passing 3.2 mm BS sieve per cent 46.5 44.4
Mean aggregate passing 3.2 mm BS sieve per cent 45.45
Tar content adjusted to mean aggregate passing 3.2 mm sieve per cent 5.27 5.17
Hot-extractor method of analysis
Before haul
Group A
After haul
Group C r , ,
Tar content per cent 5.44 5.26
Aggregate passing 3.2 mm BS sieve per cent 42.1 40.4
Mean aggregate passing 3.2 mm BS sieve per cent 41.25
Tar content adjusted to mean aggregate passing 3.2 mm BS sieve per cent 5.36 5.34
9
1 .
.
.
8. REFERENCES
BRITISH STANDARD INSTITUTION. British Standard 598:1958. Sampling and examination of bituminous mixtures for roads and buildings. London 1958 (British Standards Institution).
MINISTRY OF TRANSPORT. Rapid method of analysis for bituminous road materials. Road Research Laboratory Road Note No.10. Second Edition, London 1967 (H.M. Stationery Office).
BRITISH STANDARDS INSTITUTION. British Standard 812:1967. Methods for Sampling and testing of mineral aggregates, sands and idlers. London 1967 (British Standards Institution).
9, APPENDIX
The detailed analysis results obtained during the experiment are given in the following tables.
Table 1 Samples taken just after the discharge from the mixer analysed by the hot-extractor method.
Table 2 Samples taken just after discharge from the mixer analysed by the sieving-extractor method.
Table 3 Samples taken after simulated haul analysed by the hot-extractor method.
Table 4 Samples taken after simulated haul analysed by the sieving-extractor method.
Table 5 Samples taken after simulated haul analysed by the bottle-extraction method.
10
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(a) A f t e r d ischarge of the mater ia l f rom the mixer
H1 $2
H16 S15
$3 H4 H5 $6
SAMPLED FROM REAR
S14 H13 H12 $11
H7 $8
H I O $9
H32 S31
$17 H18
$30 H29 $28 H27
SAMPLED FROM FRONT
H19 $20 H21 $22
S2G H25
H 23 $24
(b) A f t e r s imulated haul
$33 H34
H48 $47
H 3 5 $36 H37 S38
SAMPLED FROM REAR
$46 H45 H44 $43
H39 S40
H42 $41
H64 SG3
H49 $50
HG2 $61 H60 $59
SAMPLED FROM FRONT
$51 H52 $53 H54
$58 H57
H55 $56
H = Analysed by h o t - e x t r a c t o r method S = Analysed by s i e v i n g - e x t r a c t o r method
Fig. 1. PLAN OF POSITIONS IN LORRY FROM WHICH THE SAMPLES WERE TAKEN
Rear end
Space for sampler
////,////////////////, / /
/ /
/ /
" / / / / / / ' , , j / /
/ / / / / / / / / /
" t / Space for mixed mater ia l / , / / / J
/ -. /
/ / / /
/ / / z / / , ~ / / / / / / / / /
/
/ / / ~ / / / / / / / / / / / / / . ,27 / / / . ,
. Wooden . frame
Polystyrene cladding
Space for sampler
Front end
Fig. 2. PLAN OF PARTITIONED LORRY BODY
6 0
A
E
U L.
13. v
> (1,) in
E (M
(;.)
I :
in (3
o L.
a
:E
5 0
48
46
44
42
4 0
38
36
34
32
30
28
I, S iev ing - Ex t rac to r method • H o t - E x t r a c t o r method 0 B o t t l e - Ex t rac t i on method
./
_ / / / /
/ Y /
_ . /
I I I I I l 1 1 4-1 4 -3 4.5 4-7 4.9 5-1 5.3 5"5
Ta r c o n t e n t ( p e r c e n t )
Fig. 3. RELATIONSHIP BETWEEN TAR CONTENT AND THE PERCENTAGE OF AGGREGATE PASSING 3.2 mm BS. SIEVE
II
I 5"7 5-9
(1220) Dd635247 100 7/74 HPLtd. , So ' ton G1915 PRINTED IN ENGLAND
ABSTRACT
Problems in the Analysis of Dense Slag-Tarmacadam: S G BOND and I H CZARNECKI: Department of the Environment, TRRL Supplementary Report 56 UC: Crowthorne, 1974 (Transport and Road Research Laboratory). This Report describes an experiment to deter- mine whether there was any basis for the reported difference in tar content obtained when dense slag-tarmacadam is analysed by the hot-extractor and sieving-extractor methods of analysis. The results obtained showed that there was a small quantative difference of about 0.1 per cent in tar content between the two methods of analysis, the hot-extractor results being the greater. There were significant differences between the gradings obtained by the two methods, caused by difficulty in completing the grading following hot-extraction.
ABSTRACT
Problems in the Analysis of Dense Slag-Tarmacadam: S G BOND and I H CZARNECKI: Department of the Environment, TRRL Supplementary Report 56 UC: Crowthorne, 1974 (Transport arid Road Research Laboratory). This Report describes an experiment to deter- mine whether there was any basis for the reported difference in tar content obtained when dense slag-tarmacadam is analysed by the hot-extractor and sieving-extractor methods of analysis. The results obtained showed that there was a small quantative difference of about 0.1 per cent in tar content between the two methods of analysis, the hot-extractor results being the greater. There were significant differences between the gradings obtained by the two methods, caused by difficulty in completing the grading following hot-extraction.