4.7 Structural performance
4.7.1 Walls
The principles of the structural design of Aircrete blockwork are
the same as for any type of solid masonry. The design may be undertaken
according to BS 5628 Part 1: Structural use of unreinforced masonry.
However, to obtain structural integrity, the structural design of
Aircrete block walls of dwellings should be in accordance with BS
8103 : Part 2 : Code of Practice for masonry
walls for housing or the appropriate simple rules in Approved Document
‘A’ of the Building Regulations. Approved Document A was
amended in 2004 and came into effect from 1st December 2004. The new
AD extended the rules to be applicable with the appropriate British
Standard and the new European Standards for masonry units (EN771 series).
The required compressive strengths are given in figure 13 and are
applicable when the dwelling falls within certain limitations of the AD
A rules.
The walls of buildings or parts of buildings which are outside the
scope of the rules of BS 8103 or the simple rules in Approved Document
‘A’ should be designed in accordance with BS 5628 : Part
1.
When designing to BS 5628, the partial safety factor for material
(γm) would normally be taken as 3.5.
The BS 5628 contains two categories of manufacturing control and two
categories of construction control, “Normal” category
and “Special” category.
AACPA member companies can on request manufacture Aircrete blocks in accordance with
the “Special” category manufacturing control, allowing
γm to be taken as 3.1 rather than 3.5 if desired. This has the effect
that a 100mm thick Aircrete block with a compressive strength of 8.4N/mm can be used to provide the same load bearing capacity as a 10N/mm block from a manufacturer operating “Normal” category
manufacturing control. (When specifying masonry units to EN771-4,
"Special" category has been replaced by the designation "Category I"
and "Normal" by "Category II".)
Furthermore, when the blocks are “Special” category, if
“Special” category construction control (which includes
regular testing of mortar on site), is also undertaken, γm may be
taken as 2.5.
Aircrete block walling over openings should be supported by suitable
lintels or beams.
An Aircrete inner leaf below dpc can normally be the same strength
density and thickness as the inner leaf it supports above dpc.
When solid Aircrete blockwork walls are used below dpc their thickness
should generally be not less than the overall thickness of the cavity
wall it supports above dpc. 4.7.1.1
In general purpose mortar
The structural design of Aircrete blockwork in general purpose mortar
should be in accordance with BS 5628 and mortars which are compatible
with Aircrete
should be used.
The following mortars are generally suitable above dpc: Cement:lime:sand
1:2:9 or 1:1:6 (designation (iv) or (iii) Clause 28.2 BS 5628 :
Part 1).
Plasticised mortars which are no stronger may also be suitable.
Overstrong general purpose mortar should not be specified as their
use may lead to cracking. Lower strength general purpose mortars
are more compatible with Aircrete.
Below dpc the mortar should be stronger e.g. 1:1/4:4 and sulfate
resisting cement may be required depending on the ground and ground
water conditions.
| 
