Bubble Deck Technology

Bubble Deck Technology

1. Introduction 1.1 Concrete Floor Systems Reinforced concrete slabs are components commonly used in floors, ceilings, garages, and outdoor wearing surfaces. There are several types of concrete floor systems in use today, and are shown in Figure 1-1: 

Two-way flat plate (biaxial slab) - There are no beams supporting the floor between the columns. Instead, the slab is heavily reinforced with steel in both directions and connected to the columns in order to transfer the loads.

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Two-way flat slab with drop panels- This system differs from the two-way flat plate system by the drop panel used to provide extra thickness around the columns. This strengthens the column to floor connection in consideration of punching shear.

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One-way beam and slab- This is the most typical floor system used in construction. The slab loads are transferred to the beams, which are then transferred to the columns.

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One-way joist slab- The joists act like small beams to support the slab. This floor system is economical since the formwork is readily available and less reinforcement is required.

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One-way wide module joist slab- This system is a variation on the one-way joist slab with wider spaces between the joists.

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Two-way joist slab (waffle slab) - This floor system is the stiffest and has the least deflection of those mentioned since the joists run in two directions (Concrete Reinforcing Steel Institute)

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Figure 1-1: Types of Reinforced Concrete Floor Systems (Concrete Reinforcing Steel Institute)

Reinforced concrete has many advantages for floor systems- it provides resistance to high compressive stresses and to bending stresses; it is relatively cheap to produce and construct; and it can be molded into virtually any shape and size. Disadvantages include a high weight-to strength ratio and difficulty in structural health monitoring (Reinforced Cement Concrete Design).

1.2Hollow-Core Slabs In the mid-20th Century, the voided or hollow core floor system was created to reduce the high weight-to-strength ratio of typical concrete systems. This concept removes and/or replaces concrete from the center of the slab, where it is less useful, with a lighter material in order to decrease the dead weight of the concrete floor. However, these hollow cavities significantly decrease the slabs resistance to shear and fire, thus reducing its structural integrity. This floor system typically comes in the form of precast planks that run from 4 ft to 12 ft wide and consist of strips of hollow coring with pre-stressed steel strands in between. Figure 1-2 illustrates several types of hollow-core planks used in the industry. They are combined on site to form a one-way spanning slab and topped with a thin layer of surfacing.

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Bubble Deck Technology

Figure 1-2: Types of Hollow-Core Planks

Bubble Deck Technology In the 1990's, Jorgen Breuning invented a way to link the air space and steel within a voided biaxial concrete slab. The BubbleDeck technology uses spheres made of recycled industrial plastic to create air voids while providing strength through arch action. As a result, this allows the hollow slab to act as a normal monolithic two-way spanning concrete slab. These bubbles can decrease the dead weight up to 35% and can increase the capacity by almost 100% with the same thickness. As a result, BubbleDeck slabs can be lighter, stronger, and thinner than regular reinforced concrete slabs (BubbleDeck-UK).

Currently, this innovative technology has only been applied to a few hundred residential, high-rise, and industrial floor slabs due to limited understanding. For this investigation, the structural behavior of BubbleDeck under various conditions will be studied in order to gain an understanding on this new technique and to compare it to the current slab systems. This technology will then be applied to create lightweight bridge decks since a significant portion of the stress applied to a bridge comes from its own self-weight. By applying the knowledge gathered during the behavioral analysis, a modular deck component for pedestrian bridges that is notably lighter but comparable in strength to typical reinforced concrete sections will be designed.

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Bubble Deck Technology

2. BUBBLE DECK 2.1 Materials BubbleDeck is composed of three main materials- steel, plastic spheres and concrete, as see in Figure 2-1. 

Steel- The steel reinforcement is of higher Grade. The steel is fabricated in two formsmeshed layers for lateral support and diagonal girders for vertical support of the bubbles.

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Plastic spheres- The hollow spheres are made from recycled high-density polyethylene or HDPE.

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Concrete- The concrete is made of standard Portland cement with a maximum aggregate size of 3/4 in. No plasticizers are necessary for the concrete mixture. (BubbleDeck International).

