Detecting Reinforced Autoclaved Aerated Concrete (RAAC) in Building Structures

22 Submissions
Challenge under evaluation

Challenge overview


How can we more easily detect the presence of Reinforced Autoclaved Aerated Concrete (RAAC) within building structures?

This is critical for the safety of those present in buildings, but also for construction quality control and maintenance. This challenge seeks innovative solutions to more easily and reliably, detect and assess the presence of RAAC within building structures.

RAAC, a type of concrete invented in the 1930s, and widely used in Europe, Asia and North America between 1950 and the 1990s, is now considered life-expired and liable to collapse with little or no notice, causing danger to life and leading to the immediate closure of buildings, a good proportion of which are public buildings like schools and hospitals.

The Seekers attending the Showcase Event for this Nexus Challenge, invite novel or maturing solutions, innovators and collaborators with potential relevance, including systems, tools, new materials, technologies, services, insights, expertise, best practices, start-ups, and identification of promising concepts, any of which can contribute to a submission of interest or with future potential.

Your proposals are invited in these three key areas (further described below), and we are very open to other or combined innovations:

  1. Detect the presence of RAAC; methods or technologies that are accurate and reliable even when RAAC is used in combination with conventional concrete or other materials.
  2. Detection of cracking and shrinkage; like traditional concrete, RAAC can experience cracking and shrinkage over time.
  3. Detection of moisture; RAAC is susceptible to moisture, water seeps into the concrete and can come into contact with the reinforcing steel, causing corrosion which can expand the iron pushing and cracking the surrounding concrete.


This is a Nexus Challenge seeking partners to join Wazoku Innovation Networks (WIN) for Security, to provide solutions, technologies or expertise with future potential for this Challenge. The Solver is invited to submit their written proposal. The Solver is invited to submit their written proposal. Successful entrants will be invited to Showcase their work, with the scope to pitch your idea to a curated selection of corporate partners from R&D, Corporate Venturing, Innovation, Product teams and beyond. These pitches in private sessions can help you land pilots, investment or other commercial opportunities, and help you grow faster. Wazoku will support you during the process, including mentoring and preparation for any Showcase pitch.

Proposals from Solver Scouts (WIN Scouts) who propose potentially suitable partners are also invited to participate.

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Submissions to this Challenge must be received by 11:59 PM (US Eastern Time) on November 7th, 2023.




Wazoku Innovation Networks (WIN) focus on the key themes of Climate, Health, Security, and Inclusion. These networks are where global organizations and institutions connect with the brightest start-ups and technology crowdsourced from every corner of the globe.

Nexus Challenges provide the themes and focus for WIN.

Nexus Challenges use the power of crowdsourcing, scouts and collective intelligence to identify, select, mentor and showcase best in class, often novel solutions. Spanning across verticals including Healthcare, Energy, Defense & Aerospace, Financial Services, Mobility, Infrastructure, Manufacturing, Life Sciences, Water, Materials & Packaging and beyond.

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Many public buildings are facing closure because of reinforced autoclaved aerated concrete (RAAC), a type of concrete used extensively between the 1950s and 1990s.

RAAC is now considered life-expired and liable to collapse with little or no notice, causing danger to life and leading to the immediate closure of these buildings.

Buildings can be made safe with the addition of extra support, however the huge number of particularly public buildings presents a massive challenge.  For example, in the UK, RAAC was used extensively in public buildings, including schools, hospitals and universities, at a time when budgets and materials were tight. An estimate of between one and five per cent of public buildings built between 1950 and 1990 have some of this material equating to hundreds, possibly thousands, of public buildings just in the UK. The damper, rainy conditions more common in the UK mean that RAAC’s durability issues have become apparent earlier than in many other places.

The prevalence of RAAC in commercial buildings is unclear, but likely to be similarly widespread.

It is only a matter of time before the rest of the world starts facing problems. Climate change is likely to have exacerbated the issue of RAAC failing, for example, drought can cause cracks to form in the concrete, which then allow moisture in.

RAAC is a type of concrete invented in the 1930s, that was used widely in Europe, Asia and North America between 1950 and the 1990s. Made of materials including cement, lime and sand, the concrete is heated to 200 °C under high pressure, a process called autoclaving. Aluminum flakes added before autoclaving react with lime to produce hydrogen, forming air bubbles. The resulting material is much cheaper and lighter than regular concrete, and less than half as dense. At the time, it was considered something of a wonder material as it used a sixth of the more expensive building materials, it is thermally insulating and its availability in big stacking blocks supports quick construction.




The requirement of this Challenge is to develop accurate, efficient and non-destructive methods or technologies for detecting the presence of RAAC within structural elements.

While RAAC can offer several advantages, after time it develops severe challenges and limitations:

  1. Cracking and shrinkage: Like traditional concrete, RAAC can experience cracking and shrinkage over time. Proper maintenance practices are necessary to minimize these issues.
  2. Moisture susceptibility: RAAC is sensitive to moisture during and after construction, and proper waterproofing measures are essential to prevent damage.
  3. Limited load-bearing capacity: Reinforcement added to RAAC panels improve their structural strength, but they can still have lower load-bearing capabilities than conventional building materials.

