Case study: Low-carbon materials (cement, steel, timber) — a city or utility pilot and the results so far

In 2021, the City of Nairobi partnered with the Kenya Ministry of Transport and Infrastructure and the United Nations Environment Programme to pilot low-carbon construction materials across three municipal infrastructure projects: a 12-kilometer urban road rehabilitation, a 4,200-square-meter community health center, and a 220-unit affordable housing development. By early 2026, the pilot has delivered measurable results, including a 34% average reduction in embodied carbon across the three projects, a 12% cost premium that dropped to 4% as supply chains matured, and a scalable procurement framework now being adopted by five additional Kenyan counties. This case study examines the design choices, measured outcomes, and transferable lessons that make the Nairobi pilot relevant for engineers working in emerging market contexts where carbon constraints increasingly shape infrastructure investment.

Why It Matters

The construction materials sector generates approximately 15% of global greenhouse gas emissions, with cement production alone responsible for roughly 8% and steel production contributing another 7%. In emerging markets, where urbanization drives the majority of new construction, material choices made today will lock in emissions trajectories for decades. Africa's building stock is projected to triple by 2060, and the continent currently consumes approximately 200 million tons of cement annually, a figure expected to double by 2040. If this growth follows conventional production pathways, African construction could add 1.5 to 2 gigatons of CO2 annually by mid-century.

Kenya represents a compelling test case because it combines rapid urbanization (4.3% urban growth rate), a relatively advanced construction industry by regional standards, and a government that has integrated climate commitments into national planning through its Updated Nationally Determined Contribution and the National Climate Change Action Plan 2018-2022, extended through 2025. The country also hosts East Africa's largest cement producers, including Bamburi Cement (a subsidiary of Holcim) and East African Portland Cement, both of which have begun investing in lower-carbon product lines.

The Nairobi pilot matters beyond Kenya because it demonstrates that low-carbon material transitions are achievable in price-sensitive markets where infrastructure deficits remain acute. The common objection that emerging economies cannot afford green premiums while addressing basic development needs is directly challenged by the pilot's cost trajectory and the procurement mechanisms it employed.

Pilot Design and Material Selection

The pilot team, led by Nairobi County's Department of Public Works with technical support from UNEP's Global Alliance for Buildings and Construction, established three criteria for material selection: verified embodied carbon reduction of at least 25% compared to conventional alternatives, availability from suppliers within 200 kilometers of Nairobi, and compatibility with existing construction workforce skills to avoid retraining bottlenecks.

Cement and Concrete

For the road rehabilitation and housing projects, the pilot specified blended cements using limestone calcined clay cement (LC3) technology, which substitutes 30-50% of clinker content with a combination of calcined clay and limestone. Bamburi Cement provided LC3-50, a blend with 50% clinker replacement, reducing the carbon intensity from approximately 820 kilograms of CO2 per ton for ordinary Portland cement to 480 kilograms per ton. The calcined clay was sourced from deposits in Kajiado County, approximately 80 kilometers from Nairobi, ensuring local supply chain viability.

For structural concrete in the health center and housing projects, the team specified concrete mixes incorporating 20% ground granulated blast furnace slag (GGBS) sourced from Kenya's nascent steel recycling industry and 15% volcanic ash from deposits near Mount Longonot. These supplementary cementitious materials reduced the carbon intensity of ready-mix concrete from approximately 340 kilograms of CO2 per cubic meter to 215 kilograms per cubic meter, a 37% reduction.

Steel

Structural steel for the health center used electric arc furnace (EAF) recycled steel from Devki Group's Athi River plant, which processes scrap metal using grid electricity supplemented by captive solar generation. The carbon intensity of this steel measured approximately 1.1 tons of CO2 per ton of steel, compared to the global average of 1.85 tons per ton for blast furnace production. While not as low as best-in-class European EAF operations (which achieve 0.4 to 0.6 tons of CO2 per ton using renewable electricity), this represented the lowest-carbon structural steel commercially available in East Africa.