Figure 2-1: Components of a BubbleDeck (Stubbs)

2.2 Schematic Design BubbleDeck is intended to be a flat, two-way spanning slab supported directly by columns. The design of this system is generally regulated by the allowed maximum deflection during service loading. The dimensions are controlled by the span (L) to effective depth (d) ratio (L/d) as stated by BS8 110 or EC2. This criterion can be modified by applying a factor of 1.5 that takes into account the significantly decreased dead weight of the BubbleDeck slab as compared to a solid concrete slab.

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Bubble Deck Technology In addition, larger spans can be achieved with the use of post tensioning as the L/d ratio can be increased up to 30%. (BubbleDeck-UK) L/d < 30 for simply supported, single spans L/d < 41 for continuously supported, multiple spans L/d < 10.5 for cantilevers There are five standard thicknesses for BubbleDeck, which vary from 230 mm to 450 mm, and up to 510 mm and 600 mm for specific designs pending KOMO certification. The varieties of BubbleDeck can be found in Table 2-1.

Table 3-1: Versions of BubbleDeck* (The Biaxial Hollow deck- The way to new solutions)

2.3 Types of BubbleDeck All of the BubbleDeck versions come in three forms- filigree elements, reinforcement modules, and finished planks. They are depicted in Figure 2-2. For all types of BubbleDeck, the maximum element size for transportation reasons is 3 m. Once the sections are connected on site however, there is no difference in the capacity.

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Bubble Deck Technology

2.3.1 Type A- Filigree Elements BubbleDeck Type A is a combination of constructed and unconstructed elements. A 60 mm thick concrete layer that acts as both the formwork and part of the finished depth is precast and brought on site with the bubbles and steel reinforcement unattached. The bubbles are then supported by temporary stands on top of the precast layer and held in place by a honeycomb of interconnected steel mesh. Additional steel may be inserted according to the reinforcement requirements of the design. The full depth of the slab is reached by common concreting techniques and finished as necessary. This type of BubbleDeck is optimal for new construction projects where the designer can determine the bubble positions and steel mesh layout.

2.3.2 Type B- Reinforcement Modules BubbleDeck Type B is a reinforcement module that consists of a pre-assembled sandwich of steel mesh and plastic bubbles, or "bubble lattice". These components are brought to the site, laid on traditional formwork, connected with any additional reinforcement, and then concreted in place by traditional methods. This category of BubbleDeck is optimal for construction areas with tight spaces since these modules can be stacked on top of one another for storage until needed

2.3.3 Type C- Finished Planks BubbleDeck Type C is a shop-fabricated module that includes the plastic spheres, reinforcement mesh and concrete in its finished form. The module is manufactured to the final depth in the form of a plank and is delivered on site. Unlike Type A and B, it is a oneway spanning design that requires the use of support beams or load bearing walls. This class of BubbleDeck is best for shorter spans and limited construction schedules (BubbleDeck*UK).

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Bubble Deck Technology

Figure 2-2: Three Types of BubbleDeck- Type A, B, & C

2.4 Advantages of BubbleDeck 2.4.1 Material and Weight Reduction The dominant advantage of a BubbleDeck slab is that it uses 30-50% less concrete than normal solid slabs. The bubbles replace the non-effective concrete in the center of the section, thus reducing the dead load of the structure by removing unused, heavy material. Decreased concrete material and weight also leads to less structural steel since the need for reinforcement diminishes. The building foundations can be designed for smaller dead loads as well. Overall, due to the lighter floor slabs, the several downstream components can be engineered for lower loads and thus save additional material (Wrap).

2.4.2 Structural Properties Due to the lower dead weight of the slab and its two-way spanning action, loadbearing walls become unnecessary. BubbleDeck is also designed as a flat slab, which eliminates the need for support beams and girder members. As a result, these features decrease some of the structural requirements for the columns and foundations.

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Bubble Deck Technology Additionally, BubbleDeck slabs can be designed and analyzed as a standard concrete flat slab according to research performed on its strength and ductility. As summarized by Table 2-2, the dead load-to-carrying capacity of a solid slab is 3:1 while a BubbleDeck of the same thickness has a 1:1 dead load-to-carrying capacity ratio (Wrap).

Table 2-2: BubbleDeck vs. Solid Slab (adapted from BubbleDeck*-UK)

2.4.3 Construction and Time Savings On site construction time can be shortened since BubbleDeck slabs can be precast. Type A includes a 60 mm precast concrete plate as the base and formwork for the slab. This type of slab would eliminate the need for on site erection of formwork, thus significantly cutting down construction time. Similar to modem precast concrete flooring modules, BubbleDeck can be fully shop fabricated and transported on site for installation as well. Time savings can also be achieved through the faster erection of walls, columns and MEPs due to the lack of support beams and load bearing walls for this innovative flat slab. Addition time may be saved from the quicker curing time since there is less concrete in the slab.

