Nutrient-Filled Particles Turn Porous Concrete Into Living Reservoir Slopes

Engineers in China have built a porous concrete that carries its own fertilizer supply inside, in the form of small spherical pellets embedded directly into the concrete skeleton. The material, described in Case Studies in Construction Materials, was designed for a specific and difficult environment: the reservoir drawdown zone, the band of shoreline exposed and submerged again as water levels swing up and down. These zones suffer severe ecological degradation, and conventional fixes such as cast-in-place concrete or mortared stone revetments stabilize the slope but seal it off, disrupting hydrological cycles, severing the water-soil-plant connection and worsening habitat fragmentation and biodiversity loss.

The new material builds on ecological concrete, a class of material defined by an intentionally engineered, interconnected pore network that gives plants anchorage and growth space while allowing water and air to move through. The innovation here is the nutrient substrate particle, or NSP: a 10 to 15 millimeter sphere made by extrusion-spheronization cold bonding from garden soil (55 percent), organic nutrient soil (25 percent), a 1:1 mix of sawdust and coconut coir (10 percent), slow-release fertilizer (10 percent) and binders. The particles were then mixed into ecological concrete by replacing coarse aggregate volume for volume, at replacement rates of 10, 15, 20, 25 and 30 percent.

Two particle formulations were tested. N1 used cement and fly ash as binders with a small dose of sodium silicate; N2 used cement with polyvinyl acetate emulsion. The choice mattered. After 28 days, the single-particle compressive strength of N1 reached 0.65 megapascals against 0.48 for N2, a difference the authors attribute to the pozzolanic reaction between fly ash and calcium hydroxide from cement hydration, which produces additional cementitious compounds. Bulk densities were 1,040 and 650 kilograms per cubic meter, both well below the roughly 1,350 typical of natural aggregates, confirming the lightweight character of the pellets. Water absorption was high in both, 41.7 and 42.0 percent, and leachate pH values of 9.6 and 8.6 indicated low alkalinity relative to cement-based materials.

Water stability separated the two formulations sharply. After eight dry-wet cycles of 12 hours soaking and 12 hours drying at 80 degrees Celsius, mass loss was 1.9 percent for N1 and 2.1 percent for N2, with both keeping their shape. By 16 cycles, however, N1 had lost only 3.1 percent mass with fine surface cracks, while N2 fragmented on a large scale and partially disintegrated. After 60 days of continuous soaking, N1 showed crack propagation but no evident fragmentation, whereas N2 disintegrated first. The organic emulsion binder loses adhesion under wet-heat alternation, while the inorganic fly ash system forms secondary hydration products, giving N1 better long-term bonding in water.

Encapsulation proved central to the nutrient-release design. In immersion tests, conductivity rose fastest in solutions holding raw nutrient substrate, more slowly around bare NSPs, and slowest around paste-coated NSPs, showing that granulation suppresses rapid dissolution of soluble salts and that a cement paste shell further retards ion migration. Phosphorus release followed the same pattern: bare particles leached more phosphorus than coated particles, and particles embedded in concrete leached least. Once inside the concrete, the pellets sit surrounded by paste and the aggregate skeleton, which restricts water infiltration into the pellets. Some phosphorus also appears to react with calcium and magnesium ions leached from the cement matrix to form insoluble precipitates, further lowering the detectable concentration.

In the concrete itself, the measured available phosphorus stayed low and steady: about 0.09 milligrams per liter after one day of immersion and between 0.12 and 0.18 milligrams per liter by 84 days, fluctuating mildly rather than accumulating. The authors note this reflects the available fraction measured by the standard method and that environmental impacts on receiving water bodies were not evaluated, so further study is needed. Electrical conductivity of the leachate rose quickly in the first day as organic salts and nutrients dissolved, stabilized, then declined slowly to a low point around 56 days before edging up again, a pattern the team reads as steady, controlled release of soluble ions rather than a flush of nutrients.

