Process Part II - Testing paver strength

Once we selected the concrete ratios for our conventional concrete mix and wood-aggregate mix we made several attempts at creating sample 2-layer pavers. There were a few flops:

but we eventually created a 2-layer paver using the mixes we selected earlier in the process.

Once this paver had a few days to cure we tested its strength.

Although this is the mix we will be using, we decided to make our paver in two sections instead of pouring it at once into two layers. The impermeable layer, 1/2" thick, will be cast first, then set into the mold before we cast the wood-aggregate layer, so that the impermeable layer will be set into the wood-aggregate layer.

While we were working on perfecting our concrete mix we were also getting our formwork ready. We decided on a paver in the shape of a Ginkgo leaf.

With the formwork complete, the next step was to test it! We poured three impermeable, 1/2" pavers and are waiting for them to dry to see if they are a success!

If they come out, the next step will be to insert them into the mold and pour the wood-aggregate concrete over them.

Process Part I - Selecting the concrete ratio

For the past two weeks Leo and I have been testing different combinations of wood-aggregate concrete. The first test were completed using a range of wood chips, saw dust, cement and water.

The wood chips made the aggregate too brittle to be used for a paver, the sawdust was more appropriate, but still relatively crumbly. The next round of tests integrated sand back into the sawdust mixes to attempt to add structural stability to the concrete.

During this round of tests we also began sampling regular concrete mixtures of send, cement and water to use as a control, through this process we decided that the paver would hold up to foot traffic better if it was stabilized with a thin surface layer of conventional concrete. From this process we decided on two mixes that were close to what we were looking for and continued further experiments with these two mixes. For the wood-aggregate we are using a ratio of 3 parts cement, 5 parts saw dust, 1 part sand, 4 parts water. For the conventional concrete we are using 2 parts cement, 4 parts sand (2 coarse, 2 fine) and 1 part water.

Concept - Wood Aggregate Paver

Material Changes:

Concrete has one of the highest amounts of embodied energy due to the mining processes of Portland cement. Aggregate used in concrete also contributes toward environmental degradation in water ways were the gravel is normally mined from. Reducing or replacing these elements will contribute to a more sustainable and therefore ecological product.

Conceptual Changes:

Materials commonly used in urban areas like asphalt, pavers, and concrete seal the urban surfaces and create barriers against moisture penetration. This benefits the longevity of the product, however it contributes to run off that overwhelms the storm water systems as well as changing the soil composition underneath the sealed barriers.

Porous pavers are becoming popular and allow for the movement of water to the soil underneath, helping to primarily deal with run off issues. Pavers like these are not new and have many historical precedents from around the world that were largely lost to our modernizing world. However one significant conceptual remnant of modernism has retained its value in the pavers today. The conceptual strategy about quality relies on extending longevity regardless of use or context.

There have been unique innovations like by companies like Faswall which utilizes wood waste and transforms it into mineralized wood, ie. Petrified wood. The gravel substitution as well as the reduction in cement usage provides Faswall with a CMU like product that has a large number of benefits that are both practical and environmental. The mineralizing of wood leads to a stronger product and maintains the modern aesthetic to extend the longevity of the product, one they claim can be “measured in centuries rather than decades.” Faswall uses 85%  Mineralized Wood Chips, 15% Portland Cement for their mixture. A product like this could be used for pavers since it there is less fire, life and safety issues associated to them. Pavers are in contact with the ground and pose other challenges like run off and soil composition. If pavers conceptually were conceived as a medium between the world above and the earth below how might the design change to benefit human as well as environmental conditions.

BACKGROUND INFORMATION:

Natural Soils vs. Urban Soils

Natural systems operate in a cyclical manner that allows for regeneration of nutrients into the soil, in urban areas this system is halted by human intervention. In a forest the fall of leaves and deadwood is the source of nutrients through decomposition for the future generation of flora. In an urban environment we take away the leaf litter, the grass clippings and any deadwood that might have regenerated the soil. This coupled with the patchwork form of urban green spaces, separated by areas of impermeability leads to the depletion of key nutrients and biota for soil health. In addition to lack of nutrients, these areas are inundated with water from impervious runoff that often contains contaminants and the flush of water can cause nutrient leaching in the soils of pervious areas.

