Zhengzhou, China – Soil erosion on slopes adjacent to railway lines and main roads can lead to landslides that risk both life and property, and block the thoroughfare. Planting concrete protection technology is one of the most effective methods for erosion prevention, and it also offers environmental benefits. As well as giving the slope a more secure structure, the porous material can improve rainwater runoff, and also reduce noise.
There are, however, challenges. The pH of the environment has to be appropriate for the plants, as high alkalinity can damage their roots, reducing their ability to absorb water and trace element nutrients. Various additives to the cementitious material have been tried, such as fly ash and silica, but even with a fly ash content as high as 50%, the pH still typically exceeds 12. Lower alkaline cement can also help, but this is more expensive.
Incorporating polymers into the planting concrete as an admixture is another way to improve the pH, and may also give the concrete additional beneficial properties. Now, a team at North China University of Water Resources and Electric Power in Zhengzhou has found that adding polyurethane shows promise in reducing the alkalinity of the concrete.
They said that their PU-containing material, based on Portland cement with limestone aggregate has both high strength and good ageing resistance, while also lowering the concrete’s alkalinity. They tested the porosity, pore solution pH and mechanical strength of the PU-modified cement-based planting concrete with a range of different aggregate particle sizes and binder-aggregate ratios.
Microscopic analysis was carried out on the most promising material, and its ageing resistance performance and planting performance were both assessed. They determined that the aggregate particle size and binder-aggregate ratio had a significant effect on the porosity and pH of the concrete, with the mechanical strength increasing along with the binder-aggregate ratio, and decreasing as the aggregate particles become larger.
Incorporating the PU delayed the hydration reaction of the cement, decreasing the pH. With careful selection of the different parameters, the material may prove effective in improving plant coverage rate, root length and plant height in vegetation concrete to prevent soil erosion.
The work has been published in the journal Construction and Building Materials.
