Reactive Binder Mixture Prevents Thaumasite in Cementitious Articles
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Solution Overview
Problem
Cementitious articles, particularly cementitious boards, face stability and durability issues due to the formation of thaumasite crystals under humid conditions, leading to swelling, cracking, and reduced mechanical performance.
Innovation Solution
A reactive binder mixture comprising 10 to 40 wt.% hydraulic cement, 40 to 80 wt.% calcium sulphate hemihydrate, and 1 to 35 wt.% silica source material, where the silica source material includes an alkali silicate material, is used to enhance the stability and durability of cementitious articles by preventing thaumasite formation and maintaining mechanical properties in wet environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If calcium sulphate hemihydrate is combined with cement to decrease setting time and reduce carbon footprint, then setting time is reduced and CO2 emissions are decreased, but thaumasite crystal formation increases under humid conditions leading to swelling and durability issues
Solution Approach 1:
The patent introduces an intermediary substance (alkali silicate material or pozzolanic material) that mediates between the calcium sulphate hemihydrate and the harmful thaumasite formation. This intermediary reacts with the gypsum to prevent thaumasite crystal growth while maintaining the benefits of fast setting and low CO2 emissions. The intermediary acts as a protective layer that blocks the harmful chemical interaction without interfering with the desired setting characteristics.
Solution Approach 2:
The patent converts the potentially harmful effect of calcium sulphate hemihydrate (which causes thaumasite formation and swelling) into a beneficial outcome by using it as a setting accelerator. The same calcium sulphate that could cause durability issues is instead harnessed to achieve fast setting time, while the harmful effect is neutralized by the addition of alkali silicate or pozzolanic materials that prevent thaumasite formation.
2Loss of time
If plaster is used to accelerate setting time, then setting time is reduced, but mechanical performance is lost due to thaumasite precipitation and swelling
Solution Approach 1:
The alkali silicate material or pozzolanic material serves as an intermediary that protects the mechanical integrity of the cementitious matrix. These materials react with the calcium sulphate hemihydrate to form stable compounds that prevent thaumasite crystal growth, thereby preserving the mechanical strength while maintaining fast setting characteristics.
Solution Approach 2:
The patent creates a composite cementitious material combining hydraulic cement, calcium sulphate hemihydrate, and alkali silicate or pozzolanic materials. This composite structure allows the system to benefit from fast setting (due to calcium sulphate) while the composite nature provides resistance to thaumasite formation and maintains mechanical performance through the synergistic interaction of components.
3Productivity
If cementitious preparation is used in continuous processes with fast setting time, then productivity is increased, but dimensional stability is reduced due to swelling from thaumasite formation
Solution Approach 1:
The alkali silicate material or pozzolanic material acts as a mediator that prevents dimensional instability in continuous manufacturing processes. These materials interfere with the thaumasite formation mechanism, thereby maintaining dimensional stability while allowing the fast setting time required for continuous production to be achieved.
Solution Approach 2:
The patent modifies the chemical parameters of the cementitious composition by adding alkali silicate or pozzolanic materials. This parameter change alters the chemical reactions occurring during setting, specifically preventing the formation of thaumasite crystals that cause swelling. The modified composition maintains fast setting for productivity while achieving dimensional stability through changed chemical pathways.
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 use of the reactive binder mixture significantly reduces the formation of thaumasite crystals, resulting in cementitious articles that are more durable and dimensionally stable, especially in wet and cold environments, with improved water resistance and reduced carbon footprint.
Implementation Method 1
Reactions between the formed gypsum, also known as calcium sulphate dihydrate, and cement can however result, under humid conditions, in the formation of thaumasite crystals
Implementation Method 2
The setting time may vary depending on the components of the cementitious preparation or the chosen manufacturing process
Implementation Method 3
The manufacturing process of cementitious articles such as boards includes a step during which a cementitious preparation sets, thus forming the cementitious article
Data Source
AI summary
A reactive binder mixture includes, based on the total dry matter, 10 to 40 wt. % hydraulic cement, 40 to 80 wt. % calcium sulphate hemihydrate, and 1 to 35 wt. % silica source material including an alkali silicate material.