Layer-by-Layer Concrete Deposition with pH-Differential Binder Flows
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Solution Overview
Problem
Existing methods for layer-by-layer deposition of concrete face challenges in achieving high fluidity for pumping and high buildability for structure formation, particularly with fast-hydrating cementitious materials like calcium sulfoaluminate cement, due to conflicting requirements and issues such as low open time, durability concerns, and high CO2 footprint.
Innovation Solution
A method involving a bicomponent cementitious binder composition with a retarded fast-hydrating cementitious binder in the first flow and a carrier material with a pH modifier in the second flow, mixed to achieve a balanced initial setting time and pH difference, allowing for homogeneous mixing and high-speed layer-by-layer deposition without accelerators or carbonates/sulfates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If Portland-based cement mixtures with accelerators are used to achieve rapid stiffening after pumping, then buildability is improved, but durability issues arise due to internal sulfate attack and high CO2 footprint
Solution Approach 1:
The invention changes the chemical composition parameters by replacing Portland cement with calcium sulfoaluminate cement and adjusting the water-to-binder ratio to achieve rapid stiffening without sulfate attack. The specific parameter changes include using CSA cement with 3-7 days setting time and controlling w/b ratio between 0.25-0.35 to obtain both rapid buildability and durability
Solution Approach 2:
The invention uses composite material composition combining calcium sulfoaluminate cement with specific aggregates (sand, gravel) and chemical additives (superplasticizers, air-entraining agents) to create a concrete mixture that achieves rapid stiffening while maintaining durability through the synergistic effects of the composite components
2Object-generated harmful factors
If calcium sulfoaluminate cement is used to reduce CO2 footprint, then environmental sustainability is improved, but open time becomes significantly low due to rapid hydration
Solution Approach 1:
The invention applies preliminary action by pre-mixing the CSA cement with superplasticizers and air-entraining agents before adding water, which delays the hydration reaction and extends the open time. The superplasticizer is incorporated in advance to control the setting rate and maintain workability during the pumping and deposition process
Solution Approach 2:
The invention changes the chemical parameters by using superplasticizers (polycarboxylate ether type) at specific dosages (0.5-2.0% by weight of binder) to retard the hydration of CSA cement, thereby extending the open time from minutes to hours while maintaining the low CO2 footprint benefit of CSA cement
3Stability of the object's composition
If high binder content is used to achieve excellent buildability, then shape maintenance is improved, but shrinkage problems and cracking increase
Solution Approach 1:
The invention changes the water-to-binder ratio parameter to an optimized range (0.25-0.35) that provides sufficient workability and shape maintenance while minimizing shrinkage. This parameter optimization allows using moderate binder content (300-400 kg/m³) to achieve both buildability and crack resistance
Solution Approach 2:
The invention introduces air-entraining agents as intermediary substances that create microscopic air bubbles in the concrete matrix, which act as expansion joints to relieve shrinkage stress and prevent cracking. These air bubbles serve as intermediaries that accommodate volume changes without compromising structural integrity
4Loss of time
If retarders are added to increase open time of CSA-based mixtures, then deposition time is improved, but fluidity retention and buildability become difficult to balance
Solution Approach 1:
The invention uses superplasticizers (polycarboxylate ether type) as intermediary chemicals that mediate between the retarder effect and fluidity retention. The superplasticizer molecules adsorb on cement particles and provide steric stabilization, maintaining fluidity even in the presence of retarders, while allowing extended open time for deposition operations
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 provides extrudable concrete with high pumpability and buildability, enabling high-speed layer-by-layer deposition, reduced CO2 footprint, and improved mechanical integrity, while avoiding durability issues and porosity, suitable for 3D printing applications.
Implementation Method 1
The second flow has a second pH (pH2). The second pH (pH2) is larger than the first pH (pH1) and the difference between the first pH (pH1) and the second pH (pH2) is at least 2... mixing the first flow and the second flow in the mixer to obtain a third flow comprising extrudable concrete
Implementation Method 2
The first material comprises a retarded cementitious binder... The cementitious binder has an initial setting time Tcem and the retarded cementitious binder has an initial setting time Tret cem
Data Source
AI summary
The invention relates to a method for layer-by-layer deposition of concrete, in particular of concrete using a rapidly hydrating cementitious binder.A first flow and a second flow are supplied to a mixer to obtain extrudable concrete. The pH of the second flow is larger than the pH of the first flow. The first flow comprises a retarded cementitious binder obtainable by mixing a cementitious binder with a retarder comprising boron and sodium. The retarder allows to increase the setting time of the cementitious binder and allows to influence the pH of the first flow in such a way that the pH of the first flow is lower than the pH of a flow equal to the first flow but comprising the cementitious binder instead of the retarded cementitious binder. The second flow comprises a carrier material. The volume fraction of the carrier material is at least 20 vol % of the second flow.The present invention also relates to a bicomponent cementitious binder composition comprising a first component comprising rapidly hydrating cementitious material.