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Life Plus Silex Project

Improving sustainability of construction materials using innovative silicon-based treatment

Project objective

Funding has been received from the LIFE financial instrument of the European Union to accomplish SILEX project objectives.

The overall objective of this project is to extend the lifetime and usability of construction materials made of wood and/or cement by applying environmentally friendly silicon-based water repellents. This will reduce emissions of volatile organic compounds by 80-90% in comparison with conventional concrete treatment and reduce the use of biocides in the conservation of some wood species (e.g.pine, beech). 

This project is led by Dow in collaboration with Ghent University, Institute of Building Materials Research (IBAC) at the RWTH Aachen University and the FCBA (Centre Technique du Bois, France).

Project details

Project number = LIFE11 ENV/BE/1046

The challenge

Ingress of moisture is responsible for premature degradation of construction materials due to phenomena such as gel cracking, steel corrosion in reinforced concrete, swelling and dimensional changes of wood and biological attack (by fungi, insect or microorganisms) of wood.

Current solutions 

Water beading on concrete substrate

Technical solutions exist currently to increase service life of both wood and concrete but state-of-the-art technology still has some negative environmental impact, leaving some room for improvement.

Biocides are used to reach the expected service life of wood, and silicon-based water repellents are used to protect concrete structures, although they are often formulated in such a way that the release of volatile organic content occurs.

The SILEX project will address environmental challenges specific to each construction material protection: use of biocides and fungicides for wood; release of volatile organic compound (VOC-) during concrete and cement-based materials treatment.

New innovative solutions

The use of new silicon-based products is expected to enable a decrease of the required biocide level used to extend wood service life and to decrease wood dimensional instability upon moisture entry. New water-repellent treatments for cement-based materials, concretes and their formulations are expected to lead to reduced organic volatile content release upon application.

Project achievements

Key project learnings

During the project, the partners have performed numerous activities and tests (lab and field tests for both wood and concrete) to demonstrate and validate the efficiency of:

  • Innovative low VOC hydrophober for concrete treatment
  • New Si-based hydrophobers for wood treatment

The main project achievements are the following:

  • Development and validation of new test methodologies to assess performance of water repellent formulations for wood and concrete
  • Development and validation through lab and outdoor exposure tests of innovative Si-based water repellents for wood and concrete:
    • Seven innovative Si-based water repellents for wood
    • Two new low VOC Silicone-based impregnation (active material and an emulsion) for concrete
  • Development of process capabilities (designed process and treatment conditions) and scale-up to enable treatment of wood with the new Si-based water repellent
  • Validation of the efficiency of the new Si-based water repellent formulations through lab and outdoor exposure tests (to assess initial performance and durability)
  • Design and build-up of a final demonstrator combining both construction materials (wood and concrete)

New low-VOC hydrophobers for concrete

Testing concrete

New impregnation hydrophober for concrete, releasing lower VOC upon reaction, has been developed. Both the active material and its emulsion, based on the new active material, were developed, and their performances as concrete hydrophobers were demonstrated through intensive lab and outdoor tests. SILEX formulations can lead to a reduction of calculated VOC release which should enable to reduce VOC release of the pure active material from 500 to below 100 g/L without compromising the durability performance of treated concrete. 

New si-based hydrophobers for wood

Testing wood

A set of seven formulations differing by the type of active material and/or the delivery system (water soluble vs. emulsion vs. oil dilutable) have been identified and further developed. The data generated, in the frame of the project, highlighted they could provide different benefits and could better match the requirements of the different wood species considered. These formulations have been further commercialized by Dow:

  • Three Water-dilutable formulations: DOWSIL™ 2-9034 Emulsion, DOWSIL™ IE 6683 Emulsion, DOWSIL™ 6696 Emulsion
  • Two Water soluble water repellents: DOWSIL™ 1-6184 Water Repellent, XIAMETER™ OFS-0777 Siliconate
  • Two oil-dilutable formulations: DOWSIL™ Z-6690 Water Repellent, DOWSIL™ 6691 Fluid

When the new water repellents for wood were applied on different wood species, various performance enhancements were observed, and the main results are summarized in the table below. 

Wood Species Results
Pine, an example of easy to treat non-durable softwoods Pines are generally very vulnerable to fungal decay. Organosilicon compounds could be used to partially replace the use of biocides. They can act as a non-film forming system controlling moisture dynamic, and hence improve surface quality and serviceability over a longer period. SILEX project could enable reduced use of biocides in specific conditions.
Beech, the eminent example of non-durable and dimensionally unstable hardwood Beech is considered not fit for exterior applications due to its low durability in combination with low dimensional stability. Treatment with organosilicon compounds could lead to much longer service life expectations and an improved dimensional stability performance which is important for construction materials like wood-based cladding.
Oak, the eminent European wood species for decorative/aesthetic applications The natural durability of oak is not as high as some tropical wood species used outdoors. Thanks to the innovative organosilicon products, delayed wetting in combination with sufficient drying lowers the actual swelling in practice. Treatment could also keep time of wetness low enough to improve durability of oak.

