Singapore's construction sector faces a persistent challenge: the scarcity of natural sand. With no domestic sources, the city-state imports millions of tons annually to fuel its ambitious building projects—from towering skyscrapers to essential infrastructure. Recent data indicates that natural sands imports reached approximately 32 million tons in the last twelve months ending March 2025, underscoring the vulnerability to global supply disruptions and rising costs. Amid this, a groundbreaking collaboration between Nanyang Technological University (NTU) and the National University of Singapore (NUS) has delivered compelling evidence that granite fines—a locally abundant by-product from granite quarrying—can fully replace natural sand in concrete production without compromising, and in some cases enhancing, performance.
This comprehensive study, conducted from 2019 to 2021 in partnership with Temasek Polytechnic and the American Concrete Institute Singapore Chapter, represents a pivotal advancement in sustainable materials research at Singapore's leading higher education institutions. By transforming waste into a viable resource, NTU and NUS researchers are not only addressing environmental concerns but also paving the way for greener construction practices that align with Singapore's national sustainability goals.
The Genesis of the Research: Tackling Singapore's Aggregate Dilemma
Granite fines emerge as a waste material during the crushing of granite boulders into coarse aggregates at local quarries. Singapore produces substantial volumes of this by-product—estimated at 25-30% of crushed granite output—but much of it has historically ended up in landfills, contributing to pollution and disposal costs. Meanwhile, natural river sand, essential for concrete's fine aggregate component, is entirely imported, exposing the industry to geopolitical tensions, such as export bans from neighboring countries, and escalating prices that reached around SGD 30.5 per ton recently.
The NTU-NUS initiative was spurred by the Building and Construction Authority (BCA)'s push for sustainable alternatives. Prior standards like SS EN 12620 limited fines content to 10%, but market-available granite fines often hover at 11-12%. The study pushed boundaries, testing up to 22% fines content and 100% substitution levels across common concrete grades used in Singapore: C32/40, C40/50, and C50/60.
Methodology: Rigorous Testing Across Fresh and Hardened Properties
The research team meticulously designed trial mixes, starting with control batches using natural sand and progressively substituting with granite fines at 30%, 50%, 75%, and 100% levels. Fines content was controlled at 10%, 16%, and 22% through sieving. Key adjustments included lowering water-cement ratios (from 0.63-0.67 for lower grades to 0.49-0.52 for higher ones) and incorporating superplasticizers (up to 5% by cement weight) and retarders for workability.
Fresh properties were evaluated per SS EN 206 standards: slump (S3 class, 100-150 mm), air content (<3.5%), bleeding, segregation, and setting times. Hardened properties encompassed compressive strength at 28 days, elastic modulus, water absorption, penetration depth, rapid chloride penetration test (RCPT), and carbonation resistance under both accelerated and natural exposure.
All mixes met performance criteria, with granite fines' angular particles and rough texture demanding admixture tweaks but yielding denser matrices.
Mechanical Strength: On Par or Superior to Conventional Concrete
Compressive strength results were standout. For C32/40 concrete, 100% granite fines with 16% fines achieved 97-105 MPa at 28 days, matching or exceeding the natural sand control's ~98 MPa. Higher grades like C50/60 hit 110 MPa targets. Elastic modulus remained within Eurocode ranges, peaking at optimal substitution levels (e.g., 75% for C32/40), indicating stiffer mixes due to better particle interlocking.
While tensile and flexural data aligned with expectations for the strength classes achieved, the focus on overall conformity confirmed granite fines' reliability for structural applications.
Durability Excellence: Pore Refinement Leads to Enhanced Longevity
Durability tests revealed granite fines' edge. Water absorption dropped to 1-2% (below 2.5% limit), thanks to fines filling voids. Water penetration was reduced, particularly below C60 grades. RCPT values stayed under 4200 coulombs (low permeability), though angular particles slightly increased scatter—mitigated by supplementary cementitious materials like ground granulated blast-furnace slag (GGBS) or silica fume.
