Concrete recycling has traditionally been based on the assumption that old concrete is a lifeless, fully hydrated material. The assumption is that, to reuse it in new concrete production, it must be crushed into aggregates. The concept of revival, however, suggests something different. Concrete is not truly dead, but rather frozen in time, or crystallized. With the right process, it can be reactivated.
Macrocement, part of INKAS, have developed and patented technology that enhances conventional concrete recycling by combining aggregate recycling with cement revival into a single technology.
Macrocement research has demonstrated that old concrete can be converted into a highly active supplementary cementitious material (SCM), capable of replacing up to 40 percent of portland cement in new concrete production, without compromising workability, strength, or durability.
Importantly, this material was not developed solely in laboratory conditions. It was produced using standard industrial equipment currently used in the chemical, mining, and cement industries. Real construction and demolition waste from The Miller Group, as well as returned concrete from ready-mix operations and materials from St. Marys Cement CBM, were used throughout development.
The Hidden Challenge in Concrete Recycling
Traditional recycling focuses on recovering concrete aggregates larger than 3–5 mm. However, this process produces a significant amount of fine particles, often 30 to 50 percent of the total material, which are typically unsuitable for reuse due to low density and mechanical strength, high porosity and water absorption, and surface impurities from old cement mortar. The primary issue lies in the old mortar adhering to these fine particles, creating a weak interface that reduces structural integrity.
However, this also presents the greatest opportunity. Macrocement research has shown that these fine particles contain the highest concentration of old cement, making them the ideal candidates for reactivation. The most effective approach is therefore to continue using larger fractions as aggregates, while converting the fines into reactive cementitious material.
The first principle is mechanical calcination. This process enables chemical transformation by simultaneously applying cyclic mechanical forces and localized thermal energy, both generated by the same mechanical interactions.
Recycled concrete fines are processed using industrial-scale, energy-intensive stirred media mills. Inside the mill, particles are repeatedly trapped between the grinding media (typically steel balls) and the mill wall. These high-energy collisions create localized impact zones where temperatures can briefly exceed 1,000° C.
Although these temperature spikes occur only momentarily and at microscopic scales, they produce profound structural changes within the mineral particles. Specifically, they generate crystal lattice defects and metastable structural states, which fundamentally alter the material’s internal structure.
These structural transformations restore chemical reactivity to particles that were previously considered inert. This process represents a practical, industrial-scale application of solid-state chemistry, converting recycled concrete fines into active cementitious material.
The second principle draws inspiration from horticulture, specifically, the concept of grafting young, active branches onto older trees to restore vitality. This is achieved through a process known as dry particle coating, where highly reactive fine particles, referred to as “guest” particles, are mechanically bonded onto the surface of larger recycled cement particles, which act as “host” particles. This coating forms a highly reactive outer layer on the host particles, significantly enhancing their cementitious behavior.
These reactive ‘’guest’’ particles bond mechanically to the surface of recycled cement particles. Even particles that may have been only partially activated or previously inert become effective carriers of reactive materials. As a result, the combined particle system behaves as a highly active supplementary cementitious material.
Engineering Cement at the Particle Level
Beyond activation, dry particle coating provides a powerful platform for engineering the surface properties of cement particles themselves. Using this technique, Macrocement have developed:
- Hydrophobic cement, created by coating cement particles with water-repellent materials to improve durability and moisture resistance
- An extended shelf-life cement, designed to resist degradation during storage
- Technologies for restoring aged or stale cement, extending the useful life of cement materials
These capabilities demonstrate that this technology is not limited to recycling but enables the controlled engineering of cement performance at the microscopic level.
Advantages Over Conventional Green Cement Technologies
Macrocement technology offers several key advantages over conventional green cement technologies.
- Universal: Capable of processing a wide range of industrial and mineral waste
- Efficient: Enables up to 40 percent cement replacement, compared to typical 20 percent limits
- Practical: Uses existing industrial equipment
- Cost-effective: Comparable production cost to conventional SCMs
- Flexible: Scalable across multiple facility sizes and applications
Concrete recycling no longer needs to stop at aggregates. By reactivating the cement within recycled materials, Macrocement can transform waste into a valuable resource. This approach reduces emissions, conserves raw materials, and introduces a more sustainable model for concrete production.
Concrete is not simply recycled. It is revived.
For technical detail, additional information is available at:
Self-Protecting Cement: https://macrocement.com/macrocement-self-protecting-cement/
Green Option for Recycling Stale Cement: https://macrocement.com/macrocement-green-option-for-recycling-stale-cement/