An LCA study has been performed to assess the potential environmental benefits of the 7 innovative Silicone-based solutions vs. one selected biocide currently used in the following three scenarios:

  • Scenario 1: only biocide used 
  • Scenario 2: partial replacement of biocide with the SILEX solutions 
  • Scenario 3: full replacement of biocide with SILEX solutions

Final demonstrators 

Different demonstrators combining wood and concrete treated with the innovative Si-based hydrophober for wood and concrete, developed in the frame of SILEX project, were designed and made (see pictures). These demonstrators will be exposed during more than 10 years at different partners’ premises to assess long term performance of the hydrophobic treatment.

Testing wood and concrete
Testing wood

View the Layman’s report to see more details about the project achievements.

Next steps

The wood market seems ready for new technical options which would enable formulators to decrease the utilization of biocide. In line with this, Dow has already commercialized seven water repellents for wood. This new offering is meeting strong interest, showing that the possibility to minimize biocide consumption in line with the latest EU regulations on biocides is of interest.

Dow has already started the commercialization of the developed solutions and is expecting to continue to further improve the solutions to meet the evolution of the market requirements.

In line with these objectives, after LIFE action plan has been set-up by the partners.

Concerning concrete, the market demand for low VOC impregnation for concrete is yet to develop in Europe. Data generated during the project will be a key enabler to increase awareness of customers for this new technology.

Key technical learnings

Development of new hydrophobic treatment for concrete

Application of silanes on concrete is a known method to minimize ingress of water into concrete. It is indeed key to minimize ingress of water and dissolved chloride into reinforced concrete, as the latter can trigger corrosion of reinforcement bars. 

Underside of bridge showing corroded reinforcement steel bars due to chloride ingress

Illustration of corrosion of reinforcement steel bars due to chloride ingress

The right illustrates the impact of silane treatment of the reduction of water ingress

Conventional method used to measure depth of penetration of silane into concrete upper surface.

Different methods are used either in the labs or on the job sites to assess the extent of hydrophobic treatment. Measurement of the “depth of penetration” (extent of penetration of silane into the upper layer of concrete) is important to assess the depth of the concrete which is treated by the hydrophobers (and then protected against water ingress).

Most commonly, sample of concrete must be broken apart in order to measure depth of penetration of silane treatment.

IBAC developed an innovative non-destructive method based on NMR to measure not only the depth of penetration of silane into the concrete upper layer but also the rate of reaction of the silane after application.

The NMR test method

This non-destructive method is being used to measure the ingress and the rate of reaction of selected existing and prototype hydrophobers within the frame of the SILEX project. This innovative test method provides new insights on the reactivity of hydrophobers with concrete surfaces.

The NMR test method was used to characterize a set of concrete specimens, treated with conventional and prototype hydrophobers before being aged at selected places where they could be exposed to chloride ingress.

Installation of treated concrete specimens close to a highway where de-icing salts are used during winter

Installation of treated concrete specimens close to a highway where de-icing salts are used during winter

Development of new hydrophobers for wood treatment

Wood modification aims at the improvement of properties of wood or wood-based materials, mostly to prolong the service life of the product. More specifically, resistance against physical and biological attack needs to be boosted. Given the hygroscopic nature of wood, impacting its moisture dynamical behavior is an important target to aim at.

Three European wood species treated with different siloxane products were assessed using a straightforward absorption-desorption lab test. The following pictures show how specimens of wood treated with different silicon-based water repellents are tested for water absorption and desorption.

Wood tested for water absorption and water desorption

Scots pine and beech samples were impregnated by vacuum impregnation (7 mbars during 15 minutes) under laboratory conditions and tested for water absorption and water desorption. Positive impact of wood treatment is observed. View the publication ►

Resistance against decay fungi

Resistance against decay fungi

Samples of Scots pine, sapwood and beech were treated by vacuum impregnation with three products: a hydrodilutable silane, an emulsion of silane and a cationic emulsion.

Treated wooden blocks and untreated control specimens were exposed to two wood-destroying basidiomycetes: Coniophora puteana and Coriolus versicolor. These tests were performed according to the EN 113 standard [1].

The samples were exposed to fungi attack for 16 weeks in a climatic chamber under constant climatic parameters (22°C, 70% relative humidity). The mass losses of the wood samples exposed to fungi were evaluated at the end of the test.

Resistance against subterranean termites

Against subterranean termites

Samples of Scots pine, sapwood and beech were treated by vacuum impregnation with three products: a hydrodilutable silane, an emulsion of silane and a cationic emulsion at 5% active content.

Treated wood blocks and untreated controls were exposed to termites according to EN 117 standard [2].

The test wood specimens were placed in glass jars on humid Fontainebleau sand (1 volume of water/4 volumes of sand) together with 150 Reticulitermes flavipes termite workers. Six replicates were used for each product.

The samples were exposed for eight weeks to termite attack in a climatic chamber, under constant climatic parameters (27°C, 75% relative humidity). At the end of the test, the survival rate of workers and the degree of attack were evaluated.

