No abstract

Multifunctional coating materials have enjoyed extensive development within civil engineering in the last few decades, with numerous proposals for self-sensing and self-healing repairs. Less thought has been afforded to coating material deployment, but a reliance on conventional manual methods is leading to high costs and variabilities in performance. This is prohibiting the application of new materials in the field. This paper addresses this issue by outlining, for the first time a 3D printable temperature sensing repair for concrete. The multifunctional material used in this study is a geopolymer: a durable alternative to ordinary Portland cement repairs, which can be electrically interrogated to act as a sensor. In this paper, we outline the material and 3D printing process development, and demonstrate 3D printed repair patches with a temperature sensing precision of 0.1 °C, a long-term sensing repeatability of 0.3 °C, a compressive strength of 24 MPa, and an adhesion strength to concrete of 0.6 MPa. The work demonstrates the feasibility of using additive manufacturing as a new means of applying repairs to concrete substrates, and provides one clear pathway to removing some of the barriers to the field deployment of multifunctional materials in a civil engineering context. The process shown here could enhance the design versatility of self-sensing repairs, unlock remote deployment, and de-cost and de-risk actions that prolong the lifespan and performance of existing concrete structures.

The reinforced concrete structures that support transport, energy and urban networks in developed countries are over half a century old, and are facing widespread deterioration. Geopolymers are an affordable class of materials that have promising applications in concrete structure coating, rehabilitation and sensing, due to their high chloride, sulphate, fire and freeze-thaw resistances and electrolytic conductivity. Work to date has, however, mainly focused on geopolymers that require curing at elevated temperatures, and this limits their ease of use in the field, particularly in cooler climates. Here, we outline a design process for fabricating ambient-cured fly ash geopolymer coatings for concrete substrates. Our technique is distinct from previous work as it requires no additional manufacturing steps or additives, both of which can bear significant costs. Our coatings were tested at varying humidities, and the impacts of mixing and application methods on coating integrity were compared using a combination of calorimetry, x-ray diffraction and image-processing techniques. This work could allow geopolymer coatings to become a more ubiquitous technique for updating ageing concrete infrastructure so that it can meet modern expectations of safety, and shifting requirements due to climate change.

The degradation of onshore, reinforced-concrete wind turbine foundations is usually assessed via above-ground inspections, or through lengthy excavation campaigns that suspend wind power generation. Foundation cracks can and do occur below ground level, and while sustained measurements of crack behaviour could be used to quantify the risk of water ingress and reinforcement corrosion, these cracks have not yet been monitored during turbine operation. Here, we outline the design, fabrication and field installation of subterranean fibre-optic sensors for monitoring the opening and lateral displacements of foundation cracks during wind turbine operation. We detail methods for in situ sensor characterisation, verify sensor responses against theoretical tower strains derived from wind speed data, and then show that measured crack displacements correlate with monitored tower strains. Our results show that foundation crack opening displacements respond linearly to tower strain and do not change by more than ±5 μm. Lateral crack displacements were found to be negligible. We anticipate that the work outlined here will provide a starting point for real-time, long-term and dynamic analyses of crack displacements in future. Our findings could furthermore inform the development of cost-effective monitoring systems for ageing wind turbine foundations.

Sensors and new materials can support optimised concrete maintenance, and produce the data needed to justify new, low carbon structural designs. While these technologies are affordable, the process of manual installation in a construction context comes with acute and unfamiliar risks to productivity, personnel safety, and confidence in the quality of workmanship. The installation of smart materials using robotics could address some of these issues, but there are few proofs-of-concept at the time of writing. Here, we present a robotically controlled process for spray coating geopolymers -a class of self-sensing concrete repair materials. By tuning mix design, robotic toolpaths and spray dispenser parameters, we show reliable and automated spray coating of 250 mm 2 patches in a laboratory setting. The cured geopolymer has a compressive strength of 20 MPa, and a bond strength to the concrete substrate of 0.5 MPa. Electrical interrogation of patches, via a set of four electrodes, produces strain and temperature measurements of the underlying concrete substrate with resolutions of 1 µε and 0.2 • C, respectively. This demonstration multifunctional material deposition using robotics is a step towards remote, traceable, and low-risk technology deployment across civil engineering sectors. This could support more widespread adoption of novel concrete health monitoring and repair systems in future.