SAMPLING MATERIALS USED IN HIGHWAYS CONSTRUCTION / MAINTENANCE

CONTENTS

WHAT IS A SAMPLE ?
EUROPEAN STANDARDS
SAMPLING, THE ALTERNATIVE WAY
COMMON SENSE SAMPLING

WHAT IS A SAMPLE ? A LABORATORY SAMPLE is a sample capable of being submitted to a laboratory for testing and producing a meaningful result in relation to the bulk of material from which it was a representative part. The sample MUST be representative of the mass of material it is taken to represent i.e. lorry load, stockpile, length of carriageway, etc.. You must ensure ALL relevant information is recorded relating to the sample, this information needs to be provided with the sample to the Testing Laboratory. Having sample bags, or cardboard boxes, printed as shown is a useful aid in making sure information is recorded correctly at the time of sampling, but it is still usual to write a sample certificate in a duplicate book so that both laboratory and sampler have a written record of the sample details that is able to be filed for future reference.

Correct sampling can be achieved by sampling in a prescribed manner as set out in British Standards :-

BS 598 : Sampling and examination of bituminous mixtures for roads and other paved areas 
Part 100 : Sampling bituminous mixes
or
BS 812 : Testing aggregates : Part 102 : Methods of sampling
or
BS1881 : Testing concrete : Part 101 : Methods of sampling fresh concrete on site.

These standards will instruct you on how to sample, where to sample and what sampling method and tools to be used, I will not repeat the British Standards information here, but encourage you to obtain copies of these documents and sample accordingly.
If these standards are still available I recommend you purchase copies as soon as possible, even if they are replaced as current documents they contain a lot of sensible information, and they are a lot easier to understand than the superseding British European standards.

EUROPEAN STANDARDS

There are European standards (BS EN's) being introduced and they tend to be far more theoretical in their approach to sampling than the British Standards quoted.
I do not believe the British Standards I quote have yet been superseded but if you are in dispute with a supplier it would be wise to check because the European standards could now be implemented
Whether these new standards are the standards referred to in your current contract documents is another point that you may need to clarify, as there is going to be a period of confusion during the transition from older BS standards to new BS EN standards.
However, if you have taken your sample correctly it is unlikely you will have infringed the procedures in either of the  standards.

SAMPLING, THE ALTERNATIVE WAY

Based on the "prescribed" methods stated in the standards use careful observation of the area/stockpile to be sampled, and consider the way it may have segregated in discharge, laying and placing, now take your sample from where-ever you need to for it to be representative of the whole area.

This is meant to be done "honestly", and not in a manner to achieve the result you are looking for, if you are "client" you are seeking to obtain a true reflection of quality of materials used.

And, if you are the "producer / supplier" you need an accurate assessment of what the plant is producing in order that you may make any adjustments, or not, as the case may be.

If segregation is the problem, then that is the problem, and the cause of the segregation needs to be dealt with.

The sample must be of SUFFICIENT mass , based on the nominal stone size of the material being sampled , (this is no problem with the smaller stone sizes, but needs to be at least 25 kilos for larger nominal size materials).

It need not be the "groin straining" weights set down in tables if you have sampled well, and of course you can riffle or "quarter down" your sample on site to reduce the problem of carrying and transporting heavy samples.

What you must be ABSOLUTELY sure of before submitting any sample for test is that what you have "in the bag/container" is REPRESENTATIVE of the mass or area you have taken the sample from.

If you take your sample in this manner and the supplier will not accept the result and you have to return and re-sample in a "correct" manner it is likely you will achieve a very similar result.

A BAD SAMPLE IS WORSE THAN NO SAMPLE AT ALL !

This is because action may be initiated on a result from a bad sample that once set down on paper seems very authoritative, but the information it supplies to the reader is incorrect.

If you have reasonable cause to doubt results supplied to you, or even your own results, do not be afraid to re-sample, even if it means taking "cutouts" or cores.

I repeat, the material you sampled will still be available in the road pavement / structure / trench, it may be a little more difficult to obtain your sample, but in most instances it will still be possible for sampling and testing to take place if it should be necessary

I again suggest you read the relevant British Standards, (or the relevant BS EN standards that have superseded them):-
BS 598 : Part 100,
BS 812 : Part 102
BS 1881 :Part 101,
these are not thick documents or particularly difficult to understand and are very instructive and informative.

And, if you are sending samples to UKAS (formerly NAMAS) approved laboratories they will not issue you a UKAS (formerly NAMAS) approved result unless you have sampled according to the appropriate British Standard.
You will need to attach a sample certificate providing all required information, and confirmation that you have sampled according to the appropriate British Standard

Be aware that testing laboratories that only have Quality Assurance Certificates may vary in the standard of the procedures they employ.
UKAS Accreditation provides high standard uniformity that comes from rigorous independent inspection.
It is likely that apart from the "main" laboratory, suppliers production laboratories will not have UKAS accreditation, but a form of "Quality Assurance" approval put in place by their own management structure.

COMMON SENSE SAMPLING

BUT, you may not always need a UKAS  (formerly NAMAS) approved result, you may just wish a "quick result" to monitor the quality of a material you are purchasing or indeed producing.
Speedy results from correctly taken samples that are performed in in-house laboratories can prevent long and expensive drawn out "rangles" that you can encounter from failed results to samples that are received long after a "job" has been completed.

So, for those of you who still need a basic guide on sampling without reference to British Standards, this is what you want :-

You require a sampling tool whose size is several times larger than the nominal size of the aggregate you are sampling, [e.g. you do not sample Granular Sub-base that contains 40mm. stone with a small scoop you choose one that is at least 150mm. wide and preferably bigger],
it also needs to have retaining sides on it, this is to stop the larger [coarser] stone rolling off.

All this is common sense stuff if you think about it.

This is where you do it :-

FROM A STOCKPILE
A number of increments taken in a complete circular spiral from the top of the heap to the bottom to achieve the required mass of sample.

FROM A PAVING MACHINE
An equal number of increments taken from the fully charged augers either side of the machine when the lorry discharging is halfway through tipping its load, take sufficient increments to provide the required mass of sample.

FROM A LAID AREA OF CARRIAGEWAY
A number of increments sufficient to provide the required mass of sample taken along a diagonal line for the length of carriageway in question.

FROM A "CONCRETE TRUCK-MIXER"
A number of increments sufficient to provide the required mass of sample, taken full depth from the discharge chute during the course of discharge of the complete load. 

IF YOU ARE IN DOUBT AS TO THE MASS OF SAMPLE NEEDED, TAKE AT LEAST 25 KILOS

But 15kgs. is probably sufficient if the nominal aggregate size is below 20mm. and you have taken care in your sampling procedure.

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