Thanks 2ndDivisionVet.
KEYWORDS: ancientconcrete; geopolymer; geopolymerization; geopolymers; josephdavidovits; pozzolana; pozzolano; romanconcrete
Posted on 05/28/2016 11:29:45 PM PDT by 2ndDivisionVet
Researchers at MIT are seeking to redesign concrete — the most widely used human-made material in the world — by following nature’s blueprints.
In a paper published online in the journal Construction and Building Materials, the team contrasts cement paste — concrete’s binding ingredient — with the structure and properties of natural materials such as bones, shells, and deep-sea sponges. As the researchers observed, these biological materials are exceptionally strong and durable, thanks in part to their precise assembly of structures at multiple length scales, from the molecular to the macro, or visible, level.
From their observations, the team, led by Oral Buyukozturk, a professor in MIT’s Department of Civil and Environmental Engineering (CEE), proposed a new bioinspired, “bottom-up” approach for designing cement paste.
“These materials are assembled in a fascinating fashion, with simple constituents arranging in complex geometric configurations that are beautiful to observe,” Buyukozturk says. “We want to see what kinds of micromechanisms exist within them that provide such superior properties, and how we can adopt a similar building-block-based approach for concrete.”
Ultimately, the team hopes to identify materials in nature that may be used as sustainable and longer-lasting alternatives to Portland cement, which requires a huge amount of energy to manufacture.
“If we can replace cement, partially or totally, with some other materials that may be readily and amply available in nature, we can meet our objectives for sustainability,” Buyukozturk says.
Co-authors on the paper include lead author and graduate student Steven Palkovic, graduate student Dieter Brommer, research scientist Kunal Kupwade-Patil, CEE assistant professor Admir Masic, and CEE department head Markus Buehler, the McAfee Professor of Engineering.
“The merger of theory, computation, new synthesis, and characterization methods have enabled a paradigm shift that will likely change the way we produce this ubiquitous material, forever,” Buehler says. “It could lead to more durable roads, bridges, structures, reduce the carbon and energy footprint, and even enable us to sequester carbon dioxide as the material is made. Implementing nanotechnology in concrete is one powerful example [of how] to scale up the power of nanoscience to solve grand engineering challenges.”
From molecules to bridges
Today’s concrete is a random assemblage of crushed rocks and stones, bound together by a cement paste. Concrete’s strength and durability depends partly on its internal structure and configuration of pores. For example, the more porous the material, the more vulnerable it is to cracking. However, there are no techniques available to precisely control concrete’s internal structure and overall properties.
“It’s mostly guesswork,” Buyukozturk says. “We want to change the culture and start controlling the material at the mesoscale.”
As Buyukozturk describes it, the “mesoscale” represents the connection between microscale structures and macroscale properties. For instance, how does cement’s microscopic arrangement affect the overall strength and durability of a tall building or a long bridge? Understanding this connection would help engineers identify features at various length scales that would improve concrete’s overall performance.
“We’re dealing with molecules on the one hand, and building a structure that’s on the order of kilometers in length on the other,” Buyukozturk says. “How do we connect the information we develop at the very small scale, to the information at the large scale? This is the riddle.”
Building from the bottom, up
To start to understand this connection, he and his colleagues looked to biological materials such as bone, deep sea sponges, and nacre (an inner shell layer of mollusks), which have all been studied extensively for their mechanical and microscopic properties. They looked through the scientific literature for information on each biomaterial, and compared their structures and behavior, at the nano-, micro-, and macroscales, with that of cement paste.
They looked for connections between a material’s structure and its mechanical properties. For instance, the researchers found that a deep sea sponge’s onion-like structure of silica layers provides a mechanism for preventing cracks. Nacre has a “brick-and-mortar” arrangement of minerals that generates a strong bond between the mineral layers, making the material extremely tough.
“In this context, there is a wide range of multiscale characterization and computational modeling techniques that are well established for studying the complexities of biological and biomimetic materials, which can be easily translated into the cement community,” says Masic.
Applying the information they learned from investigating biological materials, as well as knowledge they gathered on existing cement paste design tools, the team developed a general, bioinspired framework, or methodology, for engineers to design cement, “from the bottom up.”
