Cactus Used in Construction
Welcome to another update from the Construction Team on the Experimental Building Materials Programme, Composite Mixes Project. The desire for this project is to develop a strong and durable building material, which in part uses waste material instead of wholly mined materials in its creation.
You may have been following this experimental project via previous posts, where we have been endeavouring to replace sand in concrete type products with sawdust as far as is possible, whilst still achieving an end product that can be used in construction.
A Brief Update So Far
The experiments so far have been to:
- Discover the optimum mix ratio for aggregates, binders and water
- Make some control samples to measure our experimental samples against
- Find the optimum percentage of sawdust as a replacement for sand aggregate
- Try various types of binders both individually and in combinations to gauge the best performing
- Find out how the different binder combinations perform with the addition of sawdust
- Try both hardwood and softwood sawdust and observe any difference from one over another
- Discover what personal issues prevent inspiration, passion, playfulness, and true experimentation, such as a child would do, from happening naturally
What we have learned so far:
- It is important to collect as much data as possible in order to be able to converse and compare results with current products and methods, not limited to just the raw measured data but also including thoughts, feelings that come up, and idea sources
- That personal fears about many things such as maths, chemistry, lack of knowledge, getting things wrong, not playing by the current worlds rules, all prevent new ideas from coming up and truly experimenting and making new discoveries
- To open up to inspiration and what we feel to allow for logical reasoning, rather than using limited and fear based thinking about what should be the next course of direction
- To observe what examples God has created and put in front of us (such as in nature) in order to learn and benefit from the principals involved in those creations, and endeavour to replicate them as much as possible in our project design, experiments and creations
In the local area here in Wilkesdale, Queensland, Australia you may be forgiven for thinking that some areas are reminiscent of Mexico or Northern Africa, based on the number of cactus plants around. These plants are not native to Australia. The particular cacti species that thrives locally is called the Prickly Pear or Opuntia cacti. It can grow up to 4-5m tall and throughout the year produces small, lime-sized fruits that are red in colour.
According to the Queensland Historical Atlas the British introduced the Prickly Pear cactus in the late 1880s. There is a mealybug insect that feeds on the cacti and produces a red dye called cochineal. The British used this as an essential dye for their soldiers red uniforms. At the time, Mexico had a monopoly over the cochineal dye business and the British had ideas to set up their own supply, so brought the cacti plants to Australia.
By the mid 1920s more than a 24 million hectare area of Southern Queensland and Northern New South Wales was now prolifically covered in this plant. Ironically 24 million hectares is actually the size of Britain.
Many ideas on how to eradicate the cacti problem were trialled such as burning, crushing, chemically poisoning, digging it up and there were even bounties paid to the killing of birds such as Emu, Currawong and Crows to prevent the seeds from being spread.
Fortunately, a biological answer was found in the form of a moth native to South America called Cactoblastis cactorum, or as it’s more colloquially known as – Cactus Blaster. The larvae of this moth feasts on this variety of prickly pear, and eggs were initially released in many areas. Within 7 years much of the prickly pear was destroyed.
Thank-you to the Queensland Historic Atlas for that brief history lesson!
However, nearly 100 years later the cactus is still continuing to grow in many areas today, growing abundantly as an invasive species, maybe just not in the density that it was in the past.
Why Use Cactus?
There are some properties of the Prickly Pear cactus plant that could prove beneficial in the structure of composite mixture building products. From personal observations, their cactus pads (nopals) contain quite a lot of water when they are cut and this watery sap substance is slightly sticky.
The unseen structure/skeleton that holds this pad form together is also quite a fibrous webbing. The webbing structure/skeleton can be seen when all of the moisture and flesh content of the cactus pad has deteriorated.
Cornelius is working with a the theory that the sticky sap juice of the cactus pad may have not only binding properties (being sticky), but also additional properties which help the qualities of water to “stretch” further. This would be much like a man made substance called super-plasticizer (or high range water reducer) that assists in using less water in the final mix, thus avoiding diluting the strength characteristics of other binders such as cement or lime. (Further explanation of the properties of binders, aggregates and water can be found in the section ‘Relationship between Materials’ of the post: Programme Introduction: Building Materials Experiments)
Essentially super-plasticizer makes the mix strong by not requiring as much water to be used. However the mix still maintains its liquid or flow properties, so it can be wet enough to be workable into a mould.
Having a natural product with similar properties to the super-plasticizer would be beneficial because adding the sawdust to the mix usually demands slightly more water. The cactus juice may also add some flexural or elastic properties to the final product that may reduce any potential cracking. Additionally the plant fibres present in the cactus pads can act as a strengthening reinforcement to the final product.
These theories are based on simple observation and feeling/intuition rather than anything scientific.
