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Las Malvinas destacamento/Literature Review
See Las Malvinas destacamento for the project that this research was completed for.
This is a review of the available literature pertinent to the 2014 Practivistas initiative to begin construction on a police station for the community of Las Malvinas in Santo Domingo. Topics will range from building materials to general information on construction.
The Community of Las Malvinas
“The so-called 'cool' or winter season, runs from November to April. The humidity is relatively low during these months and it tends to cool down in the evenings much more than in the summer months. The coastal/beach regions [including Santo Domingo] generally experience highs of around 28°C (83°F) during the day and lows of about 20°C (68°F) in the evening...The summer season in the Dominican Republic runs from May to October. Average daily highs for the coastal/beach regions rise to around 31°C (87°F) during the day, dropping down to about 22°C (72°F) at night. It is the higher humidity during this period that can make it feel much hotter during this season” . “The south has two main seasons: a dry winter and a rainy summer...In the Santo Domingo…watershed, rainfall shows primarily one longer rainy season in summer and one dry season in winter. Although not statistically significant, it is worth noticing that, unlike stations in other areas, all three analyzed stations experienced an increase in precipitation during most months of the year….The analysis showed a tendency for fewer extreme rainfall events in Yaque del Norte watershed and more extreme events in the Santo Domingo watershed, where the increase in frequency of heavy rainfall was significant in the coastal areas (Santo Domingo and Las Américas)... During the period of 1960 to 2012, the Santo Domingo ONAMET station reported an average of 1,500 mm of rainfall per year with very high inter-annual variability. Santo Domingo receives the bulk of its annual rainfall between May and October, when monthly rainfall exceeds 150mm/month, with the peak between August and October with rainfall reaching 90 mm/month. During the driest months of the year, February and March, rainfall drops to 50mm/month” . “Hurricanes in the Dominican Republic are important events in the country’s history, with devastating impacts due to the combined effects of high winds and heavy rainfall. They occur primarily during the months of August, September, and October; with greatest intensity in the southeast and southwest regions of the country. They form in the western part of tropical North Atlantic Ocean, where high SSTs and low pressure prevail and intensify as they travel westward over warm waters…” .
Building a foundation
A foundation is a load bearing part of a building which has direct contact with the soil. Typically they begin below ground level and are the starting point of a structure. When building a foundation one should consider the type of soil being built in, the potential vertical and horizontal load being placed upon it, the building site's topography, and its resistance to earthquakes. Types of foundation will vary depending on the size and shape of the structure being built. When building on uneven, slopped, or poor quality soil, a deep foundation should be built 3 or more feet below the soil. This foundation may also vary in depths throughout. When building on even ground and in higher quality soil, a shallower foundation can be built.  In the United States the minimum strength requirement for a residential concrete foundation is 2500 pounds per square inch (psi). Apparently the building codes in Santo Domingo are the same as those in the United States  so this number could also be applied here since our structure is relatively small. Before excavating for a foundation, a survey must be taken to determine the depth etc. Once this is done the trenches can be dug and footings can be poured, if need be. These are cement layers, which are meant to distribute the load of the foundation walls, which will be poured on top. Foundation walls can be made by pouring concrete in to forms, usually wooden. The forms should be spaced at least a few inches from the walls of the trenches. When the concrete drys the forms can be removed, and construction fill - typically made from aggregate soil - can be filled in around the edges of the foundation trenches .
Soil and Building
When considering soil in terms of a building project, the four main properties of inorganic soil should be considered: mineral matter, organic matter, water and air. Soil texture can be described as "the range of individual mineral particles such as sand silt and clay," which are present in soil . However, for smaller projects there doesn't have to be very extensive investigation of the soil . Coarse textured soils (soils which are sandy or contain coarser aggregates) are better for building because water moves easily through them, and they are easy to dig in. Aside from this they have a higher load bearing capacity and are less likely to sink under the weight of the structure than clay or silty soils . 55% of soils in the Dominican Republic have a shallow top layer and are aggregated, so there is a strong possibility that the police station will be in soil suitable for building . Soils with a finer texture tend to expand and contract according to their moisture content, and this can damage foundations. .
