Welcome to the Aircrete Engineering open source hub. The purpose of this page is to share the engineering steps, research, resources, and tools we’ve used to verify the safety of our aircrete designs and structures. We will continue to evolve this page until our aircrete dome home is permitted. If building that structure demonstrates aircrete is a better choice than Earthbag construction, we will build the entire Earthbag Village as aircrete instead – open source sharing complete plans for both an Aircrete and an Earthbag Village.
For easy reference, the page is divided into the following sections:
NOTE; THUS FAR WE’VE DONE HUNDREDS OF HOURS OF MIXING AND TESTING AND HAVE YET TO GET CONSISTENT RESULTS. OUR EXPERIENCE SO FAR IS DETAILED BELOW. BASED ON OUR TESTING SO FAR, WE WOULD NOT RECOMMEND AIRCRETE AS A BUILDING MATERIAL. HOPEFULLY THE NEW ROUNDS OF TESTING WE’RE DOING WILL GET DIFFERENT RESULTS. WHATEVER THEY ARE, WE’LL PUBLISH THOSE RESULTS HERE ONCE COMPLETE.
Aircrete is a type of building material that closely resembles concrete, but the filler is foam (small air bubbles) instead of aggregates (sand and gravel). This relatively new material consists of three key components: cement, water, and detergent foam. The foam component is incorporated into a cement slurry mix, and the nearly microscopic bubbles from the foam fill the slurry with air cells. The large number of air cells distributed throughout the aircrete allows it to be far lighter and to have greater insulation properties when compared to traditional concrete. Similarly to concrete, aircrete is often poured into molds and then cured over a period of time to allow the product to harden and strengthen. The result is a cementitious block with a uniform composition.
Aircrete is intended to be utilized like concrete, but the compressive strength of aircrete is not well documented. This content was generated to document a scientific approach to defining the compressive strength of aircrete. This effort was pursued because of the many benefits associated with aircrete – it only consists of three relatively affordable ingredients which are widely available around the world (detergent, water, and cement). The most important benefit of aircrete is the ability to produce this material without heavy machinery or intensive labor – it can be made using a few everyday items. Aircrete has the potential to be an economical, lightweight, and easily accessible building material.
Open sourcing our aircrete research is important so that it can be replicated and/or so that other engineers/designers can build upon our work to improve it and/or make changes to suit their own projects/visions. Currently, there is very little information on the engineering aspects of using aircrete for structural purposes, so creating this online tutorial is helping to fill the void we see in this area. Our hope in sharing what we’ve learned is to increase public safety and improve the performance of aircrete-constructed structures.
Sustainable building materials are a foundation of One Community’s open source strategy for building a global collaboration of self-sufficient and self-sustainable teacher/demonstration communities, villages, and cities for The Highest Good of All. One of the biggest steps to building more sustainably is conducting well-designed research to answer questions of structural strength for furthering the use of non-mainstream building materials. With this in mind, we have researched the compressive strength of aircrete as part of our open source contribution to comprehensive sustainable living. This page is a collection of our initial research and will evolve with our experience.
Charles Gooley: Web Designer
Dominick Banuelos: Civil Engineering Intern
Jarot Tamba: Civil Engineering Intern
Julia Meaney (Web and Content Reviewer and Editor)
John Paul D. Matining: Civil Engineer Intern
Marcus Nguyen: Civil Engineering Intern
Yiwei He: Mechanical Engineer
Zhide Wang: Mechanical Engineer
The purpose of testing aircrete is to obtain data and knowledge of aircrete’s compression strength and compare the results to that of concrete. We are researching aircrete as a possible alternative to the current earthbag construction plans for the Earthbag Village (Pod 1). Once this compression testing is done, we intend to run a crowdfunding campaign to compare labor, costs, and how well the structures perform side-by-side. We’ll do this with internal sensors monitoring annual temperature, humidity, etc. Our expectation is that aircrete domes will outperform earthbag domes in almost all categories, confirming aircrete as another sustainable and low-cost construction material option.
Below we discuss our engineering findings and the process we used to get the results we did. We also share how to use the various spreadsheets we created. Note that all structures using aircrete must still be checked and signed off on by an engineer licensed in your state before beginning any construction. The research and hands-on experimentation journey are shared in the following sections:
Summarized in this section are the steps we have taken so far to learn more about the structural strength of aircrete. Included are links to the spreadsheets where the calculations were completed. Instructions for copying and modifying the spreadsheets are at the top of each tab within them.
The overall research and experimentation process began with the assumption that the methodology available to make aircrete was robust and reproducible. As such, at the start of the project, the goal was to make traditional concrete, various compositions of aircrete (including the standard instructions provided by Domegaia and Aircrete Harry), various compositions of stabilized earth cylinders, and stuccoed cylinders to determine their compressive strengths. During this Phase, information was gathered about the production and properties of aircrete and stabilized earth. By researching these building materials, a greater understanding was gained of how to make the different mixes. The initial planning documents included a Mixing plan and a Cleaning plan.
Initial Calculations were done during this phase to figure out how much of each material was needed for each mix. The amount of foam added was not clear from the instructions available online, so that value was deduced. It was assumed that the volume of the added foam was to be the total aircrete volume minus the volume occupied by the cement slurry. The equipment was also tested at this phase to get familiar with the overall process of making the aircrete and stabilized earth. The Little Dragon foam generator was utilized with an air compressor set to 90 PSI.
During this phase, the focus was to replicate Domegaia’s procedure, which initially appeared simple. It was discovered, however, that making aircrete is not that simple. After initial attempts at making aircrete, it was noticed that aircrete lost volume over time. In other words, aircrete did not maintain the target volume. Online resources were scoured to figure out a way to make aircrete that did not collapse/shrink and lose its target volume.
