Fiber Reinforced Concrete Casting

The video above is about the casting of steel fiber reinforced concrete. In the casting, they are also using steel rebar for an even higher resistance to stresses. I wanted to show a video like this for one reason. That reason is that, the fibers don't change much for the casting of concrete forms. When pouring the concrete into the cast, it still acts somewhat fluid, like standard concrete, and allows for the ability to mold to any shape that is needed for the structure. This is very important since, in every aspect except for cost, the fiber reinforced concrete is a feasible replacement to standard concrete and, due to its higher strength, is an even better material to use in the near future.

Ultra High Performance Concrete

Ultra High Performance Concrete (UHP) is a very interesting material. Standard concrete slabs for things such as roads or driveways are designed to resist a minimum stress of about 5000 psi. This material however, is designed to resist stresses of 21800 psi. A study on this material can be found here. The conductors of this study tested the effects of different lengths of steel fibers in the material. During this study, they found that, without cracking, the different lengths of fiber didn't effect the overall strength of the material. When the material started cracking, the longer fibers actually bridged the cracks and kept up the strength of the material better than the shorter fiber. This is something I would like to include in my paper. While it doesn't use composite fibers like the other studies I have read about, it can still be considered a flexible concrete. I wanted to write about the possibility of writing about using concrete in ways that it couldn't normally be used, like beams and girders. This UHP concrete allows for a very different use of concrete in those ways.

Economic Feasibility of Fiber-Reinforced Bridge Decks

Remember all that time ago we went to the library to learn about the databases and figure out different ways to search for our topic? Well, another term for flexible concrete is fiber reinforced concrete and the Federal Highway Administration shared a study conducted in the West Virginia University that tests the economics of using the concrete as a bridge deck. Unfortunately, the link for this study is a direct download of a word document to the study. So, if  you follow the link here it will bring you to the google search i conducted. Then, the second listing titled, "Economic Evaluations of Fiber-Reinforced Polymer Bridge..." is where the document can be found. After jumping through all these hoops to get the article, the conducted study is actually extremely interesting. For this study, the researchers checked the life cycle cost of the bridge deck. The life cycle cost includes construction and demolition costs, which are the initial cost to build the material and the final cost of the material during its removal. This cost also includes the repair costs that may occur throughout the life of the material. The issues that they ran into within their study is that, due to the extremely high initial cost of the flexible concrete it, currently, can not be competitive with standard concrete. However, they conducted an estimation of the future initial costs of the material and found that, due to the curve sets of data, the material should become economically feasible to use as bridge decks within 10 years. This isn't exactly what I wanted to see in the study, honestly. I was hoping to see that, based on the life cycle data, that the flexible concrete would be economical to use. Unfortunately, that is not the case. But, 10 years, is an extremely short amount of time and with the way technology is always changing nowadays, it could occur much quicker.

Standard Concrete vs. Flexible Concrete

Much earlier in the semester I gave an example of how concrete acts when loaded (similar to a granola bar) but have never actually shown it. The two videos below show stress tests of, first, standard concrete and, second, flexible concrete. In the standard concrete video, failure of the material occurs at the 1:59 mark showing just how rapidly a concrete structure can go from standing and bearing the load, to immediate failure and a risk to human life. In comparison, the flexible concrete doesn't show signs of total failure under similar conditions. This is due to the higher ultimate strength which means that complete failure will, eventually, occur but at a much higher load capacity. Now, the benefit to the flexible concrete in these examples is that, by bending so greatly and still carrying the applied load, the engineer who notices the extreme bending still has time to redesign the concrete and replace the beam that is being effected without the structure collapsing. While the beam in use would still be mathematically safe to carry the loads applied, having that large of a bend within the concrete would not make people within the building feel safe because bending is a sign of imminent failure. Definitely check out the videos below. It's amazing to see how, by changing the materials in the concrete, it effects the performance of the finally designed material.

Starting the Paper

Well the semester is coming to a close and, while it has been a very busy one, there is still more for me to do in all my classes. Now that I have a day, it'll be good to get a start on the paper. Recently, in class, we were assigned to put together a small outline of our paper. This actually helped a lot in figuring out what to do for the research paper. The style of the assignment was to have an argument about a topic which, due to the nature of my topic of choice, was something that didn't really have two or more sides and arguments. Due to this, I had always been thinking on what I should write about because there isn't really an argument against flexible concrete. However, by doing that in-class assignment, I realized that there is an argument against it. The material is actually fairly expensive when compared to standard concrete. While, there is no one actively stating, "We can't use flexible concrete because it is overly expensive," it is something that every individual who is conducting the studies on the material has kept in mind and have attempted to find ways to save on cost, including studying about using recycled fibers (discussed in another blog post). So this helped me in setting up the paper and discussing the counter argument about cost and helped me to have an argument against the counter argument which is that the cost over time would be smaller due to the possibility of less construction to fix potholes or cracks.