A retaining wall is a structure which is created to hold back soil and earth. They are used as a means of leveling ground so one can build on slopes. . “New polymeric materials called geosynthetics can reinforce soil so retaining walls will not fail. “In the old technology, we asked the wall to hold the soil but now, with new technology, the soil is holding itself, even in the event of an earthquake,” said Dr. Ling. Dr. Ling’s work is supported by NSF and companies in North America, Germany, Israel and Japan” .
Small spacing GRS (geosynthetic reinforced soil) walls with a structural facing have an inverse relationship between the Initial GRS Composite Modulus (kN/m^2) and the Normalized Maximum Face Deflection (mm/m) with a relationship of y = 4E+13x-3.3262 and an R2 value of 0.9484 .
Retaining walls under 4 feet tall don’t need to be as strong as those above 4 feet, so if a taller wall is necessary step-terracing will keep cost and material usage low. In places that don’t get frost and have soil that drains well, topsoil can be scraped away to form a base for walls without mortar. To build a retaining wall, one should first lay down landscape fabric in the shape of a C with the open mouth facing downhill. This will keep sediment from clogging the gravel and drainpipe by separating the gravel and topsoil. Next, add at least a 4 inch layer of gravel onto the landscape fabric. Give this layer a slight slope to allow water to drain away, then insert a perforated PVC pipe and cover it with gravel to allow the soil behind the retaining wall to drain. The sediment behind the wall should be added gradually as the wall is built and tamped against the wall to prevent sliding and make the Normal force as direct as possible. The retaining wall should have a backwards tilt of 1 inch for every 12 inches of height. Timber walls above 4 feet should be tied to the hillside. Timber walls don’t last as long as ones built from mined materials, but they aren’t very hard to built. They cost about $10-$15 USD per square face foot. Concrete block retaining walls are mortar-free and easy to assemble. They can be up to 20 feet high and be easily shaped. They cost about $12-$20 USD per square face foot. Stone, brick, and cinder block walls are difficult to make. They cost $10-$12 USD for cinder blocks and $20-$25 USD for brick or stone. Concrete walls are strong and rarely fail but aren’t very aesthetic and cost $16-$20 USD per square face foot. Two kinds of failure for retaining walls are blowout failure and wet-soil failure. Blowout failure occurs when a load is added within 3 feet of the top of the wall. Wet-soil failure happens when soil behind the wall gets saturated, which causes hydrostatic water pressure and topples the wall. Wet-soil failure is the most likely kind of failure in Santo Domingo because of the large amount of rain. It is preventable if one has adequate gravel and a perforated drainpipe .
A retaining wall will be more affordable if the top is thinner, but it is recommended to have a thickness of at least 2 feet at the top of every point in the wall to resist frost. However, frost is not much of a problem in Santo Domingo .
Types of materials used
Concrete is essentially a mixture of aggregate and paste which is usually made from cement and water. Aggregate can be shale, clay gravel, air cooled slag, cinder, sand and many other things. .Through a chemical process called hydration, the cement paste dries into the particularly hard mass known as cement. The key to getting high quality concrete is attaining the correct ratio between the ingredients. Typically cement will consist of 8% water, 80% aggregate, and 12% cement . The lower the water-cement ratio, the higher quality the concrete will be. The trade of to this lies in in the work-ability of the concrete while wet. While a lower water-cement ratio will producer better concrete, it will be much harder to work with. . Concrete blocks are building units made with one or more hollow spots. Think of a cinder block.  For this project it is likely that we will be using concrete based blocks. One of the advantages of building with concrete is that is is fairly earthquake resistant and in the case of the Dominican Republic provides a solid defense against hurricanes and keeps buildings cool. Concrete is one of the most common building materials in Santo Domingo.  One of the other major advantages of concrete is that it is very available and can be sourced from almost anywhere in the world. It is also highly recyclable. . One of the drawbacks to working with concrete is that it has a high embedded energy. Millions of tons of water is used in the process of making it and even more aggregate must be mined. On top of this, all these materials have to be shipped to various locations. Adding all of these things together, concrete is actually responsible for 5% of C02 emmissions globally .
