HEMC Viscosity Modifier for Self-Compacting Concrete Air Entrainment
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Solution Overview
Problem
Current viscosity modifying agents (VMAs) for self-compacting concrete (SCC) mortars often increase yield stress, leading to air entrapment and reduced quality, limiting the selection to a few expensive options like Welan gum and polyacrylate-based polymers, which are costly and inefficient.
Innovation Solution
A hydroxyethyl methyl cellulose (HEMC) with specific molecular substitution (MS) and degree of substitution (DS) values, ranging from 1.90 to 2.30 and 0.01 to 0.5, respectively, is used to create an SCC mortar with optimal viscosity, slump, and bleeding values, while minimizing air entrapment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional viscosity modifying agents (such as starch, clay, Welan gum, diutan gum, hydroxyethyl cellulose, or polyacrylate-based polymers) are used to increase viscosity, then segregation and bleeding are prevented, but yield stress increases and air entrapment occurs
Solution Approach 1:
The patent changes the chemical parameters of the viscosity modifying agent by specifying precise substitution degrees (DS: 1.6-2.5 and MS: 0.01-0.5) for the HEMC polymer. This parameter optimization allows the polymer to provide viscosity enhancement while minimizing yield stress increase and air entrapment, resolving the contradiction between stability improvement and harmful factor reduction
Solution Approach 2:
The patent uses a composite chemical structure (hydroxyethyl methyl cellulose) that combines features of different cellulose derivatives. This composite structure provides both the viscosity modification needed for segregation resistance and the controlled rheological properties that prevent excessive air entrapment, unlike single-structure VMAs
2Stability of the object's composition
If hydroxyethyl methyl cellulose (HEMC) with high viscosity is used, then plastic viscosity increases for segregation prevention, but slump value decreases below acceptable levels
Solution Approach 1:
The patent optimizes the viscosity parameter of HEMC by selecting polymers with viscosity below 30,000 mPa·s at 2% concentration. This parameter control ensures sufficient plastic viscosity for segregation resistance while maintaining low enough viscosity to preserve adequate slump (>290mm) for self-compacting flowability
3Ease of manufacture
If HEMC is used as a viscosity modifying agent, then cost is reduced compared to alternative VMAs, but air entrapment increases and quality decreases
Solution Approach 1:
The patent changes the substitution parameters (DS and MS) of HEMC to optimize its air-entraining behavior. By controlling these chemical parameters within specific ranges, the patent achieves both cost-effectiveness and reduced air entrapment, making HEMC a superior alternative to expensive VMAs like Welan gum and polyacrylates
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 HEMC formulation achieves a desirable slump value greater than 290 mm, V-funnel discharge time less than five seconds, and bleeding value less than three percent, with reduced air entrapment, enhancing the quality and flow properties of SCC mortars.
Implementation Method 1
A mortar suitable for use in self compacting concrete formulations is provided and comprises a hydroxyethyl methyl cellulose characterised by the sum of its hydroxyethyl molecular substitution (MS) and methyl degree of substitution (DS) being from 1.90 to 2.30 and its viscosity as a 2 weight-percent aqueous solution that is below 30,000 milliPascals*seconds
Data Source
AI summary
A mortar contains cement, one or more than one mineral additive, superplasticizer, aggregates, a hydroxyethyl methyl cellulose and water, wherein the hydroxyethyl methyl cellulose is characterized by the sum of its hydroxyethyl molecular substitution and methyl degree of substitution is 1.90 or higher and 2.30 or lower and its viscosity as a 2 weight-percent aqueous solution that is below 30,000 milliPascals*seconds.