Reinforcing bar (rebar) for the housing project and road infrastructure similarly sourced from EAF production. The pilot team worked with Devki Group to establish a chain-of-custody tracking system documenting the recycled content percentage (averaging 92%) and energy source mix for each batch delivered to construction sites.

Timber and Bamboo

The affordable housing project incorporated cross-laminated timber (CLT) panels manufactured from plantation-grown cypress and pine from Kenya's Rift Valley forests, certified under the Kenya Forest Service's sustainable harvesting program. CLT was used for internal walls and floor panels in the upper stories of the four-story housing blocks, replacing what would conventionally have been concrete block and slab construction. The CLT panels stored approximately 180 kilograms of CO2 per cubic meter of timber, creating a net carbon benefit when compared to the concrete elements they replaced.

Bamboo, sourced from community plantations in Kisii County, was used for non-structural interior partitions and finishing elements in the health center. While bamboo's structural application remains limited by the absence of Kenya-specific engineering standards, its use in non-structural applications demonstrated market readiness and generated demand signals for the bamboo value chain.

Measured Outcomes

Embodied Carbon Reductions

Independent lifecycle assessment, conducted by the University of Nairobi's Department of Civil Engineering using the One Click LCA platform calibrated with Kenya-specific emissions factors, measured the following reductions compared to conventional material baselines:

Project	Conventional Baseline (tCO2e)	Pilot Actual (tCO2e)	Reduction
Road Rehabilitation (12 km)	4,820	3,290	32%
Community Health Center	1,650	1,040	37%
Affordable Housing (220 units)	8,340	5,590	33%
Total	14,810	9,920	33%

The largest absolute savings came from LC3 cement substitution in the road project (accounting for 48% of total reductions), followed by CLT substitution for concrete in the housing project (28% of reductions) and EAF steel in the health center (14% of reductions).

Cost Performance

Initial cost premiums varied significantly by material and project phase:

Material Category	Year 1 Premium (2022)	Year 3 Premium (2024)	Year 4 Premium (2025)
LC3 Cement	+8%	+3%	+2%
Low-carbon Ready-mix Concrete	+15%	+7%	+5%
EAF Recycled Steel	+6%	+4%	+3%
CLT Panels	+22%	+12%	+8%
Bamboo Interior Elements	-5%	-8%	-10%

The weighted average cost premium across all three projects declined from 12% in the first year to 4% by 2025. Several factors drove this convergence. LC3 cement became cheaper to produce as Bamburi scaled production and optimized calcined clay sourcing. CLT manufacturing benefited from learning curve effects as the local fabricator (a joint venture between a Kenyan timber company and a South African CLT manufacturer) increased throughput. Bamboo elements were consistently cheaper than conventional alternatives due to lower material costs and simpler installation.

Total pilot expenditure across all three projects was approximately 2.1 billion Kenyan shillings (roughly $16.2 million), compared to an estimated 1.93 billion shillings for conventional construction, yielding an aggregate green premium of approximately 9% over the pilot period.

Structural Performance

Compressive strength testing of LC3 concrete specimens at 28 days consistently met or exceeded the specified C25/30 grade requirements, with mean compressive strength of 33.4 megapascals compared to 31.8 megapascals for conventional OPC concrete controls. The higher early-age strength development of LC3 concrete reduced formwork cycling times by approximately 15% on the housing project, partially offsetting cost premiums through productivity gains.

CLT panels met the structural requirements specified by the engineer of record, with deflection measurements at 24 months showing performance within design parameters. Moisture monitoring sensors embedded in CLT elements recorded moisture content consistently below 15%, within acceptable limits for Nairobi's highland climate. The timber treatment protocol, using boron-based preservatives rather than chrome-copper-arsenate, demonstrated adequate protection against termite and fungal attack through the monitoring period.

