“The Carbon Conundrum of Concrete: A Global Construction Crisis”, Harvard International Review
The consumption of concrete has skyrocketed in recent decades. Today, an estimated 30 billion tons of concrete is consumed worldwide annually. Such a staggering consumption of concrete makes it at once one of the greatest contributors (even before plastic production) of global CO2 emissions, accounting for seven percent thereof. While the environmental impacts of concrete-consumption have long been recognized, the rapid global urbanization nowadays has aggravated and made much more pronounced the consequences of concrete overuse, which is presently throwing into disarray most of the climate-related sustainability objectives.
This, sadly, is the much undesirable predicament in which many rapidly developing countries now find themselves. Pressed by acute infrastructure necessity yet lacking alternative, green building materials, these countries are left with no choice but to adopt concrete construction extensively and prematurely, that is, long before their environment and ecosystem have grown elastic enough to allow for this degree of unhampered CO2 emissions coming along with concrete overuse.
Consider this case study of China: following the country’s first modern cement plant erected in Tangshan in 1906, China’s cement industry exploded in the late 20th century and onward, with the production totaling over two billion tons by 2020–a figure which, judging from the continually increasing trend, still awaited to be eclipsed in the near future. The spirited boom of the industry was dampened when the International Energy Agency published in January 2023 a report titled “Cement Technology Roadmap: Carbon Emissions Reductions up to 2050”, which observed the absolute need for rapid decarbonization in the cement sector before any climate goals set thus far could possibly be met. This report informs and marks China’s efforts to transition from the traditional carbon-heavy construction industry to one characterized by a lower carbon model in order to sustainably manage CO2 emission levels.
Underlying Socio-Economic Inequality in Concrete Production
Two main types of cement are primarily used in concrete production, namely Ordinary Portland Cement (OPC) and blended cement. The former is concerned with the practice of heating limestone and clay in a kiln at a temperature over 1,450 degrees Celsius, whereas the latter incorporates supplementary cementitious materials like fly ash or slag. By comparison, concrete production using OPC emits considerably more CO2 than that using blended cement, making OPC the less satisfactory method. Moreover, via this method, every ton of cement produced causes about 900 kilograms of CO2 emission, quite an unideal ratio. Consequently, it is no wonder that the prevalence of OPC plants in the last century has gradually yielded to a growing popularity of blended cement production in recent years, especially in countries that are more developed. The direct outcome is a higher concentration of plants using OPC technologies in developing countries.
Negative Consequences of Excessive Concrete Production
Concrete production gives rise to various kinds of significant environmental damage, primarily through resource depletion and CO2 emissions. The former concerns the vast amounts of sand and gravel required in the production process, which, by extension, may easily lead to environmental degradation like habitat destruction, water pollution, and soil erosion through the act of excessive mining. The latter, in introducing the issues of ocean acidification and global warming, will jeopardize ecosystems that are particularly climate-sensitive, such as coral reefs. Research by the Global Coral Reef Monitoring Network shows that, between 2009 and 2018, live coral cover on reefs has shrunken by 14 percent worldwide. The corollary is that most of the world’s coral reefs will be gone if global temperatures rise by two degrees Celsius or more for a sustained period.
The production-induced warming also takes the form of localized temperature increases, a phenomenon called urban heat island effect. In Tokyo, for example, the average temperature has risen by three degrees Celsius over the last century, largely due to urbanization and the proliferation of concrete structures. Global or localized warming, the resulted higher temperatures again feed back into an increased level of energy consumption for cooling, further exacerbating environmental issues. This greatly impairs what is industrially known as the quality of life in urban areas: at present, some megacities are experiencing temperature increases of up to 15 degrees Celsius as compared to surrounding rural areas.
A Survey and Evaluation of Possible Solutions
Among the few feasible solutions having been proposed, one worth mentioning is about replacing traditional concrete with the so-called geopolymer concrete, which uses industrial by-products like fly ash or carbon-negative concrete that helps incorporate captured CO2 during the curing process. Technologies concerning this practice involve injecting captured CO2 into the concrete during mixing, whereupon it mineralizes and strengthens the product, permanently storing the CO2 as a result–CarbonCure being one of the companies that devote themselves to this method. Nevertheless, the apparent problem with such technologies lies in the fact that these often require a major overhaul of existing production processes, for which reason they have yet to attain widespread application. As a matter of fact, considering the massive global scale of concrete consumption, with each person being (directly or indirectly) responsible for a yearly average of three tons, both the production rate and the current application status of this alternative method appear, at least for now, insufficient to make a significant global impact.
One limitation of many of the solutions proposed is that they are often absorbed in the sole idea of checking CO2 emissions, thereby completely overlooking the great potential in carbon sequestration. By contrast, duly addressing both emissions reductions and carbon sequestration, the idea of urban forests integrated into concrete structures naturally proves a promising one, with the bonus capacity to improve urban environments. Precisely, the integration of plants into concrete structures effectively mitigates urban warming and, at the same time, helps store carbon. In truth, at the city level, the amount of CO2 captured through photosynthesis makes quite a significant case of carbon sequestration. For instance, the Vertical Forest in Milan, Italy, which consists of two residential towers and hosts over 800 trees, sees its greenery absorb tons of CO2 every year, cool the environment naturally, and boost biodiversity in urban localities.
Adding to the excellence of this approach is its easy adaptability: the infrastructure above can be utilized in a good number of other urban settings like skyscrapers and highway barriers. Accordingly, if we are to follow the example of the Vertical Forest in Milan, what we are seeking to achieve would be a hybrid solution that addresses more than one aspect of the concrete conundrum and shows itself relevant in various contexts. By integrating green building techniques with low-carbon concrete technologies, not only are we concerned with decreasing CO2 emissions, but we also strive for an enhanced urban livability; and, most importantly, such a practice can be extended to a wide range of situations without much difficulty. As we move forward, it is crucial to remember that no single solution can solve, once and for all, all of the environmental challenges posed by concrete production, but that only a holistic approach may near the ultimate success, potentially turning a biggest environmental threat into an opportunity for urban renewal and climate action.
