Concrete Technician

About Cocoon

Cocoon is driving the circular economy between steel and cement by turning steel slag into a low‑carbon cement substitute. We've just raised a $15m Series A and are backed by leading climate and hardware tech investors, including 2150, Brick & Mortar, Gigascale, Wireframe, and Celsius Industries. In under two years, we've gone from concept to deploying our breakthrough technology at one of the largest steel producers in the US.

Steel and cement account for nearly 15% of global CO₂ emissions, and decarbonising these industries requires completely new approaches to mix design, testing, and implementation. We’re now building our in‑house concrete capability so we can qualify SCMs, validate performance against industry standards, and support deployment of our technology at pilot and demo‑scale. To do this, we’re establishing a fully equipped concrete laboratory in London and we’re looking for a Concrete Technician to help make it happen.

We’re looking for a Concrete Technician to support the design, mix, test, and manage concrete across an extensive experimental programme. You’ll help establish our concrete lab, assist with equipment commissioning, and contribute to SOPs development, delivering mechanical and durability testing to ASTM, BSI, and related standards. You’ll support the full lifecycle of concrete development, from mix design and batching, through casting and curing, to compressive strength and durability testing while keeping meticulous data records and maintaining a safe, well‑organised laboratory.

You’ll also support field trials, coordinate external testing, and provide experimental results to our research and commercial teams. This role is hands‑on, varied, and central to Cocoon’s ability to qualify SCMs, validate performance, and scale towards real‑world deployment.

• Prepare and trial concrete mix formulations across the experimental matrix (SCM replacement, admixtures, w/b ratios) to ASTM C1709 and BSI Flex 350.
• Plan batching schedules, specimen numbers, test timelines, and weekly execution plans.
• Support optimisation of mix proportions and help troubleshoot workability, flash setting, segregation, and strength issues.
• Operate the mixer and conduct fresh property tests (slump, density, air content, bleeding).
• Record batch data (temperature, timings, slump, w/b) and maintain full QA/traceability.
• Cast cubes and cylinders; manage curing tanks, curing regimes, and specimen conditioning.
• Perform compressive and flexural strength testing at 7, 28 and long‑term ages.
• Prepare and run durability tests (RCPT, bulk resistivity, water absorption, sorptivity, permeability, drying shrinkage, sulfate resistance, carbonation depth).

• Assist in preparing and maintaining SOPs for all concrete lab processes and support commissioning of existing equipment.
• Support identification, procurement, and installation of additional equipment required for the testing regime.
• Support baselining testing of cement and benchmark materials.
• Maintain calibration, servicing, and safe operation of all equipment.
• Manage consumables (PPE, mould oil, aggregates, cement) and keep the lab organised and compliant.
• Ensure all risk assessments are in place and adhered to.

• Maintain digital logs, record raw data, and align outputs with current data storage methods.
• Process and analyse test results; prepare technical reports and summaries, and present data for internal reviews, meetings, and partner updates.
• Support training of team members in SOPs, mixing, fresh testing, and equipment use.
• Coordinate outsourcing for tests not done in‑house and manage samples, logistics, and external data integration.
• Support small‑scale field trials and demonstration pours, including onsite testing.

• Have hands‑on experience in concrete testing, materials laboratories, or construction materials research.
• Are confident working to ASTM, BS EN, and other standards.
• Enjoy practical, repetitive experimental work and take pride in process discipline.
• Communicate clearly and maintain…