Data Collection for R-Values
Each block was tested for thermal resistance over 24 hours. We built 5 test boxes, so the entire process took 17 days. Each morning, Tom woke up early, went into his unheated shop (he did this in January and February in Massachusetts, and it was COLD!) and set up a new round of tests. By the time Tom found his groove, he’d gotten the entire process down to 30 minutes. Tom added a few days of work to the process. In addition to hempcrete, Tom tested a variety of insulation materials - XPS (pink or blue board), mineral wool, cellulose, cotton batt, fiberglass batt, and cellulose at a range of packed densities. We wanted to have a baseline of established, tested materials to confirm that our equipment and testing methods were working properly. This was facilitated by the help of Energia, an insulation company where each of these materials (except the XPS) are part of their company repertoire.
The data sensors collected information every 5 minutes over that 24 period. Prior to being placed in the test box, each block was weighed, underwent a moisture reading, and this information was recorded in a spreadsheet that also noted. Production dates, binder and aggregate compositions.
Sensors were placed in 4 key areas:
1) inside the heated section of the test box, 2) outside the test box, 3) on the heated face, and 4) opposite face of the hempcrete block, which is used to track the thermal transmission of heat across the block over time.
Once all 86 blocks of hempcrete and the 10 other insulation materials had been completed, the sensor information was downloaded by Professor Weil at the University of Massachusetts, and cross-referenced with our data spreadsheet. Temperature Data from the first 15 minutes of the test will be removed from the results - this provides the box itself - an XPS contraption - time to return to a stable temperature before data collection documents the thermal resistance of the material.
We tested 3 different aggregates: local CBD hemp hurd and sunchoke (both processed by HempStone and Village Carpentry), and european hurd from the Netherlands.
We tested 13 different binders: French natural cement (Vicat), Vicat mixed with local lime in various proportions, Massachusetts lime with Canadian metakaolin clay, local lime with American metakaolin clay, Ohio Lime with each metakaolin clay. The clay and lime mixes were tested in various proportions.
Our goal: To find the best local and regional binders for use in construction and to test the liability of using local waste plant stalks in construction
Unexpected consequence: By conducting these tests, we have established methods and professional relationships to support others in testing binder solutions that are local to them. Although this is not our focus at the moment, we are excited to pursue this as needed in support of local solutions, wherever folks are located.
Stay tuned, we’ll keep you posted on our results!