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European Aggregate Sizes

Description of all screened aggregates should by now be aligned to the appropriate European Standard applicable to the desired end use. This article looks at the requirements of BS EN 13043 Aggregates for use in bituminous mixtures and surface treatments for roads, airfields and other trafficked areas. Implemented in the UK from 1 January 2004, and applicable throughout the European Union, BS EN 13043 has the status of a national standard, and all conflicting national standards (i.e., for UK single size aggregates; BS 63-1:1987, BS 63-2:1987) were withdrawn in June 2004. The intent of this article is to give a basic outline of the new system, hopefully in an understandable fashion. While this article deals specifically with aggregates for use in bituminous mixtures, the concepts outlined below can also be used in understanding the standards for concrete, BS EN 12620; unbound mixtures, BS EN 13285; and mortar, BS 13139.

In the new system, screened aggregates are now described by a series of terms, beginning with a size descriptor, followed, where required, by additional physical property requirements (such as Flakiness Index, PSV value etc.).

AGGREGATE SIZE

(following description of system and example are colour coded to aid understanding)

Sizes are described in terms of a lower limiting sieve size, "small" d, and an upper limiting sieve size, "big" D. Written as d/D [note the slash is just a separator, it is not little d divided by big D]. The sizes of both small d and big D are selected from a list of prescribed sieve sizes. For the UK, these sizes are: 1mm, 2mm, 4mm, 6.3mm, 8mm, 10mm, 12.5mm, 14mm, 16mm, 20mm, 31.5mm, 40mm, 63mm (taken from 'Basic set plus set 2'). For convenience, 6.3mm can be referred to as "6mm", and 31.5mm as "32mm".The ratio of D/d must not be less than 1.4.

Aggregates are then designated as being either GC (coarse), GF (fine), or GA (all-in). Aggregate is classed as coarse if D is greater than 2mm, fine if D is less than 2mm, and all-in if D is less than 45mm and d is 0.

Next, the required minimum percentage passing D is given, followed (for coarse aggregates only) by the maximum percentage allowed to pass d.  Minimum percentage of D can be either 90% or 85%. For coarse aggregates, maximum percentage of d can be 10%, 15%, 20% or 35%. For all-in aggregates, d is always zero.

For example, coarse aggregate previously called 20mm single size, and suitable for pre-coated chippings, would be designated as:

Pre Coated Chipping Clip

SPOT THE DIFFERENCE

Spot The Difference

To complicate matters more, for fine and all-in aggregate, where D <= 8mm, the standard requires producers to declare a "typical grading", which, where required, must be within a given Tolerance Category designated according to a set ± value on the D/2 sieve, i.e., GTC10, GTC20 or GTCNR (no requirement).  A typical quarry dust could be designated 0/4 GA85 GTC20.

To give guidance regarding UK practice with respect to BS EN 13043, the British Standards Institute has issued "PD 6682-2:2003 Aggregates for bituminous mixtures and surface treatments for roads, airfields and other trafficked areas – Guidance on the use of BS EN 13043". PD 6682-2 gives comparative tables (Tables 3 and 4) of the now superseded BS 63 aggregate sizes, versus the new European grading categories. For convenient reference, they are summarised in the tables below:

 


Recommended grading categories for coarse aggregate for asphalt & bitmac within the UK
Old BS 63 single sized aggregate (mm) 40 28 20 14 10 6 3
Recommended BS EN 13043 grading category 20/40 Gc85/20 20/31.5 Gc85/35 10/20 Gc85/20 6.3/14 Gc85/20 4/10 Gc85/20 2/6.3 Gc80/20 1/4 Gc90/10
Grading specification (sieve size, % pass by mass) 63mm 98-100
40mm 85-99*
20mm 0-20
10mm 0-5
.063mm 0-4
63mm 100
40mm 98-100
32mm 85-99*
20mm 0-35
10mm 0-5
.063mm 0-4
40mm 100
32mm 98-100
20mm 85-99*
10mm 0-20
4mm 0-5
.063mm 0-4
32mm 100
20mm 98-100
14mm 85-99*
6mm 0-20
2.8mm 0-5
.063mm 0-4
20mm 100
14mm 98-100
10mm 85-99*
4mm 0-20
2mm 0-5
.063mm 0-4
14mm 100
10mm 98-100
6mm 80-99*
2mm 0-20
1mm 0-5
.063mm 0-4
8mm 100
6mm 98-100
4mm 90-99*
1mm 0-10
0.5mm 0-2
.063mm 0-4

*Where the percentage passing D is greater than 99%, the producer must declare the typical grading, including sieves D, d, d/2 and sieves intermediate between d and D.

