Colloidal Silica Admixture Reducing Shotcrete Rebound
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Solution Overview
Problem
Existing chemical admixtures for shotcrete that accelerate early strength development lead to rebound waste, consolidation issues, and long-term strength concerns, while colloidal silica enhances early strength but increases water demand and reduces workability.
Innovation Solution
A stable liquid suspension comprising a polycarboxylate polymer cement dispersant, colloidal silica, and a siloxane compound, where the components are blended to form a uniform colloidal dispersion, improving the compatibility and miscibility of the mixture, thereby reducing rebound and enhancing strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If set accelerating chemical admixtures are used to improve early strength, then early compressive strength is improved, but rebound waste increases and consolidation issues occur
Solution Approach 1:
The patent combines multiple previously separate admixture components (colloidal silica, siloxane compound, and polycarboxylate polymer dispersant) into a single integrated additive composition. This merging allows the components to work synergistically, where colloidal silica and siloxane provide early strength enhancement while the polycarboxylate dispersant maintains workability and reduces rebound, resolving the contradiction between early strength gain and rebound waste
Solution Approach 2:
The invention creates a composite admixture system where inorganic components (colloidal silica, siloxane) are combined with an organic polymer dispersant (polycarboxylate). This composite structure allows the inorganic portion to accelerate strength development while the organic polymer portion controls rebound and maintains mix workability, effectively addressing both sides of the contradiction simultaneously
2Strength
If colloidal silica is used to enhance early strength, then early strength is improved, but water demand increases and workability is reduced
Solution Approach 1:
The polycarboxylate polymer dispersant acts as an intermediary substance that mediates between the colloidal silica particles and the cementitious mixture. It adsorbs onto the high-surface-area silica particles, preventing them from excessively absorbing water and disrupting the mix. This intermediary action allows the silica to provide early strength enhancement while the dispersant maintains adequate water availability and workability
Solution Approach 2:
The invention changes the physical-chemical parameters of the colloidal silica by surface-modifying it with siloxane compounds and coating it with polycarboxylate polymer. This parameter modification reduces the surface energy and water demand of the silica particles, allowing them to enhance early strength without proportionally increasing water demand and loss of workability
3Loss of substance
If colloidal silica is used to reduce rebound, then rebound is reduced, but viscosity increases and pumpability is adversely affected
Solution Approach 1:
The polycarboxylate polymer dispersant serves as an intermediary that coats the colloidal silica particles, preventing them from aggregating and excessively increasing mixture viscosity. This intermediary layer maintains particle dispersion and reduces internal friction, allowing the silica to reduce rebound while the dispersant preserves adequate flowability and pumpability
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 solution achieves improved early-age strength development, reduced rebound, and enhanced finishability of shotcrete, with a synergistic effect on compressive strength and surface finish, addressing the limitations of existing admixtures.
Implementation Method 1
a polycarboxylate polymer cement dispersant
Implementation Method 2
due to a pozzolanic effect on early strength enhancement of cement binder
Implementation Method 3
at least one siloxane compound wherein the silicon atoms and oxygen atoms are linked within a linear or cyclic backbone structure
Data Source
Figure 1~2
Figure 3A~4C
Figure 5
AI summary
The present invention provides an admixture composition comprising a liquid suspension of colloidal silica, siloxane, and polycarboxylate polymer cement dispersant for enhancing early age strength, finishability, and other properties in hydratable cementitious compositions such as concrete (e.g., shotcrete). An inventive method involves mixing the components together in a specific sequence, thereby to obtain a stable liquid suspension. This attainment of a stable liquid suspension is surprising and unexpected because (i) the polycarboxylate polymer cement dispersant and siloxane components are incompatible and immiscible with one another; and (ii) that colloidal silica and siloxane compound are incompatible and immiscible with one another. Yet, the present inventors achieved an additive in the form of a stable liquid suspension which can be conveniently dosed into concretes and shotcrete mixtures, to enhance early age strength, and to improve workability and rheology in terms of finishability of concrete surfaces and improved rebound performance in shotcrete applications.