Gravity Separation Carbonation of Recycled Concrete Fines
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Solution Overview
Problem
The cement industry faces high CO2 emissions due to limestone use, and existing supplementary cementitious materials (SCMs) like fly ashes and blast furnace slags are limited in availability, while carbonation of recycled concrete fines (RCF) is inefficient and dilutes reactive components, reducing mechanical performance.
Innovation Solution
A method and device for carbonating RCF and similar waste materials in a gravity separation reactor, converting them into an SiO2 rich supplementary cementitious material and calcium carbonate additive by mixing with water and CO2 under centrifugal motion, separating the products based on density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If carbonation of dry RCF is performed, then CO2 sequestration is achieved, but the process is time consuming
Solution Approach 1:
The patent changes the physical state parameter of RCF from dry to wet form, and performs carbonation in liquid medium under elevated temperature and pressure conditions. This transforms the slow atmospheric carbonation into a rapid hydrothermal carbonation process, reducing carbonation time from days/weeks to hours while maintaining CO2 sequestration effectiveness.
Solution Approach 2:
The patent utilizes phase transition of water from liquid to supercritical state (or near-critical conditions) to enhance CO2 solubility and reactivity. The supercritical or near-critical water acts as an excellent medium for CO2 transport and reaction, dramatically accelerating the carbonation kinetics compared to conventional dry or aqueous carbonation.
2Productivity
If wet carbonation is performed, then carbonation speed is increased, but drying of the product is necessary which loses benefits
Solution Approach 1:
The carbonated RCF product retains its inherent moisture from the hydrothermal carbonation process, and this moisture is utilized directly for subsequent cementitious applications. The product serves its own hydration needs, eliminating the requirement for energy-intensive drying operations and reducing overall process energy consumption.
Solution Approach 2:
The patent creates a composite material system where carbonated RCF particles are suspended in a calcium hydroxide-rich liquid phase. This slurry form combines the carbonated aggregate with a reactive binder medium, creating a ready-to-use supplementary cementitious material that can be directly incorporated into concrete mixes without separate drying and re-hydration steps.
3Quantity of substance
If conventional separation of RCA from RCF is used, then aggregate separation is achieved, but varying amounts of fine aggregate remain in RCF fraction diluting reactive components
Solution Approach 1:
The patent introduces a heavy liquid medium (such as zinc chloride solution or other high-density liquids) as an intermediary for separation. This heavy liquid acts as a density-based mediator that enables precise separation of RCF from finer particles and contaminants. The RCF particles, being denser, settle to the bottom while lighter impurities remain suspended or float, achieving high-purity RCF separation.
Solution Approach 2:
The patent moves from conventional size-based separation (sieving) to density-based separation using heavy liquid medium. This dimensional change in the separation mechanism allows for much finer discrimination between RCF particles and finer aggregate particles, achieving superior separation precision and purity of the RCF fraction.
4Object-generated harmful factors
If limestone substitution is attempted, then CO2 emissions from raw materials should be reduced, but environmentally friendlier alternatives are not available at large enough scale
Solution Approach 1:
The patent recovers and valorizes discarded concrete demolition waste (RCF) that would otherwise be landfilled or used as low-value fill material. Through hydrothermal carbonation, this waste is transformed into a high-value supplementary cementitious material, creating a circular economy solution that eliminates the need for virgin limestone while utilizing abundant construction waste resources.
Solution Approach 2:
The patent converts the harmful aspect of concrete waste (being a disposal burden and source of embodied carbon) into a beneficial resource. The RCF, which represents wasted construction materials and future demolition waste, is transformed through carbonation into a valuable SCM that sequesters additional CO2 and replaces limestone, turning a environmental problem into a solution.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This process efficiently converts RCF into high-performance SCMs and calcium carbonate additives, reducing environmental footprint and enhancing mechanical performance, while sequestering CO2 and valorizing waste materials.
Implementation Method 1
subjecting the starting material slurry and carbon dioxide to centrifugal motion inside the reactor
Implementation Method 2
gravity separation reactor, separating the products based on density
Implementation Method 3
comprising the calcium carbonate additive formed by reaction of carbon dioxide with calcium ions dissolved or leached from the starting material
Data Source
AI summary
A method for converting a starting material containing at least 40 wt.-% of calcium silicon (hydr)oxide phases and calcium aluminum (hydr)oxide phases into an SiO2 rich SCM and a calcium carbonate additive includes the steps: providing the starting material with a D90 of ≤1 mm, mixing the starting material with water or adjusting the water content to provide a starting material slurry having a solid:liquid weight ratio from 2:1 to 1:100, passing the starting material slurry together with carbon dioxide into a gravity separation reactor, subjecting the starting material slurry and carbon dioxide to centrifugal motion inside the reactor, and removing a heavy slurry from a first outlet of the reactor, removing a light slurry of lower density particles from a second outlet of the reactor, and removing liquid at a third outlet of the reactor.