Sandwich Construction

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Phone: 0049 (0) 841/97367-0
Fax: 0049 (0) 841/97367-20

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Compelling Reasons to use the Forster Sandwich Construction Method

+ Minimal Complexity
+ Minimal Cost
+ MinimalTime

= 100% Radiation Shielding with proven Top Quality

Mineral filling materials replace metre-thick concrete

Using radiation sources in radiotherapy, research and industry require shielding in order to reliably meet the statutory limit values for the environment. In many cases, this needs walls with a thickness of several metres.

The conventional method is to build a radiation protection building from massive high-density concrete. This causes difficulties in building the walls without cracks. The costly aggregates enter into a permanent bond with the concrete and the extremely thick walls of the building pose a great challenge when dismantling it again.

Thanks to the new Forster Sandwich Construction method for the radiation protection structure, 

- dry mineral filling between thin prefabricated walls -

the protection against radiation and the supporting structure can now be separated. This comes with significant advantages for builders, investors and users alike.


Reduced construction time

Using prefabricated parts in combination with dry filling materials enables significantly reduced construction times.

By using prefabricated parts with controlled cracking characteristics, the construction time can be reduced by approximately 50 %. Individual rooms for medical linear accelerators on undeveloped ground are currently constructed by an experienced construction team within approx. 4 weeks including installation of the radiation protection gate. Minimum material humidity is used for mineral filling inside the structure. Therefore, the finished construction dries quickly and evenly so that accelerators can be set up approx. 2-3 weeks after completion of the shell structure.

The Sandwich Construction method can be used all year round in Europe without causing any damage to the construction, be it snowfall and temperatures down to 5°F or summer during periods of great heat. This is inconceivable in massive concrete construction. This method often requires cooling the fresh concrete with nitrogen or crushed ice in order to prevent premature setting and large shrinkage cracks.

Cost minimisation

Due to the variety of available construction and filling materials, there is no dependency on monopolistic suppliers. This keeps the construction costs low.

After testing for suitability, many locally available minerals or recyclable materials from industrial sources can be used for construction. This keeps material and transport costs to a minimum. A sophisticated design of the Sandwich Construction eliminates the need for costly and toxic lead as well as cost-intensive high-density concrete.

Using the Sandwich Construction method avoids rendering costly materials such as iron ore, barite, basalt or lead permanently unusable by mixing them with cement and water as they will not be bound inseparably in the rubble after demolition, which will then be disposed of for cost reasons. The Sandwich Construction method is therefore characterised by a very high degree of material efficiency and sustainability as opposed to the massive concrete construction method. This enables the implementation of closed raw material cycles according to environmental protection regulations.

By reducing the amount of concrete to a minimum required for statics, the reinforcing steel used is also reduced to the absolute minimum required for construction.


In Sandwich Construction there are no issues with shrinkage cracks due to large amounts of hydration heat being generated during setting of cement in massive concrete. Hence, a greater degree of reinforcement in concrete to prevent shrinkage cracks in the concrete is not required. Shrinkage cracks do not at all occur in the compacted mineral filling used in Sandwich Construction. Continuous quality assurance at the construction site can be implemented using compaction measurement devices as used in road construction. Separation processes of the minerals used in Sandwich Construction during installation are physically impossible. This is a likely possibility when constructing with liquid mass concrete and there is an even higher chance of this when inexperienced construction teams and/or unsuitable concrete mixtures are used in constructing high-density concrete.

When using Sandwich Construction in combination with double wall concrete elements, significantly longer expansion joints become permissible in radiation protection facilities without risk of structural damage. This would be unconceivable in massive concrete built as per the state of the art.

The mixtures for the mineral filling in Sandwich Construction can contain various materials in order to optimise the structure for the specific radiation exposure and kind of radiation. This is not possible in massive concrete construction as it would compromise concrete curing and the final strength resulting in failure to pass the suitability tests required by the construction authorities.

The Sandwich Construction can be designed in such a way that no points with compromised radiation protection occur in the vault floor that may be caused by ventilation ducts and other supply lines. This is a significant cost reduction factor as those weak points do not have to be shielded separately using lead etc.

In Sandwich Construction, the mineral filling can be interrupted anywhere without any problems whatsoever. Furthermore, construction joints within the supporting concrete structure can be designed entirely according to operational requirements. In massive concrete construction, this is subject to numerous construction requirements that drive up the price of the structure.


"Thinking radiation protection buildings all the way through"

If after several years of utilization it becomes necessary to replace the installed equipment with a new instrument offering higher power, it is very easy to improve the shielding enclosure of the sandwich structure without any demolition. In such cases one simply opens the upper ceiling layer and removes the existing filling with standard construction machinery such as a bucket excavator or a vacuum truck. Subsequently, a mineral filling with enhanced radiation protection properties is installed. With this procedure it is not necessary to remove or disturb the structural components of the supporting structure.