2.4.4 Cost Savings In relation to the savings in material and time, cost reductions are also typical with the BubbleDeck system. The decreased weight and materials mean lower transportation costs, and would by more economical to lift the components. With less on-site construction from the full and semi-precast modules, labor costs will decrease as well. In addition, money can be saved downstream in the design and construction of the building frame elements (columns and walls) for lower loads. civil

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Bubble Deck Technology There is a slight rise in production costs for the BubbleDeck slab due to the manufacturing and assembly of the HDPE spheres. However, the other savings in material, time, transportation and labor will offset this manufacturing price increase (Stubbs).

2.4.5 Green Design The number of owners, designers and engineers who desire green alternatives is growing exponentially. BubbleDeck is a fitting solution for lowering the embodied carbon in new buildings. According to the BubbleDeck Company, 1 kg of recycled plastic replaces 100 kg of concrete. By using less concrete, designers can save up to 40% on embodied carbon in the slab, resulting in significant savings downstream in the design of other structural members. Carbon emissions from transportation and equipment usage will also decrease with the use of fewer materials. Additionally, the bubbles can be salvaged and reused for other projects, or can be recycled. Generally, for every 5,000 m2 of BubbleDeck floor slab, the owner can save: 

1,000 m2 of on-site concrete

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166 concrete truck trips

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1,798 tonnes of foundation load, or 19 less piles

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1,745 GJ of energy used in concrete production and transportation

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278 tonnes of CO2 emissions (BubbleDeck*-UK)

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Bubble Deck Technology

3. STRUCTURAL PROPERTIES AND DESIGN 3.1 General Research has been performed at several institutions in Denmark, Germany and the Netherlands on the mechanical and structural behavior of BubbleDeck. Studies include bending strength, deflection, shear strength, punching shear, fire resistance, and sound testing.

3.2 Bending Strength: Bubble Deck where compared to a solid decks both practically and theoretically. The results showed that for the same deck thickness the bending strength is the same for BubbleDeck and for a solid deck and that the stiffness of the Bubble Deck is slightly lower.

3.3 Shear Strength and Punching Shear: The results of a number of practical tests confirm that the shear strength depends on the effective mass of the concrete. The shear capacity is measured to be in the range of 7291% of the shear capacity of a solid deck. In calculations, a factor of 0.6 is used on the shear capacity for a solid deck of identical height. This guarantees a large safety margin. Areas with high shear loads need therefore a special attention, e.g. around columns. That is solved by omitting a few balls in the critical area around the columns, therefore giving full shear capacity.

3.4 Sound A comparison was made between Bubble Deck and one-way prefabricated hollow deck of similar height. The noise reduction with Bubble Deck was 1 db higher than the one way prefabricated hollow deck. The main criterion for reducing noise is the weight of the deck and therefore Bubble Deck will not act otherwise than other deck types with equal weight. The Bubble Deck construction is following every usual criteria, and can be calculated according to usual principles. The construction is not deviating, in any way, from what is already known and used. The construction is analogous to an equivalent solid deck.

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3.5 Deflection: Due to the bubbles a Bubble Deck slab is not as stiff as a solid slab – but this effect is small. Studies and tests have shown that Bubble Deck has approximately 87% of the flexural stiffness of a solid slab. If no other measures were taken, this would mean marginally higher deflections at SLS than in an equivalent solid slab in direct proportion to this ratio. However, the effect can be compensated for by adding a modest amount of steel even though the deflection is significantly mitigated by the fact that Bubble Deck is lighter and in long term SLS, where frequently the load combination comprises 100% permanent load and a proportion such as 33% imposed load, the permanent weight saving maximizes Bubble Deck’s effect. Long term SLS is frequently the governing criteria for flat slab designs.

