Working with Leca LWA and Water. Leca LWA is a light weight expanded clay, formed by heating and firing natural glacial formed clays in a rotary kiln at temperatures up to 1150 C. The process transforms the clay into various sized lightweight granules, which have a hard ceramic shell and porous core. The most common grade of Leca LWA used in construction is the 10/20mmR due to the increased advantage of lightweight, free draining and insulating properties of this particular size. Figure 1 the Leca granule Where moisture and / or water are present within Leca LWA fill, installed or preinstallation, there are three areas to consider: a) Moisture effect on compaction b) uplift through buoyancy of the Leca LWA fill c) increased pressure to the underlying sub-soils This document will give advice on those elements that need to be measured to allow careful consideration during design stage. In the first instance, it is important to understand that compacted Leca LWA fill is highly porous. With the introduction of water, initial absorption is rapid however the absorption rate slows considerably once reaching the granules maximum moisture content. When placed in water, after a 5 minute period the 10/20mmR Leca LWA granule will take on about 21% water content. After 24 hours the water content will be approximately 36 % which then corresponds to approximately 30 % of the internal pores being filled with water.
Leca LWA laboratories performed long term tests using the BS EN 1097-6 test method. After 13 years (5000 ), the curves for Leca LWA 10/20mmR and 4/10mmR have not flattened indicating that the Leca LWA is still absorbing water. The same samples have now been tested for in excess of 13 years and this we believe to be the longest controlled test to date. This is the results visualised in a time water absorption chart. Absorption, % 150 Water absorption Leca (pyknometer method) 100 Leca 2-4 Leca 4-10 Leca 10-20 50 0 5 years 10 years 0 1000 2000 3000 4000 5000 Time, In the Production Control department at the Leca LWA plant in Hinge, Denmark water absorption is tested and declared according to BS EN 1097-6 Tests for mechanical and physical properties of aggregates - Part 6: Determination of particle density and water absorption. The water absorption is tested after 5 minutes, after 60 minutes and after 24 hours. A copy of the CE declaration for Leca LWA 10/20mmR is available upon request
A) Moisture effect on compaction Leca LWA 10/20mmR lightweight aggregate is delivered with a moisture content of up to 35%. For conventional fills, potentially high moisture contents such as this can affect the materials use on site. This section is intended to show the affect of moisture content on the Leca LWA 10/20mmR for compaction purposes. Density/moisture content relationship tests were conducted on the Leca LWA 10/20mmR in December 2007 using the 2.5kg Rammer Method in accordance with BS1377: Part 4 : 1990 Clause 3.3. Tests were conducted at a range of moisture contents ranging from 10.4% - 41.2%. The results of these tests are indicated below in table 1 and Graph 1. Moisture Content (%) Dry Density (Mg/m³) 10.4 0.488 20.2 0.477 29.5 0.488 36.2 0.476 41.2 0.462 TABLE 1 GRAPH 1 As can be seen from graph 1, the moisture content has little to no affect on the levels of compaction achieved within the expected moisture content range of delivered Leca LWA.
B) Uplift through buoyancy of the Leca LWA fill After installation with normal compaction of 8-12%, approximately 40% of the overall Leca LWA fill will remain as voids between the granules as shown in Figure 1. This means that for every 1m 3 Leca LWA fill, there can be up to 400 litres of water when fully submerged and buoyancy must then be take into account. As also can be seen within figure 1, there is a percentage of open voids within the granule to consider when the material is submerged. When dry and stored in normal external conditions, Leca LWA can take on a water content of about 30% within the granules in approximately half an hour. Once Leca LWA has been installed below surface level but above the water table the material can contain a water content of up to 45% in 3 5 years. Submerged in water, laboratory testing currently in excess of 13 years has proved that the maximum long term moisture content in the granules is expected to be no more than 85%. When considering the calculation of buoyancy, Archimedes law is our reference. Any object, wholly or partially immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object. Buoyancy = weight of displaced fluid. If the fluid is water, given that compacted Leca LWA consists of approximately 40% voids and consequently 60% granules/m 3, the buoyancy is 600 kg/m 3. The density of compacted 10/20mmR Leca LWA, including initial moisture content is 380 kg/m 3 (see Table 2) giving a resulting buoyancy of (600 380) 220 kg/m 3 which can easily be counteracted with normal road construction. A normal 190mm gravel layer can counteract buoyancy: (1800 kg/m 3 x 0.12m) = 220 kg/m 3 With time the density of the Leca LWA will increase thus decreasing buoyancy. To date Leca LWA have never been informed of any buoyancy issues when effective counteraction has been installed, even when Leca LWA has been supplied for use directly into water for harbour constructions.