Given Domegaia’s successes with Seventh Generation Dish Soap, and given that Seventh Generation Dish Soap is an affordable, easily accessible, and environmentally conscious foam option, the suitability of this foaming agent was explored. The following 15 trials were conducted using Seventh Generation Soap and Domegaia’s Little Dragon. These trials consisted of testing different mixer types, mixer speeds, mixing times, proportions of ingredients, etc. Even after adjusting several variables to mitigate aircrete collapse, the trials below resulted in overall failure – loss of overall volume during curing. The findings and experience are summarized in 3 formats:
The first three trials showcased the inconsistency of working with aircrete. These trials were all conducted in the same manner, utilizing the same amount of cement, water, foam, and soap solution, as well as the same mixing method and timing. The result was that all three trials failed. During Trial 1, the aircrete collapsed by about half of its volume early in the curing process. Aircrete from Trial 2, which was an exact replication of Trial 1, experienced collapse further into the curing process. Aircrete from Trial 3, which was an exact replication of Trials 1 and 2, collapsed early in the curing process. The conclusion of these first three trials proved that aircrete was not easily replicable and there was an issue with either the materials, mixing method, conditions, or mixing tools.
During Trial 4, a different type of mixing attachment to the drill was utilized. Previous trials were performed using an auger drill bit. Trial 4 utilized an egg beater-style mixing bit. The idea behind this decision was to mix the aircrete quicker. This trial also resulted in aircrete collapse.
During Trial 5, the cement slurry was added to a bucket that already contained the foam. The idea behind this decision was that having the foam on top of the slurry (as was done in all previous trials) was not allowing the cement slurry to combine with the foam well. So, with foam being of lighter weight than cement slurry, gravity would be in our favor and help to pull the cement slurry down into the foam. However, the aircrete still collapsed during curing.
Trial 6 was similar to Trial 5, in that the introduction of foam into the mix was from the bottom. This time the foam was injected directly from the foam wand into the cement slurry. This meant that the foam was not measured into a separate bucket and then added to the slurry, like in previous trials. Directly injecting the foam into the cement slurry allowed for faster and more thorough mixing. Also, the foam did not spend time in a separate bucket, where bubbles were likely losing integrity before being added to the slurry. Trial 6 was also a failure and the aircrete collapsed soon after it started to cure.
Trial 7 used a different mixing method and vessel – a cement mixer. Although this provided a quick way to produce aircrete in large quantities, the aircrete lost a lot of volume in the mixer. Thus the mixer was deemed not well suited for mixing such a delicate material.
Distilled water was used in Trail 8. This idea came from a forum where a member who was experiencing a collapsing aircrete, later determined it was due to his faucet water being “hard”. The hardness of water is a measure of the amount of dissolved calcium and magnesium in water. As shown below, hardness has a significant impact on the formation of suds.
This trial was performed using the egg beater-style mixer but this time, distilled water was used instead of the water provided in the laboratory to make cement slurry. Unfortunately, distilled water was not used to make the foam solution. This trial was a failure and showed similar results to others – the aircrete collapsed during the curing process.
After this trial was done, a hardness test of the tap water was carried out. It was found that the water in the lab is very hard, measuring 13 grains of CaCO3 (calcium carbonate) per gallon, or 223 mg of CaCO3 per liter. The table below shows the hardness scale.
For Trial 9, a single batch of Aircrete was mixed in the compression testing cylinder itself. Previous mixes were done in 5-gallon buckets that were 12 inches in diameter and 15 inches tall. The compression cylinder is significantly smaller – 6 inches in diameter and 12 inches tall (about 1.5 gallons). When using the 5-gallon bucket, the mixer bit was not able to be fully submerged in the cement slurry which meant it was not getting properly mixed. Using the compression cylinder now allowed for the mixer bit to be fully submerged in the slurry. The figure below demonstrates this. Trial 9 proved to be successful – this Aircrete batch did not collapse.
Trials 10, 11, and 12 were performed solely to determine the replicability of the success of Trial 9. After performing the exact same procedures, all trials were a failure, meaning they resulted in collapse.
Trial 13 tested the same concept tested in Trial 9 but was implemented using a larger amount of aircrete (enough for 3 curing cylinders) in a 5-gallon bucket to insure that the mixer was fully submerged. Also, at this point, the aircrete was made not using a calculation of how much foam to add, but by adding as much foam as was necessary to get the desired volume. This trial was a failure – the aircrete collapsed.
Trial 14 followed the same basic procedure as Trial 13, but used a lighter mix (more foam and less cement slurry in the aircrete). Standard aircrete (the recipes used up to this point) is approximately 20% slurry and 80% foam by volume. This lighter mix was 10% slurry and 90% foam by volume. This trial was also a failure – the aircrete collapsed.
Trial 15 utilized the method stated in Trials 13 & 14 but the trial was done with the “heaviest” aircrete mixing quantities. This meant that this mix had the greatest amount of cement and the least amount of foam compared to all of the previous trials. This heavy mix was 60% slurry and 40% foam by volume. Trial 15 was successful and the aircrete did not suffer collapse. This was likely due to the small amount of foam in this mix of aircrete and the fact that the air cells of the foam are the components of the aircrete which have the ability to reduce the initial/target volume.
With all of these failed attempts, more research was conducted to find out how to make an aircrete mix that did not collapse during the curing process. There were many factors in the aircrete making process that could affect the final product. Additional online research was completed to help resolve the shrinkage issues encountered. The findings of the second round of online research are summarized here. The overarching finding was that other foaming agents work better than Seventh Generation Dish Soap and that mixing is an important aspect of making aircrete that doesn’t collapse.
The second round of research described above led to further exploration into the foaming agents, which led to additional trials: Trials 16 through 26.
