This project is part of the Summer 2013 Practivistas Dominicana project, led by Lonny Grafman in the Dominican Republic. Six students, three from Humboldt State University (HSU) in California and three from Universidad Iberoamericana (UNIBE) in Santo Domingo, will be collaborating with the community of Las Malvinas to construct two of four walls for a "Botica Popular" in the community. This team will be experimenting with cinder blocks made of various upcycled materials such as sawdust, paper and rice hulls mixed with cement and pressed using an industrial cinder block maker. At the same time another team will be working on building the other two walls out of ecoladrillo, or upcycled plastic bottles.
Objective
The community of Las Malvinas is seeking to construct a Botica Popular, or government-funded pharmacy, in their community. The objective of this project is to build two out of the four walls of the Botica with alternative concrete blocks made with sawdust, rice hulls or paper mixed with concrete and pressed in an industrial block press. With the climate in the Dominican Republic, the blocks need to be able to withstand heat, rain and the test of time. They also need to be cheaper to make than "traditional" concrete blocks and made from local materials that the community can consistently use in the future to produce more blocks.
Entirely concrete cinderblocks have a high embedded energy, with an average of 0.67 MJ/kg and 0.073 kg Co2 per kg with a density of 1450 kg/m3[1].
Timeline
Friday June 7, 2013
Our group had an opportunity to meet Jacob, an Engineering student at UNIBE who showed us his experiments with sawdust-concrete and recycled styrofoam-concrete. He had been experimenting with different ratios of sawdust to concrete and testing the strength of different mixes. His experiments also included using wire to increase the tensile strength of the concrete slabs. He will likely be a useful contact while working on this project.
Saturday June 8
First day to work on mixes. We went to Las Malvinas in the morning and, with Ginger's help, secured a barrel of sawdust from the coffin manufacturer who will be providing our material and the block-making site next door where we and members of the community will be doing experiments and making blocks with sawdust and other materials. We also were given two bags of lime and loaned two barrels for mixing the sawdust, lime and water to soak. After an initial mix, the owner of the plant arrived and made some changes to the mixture we had put together, encouraging us to "go big" with our experiments. There was a high level of interest from the community members who came to work with us - they really ended up taking over much of the work, sifting, mixing and all the while peppering us with questions. A kid from the community spent most of the afternoon with us helping mix the sawdust, lime and water. We will be returning to the site on Wednesday to try more mixes and Thursday is the day to press blocks.
Literature Review
Diluting Concrete
A fellow student at UNIBE shared some of his research into making blocks with sawdust and other materials. This research is currently underway, however in his experimentation, he was using sawdust for more than simply diluting the concrete, he was actually using it as a replacement for river sand. This is a potential area for experimentation in this project. His blocks were very durable, able to withstand approximately 2900 Newtons of force [2].
Lime
For this project, we will be using lime in several stages.
Mg and CaO are the active ingredients in lime. While other components in the lime can be present, they are considered impurities in the mixture. Hydrated lime is expressed as CaO+H2O>Ca(OH)2, which is the powdered dry material often used in plasters.
The action of slaking lime is a process of adding water to the powdered lime mixture until the powder can not absorb any more water. The CaO is responsible for this behavior of absorption and reaches a limit which becomes obvious due to a layer of excess water on top of the lime slurry.
Paper-Crete
Papercrete is an alternative construction material that, in general, is made up of milled paper and an adhesion component like clay or cement. Since paper comes in many forms, i.e. junk mail, magazines, beer cartons, newspapers, etc., so does papercrete. While there is no definitive code for building with papercrete, various forms of papercrete masonry have been successfully employed.[3] Paper is a common waste product and can be sourced for free, making papercrete an affordable, green masonry alternative. In Santo Domingo, Republica Dominicana recycling services are not readily accessible and waste management is a visible environmental issue. The use of papercrete construction can be a paper-waste outlet for growing communities, while reducing the cost of building materials.
The papercrete blocks from 2012 In last year's Practavistas program, the Las Malvinas group worked on building a schoolroom out of papercrete and ecoladrillo. Their process involved pulping the paper with a blender in a mix of 4 parts paper to 1/8 part lime and 8 parts water, then letting the mixture dry. This was then mixed with concrete and water and the slurry was pressed into blocks [4]. In a visit to the site this summer, the papercrete wall in the schoolroom appeared to be in very good condition, better, in fact, than the ecoladrillo.
Papercrete has an R-value between 2.0 and 3.0, making it a suitable building material for the Dominican Republic's warm climate, (concrete's is about 0.08). Papercrete has a compressive strength of about 150 lbs per square inch.[5]
Recipes
Here is a starting formula provided by LivingInPaper.com for a 200-gallon batch[6]:
160 gallons (727 liters) of water
60 pounds (27 kilograms) of paper
1 bag or 94 pounds (43 kilograms) of Portland cement
15 shovelfuls or 65 pounds (29 kilograms) of sand
Here is a by volume mix provided by Papercrete.com[7]:
12 parts paper
4-6 parts soft clay
2-3 parts lime putty
Sawdust-Crete
BMP Association LTD is a company based out of Moscow that produces equipment for companies and experiments with different and new building materials, including sawdust concrete. They claim several benefits of using sawdust concrete:
Fireproof
Indoor humidity control
Frost-proof
Resistance to mold and fungi
Compatibility with various other materials and finishes
Much lower heat conduction than bricks: 0.08-0.17 Wt/m as opposed to 0.5-1.5 in brick.
According to their website, this means that it takes half as much energy to heat a home with 20cm sawdust-crete walls than with 50cm brick walls.
Much lower density: 400-850 kg/m3 as opposed to 1550-1950 [8]
Timbercrete is a company based out of Australia that specializes in bricks, pavers and finishes
Recipes
This recipe was found on the Digest blog and is recommended for a durable concrete.
Sawdust is first mixed with minerals to resist decay, molding and rot. May somewhat mimic natural process of wood petrification.
85% wook
12% cement
3% fly ash
The resulting product weighs half as much as ordinary concrete, can be pressed into blocks skin to Concrete Masonry Units and has an r-value of 18. [11]
This recipe is used for making bat caves:
4 Quarts wood chips
1 Quart cement
Recommends only using CaCl in the water because sugars in the wood chips can keep the concrete from binding. [12]
The NSW Good Wood Guide offers this recipe for a sawdust-crete. This site reccomends use as a non-load bearing infill.
3 parts sawdust - hardwood used for best results
2 parts sand
1 part cement
Blend the dry ingredients, first sand and sawdust then concrete.
Add water, only enough to hold, but not produce excess when the mixture is squeezed. [13]
Rice Hull-crete
In the community presentation with Las Malvinas rice hulls were mentioned as a potential resource for the community. A study done in India analyzed the possibility of using rice hulls in concrete blocks. In the study rice hulls were added at 0.5, 1.0 and 1.5 percent as compared to the amount of concrete added to the mixture. Although workability of the concrete decreased, other factors such as tensile strength, impact strength, displacement and energy absorption were improved significantly. Also, the blocks with rice hulls added were found to tend to crack before failure as opposed to the plain concrete blocks, which would tend to fail without much warning.[14]
Recipes
One recipe for rice hull blocks from the book "Rice"
↑Sivaraja, M., S. Kandasamy. Potential Reuse of Waste Rice husk as Fibre Components in Concrete. Vol 12. No 2. 211. Asian Journal of Civil Engineering. pp 205-217.