Upon the idea to trial the cactus as a part of a composite mix, research was done into the plant juice, and it was found that the juice may also have some waterproofing qualities. There have been reports that, historically, Mexicans in rural areas used the juice in a lime mortar as a method to extend the durability of the external finish to their houses. Click here to view a reasearch paper on this topic (Source: Juan Antonio Ferriz Papi, https://www.researchgate.net/profile/Juan_Ferriz-Papi)
Potential benefits of using cactus products in composite building materials:
- Cactus is easily sourced
- As an invasive species, large scale use and removal of prickly pear cacti could benefit beyond locally to many other effected land areas and reduce its existence
- Use and removal would benefit the people (making things from it) and the environment (the water taken up by the cactus plant can remain in the ground to support native seeds to sprout and increase habitats for native animals)
If none of that turns out to be effective in the God’s Way Ltd composite mix materials project, both the fruit and the pads of the prickly pear are regarded as edible. That may be a follow up investigation of a different nature for projects in another branch of the organisation.
Making a Sample Mix
Firstly some cactus needed to be turned into liquid. This was easy. Take a walk outside on most Wilkesdale properties and within 15 metres are prickly pear trees.
A pair of BBQ tongs, a long bladed knife and a bucket were required to harvest some younger pads from the cactus tree. These were selected as they seemed to have a less woody and more liquid nature. Then the cactus pads were taken to the kitchen, cut into smaller pieces and fed into an older food processor. The resulting ‘mush’ was then stored in a jar and left to settle overnight.
The pulp and juice water in the ‘mush’ were then separated by straining.
The juice component was weighed and calculations were made to replace approximately 1/3 of the water required for the water to binder ratio of the mix with cactus juice.
The sample mix bound together well. And a lower water to binder ratio was achieved. So it appears that the cactus juice may have some super-plasticizer qualities. Further investigation is warranted.
The Test Batch #14 Document tells the story of the test mix using the cactus juice: 20180522 Test Batch 014
The test samples created retained the smell of the cactus juice which was a pleasant, cut grass kind of smell.
The cactus pulp that had earlier been separated from the juice was spread on top of a paver test sample, in as an additional experiment to see if the pulp had any waterproofing qualities.
An Interesting Side Experiment
As a part of some extensive environmental projects that God’s Way Ltd was undertaking during this project, a temporary ground cover that could have seeds implanted into it (to give the seed shade and retain moisture for germination) was needed. So the following experiment took shape.
After straining the cactus juice used in the brick batches (#14 & 18) a pulp by-product remained. This pulp was a waste product and part of the ethos of our experimentation process was to make use of waste products.
The cactus pulp was mixed with yet another waste product (shredded paper) and made into a spreadable paste.
This was left on a piece of 4mm thickness hardwood plyboard for over six months in the weather. Over that time the ply became de laminated and fell into many parts. The cactus pulp/paper was still intact and could be picked up and flexed.
This side experiment has given us some indication that the cactus juice has some waterproofing qualities. This could be helpful to aid in natural protection of the sawdust in mixes. The natural fibres in the cactus pulp also offer tensile strength (as indicated by the ability of the product to flex) as well as binding properties (that caused the sample to remain in the same shape and form over time).
Conclusion & Future Direction
Testing an idea based on inspiration, intuition and reasoning based on naked-eye/sense observation of the plant’s properties was far more fun than experimenting based on already established parameters of composite products. Not knowing if the cactus experiment would be a complete fail or a success was more exciting and thus there was more feeling of enthusiasm for the experiment.
At this stage the project team are experimenting with different ideas and materials and using simple observation during the mixing and after drying to ‘measure’ the results. Basic comparisons are also made against other samples from previous tests and control samples. The project will eventually conduct testing for parameters such as compressive, flexural, and tensile strength and permeability testing too. Some of these tests will be created by the team, as the equipment used for industry testing is often only made for laboratories, which means that they are specialised and beyond the scope of economical purchase for God’s Way Ltd at this time.
When the team has developed reliable tests which can be performed by God’s Way Ltd and have found success in some of the samples, the test samples can be repeated, and those new samples sent off for professional testing.
In regards to the cactus plant being used as a potential product in the composite mix experiments, it is looking like a promising option.
We could be a little bolder next time and use a lot more of the cactus juice perhaps in a future test.
God’s Way Visionary & Founding Member
Construction Branch Manager
Information Sharing Auditor & Editor
Date event occurred: 22 May 2018
Branch Manager: Alan Miller (Jesus)
Programme: Building Materials Experiments
Project: Composite Mix Building Materials
Attendees: David Walsh (Cornelius), Tristan Miller, Peter Lytton-Hitchins
Location: Wilkesdale, Queensland, Australia