Table 2 Density of compacted 10/20mmR Leca LWA, including initial moisture content C) Increased pressure to the underlying sub-soils Leca LWA 10 20 mm (Hinge Plant) Reference CE declaration (16040000) Average Loose bulk density 215 kg/m 3 Compaction 8 12% Average Compacted Bulk density 235 kg/m 3 215 x 1,1 = 236,5 ~ 235 kg/m 3 Approx. 43% voids between granules when 10% compacted. This is calculated by relating the bulk density with the declared particle density of 410 kg/m 3. 1m 3 Leca LWA 10/20mmR = 570 litre Leca LWA granules (1000 litre 430 litre voids). 410 235 410 = 0,426 ~ 43 % Tests and calculations have proved there to be approximately 84 % internal voids within Leca LWA granules. The 570 litre Leca LWA granules consist of 16 % (90 litres) furnaced clay. The remainder is 480 litres of internal voids. When Leca LWA is submerged, the internal voids are almost instantly filled with 30 % water. This is calculated by relating the declared particle density with the density for furnaced clay of 2610 kg/m 3. 2610 410 2610 = 0,843 ~ 84 % 570 x 0,16 = 91,2 ~ 90 litre 570 90 = 480 litre 480 x 0.3 = 144 litre 30% is equal to 144 litre of water. Total weight with 30% water content = 380 kg The moisture content is 38 % 235 kg Leca LWA grains + 145 kg water = 380 kg This is calculated by relating the dry bulk density with the actual density. 380 235 = 38,2 ~ 38 % 380 To fully consider the expected increase in pressure to the underlying sub-soils when fully submerged, the following Table 3 provides densities assuming the compacted Leca LWA 10/20mmR is at its heaviest worst case scenario.
Element Density state Correction factor Density 10/20R (kn/m³) Loose density Mean value 2.15 Material variation Tolerance value 1.15 2.47 Compaction Dry compacted density 1.12 2.77 Granule water content 30% saturated 1.3 3.60 Granule water content 45% saturated 1.45 4.02 Granule water content 85% saturated 1.85 5.12 Granule water content 100% saturated 2 5.54 Table 3 Worst case tolerances for increased pressure The loose density is the 'dry bulk' density of Leca LWA i.e. 10/20mmR which is then multiplied by 15% to give the heaviest the material is likely to be due to increased fines or smaller aggregate (i.e. tolerance). Compaction is between 8-12% reduction in volume and is therefore multiplied by 12%. This added to the expected percentage of moisture likely to penetrate the Leca LWA in the short term as previously described is 30% water intake. Installed and longer term is likely to be 45% and over a lifetime, the penetration seems to peak at 85%. To consider the voids around the Leca LWA granules after compaction, this can be calculated using the following equation: - external porosity = particle density - bulk density granule density Example: - for 10/20mmR the dry bulk density is 215kg/m³ and the particle density is 410kg/m³. The average compaction is 10% external porosity = 410 - (215 x 1.1) x 100% = 42% 410 Therefore for 10/20mmR Leca LWA at 100% saturated = 554kg/m³ + 420kg/m³ (water) = 974kg/m³ Where temporary flooding is expected it is not possible to give an exact density. However, Leca LWA would in a few years reach a long term density of approximately 450 kg/m 3. During temporary flooding more water will be absorbed into the Leca LWA and drain again when the flooding subsides therefore we would advise to use a density of 500 kg/m 3 as a maximum density for the settlement calculations.