The Roadmap to Net-Zero Cement
在快速建設和城市發展的時代，水泥已成為支撐AEC行業延續的重要商品。作為混凝土的主要成分，水泥生產佔混凝土碳足蹟的 95%，因此成為僅次於鋼鐵行業的世界第二大二氧化碳工業排放國。作為建築中使用的主要材料，水泥生產釋放的高碳排放也增加了 AEC 部門的碳足跡，使該部門負責全球 39% 的溫室氣體 (GHG)。隨著許多新興國家住房不足的猖獗以及基礎設施的改善，建築業將繼續佔據主導地位並排放更多的溫室氣體。因此，了解這些重要的 AEC 材料的價值鏈並努力減少碳排放總量非常重要。
2017年，僅水泥行業就佔全球碳排放量的約8%，二氧化碳排放率為90%，這意味著每生產一噸水泥，約有900公斤的二氧化碳排放到大氣中。在過去的幾十年裡，水泥行業發展迅速。從 1995 年的 13.90 億噸水泥產量增長到 2010 年的 33 億噸，2020 年達到 41 億噸，佔行業年增長率的 4.4%。在全球範圍內，水泥和混凝土行業佔全球 GDP 的 13%。然而，即使年產量如此驚人，印度等一些國家仍面臨水泥短缺的問題，因為僅在 2011 年至 2013 年期間，中國等快速發展的國家在整個 20 世紀使用的水泥數量就超過了美國。
水泥生產有兩個主要階段。第一階段稱為熱循環，在該過程中石灰石、粘土和鐵礦石的混合物在窯中加熱，直至達到 1450oC 左右形成熟料。水泥生產中的大部分 CO2 排放都是在此過程中產生的。將石灰石轉化為熟料的排放量佔排放量的 60%，而另外 40% 來自水泥窯和其他過程中燃料的燃燒。熱循環之後是冷循環，其中熟料與石膏和化學添加劑等其他成分一起研磨，形成我們稱為水泥的最終產品。加上碳排放量，水泥廠都是用水大戶。對於每噸水泥，生產過程使用大約 60-130 公斤的燃料，具體取決於生產的水泥類型，以及 110 千瓦時的電力。在一些國家，水泥廠也可能發現使用廢物衍生燃料作為化石燃料的替代品，以支持循環經濟並減少其碳足跡。
2021 年 10 月，由全球領先的水泥和混凝土製造商組成的組織全球水泥和混凝土協會 (GCCA) 決定啟動“全球淨零路線圖”，這是一項七點計劃，旨在將二氧化碳排放量減少到 2030 年減少 25%，到 2050 年實現碳中和。該路線圖預計到 2030 年防止多達 50 億噸碳進入地球大氣。未能遵循低碳流程的水泥廠和公司面臨潛在風險罰款。全球淨零路線圖的七點如下：
一些大公司試圖遵守新的路線圖計劃並採取一些行動。 LafargeHolcim 與一家名為 Solid Technologies 的美國初創公司合作開發可將整體碳足跡減少 70% 的混凝土。該過程將涉及原材料的不同成分和在較低溫度下加熱。具體生產過程也將選擇添加二氧化碳而不是水的替代方案。 Heidelberg Cement、CRH Plc、Ecocem 和 CEMEX 等其他公司也採取了類似的步驟，減少在組合物中使用熟料，添加其他替代成分，並在較低溫度下加熱。
在更環保的水泥努力的另一邊，博士。名為 David Stone 的學生早在 2015 年就提出了一種水泥替代品。他使用碳酸鐵作為水泥替代品的主要成分，這創造了一個完全綠色和負碳的過程。鋼塵是鋼鐵廠的一種副產品，不被回收，通常直接進入垃圾填埋場，與磨碎的玻璃中的二氧化矽一起用於此過程。水泥替代品已獲得專利，名稱為 Ferrocrete，並以 Ferrock 名稱出售。與傳統水泥相比，“綠色水泥”是一種更好的替代品，因為它更堅固，並且在暴露於高溫或鹽水時不會分解。最重要的是，由此產生的混凝土也是柔韌的，允許使用抗裂和抗衝擊材料。然而，儘管擁有所有這些優越的優勢，但 Ferrock 的製造成本仍然被認為更昂貴且更難獲得。
In the era of rapid construction and city development, cement has become an important commodity to support the continuation of the AEC sector. As a main ingredient of concrete, cement production accounts for up to 95% of concrete’s carbon footprint, subsequently granting them the position as the world's second-largest industrial emitter of carbon dioxide after the iron and steel sector. Being the main materials used in construction, the high carbon emission released by cement productions also add up to the AEC sector’s carbon footprint, making the sector responsible for 39% of global greenhouse gasses (GHG). With the rampage of insufficient housing in lots of emerging countries and hand in hand with infrastructure improvement, the construction sector will continue to reign and emit more GHG. Thus, it’s important to understand the value chain of these important AEC materials and make efforts to reduce the total carbon emission.
