A Review on the Performance of Kenaf-Crete Incorporating Partial Replacement of Fine and Coarse Aggregates With C&D Waste

Abstract

This study examines the structural performance and durability of a sustainable concrete composite which combines natural aggregates, construction and demolition (C&D) waste, and Kenaf fibre as an additive to enhance its overall performance.” In total, two experimental mixes have been studied:M1 (replacing 50% coarse aggregate) and M2 (replacing 50% coarse aggregate and 45% fine aggregates). The outcomes show that although M1 mix reached the required design strength, M2 mix experienced a small decrease in compressive performance due to the increased porosity of the reused aggregate. However, in order to make up for this drawback, Kenaf fibers were added to the composite which helped increase ductility and improve the materials\' resistance to microcracks. Tests related to the durability of the mixture (water resistance, acidity resistance) also differentiated between M1 and M2 mixes. Namely, the former had better water resistance and less vulnerability to acids due to a dense matrix within, thus making M1 mix a more attractive option for further applications with 25-30% CO2 emission reduction.

Introduction

This study investigates the use of recycled construction and demolition (C&D) waste and kenaf fibres in M25 grade concrete to develop a more sustainable and durable construction material. The main aim is to replace natural aggregates with recycled materials while improving mechanical and durability performance through natural fibre reinforcement.

Background

The construction industry consumes large amounts of natural aggregates and generates significant waste, making recycled aggregates an important solution for a circular economy. However, recycled aggregates increase porosity, weak interfacial transition zones (ITZ), and water absorption, which reduce concrete performance. Natural fibres like kenaf can improve crack resistance and tensile strength but may also increase porosity if not properly used. Therefore, balancing sustainability with durability is essential.

Materials and Mix Design

Two mixes were developed:

• M1: 50% replacement of coarse aggregate with recycled aggregate, natural fine aggregate retained.
• M2: 50% coarse + 45% fine aggregate replaced with recycled materials.

Both mixes included alkali-treated kenaf fibres (5% NaOH) to enhance bonding and crack resistance.

Key Findings

• M1 performed well, achieving M25-grade compressive strength (≈26.3 MPa) and improved tensile and flexural strength.
• M2 performed poorly in compression (≈12.8 MPa, equivalent to M10 grade) due to high porosity, weak ITZ, and excessive water absorption from recycled fine aggregates.
• Kenaf fibres significantly improved tensile strength, crack resistance, and ductility in both mixes, even when compressive strength was low.

Durability Results

• M1 showed acceptable water absorption and durability, close to M25 standards.
• M2 exhibited high water absorption, high porosity, and poor density, leading to low durability and higher permeability.

Observations

• Recycled aggregates increase sustainability but reduce strength when used excessively, especially fine aggregates.
• Kenaf fibres enhance tensile behavior and control cracking but cannot compensate for severe matrix weakness in highly recycled mixes.
• Proper balance of natural and recycled materials is crucial for performance.

Conclusion

The mechanical properties and durability of the kenaf fibre reinforced concrete incorporating C&D wastes as recycled aggregate were examined in this study. As observed from the analysis above, it can be said that the percentage replacement of the aggregate has a considerable influence on the strength and durability parameters of the concrete. In this regard, Mix M1, having a 50% coarse aggregate replacement rate, exhibited acceptable mechanical strength. The compressive strength attained by Mix M1 was 26.30 N/mm² at 28 days, which is higher by 5.2% compared to the targeted M25 grade concrete compressive strength of 25 N/mm². On the other hand, Mix M2, with a 50% coarse and 45% fine aggregate replacement rate, had a compressive strength of 12.81 N/mm², a reduction by 51% from the target strength. Thus, it is evident that the high application of the recycled aggregate, particularly fine aggregates, in the concrete causes a substantial reduction in compressive strength owing to an increase in porosity and weak interfacial bond strength. Regarding split tensile strength, both mixes surpassed the conventional split tensile strength of 3.5 N/mm². Mix M1 had a split tensile strength of 5.36 N/mm², while Mix M2 attained 5.33 N/mm², showing a slight variation of 0.56%. As for the results of the, again, there is evidence of better performance of the M1 mix. Indeed, flexural strength of the M1 mix exceeded the strength values typical for ordinary M25 concrete. Meanwhile, Mix M2 demonstrated lower levels of flexural strength, and although the mixture developed its strength during the curing process, the flexural strength value remained worse in comparison with the other sample because of weaker matrix structure. The reason for the lower flexural performance of the M2 mix in comparison with M1 is a worse interfacial transition zone and higher porosity of M2. Despite that, in case of both tested materials, the addition of kenaf fibres resulted in better ductility and delay of cracks formation. In analysis about durability of the mixes, we can conclude that M1 performed better. Thus, the water absorption coefficient of M1 at 56 days of curing amounted to only 2.79%, which differs from the acceptable level of 2.5% by only 11.6%. On the contrary, water absorption of the M2 mix exceeded 4%, which is almost twice the accepted norm. The effect of acidity on the mixes was another aspect that demonstrated the differences in their durability. Mix M1 initially had an 13.37% strength reduction but then improved its performance by reducing the strength loss to 8.50% after 56 days; hence, there is an increase in performance by about 36.4%. Conversely, mix M2 had a maximum strength loss of 18%; hence, an increase of more than 111% compared to the final strength loss of M1, which demonstrates that it lacks chemical resistance and durability. In summary, the experiments conducted prove that a mix with aggregates partially replaced by waste, such as M1, will have balanced performance, while an excess replacement percentage like that of mix M2 causes severe compressive strength losses greater than 50%, as well as durability loss. In conclusion, although the use of kenaf fibres provides notable improvements in tensile strength, flexural strength, and crack resistance, they are not enough to offset the decrease in compressive strength owing to high porosity. An optimal mix design is thus necessary for achieving the right combination of sustainability and structure. From the findings, Mix M1 could be a good choice in terms of both sustainability and structural performance while Mix M2 would be inappropriate due to its decreased strength and durability.

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Copyright

Copyright © 2026 Afra A, Ishwarya K R , Jayasri S , Arun Kumar Bharathi P , Vishnu A . This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.