Hydro-Physical Behavior of Bermuda Grass Roots in Fly Ash–Calcined Clay Porous Concrete for Green Infrastructure

Urban green infrastructure increasingly depends on engineered substrates that support vegetation while enhancing stormwater infiltration, erosion control, and material sustainability. This study investigates the hydro-physical adaptation of Cynodon dactylon (Bermuda grass) roots in porous concrete substrates modified with fly ash and calcined clay for green infrastructure applications. While root biomechanics in natural soils are well understood, little is known about how roots adapt to rigid substrates such as porous concrete, especially in terms of their hydro-physical behavior. To address this gap, key hydrological traits, including root suction and gravimetric water content (GWC) were measured to assess root responses to the water retention and structural conditions of the substrate. The porous concrete substrate where Bermuda grass was planted exhibited a porosity of 24.14% and an initial pH 11.37, which was reduced through SCM integration, creating favorable conditions for vegetation establishment. Root diameters ranged from 0.27 to 0.59 mm, suction values from − 115 MPa to − 140 MPa, and GWC from 0.099 to 0.892 gg−1, indicating diverse water retention responses at the individual root level. These findings highlight the viability of engineered bio-compatible substrates for green infrastructure applications. By integrating sustainable materials and plant-compatible chemistry, this study supports the design of multifunctional systems that enhance vegetation performance while promoting circular use of industrial by-products.