The framework is essentially a set of guidelines that engineers can follow, in order to determine how certain additives or ingredients of interest will impact cement’s overall strength and durability. For instance, in a related line of research, Buyukozturk is looking into volcanic ash as a cement additive or substitute. To see whether volcanic ash would improve cement paste’s properties, engineers, following the group’s framework, would first use existing experimental techniques, such as nuclear magnetic resonance, scanning electron microscopy, and X-ray diffraction to characterize volcanic ash’s solid and pore configurations over time.
Researchers could then plug these measurements into models that simulate concrete’s long-term evolution, to identify mesoscale relationships between, say, the properties of volcanic ash and the material’s contribution to the strength and durability of an ash-containing concrete bridge. These simulations can then be validated with conventional compression and nanoindentation experiments, to test actual samples of volcanic ash-based concrete.
Ultimately, the researchers hope the framework will help engineers identify ingredients that are structured and evolve in a way, similar to biomaterials, that may improve concrete’s performance and longevity.
“Hopefully this will lead us to some sort of recipe for more sustainable concrete,” Buyukozturk says. “Typically, buildings and bridges are given a certain design life. Can we extend that design life maybe twice or three times? That’s what we aim for. Our framework puts it all on paper, in a very concrete way, for engineers to use.”
This research was supported in part by the Kuwait Foundation for the Advancement of Sciences through the Kuwait-MIT Center for Natural Resources and the Environment, the National Institute of Standards and Technology, and Argonne National Laboratory.
Doesn't sound like science to me. Sounds like Political Correctness searching for grant money.
SLUMP TEST
Roman concrete was so good it didn’t need re-bar in it. That’s good stuff.
Same here - wonder if the show was rigged to make it seem better than advertised.
LOL!!
“If we can replace cement, partially or totally, with some other materials that may be readily and amply available in nature, we can meet our objectives for sustainability,” Buyukozturk says.
Just to be clear: if you fall on concrete hard enough, your bones break, not the concrete.
I’m curious, how does a sealer prevent cracking.
There are many reasons why cement cracks, a poor/wrong mix is one, how it cures, thickness is another, ground heaving, improper soil preparation, rebar placement and there are probably others.
Our ground up here moves a lot during the seasonal changes which is our number one reason for cracking. I knew guy that put zero rebar in a basement. After a year there were 1/2 inch gaps in the basement cracks.
To prevent cracking from ground heaving, a nearby air base runway, they removed the soil 8 feet down and back filled it with a uniform aggregate and compacted to a certain specification, then poured the concrete over it.
Yes, It took us centuries to get back to where the Romans were. Pantheon dome uses heavy aggregates close to the drum, as the section moves up toward the oculus the aggregate gets progressively lighter (volcanic) - genius!
Greeks had them beat as far as beauty though.
now...??....... they are thinking about using nanotech stuff?
i guess we are living at a snails pace , fast !
Here too!
From a video I once saw, towards the top of the dome, they used small ceramic hollow balls as filler in the wall. This served to lighten the mass near the top.
You want the water in concrete to hydrate not evaporate. The sealer locks in the water so it does not evaporate. Thus giving you stronger concrete and less micro voids from evaporation.
That being said too much water will also weaken the concrete. People add more water to make the mix more workable.
Concrete by its nature is strong in compression and weaker in tension. This is why re-bar is added for tensile strength.
Not an expert but many years in construction.
Microscale reinforcing rods? Great... and when the structure needs to be torn down and replaced>.. what then?
didn’t you post something once about ancient concrete being stronger than what we use today?
the article uses the generic term cement when as you have pointed out is Portland cement as opposed to say asphalt cement or epoxy cement
For those journqalists that don’t know the difference between cement and concrete, this article might be quite confusing.
lastly, the term “a random assemblage” is used by the authors when in truth Portland cement concrete for engineering structures is a carefully engineered product for a specific task.
The main ingredients are Portland cement and aggregate of various sizes that include rock (aka stone) and sand. Some would say the rock is aggregate. The size and amounts of the rock and sand particles are designed for the specific purpose of the concrete.
Additionally there are lots of various additives that are included by the engineering design to suit the need.
There are female engineers working on grants at more than MIT making a difference by checking out obsolete concrete formulations
It’s in one or more of those keywords, and it happened more than once if memory serves. :’) I’ve visited most of those topics today, making sure the keywords were in order. :’)
Roman underwater concrete:
http://www.freerepublic.com/focus/chat/1380333/posts
...do as the Romans did:
http://www.freerepublic.com/focus/chat/3027618/posts
This one has a first sentence that will blow your hat right off!
http://www.freerepublic.com/focus/chat/2250645/posts
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