Development and Performance Evaluation of Cold-Pressed Cement-Free Bricks using Detarium Senegalense Bio-Binder

Technical Summary: Development and Performance Evaluation of Cold-Pressed Cement-Free Bricks using Detarium Senegalense Bio-Binder

Problem Statement
The global construction industry faces significant environmental challenges, contributing approximately 35–39% of global energy consumption and CO₂ emissions, largely due to Portland cement production. While research has explored various sustainable alternatives, including plastic-infused concrete and geopolymer binders, there remains a critical gap in the development of completely cement-free masonry units that utilize plant-derived bio-binders as the sole stabilizer. Specifically, the adhesive properties of underutilized tropical seed gums, such as those from Detarium senegalense, have not been systematically investigated for binding construction materials. This study addresses the need for low-carbon, non-load-bearing construction materials by assessing the viability of using Detarium senegalense seed powder as a natural bio-binder in cold-pressed bricks.

Methodology
The research employed a cold-pressing technique to manufacture interlocking bricks without thermal firing or chemical stabilization.

• Materials: The primary aggregates were fine sand (filtered to 250 μm) and Detarium senegalense seed powder (ground to pass a 150 μm sieve). The bio-binder paste was prepared by mixing the seed powder with distilled water at a 1:1.2 (w/v) ratio, heated to 80°C to activate the polysaccharides and proteins, and then cooled.
• Mix Proportions: Three formulations were created with bio-binder contents of 10, 20, and 30 wt.% of the total dry mass, with fine sand comprising the remainder. The target density was 1600 kg/m³.
• Production: Mixtures were manually compacted into steel molds (150×100×50 mm) using a hydraulic press for 30 minutes. Specimens underwent a controlled curing process: 7 days in humid conditions, followed by oven-drying at 100°C, and finally air-drying in shaded areas for 7 days.
• Testing: Physical and mechanical properties were evaluated according to ASTM standards (C39, C642, C140, etc.). Tests included dry density, water absorption (WA), thickness swelling (TS), and compressive strength using a Universal Testing Machine. Microstructural analysis was conducted via Scanning Electron Microscopy (SEM) to observe particle bonding and matrix continuity.

Key Results

• Density: Increasing the bio-binder content resulted in higher brick densities, rising from 1386.91 ± 56.68 kg/m³ (10% binder) to 1521.49 ± 50.97 kg/m³ (30% binder). This was attributed to improved particle packing and encapsulation by the binder.
• Water Absorption and Stability: Water absorption increased with binder content, ranging from 10.29% (10% binder) to 16.92% (30% binder). Crucially, all specimens exhibited visible shape distortion after 24 hours of immersion, indicating low moisture resistance and making reliable thickness-swelling measurements impossible.
• Compressive Strength: The 20 wt.% formulation yielded the optimal mechanical performance with a compressive strength of 5.53 ± 0.10 MPa. The 10 wt.% formulation showed lower strength (5.11 MPa) due to insufficient bonding, while the 30 wt.% formulation suffered a decline to 4.75 MPa. The reduction at 30% was attributed to binder agglomeration, microcracking, and differential shrinkage during drying, which disrupted the rigid sand skeleton.
• Microstructure (SEM): SEM analysis confirmed that the 20% formulation possessed a continuous binder bridge and uniform particle encapsulation with low porosity. In contrast, the 10% sample showed voids and discontinuous bridges, while the 30% sample exhibited binder agglomeration and structural discontinuities.

Significance and Claims
The authors claim that this study provides the first empirical evaluation of Detarium senegalense as a natural, sole binder for cement-free bricks produced via cold-compaction. The research demonstrates that Detarium senegalense seed powder has the potential to replace Portland cement entirely for specific applications.

The study concludes that the 20 wt.% bio-binder formulation represents the optimal balance, offering the highest compressive strength and structural integrity suitable for non-load-bearing construction, such as partition walls, rural infrastructure, and temporary buildings. The authors emphasize that the cold-press manufacturing process reduces energy consumption and carbon emissions by eliminating the need for firing. However, the paper modestly notes that the current water resistance is insufficient for extended outdoor use or structural applications. Consequently, the authors state that future improvements, such as hydrophobic surface treatments or bio-mineral hybrid systems, are necessary before these bricks can be recommended for broader outdoor or structural deployment.