Section B Substructure
Material for use under concrete floors
It is important that all granular fill material is fit for the purpose it is intended. The recommendations are as follows:
The hardcore bed should be a minimum of 150 mm thick. Hardcore should conform with I. S. EN 13242:2002 (1) and meet the specification as outlined in Annex E of the accompanying guidance document to this standard, SR 21: 2016 (2). The hardcore layer should be well compacted, clean and free from any matter that would likely cause damage to the concrete. Specific guidance is given in Clause 3.4.2 of SR 21: 2016 on limiting the presence of a reactive form of pyrite which may give rise to swelling or sulphate attack on concrete.
A blinding layer should be provided, for fines material in accordance with the specification given in Annex E of SR 21: 2016. The blinding layer should be of sufficient depth to ensure surface voids are filled and therefore providing an even surface free from any sharp projections. It is important to ensure that there are no sharp projections as they may damage radon or damp-proof membranes.
(1) Irish Standard I.S. EN 13242: 2002 – The standard of aggregates for unbound and hydraulically bound materials for use in civil engineering work and road construction.
(2) Standard Recommendation (SR) 21: Guidance on the use of I.S. EN 13242:2002 +A1 :2016 – Aggregates for unbound and hydraulically bound materials for use in civil engineering work and road construction.
I.S. EN 13242 and SR 21 are available from the National Standards Authority of Ireland www.standards.ie
Table E.1— Recommended properties, test methods and test frequencies for unbound granular fill for use under concrete floors and footpaths of Annex E from SR 21 is reproduced below. The information provided below, as with all standards referenced throughout, should be confirmed as the most up to date version prior to reliance on the information.
Table B4 - Example specification for unbonded granular fill for use under concrete floors and footpaths
Important Notes - All granular material should be fit for the purpose for which it is intended and recommendations for material to be used under concrete floors and footpaths are contained in I.S. EN 13242 and SR 21. When ordering material for use under floors and footpaths confirmation should be obtained that the granular fill material is suitable for use in its intended purpose and confirmation of same should be provided on the delivery docket that the material is for use in these areas is in accordance with these recommendations.
Compacted layers of granular fill material should not exceed 225 mm in thickness.
Should the depth of granular fill be required to be in excess of 900mm due to specific site conditions then a suspended floor construction should be used.
The purpose of blinding is to sufficiently fill surface voids and provide firm and even support for support chairs for reinforcing steel in the case of reinforced slabs. It is also necessary to provide a good surface for working.
Avoid sharp points in the blinding which may puncture or damage the damp-proof membrane.
Image – Blinding in progress