Mitigating urban soil challenges: The versatility of ESCS lightweight aggregates

According to the University of Michigan’s Center for Sustainable Systems, 83% of the U.S. population lives in urban areas. By 2050, this figure is projected to increase to about 89%. As cities expand to meet the needs of growing populations, there may be more need to strategize ways to mitigate soil degradation, which is the decline in soil condition caused by improper use or management.

In urban areas, soil consolidation and compaction are two common causes of soil degradation, leading to environmental challenges such as erosion and increased runoff. For example, when soil is compacted, the spaces between soil particles decrease, limiting the amount of water that can percolate into the soil leading to increased stormwater runoff. This settlement can also compromise the structural integrity of the buildings and infrastructure built on the soil.

Furthermore, because compaction disrupts the natural structure of soil by creating smaller particles, it hinders the penetration of oxygen and water to root zones. The lack of proper nutrients in the roots impacts plant growth and reduces the soil’s ability to resist erosion.

Mitigating such impacts on soil requires deploying innovative building materials and techniques at the grass-roots level and at scale. Lightweight aggregates, such as expanded shale, clay, and slate (ESCS), have the proven performance to enhance soil stability through various applications, whether stabilizing internal soil structure or supporting vegetation growth to mitigate soil erosion. But what makes ESCS particularly effective for these applications?

ESCS — porous makeup that makes a difference

ESCS is a lightweight, chemically inert ceramic material produced by expanding and vitrifying select shales, clays and slates in a rotary kiln at 2,200 degrees Fahrenheit. As the material cools down, the bubbles form an unconnected network of pores surrounded by a hardened, high-quality ceramic material. The lightweight aggregates’ uniform network of pores ranges in size from approximately 5 to 300 μm, occupying as high as 50% of the aggregate’s volume in its loose state.

In addition to being lightweight, the porous nature of the aggregate also enhances filtration properties. It allows the ESCS to hold and penetrate water into the soil. This low-density, hardened structure of the aggregate, paired with drainage capabilities, is key to ESCS’s ability to enhance soil conditions in urban areas.

Creating more stable but less compact soil mixtures

The challenge in urban regions, especially those with clay-rich soil, is that the soil sinks and swells due to compaction during construction activities. On the one hand, this can lead to a higher volume of soil lost to runoff when it swells. Conversely, a more compact, clay-rich soil reduces water and oxygen penetration, which may clog the filter materials or drainage layer, prompting shallow rooting and increased water loss to evaporation.

Mitigating these issues, ESCS lightweight aggregate in engineered soil offers practical solutions in such situations. Its kiln-fired manufacturing process, in addition to creating a network of voids for water management, also enables a larger surface area than conventional materials like sand. While ordinary sand typically has a specific surface area of about 0.0011 square meters per gram (m2/g), fine ESCS media below 4.75 mm can achieve up to 50 m2/g.

The aggregate’s increased surface area creates a stronger soil structure through improved particle interaction. As a result, when soil is amended with ESCS in landscapes, the fill retains its stability. This applies to clay-rich soils as well. The form and porosity of the aggregate also help enhance water infiltration while reducing runoff velocity mitigating soil erosion through stormwater runoff. More stable soil can handle the load of the infrastructure built on top, helping prolong a building’s service life.

Supporting vegetation growth to prevent soil erosion

Along with stability, there are more benefits to using ESCS in the soil mixture. With their porous makeup and larger surface area, engineered soil with ESCS can penetrate the required water and oxygen to the root zone. Because the aggregate is non-toxic and inert, the engineered soil can work cohesively with natural ecosystems.

Moreover, ESCS’s interstitial voids act like tiny reservoirs, helping retain as much as 12 to 35% of the aggregate’s weight in absorbed water and water-borne nutrients. Water and nutrients are steadily released into the plant root network as the soil dries. These characteristics create a buffer to help protect plant life from high concentrations of chemicals and persistent drought. Due to its ability to reduce soil compaction and facilitate vegetation growth, ESCS-amended soils are an excellent choice for green infrastructure applications like turfs, lawns, rain gardens, bioswales and more.

Because ESCS’s porous structure enables a steady water supply to plants even during dry periods, it also supports several water conservation benefits in horticulture through improved water retention, enhanced drainage, reduced water runoff, efficient use of irrigation and sustainable growing medium. Its ability to provide adequate water supply while also improving drainage helps prevent overwatering and consequent waterlogging or surface runoff. Less water waste leads to overall water savings.