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Weber Saint-Gobain - Official website of the company


What is Leca® LWA ?

It is clay fired at very high temperature.

Leca® LWA was first produced in Scandinavia in the 1930's for the production of lightweight blocks, it was soon discovered that the insulating properties of the material could be of benefit to failing highways and railways througout Scandinavia and in 1958 following many years of testing Leca® LWA was accepted as a properietary fill material in the Scandinavian countries.

The raw material selection and production of Leca® LWA is strictly controlled to ensure a uniform, high quality product that is structurally strong, stable, durable and inert in addition to being lightweight and insulating.  Today Leca® LWA is used in many applications such as Geotechnical Fill, Masonary Blocks, Horticultrual Blends, Filtration and Bio-filtration.

How is Leca® LWA manufactured?

Leca® LWA ia a ceramic lightweight aggregate produced by expanding selected clays; glacial clays tend to contain most of the essential properties allowing expansion when heated to their optimum.Once treated, the excavated clay is passed through a rotary kiln and fired to a temperature of approximately 1150°C.  This process expands the material 4 to 5 times its original volume creating ceramic pellets with a cellular inner structure.

Where are the materials sourced/produced?

a. We have kilns across Europe but our material is imported from our Danish kilns in Hinge, Randers, Denmark and we mainly use Kings Lynn Port.

b. Kings Lynn is our most cost effective port.  Generally we can keep stocks of 6 - 7,000m³ at the quay side but provided we know the programme, we can arrange shipments on a regular basis to prevent stock from running out.  If the volume was in excess of 100,00m³, we would need a least a months notice to ensure the kilns production is programmed accordingly.

Will any measures be needed to protect the fill material from degrading under any circumstances?

a. Provided a geotextile is used to separate the Leca® LWA from any material containing fines and an adequate capping layer is used, no.

b. During construction however, in order to limit mechanical breakage which usually occurs in the top 75 - 100mm layer, it is best to compact using the deepest compaction layers possible - up to 1 metre.  This breakage though will not affect the performance of the Leca® LWA but may increase the reduction in volume from 8-12% to as much as 15-20% if thinner layers are installed and heavy equipment used.

c. Leca® LWA is ceramic (fired clay) which is not known to degrade.

What is the steepest slope that can reasonably be achieved for the embankments given that they may be up to 11m high?

a. Page 5 of the attached construction control document states a 1:2 slope however, other methods are available should the slope face need to be increased.  Refer to slope stability sketch on page 11 of the attached Leca®
LWA brochure.

b. The angle of friction given for Leca® LWA 10-20mm is 35-39 degrees (average 37°).

Will the material have any adverse affects or environmental issues regarding flora & fauna?

a. None - refer to all of the Leca® (FiboExclay) doc attached

b. Leca® is used by many horticulture applications such as green roofs, soil mixes to increase aeration to the roots and by the British Orchid Grower Association.

Are there any issues with destabilisation of embankments by animals?

a. None known.  We would not expect any different problems to that experienced by embankments of traditional fill.

Will roots of trees etc., potentially destabilise the embankments?

a. Again none known but we would not expect any different problems to that experienced by embankments of traditional fill.  It is more likely that root growth through the Leca® LWA would bid the material adding strength.

As embankments are in possible flood risk areas, what are the issues associated with floatation/degradation of the materials or might there be any other issues caused by the embankment location?

a. Leca® LWA is a stable ceramic pellet hence no degradation has been experienced or expected to the material.  The compacted fill allows water to rise filling all the voids between the pellets and then quickly drain away.  The individual pellets will absorb a percentage of the water, increasing over time with experience being a maximum of approx 85% of material weight with long term saturation.  They will though dry out eventually once the water has subsided.  For more information, please refer to the 'working with Leca® LWA and water' doc.

What differential settlement issues might there be if high embankments are constructed from lightweight materials but when the embankment reduces in height more standard fill material being adopted. If so how are these issues resolved?

a. The embankment shouldn't reduce in height using Leca® LWA unless there are extenuating circumstances in the sub structure or the height needs to be reduced mechanically.

b. If the embankment is settling due to soft sub-soils then providing the standard fill is installed evenly as a new capping layer there should be no issue.

c. If the embankment is reduced mechanically then replace the geotextile separator and re-cap as per the original installation.  If differential settlements are likely then a geogrid could be used to spread any load that might be expected, always check calculations based on difference in loadings.

Where trenches etc., have to be dug in the material, what issues are there & how have they been overcome elsewhere?

a. As with all trenches; adequate trench support should be used when digging beyond maximum unsupported depth criteria or if the conditions are deemed unstable. Leca® LWA pellets have open pores on the surface (see diagram, page 1 of 'working with Leca® LWA and water' doc) which helps in achieving the friction angle of 37deg.  When compacted, the pellets interlock and will remain that way when compacted and capped, for this reason, the  Leca® LWA should stand without total ravelling for a limited period i.e. to allow the installation of draimage, ducting etc. (see picture on rear of Royal Albert case study) - however, we would recommend that relevant Shoring equipment is used in accordance with Health and Safety Guidelines.

