3D printed temperature-sensing repairs for concrete structures

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.

Self-Sensing Alkali-Activated Materials: A Review

“…The first region of temperature sensing of reported applications is situated approximately between -30 • C up to around 50 • C. This section encapsulates most of the temperature sensing tests that have been carried out and corresponds to the majority of field and civil engineering applications. The behaviour for this temperature range is fairly straightforward as when the temperature increases, the resistance of the material decreases [24,26,27,65,87,131,139,[148][149][150].…”

“…. Self-sensing AAM substrates (a) metakaolin AAM with wound wires [55] (b) metakaolin AAM printed coating with stainless steel wires [27] (c) fly ash AAM with stainless steel wires [65].…”

“…However, embedding can result in additional stresses to the AAM matrix, resulting in cracking during curing [115,116]. Embedding thin wires (rather than large electrodes) can reduce stress concentration and minimize the mechanical impact of the electrodes on the AAM during curing [27,65].…”

“…In addition, Sellami et al [94] mentioned that for temperatures Figure 9. Fractional change in impedance-frequency response for 3D printed metakaolin AAM between 10-30 • C adapted from [27].…”

“…However, as the understanding and the technology of AAM progresses, the need for these additional sensing devices has diminished: interrogation of changes in the electrolytic conductivity of AAM allow them to be directly used as a sensing tool in their own right [22]. As a result, AAM have increased the number of supporting roles in structural health monitoring and maintenance, being used as both structural self-sensing elements (e.g., AAM concrete cubes and beams) [23][24][25], and as self-sensing coatings for OPC concrete substrates [26,27].…”