Trial 16 was done in 2 parts. First, several foaming agent options available at grocery stores were tested to determine the integrity/longevity of the foam. Then, the difference between Drexel and Seventh Generation Dish Soap was explored. Foam agent testing results are detailed here.
Part 1 – Suave outperformed the rest of the foaming agents. At the 40-minute mark, all foam agents were at a similar height. Then at the 60-minute mark, there was a large gap between the Suave foam and the rest. Dawn also performed better than Seventh Generation Dish Soap according to the data below.
Part 2 – The results for the foam test comparing Seventh Generation Dish Soap and Drexel determined that the foam produced by Drexel was far superior to the foam produced by the Seventh Generation Dish Soap detergent. The foam from the Drexel had far less loss of volume within the given time frame. In addition, the foam solutions that consisted of a higher concentration of detergent produced a longer-lasting foam. This was true with both Drexel and Seventh Generation Dish Soap detergent. Additional pictures for each time stamp are available here.
For Drexel, the following amounts were tested: 2 oz, 4 oz (standard), and 6 oz to 2.5 gallons of water. For Seventh Generation Dish Soap, the following amounts were tested: 8 oz, 10 oz (standard), and 12 oz to 2.5 gallons of water. Overall, the Seventh Generation Dish Soap was less stable than the Drexel. The foam made with Seventh Generation Dish Soap began to lose volume at about 40 minutes. Drexel didn’t start losing foam volume until closer to 100 minutes after making the foam. After 2 hours, the foam made with Drexel using the recommended foam recipe had lost 1.5 cm of head, whereas Seventh Generation Dish Soap had lost 19.5 cm of head during the same time period:
The results are summarized in the table below.
Trials 17-20 were done to determine if the successful findings from Trial 16 could be replicated. Unfortunately, all 4 of the trials failed – the aircrete collapsed.
Trial 21 tested the effects of increasing the amount of detergent added to the foaming solution since the foam was thought to be a major factor in these aircrete failures. Several foam tests were run to see if a greater amount of Drexel in the foam solution would provide a longer-lasting and better quality foam – results are summarized here. For this trial, 6 oz of Drexel was used in the solution rather than the previous (and expert-recommended) 4 oz. The result was a better foam and the aircrete did not collapse.
Trials 22, 23, and 24 consisted of 4.5-gallon batches of aircrete. Trial 22 was a standard mix using 9.4 lbs of cement, 0.6 gallons of water, and 5.6 gallons of foam. Trial 23 consisted of 20% more cement in the slurry, with 11.28 lbs of cement, 0.7 gallons of foam, and 4.5 gallons of foam. Trial 24 consisted of less water in the cement slurry, with 9.4 lbs of cement, 0.5 gallons of water, and 6.8 gallons of foam. The standard mix and 20% more cement mix were successful and did not experience any collapse. However, the mix that consisted of decreased water and increased foam collapsed.
When it was noticed that the Domegaia Little Dragon foam generator was not maintaining its pressure, the Aircrete Harry foam generator was purchased, tested, and used for the remainder of the testing. For Trial 25, the Domegaia and Aircrete Harry foam generators were tested side by side. Foam was generated using each machine and its volume was measured over time. The two machines produced very similar results, but Aircrete Harry’s machine did slightly better as the foam maintained its volume a little better, with 1 cm less collapse. Foam generator testing results are detailed here.
Aircrete Harry Foam Generator: Appearance of foam after X amount of time had passed
Domegaia Little Dragon:
Trial 26 focussed on identifying the maximum foam limit of the aircrete mix. First, the highest foam content was identified while maintaining the target volume during curing. This testing began with a recipe using 95% of foam to 5% of cement slurry which resulted in shrinkage. Then, the foam percentage by volume was decreased and the cement slurry was increased incrementally by 5% until the successful foam limit was reached. The upper limit of foam that worked the best was 85% foam to 15% cement slurry by volume. This successful foam limit was 7% more foam than the standard mix. Details are available here.
The original task, which included testing stabilized earth and stucco, was narrowed to only experimenting with aircrete and future teams of students would pursue other questions worth answering in the quest for a more sustainable building material. Since Trials 21 and 22 proved to be successful (e.g. aircrete that did not collapse during the mixing, pouring, and curing process), the Compression Testing Phase was initiated. This phase is discussed below in the following sections:
The impact of 6 cementitious recipes, as well as 5 curing times, on compressive strength was explored. The 6 cementitious recipes included a control mix (standard concrete mix) and 5 aircrete mixes. The 5 curing stages included 48 hours, 1 week, 2 weeks, 3 weeks, and 4 weeks from when the cylinders were made. Each mix type and curing time were done in replicas of 5. After the cylinder had time to cure for that corresponding time, the molds were removed from the cylinder and its compressive strength (pounds per square inch) was tested using a compression testing machine. The test parameters are summarized in the table below:
The Experiment 1 Phase (Aircrete Data Collection Sheet) involved a cylinder building day to make 125 cylinders of aircrete and 25 cylinders of concrete that were used for compression testing. A practice day was held to get familiar with the cylinder making process (Pre-Run Work Plan), prior to constructing the 125 cylinders of aircrete and 25 cylinders of concrete. On the day of making all the cylinders, volunteers were divided into three teams. The following link share the instructions used on the day of making all the cylinders: Prep Team Instructions, Foam Team Instructions, and Cylinder Making Day Procedures. The Compression Testing Phase was completed at 48 hours, 1 week, 2 weeks, 3 weeks, and 4 weeks after the day of making of the cylinders (e.g., Curing times of 48 hours, 1 week, 2 weeks, 3 weeks, and 4 weeks). The data was recorded for each of the cylinders with the weight, compressive strength, and pictures. Once all those data were completed in the data collection sheet.
