Design of soil structures using Crushed Stone Wool insulation
FIBERING PROCESS
Figure 1. Stone wool insulation production and produced by-products.
The grain size of the by-products may be controlled by changing the crushing method. The edge trim is possible to crush into the two different fractions: RR-type grain size # 10…100 mm [Figure 2a] and PR-type grain size # 1…10 mm. The technical properties of the material do not differ notably according to the grain size. Crushed Stone Wool is also possible to pack in bags which considerable improves the compressibility of Crushed Stone Wool [Figure 2b].
At construction sites stone wool demolition waste may be crushed by mobile crushing equipment. Some tests have been performed and the results have been very promising. The grain size of the waste pieces is similar to industrially produced Crushed Stone Wool. In the future the utilization of stone wool demolition waste at construction sites is expected to
grow. In 1996 the amount of demolition stone wool waste was 900 m3and it is estimated to
increase to 14 000 m3/year between 1996 and 2010.
a) b)
3. Technical properties of Crushed Stone Wool
3.1 Chemical properties
Stone wool insulation is manufactured from natural minerals and its chemical composition may be compared with natural sand and stone. The binder content of stone wool insulation is 0.7…4.5%. The binder is phenol formaldehyde resin modified by urea. Oil is used as an admixture to improve the water-repellent properties of stone wool insulation. The main
components of Stone wool insulation are silicon oxide (SiO2), aluminum oxide (Al2O3) and
calcium oxide (CaO) and iron oxide (FeO) [Figure 3].
Chemical composition of Crushed Rock Wool
SiO2 40-50 % Al2O3 12-18 % FeO 5-10 % CaO 10-20 % MgO 10-20 % Na2O <2 % K2O <2 % TiO2 <2 %
Figure 3. Main components of stone wool insulation.
3.2 Physical properties
In factory conditions the edge trim separated straight from the product line is very dry (water content < 1 weight-%). In the ground conditions the normal water content settles between 20…25 weight-%. The other physical properties of Crushed Stone Wool to a considerable degree depend on the loading above the Crushed Stone Wool layer. Table 1 shows how the technical properties change with increased loads. The thermal properties of the material convert according to loading and water content, but as a dimensioning factor for thermal conductivity the value 0.10 W/mK may be used.
Table 1. Technical properties of Crushed Stone Wool according to loading.
Loading [kN/m2] Volume Weight [kN/m3] Settlement [%] Water Permeability [m/s] Capillary Rise [m] 10 1.6 25 10-4…10-5 0.07…0.10 20 2.0 37 10-4…10-5 0.07…0.10 30 2.2 45 10-4…10-5 0.07…0.10 3.3 Environmental aspects
4. Design of insulated structures using Crushed Stone Wool
4.1 Design principles
The design principles are based on existing instructions and regulations referring to insulation materials and methods in Finland but also the investigation results of Crushed Stone Wool are taken into account. The thermal properties of Crushed Stone Wool are considered when designing insulated soil structure.
4.2 Insulated soil structures
The insulation of soil structures will enable the reduction of frost heave damage when the subsoil is frost-susceptible. The most potential insulated soil structures using Crushed Stone Wool are lightly loaded soil structures like:
- Bicycle and pedestrian tracks
- Transition structures beside buildings and - Yards and parking places (no heavy traffic).
In Raahe, Crushed Stone Wool was tested as an insulation material in a bicycle and pedestrian track. The asphalt pavement of the old road structure was badly damaged because of frost heave. The new structure was improved by building an insulation layer of Crushed Stone Wool, with a final layer thickness of 100…200 mm depending on the thickness (400…800 mm) of the superstructure above. The type picture of the structure in presented in Figure 4. The overall length of the test road was 100 m.
DRAINAGE COURSE > 100 mm
SUB-BASE 210 mm
BASE COURSE 150 mm
PAVEMENT 40 mm
CRUSHED STONE WOOL LAYER 100-200 mm GEOTEXTILE
(STEEL NET FOR MORE STRENGHT)
Figure 4. Cross-section of the bicycle and pedestrian track in Raahe where Crushed Stone Wool was used as an insulation material in very frost-susceptible subsoil.
Inside the test structure sensors were installed to measure the water content, the temperature and the thermal conductivity of the Crushed Stone Wool layer. The temperatures of the superstructure and subgrade (up to 2 m from the asphalt surface) were also measured. The measurings have been executed for two years back and the test road has served as planned. No damage has appeared such as longitudinal pavement cracking caused by frost heave. No uncontrolled settlements have arisen so far even though this was a risk due to the soft nature of Crushed Stone Wool. According to the temperature measurements the Crushed Stone Wool layer efficiently prevents very frost from penetrating under the superstructure to the frost-susceptible subsoil. The deviation of
temperature above and below the insulation layer is 4…5°C degree during the coldest time of the winter.
