Carbonatable Cement pH Control for Steel Corrosion
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Solution Overview
Problem
Conventional concrete production using ordinary portland cement (OPC) is energy-intensive and generates significant CO2 emissions, leading to environmental concerns and corrosion issues with embedded steel reinforcement due to pH changes in the concrete's pore solution during carbonation.
Innovation Solution
Development of novel curing methods and formulations for carbonatable low calcium silicate-based cements that maintain a high pH in the pore solution, preventing or delaying corrosion of steel reinforcement by controlling the carbonation process to achieve compressive strengths of 3,000 to 10,000 psi with a stable pH above 9.5.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional OPC is used for concrete production, then compressive strength and durability are achieved, but CO2 emissions and energy consumption increase significantly
Solution Approach 1:
The patent changes the chemical composition parameters of cement by using low calcium silicate-based cements with controlled Ca/Si ratios instead of conventional OPC, and adjusts curing parameters by controlling CO2 exposure conditions to achieve carbonation curing that reduces emissions while maintaining strength
Solution Approach 2:
The patent converts harmful CO2 emissions into a beneficial curing agent by exposing the concrete to controlled CO2 environments during curing, allowing CO2 to react with calcium hydroxide to form calcium carbonate, thereby sequestering carbon while strengthening the concrete structure
2Object-generated harmful factors
If carbonation curing is applied to reduce CO2 footprint, then environmental benefits are achieved, but pore solution pH drops causing steel corrosion
Solution Approach 1:
The patent changes the chemical composition of the cementitious material by using low calcium silicate-based cements with specific Ca/Si ratios and incorporating supplementary cementitious materials that buffer pH changes during carbonation, thereby maintaining adequate alkalinity to protect steel reinforcement
Solution Approach 2:
The patent introduces supplementary cementitious materials as intermediary substances that mediate between the carbonation process and the pore solution chemistry, buffering the pH drop and preventing steel corrosion while allowing carbonation to proceed for carbon sequestration
3Strength
If water is removed during pre-conditioning to control carbonation, then compressive strength is improved, but water resistance may be compromised
Solution Approach 1:
The patent changes the moisture content parameter during pre-conditioning to optimal levels that facilitate carbonation and strength development, then compensates by ensuring adequate water-cement ratio and proper curing to maintain water resistance without compromising compressive strength
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 method effectively prevents or delays corrosion of steel reinforcement while maintaining adequate compressive strength and water resistance, enhancing the service life and durability of concrete structures.
Implementation Method 1
carbonatable cement refers to cement that is principally cured by reaction with carbon dioxide, CO2, in any of its forms
Implementation Method 2
Hydration of OPC in the presence of water produces a solution within the porous material that consists mainly of alkali hydroxides, such as, Ca(OH)2, NaOH and KOH
Implementation Method 3
pre-conditioning the predetermined shape to remove a predetermined amount of the water from the predetermined shape
Data Source
AI summary
A method of producing a carbonated composite material includes: providing a carbonatable cementitious material in particulate form; mixing the carbonatable cementitious material with water to produce a mix; forming a predetermined shape with the mix, wherein the predetermined shape has an initial pore structure containing an initial pore solution having a first pH; pre-conditioning the predetermined shape to remove a predetermined amount of the water from the predetermined shape to produce a pre-conditioned shape; carbonating the pre-conditioned shape in an environment comprising carbon dioxide to produce a modified pore structure containing a modified pore solution having and a second pH, wherein the difference between the first pH and the second pH is represented by a ΔpH, and the ΔpH is 1.0 or less.