The items listed below were utilized to produce the aircrete and concrete materials. Links to each of the materials are provided for ease of access and replication of the project’s processes.
In addition the following link has a materials list utilized during the project: Materials request list. The following materials requested were items that were still needed to conduct testing on this project. The items below are all the necessary materials for this project.
This section has details on how concrete was produced. Step-by-step instructions are provided below for replication and production of ready mix concrete. Concrete rated at 4000-PSI was used because it is a more commonly used strength of concrete for applications regarding similar structures such as smaller dome structures like One Community intends to utilize aircrete for.
The choice to use 4000 psi concrete for the compression test was also based upon the following reference. Portaggregates.com states that this strength of concrete is usually used for foundations and footings but is a great option for backyard sheds and workshops due to its strength and surface durability.
Cor-Tuf.com states that traditional concrete walls and columns tend to have a range of 3000-5000 psi. Although it is sufficient to use 3000 psi strength concrete, the 4000 psi option was chosen to produce concrete and to stay consistent with existing widely available ready mixes. (Details)
Besides its concrete’s strength and durability, the reasoning stemmed from the reasons behind why aircrete (cement, Seventh Generation Dish Soap, water) was being tested in the first place. This was because it is cost efficient and these products are more widely available to people around the world. Therefore, this was one of the ideas behind why this particular concrete mix was utilized which is readily available and cost efficient. The quikrete bag of concrete is very popular and can be easily obtained at local hardware stores and it also is rated for a compression strength of 4000 PSI.
Quikrete® Concrete Mix (No. 1011) 4000 PSI rated concrete was utilized in the experiment and therefore the instructions are intended to use the same Quikrete concrete material.
Video Description: Step-by-step instructions showcasing for replication and production of Quikrete® Concrete Mix (No. 1011) 4000 PSI rated concrete.
First determine the desired amount of concrete the project requires. This will require one to take measurements of the volume needed to obtain the correct quantity of concrete desired. The following link is useful for determining the amount of concrete mix and water to use for the desired amount of concrete needed: Concrete Mix Calculations. The user can type in the desired amount, then follow the specifications given in the spreadsheet.
The numbers mentioned provide the user with some background on the findings. According to the manufacturer, every 90 pound bag of Quikrete Mix requires approximately 7 to 10 pints (7.3-10.43 pounds) of water. This combination produces approximately 0.675 cubic feet of concrete. Each project will require a different amount of concrete and 0.675 cubic feet of concrete is not always desired.
Instructions for a single compression testing cylinder (if needed): The goal in this paragraph is to produce enough concrete to fill a standard compression cylinder mold (approximately 1.5 gallons or 0.196 ft^3). To produce 1.5 gallons of concrete to fill a single cylinder, use 10 lbs of mix and aim to use between 0.8-1.1 lbs of water.
After having the desired amount of dry concrete and water set aside, prepare the rotating concrete mixer by assuring the interior of the barrel is clean and to a certain extent free from debris.
These steps can also apply to the use of a large mixing tray if a concrete mixer is not readily available. Typically the utilization of a mixing tray is needed when the desired amount of concrete is of a smaller amount.
To start properly mixing your concrete, pour about half the portion of the required water into the concrete mixer. Adding the water first will help prevent the dry concrete from sticking to the mixer and allow the contents to mix more thoroughly. Modulate the concrete mixer by tilting it to different angles to ensure the water has coated the majority of the interior of the mixer.
When performing this procedure in a plastic mixing tub the same steps will apply. Add water to the mixing tub first. Adding water first will prevent the mix from sticking to the bottom of the tub and better prevent clumping in corners of the tub.
Next it is important to add the concrete dry mix in increments and not in one attempt. Pour about half of the required concrete mix into the mixer and start mixing the contents together making sure the contents mix thoroughly. After a few rounds of mixing, add the rest of the water into the mixer and allow the mixer to combine those materials together. After it is thoroughly mixed, add the rest of the concrete dry mix into the slurry and allow the mixer to rotate until all contents are thoroughly combined. The concrete is thoroughly mixed when there are no areas of the slurry that consists of dry material. The slurry should have a uniform consistency.
If utilizing a mixing tub, use one’s hands to thoroughly push together, spread, and thoroughly mix the concrete slurry. The concrete will be fully mixed when there are no areas in the slurry which still contain dry mix.
Concrete dries quickly thus it is important to keep the mixer rotating if the concrete will not be used immediately. This will prevent the slurry from hardening when not in use.
It is industry standard and important to check one’s concrete mixture to ensure that it is up to the manufacturer’s specifications and that it is not overly wet or dry. A wet mix typically means that an excess of water was added to the mix and thus it will have a higher chance of shrinking/cracking during the curing process. A dry mix will yield a concrete mix that is difficult to shape and work with.
To check for proper concrete content and mixing, one must utilize a slump cone to check for the slump of one’s concrete. In a slump test you place a slump cone securely to its base, fill the cone with concrete in 3 parts. Every ⅓ of its way up you must take a rod and tamp mixture 25 times. This ensures that pockets of air are penetrated and removed from the mix. The image below shows the types of slump and most importantly the slump procedure.
Once the cone is filled to the top, scrape off the excess concrete protruding the cone. The cone is now completely filled with all of the air pockets removed. Next (if needed, not all slump test bases have hinges/hold downs) unhinge the cone from the base, lift the cone in an upward motion leaving the concrete contents on the base. Measure the amount of droop or slump that occurs after the cone is removed. Ideally the goal is to aim for 2-3 inches of slump – Quikrete manufacturer recommends 2-3 inches of slump for their product. The manufacturer’s recommended slump can be found at the following link: Slump Requirement. A collapsed slump is one which contains too much water, while a zero slump has too little water. Refer to the image below and see the following link to learn more about the slump test. Slump Test information .
