Microsoft agrees to buy up to 622,500 tonnes of Sublime's low-carbon cement

May 23, 2025 — Microsoft signed a binding contract to buy low-carbon cement from Sublime Systems, a startup that makes cement with an electrochemical process instead of a kiln, World Cement reported. Here's what happened, what it cost, and what went wrong.

Cost and outcome (as of May 28, 2025)

Outcome: Microsoft's purchase "will deploy up to 622 500 t of Sublime Cement® over a six- to nine-year period," from Sublime's first commercial factory in Holyoke, Mass., and a later full-scale plant. ENR's headline rounds it to 622,000 tons. (World Cement, May 23, 2025; ENR, May 28, 2025)
Cost: No price was disclosed.
Status: Holyoke was still being developed when the deal was announced.

How the deal works

Microsoft gets a priority option to use Sublime Cement in its own projects, including data centers and office buildings, "when geographically possible," World Cement reported. Where it can't, it can buy environmental attribute certificates (EACs) separately from the physical cement, much as renewable energy certificates are split from the electricity. (World Cement, May 23, 2025)

The EAC purchases will be third-party verified and are expected to run on a future "book and claim" system, World Cement said. Microsoft's Katie Ross said the approach "helps both buyers and sellers overcome geographic, supply chain, cost, and other barriers." (World Cement, May 23, 2025)

The deal follows a September 2024 memorandum of understanding in which the two committed to a transaction that was "verifiable, additional, and catalytic." (Sublime Systems, Sept. 25, 2024; World Cement, May 23, 2025)

"Microsoft aims to accelerate the mass production and adoption of clean construction materials," said Jeff Leeper, Microsoft's vice president of global datacenter construction. Sublime CEO Leah Ellis said the deal answers "the lack of long-term cement transactions contrasted with the immediate need for innovators to demonstrate bankable customers." (World Cement, May 23, 2025; ENR, May 28, 2025)

The technology, as described

Sublime says its electrochemical process breaks down rock and industrial waste feedstocks without the 1,450°C kilns that ordinary portland cement needs, and that its ASTM-compliant cement is a drop-in replacement. ENR describes it as an electrolytic process that converts limestone to lime at room temperature. (World Cement, May 23, 2025; ENR, May 28, 2025; Sublime Systems, Sept. 25, 2024)

ENR reported that Sublime had completed its first two concrete projects in Boston with Turner Construction and Boston Sand and Gravel, and that contractors will ultimately buy the concrete for Microsoft's projects. "We are really focused on figuring out the right agreement structures with the general contractors," said Sublime's Cory Waltrip. (ENR, May 28, 2025)

In its 2024 post, Sublime said Holyoke was expected to produce 30,000 tonnes a year and could open as early as 2026, and that it ran a pilot plant in Somerville, Mass., of more than 250 tonnes a year. (Sublime Systems, Sept. 25, 2024)

What went wrong

Federal money in the mix. World Cement's report cites Sublime's "up-to US$87 million award" from the Energy Department for its Holyoke work; the announcement doesn't say how much of the plan depends on it. (World Cement, May 23, 2025)
Two descriptions of the chemistry. ENR says limestone is converted to lime; Sublime says its approach avoids limestone feedstock. We haven't seen a technical document that resolves this. (ENR, May 28, 2025; Sublime Systems, Sept. 25, 2024)
Scale is still ahead. The 622,500 tonnes depends on a full-scale factory that, by World Cement's account, is still to come after Holyoke. (World Cement, May 23, 2025)
What we don't know yet: the price, how much will be physical cement versus certificates, and the Holyoke plant's current schedule.

Our follow-up question for Sublime Systems

What is Holyoke's current schedule, and how will the Microsoft volume be split between physical cement and certificates?

Sources

World Cement, “Sublime Systems and Microsoft sign long-term purchase to transform clean cement market,” May 23, 2025. worldcement.com
ENR (Jeff Yoders), “Microsoft Opts to Buy 622,000 Tons of Low-carbon Cement Products From Sublime Systems,” May 28, 2025. enr.com
Sublime Systems, “Microsoft Signals Intent to Purchase Environmental Attributes of Low-Carbon Cement Developed by Sublime Systems,” Sept. 25, 2024. sublime-systems.com

Disclosure: [not in copy] Editor placeholder