In contrast to the conventional construction method using poured concrete, a sandwich construction can be deconstructed quickly and economically using standard demolition equipment. The bulk mineral filling and the structural elements can be cleanly separated from each other and can be sold to the construction industry.

Sandwich Construction - a sophisticated solution

Using high-quality prefabricated concrete components with an even steel formwork surface enables direct application of wallpaper or paint. Plastering of surfaces or installing gypsum board linings is not required. This creates hard and tough surfaces that are resistant to damage e.g. from contact with bed frames. In addition, skirting boards and edge protection measures are not required either.

In conventional construction, it is common to design long mazes behind the entries. With the introduction of Sandwich Construction we were able to establish a significantly improved workflow for radiation protection rooms for linear accelerators using mini mazes. This has allowed us to reduce the distance that has to be covered by personnel and patients between door and treatment couch from typically 12 meters to just 6 meters each way. With the same staffing and same shift length this increases the patient throughput significantly.

Utilizing the mini maze technology we can replace extremely heavy radiation protection doors traveling on tracks in the floor by much lighter high-speed doors suspended from the top. These can travel with a top speed of up to 0.30m/s, leading to a significantly reduced time for opening and closing. Radiation protection doors are the key to workflow optimization.

Radiation protection doors in Sandwich Construction totally avoid the flammable paraffin derived from petroleum. The use of lead can also be avoided.

Investment advantages

The Sandwich Construction method enables manufacturing of mobile radiation protection rooms that can e.g. be used temporarily for testing purposes or in emergency situations in parking lots during renovation of existing hospitals in order to keep up treatment operations for patients.

In Germany, temporarily used mobile radiation protection rooms have reduced period of depreciation of 10 years as opposed to 50 years for fixed installations. This is a significant tax advantage for investors.

A building permit is not required for mobile protection facilities. Applying for an operating permit with the competent authority for radiation protection is sufficient. Furthermore, there is no need to involve a test engineer for construction statics. This reduces costs and significantly accelerates the construction progress. This procedure is inconceivable in constructions with massive concrete.

Reduction of dismantling guarantees on leased land.

The dismantling costs of a conventional massive concrete building are multiple times higher than for a radiation protection room in Sandwich Construction, which is why a significantly smaller amount is required for the guarantee along with the associated bond premium.


The sandwich building enclosures can be constructed using precast concrete panels, double wall panels finished with on-site concrete, steel plates, and other materials. After testing for suitability, many locally available minerals or other materials can be used for construction. Due to the variety of available construction materials, there is no dependency on monopolistic suppliers. This keeps the construction costs low.

Special Requirements

If the presence of strong magnetic fields is expected, the "Sandwich" can be constructed entirely from non-magnetisable components.

In the high energy domain, depending on radiation type and power, several individual and separated layers of various mineral fillings can be installed, which are carefully chosen through radiation protection design calculations in order to optimize the radiation protection. For example, spallation layers can be installed towards the inside of the shielding enclosure, which are then followed by layers of natural gypsum for the moderation of neutrons.

In case of operation at high energy it can be unavoidable that after lengthy operation the innermost layers of the construction become activated to a previously known extent This can be taken into account using the Sandwich Construction method by employing a layered design, which will allow economical disposal, depending on the level of activation of the individual layers. Based on experience from deconstruction of nuclear power plants, this is almost impossible in constructions from massive poured concrete.

To counter the problems caused by high hydration temperatures in massive concrete construction, cement is often replaced by fly ash in the mixing recipe. While the pozzolan qualities are similar to those of cement, the origin of the fly ash is unknown in most cases. If they originate from filters for the exhaust of incinerator plants or similar installations, it cannot be guaranteed that this fine dust does not contain contaminations. These then enter the concrete exposed to radiation and can become activated. This can be entirely avoided using the Sandwich Construction method as for the dimensions typically used here, the mixing recipes do not include any fly ash.

In high-energy applications, it is very important to assure that no materials capable of being activated such as Cobalt 59. Europium, and Caesium enter the radiation shielding. By way of appropriate selection of raw materials, the Sandwich Construction allows to guarantee the purity of the material in every single cubic yard using chemical analysis methods during the preparation phase.  This is not that easy when using massive concrete.

Did we spark your interest? You will find a selection of completed project from all areas under References. We will be pleased to send you a collection of technical publications and further information upon request. Do not hesitate to contact us. We will be more than happy to take care of your project!

Any questions?

We are happy to help!

Phone: 0049 (0) 841/97367-0
Fax: 0049 (0) 841/97367-20

Date Outline

Currently there are no events.