Inside RAAC blocks, steel bars provide support. The steel is encased by a protective layer, often a mix of latex and cement or sometimes acrylic powder to prevent corrosion if water gets into the concrete’s pores. The problem is that over time, this reinforcement can erode and the concrete can fail catastrophically and suddenly.

Also if water seeps into the concrete and comes into contact with the steel, it can cause the metal to rust. As the concrete absorbs carbon dioxide over many years, its pH drops, which also increases the risk of corrosion. Corrosion can significantly increase the volume of the iron. The expanding iron can then push and crack the surrounding concrete, causing it to snap or fail. This swelling or cracking is often not visible from the outside, with it all happening on the inside.

Overloading RAAC structures or cutting the concrete to make room for skylights and ventilation, can increase this chance of failure.

The material’s primary issue has been it’s need for the provision of ongoing maintenance, refurbishment and rebuilding budgets.

Detecting the presence and distribution of RAAC within structural elements (such as walls, columns, or beams) is essential for safety.

Key solution requirements:

  • Detection Sensitivity: Develop methods or technologies that can accurately and reliably detect the presence of RAAC even when it is used in combination with conventional concrete or other materials.
  • Versatility: Solutions should be adaptable to various structural elements, including walls, columns, and beams, and should be applicable in different construction and construction mix scenarios.
  • Non-Destructive Testing: Solutions should be non-destructive, minimizing the need for physical probing or invasive techniques that can damage the structure.
  • Quantification: Provide a means of quantifying the amount and distribution of RAAC within the structural element.
  • Real-time Assessment: Enable real-time or near-real-time assessment, suitable for both construction quality control and long-term maintenance inspections.
  • Cost-effectiveness: Develop solutions that are cost-effective and can be easily integrated into existing quality control actions, in terms of equipment, materials and effort.

Solutions with Technology Readiness Levels (TRLs) 1-9 are invited; with ideas about WHAT to do; concepts/solutions with HOW to achieve this; collaboration proposals about existing mature technologies and/or WHO can provide these. 

The below graphic will indicate what some potential opportunities from this Challenge might be, if you are shortlisted and there is sufficient potential to Showcase your proposal:

Nexus Challenges have the following features:

  1. Wazoku and experienced theme advisors will evaluate your submission to decide its relevance for inclusion as a successful entrant to Showcase.
  2. The Showcase preparation stages will take place starting within 30 days of the submission due date.
  3. Wazoku will support you during the process, including mentoring and preparation to Showcase your proposal.
  4. In the event further contact is requested following your Showcase activities, you can negotiate the terms of the contract (including scope of work, tasks, and duration) directly with the interested Seeker.
  5. If you are successful in winning any business or investment, a flat 10% success fee will be payable to Wazoku for any financial benefits gained through the process.
  6. Successful WIN Scouts will be compensated by Wazoku from the success fee.
  7. Any confidentiality and intellectual property rights in your Proposed Solution will be managed in accordance with the Challenge Agreement for this Challenge.



Please login and register your interest, to complete the submission form.

The submitted proposals must be written in English and should include:

  1. Participation type – you will first be asked to inform us how you are participating in this challenge, as a Solver Individual, Solver Organization, Expert or WIN Scout.
  2. Solution Key Area - the Key Area your proposal addresses; 1, 2, 3 or a combination.
  3. Solution Stage - the Technology Readiness Level (TRL) of your solution, TRL1-3 ideation stage, TRL4-6 proof of concept stage, TRL7-9 production ready stage or not applicable (if your submission is as an expert or scout).
  4. Experience - expertise, use cases and skills you or your organisation have in relation to your proposal (up to 500 words).
  5. Problem & Opportunity - the Problem you are addressing in the Key Area and who benefits by your solution (up to 500 words).
  6. Solution Features - the key features of your solution and how they address the problem (up to 500 words, there is space to add more).
  7. Solution Risks - any risks you see with your solution and how you would plan for this (up to 500 words).
  8. Timeline, capability and costs - describe what you think is required to deliver the solution, estimated time and cost (up to 500 words).
  9. References - provide links to any publications or press releases of relevance (up to 500 words).

WIN Scouts proposing potentially suitable partners, will be asked during submission to invite a relevant contact, this being an employee with the relevant authority at the proposed partner. For the partner to be considered as a potential entrant, the same information as detailed above, is required for our evaluation that the proposed partner has future potential relative to the solution requirements.

Wazoku encourages the use by Solvers of AI approaches to help develop their submissions, though any produced solely with generative AI are not of interest.

Find out more about WIN and Nexus Challenges.

Submissions to this Challenge must be received by 11:59 PM (US Eastern Time) on November 7th, 2023.

Late submissions will not be considered.

Your submission will be evaluated by the evaluation team first reviewing the information and content you have submitted at the submission form, with attachments used as additional context to your form submission. Submissions relying solely on attachments will receive less attention from the evaluation team.

After the Challenge submission due date, the Wazoku evaluation team will complete the review process and make a decision with regards to those selected as entrants to Showcase your proposal, according to the timeline in the Challenge header. All Solvers who submit a proposal will be notified about the status of their submissions.

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