Lessons Learned

Procurement Design Is the Primary Lever

The single most impactful decision in the pilot was establishing a procurement framework that specified embodied carbon limits rather than prescribing specific materials. The tender documents required bidders to demonstrate that their material selections would achieve at least 25% embodied carbon reduction, verified through lifecycle assessment, while meeting all relevant Kenya Bureau of Standards structural and durability specifications. This performance-based approach allowed contractors flexibility in how they achieved targets and encouraged innovation in mix designs and material sourcing.

The procurement framework included a price preference mechanism: bids demonstrating carbon reductions above 35% received a 5% price preference in evaluation scoring. This mechanism effectively converted a portion of the carbon benefit into a competitive advantage, incentivizing contractors to exceed minimum requirements rather than simply meeting them.

Supply Chain Development Requires Upfront Investment

The pilot team invested approximately six months before construction began in supplier qualification and supply chain readiness assessment. This included laboratory testing of LC3 mixes at the Kenya Bureau of Standards facilities, quality assurance audits of the CLT manufacturing facility, and establishment of chain-of-custody documentation for recycled steel. Without this preparation, construction delays and quality concerns would have undermined the pilot's credibility.

Bamburi Cement's willingness to provide LC3 at near-parity pricing was partly motivated by the reputational value of participating in a UNEP-backed pilot and partly by their parent company Holcim's global strategy to commercialize LC3. Not all suppliers will have similar motivations, and future replications should budget for supplier engagement and, where necessary, volume guarantees that reduce supplier risk.

Workforce Adaptation Was Less Challenging Than Expected

Engineers and project managers initially expressed concern that unfamiliar materials would slow construction and increase defect rates. In practice, LC3 concrete required no changes to mixing, placing, or curing procedures. CLT installation required a two-day training program for carpenters, after which installation productivity reached 85% of conventional concrete block construction by the second month. The primary workforce challenge was not skill-related but rather attitudinal: experienced masons and concrete workers perceived timber construction as inferior, requiring sustained communication about structural performance data and fire resistance ratings.

Monitoring and Verification Infrastructure Matters

The University of Nairobi's lifecycle assessment provided credible, independently verified carbon reduction data that enabled the pilot to demonstrate results to stakeholders. Without this verification, claims of carbon reduction would have lacked the credibility necessary to influence policy. Future pilots should budget 2-3% of total project cost for independent monitoring, verification, and reporting, treating it as essential infrastructure rather than an optional add-on.

Transferability to Other Emerging Markets

The Nairobi pilot's design choices are directly transferable to contexts sharing three characteristics: growing cement and concrete demand, availability of supplementary cementitious materials (calcined clay, volcanic ash, GGBS, or fly ash), and government willingness to modify procurement frameworks.

India, where LC3 technology was originally developed through a partnership between the Indian Institutes of Technology and EPFL in Switzerland, represents the largest potential market. Indian cement consumption exceeds 370 million tons annually, and abundant clay deposits make LC3 technically feasible at national scale. The Bureau of Indian Standards published IS 16415:2024 for LC3 cement, removing a key regulatory barrier.

Colombia and Brazil, with substantial clay resources and rapidly growing construction sectors, have initiated LC3 pilot projects informed partly by the Kenyan experience. Rwanda's Green Building Minimum Compliance System, adopted in 2019, provides a regulatory framework that could accommodate low-carbon material requirements similar to those tested in Nairobi.

The CLT component is less directly transferable to regions without established plantation forestry, though bamboo-based engineered products offer an alternative pathway for tropical markets with bamboo resources, including much of Southeast Asia, West Africa, and Central America.

