Oxidation of Carbonated Recycled Concrete Paste for Reliable Reactivity
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Solution Overview
Problem
Manufacturing supplementary cementitious materials from recycled concrete paste (RCP) with reliable reactivity is challenging due to the variable composition of RCP and exhaust gas, leading to inconsistent carbonation results, particularly when using exhaust gas with low oxygen and high sulfur dioxide content, which results in sulfur compounds with oxidation states below S6+, affecting the early strength development of composite cements.
Innovation Solution
A method involving the carbonation of recycled concrete paste with exhaust gas containing 2 to 15 Vol.% O2 and/or 35 to 400 vppm SO2, followed by oxidation with an added oxidizing agent to transform sulfur compounds with oxidation states below S6+ into sulfate, optimizing the reactivity of the carbonated recycled concrete paste.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If carbonation of recycled concrete paste is performed with exhaust gas containing low oxygen and high sulfur dioxide content, then CO2 utilization is achieved, but the reactivity and early strength development of the resulting supplementary cementitious material deteriorates due to formation of sulfur compounds with oxidation states below S6+
Solution Approach 1:
The patent converts the harmful effect of sulfur dioxide present in exhaust gas by introducing an oxidation step that transforms sulfur compounds with oxidation states below S6+ into sulfate (S6+). This principle transforms the harmful sulfur compounds into beneficial sulfate, which improves the reactivity and early strength development of the carbonated recycled concrete paste while maintaining the CO2 utilization benefit.
Solution Approach 2:
The patent changes the oxidation state parameter of sulfur compounds from below S6+ to S6+ through controlled oxidation. By adjusting the oxidation conditions (such as oxygen exposure, temperature, or oxidation agents), the sulfur compounds are transformed into sulfate form, which fundamentally changes the chemical properties and improves the reactivity of the supplementary cementitious material.
2Adaptability or versatility
If variable composition of RCP and exhaust gas is used for carbonation, then material availability and flexibility are improved, but manufacturing precision and consistency of carbonation results deteriorate
Solution Approach 1:
The patent applies a preliminary oxidation step after carbonation to standardize the sulfur content in the final product. By oxidizing sulfur compounds to sulfate regardless of the variable composition of input materials, this preliminary action ensures consistent reactivity and performance outcomes, compensating for the variability in RCP and exhaust gas composition.
Solution Approach 2:
The oxidation step acts as a feedback mechanism that corrects the variability introduced by variable input compositions. By consistently applying oxidation to convert all sulfur compounds to sulfate, the process provides a self-correcting mechanism that maintains product consistency despite fluctuations in raw material quality or composition.
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 method enhances the early strength development of composite cements, ensuring reliable reactivity comparable to known pozzolans like fly ash, while reducing CO2 emissions by utilizing recycled materials in a closed-loop process.
Implementation Method 1
carbonation of the starting material with carbon dioxide contained in exhaust gas to provide carbonated recycled concrete paste
Implementation Method 2
oxidation of the carbonated recycled concrete paste simultaneously or subsequently to the carbonation with an added oxidizing agent to provide the supplementary cementitious material
Data Source
Figure 1~2
AI summary
Method for improving the reactivity of carbonated recycled concrete paste comprising sulfur in an oxidation state lower than 6+ as supplementary cementitious material comprising the steps: - providing a starting material comprising recycled concrete paste, - carbonation of the starting material with carbon dioxide contained in an exhaust gas containing from 2 to 15 Vol.-% oxygen and/or from 35 to 400 vppm sulfur dioxide to provide carbonated recycled concrete paste, and - oxidation of the carbonated recycled concrete paste simultaneously or subsequently to the carbonation with an added oxidizing agent to provide the supplementary cementitious material, and method for making composite cements.