In 2017, the cement industry alone is responsible for approximately 8% of the global carbon emission with a 90% carbon dioxide emission rate, meaning that for every ton of cement produced, around 900kg of CO2 is released to the atmosphere. The cement industry has been growing rapidly within the last couple of decades. From producing 1,39 billion tones of cement in 1995, it has grown to 3,3 billion tons in 2010, and an outstanding 4,1 billion tonnes in 2020, allowing for 4,4% of the industry annual growth. Globally, the cement and concrete industry accounts for 13% of the global GDP. Yet, even with this staggering amount of annual production, some countries like India are still experiencing cement shortages because between 2011-2013 alone, countries with rapid development like China have used more cement compared to the US in the entire twentieth century.
There are two main phases in cement production. The first phase is called the hot cycle, a process where a mixture of limestone, clay, and iron ore is heated in a kiln until it reaches around 1450oC to form clinkers. Most CO2 emissions in cement production are generated in this process. Converting the limestone into clinker accounts for 60% of the emission, while the other 40% came from the combustion of the fuels in cement kilns and other processes. The hot cycle is later followed by the cold cycle in which the clinkers are ground together with other ingredients like gypsum and chemical additives to form the final products that we know as cement. Added to the amount of carbon emitted, cement plants are all large consumers of water. For each ton of cement, the production process used around 60-130 kg of fuel depending on the type of cement produced, and 110kWh of electricity. In some countries, cement plants might also be found to use waste-derived fuel as a replacement for fossil fuel to support a circular economy and reduce their carbon footprints.
As a highly competitive commodity with few options for diversification, cement is still a very conservative industry. Although there has been an effort of replacing clinker in cement production with other alternatives like granulated slag, fly ash, and other materials, the process of clinker formation itself is still irreplaceable. Added to that, the level of technology in cement plants is still highly volatile, depending on the country’s level of advancement. With cement having a high weight to commercial value ratio, cement is not an ideal commodity for a long supply chain and procurement route. It means that the material is almost always sold domestically, further reducing the opportunity of using a greener option produced in farther countries.
In October 2021, The Global Cement and Concrete Association (GCCA) – an organization comprised of the leading cement and concrete manufacturers across the globe, decided to launch a ‘Global Net-Zero Roadmap’ a seven-points-plan to reduce CO2 emission by 25% in 2030 and achieve carbon neutral by 2050. The roadmap is expected to prevent up to five billion tonnes of carbon to enter the earth’s atmosphere by 2030. Cement plants and companies that failed to follow the low carbon process are at risk to face potential fines as well. The seven points of the Global Net-Zero Roadmap are as follow:
1. Savings in clinker production
2. Savings in cement and binders
3. Efficiency in concrete production
4. Carbon capture and utilization storage
5. Decarbonisations of electricity
7. Efficiency in design and construction
Some major companies have tried to comply with the new roadmap plan and initiate some actions. LafargeHolcim has partnered with an American start-up company called Solid Technologies to develop concrete that could reduce the overall carbon footprint by 70%. The process would involve the different compositions of raw material and heating at a lower temperature. The concrete production process would also choose an alternative option of adding carbon dioxide instead of water. Other companies like Heidelberg Cement, CRH Plc, Ecocem, and CEMEX have also followed a similar step by reducing the use of clinker in the composition, adding other alternative ingredients, and also heating at a lower temperature.
On the opposite side of the greener cement efforts, a Ph.D. student named David Stone has come up with a cement substitute back in 2015. He uses iron carbonate as the main ingredient for cement replacement, which creates an entirely green and carbon-negative process. Steel dust, a by-product of steel mills that is not recycled and often goes directly to the landfill is used in this process, along with silica from ground-up glass. The cement replacement has been patented as Ferrocrete and was sold as Ferrock. The ‘green cement’ is a better substitute compared to traditional cement as it was stronger and doesn’t break down when exposed to high heat or saltwater. On top of that, the resulting concrete is also flexible, allowing for crack and impact-resistant materials. Yet, with all those superior benefits, the manufacturing cost of Ferrock is still considered to be more expensive and less accessible.
As important materials in the construction sector, the production of cement will continue to be a necessary ingredient to support the builds of safe and permanent housing, roads, bridges, or other infrastructure, and all in all, promoting economic growth all over the globe.
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About the Author
Xaveria Livienna is a freelance writer and researcher for the Taiwan Architecture and Building Center, currently pursuing an MBA degree in National Taiwan University of Science and Technology. Her main interests revolve around digital and content marketing, as well as CSR and sustainability.
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