The effects of road surface concrete grinding residue (CGR) on selected soil properties and plant growth

Diamond grinding is a widely used operation for smoothing cement concrete road surface, which can improve road riding quality and longevity. Concrete grinding residue (CGR) is a byproduct from diamond grinding. CGR deposited along roadsides can affect soil chemical properties, while studies of CGR influences on soil physical properties and plant growth are limited. This study focuses on CGR impacts on soil physical properties, including soil bulk density, saturated hydraulic conductivity, surface water infiltrability, and plant growth, including plant species, plant biomass, and seedling emergence. A preliminary roadside measurement, a greenhouse study and a controlled field experiment were performed. For the preliminary roadside measurements, soil physical properties and plant biomass measurements were made within CGR affected areas and non-CGR areas at two Minnesota highway roadside locations. For the greenhouse study, the seedling emergence rate and plant biomass of Indian grass, Canada wild-rye, Partridge pea and Wild bergamot were measured in a 60-day period, in pots with 0, 2.24, 4.48, 8.96 kg m-2 CGR rates and two application methods, i.e., uniformly mixed with soil or directly applied on the soil surface. For the controlled field experiments, CGR with rates 0, 2.24, 4.48, 8.96 kg m-2 was applied to replicated 4 m2 plots in an Iowa field, and soil physical properties and plant biomass were measured before, one month, seven months and twelve months after the CGR application; while plant identifications were performed before, ten months and twenty months after the CGR applications. CGR showed non-significant effects on soil physical properties in all of the experiments, except for one roadside location, where the soil bulk density values in the CGR affected areas were significantly larger than those in the non-CGR areas, and the saturated hydraulic conductivity values in the CGR affected areas were significantly smaller than those in the non-CGR areas. CGR did not have significant effects on plant biomass, seedling emergence and plant species indices, such as richness, diversity and evenness. However, from the controlled field and greenhouse experiments, relatively small CGR rates tended to promote plant growth, while relatively large CGR rates tended to inhibit plant growth. In conclusion, CGR did not cause significant effects on soil physical properties and plant growth, and no local environmental risks were observed for CGR applications up to 8.96 kg m-2