Recycled Fibers in Flexible Concrete

Another thought I had about flexible concrete, "What if the fibers within the concrete were recycled and used in another slab of concrete?" A study conducted by Shi Yin and others from James Cook University in Australia (found here) tested exactly that. They found some interesting stuff from this study. With multiple samples of concrete tested at both high (5800 psi) and low (3600 psi) stress levels, they found that the recycled fibers weren't as feasible as the new fibers in the higher stress test. This is due to the fact that, due to being placed under stress previously, their tensile strength was greatly reduced which meant that they have a higher chance of breaking under the higher stress. But, when tested in the lower stress test, the recycled fibers outperformed the new fibers. This may seem weird but it's due to a mechanical property called the Young's Modulus, a relation between stress and elongation of the fiber. When previously placed under stress, these fibers tend to increase their Young's Modulus causing the fiber to better resist elongation when under stress. Due to this, the recycled fibers would barely elongate under a lower stress when compared to the new fibers, which had a lower Young's Modulus. This is a very interesting find that kind of didn't go the way I thought it would (or would have liked to see it go). While it would be useful to reuse these fibers in sidewalks after being used in roadways, it will, unfortunately, not be useful in another roadway which will not help in reducing the price of flexible concrete.

Some Questions Answered

I've had a few thoughts floating through my head that I haven't really been able to answer but it seems I've found a magazine article that explains some of it. Found here, the article, written by Zach Zorich back in 2005 for Discover Magazine, helped answer the questions, "Who's studying flexible concrete?" and "How much does flexible concrete cost?" With this article and the video I found 2 weeks ago, it seems that, if I want to look into the studies done on flexible concrete, I should look for professor Victor Li of the University of Michigan. He seems to be one of the main Civil Engineers working on this type of project. Also from the article, it was stated that flexible concrete is approximately 3 times more expensive than standard concrete. Standard concrete is somewhere close to $100 for every cubic yard created. That means flexible concrete would be in the $300 range for every cubic yard. To put this into perspective, a single car driveway is usually designed to be 10 feet wide and 18 feet long. Then, on top of that information, the slabs of concrete are designed to be, at a minimum, 4 inches thick. With a bit of math, this driveway uses 2.22 cubic yards of concrete resulting in costs of $222 for standard concrete use and $666 for flexible concrete use. While this doesn't seem like much, think about trying to do this on thousands of miles of roads throughout the country which, due to heavier loads like tractor trailers and hundreds of cars passing over per hour, the cost would be astronomical. But, this is information from almost 11 years ago (hard to think it has been 11 years since 2005) which means that it is entirely possible the Professor Li, along with many other Civil Engineers who may have tasked themselves with studying this relatively new material, were able to reduce the cost of flexible concrete. These were just a couple things I have been thinking about and now have a basis on where to look next.

Carbon Nanotubes and Cement

In class the other day, while working in the library, I found an interesting study done that I was actually curious about (which can be founder here). I was curious about how the use of carbon nanotubes would effect flexible concrete. This conducted test measured multiple different strengths with multiple different forms of carbon nanotubes and was able to show that they actually do increase the strength within a cement mixture, a key part in concrete and flexible concrete. The amazing thing about carbon nanotubes is just how ridiculously small they are. As seen within the study, images were taken of the various forms of nanotubes tested and have to be referenced on the micrometer scale. That's .000001 meters or 1/39360000". Due to their size and tested strengths, they are a material that has one of the highest strength to weight ratios ever recorded. The only issue is that they, currently, can only be made to be extremely short in length, short enough that the nanotubes can still be measured in that micrometer scale. This also leads to an economical issue since the production of these ridiculously small objects tends to be very expensive. Hopefully one day they won't be and who knows what can come of this relatively new material. I'm looking forward to seeing if there is a way to make the nanotubes possible on the economic side in my next bout of research because, as seen in the conducted study, they worked extremely well on the strength side.

Professor Li | University of Michigan

Beginning my research, this was one video that came up. Professor Li of the University of Michigan College of Engineering has been studying bendable concrete for some time now. He has even gone as far as placing test strips on roads to see if it is a feasible replacement to standard concrete. It was very interesting to learn about some other things about flexible concrete. It had never crossed my mind that the steel could rust and expand causing the concrete to crack which is a force that can easily be mitigated by the flexible concrete. I also didn't think that the flexible concrete could fix its cracks with just air and water. This is important considering, in places like Buffalo where the winter weather tears roads apart, pot holes may never be able to form since the water that would fill the cracks could then help fix those cracks.

This video is also helpful in showing how differently standard and flexible concrete act under normal, every-day loading capacities and even how much higher of a load the flexible concrete can take when compared to standard concrete.

Introduction

Hello, welcome to my blog. For this blog I will be discussing some of the research I am doing for my University at Buffalo English 201 paper. For this paper I am looking to research flexible concrete.

Normally, concrete is a mixture of water, sand, small rocks (also known as aggregate), and cement. This mixture remains slightly fluid and allows you to pour it over steel rebar and form it into any shape needed for the structure. When the concrete is loaded with a weight, whether this is a car on a driveway or a house on its foundation, the concrete wants to bend downward which causes the bottom side of the concrete to separate and crack. This is where the rebar comes into play. The rebar takes the tensile loading that causes the concrete to crack. It is fairly easy to imagine how these two different materials act in tensile loading. To imagine concrete, take a granola bar and pull on both ends. Then, to imagine steel rebar, take a piece of string and pull on both ends. You should notice that, when compared, the string takes a lot more force to break than the granola bar. When putting concrete together with steel, a high strength material is created.

For flexible concrete, the aggregate and steel are replaced by high strength fibers and allow for a similar material to be built. The only exception to this is that it will be a much lighter weight material and, possibly, a cheaper and higher strength material. With this paper, I'm hoping to research the feasibility of flexible concrete as a replacement to standard concrete for home foundations, driveways, load-bearing columns, and explore some of its other uses along with exploring its financial feasibility.