Carbonation resistance shone brightest: 100% substitution yielded the lowest rate (k=14.73 mm/√years accelerated, 2.04 mm/year natural), requiring just 20.4 mm cover for 100-year service life versus 26-46 mm for controls. After 20 months natural exposure, depths were negligible. For details on the testing protocols and raw data, refer to the study's final report.
Environmental and Economic Wins: A Circular Economy Boost
A companion life-cycle assessment in a 2022 NTU-led review paper estimated 20% environmental impact reduction with 26-50% substitution—factoring cradle-to-gate for Singapore, including transport and landfilling avoidance. Full replacement slashes sand imports (Singapore's ~32 million tons annually) and leverages cheaper granite fines (~SGD 19/ton vs. SGD 30.5/ton sand), yielding cost savings especially in lower grades.
This aligns with Singapore's Green Plan 2030, reducing landfill burden and import dependency. BCA's recommended specification endorses up to 16% fines with methylene blue value <0.8 g/kg, ensuring quality. Full guidelines are in BCA's specification document.
Spotlight on Trailblazing Researchers at NTU and NUS
Principal Investigator Assistant Professor Qian Shunzhi (NTU's School of Civil and Environmental Engineering) specializes in advanced construction materials like engineered cementitious composites and 3D-printable concrete. His leadership drove the project's innovative mix optimizations. Co-PI Professor Tan Kang Hai (NTU), Director of the Protective Technology Research Centre, brings decades of expertise in structural engineering and sustainable materials, influencing Singapore's fire-resistant concrete standards.
From NUS, Associate Professor Qian Xudong contributed durability expertise, with his work spanning fracture mechanics and data-driven structural assessments. Their interdisciplinary team, including Temasek Polytechnic's Wong Sook Fun and ACI's Lu Jinping, exemplifies higher education's role in applied research. For more on Qian Shunzhi's profile, visit NTU ERI@N.
From Lab to Site: BCA Guidelines and Industry Uptake
BCA has integrated findings into practical guidance: granite fines must meet SS EN 12620 for grading (0/4 mm max), density (2000-3000 kg/m³), chlorides (<0.01%), and sulphates (≤0.8%). Trial mixes are mandatory, with superplasticizers ensuring S3 slump. Early adopters report success in non-structural elements, with potential expansion to high-rises via durability enhancements.
The 2022 review by NTU's Ziyang Li et al. in Construction and Building Materials reinforces global viability, spotlighting Singapore's context. Access the abstract at NTU DR-NTU.
Implications for Higher Education: Fostering Green Engineering Talent
At NTU and NUS, this research integrates into curricula like NTU's Bachelor of Engineering (Civil), emphasizing sustainable materials and life-cycle thinking. Students engage in labs mimicking study protocols, preparing for BCA-accredited roles. Programs highlight 3D printing and self-healing concretes, aligning with Singapore's Smart Nation vision.
Civil engineering enrollment at NTU exceeds 1,000 annually, with electives on green construction drawing from such breakthroughs. NUS'sResilient Infrastructures cluster trains future experts in durable, eco-friendly designs.
Career Opportunities in Sustainable Civil Engineering
This innovation opens doors for graduates. NTU and NUS alumni lead at firms like Lum Chang and BCA, specializing in low-carbon mixes. Roles in research, mix design, and quality control demand knowledge of admixtures and durability testing. With Singapore's construction output projected to grow, demand for sustainable specialists surges—check opportunities at specialized job boards.
- Research Assistantships: Hands-on with NTU's PTRC.
- Faculty Positions: Advance granite fines applications.
- Industry Roles: Optimize premix concrete at ready-mix plants.
Challenges, Solutions, and Future Horizons
Challenges include variability in granite fines sourcing and higher admixture needs for high-strength mixes. Solutions: standardized sieving and mineral additives like GGBS (reducing embodied carbon further).
Future: NTU explores 3D-printed granite fines concrete; NUS eyes hybrid aggregates. Scaling could cut Singapore's sand imports by millions of tons yearly, exemplifying university-industry synergy.
This NTU-NUS study cements granite fines' role in sustainable concrete, inspiring a new generation of engineers at Singapore's universities to build resiliently.
Photo by Afifi Zulkifle on Unsplash