Amine Sacrificial Agents for Fly Ash Air Entrainment
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Solution Overview
Problem
The use of fly ash in cementitious mixtures often leads to air entrainment problems due to the detrimental effects of residual carbon, which interferes with the functionality of air entrainment agents, resulting in erratic concrete air contents and reduced compressive strength, especially with high carbon content fly ash, and existing solutions are either costly or ineffective.
Innovation Solution
Incorporating a sacrificial agent, such as primary, secondary, or tertiary amine compounds, into the cementitious mixture to neutralize the adverse effects of fly ash components on air entrainment, allowing for predictable and adequate air content levels, even with high carbon content fly ash, without interfering with cement hydration or other concrete properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If fly ash is used in cementitious mixtures to reduce portland cement consumption and improve concrete properties, then cost reduction and improved rheology/permeability/strength are achieved, but air entrainment properties deteriorate due to residual carbon interfering with air entrainment agents
Solution Approach 1:
A sacrificial agent is introduced as an intermediary substance that preferentially reacts with or adsorbs residual carbon in fly ash, preventing the carbon from interfering with air entrainment agents. This mediator protects the air entrainment process by sacrificing itself to neutralize the harmful carbon components.
Solution Approach 2:
The harmful residual carbon in fly ash is converted into a beneficial situation by using sacrificial agents that selectively interact with the carbon. The carbon's adsorption capability, which causes problems with air entrainment agents, is harnessed to adsorb the sacrificial agent instead, thereby protecting the air entrainment process.
2Reliability
If higher dosages of air entrainment agents are used to compensate for carbon adsorption, then air content may be maintained, but cost increases and other concrete properties may be adversely affected
Solution Approach 1:
The sacrificial agent serves as a protective intermediary that allows air entrainment agents to function at normal dosages. By placing the sacrificial agent between the carbon and the air entrainment agent, the harmful adsorption interaction is redirected, preserving the air entrainment mechanism without requiring excessive dosages.
Solution Approach 2:
The chemical environment is modified by introducing the sacrificial agent, which changes the interaction dynamics between carbon and air entrainment agents. This parameter change in the chemical system allows air entrainment to proceed effectively at standard dosages rather than requiring increased concentrations.
3Quantity of substance
If fly ash with high carbon content is used to maximize ash replacement, then cement consumption is reduced further, but air entrainment becomes erratic and compressive strength is reduced
Solution Approach 1:
High carbon content fly ash, which would normally be considered problematic or low-quality material, is transformed into a usable ingredient through the sacrificial agent treatment. The carbon's harmful adsorption property is redirected to adsorb the sacrificial agent instead of the air entrainment agent, enabling high-carbon fly ash to be used effectively.
Solution Approach 2:
The chemical parameters of the mixture are altered by adding the sacrificial agent, which changes the competitive adsorption equilibrium. This allows high carbon content fly ash to be incorporated without compromising air entrainment or strength, effectively expanding the usable range of fly ash carbon content levels.
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 sacrificial agents enable consistent air entrainment, maintaining adequate air content levels and concrete strength, accommodating variations in fly ash properties without causing excessive air entrainment or other detrimental effects, thus enhancing the usability of fly ash in concrete.
Implementation Method 1
Fly ash-carbon, a residue of incomplete coal or other hydrocarbon combustion, is in many ways similar to an 'activated carbon.' For example, like activated carbon, fly ash-carbon can adsorb organic molecules in aqueous environments. In cement paste containing organic chemical admixtures, the fly ash-carbon can thus adsorb part of the admixture, interfering with the function and performance of the admixture.
Data Source
AI summary
A method of producing cementitious mixtures containing fly ash as one of the cementitious components, under air entrainment conditions is described. The method involves forming a mixture comprising water, cement, fly ash, optionally other cementitious materials, aggregate, conventional chemical admixtures, and an air entrainment agent and agitating the mixture to entrain air therein. Additionally, at least one amine sacrificial agent is included in the mixture. The cementitious mixtures and hardened concretes resulting from the method and fly ash treated with sacrificial agent, or air entrainment agent/sacrificial agent combinations, are also described.