Subject matter

Infrastructures and buildings are exposed to microorganisms in a variety of contexts.

In many cases, microorganisms have detrimental effects on structures and the construction materials which comprise them. 

Structures exposed to aggressive aqueous media containing microorganisms (waste water, soft water, fresh water, ground water, sea water, agricultural or agro-industrial environments), often concrete structures, can suffer deterioration that can be detrimental (loss of alkalinity, erosion, spalling of the concrete skin, corrosion of rebars, loss of water- or airtightness…). The deleterious effect of microorganisms, mainly bacteria and fungi, on the cementitious matrix has been found to be linked, on the one hand, with the production of aggressive metabolites (acids, CO₂, sulphur compounds…, depending on the case) but also, on the other hand, with some specific, physical and chemical effects of the microorganisms themselves through the formation of biofilm on the surface. Moreover, the intrinsic properties of the cementitious matrix (porosity, roughness, mineralogical and/or chemical composition…) can also influence the biofilm characteristics, but these phenomena have not been understood thoroughly as of yet. 

These deteriorations lead to a significant increase in the cost of repairing structures and to loss of production income, but may also lead to pollution issues resulting from waste water leakage to the environment for example. Also, building facades, and notably concrete external walls, can be affected by biological stains, which alter aesthetical quality of the construction, sometimes very quickly, and lead to significant cleaning costs. Microorganisms, mainly algae, responsible for these alterations have been quite well identified. Research is now rather focused on determining colonisation mechanisms, and notably influencing material-related factors, and on development of preventive or curative, and preferentially environmentally friendly, solutions to protect external walls. However, up to now, no clear results about the efficiency of these various protection solutions are available.

In indoor environments, proliferation of bacteria and fungi on building materials is responsible for health problems (respiratory and cutaneous pathologies) through the production of microbial volatile organic compounds, allergens and toxins. The bio-receptivity of construction materials conditions the proliferation of microorganisms on their surfaces, but this key parameter is not well understood. This is a significant issue all the more, as the economic and societal consequences of bacterial proliferation inside buildings are very important.

However, in some cases, microorganisms can have beneficial effects on cementitious materials when they are used for example as a way to protect and/or repair concrete in applications such as bacteria-based self-healing materials. New formulations of cementitious materials, incorporating selected bacteria and suitable chemical precursors, are developed with the aim to fill micro-cracks in concrete and thus improve the durability properties.

In other types of applications, the formation of microbial biofilm on the surface of cement-based materials can act as a protective layer against biological deterioration, e.g. either by the excretion of protective organic polymers (EPS=ExoPolymeric Substances) or by the proliferation of non-aggressive microbes capable of competing with undesirable microorganisms.

More and more research efforts are devoted to these topics related to cementitious materials-microorganisms interactions within local or trans-regional initiatives. It is now necessary to implement concerted approaches and comparison of research outcomes to move toward a better understanding of the phenomena and furthermore, to standardization (of test methods for example, there is a real shortfall in the domain) and/or certification.

This technical committee aims to be a part of this concerted approach. The TC will be mainly focused on cementitious materials. In some cases, other mineral materials can also be considered.

The aim of the TC is to address 4 main topics listed hereafter (see in table 1, the list of members involved in each topic):

Topic 1: Deterioration of cement based materials by microorganisms in different contexts (waste water collecting networks and plants, agricultural plants, biogas systems, agrofood environments…). 

Among relevant topics that will be covered:

- Characteristics and composition of real media and inventory of microbial and chemical phenomena,

- Mechanisms of material-microorganisms interactions: impact of microbial biofilms on the material (physical and chemical action), but also impact of the material (composition, surface properties…) on the biofilm structuration, microbial diversity and production of EPS

- Test methods (laboratory pilot to investigate the mechanisms of interactions, to qualify concrete resistance, in-situ testing…)

- Performance of concrete with microbial proliferation/attack,

- Modelling of the attack and related mechanisms, prediction of service-life

Topic 2: Algal colonization on building materials and protection of materials.
If microorganisms responsible for  visible stains on facades are quite well identified, some related aspects remain to be tackled:

- Influence of material properties (porosity, roughness, composition…) on proliferation (kinetics, composition of microbial community)

- Test methods for evaluating algal fouling of materials: accelerated vs. in-situ testing (are the accelerated tests not too severe? What are the accelerating factors?), quantification of algal proliferation (which methods are available?)

