Picture of the final prototype, ready for use
The Problem and Project: Developing Thermal-Controlled Formwork for Winter Concrete Pours
For my ENGR 499 Capstone Design project, I worked in a group of 6 (4 mechanical, 2 electrical) to design a solution for low-temperature concrete curing of foundational walls for Kelowna multi-family housing developments. The reason why low-temperature concrete curing is a problem is that below 5℃, the strength and overall integrity of the concrete is reduced after curing.
With Traine Construction & Development (Traine), a Kelowna-based construction company, as our client, we were faced with a unique problem that challenged our domain knowledge, giving the opportunity for everyone on the team to learn something new.
As one of the two electrical engineering students on the team, it was on us to develop the electrical part of the solution that best solved the problem.
A picture of a Peri gang form, a structure used to hold the concrete in place while it cures
Initial Project Ideation
During ideation, each team member proposed a solution. My idea was to insulate the concrete with a blanket and use a fan to blow in warm air, reducing the heated space compared to traditional heaters. This differed from the chosen heated blanket design, as it relied on trapping warm air rather than generating heat. Essentially, it optimized construction enclosures by heating only the formwork and concrete, saving energy.
The Blanket
After exploring further solutions such as space heating and heating the gang forms themselves, the team ultimately landed on a heated-blanket approach. This is because non-heated blankets are not sufficient to heat concrete in -10°C conditions, which was the edge of our scope for temperature.
Importantly, heated blankets for concrete curing already exist on the market. While these blankets work in theory, after Brandon (the other electrical engineering student in the group) and I performed calculations into their power efficiency and choice of materials, it was apparent that these blankets left room for optimization in efficiency. Additionally, these blankets were generic in their usage and not specialized for any one design application. This gave the team the objective of designing a blanket that maximizes thermal efficiency through optimal choices in material selection/layout as well as with the implementation of the heating element.
The Heating Element
Heating cables (left) and heating mats (right)
Upon deciding on a heated blanket, Brandon and I started looking at heating element choices. It was agreed early on that commercial options were to be explored, as this reduces the complexity in development and implementation while maximizing safety. Looking online, I came across two viable candidates: a heated mat and a heated cable. While I initially preferred the heated mat due to its ease in installation, doing the calculations proved that the cost, weight, and power consumption were a poor choice in comparison to the heated cable.
Table from the Final Report comparing the heating mat and heating cable
Into the Prototype
Wiring layout of the prototype (left) and the inside of the prototype (right)
Once we finalized what heating element was to be used, Brandon and I calculated how “dense” the wire needs to be coiled in the blanket to achieve the defined power requirement of 88 W/m2. The materials for the blanket were then ordered and the prototype was assembled.
Testing and Results
A graph showing the relative strengths of the concrete
With the prototype assembled, now came the fun part of testing. To do this, the following testing scheme was devised. To begin, three copies of a custom-designed concrete mold were created. Following this, concrete was simultaneously poured into these molds. Next, one mold was cured for 72 hours in an ideal concrete curing environment and served as the control. The other two molds were transported to a cold environment (in this case, a local curling rink) where the ambient temperature was consistently around 3°C. One of these two molds was surrounded by the heating blanket and the other was not.
After the designated curing time, all concrete samples were brought back to the university’s concrete testing facility where they underwent hydraulic press testing.
The results of this testing can be seen in the above graph, where the time the hydraulic press was applied is measured on the x axis and the applied force of the press on the y axis (the higher the y axis, the stronger the concrete). As can be seen from the graph, the “cold concrete” was the first to break (in a similar manner as seen in the video), followed by the baseline, and finally by the concrete covered by the blanket.
The concrete sample under a hydraulic press
These results are exciting as they show that not only does our solution work, but it performs significantly better than the baseline. The group hypothesizes that this is the case due to the prototype working so well as to accelerate the curing of the concrete, leading to greater strength earlier in time. Such a result opens the opportunity for using our solution as a “curing accelerator.”
Other Major Project Contributions
Beyond working with Brandon and the rest of the team to select the best heating element for the blanket, I took up an active role in facilitating communication within the group. This included running the group’s Discord server, keeping in contact with the group’s Faculty Advising Team, and coordinating with Isaiah to determine dates for the various Client Update Meetings interspersed throughout the semester.
Additionally, I kept a close eye on the formatting and correctness of the group’s various reports. For instance, I caught that the submission requirement called for the final report to be in 12-point font, whereas our report was still in 11-point font. We were then able to correct the issue before the deadline.
Conclusion
The goal of this capstone course is to apply engineering knowledge from courses taken throughout the program to produce a self-guided engineering design with assistance from a faculty advisor. While working with concrete is not the first thing that comes to mind when one thinks of an electrical or mechanical engineer, we as a group collectively expanded our domain knowledge to successfully solve the engineering problem at hand. Using the knowledge gained throughout this course, I hope to continue to work in multidisciplinary teams to solve complex engineering problems.