Mechanical performance set the limits of the design. With 25 percent target porosity, 28-day compressive strength fell from 6.7 megapascals in plain ecological concrete to 3.4 megapascals at a 30 percent N1 replacement and 2.3 megapascals at 30 percent N2 replacement, because the soft, lightweight particles cannot carry load like crushed stone. Strength rose as porosity fell: at 20 percent NSP content, the 20 percent porosity mix reached 6.4 megapascals against 4.2 for the 25 percent porosity version. Mixes with 20 percent porosity and up to 25 percent replacement, or 25 percent porosity and under 15 percent replacement, stayed above the 5 megapascals required for slope protection. Permeability stayed above 1 millimeter per second in all modified mixes, meeting drainage needs under conventional rainfall, and was governed mainly by porosity rather than NSP dosage.

Durability testing exposed a clear weakness. After eight sulfate dry-wet cycles in sodium sulfate solutions of 2, 4 and 6 percent, mass first increased then decreased, with damage shifting from crystal diffusion to paste cracking, spalling and particle disintegration. Higher NSP dosage meant greater late-stage mass loss, and compressive strength corrosion coefficients dropped steeply at high dosages: to 48.23 percent for one 20 percent replacement mix in 4 percent sulfate solution and to 47.36 percent in 6 percent solution, a fall of more than half. In clean water, by contrast, strength coefficients declined only slowly. Hydrodynamic scouring told a different story. After 30 wet-dry scour cycles at a flow velocity of 2.0 meters per second, mass loss stayed within 1 percent for N1 mixes and about 2 percent for N2 mixes, and compressive strength remained essentially stable around 100 percent, because scouring damages only surface-exposed particles and the interfacial transition zone without triggering structural deterioration. The authors stress these are short-term accelerated laboratory results, not long-term field evidence, and that sulfate-rich environments require careful evaluation or avoidance.

The planting trials brought the ecological function to life. Four slope-protection grasses were sown onto the concrete with a thin acidic growth medium: tall fescue (Festuca arundinacea), perennial ryegrass (Lolium perenne), Kentucky bluegrass (Poa pratensis) and bermudagrass (Cynodon dactylon). Tall fescue germinated best, above 80 percent, with ryegrass and bermudagrass near 70 percent and Kentucky bluegrass below 60 percent. Fescue and ryegrass sprouted around day three and developed roots longer than 10 centimeters within 30 days; fescue penetrated the 80-millimeter-thick, 25 percent porosity concrete to reach the underlying soil in about 30 days, ryegrass in about 40. Higher porosity sped root penetration, and plant height increased stepwise with NSP dosage, while non-NSP concrete showed more leaf chlorosis and wilting. Because the planting system included both a top substrate and underlying garden soil, the results reflect combined effects, and the authors say additional controls are needed to isolate the particles’ contribution.

Alkalinity remains the fundamental constraint. NSP addition lowered concrete leachate pH by roughly one unit, to about 11.3 at the maximum 30 percent dosage, which is still strongly alkaline and unsuitable for direct rooting. The favorable pH seen in the planting trials came mainly from alkali-reduction soaking of specimens, acidic planting substrates and curing treatments, with the particles acting only as a partial buffer; topsoil amended with acidic fertilizer held a pH of 6 to 7, while the underlying garden soil rose early from alkaline leaching before settling between 7 and 8. Within those limits, the study supports a practical window: lower porosity with restrained replacement for strength-critical revetments, higher porosity with more particles where rapid greening matters, N1-type particles where water stability governs, and species such as tall fescue and perennial ryegrass for establishment. Field-scale trials, long-term multi-factor durability assessment and quantification of the particles’ true contribution to plant growth remain the necessary next steps before reservoir drawdown zones see this material at scale.

Subject of Research: Development and laboratory testing of nutrient substrate particle-modified ecological concrete for reservoir drawdown zone restoration

Article Title: Nutrient substrate particle-modified ecological concrete for reservoir drawdown zone restoration: Preparation, performance and application

Article References: Lei, J., Tan, J., Chen, X., Abuel-Naga, H., & Deng, H. (2026). Nutrient substrate particle-modified ecological concrete for reservoir drawdown zone restoration: Preparation, performance and application. Case Studies in Construction Materials, 25, Article e06637. https://doi.org/10.1016/j.cscm.2026.e06637

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06637

Keywords: ecological concrete, reservoir drawdown zone, nutrient substrate particles, slow-release fertilizer, phosphorus release, slope protection, sulfate erosion, plant compatibility, porosity, compressive strength, vegetation restoration, durability