- Methods to protect materials against microbial proliferation (design of concrete, biocides, photocatalysis, hydrophobic coatings, competitive microorganisms…): what possibility, what efficiency?

Topic 3: Proliferation of microorganisms (bacteria, fungi) on building materials in indoor conditions.

Many aspects of this problem have still to be covered:

- Diversity of microorganisms responsible for health trouble in buildings and the societal and economic consequences

- Test methods (i) to collect and (ii) to identify microorganisms (in-situ and laboratory testing), and (iii) to characterize bio-receptivity of materials

- Bio-receptivity of traditional building materials and influence of environmental parameters on the proliferation

- Solutions to limit microbial colonization on building materials

Topic 4: Bacteria-based self-healing cementitious materials.

The TC will notably consider:

- Bacterial species candidates

- Procedures/methods to insert bacteria in cement-based matrices

- Precursor materials and substrates

- Mechanisms of material’s protection

- Which materials properties can be improved

- Durability of self-healing concretes

- Potential negative effects on material properties / possible health issues

As mentioned earlier, cement-based materials will be mainly considered.  For topics 2 and 3, other mineral materials (gypsum, stone, brick…) and wood and other organic materials (painting, wall papers…) may also be considered but only for comparison purposes.

Terms of reference

The TC is expected to run for 5 years (2014-2019).

Members will be recruited from academia but also from industry (provider of materials and products for specific environments).

The TC will be organized in four working groups matching the four main topics envisaged.

Some common aspects of the four topics (typically bio-receptivity of materials and microbial biofilm colonisation of cement-based materials) could constitute transversal actions.

The work will consist in bibliographical research, exchanges around experiences, methods and results.

If appropriate, round robin tests may be organised within the working groups.

Discussion of tests methods and subsequent recommendations will be an important function of the TC.

Detailed working programme

The tentative working programme is as follows:

The TC will be inaugurated at the Calcium Aluminate Cements Conference, to be held in Avignon, France in May 2014, in which a major part of the TC will participate.  The conference will also be the opportunity to recruit other interested researchers.

One workshop, one symposium and a final conference should be organized during the TC life.

-          May 2014: Introductory meeting, CAC conference, Avignon.

• Introduction of members, suggestion of new members,
• overview of members’ competences and experience,
• Plan of activities, organisation of initial workshop

-          Sept. 2014: Workshop for the members and second meeting : RILEM week, DBMC Conference, Sao Paulo Sept. 2014

• Workshop: presentations by TC members (opened to any RILEM member)
• Overview of experience, problems and points of attention.
• Decision on most important points for further TC work.
• Constitution of working groups
• Assignments of group leaders
• First discussions on working programme for the different groups. Overview, literature review, round robin tests, recommendations. Ideally, one small round robin test per working group.

-          Second half of 2014: exchanges within working groups

• Discussion of working programme for each group
• First informal exchanges with scientific contents
• Compilation of literature reviews
• Discussion about round robin tests

-          Spring 2015: third meeting

• Finalization of each working group programme
• Discussion of procedures and results
• Programme of small round robin tests
• Preparation of international conference for 2016
• Preparation of state-of-the-art report (STAR) – organization of the STAR, tentative contents. Decision of contributions

-          June 2016 : 4^th meeting and symposium

• International symposium, location (university of a TC member) to be decided

-          Sept. 2016: 5^th meeting during RILEM week

• Preparation of STAR report – progress on contents and contributions, input from the conference
• Round robin tests, results, discussions
• Recommendations

-          Sept. 2017 : 6^th meeting during RILEM week

• STAR
• Preparation of the final conference

-          2018: 7^th meeting and Final conference. Input from the final conference for the STAR

-          Sept 2019 : 8^th meeting

• Finalization of STAR
• Summary of TC findings in Materials and Structures paper (recommendations on test methods)