5. Design of lightweight earth structures using Crushed Stone Wool
Crushed Stone Wool may be utilized as a lightweight material filling in different kinds of
soil structures. The dimensioning value varies between 2.0…2.5 kN/m3 according to the
purpose of utilization. Figure 5 presents a case where an old waste water settling pool was modified to a new waste water treatment plan in the unloading station of Metsä-Tuomela in Nurmijärvi. Extra earth filling around the new waste water treatment plan would have caused additional settlements which was why lightweight Crushed Stone Wool was used to replace natural soil. The total amount of Crushed Stone Wool was approximately 280 tons.
The volume of the pool was about 770 m3[Figure 5].
Figure 5. Cross-section of waste water settling pool in Nurmijärvi. Crushed Stone Wool was used as a lightweight material filling to eliminate settlements.
In embankments and noise barriers the lightweight property of Crushed Stone Wool may be utilized when situated in soft subsoil. The packed material [Figure 2b] may be the most suitable to build these kind of structures. The amount of material as a material filling
in a noise barrier varies between 1000…3000 m3 for every 100 meters. The density of
packed Crushed Stone Wool varies between 185…220 kg/m3 depending on loading. For
the dimensioning the unit weight value 2.0 kN/m3 may be used for packed Crushed Stone
Wool.
The compressibility of packed Crushed Stone Wool is not remarkable when the height of the noise barrier is < 3.0 meters. All expected settlements inside the Crushed Stone Wool structure take place immediately during the construction. Under the noise barrier a drainage course should be planned because of a capillary rise of ground water (clay
subsoil) is to be expected. It is necessary to make small holes (∅=50 mm) in the bottom
side of the bags to ensure the leakage water to flow through the structure. If water remains inside the structure, the weight of the material filling and the whole structure increases and
SOFT GROUND
BEARING GROUND
CRUSHED STONE WOOL IN BAGS GROWTH BASE 100...200 mm GEOTEXTILE EARTH FILLING GRASS DRAINAGE COURSE CAPILLARY RISE DENSITY 185...200 kg/m3 CRUSHED STONE WOOL BAG UNIT
Figure 6. Noise barrier using packed Crushed Stone Wool as a filling material. The size of one bag
is length∼0.8 meters, width∼0.4 meters and height∼0.3 meters.
6. Conclusions
Both the laboratory investigations and the experiences from the cases in Raahe and Nurmijärvi have been promising and the results positive. The utilization of Crushed Stone Wool gives a lot of benefits to soil structures such as good insulation against frost damage, lighter soil structures and reduced amount of demolition waste. The monitoring of the structures continues and all the new experiences gained are analyzed and noticed in planning new structures in the future. The aim is to take the utilization to a level where almost all produced stone wool insulation by-products and the main volume of demolition stone wool will be recycled.
References
Crushed Stone Wool in Earth Structures – The Bearing Capacity of Packed Crushed Stone Wool. 1998. Research Report (in Finnish). Partek Paroc Oy Ab, Innogeo Oy. Helsinki. 23 pages.
Crushed Stone Wool in Light Weight Structure – The Unloading Station of Metsä-Tuomela in Nurmijärvi. 1999. Research Report (in Finnish). Partek Paroc Oy Ab, Innogeo Oy. Helsinki. 7 pages.
Höynälä, H. 1998. The Geotechnical Properties of the By-products of the Stone Wool Industry. Master’s thesis (in Finnish). The University of Oulu, Civil Engineering, Geotechnics. Oulu. 71 pages.
Kujala, K., Palko, J. 1998. The Environmental Qualification of Crushed Stone Wool used in Earth Structures. Research Report (in Finnish). Oulu. 4 pages.
Insulation Layer of Pedestrian and Bicycle Tracks using Crushed Stone Wool. 1998. Intermediate Report of Test Road (in Finnish). Partek Paroc Oy Ab, Innogeo Oy. Helsinki. 25 pages.
The Utilization of Crushed Stone Wool in Earth Construction. 1998. I: Design and Dimensioning Descriptions, II: General Work Descriptions and Quality Requirements (in Finnish). Partek Paroc Oy Ab, Innogeo Oy. Helsinki. 31 pages.
VTT, Chemical Technology, Environmental Technology, Research Report KET 2598/98 (in Finnish). Espoo. 4 pages.