Without re-iterating too much, concrete is an extremely taxing material on the environment so I would only recommend its use if it was at least manufactured with local aggregates to cut down on the environmental burden of importing heavy raw materials which we have on the islands. The addition of supplements to Portland cement or alternatives as mentioned in the previous chapter I believe are possible and with further research and development these should be incorporated in the future. In any case, it is hard to deny the structural ability of concrete and especially the ease at which pre-fabricated pre-cast concrete pieces can be produced. I mentioned previously that GPRM in Kapolei, Oahu is already creating many precast products for use in tall buildings, roadways, bridges and other large projects. Their ability to produce pre-cast pieces for a project like this would only be a matter of designing the specific structural pieces for production. Other pre-cast manufacturers could be set up if the market would support their use making the product even less costly. There are a few reasons why pre-cast concrete should be chosen for the new Hawaiian home.
The most obvious advantage for precast concrete parts is the ease and speed of installation.
Pieces can be designed with simple connections and fit together on site with a crane and a few people.
Material costs are cheaper because the pre-cast manufacturer will be buying or producing raw materials in bulk giving them more control and consistency of the product for their money. Pre-cast concrete parts are made using reusable molds making different shapes and sizes, steel reinforcement and concrete pouring more efficient, easier and more controlled. When simple components can be repeated in the design the process is more affordable and streamlined only requiring a few different types of molds for even very large projects. In the most cost efficient pre-cast structures, architects, engineers and pre-cast manufacturers limit the different individual pieces to only a few variations;
repeatability is affordability. The molds are also usually in very controlled environments taking weather delays and other variables out of the equation and allowing proper curing times before the pieces are needed for installation. When they are installed in the field they are already at full strength, there are no issues with curing from weather delays or other variables which can compromise the product.
Poured in place concrete has some disadvantages when compared to its pre-made sibling.
When concrete is poured in place it requires forms which must be made or put together on site by skilled workers. Reinforcement steel must then be set and tied in place by skilled steel workers, and then concrete is poured and finished by skilled masons. Concrete must either be bought and delivered
to the site which may require special coordination or machines to pump the product or mixed on site which requires mixing machines, extra labor and potentially consistency issues with the mix. Once the concrete is set and finished extra curing time is required before other stages of the project can commence. There are also limitations to what can be done with poured in place concrete. In other words, it would be incredibly costly, inefficient and difficult to make forms to span or cantilever large distances or create specialized types of structural forms.
Pre-cast concrete, when protected from the direct heat of the sun provides a thermally stable, strong, quick and healthy component for use in this project. There are no chemicals to pollute indoor air and when maintained, mold and other contaminants are unlikely to form. With the addition of local aggregates and binding agents the product is also more environmentally sustainable and culturally significant. Concrete is also termite proof, extremely fire resistant and when properly reinforced can withstand earthquake and wind forces. Pre-cast structures are also easily made into elevated structures giving them advantages during flooding. For these reasons this project will incorporate pre-cast concrete parts for the key structural portions of the project.
8.3
MASONRY
Masonry in the form of natural stones or pōhaku in Hawaiian, exist in a few usable types in Hawaiʻi. These are ʻAʻā and Pāhoehoe lavas and more smooth basalt river rocks and field stones. There are other types of stone in Hawaiʻi but the most common and usable for construction are these. Coral was used as a masonry unit for a time in the state and can be seen at Kawaihaʻo church, the Chamberlain house, and other early western influenced Hawaiian buildings. However, the cutting and removal of coral from the ocean has significant environmental and ecological impacts and is no longer used as a construction material locally.
There are a few big advantages to using masonry in Hawaiian residential architecture. The product is locally sourced and is incredibly abundant. Lava rocks and other stones give architecture a regional character and feel which is unique to the islands. They are culturally significant as heiaus, buildings and walls have been built out of them for centuries. Hawaiian masonry can be successfully dry stacked reducing the need for mortar or otherwise constructed in a manner like other masonry walls. When designed correctly a masonry wall can be incredibly strong and can carry significant loads and when protected from the sun and properly ventilated work well climatically. Masonry is also healthy, not requiring chemicals or harboring VOCs which may make inhabitants sick. Finally, locally sourced masonry does not have an impact on carbon emissions and typically the environmental and ecological impact is negligible.
Figure 8.8: Pāhoehoe, ʻAʻā and River Rocks
Source: Own work
Despite these advantages there are some issues with masonry which make it difficult to use.
Hawaiian masonry can be expensive depending on the source. Native lava rocks and other stones are either acquired from private quarries, private land or acquiring a permit from necessary land owners to pick or harvest the stones from the land. Lava rocks and other stones are also heavy and require many pieces to form walls making installation time and labor costs very high. Further, there is a high level of skill involved with building solid and accurate walls making large scale use of masonry cost or time prohibitive. For this project, we will not focus on masonry as a primary structural system. This dissertation attempts to create a kit of parts available to architects and builders to adapt to the numerous architectural variables and design challenges that the islands face. Masonry has a special place in Hawaiian culture and architecture but the time for installation and difficulty of adapting individual stones to other pre-fabricated systems takes it out of the scope of this project.