3.6 Durability The durability of Bubble Deck slabs is not fundamentally different from ordinary solid slabs. The concrete is standard structural grade concrete and; combined with adequate bar cover determined in accordance with EC2 or BS8110; is what provides most control of durability commensurate with normal standards for solid slabs. When the filigree slabs are manufactured, the reinforcement module and balls are vibrated into the concrete and the standard and uniformity of compaction is such that a density of surface concrete is produced which is at least as impermeable and durable, arguably more so, to that normally produced on site. Bubble Deck joints have a chamfer on the inside to ensure that concrete surrounds each bar and does not allow a direct route to air from the rebar surface. This is primarily a function of the fire resistance but is also relevant to durability. Cracking in Bubble Deck slabs is not worse, and probably better, than solid slabs designed to work at the same stress levels. In fact Bubble Deck possesses a continuous mesh, top and bottom, throughout the slab and this ensures shrinkage restraint is well provided for and that cracking is kept to a minimum whether it is intrinsic or extrinsic cracking.

3.7 Seismic Design: This is a specialist area outside the scope of this brief technical note. However, the concerns in Seismic design are largely similar to any flat slab structure. Punching shear under seismic conditions is the most critical issue and damage at the slab-column junction during

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Bubble Deck Technology sway reversals should be properly considered as well as amplification of the punching shear due to the vertical component of ground acceleration. In computing the building’s response, the seismic designer should be closely engaged with determination of the mass and the effect of this on modal spectrum. Using Bubble Deck a significant reduction of mass in the floor plate may be realized together with an increase in modal frequency and reduction in the sway forces due to lateral acceleration.

3.8 Load Carrying Capacity A solid slab can only carry load one third of its own weight, and have problems with long spans due to its high weight. Bubble Deck’s biaxial deck solves this problem by eliminating 35 % concrete, while maintaining strength. Hence, a Bubble Deck slab has the same applied load capacity with only 50 % of the concrete required for a solid slab, or with the same slab thickness has twice the load capacity using 65 % of the concrete. Shear capacity is more than 65 % of a solid deck with same height. In calculations are used a factor 0.6. In critical areas (around columns), balls can be omitted to achieve full capacity

3.9 Contact Between Bubbles And Reinforcement The potential for any contact is only theoretical because the balls do not perfectly fit between reinforcement bars and moves slightly during assembly / site concrete compaction so that some grout surrounds it and provides a measure of passivation. However, even if there were contact between the ball and the steel, the environment inside the void is very dry and protected - there is also no breach (apart from micro cracking) of the concrete to the outside air. It is a better situation than exists with inclusion of plastic rebar spacers within solid slabs that create a discontinuity within the concrete between the outside air and the rebar in solid R.C. slabs. We therefore have a situation that is better than existing with plastic rebar spacers and these have been permitted for many years. We have had balls cut open in Holland and Denmark and there has been no sign of significant corrosion.

3.10 Effect of Bubble Voids Upon Stiffness Unlike hollow core units, Bubble Deck voids are discrete balls and not prismoidal voids running the length of the span. This makes a huge difference to the performance civil

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Bubble Deck Technology compared to hollow core sections. Tests carried out in Denmark, Germany and Holland (See Reports A1 & A2) show that the flexural stiffness is approximately 87% to 93% of the same thickness of solid slab - In design we use an average of 90% and, in addition, we factor the cracking moment by 80% as recommended in Dutch research. In fact one of the major benefits of the system is its virtue of reducing deflections for a given span because the onethird weight reduction overwhelmingly more than compensates for the very small reduction in stiffness.

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Bubble Deck Technology

4. SITE ERECTION AND INSTALLATION

4.1Stage 1- Erect Temporary Propping During erection each slab must be placed on suitable temporary propping beams arranged in parallel rows mounted on props sufficient to adequately support the weight of the pre-cast filigree elements plus the loose reinforcement fixed on site, concrete poured on site and all other site construction loads applied during final pouring of the concrete topping and curing of the slab.

Typical arrangement of props and propping beams

4.2

Stage 2– Delivery, Lifting and Placing Elements

Site Delivery: The elements are delivered on flatbed trailers typically between 12m to 13.6m long, excluding drivers cab. The filigree elements will be stacked on top of each other up to a maximum 2.5 m overall height. For example, with BD280 slabs there will be maximum 7 layers of slabs, with a transport height of 250mm each plus wooden packers typically 50mm deep separating each element, making an overall height of 2.1m above the trailers bed. Each individual load will be planned so the weight of a load will be a maximum 29 Tonnes and you must provide suitably hard and level access for our delivery transport to reach the offloading position you have determined.

