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Waste coffee grounds make concrete 30% stronger
Researchers have found that concrete can be made 30% stronger by replacing a percentage of sand with spent coffee grounds, an organic waste product produced in huge amounts that usually ends up in landfill. The method also reduces the use of natural resources like sand, further contributing to a greener circular economy approach to construction.
It’s estimated that, worldwide, the total amount of spent coffee grounds (SCG) produced annually is 60 million tons (54 million tonnes), making it the most abundant waste generated in coffee preparation. Traditionally, most of those coffee grounds end up in landfill.
Now, researchers from RMIT University have found a practical, first-of-its-kind use for this particular kind of waste: incorporating it into concrete.
“The inspiration for our work was to find an innovative way of using the large amounts of coffee waste in construction projects rather than going to landfills – to give coffee a ‘double shot’ at life,” said Rajeev Roychand, the study’s lead author.
Due to their fine particle size, SCG have been proposed as a useful component in civil and construction applications. So, the researchers decided to put this to the test. They first collected SCG from various cafés around Melbourne, Australia, and dried them to remove moisture. Then the dried organic material was heated at two different temperatures – either 350 °C (662 °F) or 500 °C (932 °F) – using a low-energy, oxygen-free process called pyrolysis to create biochar.
Twelve mix designs were used to compare the effects of SCG in the form of untreated SCG, 350-degree-heated SCG and 500-degree-heated SCG, on the mechanical and microstructural behavior of concrete. The different SCGs were incorporated into ordinary Portland cement at 0%, 5%, 10%, 15% and 20% volume as a replacement for fine aggregate. Here, the fine aggregate used was natural sand.
Fresh concrete was poured into molds and vibrated to remove air pockets. It was then cured at room temperature for 24 hours, demolded and cured in a water tank until it was tested for compressive strength and analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Compressive strength is the maximum compressive stress a solid material can sustain without fracturing.
The researchers found that, of all the concrete composites they tested, the one that replaced 15% of sand with SCG pyrolyzed at 350 °C (662 °F) led to a significant improvement in its material properties, resulting in a 29.3% enhancement in compressive strength.
While the research is still in its early stages, the researchers say the results are promising and, given the ubiquity of coffee, could potentially be used in construction around the world.
“The concrete industry has the potential to contribute significantly to increasing the recycling of organic waste such as used coffee,” said co-lead author Shannon Kilmartin-Lynch. “Our research is in the early stages, but these exciting findings offer an innovative way to greatly reduce the amount of organic waste that goes to landfill.”
In addition to saving space in landfills, the concrete production technique also addresses another environmental issue: the preservation of finite natural resources. We extract roughly 40 to 50 billion tons of sand and gravel each year for use in construction.
“The ongoing extraction of natural sand around the world – typically taken from river beds and banks – to meet the rapidly growing demands of the construction industry has a big impact on the environment,” said Jie Li, co-corresponding author of the study. “With a circular-economy approach, we could keep organic waste out of landfill and also better preserve our natural resources like sand.”
The researchers plan to carry out long-term mechanical and durability tests on the 350-degree-heated coffee biochar for its potential applications in the construction industry, and further explore the effect of using different pyrolyzing temperatures on the material’s performance.
注释：
incorporate: v
表示" 合并；组成公司"，means " contain"，如：I will incorporate the new findings in my report. 我要把新发现并入我的报告。
microstructural: adj
表示" 显微结构的"，如：The photograph made with a microscope, which records a microstructural image. 在显微镜下拍摄，记录显微组织结构形态的照片。
demold: v
表示" 脱模", 如：Choose the outer surface of the goods as the parting plane to make goods demold successfully. 本模具考虑到年产量、工厂的设备及塑件的精度要求，选择了一模四腔。
microscopy: n
表示" 显微镜学；用显微镜检查"，如：Her recent work in electron microscopy stimulated a new line of research. 她最近的工作，在电子显微镜学上开创了一个新的研究领域。
pyrolysis: n
表示"热解；高温分解"，means "transformation of a substance produced by the action of heat"，如：The riverbed sludge plays a catalytic role on coal slime pyrolysis. 污泥对煤泥水的热解起到一定的催化作用。
aggregate: v
表示" （使）聚集；总计"，means "combine different items, amounts, etc. into a single group or total; reach a total of; add up to; add amounts together; Occasionally the cells might aggregate to form lentoid bodies.
偶而，细胞能聚集形成类晶体球体。"，如：The television audience aggregated 30 millions. 电视观众合计达3000万人。
durability: n
表示"持久性；耐久性"，means "permanence by virtue of the power to resist stress or force"，如：Nothing can rival cotton for durability. 什么东西也赶不上棉花经久耐用。
中文简要说明：
新阿特拉斯(New Altas)报导，澳洲皇家墨尔本理工大学(RMIT University)的拉吉夫•罗伊乍得(Rajeev Roychand)教授，正在尝试更环保的混凝土配方，在研究过程中，就把咖啡渣加入水泥里，做为代替河沙的骨材。
罗伊乍得(Rajeev Roychand) 表示：「这算是为咖啡加上了另一种用途。」
研究人员从墨尔本各地的咖啡馆收集咖啡渣，并将其干燥以除去水分，然后加热到350度与500度，这种为热解，形成有机炭。
研究人员将350 度与500 度加热的咖啡渣，以不同的比例掺进波特兰水泥中，作为替代沙子的骨材，比例从0%、5%、10%、15% 到最大比例的20%，这些比例不同的混凝土在室温下固化24小时，之后开始测试强度，并以扫描式电子显微镜（SEM）进行分析。
研究人员发现，进行350度热解的咖啡渣，以15% 的比例混入水泥中，这种混凝土的强度最好，与普通配方相比，提高了29.3%的抗压强度。
虽然这项研究仍处于早期阶段，但研究人员表示，前景非常有希望，而且鉴于咖啡的全球使用量，它有可能成为世界各地的建筑材料。
研究团队成员林奇 (Shannon Kilmartin-Lynch) 表示：「这种创新方法，可以大大减少垃圾量，即使是生物废料，也是需要减少进入垃圾填埋场的数量。」
除了节省垃圾填埋场空间外，咖啡混凝土还解决了另一个环境问题：保护有限的自然资源。为了建设，全球每年大约采掘40至500 亿吨的河沙和砾石。
咖啡是全世界消耗量最高的饮料，这也导致咖啡渣的数量相当大很特别，据估计，全球每年产生的咖啡渣总量，达到惊人的5400万公吨。这种植物型废料一般来说都是「回归自然」，填进埯埋场里分解。然而这也不环保，分解过程也会产生二氧化碳或甲烷。新的研究发现，把咖啡渣填进水泥里拌成混凝土，是一种更好的做法，强度非但没有减弱，还提高 30%。而且也减少了河沙等自然资源的消耗，兼顾环保与实用，一举多得。
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