Invasive Water Hyacinth Fibres Could Reinforce Fully Recycled Concrete

Concrete is the most consumed man-made material on Earth, and its appetite for natural stone and sand is one of the quiet drivers of environmental degradation. At the same time, demolition waste piles up in landfills while waterways across the tropics choke on an aggressive aquatic invader. A new experimental study published in Environmental Science and Pollution Research brings these two problems together in a single mix design: concrete made entirely from recycled concrete aggregate, reinforced with fibres extracted from water hyacinth, one of the world’s most notorious invasive plants.

The research team, led by Worathep Sae-Long and Thanet Thongdetsri of the University of Phayao in Thailand, together with collaborators at Prince of Songkla University, King Mongkut’s University of Technology North Bangkok, Khon Kaen University, Rajamangala University of Technology Srivijaya, Burapha University and Kasetsart University, set out to test whether a waste-derived bio-fibre could compensate for the well-known mechanical weaknesses of recycled aggregate concrete. Their findings suggest that, with the right fibre treatment and dosage, it can.

The experimental programme was deliberately ambitious in its scope. Natural coarse aggregate was replaced by recycled concrete aggregate at 0% and 100% by volume, pushing the concept to its limit rather than settling for the partial substitution rates common in practice. Water hyacinth fibres were then added at 0.5% and 1.0% by weight of cement, and four distinct fibre categories were compared: treated bark, untreated bark, treated core and untreated core fibres. This matrix of variables allowed the researchers to isolate the effects of aggregate source, fibre dosage, fibre origin within the plant, and surface treatment on the resulting concrete performance.

The environmental arithmetic of the mix design is striking on its own. By adopting 100% recycled coarse aggregate, each cubic metre of concrete avoided the extraction of approximately 906.91 kilograms of natural stone, while the fibre additions converted between 1.67 and 3.33 kilograms of invasive aquatic biomass per cubic metre into structural reinforcement. Water hyacinth, which reproduces so aggressively that it can double its coverage in weeks and block navigation, hydropower intakes and irrigation channels, is usually a disposal burden. Here it becomes a raw material with a genuine engineering function.

The mechanical results tell a nuanced story of trade-offs. Replacing all natural coarse aggregate with recycled material reduced the 28-day compressive strength by between 12.81% and 25.56%. The culprit, confirmed by microstructural observations, lies in the interfacial transition zones: the thin layers of paste that bond aggregate to matrix. Recycled aggregates carry remnants of old mortar on their surfaces, creating weaker and more heterogeneous transition zones that fail earlier under load than the dense interfaces formed around natural stone.

Adding water hyacinth fibres deepened that compressive penalty. Depending on the fibre type and dosage, compressive strength dropped by a further 20.94% to 48.58%. The authors attribute this mainly to fibre-induced voids, reduced compaction of the fresh mix, and local discontinuities in the cement matrix where fibre clusters disrupted the paste structure. Organic fibres are also hydrophilic, and their tendency to absorb water and clump during mixing makes workability a persistent challenge at higher dosages. In compression, where failure is governed by matrix density and continuity, the fibres simply get in the way.

Where the fibres shine is in tension and flexure, the properties that matter most for cracking resistance and structural resilience. Splitting tensile strength increased by 35.76% to 64.24% compared with unreinforced recycled aggregate concrete, a gain the researchers link to crack bridging and stress transfer across developing cracks. When a crack opens in fibre-reinforced concrete, fibres spanning the crack carry load that would otherwise tear the matrix apart, delaying failure and softening the material’s response.

The standout performer was treated bark fibre at the 0.5% dosage. This combination delivered the best flexural response of the entire study, achieving a flexural strength of 5.39 megapascals and increasing flexural toughness by 56.97%. Toughness, the total energy a beam absorbs before failure, is arguably the more meaningful figure: it measures not just how much load the concrete resists but how gracefully it deforms. The researchers attribute the superior performance of treated bark fibres to their higher intrinsic tensile strength, fibrillated surface texture, and improved bonding with the surrounding cement matrix, all of which help fibres anchor themselves and pull out gradually rather than slipping or snapping prematurely.

Beyond the laboratory tests, the team developed empirical equations to predict strength within the investigated range and built a nonlinear finite element model to simulate the structural behaviour of the fibre-reinforced recycled concrete. The model reproduced measured peak loads with errors of just 2.90% to 5.74%, an encouraging level of accuracy that suggests existing computational tools can be adapted to design with these unconventional materials. The authors caution, however, that their predictive equations are valid only within the range of variables they tested, so engineers should not extrapolate them to other mix proportions or fibre contents without further validation.

The broader significance of the study lies in its demonstration that two waste streams, one mineral and one biological, can be combined into a construction material with genuinely useful structural properties. Fully recycled aggregate concrete has long been viewed with scepticism by structural engineers because of its strength and durability penalties, and natural fibre reinforcement has often been dismissed as a laboratory curiosity. By showing that treated water hyacinth bark fibres can boost tensile resistance and toughness in a mix containing no natural stone at all, the Thai team offers a template for circular-economy construction in regions where both demolition waste and invasive biomass are abundant. The compressive strength reductions remain a real limitation that will confine early applications to non-structural or lightly loaded elements, pavements and repair mortars rather than high-rise columns. But as a proof of concept, the work makes a compelling case that the weeds clogging the world’s lakes may hold part of the answer to making concrete more sustainable, one cubic metre at a time.

Subject of Research: Mechanical properties of recycled aggregate concrete reinforced with water hyacinth fibres

Article Title: Experimental investigation of the mechanical properties of recycled aggregate concrete reinforced with water hyacinth fibres for sustainable construction

Article References: Sae-Long, W., Thongdetsri, T., Chompoorat, T., Limkatanyu, S., Sukontasukkul, P., Pannachet, T., Boonpichetvong, M., Yaibok, C., Imjai, T., & Pimanmas, A. (2026). Experimental investigation of the mechanical properties of recycled aggregate concrete reinforced with water hyacinth fibres for sustainable construction. Environmental Science and Pollution Research, 33(28), 14470-14504. https://doi.org/10.1007/s11356-026-38179-9

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38179-9

Keywords: recycled aggregate concrete, water hyacinth fibres, natural fibre reinforcement, sustainable construction, compressive strength, splitting tensile strength, flexural toughness, interfacial transition zone, finite element modelling, microstructure, invasive biomass, circular economy