Civil Engineering Reference
In-Depth Information
BS 5628
BS EN 1996
Proportions of constituents from BS 5628-1
Ability to
accommodate
movement
Increasing
compressive
strength
Cement : lime :
sand
Cement : sand
Cement
(including filler
other than
lime) : sand
Cement (inc
lime) : sand
M20
Designed mortar from Table 1 - BS EN998-2
M15
Designed mortar from Table 1 - BS EN998-2
(iii)
M12
1 : 0 to 0.25 : 3
1 : 3
-
-
M10
Designed mortar from Table 1 - BS EN998-2
(iii)
M6
1 : 0.5 : 4 to 4.5
1 : 3 to 4
1 : 2.5 to 3.5
1 :3
M5
Designed mortar from Table 1 - BS EN998-2
(iii)
M4
1 : 1 : 5 to 6
1 : 5 to 6
1 : 4 to 5
1 : 3.5 to 4
NB - M4 is the minimum strength for reinforced masonry
M2.5
Designed mortar from Table 1 - BS EN998-2
(iv)
M2
1 : 2 : 8 to 9
1 : 7 to 8
1 : 5.5 to 6.5
1 : 4.5
M1
Designed mortar from Table 1 - BS EN998-2
Further guidance is given in BS EN998-2 Table 1 & NA to BS EN1996-1, Table NA.2 & BS 5628 table 1 (© BSI, London, UK)
Adapted from and courtesy of the British Standards Institution (BSI)
Table 20.2
Typical mortar designations. Permission to reproduce extracts from British Standards is granted by BSI
In accordance with BS EN998-2 mortars can be either
designed or prescribed. Designed mixes are performance spe-
cified by the designer with the composition defined by the
manufacturer. Designed mixes may include the following
performance criteria: compressive strength, type of mortar,
chloride content, air content, water absorption and maximum
aggregate size. A full list is provided in clause 6 and table ZA.1
of BS EN998-2.
Prescribed mixes are similar to those defined in BS 5628
in which mortar is defined using predefined mix proportions.
Similar mixes are present in the National Annex to part 1 of BS
EN1996, with further guidance given on the permitted types of
cement to be used.
Mortars can be manufactured in a number of ways including
site mixed, factory mixed or pre-batched.
Units > 250 mm high, overlap length at least 20% of the height
■
or 100 mm.
At junctions and corners the overlap should be equal to the width
■
of the units.
In natural stonework, bonding requirements in BS EN1996
vary to those of brick or blockwork. Clause 8.1.4.2 suggests
minimum overlap of least 40 mm or 0.25 times the dimension
of the smallest unit. For natural stonework in cavity construc-
tion bonding units with a length approximately two-thirds of
the wall thickness should be placed at a maximum of 1 m cen-
tres vertically and horizontally.
Stack bonding (masonry with no overlap) can be used for
decorative purposes and is normally an architectural feature.
BS EN1996 suggests that where masonry bonding does not
conform to the above limits, reinforcement should be used to
provide adequate resistance, this is often combined with an
increased number of wall ties per square metre in cavity con-
struction (Chudley and Greeno, 2008).
20.2.5 Bonding of brickwork (clauses 8.1.4)
Brickwork and blockwork can be bonded in a number of ways.
Brickwork has greater flexibility to create patterns; however,
blockwork can follow similar principles by either cutting of
blocks or using special units.
BS EN1996 discusses the bonding of both cut and manu-
facturer units and suggests that units should generally be
bonded together based on experience or proven practice.
Typical brickwork bonds are shown in
Figure 20.1
(Chudley
and Greeno, 2008).
The basic bond requirements for manufactured brick and
blockwork are given in clause 8.1.4.1 as:
20.2.6 Types of construction
20.2.6.1 Cavity walling (clause 8.5.2.2)
Cavity walling has been popular in the UK since the 1930s
(IStructE, 1996) and is used in domestic and commercial con-
struction. This form of construction helps mitigate damp by
introducing a cavity between the internal and external leaves
of masonry. Cavities are now often filled with insulation to
increase thermal performance, making it ideal for domestic
construction in mild climates.
The internal and external walls are tied together using wall ties
at regular centres. Provided the ties have sufficient tensile and
Units < 250 mm high, overlap length at least 40% of the height
■
or 40 mm.