Among the components of healthy soil often depleted are oxygen and nitrogen. One cause of the lack of oxygen is compaction, but the lack of organic matter on site is another key contributor. A good growing medium will contain plenty of organic matter which creates more space for air than a compacted soil. It also is the catalyst for biota, which in turn create oxygen as a by-product to their digestion. This relates directly to nitrogen depletion in urban soils. There is known to be a high amount of organic nitrogen, but this must be converted to mineral nitrogen through microbial decomposition before it can be take up by plants. Nitrogen is key to urban plant  health as it is the nutrient that contributes to green growth and plant take up needs are extremely high which is problematic in depleted urban settings.

In urban gardening compost is often introduced to the soil to mimic the natural process of decomposition of organic matter. To maximize the decomposition of compost, a mix of plant materials that creates a carbon to nitrogen ratio of 25-30:1 is optimal. There are certain plants and plant products that have this optimal ratio. Examples of plants in a close to optimal range are wood ash (25:1), hay (25:1), weeds (30:1), grass (20:1), coffee grinds (20:1) and seaweed (19:1). In addition to the decomposition making nitrogen available for plant uptake, it reintroduced biota and oxygen to the soil profile.

The introduction of wood as an aggregate can perhaps help create a healthier urban soil in the future. As the wood breaks down it will help the process of decomposition reinoculate the soil with life.

Seeds and Succession

Natural systems not only cycle their nutrients but also the type of system occupying an area. As one system is either removed by humans, natural disaster or old age another system fills in the space. When an urban area is abandoned with just bare ground the successional process starts at the beginning with small grasses invading the barren space. Perhaps these wood aggregate pavers can provide nutrients for soil health and seeds ready to repopulate the abandoned space left behind.

HYPOTHESIS:

The suggestion is to question the longevity to more appropriately consider the other environmental and use variables of a location. The wood used in Faswall’s product petrifies wood, but what if we could leave the wood as a medium to restore the surrounding environment.

Wood waste in urban areas offers an opportunity to utilize untapped resources. An experiment that utilizes wood chips as aggregate, mulch as water, and utilizing a lesser ratio similar to the Faswall content could provide a product that is significantly more utilized than current pavers on the market. The following is a ratio in table form.

Replacements:

Aggregate                  =          Douglas Fir Bark Nuggets (85%)

Water / Moisture        =          Leaf litter + Additive Water

Cement                      =          Less Cement (15%)  

This mixture and material choice is influenced by my research into conceptualizing architecture as deadwood in our forest. The recycling of nutrients and aligning our uses with the flows of the ecological cycles, like deadwood does in the forest, has a more efficient ability to utilize the product to benefit many more factors than just humans. In this case the pavers are not just human use elements, but first recognizes the place they are in and the processes they play with the environmental cycles like water. This is physically expressed through process of decomposition, which directly challenges the modern appeal for these types of products. The challenge will be to design a product that “wears” in way that is allowable and even desirable to our human tastes.

EXPERIMENT:

Tests:

First we will conduct multiple tests on what mixture will work to provide the ideal paver. We will do this by calibrating the mixture between the 3 mixtures starting first with the 85% aggregate and 15% cement mixture as modeled by Faswall. The leaf litter mixture will be highly dependent on what is available.

Plants | Light | Modularity

When I was in Naoshima, Japan, I came across a simple stone stair that left a not so simple impression on me. It was a granite slab with a rough cut face. In the bottom left corner, a small and intentional divot was cut. On the particular day that I happened to walk up these steps, this divot was filled with rain water, which created a glowing reflection of the sky. The contrast of the rough masonry against the mirror-like surface of the water was the inspiration for my module.



I attempted to create a vessel that embodied this material relationship, and one that utilized the versatile dimensions of a standard modular brick [3 5/8 x 2 1/2 x 7 5/8]. The idea was to create a vessle that acted as a place to grow and as a water feature. It could be used as a paver, or as a cap for a garden wall.

My Concrete Concoction:
-1 part fine aggregate
-1 part coarse aggregate
-1 part cement
-Add water as needed

Major lessons learned: As for the module itself, I had no major hang-ups since the design was very linear and simple. The blog, however, is where my lesson for assignment lies, and here it is: when you open your post to edit it, make sure you know what you're doing, or else you might just delete it accidentally. Oops; second time's a charm.