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Loaded trailers arriving on site

Lifting and Placing Filigree Elements: The filigree elements must ONLY be lifted by the lattice beam girder reinforcement. Lifting hooks must ALWAYS be attached under the upper angles of the girder reinforcement diagonal web bars. Lifting hooks must NEVER be attached to the upper reinforcement mesh as this would be unsafe.

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Bubble Deck Technology

4.3

Stage 3 – Fixing Loose Site Reinforcement

Site installation drawings are provided for loose site reinforcement (supplied by others) fixed at the bottom of the slab (directly on top of the pre-cast concrete filigree permanent formwork without spacers or on top of site shuttering on spacers) and reinforcement fixed at the top of the slab (directly onto top mesh reinforcement), together with accompanying bar bending schedules. These must be studied and closely followed at all times.

4.4

Stage 4 – Constructing Shuttering Once the perimeter loose reinforcement has been installed work on erecting perimeter

and construction joint shuttering can commence. Temporary works are our responsibility to determine.

4.5

Stage 5 – Preparation for Concreting The pre-cast concrete permanent formwork edges are manufactured to a high

accuracy and care taken to get a tight joint during laying the elements can render joint filling unnecessary. When joints between slab elements have not been closely butted they must be filled to prevent grout seepage. Should this be required joint filling can be undertaken with either mortar grout or a small bead of silicone sealant inserted at the bottom of the splay joint between elements. This is most easily undertaken prior to installing the loose splice reinforcement.

4.6

Stage 6 – Bubble Deck Site Inspection The technical representative will visit the site and undertake a full inspection of the

BubbleDeck element and loose reinforcement installation. Following inspection, the technical representative will issue you with an inspection record listing any work that needs to be undertaken prior to site concreting, or confirming the installation is ready for concreting and the work is to our approval.

4.7

Stage 7 – Pouring Topping Concrete When pouring concrete evenly distribute across the area and avoid placing in heaps.

Due to the limited space between the bubbles a thin vibrating poker MUST be used to compact the concrete, remove any entrained air and to ensure a good flow around the bubbles. Avoid separation occurring due to the vibrating of shuttering, reinforcement and/or

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Bubble Deck Technology bubbles that can result in segregation of the concrete mix. Once the concrete has been poured a steel beam or power float is then used to level the top and finish to an even and level surface.

Pouring, Vibrating & Floating Site Concrete

4.8

Stage 8 – Removing Temporary Propping During construction planning the minimum period for removal of propping before

back-propping is confirmed. This is usually between 3 to 5 days from pouring of the site concrete as long as the early concrete test results have confirmed the site concrete has reached at least 60% of its final design strength, but can vary dependant upon our floor slab design, strength of site concrete, and ambient temperatures.

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Bubble Deck Technology

5. EXAMPLES OF BUBBLE DECK TECHNOLOGY 5.1 Millennium Tower Rotterdam The first high rise building erected with BubbleDeck filigree-elements and the second highest building in Netherlands, 34 stories and 131 meter high. BubbleDeck was chosen, in spite of being a completely new product, because of its advantages in cost, construction time and flexibility and because of environmental issues. Beams could be excluded resulting in two more stories than planned in the beginning for the same building height. Built in 19982000.

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5.2 Car park Car park built with BubbleDeck in Frankfurt Germany in 2001. BubbleDeck was chosen to reduce the weight of the decks and to get wider spans.

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6. CONCLUSION Bubble Deck will distribute the forces in a better way than any other hollow floor structures. Because of the three-dimensional structure and the gentle graduated force flow the hollow areas will have no negative influence and cause no loss of strength. Bubble Deck behaves like a spatial structure - as the only known hollow concrete floor structure. The tests reveal that the shear strength is even higher than presupposed. This indicates a positive influence of the balls. Furthermore, the practical experience shows a positive effect in the process of concreting – the balls cause an effect similar to plasticizer additives. All tests, statements and engineering experience confirm the fact that BubbleDeck in any way acts as a solid deck – and therefore will follow the same rules/regulations as a solid deck (with reduced mass), and further,leads to considerable savings.

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7. BIBLIOGRAPHY 1. www.BubbleDeck.com 2. Magazine “Corner Stone”, Page No”:30 & 31, autumn 2004 edition. 3. www.bubbleDeck-UK.com

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