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Last edited 23 Feb 2018
Compressive strength of expanded polystyrene for civil engineering
Expanded polystyrene (EPS) has been successfully used as a light weight fill material in civil engineering applications for many years. However there is conflicting information in the market place regarding the compressive strength properties of EPS. So what is fact and fiction?
 Short term compression
The EPS market has traditionally quoted 1% compressive strength figures in literature, data sheets and websites which are based on short term rapid load tests. These tests are short term compression laboratory tests involving a load being applied and then removed after a short period of time. See Table 1.
This data obtained from a 1994 Transport Research Laboratory Report applies only to embankments and landscaping applications NOT civil engineering applications with long term imposed loads. The report has been superseded by BS EN14933:2007 Thermal insulation and light weight fill products for civil engineering applications — Factory made products of expanded polystyrene (EPS) — Specification.
 Long term compression
For civil engineering applications BS EN14933:2007 recommends that engineers use 2% compressive stress figures to calculate the required grade of EPS material. These figures are extrapolated in accordance with BS EN1606:2013 to provide 50 year long term data reflecting the actual compressive creep that would take place over the life span of the EPS once installed and carrying the maximum imposed load. See Table 2.
 Product classification
EPS products are also classified into types based on the 10% compressive strength figures, an extract of Table C.1 - Classification of EPS Products is shown in Table 3 below taken from BS EN14933:2007.
 Product comparison
The Construction Products Regulations (CPR) makes the technical specification of construction products transparent which means manufacturers must comply with harmonised standards such as BS EN14933:2007 when placing products on the market.
Table 4 compares the physical properties of some of the most popular EPS products manufactured to BS EN14933:2007 and sold in the UK for use in civil engineering applications. For the purpose of this comparison we have used the Compressive Strength at 10% figure and Nominal Density (kg/m3) to show the products are identical in terms of performance*
As is evident from the comparison table the products are identical in terms of performance as per the requirements of BS EN14933:2007 and therefore engineers can specify like for like product without concern.
NB Data obtained from RIBA Product Selector, manufacturers Declaration of Performance certificates and manufacturers websites.
--Styrene Packaging and Insulation Ltd 11:31, 18 Jan 2018 (BST)
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