Rebar is common steel used in the form of steel bars or a grouping of steel wires that are used to increase the tensile strength of concrete. Adding rebar, which has incredible tensile strength, to concrete, which has very high compression strength but low tensile strength, creates reinforced concrete . The addition of rebar allows for the concrete to endure much heavier loads.
|Imperial Bar Size||Weight Per Unit length (lb/ft)||Nominal Diameter (in)||Nominal Area (in2)|
Cement is a substance used to bind various aggregates together. It sets independently and binds material together once it is hardened. “Cement refers to the commodities that are produced by burning mixtures of limestone and other minerals or additives at high temperature in a rotary kiln, followed by cooling, finish mixing, and grinding” . Cement can be categorized into two types: hydraulic or non-hydraulic. . Hydraulic cement contains hydraulic calcium silicates. It is able to set and harden under water while maintaining its structural integrity . The main chemical composition of cement consists of calcium oxide (lime), silicon dioxide (silica), aluminum oxide (alumina), iron oxide, water, and sulfate . One of the benefits of working with cement is that it is highly versatile. By altering one or more of the chemical components, the structure and form of the cement can vary greatly. The chemical makeup can be altered for a shorter hardening time, increased strength at early or late hardening stages, and increased durability . One of the disadvantages of cement is that the production requires a very large amount of energy. .
Alternative Building Blocks
Rice Hull Concrete
Rice hull concrete, referred to as HullKrete, is produced by the addition of rice hulls in a concrete mixture. HullKrete has been used before in Las Malvinas in the botica popular project. The mixture used contained rice hull, sand, gravel, cement, and a drying additive .
Paper-crete involves the tearing of various paper materials, such as: newspaper, magazines, and junk mail. After the paper is shredded or torn, it is soaked in water and lime and then pulped. After being pulped the mixture is then dried until moist and then mixed and pressed into blocks. Paper-crete has been used in the construction of the schoolroom and ecolodrillo in Las Malvinas. The paper-crete blocks proved to be structurally sound while also being cheaper than traditional cement blocks  .
Sawdust concrete, or sawdust-crete, is another potential alternative to traditional concrete blocks. Sawdust-crete has several key features that differentiate it from traditional concrete. Sawdust-crete is much more sustainable than traditional concrete. It is both fireproof and frostproof, rot resistant, mold and fungi resistant, much lighter than traditional concrete, and has the ability to control interior humidity levels  .
- Embassy of the Dominican Republic in the United States. N.p., n.d. Web. 7 June 2014. <http://www.domrep.org/kids.html>
- Torres, Ruben, et al. Dominican Republic Climate Change Vulnerability Assessment Report. Comp. Patricia Caffrey, Leif Kindberg, and Carter Stone. N.p.: n.p., 2013. US Aid from the American People. Web. 6 June 2014. <http://www.usaid.gov/sites/default/files/documents/1862/ Dominican%20Republic%20Climate%20Change%20Vulnerability%20Assessment%20Report.pdf>
- http://www.fao.org/docrep/s1250e/S1250E0i.htm#Concrete foundations
- "Civil Engineering, Macro to Micro." Fu Foundation School of Engineering and Applied Sciences Engineering News (2006): n. pag. Web. 7 June 2014.<http://engineering.columbia.edu/web/newsletterarchive/fall06/feature3.php>
- Holtz, Robert D., and Wei F. Lee. Internal Stability Analyses of Geosynthetic Reinforced Retaining Walls. N.p.: n.p., 2002. Washington State Department of Transportation. Web. 7 June 2014. <http://www.wsdot.wa.gov/research/reports/fullreports/532.1.pdf>
- Wagner, John D. "Engineering a Retaining Wall." This Old House: n. pag. This Old House. Web. 7 June 2014. <http://www.thisoldhouse.com/toh/article/0,,219681,00.html>
- Merriman, Mansfield. A Text-book on Retaining Walls and Masonry Dams. New York: John Wiley & Sons, 1892. Google Books. Web. 7 June 2014. <https://archive.org/stream/atextbookonreta01merrgoog#page/n8/mode/2up>