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Posted: Thu May 21, 2009 2:37 pm
by martin.ball
I notice that the Specification for Highways works includes clauses for several other aggregate grades aswell as type 1 - how do these compare to type 1 - and can they be used in place of or with increased thickness?
many thanks.
Posted: Thu May 21, 2009 6:37 pm
by msh paving
those spec. are off no use to you, stay with type 1 MSH 
Posted: Thu May 21, 2009 8:45 pm
by DNgroundworks
Out of interest what is the difference between type1 and type 2?
Posted: Thu May 21, 2009 10:43 pm
by GB_Groundworks
There are 2 types of GRANULAR SUB-BASE:-
GSB Type 1 and GSB Type 2, these materials are specified and described in the,
Specification for Highway Works, the "800" Series
GSB Type 2 is a much finer material, has a much wider grading envelope and is of a lesser "engineering" quality than GSB Type 1 which has a "tighter" grading envelope allowing much less fines and encouraging a "well graded" material.
N.B. Be aware that these materials are now collectively know as "Unbound Mixtures, Type 1 or 2, or several other variations, again I leave the original description in this text but be aware of the changes, read the current "800 Series" for guidance, able to be download from the previously provided website link.
The SUB-BASE can also acts as a drainage layer, and some organisations have a "Type 3" GSB, designed to have less fines content to improve the drainage properties of the material.
http://www.standardsforhighways.co.uk/mchw/vol1/pdfs/series_0800.pdf
Edited By GB_Groundworks on 1242942336
Posted: Fri May 22, 2009 9:17 pm
by Big Phil
The difference is that Type 2 allows the use of Gravel & Sand which leads to slightly finer grading, this was introduced by highways engineers in the South East as their geology is predominately Sand & Gravel and importing Limestone is too costly. There is also a spec limit on optimum moisture content, but unless you're a highways engineer this may not be a concern :laugh:
Type 1 and 2 grading tolerances overlap eachother, so in many cases it can be the same material as supplied.
Type 3 subbase is more open graded to allow drainage and is great for SUDS construction.
Posted: Mon May 25, 2009 6:55 pm
by Mainland
You dont need to worry about any other spec than type 1 for diy applications.