If the concrete’s slump was within range, then the concrete is ready for use. If the slump exceeded the allowable range of slump you can still adjust the mix to achieve the allowable range of slump. To fix a concrete mix which has zero slump, place the concrete back in the mixer and add small amounts of water to hydrate the mix and then repeat Step 4 to check its slump range. To fix a concrete mix which has collapsed or sheared slump, place the mix back in the mixer and add in small portions of dry concrete mix to thicken the contents more. In any case adjust the mix accordingly and repeat the slump test until desired slump is achieved. A concrete mix with a proper amount of slump guarantees a workable, strong and long lasting concrete product. The image below is a slump test done utilizing the above mixing process. The slump shown is within the manufacturer’s specifications of 2-3 inches.
(Slump Test results)
At this point the concrete mix has been mixed thoroughly, is hydrated properly and is ready for use. It is important to keep the mix moving if concrete is not used right away.
When adding the concrete to the cylinder, fill the cylinder ⅓ full. After filling ⅓ of the cylinder, take a rod and tamp the length of the concrete added 25 times. After tamping (aka rodding) 25 times, use your hand or tool to mallet the cylinder 10 to 15 times to consolidate. Add another ⅓ and repeat rodding and malleting. Once the cylinder reaches the top, use the rod to strike the excess concrete from the top.
Video Description: Step-by-step instruction showcasing for replication and production of the standard aircrete mix.
The aircrete mixing process used for the Compression Testing Phase of the project, was curated through a series of trial attempts to create aircrete, more specifically the 21 trials previously noted above. The aircrete making process used here differs from that of popular aircrete pioneers such as Domegaia and Aircrete Harry. The aircrete production process was recorded and documented and can be viewed in the following link:
Video Description: Step-by-step instruction showing how to replicate and produce foam using Drexel by finding the density.
An important component of the aircrete making process is the use of a foam generator. A foam generator created by Aircrete Harry was used. Aircrete Harry’s website provides a multitude of information regarding his machine as well as the proper setup. The first step is to properly assemble and set up the Aircrete Harry Foam Generator (information about the AH Foam Generator can be found here). On the website one can obtain the written instructions on the proper assembly and use of Aircrete Harry’s Foam Generator. Proper setup of the foam generator requires the inlet and outlet line to be primed. A video is provided on the website that also demonstrates how to correctly prime the line before using the machine. The following link (Foam Tutorial) is a video recording which showcases the process utilized in order to create a foam which meets the requirements for use in an aircrete mix:
Here are the step by step procedures for making aircrete.
The first step to making aircrete is to set up Aircrete Harry’s foam generator. A simple list of materials needed for this procedure is listed below (A more informative list can be found here):
The ratio used for the foam was 6 ounces of Drexel to 5 gallons of water. To make this, fill a 5 gallon bucket with 5 gallons of water. Use a measuring cup to measure 6 ounces of Drexel, then pour into the 5 gallon bucket with the 5 gallons of water. Mix the Drexel and water solution thoroughly with a mixing paddle. Stir the solution until a small amount of foam begins to form at the top.
The air compressor was set to 90 PSI. Turn on the compressor a few minutes prior to use and keep it running. This allows the compressor to fill its tank and discharge the correct amount of air. Set the compressor 90 PSI throughout the entire process.
To properly set up the aircrete foam generator it is important that the provided hoses are placed in accordance with labels provided on the generator (picture shown on the right). The 3 hoses are connected to 3 separate ports labeled: foam solution in, air in, and foam wand. Place the hose labeled “foam solution in” into the 5 gallon bucket containing the water and Drexel solution. Place the hose labeled “foam wand” into a large container during the priming of the generator. Connect the “air in” hose to the air compressor stated above
Power the foot switch by connecting it to an outlet. This foot switch allows ease of use by allowing the user to modulate the machine on and off, thus providing foam at will.
The Aircrete Harry’s Foam generator utilizes an air valve which allows the user to allow or block air coming from the compressor into the foam generator.
First, prime the generator by first closing the air valve and stopping any air from flowing into the generator – when air is off, the valve will be perpendicular to the direction of the hose. With the valve closed and all the hoses in the respective places, use the footswitch to turn on the generator and let the generator pump the soap solution up through the “foam solution in” hose and out of the “foam wand”. After allowing the solution to cycle through for 5 seconds the generator is sufficiently primed. This means that the foam solution has filled the foam generator and the hoses.
After priming the foam generator, open the air valve (when open the air valve is turned so it is parallel with the air hose). Once the air valve is opened, the air from the compressor will flow through the foam generator and foam will discharge through the foam wand, thus providing the foam needed for the aircrete. Note: The foam will need to be tested before use and this step is stated in Step 6: Foam Density Measurement shown below.
The following tools were used to weigh the water and cement: cement scoop, large scale (ounces and pounds), and various bowls/containers. First, set the scale on a flat surface and power it on. It is important that the scale is free of any debris on or underneath it. Once free of all debris, set the container on the scale and set it to zero. Pour cement into the containers and weigh out in pounds. Then repeat for the water.
To perform the foam density measurement, use the setup for the foam generator in steps 2, 3 and 4. Use a scale that measures in units of grams and place a 1 quart bucket on the scale and zero the scale. Take the 1 quart bucket to the foam generator.
At the foam generator, step on the foot pedal, prime the machine and open the air valve to discharge the foam. While doing this, look at the pressure on the air compressor and make sure it is first set to 90 psi. Allow the foam to discharge for 3 seconds, then fill the quart cup completely. It is important that there are no gaps in the filled cup. Once it is filled, switch off the generator and close the air valve. Remove the excess foam, by scraping it off and place it on the scale.
Confirm that the weight of the foam is between 90 and 100 grams but aim for 95 grams. This translates to a density of 90-100 grams per quart which is required for Aircrete.
