将秩序置于混乱是制造更坚固，更绿色的水泥的关键，即结合混凝土的糊状物。
赖斯大学的科学家已经解码了水泥的动力学特性，并开发了一种“编程”微观，半晶体颗粒的方法。该过程将颗粒从无序的团块转变为结合的立方体，球形和其他形式，这些形式结合在一起，使材料变得不那么多，更耐用。
他们的研究出现在皇家化学学会《材料化学try A.
The technique may lead to stronger structures that require less concrete — and less is better, said Rice materials scientist and lead author Rouzbeh Shahsavari. Worldwide production of more than 3 billion tons of concrete a year now emits as much as 10 percent of the carbon dioxide, a greenhouse gas, released to the atmosphere.
Through extensive experiments, Shahsavari and his colleagues decoded the nanoscale reactions — or “morphogenesis” — of the crystallization within calcium-silicate hydrate (C-S-H) cement that holds concrete together.
他们首次将C-S-H颗粒构成了各种形状，包括立方体，矩形棱镜，树突，核心壳和菱形，并将其映射到希望从底部上锻炼混凝土的制造商和建筑商的统一形态图。
“We call it programmable cement,” he said. “The great advance of this work is that it’s the first step in controlling the kinetics of cement to get desired shapes. We show how one can control the morphology and size of the basic building blocks of C-S-H so that they can self-assemble into microstructures with far greater packing density compared with conventional amorphous C-S-H microstructures.”
他说，这个想法类似于金属晶体和聚合物的自组装。Shahsavari说：“这是一个热门地区，研究人员正在利用它。”“但是在水泥和混凝土方面，控制其自下而上的组装非常困难。我们的工作为这种高级合成提供了第一个食谱。
他说：“种子颗粒首先在我们的反应中自动形成，然后它们在其周围的其余材料形成时占主导地位。”“这就是它的美。在原地，种子介导的生长，不需要外部添加种子颗粒，就像行业中通常这样做以促进结晶和生长。”
Previous techniques to create ordered crystals in C-S-H required high temperatures or pressures, prolonged reaction times and the use of organic precursors, but none were efficient or environmentally benign, Shahsavari said.
The Rice lab created well-shaped cubes and rectangles by adding small amounts of positive or negative ionic surfactants and calcium silicate to C-S-H and exposing the mix to carbon dioxide and ultrasonic sound. The crystal seeds took shape around surfactant micelles within 25 minutes. Decreasing the calcium silicate yielded more spherical particles and smaller cubes, while increasing it formed clumped spheres and interlocking cubes.
一旦方解石“种子”形式,它们触发lecules around them to self-assemble into cubes, spheres and other shapes that are orders of magnitude larger. These can pack more tightly together in concrete than amorphous particles, Shahsavari said. Carefully modulating the precursor concentration, temperature and duration of the reaction varies the yield, size and morphology of the final particles.
The discovery is an important step in concrete research, he said. It builds upon his work as part of the Massachusetts Institute of Technology team that decoded cement’s molecular “DNA” in 2009. “There is currently no control over C-S-H shape,” Shahsavari said. “The concrete used today is an amorphous colloid with significant porosity that entails reduced strength and durability.”
混凝土是Shahsavari的Rice Lab的一个焦点，该实验室研究了其宏观制造和固有的纳米级特性。由于混凝土是世界上最常见的建筑材料，也是大气二氧化碳的重要来源，因此他坚信开发“更绿”混凝土的重要性。
The new technique has several environmental benefits, Shahsavari said. “One is that you need less of it (the concrete) because it is stronger. This stems from better packing of the cubic particles, which leads to stronger microstructures. The other is that it will be more durable. Less porosity makes it harder for unwanted chemicals to find a path through the concrete, so it does a better job of protecting steel reinforcement inside.”
The research required the team to develop a method to test microscopic concrete particles for strength. The researchers used a diamond-tipped nanoindenter to crush single cement particles with a flat edge.
他们对缩进器进行了编程，以从一个纳米颗粒移动到另一个纳米颗粒，并将其压碎，并在一项运行中收集数百个各种形状颗粒的机械数据。Shahsavari说：“其他研究小组已经测试了散装水泥和混凝土，但是从未探测过单个C-S-H颗粒的力学以及形状对单个颗粒力学的影响。”
他说，该项目期间制定的策略可能会对其他应用产生影响，包括骨组织工程，药物输送和难治材料，并可能影响诸如陶瓷和胶体等其他复杂系统。
Filed Under:Materials • advanced
