Senior Capstone Paper

Embed Size (px)

Text of Senior Capstone Paper

  1. 1. The Design and Creation of Sustainable Concrete using Alternative Binders to Cement and an Alternative Base Mix By Alexander May
  2. 2. Description and Purpose of Experiment: The purpose of this experiment was to provide myself with hands on experience into the introductory process of creating a sustainable building material (a building material that seeks as its end to be both structurally useful in building applications and to negatively impact as little of the human and natural environment as possible). Throughout this process it was my goal to: 1. Conduct research so that I could create a sustainable building material using an informed and intelligent process. 2. Create a material mix design outlining what materials and how much of each material I would use in the creation of my building material. 3. Begin the experimentation process that is necessary to go from the creation of a mix design to the creation of a viable building material. It is also important to note that throughout this process I would be working alongside and guided by architect and former builder Tom Hahn, Associate Director of the Ecosa Institute. The building material that we chose to create was a more sustainable concrete than standard concrete. Concrete is used 10 times more than any other construction material (1.1). And I can understand why it is so widely used, when I look at its benefits from a construction prospective. It is an incredibly strong and long lasting material. Its plastic quality resulting from its need to be poured before it hardens, allows for it to be used in rapid and versatile building applications. And the materials that constitute it are abundant. But taking a step back and evaluating how the use of concrete affects the wellbeing of humans and the natural environment, it is my belief that along with concretes significant benefits come its significant problems. And it was my goal, to have the addressing of these problems, guide the creation of my own sustainable building material. One significant problem I believe concrete to have, comes from its reliance on using cement as a binder. The first problematic factor of this reliance is that the production of cement results in high emissions of the greenhouse gas C02. These emissions contribute to 3% of global human created C02 emissions (2). The second problematic factor of this reliance comes from the large scale quarrying that is required to acquire limestone, the main material that used in the manufacturing of cement. Limestone quarrying can result in water and air pollution and a massive degradation of the above ground environment (3,4). The second problem I am inspired to address through the creation of my sustainable concrete is that of the offsite quarrying that is typically carried out when sourcing the rest of the materials that make up concrete. This problem I believe is on a much smaller scale than the large scale quarrying related to making cement, because many of the remaining materials that go into concrete come from an average of 30-50 miles away in many parts of the country (5). This leads to the quarrying impacts of sourcing the remaining concrete materials to be more dispersed and therefore less detrimental than large scale quarrying. But I still believe it is important to ask the question, Can this can be addressed? Because the more construction projects can use onsite materials to build with, the less offsite excavation is required, resulting in less negative human and environmental impacts. In response to addressing the problem of concretes reliance on cement, we chose to experiment with using alternative binders to cement in the creation of our concrete. In
  3. 3. order to be acceptable for this experiment, any alternative binder we chose, had to emit less C02 in its production than cement and/or have less of an impact from quarrying in its production. In response to the second problem, that of concretes reliance on offsite quarrying, we designed our base mix (materials minus the binders that would make up our concrete) attempting to partially replicate what it would be like to make a concrete with onsite materials. With the general idea of what our sustainable concrete would consist of, we then outlined the process of how we were going to actualize our idea. First we would choose our alternative binders and base mix materials that would go into our concrete. Then we would choose what percentage of each material would constitute our base mix. This base mix would be what each alternative binder would be combined with when making our concrete. Then we would test the compression strength of that base mix design using cement as our binder. Compression strength is one of the main attributes that standard concrete is quantitatively evaluated on, and the strength by which we would be evaluating the quality of our sustainable concrete. If cement gave our base mix sufficiently strong compression strength, we would know that our base mix ratios were adequate. If cement, a standard and already well-designed binder, could not bind our base mix or give it sufficient compression strength, we would need to redesign our ratios, rechoose our materials or both. Assuming that our base mix made a viable concrete with cement, we would then proceed to test our base mix with our alternative binders. After evaluating the strength of those results, we would then discard the alternative binder mixes that were too weak and revise the mix designs of the strongest ones. And lastly we would conduct one more round of testing to evaluate the compression strength of our revised concrete mixes. We would test the strength of each concrete mix by making industry-standard structural test cylinder samples of each mix and then sending the cylinders to a materials testing lab for compression testing. Also because we wanted our cylinders to represent concrete that could be actually used in the field, it was necessary for the consistency of our concrete mixes to have pourable consistencies. A note on the evaluation of our concrete regarding its compression strength: Compression strength is the strength at which a material can resist compression forces or two positive forces pushing in towards the center of a material from two opposing sides. If you place an object in one hand, then put your hands flat together with the object in the middle and push your hands together, you are generating a compression force on the object. If you exceed the compression strength of the object it will break, if not then you are not applying a strong enough compression force. The compression strength of our concrete mixes would be based on how many pounds per square inch (PSI) of compression force they could resist before breaking (fracturing, crumbling etc.) The testing lab that we would be sending our cylinders to has a machine that exerts a compression force on a cylinder while displaying that force in PSI on a scale. When the cylinder breaks, one only has to read the scale to see how much of a compression load the
  4. 4. concrete cylinder withstood. A standard concrete can take a compression load of 3000 PSI (6). A concrete of this strength is generally used in building applications such as making concrete patios and walkways (6). To give an example of how strong 3000 PSI is, it would take an area of concrete the size of 2 silver dollars or 2 square inches to withstand the weight of an average (how many pounds) American car (7). But the strength of concrete or any other impressive building material did not just become what it is overnight. Concrete has had a tremendous amount of money put into its research and development. Because we were unsure what compression strength our concrete would exhibit, we needed a range at which to evaluate the quality of our concrete. And this range needed to be based on the minimum strength at which we would consider our concrete usable/viable in the field. Because concrete is generally used as a load bearing material, we chose to evaluate the viability of the compression strength of our concrete from the perspective of it being used as a structural load-bearing wall. If we were to design a structure with 12 wide or thick load-bearing walls, an average roof in our climate would exert 13.75 PSI on each load-bearing wall (see appendix A. for more detailed explanation). Therefore the minimum compression strength or (Fc) at which we would evaluate if our concrete were sufficient was if it reached an Fc of 13.75 PSI. That is the design strength, after safety factors were applied. The safety factors that we would be applying came from the safety factors that Bruce King provides for earthen walls in his book Buildings of Earth and Straw (8). Even though we were designing a concrete, the material composition with our decomposed granite and natural binders would be closer in composition to earthen building materials like rammed earth or poured earth, rather than to standard concrete. The same would be true even when we would be using cement as a binder. The method of applying the safety factors are: Take the ultimate compression strength or the compression strength that our cylinders would break at and divide that number by 10. The number that would result from this safety factor would be our concretes Fc or the compression load, which our concrete could safely support. So in order to find our minimum compression strength that we would consider our concrete sufficient at, we would need to reverse the safety factor and multiply 13.75 x10 which=137.5 PSI or our minimum acceptable strength. Of course, higher Fc values are better, as they allow for greater safety factor, higher loads (perhaps because of greater roof weights or spans) and taller walls. Background on Alternative Binders and Base Mix Materials:
  5. 5. Alternative Binders: The five alternative binders we chose for this experiment were: prickly pear juice, psyllium husk, li