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THE NORWEGIAN INSULATED BLOCK CONCEPT

M.Sc./Civ.Eng. Bj0rn vik, R&D manager M.Sc./Civ.Eng. Oddvar Hyrve, Tech.manager

Aker ExClay Norway/ Norsk Leca

ABSTRACT

The Norwegian insulated sandwich block concept, with PUR foam between two slender blocks made of lightweight aggregate (LWA) concrete, has been a success in the Norwegian market. This block concept has led to new architectural trends in the traditional timber frame house country of Norway, and ma de block masonry visible in the landscape. This document gives a description of the block concept, documentation of properties connected to thermal insulation, sound, fire, strength etc. This paper also gives practical advices connected to design, details and workmanship, and 'some idéas about the (patented) production technology.

1. INTRODUCTION

The Aker ExClay group, with origin and headquarters in Oslo, Norway consists of the companies Norsk Leca (Norway), Svensk Leca (Sweden), Fibo (Denmark), Leca Deutschland (Germany) and Leca Portugal.

The basic product of the company is the Lightweight Expanded clay Aggregate, in many countries known under the registered product name LECA.

Compared to other countries, the history of Leca in Norway is a very special one. The lightweight aggregates produced in Norway was only to a very little extent made available to the open market. The major part of the production went into more refined products like lightweight blocks, elements and chimneys produced within our own company.

Making the product sortiment of Norsk Leca on a relatively high leveI of technology and know-how, very soon gave us a dominating position in the Norwegian market, and also allowed us to influence the building traditions. New products and technology from Norsk Leca has an impact and confidence in the market, and gives us the economy to play a leading role also in the international development of masonry. In fact we had the unique situation in the timber frame country Norway (1987) with a sal e of 1 m' Leca masonry per inhabitant, or approximately 80 % of the total masonry market.

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The Norwegian insulated block concept described in this document was introduced to the market in 1982. So far we have sold approximately 2.000.000 m2 of this product in Norway, with continuously increasing market shares.

2. THE PRODUCT "LECA ISOBLOCK"

2.1 The Product concept

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Fig. 2. I. The 3 componeflts 01 lhe Leca Isoblock syslem: Standard-, Corner- and U-block.

The basic element of the concept is a sandwich block, with polyurethane (PUR) foamed between two slender lightweight aggregate (LWA) concrete blocks. The system consists of three components: The Standard block, the Corner block and the U­block. The design of the block, and the product properties has already been changed a couple of times since the first introduction on the market, due to changing building regulations and requirements from the market. The actual block of to day has the design shown in figo 2.1. The LWA concrete density is 900 kg/m' and the compressive strength 4,0 N/mm2.

The polyurethane (PUR) is CFC-free, with a design lambda-value of 0.026 W/mK according to Norwegian Standards and third party controlo

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2.2. Thermal properties

2.2.1. The history of thermal insulation

The massive Leca block was introduced on the Norwegian market in the middle of the 50-ies as an insulating product. The U­value of 0.8 W/m'K was accepted in externaI walls until after the oil crisis in the 70-ies, when concern to energy conservation was really put on the agenda.

In 1978 the first insulated block was introduced in Norway, with a loose 100 rnrn piece of polystyrene put into a cavity. The block was procuced on a German licence (Gebhardt, Aichstetten) and gave an U-value of 0.45 W/m'K with wall thickness 300 mm.

The revised building regulations of 1981 lowered the maximum allowed U-value to 0.35 W/m'K, and it was not possible any more to fullfill this with a block containing thermal bridges.

The only way to go, was to develop a sandwich block concept. The first prototypes of the sandwich type Leca Isoblock with PUR was produced as early as in 1977, just to "see if it was possible". In 1980 the development work was intensivated, including comprehensive documentation work and pilot building projects. It was possible to reduce the thickness of the wall from 300 to 250 mm and at the same time reduce the U-value from 0.45 to 0.35 W/m'K.

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So far everybody were happy, and the annual sales volumes were steadily increasing. But then it came as a shock to the world: The CFCs used in PUR (and a lot of other applications) were hazardous to the ozone layer!

One of the reasons for using CFCs in PUR is the very low therrnal conductivity of the CFC gas. No alternatives known to day have the same good therrnal properties as CFC. After 2 years of massive research and development it was possible to introduce a new CFC-free Isoblock in 1989. It was necessary

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however to increase the thickness of the insulation layer to compensate the somewhat higher thermal conductivity of the new PURo By using a stronger LWA concrete in the leafs (increase from 3 to 4 MPa) it was possible to maintain the same total thickness 250 mm and the same load capacity of the wall, and even lower the total U-value by 10 %.

2.2.2. The sandwich principIe

The requirements of Northern Europe to thermal performance do not allow block systems with thermal bridges, within reasonable wall thicknesses. If the wall is to be built up by one single block, the sandwich principIe must be used. For this purpose polyurethane is a most unique material. PUR has got an extremely low thermal conductivity, allowing the wall to be as thin as possible. At the same time PUR is an exellent adhesive keeping the two block leaves together.

Due to joints in the masonry, the PUR layer will not be continuos. Tests have shown that 10 mm gap of stillstanding air in the horizontal joints have little effect on the total U-value of the wall. Twin mortar joints of lightweight mortar is recommended. The vertical joints must be as tight as possible, and no mortar is used here. In normal wall hights the U-block with its thermal bridge will take 10 % of the wall area. This is included in the U-values given in figo 2.2.1.

