New strategy for less polluting road construction

A good road needs a good foundation. In its construction, it is essential to stabilize the soils, which in many areas have a clay base, in order to give them greater resistance and load capacity and less plasticity and swelling. Lime is used as a stabilizing material, but its production involves the consumption of natural resources and also generates high rates of carbon dioxide (CO2), causing a high environmental cost. Therefore, the search for other formulas for stabilization is a challenge of sustainable construction.

Faced with this challenge, the Construction Engineering research group at the University of Córdoba (UCO) in Spain has developed a stabilization technique that reduces the use of lime by 66% and reduces the carbon footprint by half using industrial byproducts and silica-based nanomaterials. Furthermore, in tests they have verified that this technique improves the technical properties of the soil, with less plasticity and swelling and greater load capacity.

The process to reach the optimal mixture was very thorough. “We selected four wastes: two types of ash from the burning of forest biomass, steel mill slag derived from steel production and construction and demolition waste. We carried out a complete analysis of their mechanical and microstructural properties, we examined their leaching to verify that the water did not carry the components and contaminate aquifers and we quantified the environmental improvement of the reduction of tons of CO2 that it stopped emitting into the atmosphere, in an execution of equal sections with each of these materials” explains researcher José Luis Díaz, author of the study together with Julia Rosales, Manuel Cabrera and Francisco Agrela, from the same group.

The novelty of the process is that, in addition to these wastes that had already been previously studied, a “very small” amount of a silica-based nanomaterial is added. “By adding this material in a very low percentage (0.056%) a reaction was produced that formed a kind of cementitious gel very similar to cement that creates a kind of “impermeable” layer and prevents water or heavy materials that could accumulate. filter out the white steel slag from being filtered out” continues the researcher.

From left to right, researchers José Luis Díaz, Francisco Agrela, Manuel Cabrera and Julia Rosales. (Photo: University of Córdoba)

As Manuel Cabrera explains, “the idea was to use different percentages to ultimately find the specific dosage and reach that inflection point where the properties and environmental impact are improved, but no significant changes occur in the material.”

The mixture of biomass bottom ash or white steel slag (these were the two byproducts that worked best) with 0.5% lime and 0.056% silica-based nanomaterial was the winning combination when it came to increasing the mechanical properties of the soil and reduce the environmental impact to 50%.

With these recycled materials “we are giving a second life to waste that otherwise would be accumulated in a landfill and we are also improving the mechanical properties of the road, increasing its firmness and bearing capacity, something decisive if we take into account that it is used to stabilize the ground on rural roads where there may be more tractor or truck traffic,” says Julia Rosales.

This work was part of the ECARYSE project “in which we worked together with the company SACYR to improve soil stabilization processes,” says professor and principal researcher of the group Francisco Agrela, “and within which we were able to use this soil stabilization technique. floors in a project that the company had in Villacarrillo”.

The study is titled “Evaluation of geotechnical, mineralogical and environmental properties of clayey soil stabilized with different industrial by-products: A comparative study”. And it has been published in the academic journal Construction And Building Materials. (Source: University of Córdoba)