미 연구팀, 더 강하고 더 청정한 콘크리트를 만드는 나노 구체 개발 Spheres can make concrete leaner, greener

Spheres can make concrete leaner, greener

(Nanowerk News) Rice University scientists have developed micron-sized calcium silicate spheres that could lead to stronger and greener concrete, the world’s most-used synthetic material.

Manufacturing.net

미 연구팀, 더 강하고 더 청정한 콘크리트를 만드는 나노 구체 개발 라이스 대학(Rice University  저렴한 비용, 더 적은 에너지 사용   미국 라이스 대학(Rice University)의 연구진은 더 강하면서 더 청정한 콘크리트를 만들 수 있는 새로운 마이크론 크기의 규산칼슘 구체를 개발했다. 이 구체는 저렴한 비용으로 만들 수 있고 기존 콘크리트보다 더 적은 에너지를 사용한다. 시멘트는 가장 좋은 구조를 가지고 있지 않다. 시멘트 입자는 무정형이고 무질서하기 때문에 균열에 취약하다. 이번 연구진은 계면 활성제와 같은 역할을 하는 용액 속에서 구체를 형성했다. 이 구체는 포틀랜드 시멘트보다 강하고 단단하며 탄력 있고 내구성이 강하다. 이 새로운 소재는 다공성이 아니며 규산칼슘 고체가 계면 활성제 시드(seed)로 둘러싸여 있는 구조로 되어 있다. 이 소재는 조개껍질, 특히 진주에서 영감을 받았다. 진주의 강도는 딱딱한 무기물과 부드러운 유기물이 교대로 적층됨으로써 발생한다. 이번 연구에서는 계면 활성제, 용액, 농도, 온도를 조절해서 구체 직경을 100 나노미터에서 500 나노미터 사이로 조절할 수 있었다. 이것은 매우 단순하지만 보편적인 빌딩 블록이고 많은 생체 적합 물질의 주요 특징이다. 구체는 화학적 작용과 대규모 제조 관점에서 다른 형태보다 우수하기 때문에서 중요하다. 즉, 더 빨리 합성되고 자기 조립하며 대규모로 쉽게 제조할 수 있다. Rice University engineers learned to control the size of synthesized calcium silicate spheres developed to strengthen concrete, the world’s most-used material. This microscope image shows spheres compacted into a pellet. Courtesy of the Multiscale Materials Laboratory/Rice University News 라이스 대학의 엔지니어들은 세계에서 가장 많이 사용되는 재료인 콘크리트를 강화하기 위해 개발된 합성 칼슘 규산염 구체의 크기를 조절하는 방법을 연구했다  이 현미경 이미지는 알갱이로 압축되어 있는 구들을 보여준다. 멀티세일 소재 연구소 edited by kcontents 입자 크기와 모양이 콘크리트와 같은 벌크 재료의 기계적 특성과 내구성에 중요한 영향을 끼쳤다. 또한 자기 조립된 구조체 사이의 틈새를 메우기 위해서 다른 직경의 구형을 혼합할 수 있어 더 높은 충진 밀도와 내구성을 가질 수 있었다. 이 새로운 소재는 시멘트의 강도를 높여서 무게를 줄이게 하고 필요한 에너지를 감소시켜서 시멘트 제조와 관련된 탄소 배출량을 줄인다. 비정형 입자를 가진 기존 시멘트보다 효율적으로 포장되기 때문에 오염 물질로부터 내성이 강하고 유지 보수비용이 적게 드는 장점을 가진다. 이 나노구체는 시멘트뿐만 아니라 뼈 조직 공학, 단열재, 세라믹, 복합재료 등에 유용하게 적용될 수 있을 것이다. 이 연구결과는 저널 Langmuir에 “Size- and Shape-Controlled Synthesis of Calcium Silicate Particles Enables Self-Assembly and Enhanced Mechanical and Durability Properties” 라는 제목으로 게재되었다(DOI: 10.1021/acs.langmuir.8b00917). ndsl.kr

edited by kcontents

To Rice materials scientist Rouzbeh Shahsavari and graduate student Sung Hoon Hwang, the spheres represent building blocks that can be made at low cost and promise to mitigate the energy-intensive techniques now used to make cement, the most common binder in concrete.

The researchers formed the spheres in a solution around nanoscale seeds of a common detergent-like surfactant. The spheres can be prompted to self-assemble into solids that are stronger, harder, more elastic and more durable than ubiquitous Portland cement.

Packed, micron-scale calcium silicate spheres developed at Rice University are a promising material that could lead to stronger and more environmentally friendly concrete. (Image: Multiscale Materials Laboratory)

“Cement doesn’t have the nicest structure,” said Shahsavari, an assistant professor of materials science and nanoengineering. “Cement particles are amorphous and disorganized, which makes it a bit vulnerable to cracks. But with this material, we know what our limits are and we can channel polymers or other materials in between the spheres to control the structure from bottom to top and predict more accurately how it could fracture.”

He said the spheres are suitable for bone-tissue engineering, insulation, ceramic and composite applications as well as cement.

The research appears in the American Chemical Society journal Langmuir ("Size- and Shape-Controlled Synthesis of Calcium Silicate Particles Enables Self-Assembly and Enhanced Mechanical and Durability Properties").

The work builds on a 2017 project by Shahsavari and Hwang to develop self-healing materials with porous, microscopic calcium silicate spheres. The new material is not porous, as a solid calcium silicate shell surrounds the surfactant seed.

But like the earlier project, it was inspired by how nature coordinates interfaces between dissimilar materials, particularly in nacre (aka mother of pearl), the material of seashells. Nacre’s strength is a result of alternating stiff inorganic and soft organic platelets. Because the spheres imitate that structure, they are considered biomimetic.

The researchers discovered they could control the size of the spheres that range from 100 to 500 nanometers in diameter by manipulating surfactants, solutions, concentrations and temperatures during manufacture. That allows them to be tuned for applications, Shahsavari said.

“These are very simple but universal building blocks, two key traits of many biomaterials,” Shahsavari said. “They enable advanced functionalities in synthetic materials. Previously, there were attempts to make platelet or fiber building blocks for composites, but this works uses spheres to create strong, tough and adaptable biomimetic materials.

“Sphere shapes are important because they are far easier to synthesize, self-assemble and scale up from chemistry and large-scale manufacturing standpoints.”

Calcium silicate spheres synthesized at Rice University and packed into a pellet hold together under compression. The spheres are building blocks that can be made at low cost and promise to mitigate the energy-intensive techniques now used to make cement, the most common binder in concrete. (Image: Multiscale Materials Laboratory)

In tests, the researchers used two common surfactants to make spheres and compressed their products into pellets for testing. They learned that DTAB-based pellets compacted best and were tougher, with a higher elastic modulus, than either CTAB pellets or common cement. They also showed high electrical resistance.

Shahsavari said the size and shape of particles in general have a significant effect on the mechanical properties and durability of bulk materials like concrete. “It is very beneficial to have something you can control as opposed to a material that is random by nature,” he said. “Further, one can mix spheres with different diameters to fill the gaps between the self-assembled structures, leading to higher packing densities and thus mechanical and durability properties.”

He said increasing the strength of cement allows manufacturers to use less concrete, decreasing not only weight but also the energy required to make it and the carbon emissions associated with cement’s manufacture. Because spheres pack more efficiently than the ragged particles found in common cement, the resulting material will be more resistant to damaging ions from water and other contaminants and should require less maintenance and less-frequent replacement.

Source: Rice University

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