If the promises and disenchantments of modernity could be measured by weight, concrete would be a perfect metric. After water, concrete is the most widely used substance on the planet and one of the most carbon-emitting industries. It is a symbol of economic growth, urbanization, development, and status. It is also synonymous with corruption, manifesting in the overabundance of white elephants that remain standing for years or even decades. As concrete corrodes, it also reveals the corrosive effects of corruption. The construction industry is said to be one of the most corrupt, and the one that concentrates the largest volume of bribes.

The relationship between corrosion and concrete suggests forms of unbuilding that are both material and political. In the Colombian Putumayo, a region situated at the junction of the Andes and the Amazon, there are two large and deeply contentious projects where corruption has become a corrosive force shaping a seemingly perpetual cycle of construction and unbuilding. One of them is a road that for decades has aimed to connect this region with the neighboring department of Nariño, putting an end to a treacherous road known as the “trampoline of death” (Uribe 2017). The other is a series of water infrastructures targeted at managing the rivers that flow through Mocoa, the capital of Putumayo, devastated by a torrential flood in 2017.

In both projects, the promise of concrete is expressed in related, but distinct, ways: while in the road is to contain the unstable and steep topography that threatens or hinders flows through the infrastructure, the rivers’ infrastructure seeks to control water streams, preventing catastrophes like the one in 2017. In practice, however, it is difficult to differentiate the purpose of both infrastructures. In Mocoa, the image of machines and workers injecting concrete into riverbeds to erect bridge columns or weirs, or carpeting the mountain with retaining walls, has become an everyday landscape marked by waves of construction, suspension, collapse, ruin, and reconstruction. Here, every act of building seems to foreshadow processes of unbuilding.

The hardness of concrete, one of its most appreciated properties, is also one of its greatest weaknesses (Harvey 2010). Both the road and the river projects are located in the piedemonte Andino-Amazónico, one of the rainiest places on earth. The combination of steep slopes and recent geological formations makes the terrain extremely unstable. The excess of concrete in all dimensions and shapes reflects the incessant and, to a large extent, unsuccessful struggle to contain this volatile nature. Engineering textbooks abound with terms—such as “mass slides,” “ground collapse,” “soil liquefaction,” “environmental attack,” and others—allude to the array of tectonic and environmental forces that constantly threaten the integrity of concrete.

In addition to these hazards, there is corrosion. Concrete can be more or less porous depending on how it is processed (e.g., the ratio between water and cement in the mix, its curing time, the type and size of aggregates). Excess humidity in the environment increases the flow of water and other corrosive substances through its pores, which upon contact with the steel it covers—the material that gives it its characteristic strength—rusts. The corrosion of the metal increases its volume, generating fractures in the concrete and, therefore, precipitating its deterioration and eventual disintegration. These fractures can also be the result of ground movement, leaving steel structures exposed to the environment and, consequently, accelerating their corrosion. In the piedemonte, corrosion is relentless and faster than in other environments, and produces an aesthetic and affective effect that exposes the limits of its promise.

However, in Mocoa corrosion has significance that transcends its chemical nature. The proliferation of concrete works that seem to have no purpose, either because they lack basic engineering logic and systematically deny the nature of the terrain, or because they are left unfinished, abandoned, or resume without explanation or apparent reason, feeds the perception that corrosion is not the cause of their ruination, but an inevitable effect of their nonsense.

In its inevitability, corrosion also reveals its indissoluble bond with corruption. For those who live amid an excess of cement infrastructures that literally seem to go nowhere, this bond transcends the rumors and denunciations of contractors and politicians who enrich themselves with contracts for their building or repair. To them, it is as if corruption is another corrosive agent that permeates the elements that give life to concrete, consumes it from within, and anticipates its demise. In this infra-structural nexus between corruption and corrosion, the building and unbuilding of concrete coexist as two simultaneous, indistinguishable forces.

People of the piedemonte inhabit and relate to the road and rivers' concrete landscape in different ways. Some try to quantify its excesses. “They say one concrete block is worth more than 7 million pesos (USD $1,500) and this wall has more than two hundred blocks,” a peasant and road worker once told me, perplexed, as he recounted the story of a retaining wall that was built through the middle of his farm. Others visit the recently finished bridges and dams and stay for a while looking for the best spot to take selfies, or because they have been told that it is good deal to buy land there because the works will increase its value. Others walk around with noticeable disappointment at the state of the works. And some, especially those used to the natural rhythms of the piedemonte, wait impassively for things to corrode deeper still and for new cycle of (un)building to begin.