If the measured foam is not between 90-100 grams per quart, the air pressure needs to be adjusted and the density needs to be re-checked. Adjust the air pressure until the correct foam density is achieved. The air pressure is in units of pounds per square inch (psi) and can be changed by turning the knob to either increase the air or decrease the air flow. For example, adjusting for a heavier density foam decreases the air pressure, and adjusting for a lighter density foam increases the air pressure. A picture for reference is shown on the right.
Mix the cement slurry by taking the previously measured container of water (the water for the cement slurry) and place water into a 5 gallon bucket. Place the drill and auger into the 5 gallon bucket. Add the cement into the water in small increments – This prevents the cement from clumping and sticking to the bottom of the 5 gallon bucket. As cement is added, mix the slurry throughout the entire process. The drill can be modulated to run slowly or quickly depending on the trigger pressure placed on the drill.
Operate the drill until the cement and water are thoroughly mixed. If the foam is not readily available it is important to mix the cement and water continuously to prevent hardening of the materials.
Before adding the foam to the cement slurry, it is important that the foam is at the correct density which was done during step 6. With the density already measured, discharge the foam into a measuring bucket and obtain the desired amount of foam. Once the correct amount of foam is obtained, take the foam and pour it into the cement slurry mixture. If all the foam does not fit at one time, add it in increments or pour half and then the other half. The total foam content that the cylinders were based upon resulted from the overall volume left in the cylinder mold. From the testing of how much cement slurry filled the cylinder mold, the rest of the mold needed to be filled in with foam to get the total volume of aircrete being made to be 1.5 gallons of aircrete. The ratio of the different mixes had to change to the amount of foam added to the cement slurry in order to get the maximum amount of foam. Note that about an additional 1 to 2 gallons of foam had to be added to account for the foam breaking down during the mixing process.
This visualization of what is happening in the bucket is helpful when mixing cement slurry and foam: At the bottom of the bucket there is a thick cement/water slurry and on top of that is light foam. The goal is to mix the contents thoroughly by bringing the cement up into the foam and drawing the foam down into the cement slurry. Use a drill with an auger attachment to mix the cement slurry into the foam. Spin drill in both directions – one direction pulls the cement up and the other direction pushes the foam down.
Modulate the drill at a medium speed, avoid mixing at full speed. First, have the drill with the settings set to rotate the auger counter clockwise. The counterclockwise direction rotates the auger and draws the material from the bottom to the top (in this case bring the cement into the foam). Then drill in a clockwise rotation to bring the top mixture down to the bottom (in this case bring foam into the cement). Alternate between the counter clockwise and clockwise mixing to ensure that the aircrete goes through a more thorough mix and the foam and cement slurry are combined into each other well. In addition, raise the drill up and down slowly while mixing to further aid in thorough mixing and therefore achieving a homogeneous distribution throughout the bucket. Also, tilt the drill in different directions to get a proper mix. Tilting the drill adds another mixing characteristic where the material in the bucket does not only spin in one direction but it spins in multiple directions. This again creates a more thorough mix because of the added complexity of the tilted drill.
Mix the aircrete as quickly as possible, which helps in keeping the foam’s (tiny bubbles) integrity and structure. Mixing is complete when the aircrete mix is uniform in color and consistency.
After the aircrete is completely mixed, pour into the cylinder molds for curing. Scrape any excess aircrete mix that is protruding on the top by scraping off with a straight edge. Finish by cleaning the surrounding surfaces and place the lid on top of the cylinder mold.
Video Tutorial: Cylinder Mold Removal (follow the link for a video tutorial)
Video description: Step-by-step instruction on how to utilize the T-Handle Mold Stripper.
Here are step-by-step instructions to utilize a T-Mold Stripper for removal of cylinder mold.
Compression Testing Tutorial
Video Description: Step-by-step instruction showing how to utilize the compression testing machine.
Here are step-by-step instructions for compression testing the cylinders:
Compression testing was done on a control mix (standard concrete mix) and 5 aircrete mixes at each curing stage of the cylinder, namely after 48 hours, 1 week, 2 weeks, 3 weeks, and 4 weeks from when the cylinders were made. Each mix type and curing time were done in replicas of 5. After the cylinder had time to cure for that corresponding time, the molds were removed from the cylinder and its compressive strength (pounds per square inch) was tested using a compression testing machine.
Raw data is available here for concrete and aircrete. The quikrete mix (standard concrete) is rated at 4000 psi when it has cured for a period of 28 days. Looking at the results, the average psi strength from all 5 cylinders increased from 1800 psi at 48 hours to 4000 psi at 28 days. The data for this are summarized here. From the current state of knowledge that we have, we know that the cement/concrete strength increases over a period of 28 days. The results from these cylinders show exactly that. As a result, the concrete cylinders were a success as it reached the targeted rating.
The results for aircrete are less clear because substantial collapse occurred with the light and standard aircrete cylinders. Of the 25 light aircrete cylinders, 18 experienced collapse, which represents 72% of the total cylinder. Fewer standard aircrete cylinders experienced collapse, but nonetheless, more than expected. Out of 25 standard cylinders, 12 experienced collapse, which represents 48% of the total cylinder. This is not considered acceptable. Since this was an issue, there were aircrete cylinders that were not usable because they were too small to fit into the compression machine. It needs to be a full cylinder in order to have an accurate data reading.
