Durability

Hanson’s aggregate blocks are inherently durable and if used in accordance with the appropriate British/European Standards, will last the lifetime of the construction into which they have been built. They possess good frost resistance and in general, provided they are selected following the recommendations of BS 5628: Part 3, clause 5.6 and Table 12, problems should not occur.

Strength and durability
Durability is governed by the characteristics of the units. The strength of concrete bricks would determine the suitability of the units (16.5 or 22.5 N/mm², depending on the application and exposure condition). In the case of aggregate blocks to be used near or below ground level, the unit should meet one of the following criteria.

a) Block density of at least 1500kg/m³, or
b) Made with dense aggregate to BS EN 12620, or
c) Having a compressive strength of at least 7.3N/mm³

All dense blocks, together with 7.3N/mm² lightweight blocks, would be suitable for the above condition. In the case of contact with foul drainage, Engineering Quality Concrete Bricks (EQCB) of 48N/mm² should be used.

Sulphate resistance
Where the masonry remains wet and sulphates are present, the selection of the unit needs further consideration. However, aggregate blocks have been used successfully below ground level for many years, with a proportion used on sites where sulphates are present and yet no failures have been reported. Whilst blocks meeting the general requirements for use below d.p.c. have been accepted as suitable for use in sulphate soil classification DS-1, work by the Concrete Block Association, has shown that the 7.3N/mm² aggregate blocks tested were able to withstand conditions equivalent to sulphate soil classification DS-3.

Carbonation is a major factor in achieving the necessary durability and results from the open texture and permeability of the aggregate block by allowing the surface to dry between the manufacturing and backfilling operations.

7.3N/mm² Evalast blocks manufactured using OPC, OPC-PFA, or SRPC binder would be suitable for up to and including sulphate soil classification DS-3 as determined by the method given in BRE Special Digest 1. Where OPC is the sole binder, backfilling should not take place for 28 days. (Please consult Hanson’s Product Services department for further information).

Note: The use of 7.3N/mm² Fenlite blocks is possible in aggressive soil conditions. Please consult Hanson’s Product Services department for further details.