2.3. Other properties

2.3.1. Fire resistance CD

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Fig. 2.3./. Full scalefire test according to NS 3904 (/SO 834) carried out at The Norwegial/ Fire Resaerch Laboratory: I . Temperature betweel/ inller leaf and PURo 2. Temperature between outer leaf mui PURo 3. Temperature on outer suiface. The temperature inside the ovell is ill accordance with ISO-curve, i.e. 1050 °C after 2 hours offire.

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A fire resistance of A 120 covers the most applications of residential and other ordinar buildings. The LWA concrete of the leaf of the Isoblock gives a good fire protection to the PUR core. By using the Corner block and U-block it is possible to obtain a complete protection also in window openings etc. The fire classification is depending on a rendering on at least one side of the masonry. Studies carried out on Isoblock buildings damaged by fire show only surface damages on the walls. Fire retarders may be added to the PUR mixture, but in Norway this is not required.

2.3.2 Sound insulation

The sandwich construction with two slender block leafs combined with a flexible PUR core gives a considerable drop in airborne sound reduction in a minor frequenze band (400Hz). By this reason the Isoblock is not recommended in internaI walls with requirements to sound reduction. In externaI walls with traffic sound the reduction will normally be sufficient compared to other normally used constructions.

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2.3.3 Load capacity

Fig. 2.3.2. Full scale test 01 sound reduction according to NS 8171, with a thin cement rendering on both sides 01 lhe wall.

The safety factor for normal masonry is 2,5, which gives a design value for vertical loading of 0,96 N/mm' according to NS 3475. Slenderness and eccentricity are criticaI factors which must be taken into account.

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Fig. 2.3.3. Design values for 10iU/ capacity, by vertical actioll. Loads shall be multiplied with safety factors accordillg to NS 3479 (values in the rallge of 1.0 - 1.6).

2.3.4. Hoisture control

Penetration of rain water is avoided by the use of adequate surface treatment and proper details around windows etc. The porous structure of the LWA concrete will to some extent ventilate away minor quantities of moisture.

Water vapour diffusion from the inside will be stopped by the diffusion tight PUR-layer. Experiences so far have shown that the diffusion through the somewhat open joints is neglible, og has no practical effect.

2.4 FieId of appIications

Fig. 2.4. me "Iso Cubo system, ali example o/modem desigll of chained sillglefamily residential hOllses based 011 Leca lsoblock.

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Leca Isoblokk is ideally suited for external wall, loadbearing or nonloadbearing. On the basis of Norwegians regulations and design codes the range of loadbearing structures with Leca Isoblock is limited to 3-4 stories. With a loadbearing framework of concrete or confined masonry, the Leca Isoblock may be used also in industrial buildings as a outer shell.

The traditional Norwegian way of housebuilding is the timber frame house with a wooden surface. New trends due to international influence and environmental aspects show increasing interest for masonry also in residential buildings. To some extent the market has recognized the masonry house as "exclusive". The tradition of do-it-yourselv on the single family dwelling market is also positive for Isoblokk masonry.

3. CONSTRUCTION. AND DETAILING

The Leca Isoblock "package" is specially designed for the do­it-yourselfer, with reinforcement system, lightweight mortar, dry mortar for rendering and surface treatment and easily understandable manuals for design and workmanship. The simplicity of the system makes it at the same time very cost effective for professional contractors. Idéas and complete drawings for single family houses are available, and it is also possible to order complete houses of certain designs from selected contractors.

Twin strips of mortar (shell bedding) must be used, and no mortar in vertcal joints. Reinforcement shall be placed in every 2. horizontal joint to prevent cracking from shrinkage and temperature movements. Long walls should be provided with movement j oints. As final, surface treatment we strongly recommend cement- og sil'ícate-based paintings. Due to the open porous s ,tructure of the LWA concrete, special attention must be ma de to prevent air infiltration into the walls and into the buildings.

4. PRODUCTION TECHNOLOGY

The first 2 production plants in Norway were based on a carouselle principle, with limited capacity because of much handling and man-work. As the sales volumes increased, it was necessary to develop a complete new production technology. In 1987 the first continuous production line was put in operation. Blocks are taken directly from the curing chamber and automatically placed in pairs on a conveyor belt, foamed together with PUR, and properly cured during the time it takes to pass the conveyor. The patented production line is developed by our Danish sister company AIS Fibo. Since that time 2 production units are sold to Finland, and a second unit is put into operation in Sweden within our own company group.

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Fig. 4. The principie of malerial flow Ihrough a Leca Isoblokk piam: I. Blocks coming from curing chamber. 2. Pairs of blocks automalical/y pUI onto double conveyor belt. 3. Conveyor belt. 4. Shrink wrapped paI/eIs of I m' Isoblocks.

5. FURTHER OEVELOPMENT POSSIBILITIES ANO TRENDS

The sandwich Isoblock concept as described in this document is flexible for further development and alternative solutions. A splitted version is introduced to the Norwegian refurbishment market this year. A non symmetric Isoblock with load carrying capacity on one side and a thin pigmented leaf on the other side is also possible. For even better thermal performance the possibility of toung- and groove-solution in the insulation layer is discussed. A better U-value may also be obtained by increasing the thickness of the PUR layer and the total thickness of the block. The production principIe is flexible to most of these wishes.

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Fig. 5. Leca Iso Rehab, a splilled version ofthe Isoblokk, introduced lo lhe Norwegian reJurbishment market Ihis year (1991) .