Additionally, the Aircrete cylinders had greater variability in their weight than concrete cylinders, as shown in the plot below:
This indicates inadequate mixing. The percent deviation was about 1% for concrete and 25% for the light aircrete, followed by a gradual decrease with aircrete containing more cement:
To assess the compressive strength, the cylinders that collapsed or shark were taken out of the final assessment. Aircrete was much weaker than concrete, but generally exhibited an increase in compressive strength over longer cure times and with increased amounts of cement:
The heaviest aircrete was the strongest, but still much lower than standard concrete (600 psi versus 4100 psi, respectively). Another noteworthy observation was that the light and standard mixes were not fully drying in the cylinders when it was time for the compression test, even after 28 days. When it was time to remove them from the cylinders, water would rush out and because of that, the cylinders were still moist. When it got put into the compression test, the machine continued to apply pressure because it could not read that the cylinder had already reached its peak and because of this, the data was inaccurate. The cylinder just got squashed together and became compacted as it went through the testing.
At the start of the project, it was thought that the instructions available online for making aircrete were robust. With this not being the case, a slough of pre-experiments were completed and in the end were not able to recreate online successes, because they were not able to make aircrete that consistently retained its volume. This effort, which lasted just under a year, ended up having a lot of unknowns that were discovered during the journey and the search for aircrete that maintains its volume continues. The standard and light aircrete mixes proved to be delicate mixes that were not easily reproducible. The aircrete mixes with 60% or less foam (i.e., more cement) did not experience collapse, but did experience variable weights indicating the difficulty in achieving adequate mixing. Also the presence of moisture in the aircrete cylinders indicates that allowing a longer cure time or curing outside of the molds may result in increased compressive strengths specifically for the cylinders with high foam content.
Based on the lessons learned and the sustainability potential of aircrete, additional experiments are recommended. Continued exploration is warranted and recommended next steps for aircrete include:
A new mixer and using soft water instead of hard water. The new mixer could consist of a double bit to provide a more thorough mix and would save time. This would have resulted in the cement more evenly distributed thus resulting in a homogenous mixture. Another aspect is using soft water because the water used was hard water. Hard water makes the micro-bubbles collapse, thus quickly causing the aircrete to collapse and loss of stability.
Also test-worthy are longer curing time for all the mixes and possibly removing the mold once the cylinders can self-hold itself and finishing the curing of the cylinder out of the mold. A good test with this could include outdoor curing which could cure the cylinder faster.
For added compressive strength, stucco application is recommended. The two methods for stucco application worth testing are Domegaia and Aircrete Harry’s(1,2) method for application.
Once the fundamental issue with the standard aircrete shrinkage is resolved, attention is needed to establish the lightest possible aircrete mix. This is particularly beneficial for using aircrete as an insulative material.
Another environmentally friendly building material is Stabilized Earth. Stabilized Earth was dropped from the original project like other components of the test because of time constraints. More detailed research of Stabilized Earth and determination of its compressive strength is needed, as there is a knowledge gap and insufficient data for this building material.
A repeat of the final testing discussed in this report is warranted once the above mentioned concerns are ironed out. This includes the original aircrete, Stabilized Earth, stucco, and concrete which would have been close to 300 test cylinders plus trial and error cylinders.
Given the findings from this 1-year long experimental phase, aircrete still has potential and some variables should be investigated further, as outlined above, before solidifying the recommendations on how applicable aircrete structurally or for use as insulation.
Here are the resources we’ve found useful and used for everything on this page. Use this page (click here) if you have a resource you’d like to suggest be added here
Aircrete Harry: Aircrete Collapsing Time Lapse: “Aircrete Collapsing Time Lapse.” YouTube, Aircrete Harry, 2 Sept. 2018, http://www.youtube.com/watch?v=hPxrsHNGKuo.
Aircrete Harry: Aircrete Column Foam Agent Test Part 1 of 2: “AirCrete Column Foam Agent Test Part 1 of 2.” YouTube, Aircrete Harry, 27 Aug. 2017, http://www.youtube.com/watch?v=y8tfn7RSFx8&t=573s.
Aircrete Harry: Aircrete Final Test Results AFter 4 weeks of Curing
“Aircrete Final Test Results After 4 Weeks of Curing.” YouTube, Aircrete Harry , 4 Sept. 2018, http://www.youtube.com/watch?v=dI8WMa6lzkE&t=1s.
Aircrete Harry: Aircrete Foam Generator
“Aircrete Foam Generator.” YouTube, Aircete Harry, 14 Sept. 2018, http://www.youtube.com/watch?v=biVuBSGiYh0.
Aircrete Harry: New Dome Building System
“Aircrete Harry NEW Dome Building System.” YouTube, Aircrete Harry, 2 Dec. 2020, http://www.youtube.com/watch?v=DVk6xNFduH4.
Aircrete Harry: Aircrete Tools
“Aircrete Tools.” YouTube, Aircrete Harry, 31 Aug. 2018, http://www.youtube.com/watch?v=6p-gWB3PDqM.
Aircrete Harry: Best Aircrete Foaming Agents for your Money
“Best Aircrete Foaming Agents for Your Money.” YouTube, Aircrete Harry, 29 July 2018, http://www.youtube.com/watch?v=rY-oHAYjQ1E&t=581s.
Domegaia: Domegaia’s Little Dragon Foam Generator Kit
“Domegaia’s Little Dragon Foam Generator Kit.” YouTube, Domegaia, 21 Sept. 2018, http://www.youtube.com/watch?v=u3Cx5YRuUyc&t=622s.
Domegaia: Domegaia’s Low Cost Aircrete Housing
“Domegaia’s Low Cost Aircrete Housing.” YouTube, La Maison Du 21e Siècle André Fauteux , 4 Jan. 2022, http://www.youtube.com/watch?v=hDdIrpXTgJE.
Domegaia: Domegaia Aircrete Mixing Part 3: Foam Generation
F, David, director. Domegaia Aircrete Mixing Part 3: Foam Generation 4K. YouTube, Domegaia, 12 Sept. 2020, http://www.youtube.com/watch?v=CtzutTv4aLA&t=17s.
