This comprehensive source of information on the use of marine aggregate in construction provides technical information and links to sources of detailed information to assist in specifying and use of marine aggregate. The Marine Aggregate Information Centre is managed on behalf of The Crown Estate and supported by the Marine Aggregate Industry
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CHLORIDES

Chlorides may be present in concrete from other constituent materials, eg. cement and admixtures, the contribution from aggregates should therefore be kept in perspective.

The issues relevant to chloride content are:

1. Protection of  reinforcement

The use of marine aggregates has not been a significant cause of reinforcement corrosion. Field evidence shows that, provided that the chloride levels in the hardened concrete do not exceed the limits specified in BS8500, and that the normal criteria for concrete quality and depth of cover are applied, there is no significant additional risk from the use of marine dredged aggregate in concrete.

Guidance given in European and British standards for chloride ion content can be summarised as follows-

BS EN 12620
Requires the producer (supplier) to declare the water soluble chloride ion content. (A value of 0.01% may be used if the chloride ion content in the combined aggregate is known to be 0.01% or lower).

BS EN 206 -1
Defines the chloride class depending on type of reinforcing to be used. The class specifies the maximum chloride content on concrete by mass of cement from the total contribution of all the constituents

The actual limits are shown  in the table below-

chloride table


BS 8500 -1

Gives UK guidance on the appropriate chloride class that should be specified. Concrete that has to be prestressed (and concrete containing reinforcement or other embedded metal that is to be heat cured) should be specified as chloride class CL0,01. However in post tensioned prestressed concrete and unbonded concrete, BS 8500 advises that the chloride class is dependent upon the type of structure, construction method and exposure. For example, for internal post-tensioned office construction, a chloride class of Cl 0,40 is appropriate.


2. Alkali Silica reaction


Since marine aggregates are petrologicaly similar to adjacent land based deposits they are no more or less susceptible to ASR. There is however a contribution to available alkali from the chloride content. Whilst this contribution is relatively small, it is required to be taken into account by the concrete producer when conforming to the guidelines and specifications relating to minimising the risk of alkali silica reaction. The marine aggregate provider is able to provide chloride ion content certification. Further guidance can be found in BRE Digest 330 (Alkali-silica reaction in concrete).


3. Control of Chloride during processing

It is not unusual for processing plants to have electronic monitoring equipment installed to assist in the monitoring and management of the chloride content in the wash water during aggregate processing. Testing of the final product forms part of all marine aggregate producers factory control procedures as required by BS EN 12620.

All marine aggregate producers are required to provide chloride ion content certification in compliance with BS EN 12620 and PD 6682-1.

Further information

Click on the orange links below for further information. These links are to external websites and will open in a new browser window.

British Standards Documents
BS EN 12620:2013

BS EN 12620:2013
Aggregates for concrete

PD 6682-1:2009+A1:2013

PD 6682-1:2009+A1:2013
Aggregates for concrete. Guidance on the use of BS EN 12620

link logo 3  BS EN 206-1:2000

BS EN 206-1:2000
Concrete – specification ,performance, production and conformity

BS 8500-1:2006+A1:2012

BS 8500-1:2006+A1:2012
Concrete - Complementary British Standard to BS EN 206-1. Method of specifying and guidance for the specifier

BS 8500-2:2006+A1:2012

BS 8500-2:2006+A1:2012
Complementary British Standard to BS EN 206-1. Specification for constituent materials and concrete