In Christian metaphor, "building a house on sand" symbolizes folly. However, with the development of technology, it is not impossible to build real estate on sand. The key lies in choosing the right sand. The wrong kind of sand, like rounded desert sand or alluvial sand that becomes unstable during the rainy season, is not suitable for building. Nowadays, with the proper foundation or technology, it is possible to build stable structures on sand. Burj Khalifa and Palm Jumeirah in Dubai are typical examples.
But even the best compaction techniques can't turn desert sand into new land. From the moment they were completed, these artificial islands have been in a constant battle with nature, battling tidal systems that erode them and slowly wash away the sand.
Reclamation creates another kind of "building on sand" Similar practices have been practiced in the Netherlands since the 14th century, and the trend has spread to Asia as it modernized. Since the 19th century, Tokyo has added 25,000 hectares to the ocean, and China is also expanding its coastal cities. Today, national territorial waters are based on coastlines, making land reclamation a new frontier of diplomacy in the 21st century, affecting fisheries, resource extraction, and military layout. Additionally, demand for flood control sand is accelerating with climate change and rising sea levels, and plans by the Maldives and Singapore to address this challenge through reclamation have resulted in Singapore becoming the largest importer of sand.
Although we are used to thinking of sand as an endless common resource, in reality, not all sand is the same. This explains why desert countries like Dubai import sand from Belgium, the Netherlands, and even the UK—certain types of sand are more important for industry and construction. In comparison, we have very little regulation and monitoring of sand extraction, making it extremely difficult to assess the total amount of sand dug up and moved throughout human history.
Research shows that humans extract 24 times more material each year than natural erosion processes remove, underscoring how humans have become a powerful geological force on Earth since 1955. Such large-scale mining activities have not only changed the surface of the earth but also defined, to some extent, a new geological era - the Anthropocene. The total amount of material we have excavated over the past century is an almost unimaginable 6.7 teratons.
The source of sand is becoming increasingly important. Because sand is not only a building material, it also plays a key role in natural ecosystems, such as supporting the growth of riverbank plants, forming natural barriers, and serving as biological habitats. However, in many non-developed countries, sand is often mined unregulated. It is then shipped to Europe and the Canary Islands for use in construction and tourist beaches in developed countries.
In some parts of Asia and Africa, the huge demand for construction sand has led to overexploitation of these natural resources. This is especially true in the Mekong Delta. The banks are gone, replaced by steep drop-offs created when the sand was dug away, and about two square miles of land are being lost each year. In India, the "sand mafia" has come to represent a network of corruption that involves everyone from those who dig sand from river beds and beaches to the supply chains that transport it to construction sites to real estate developers, police, and even, rumored to be some politicians. In this regard, the United Nations Environment Program has even listed sand as a strategic mineral, emphasizing its importance in maintaining modern social infrastructure and economic development.
If you were to improve the lives of low-income families in a developing country, would you choose to provide cash, nutritional supplements, or a bag of cement? The answer may be surprising: cement. An example of this is demonstrated in Mexico, where cement was provided to low-income families to lay floors. As a result, parasitic infection rates dropped by 78%, diarrhea, and anemia in children were significantly reduced, and school performance and mothers' happiness were improved. Additionally, replacing dirt roads with concrete pavements can significantly increase wages for nearby residents and increase child school enrollment.
We often underestimate the importance of the built world. Of all building materials, none has made as big an impact as quickly as cement. Concrete greatly simplifies the construction process compared to masonry. You pour the concrete into the mold, and a job that would have taken days or weeks can now be completed in just a few hours.
The wonder of concrete also lies in its complexity and ever-changing properties. Even in the drab, seemingly lifeless concrete buildings of the city, chemical reactions are still going on inside, and the concrete continues to harden and react. Even giant structures like the Hoover Dam continue to become stronger over the years gradually.
To clarify, concrete and cement are not the same. Cement, the binding agent for concrete, is a powder obtained by calcining and pulverizing limestone or chalk with clay, sand, and other additives such as iron oxide. When water is added, the calcium and silicon in the cement react with the water to form a gray gel filled with countless microscopic stony tentacles. These tentacles, or crystals of calcium silicate, hydrate, intertwine, and expand, locking in moisture and forming a skeleton-like stone structure. Add gravel and sand to the mix, and the tentacles not only bind themselves but also surround the gravel and sand, creating concrete—a rock that can be poured.
Although humans only began mass-producing the material, a mixture of sand, aggregate, and cement, just over a century ago, there are now more than 80 tons of concrete per person on the planet. This amount far exceeds the combined weight of all living things on Earth: every cow, every tree, every human being, and all plants, animals, bacteria, and single-celled organisms. We produce enough concrete every year to cover the entire land area of England.
Take Tianjin, for example, a megacity with a population of 15 million that stretches from the coastline to near Beijing. In 2014, Tianjin was dubbed the "Tall Building Capital of the World," and in the same year, China's cement production rate showed exponential growth. Tianjin's construction boom has subsided in recent years, turning what was once a bright spot in economic growth into a weak link. The Chinese government limited the number and height of new skyscrapers in 2020 and began demolishing many unfinished towers in 2021.
Although concrete recipes are easy to get right, mistakes do happen. The massive damage caused by the 2010 Haiti earthquake was partly attributed to shoddy construction. Nearly one in 10 bridges in the US are structurally defective, and the situation in the UK is probably even worse, with almost half of motorway or A-road bridges defective. "Reinforced concrete" can support the construction of bolder buildings and bridges, but when the recipe is wrong, it can lead to more disasters. For example, when an apartment building collapsed in north Miami in 2021, investigators pointed to cracked concrete and corroded steel as possible culprits.
Cement production is one of the world's largest sources of carbon emissions, accounting for 7-8% of global carbon emissions, more than the aviation industry and deforestation combined. The production of cement is divided into two main links: chemical reaction and high-temperature heating. Currently, more than 50% reductions in carbon emissions have been achieved in developed economies such as the UK and the US by using alternative fuels to heat kilns and adding other substances to reduce cement clinker. However, carbon emissions from chemical reactions are difficult to eradicate. Current solutions include diluting clinker and carbon capture and storage technology, but these methods are expensive and have yet to be widely used.
In some countries, carbon emissions issues are further exacerbating shortages of materials needed to make cement. Despite the total abundance of limestone, many countries became reluctant to sign new mining/quarrying licenses. Without limestone, the core binder of cement is gone. In 2021, Sweden faced a sudden shortage of concrete after the Supreme Land and Environment Court decided to deny the country's largest cement producer a new limestone mining license on the island of Gotland.
In addition, concrete production also relies heavily on an adequate and consistent supply of water to carry out chemical reactions. Our huge demand for concrete is so great that its use alone accounts for approximately one-tenth of the world's industrial water use. By contrast, most of the world's fresh concrete is currently poured in countries with drought and water shortages.
Although cement-replacement technologies exist, such as alkali-activated cement, questions remain about its long-term durability. Despite the challenges, new technologies and materials are being developed to reduce the environmental impact of cement, such as hemp-based concrete and graphene-infused "concrete," which promise to be stronger and more environmentally friendly. Innovative products, such as self-healing and self-cleaning concrete, are also being researched.
While there are many challenges, the world is in a new race to reinvent carbon-free concrete. Promisingly, more than 50% of new concrete patents are filed by Chinese companies and academic institutions, indicating that future breakthroughs may come from China. However, even if the carbon emission problem is solved, the production of concrete still requires the consumption of large amounts of water, limestone, and sand. These are limited resources, and their extraction and use will continue to pose a threat to the ecosystem.
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