Aircrete Harry: How to Make Aircrete in a Mortar Mixer
“How To Make Aircrete In a Mortar Mixer.” YouTube, Aircrete Harry, 23 July 2021, http://www.youtube.com/watch?v=4MdIyIEIjXc.
Aircrete Harry: How to Make Aircrete Part 1
“How To Make Aircrete Part 1.” YouTube, Aircrete Harry, 1 Sept. 2018, http://www.youtube.com/watch?v=m28yNWnisvQ.
Aircrete Harry: How to Make Aircrete Part 2
“How To Make Aircrete Part 2.0.” YouTube, Aircrete Harry, 2 Sept. 2018, http://www.youtube.com/watch?v=3gvQnWMTdIQ&t=1s.
Aircrete Harry: How to Make Aircrete Part 3
“How To Make Aircrete Part 3.” YouTube, Aircrete Harry, 2 Sept. 2018, http://www.youtube.com/watch?v=NEX1O9VM_1M.
Aircrete Harry: How to Make Aircrete Part 4
“How To Make Aircrete Part 4.” YouTube, Aircrete Harry, 2 Sept. 2018, http://www.youtube.com/watch?v=RrnxFmk5rMc.
My Tiny Wagon: How to Make Aircrete Using the Dragon XL
“How to Make AirCrete Using the Dragon XL.” YouTube, My Tiny Wagon, 4 Aug. 2019, http://www.youtube.com/watch?v=fPg23c39LiU.
Domegaia: How to Make Aircrete with Domegaia’s Little Dragon and Foam Injection Mixer
“How to Make Aircrete with Domegaia’s Little Dragon and Foam Injection Mixer.” YouTube, Domegaia, 22 Sept. 2018, http://www.youtube.com/watch?v=XVklJJRnaYM&t=18s.
Aircrete Harry: How to Operate the Aircrete Harry Foam Generator
“How To Operate The Aircrete Harry Foam Generator.” YouTube, Aircrete Harry, 30 Aug. 2019, http://www.youtube.com/watch?v=p8DtiI7VTG8.
Domegaia: How to Use Domegaia’s Aircrete Foam Injector Mixer
“How to Use Domegaia’s Aircrete Foam Injector Mixer.” YouTube, Domegaia, 22 Sept. 2018, http://www.youtube.com/watch?v=yICB1yc6eMo.
“Domegaia Home.” Domegaia, http://www.domegaia.com/.
Need Assistance with Air-Crete Making
HandyDan. “Need Assistance with Air-Crete Making.” Domegaia, 30 Mar. 2018, http://forum.domegaia.com/topic/216/need-assistance-with-air-crete-making.
How to Make Aircrete
“HOW TO MAKE AIRCRETE.” DIY Aircrete, http://diyAircrete.com/howtomakeAircrete/.
Aircrete Is Collapsing
Leroy. “Aircrete Is Collapsing.” Edited by Hajjargibran, Domegaia, 24 Aug. 2018, http://forum.domegaia.com/topic/41/Aircrete-is-collapsing.
Making Foam Concrete
“Making Foam Concrete.” FoamConcreteWorld.com, Foamconcreteworld, 5 Feb. 2022, http://foamconcreteworld.com/making-foam-concrete/.
Aircrete Guide: Everything You Need to Know
Roberts, Tobias. “Aircrete Guide: Everything You Need to Know.” Rise, 18 Jan. 2020, http://www.buildwithrise.com/stories/Aircrete-everything-you-need-to-know#:~:text=What%20is%20Aircrete%3F,material%20with%20impressive%20compressive%20strength.
Aircrete has the potential to be an economical, lightweight, and easily accessible building material. Open sourcing the aircrete research is important so that it can be replicated and/or so other engineers/designers can build-upon our work to improve it and/or make changes to suit their own projects/visions. Summarized in this page are the steps taken to answer unanswered questions, such as is aircrete truly DIY and how strong is it and how quickly can it be used for building to ensure that structures using aircrete are safe. We will continue to build upon our findings.
Q: What is Aircrete?
Aircrete is a mixture of foam from a foaming agent such as Seventh Generation Dish Liquid or Drexel that is mixed with cement slurry until homogenous.
Q: How did you know the consistency?
The consistency was based on time and color consistency of the mix. This was a limiting point because a test or parameter to accurately test evenly consistency of the mix was not used to tell if one part of the mix is heavier than another. Further testing will include a density test and a comparison of the measured density with what was expected.
Q: How was the ratio of Aircrete determined?
Aircrete ratio was determined in a few ways. One was to use the Domegaia ratio and scale it down. The other way was Aircrete Harry’s proportion which was already scaled down; however, to convert it to a cylinder amount, the ratio was scaled down more. The last way which was used during the experiment was by volume.
Q: What problems were recurring throughout the project that needed to be improved or thoroughly checked?
Some of the constant difficulties we ran into was one of the little dragon pressures not being constant for a longer period of time. An example is one time the density was 95 gram per liter and 10 minutes later the density fell by 10 and then a minute later it was less. This may have been a machine malfunction that we did not find until the later part of the project.
Another difficulty was the shrinkage during mixing and curing phase because of the inaccurate consistency of mixes. These happened only during light and standard because mixes with high foam ratios are more delicate/less stable, thus more susceptible to collapse, resulting in a lower final volume of aircrete than targeted.
Q: Why use Aircrete?
Aircrete is another building resource that is more affordable, lighter (makes it easy to transport and use), and less toxic than concrete because there is less cement in the mix.
Q: Why not use other types of building material?
There are other options such as stabilized earth, recycled materials, and shipping containers. These are all options that One Community has envisioned in their question for a better world. Beside Stabilized Earth which One Community has researched, aircrete was the other concrete-like building resource that needed to be tested.