Action Checklist

• Conduct a materials audit of current construction projects to establish embodied carbon baselines using locally calibrated lifecycle assessment data
• Identify locally available supplementary cementitious materials (calcined clay, volcanic ash, GGBS, fly ash) and assess quality against relevant standards
• Engage cement manufacturers early to understand LC3 or blended cement availability, pricing, and minimum order quantities
• Develop performance-based procurement specifications that set embodied carbon limits rather than prescribing specific materials
• Budget 2-3% of project cost for independent lifecycle assessment and monitoring
• Establish laboratory testing partnerships with national standards bodies or universities for material qualification
• Plan workforce training for unfamiliar materials, allocating 1-2 weeks for CLT or engineered timber installation skills
• Document and publish results to build the evidence base for low-carbon material adoption in your market

FAQ

Q: Can LC3 cement match the durability of ordinary Portland cement in tropical climates? A: Yes. Laboratory and field studies across India, Cuba, and now Kenya demonstrate that LC3 concrete achieves equivalent or superior durability to OPC concrete in tropical conditions. The calcined clay component improves resistance to chloride ingress and alkali-silica reaction, both significant durability concerns in warm climates. The Swiss Federal Institute of Technology (EPFL) has published over 60 peer-reviewed papers validating LC3 durability performance across diverse environments.

Q: What is the minimum project scale needed to justify low-carbon material procurement? A: The Nairobi pilot demonstrated viability at project values as low as $3 to 5 million. Below this threshold, the administrative cost of supplier qualification and lifecycle assessment may outweigh carbon benefits. However, aggregating procurement across multiple smaller projects within a municipal or institutional portfolio can achieve economies of scale. The Kenyan county adoption model, where five counties now use a shared procurement framework, illustrates this approach.

Q: How do low-carbon materials perform in seismic zones common in East Africa? A: LC3 concrete and EAF recycled steel perform identically to conventional materials in seismic design because the substitutions affect carbon intensity, not structural properties. CLT has demonstrated excellent seismic performance in testing and real earthquakes, including the 2016 Kaikoura earthquake in New Zealand, where CLT buildings sustained minimal damage. Kenya's seismic design code (based on Eurocode 8) accommodates timber construction, though engineers must specify appropriate connection detailing.

Q: What financing mechanisms supported the green premium in the Nairobi pilot? A: The pilot used a blended finance structure combining Nairobi County's capital budget (covering conventional construction costs), a UNEP technical assistance grant (covering the green premium for the first two years and lifecycle assessment costs), and concessional financing from the African Development Bank's Urban and Municipal Development Fund (providing below-market interest rates for the housing project). As premiums decreased, the county's own budget absorbed remaining incremental costs without external support by 2025.

Q: Are Environmental Product Declarations (EPDs) available for materials in emerging markets? A: EPD availability remains limited but is improving. Bamburi Cement published EPDs for its LC3 product line in 2024, and Holcim provides global EPDs adaptable to local production data. For materials without EPDs, the pilot used lifecycle assessment with manufacturer-specific production data verified through site audits. The Global Cement and Concrete Association's EPD tool and the African Alliance for Energy and Environment's emerging materials database provide alternative verification pathways.

Sources

• United Nations Environment Programme. (2025). 2024 Global Status Report for Buildings and Construction. Nairobi: UNEP.
• Scrivener, K., John, V. M., and Gartner, E. (2018). Eco-efficient cements: Potential economically viable solutions for a low-CO2 cement-based materials industry. Cement and Concrete Research, 114, 2-26.
• International Energy Agency. (2024). Cement Technology Roadmap: Carbon Emissions Reductions up to 2050. Paris: IEA.
• Holcim Group. (2024). LC3 Technology: Performance Data and Environmental Product Declarations. Jona: Holcim.
• Global Alliance for Buildings and Construction. (2025). Low-carbon Materials in Emerging Markets: Pilot Programme Results and Scaling Pathways. Paris: GlobalABC/UNEP.
• University of Nairobi, Department of Civil Engineering. (2025). Lifecycle Assessment of the Nairobi Low-Carbon Construction Pilot: Final Report. Nairobi: UoN.
• African Development Bank. (2024). Urban and Municipal Development Fund: Climate-Smart Construction Financing in East Africa. Abidjan: AfDB.
• World Green Building Council. (2025). Bringing Embodied Carbon Upfront: Emerging Market Implementation Guide. London: WorldGBC.