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GUIDANCE NOTES
AGGREGATES FOR SURFACE DRESSING
Members are reminded that BS63 Part 2 will be withdrawn in June and
replaced by new European Specifications. The following is guidance on
ordering chippings in accordance with the new specifications.
Guidance Note on Ordering Chippings to Avoid Oversize
British Standards 63 will be withdrawn from June 2004 and will be
replaced by BS EN13043:2002.
Members ordering chippings for surface dressing using BS EN 13043:2002
should be aware that there is a risk of up to 2% oversize in the
delivered material.
To avoid this risk members when inviting quotations, should advise their
suppliers that as permitted by Table 2 of BS EN 13043:2002 they require
100% passing D and require the supplier to document and declare the
typical grading with his quotation.
For reference see the note to table 4 on page 6 of PD 6682 – 2:2003.
March 2004
DOUBLE SURFACE DRESSING
Delegates to the Technicians’ Training Courses have indicated that they
find the guidance in the Road Note difficult to follow.
The following guidance note has been prepared by the Technical Committee
to clarify the process. This is not intended to be a substitute for the
Road Note.
RSDA NOTE ON BINDER SPREAD RATES FOR
DOUBLE SURFACE DRESSINGS
Uncertainty has been expressed about the Design Guidance in Road Note 39
(5) about the calculation of binder-spread rates for double surface
dressings.
This note attempts to clarify the matter.
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First Layer |
1 |
Obtain stage
1 “A” factor from Table 9.2.3c for the relevant size of chippings. |
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2 |
Stage 2
factor “B” is obtained from Table 9.2.4 for the shape of chipping
being used, as for other types of dressings. |
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3 |
Apply stage
3 adjustment factor (paragraph 9.2.5 & tables 9.2.5a and b) for
surface condition only. Other stage 3 adjustment factors are as
shown in paragraph 9.2.5 (i.e. a sum of 1) |
| |
|
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Second Layer |
1 |
Obtain stage
2 “A” factor from Table 9.2.3c for the relevant size of chippings |
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2 |
Stage 2
factor “B” is obtained from Table 9.2.4 for shape of chipping being
used. |
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3 |
Stage 3
adjustment factors are applied as shown in paragraph 9.2.5, ie
normal for surface condition (factor 1) and the remaining adjustment
factors as found on site |
As for all other recommendations in the Road Note, the information
given is “guidance” only – not a specification. Consequently, the stage
1 binder spread categories for the individual layers in table 9.2.3c may
be varied for specific binders and site conditions.
For instance there is a school of thought that suggests that the first
layer has more binder because it is holding the bigger chip, but
conversely it can be argued that the second layer has more surface area
to cover, as it is being applied to a textured surface. These are issues
which are clarified by experience, however as a general guide you should
expect the over all rate of spread to be at least 0.3 litre / sq metre
greater than the corresponding racked in dressing.
In any event any variation in the binder-spread category for one of the
layers should be offset by a similar opposite variation in the other
layer. (See the second paragraph in 9.2.3)
Advice on such variations should be obtained from the binder supplier
and / or contractor being used.
April 2003
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