Carbonatable Cementitious Powder with Controlled Ca/Si Blending
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Solution Overview
Problem
Existing cementitious powders derived from fiber cement waste exhibit inconsistent quality and strength due to variations in composition, particularly in Ca/Si and Al/Si ratios, leading to variations in mortar strength.
Innovation Solution
A method involving the comminution and mixing of fiber cement waste materials with specific Ca/Si and Al/Si ratios, followed by carbonation, to produce a cementitious powder with a balanced Ca/Si ratio of 0.9-1.5 and Al/Si ratio of 0.04-1, and controlled organic fiber content of up to 2% by weight, ensuring consistent quality and improved flowability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of repair
If fiber cement waste material is used to produce cementitious powder, then recycling and sustainability are improved, but composition consistency and mortar strength are worsened due to variations in Ca/Si and Al/Si ratios
Solution Approach 1:
The patent applies parameter changes by precisely controlling the Ca/Si ratio (0.8-1.2) and Al/Si ratio (0.05-0.5) of the cementitious powder through selective blending of fiber cement waste with different compositions. This ensures consistent chemical parameters that guarantee reliable mortar strength while maintaining high recycling content (at least 80% by weight), thus resolving the contradiction between sustainability and composition consistency.
Solution Approach 2:
The patent creates a composite cementitious material by combining fiber cement waste particles with controlled calcium silicate hydrate content and specific ratio parameters. This composite approach allows tuning of the overall composition to achieve both high recyclability and consistent mechanical properties, overcoming the variability inherent in single-source waste material.
2Ease of operation
If organic fibers are completely removed from fiber cement waste, then flowability is improved, but fiber content drops below the required 0.1-2% range
Solution Approach 1:
The patent applies partial action by removing most organic fibers to improve flowability, but retaining a controlled amount (0.1-2% by weight) to maintain adequate fiber content. This partial removal strategy achieves the optimal balance between flowability requirements and the need for sufficient fiber reinforcement in the final cementitious product.
Solution Approach 2:
The patent applies local quality by creating a non-uniform distribution where most of the material consists of fine comminuted particles for good flowability, while a small controlled portion retains organic fiber characteristics. This localized retention of fibers in specific amounts provides reinforcement without compromising overall flow properties.
3Ease of operation
If fiber cement waste is comminuted to reduce fiber length, then flowability is improved, but particle size distribution control becomes more difficult
Solution Approach 1:
The patent controls particle size distribution parameters by adjusting comminution intensity to achieve an average fiber length of 0.25-0.50 mm while maintaining a balanced particle size distribution. This parameter control ensures both improved flowability from reduced fiber length and consistent performance through controlled particle characteristics.
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
The resulting cementitious powder achieves consistent compressive and flexural strengths in mortars, minimizing variations in mortar performance and enabling the use of recycled materials as a supplementary cementing material with reduced CO2 output.
Implementation Method 1
A carbonation step is typically performed on such recycled concrete. This carbonation step transforms any calcium-silicate hydrates (also known as CSH) in cured cement into calcium carbonate and an alumino-silica gel.
Data Source
Figure 1a~1b
Figure 2(a)~2(b)
AI summary
A method of generating a carbonatable cementitious powder with a predefined Ca/Si ratio, comprising the steps of: - comminuting fiber cement waste material; - removing organic fibers from said comminuted fiber cement waste material, to obtain a first waste powder, - comminuting a further waste material with a Ca/Si ratio of at most 0.6 and a SiO2 content of at least 50wt% as identified with XRF, therewith providing a second waste powder, and - mixing the first and the second waste powder.