Read the FCBA publication presented during the 47th Annual Meeting of the International Research Group on Wood Protection (IRG47) ►

Assessment of moisture dynamics into modified wood is being explored by Wood Lab (UGENT)

A detailed investigation of a selection of modified oak material was performed using neutron radiography at the NEUtron Transmission RAdiography (NEUTRA) beamline of the Paul Scherrer Institute (PSI) in Villigen, Switzerland. The technique enables visualization of water ingress and desorption in samples. The straight forward absorption-desorption lab test, as well as the high-end neutron approach, enable a detailed investigation of the moisture dynamics of modified wood and, in that way, the efficacy of treatment.

View the latest results ►

Some moisture measurements are currently being assessed at the UGent premises. Wood specimens (untreated and impregnated with hydrophobers) are mounted on load cells of the CMM. The system records weight of wood samples on a regular basis. Weather data are collected thanks to a weather station near the exposition site.

The continuous moisture measurements follow the moisture variation depending on weather conditions. 

Read the UGent publication presented during IRG47 ►

[1] NF EN 113 : 1996. Wood preservatives – Test method for determining the protective effectiveness against wood destroying basidiomycetes – Determination of the toxic values.

[2] NF EN 117 : 2004. Wood preservatives – Determination of toxic values against Reticulitermes species (European termites) (Laboratory method).

Event attendance information

Past events and publications

  • Action D4: Publication and posters were presented by the partners attending the different congresses/conferences.
  • SLF Congress in Gothenburg, Sweden: Attended by Dow Corning, an article was submitted and accepted and a presentation was given during this Congress. Read the article ►
  • 8th European Conference on Wood Modification in Helsinki, Finland: Attended by UGent, FCBA, a poster and paper were in the proceedings. View the poster ►
  • European Technical Coating Congress in Birmingham: Learn about our presentations and publications ► 
  • 47th Annual Meeting of the International Research Group on Wood Protection (IRG47 A) ► (IRG47 B) ►
  • International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Moisture, 22–24 August 2016, Lyngby, Denmark
  • International Symposium Non-Destructive Testing in Civil Engineering, Berlin, 15-17.9.2015
  • “Organosilicon-based impregnation hydrophobers for wood.” Jean-Paul Lecomte, Joris Van Acker, Magdalena Kutnik, Jan Van den Bulcke, Mathilde Montibus, Sabrina Salvati, Sarah Derocker, Presentation at IRG 48, Ghent, June 2017 (Organized by the SILEX partner UGENT) Read the article ►
  • “Organosilicon-based impregnation hydrophobers for wood.” Jean-Paul Lecomte, Joris Van Acker, Magdalena Kutnik, Jan Van den Bulcke, Mathilde Montibus, Sabrina Salvati, Sarah Derocker, presentation at the European coating congress, Nuremberg, April 2017.
  • Organosilicon-based hydrophobic impregnation treatments for wood. By J.-P. Lecomte, S. Sabrina Salvati, S. Derocker, J. Van Acker, J. Van den Bulcke, M. Kutnik, M. Montibus, European Coating Journal, 02/2018, Read the article (EN) ► Farbe und Lack (DE) ►
  • O. Weichold, U. Antons, Assessing the Performance of Hydrophobing Agents on Concrete using Non-Destructive Single-Sided Nuclear Magnetic Resonance, J. Infrastruct. Syst. 2015, submitted, revised version returned;
  • O. Weichold, S. Hutt, S. Keine, R. Schulte Holthausen, Non-Destructive Moisture Measurement in Building Materials Using Single-Sided Nuclear Magnetic Resonance, Proc. Int. RILEM Conf. on Materials, Systems and Structures in Civil Engineering, Segment on Moisture in Materials and Structures (PRO 112) 2016, 361–368

Executive summary and achievement of the project.

During the project, the partners have screened and fine-tuned innovative Si-based formulations that could meet the expected environmental benefits targeted by the project for both construction materials (i.e. wood and concrete as well as developed testing methodologies, to assess the performance of the SILEX products.

In a second phase, the new products have been tested through lab and outdoor exposure conditions and the results have been analysed. In parallel to these intensive tests, activities aiming at improvement the treatment process (including scale-up) have been also performed. On top of that, based on the first results, Si-based water repellent for wood have been further optimized.

To ensure a fast and efficient commercialization of the demonstrated new formulations, tests according to the most stringent EU standards have been performed, guaranteeing that the developed products are ready for the EU markets.

Demonstrators combining wood and concrete have been built with the most performing formulations and have been placed in Ghent University and Dow premises. These demonstrators will be used as showcase to illustrate the upgraded performances achieved thanks to the SILEX solutions.

Finally, the environmental impact and market analysis have been performed during the project.

As further detailed, the project expected results have been reached and the next steps will be now to ensure the commercialization of the different formulations.

Read the Layman’s reports ►

Our Partners

In order to reach the objectives, the SILEX project has been set up to integrate the expertise of different partners: Dow and its expertise in silicone formulations developments, Ghent University with their experience in measurements of moisture dynamic in woods, FCBA and its knowledge in wood treatment and utilization and RWTH Aachen with their experience in cement-based construction materials.