Recommended grading categories for surface treatments or as chippings for rolling into asphalt within the UK
Old BS 63 single sized aggregate (mm) 20 14 10 6 3
Recommended BS EN 13043 grading category 14/20 Gc85/20 8/14 Gc85/15 6.3/10 Gc85/20 2.8/6.3 Gc80/15 2/4 Gc85/20
Grading specification (sieve size, % pass by mass) 40mm 100
32mm 98-100
20mm 85-99*
14mm 0-20
6mm 0-5
.063mm 0-1
32mm 100
20mm 98-100
14mm 85-99*
8mm 0-15
4mm 0-2
.063mm 0-1
20mm 100
14mm 98-100
10mm 85-99*
6mm 0-20
2.8mm 0-5
.063mm 0-1
14mm 100
10mm 98-100
6mm 85-99*
2mm 0-15
1mm 0-2
.063mm 0-1
8mm 100
6mm 98-100
4mm 85-99*
2mm 0-20
1mm 0-5
.063mm 0-2

*Where the percentage passing D is greater than 99%, the producer must declare the typical grading, including sieves D, d, d/2 and sieves intermediate between d and D.

 

PHYSICAL PROPERTIES OF AGGREGATE

BS EN 13043 gives categories for a range of other aggregate properties. Not all properties stipulated have to be met. Each EU member country has its own National Guidance (for the UK, PD 6682-2) which gives guidance on which particular properties have to be met for aggregates used in each member country. BS EN 13043 aggregate properties are listed below, with comment regarding whether or not they have been adopted by the UK:


BS EN 13043 Property
United Kingdom position

MBF

Fines quality (methylene blue test)

Used to assess level of harmful fines, e.g., swelling clay. No history of problem in the UK. MBFNR category should be adopted.

FI

Shape of coarse aggregate (flakiness index)

Use
Old BS 
Recommended EN cat.
HRA/Bitmac
45
FI35
Porous Asphalt
25
FI20
Surface treatments
35 or 25
FI30or FI20
Coated chippings
25
FI20

Note the lower flakiness values in the EN recommended categories are not indicative of tighter tolerances, but arise from the use of different equipment (round bar sieves, different length/width ratio). The new sieves produce values which in all cases are lower than those obtained with the old slotted BS flakiness sieves.

SI

Shape index

Replaces BS 812 elongation test, but not recommended for use in the UK. Category SINR should be adopted

C

Percentage of crushed and broken surfaces

Not considered necessary in the UK. Category CNR should be adopted.

ECS

Angularity of fine aggregate

Not considered necessary in the UK. Category ECSNR should be adopted.

LA

Resistance to fragmentation (Los Angeles test)

Replaces the 10% fines test. As the tests do not measure the same properties, there is no direct correlation between the two. Category LA30 recommended for coated materials and surface treatments.

SZ

Impact value

Based on a DIN test method that requires the use of special equipment not available in the UK, therefore category SZNR is recommended.

PSV

Resistance to polishing of coarse aggregate

Same as old BS 812 PSV test. Where Highways Agency Design Manual For Roads and Bridges values do not coincide with BS EN 13043 categories, category PSVDeclared should be adopted

AAV

Resistance to surface abrasion

Same as old BS 812 Aggregate Abrasion test. Where Highways Agency Design Manual For Roads and Bridges value is 10, category AAV10 should be chosen. For other values, category AAVDeclared should be adopted.

MDE

Resistance to wear of coarse aggregate (micro-Deval coefficient)

Not considered relevant to UK asphalt applications. Category MDENR should be chosen.

AN

Resistance to abrasion from studded tyres

Not relevant to UK. Category ANNR has been adopted.

WA

Water absorption value as screening test for freeze-thaw resistance


MS

Magnesium sulphate soundness


F

Resistance to freezing and thawing

For aggregates in the UK, if water absorption conforms to WA242 [or WA241], no further testing is required. If not, an MgSO4 test should be carried out, and if the aggregate conforms to MS25 ,it should be considered suitable for general purpose use.
MgSO4 soundness test is recommended, rather than F freeze thaw. MgSO4 is same as old BS 812 test, but result is reported as percentage lost, not remaining.
Resistance to thermal shock It is not anticipated that this test will be adopted in the UK.

SB

"Sonnenbrand" of basalt

Not applicable to UK materials, but may be of value w.r.t. imported basalt aggregates. Category SBNR should be chosen.