Safety fencing will be required on the embankments, will the material provide adequate support for normal driven posts or will another foundation system be required?

a. If it is a crash barrier, it would probably be best to increase the depth of the capping layer in that area in where posts are planned.  However, if it is simply a safety fencing or perimeter fence or sign post, etc., it is usual that a minimum 250/300mm diameter sleeve is initially positioned in the Leca® LWA, ready to accept the posts which are then concreted and secured in to position.

The embankments may be landscaped, porentially with trees. How will the material support & nourish the planting that may be required?

a. See page 37 to 39 within the Leca® LWA (Fibo Exclay) doc. and page 13 of the Profilbrochure (Danish marketing doc).

b. Pages 36 - 39, if the material is needed as a support to the planting of mature trees, then it may be advised to insert a former into the area where the tree roots are to be planted and when planting is to take place mix the soil with Leca® LWA, remove former and plant as normal; however if the plants are young as they are in most cases such as this then planting directly into the topsoil capping layer will suffice and let nature do it's thing as we can see by the photos of the recently planted M1 project.

Might the material restrict growth of the possible landscape planting on the embankments?

a. No - refer to the entire Leca® LWA (FiboExclay) doc.

b. Leca® LWA is used as a growing medium so will actually promote growth.  In this instance there will be a geotextile and topsoil between the Leca® LWA and the vegetation during planting, however, after a period of time the roots will find their way through the woven geotextile and work with the Leca® LWA where they will receive air and moisture trapped naturally within the material. 

What is the carbon footprint of providing the material - especially in comparison to other locally sourced standard bulk fill materials?

a. A new study is currently being carried out on the material as our data is not current - we envisage that this will be available later this year.

b. Due to the fact that Leca® LWA is produced in a kiln the figure starts out quite high, however, working with the Danish Government, materials that would normally go to landfill are used in the burning to heat the kilns which in turn reduces the carbon footprint of the material.  The heat produced is also re-directed as a renewable energy for the factory/offices.

  • Then we move the material a short distance to the port and ship from Denmark to England, as we are able to ship so much material on one cargo the CO2 emissions per m³ are reasonably low.  Once the material reaches the porth in the UK it stays there until it is required by the customer, so there is no double handling to various stock yards.  When it is needed we transport as much as we can on one vehicle - i.e. the walking floor trucks which in June 2011 one delivery was calculated at 102m³ but generally they would be between 75 - 90m³.  Thus reducing the amount of delivery vehicles by up to 8!
  • When the material is on site the overall energy exerted during the placement and compaction is by far reduced due to deeper compaction layers, less volume reduction during compaction and fewer passé with plant to achieve compaction.

Are there any issues on placing the materials?

a. Leca® LWA is easier to p;lace than traditional fills as it is so light to handle and can be installed in construction layers of up to 1metre depths.

Are the materials inert or subjecrt to degradation by fuel spillage, acids, fire etc?

a. Leca® LWA is fired clay making it inert and not subject to degradation, the material will not be affected by chemicall spill, rehydrate or combust.

Are materials subject to creep?

a. Data shows less than 3% creep in 100 year test which is as good, if not better than crushed rock.

Are there any particular storage issues such as dust, moisture loss etc., that could affect stockpiling (additonal costs for protection)?

a. We recommend storage to be on clean hard standing or geotextile covered area to avoid the migration of sub-soils or localised stone/rock being dragged into the material.

b. Inclement weather will not adversely affect Leca® LWA, it may increase in density if wet through, howver it will dry again and regain the lower density.

c. If storing in very dry weather conditions it may be advisable to damp/wet the Leca® LWA to avoid airborne dust.

d. If there is watercourse that is subject to flooding nearby then bunding would definately be recommended, or find an alternative storage area.

Are there any placing / compaction issues?

a. No - only bonuses in weight reduction and time savings on programme.

b. During construction in order to limit mechanical breakage which usually occurs in the top 75 -100mm layer due to point load of tracks on the pellet and vehicle turning etc., it is best to compact using the deepest compaction layers possible up to 1 metre and not 'over-compact' the material.  This breakage though will not affect the performance of the Leca® LWA but may increase the reduction in volume from 8-12% to as much as 15-20%.  In order to reduce the possibility of this breakage, in areas on particularly thin layers i.e. 150 - 500mm, you should reduce the size, type or weight of compaction equipment i.e. vibrating plate compactor if feasible.  (please refer to page 2 of the Leca® LWA Construction Control Doc).

Are geotextiles required for side slope stabilisation?

a. Geotextiles are not normally used for stabilisation but simply to prevent the migration of fines in to the Leca® LWA fill.

b. Geogrids on the other hand may be needed if the side slope was to be greater than 37 degrees but we can assist with specifics when it comes to it, rather than give a general answer.

Is a drainage layer required?

a. No, but om areas prone to flooding it may be a good idea to install weep pipes in the base of the embankment to allow the water to drain out of the Leca® LWA fill when waters subside.  If not, the capping layer may act as a tanking.

Are there any requirements for/issues with wick drains?

a. No issues.  If they were required, that would be identified during the design considerations due to loading etc.  Wick drains have been used with this material but it is advisable to consider the self draining properties of Leca® LWA before designing in wick drains which may not be needed.

Are there any durablility issues?

a. Long term durablility under dynamic load compaction tests shows Leca® LWA to perform better with less long term crushing, than stone.

What is the cost per m3

Costs vary depening on location, site conditions, special requirements that may be needed and the size of vehicles required.