Lost Formwork Concrete-Steel Connection Gap Filling
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Solution Overview
Problem
Existing concrete-steel connections in lost formwork often develop gaps and cavities due to concrete shrinkage, leading to stress peaks and poor sealing, which existing methods struggle to reliably eliminate or prevent.
Innovation Solution
A two-component filling material system is applied between the steel formwork and concrete, comprising a volume-increasing material and an activator, which expands and fills gaps after the concrete has hardened, providing a force-transmitting and sealing connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If concrete is poured behind steel formwork to create lost formwork structures, then permanent formwork is achieved without removal, but shrinkage cracks and voids form between the concrete and steel during hardening
Solution Approach 1:
A bonding resin is applied to the steel formwork surface before concrete pouring to prevent shrinkage cracks and voids from forming in the first place. This preliminary protective action addresses the root cause of connection integrity issues during the concrete hardening process.
Solution Approach 2:
A bonding resin layer is introduced as an intermediary substance between the steel formwork and concrete. This intermediate layer compensates for volume differences during shrinkage and maintains continuous contact, preventing void formation and ensuring reliable connection throughout the hardening process.
2Reliability
If drilling and filling with concrete milk or resin is performed to repair cavities, then some voids are filled, but complete filling is impossible due to difficult access and limited pressure
Solution Approach 1:
The expanding foam agent automatically fills cavities itself through chemical expansion, eliminating the need for external drilling and injection operations. The material self-propagates into difficult-to-access voids without requiring mechanical pressure or human intervention, achieving complete filling where traditional methods fail.
Solution Approach 2:
A foam agent is introduced that undergoes phase transition from liquid to gas/expanded foam state within the cavities. This phase change enables the material to automatically expand and fill all void spaces, including those difficult to access, without requiring external pressure application.
3Reliability
If bonding resin is applied before concrete pouring, then adhesion is improved, but the resin does not work during the 28-day primary curing time and cannot prevent cracking
Solution Approach 1:
The protective system operates continuously throughout the entire 28-day curing period. The expanding foam agent provides ongoing protection during concrete hardening, maintaining cavity-free contact between steel and concrete throughout the full duration when cracking is most likely to occur, rather than only initially or after curing.
Solution Approach 2:
The expanding foam agent is applied in advance before concrete pouring and remains active throughout the curing process. This preliminary and sustained action prevents crack formation during the critical 28-day period when concrete is most vulnerable, extending protection beyond what traditional pre-applied resins provide.
4Quantity of substance
If conventional filling methods are used with limited pressure, then some cavities are filled, but complete penetration and filling of all cavities cannot be achieved
Solution Approach 1:
The foam agent utilizes phase transition from liquid to expanded foam state to achieve filling without external pressure. The chemical expansion process generates internal volume increase that automatically penetrates and fills all cavity spaces, eliminating the need for high-pressure injection equipment and achieving complete material penetration.
Solution Approach 2:
The filling material performs self-filling through chemical expansion, generating its own filling force without requiring external pressure application. This self-service mechanism enables complete cavity penetration even in difficult-to-access locations where pressured injection cannot reach.
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
This solution minimizes stresses between steel and concrete, ensures a gap-free connection, and prevents liquid ingress, thereby enhancing structural integrity and durability against corrosion and frost.
Implementation Method 1
a material that, after excitation, increases in volume... the filler material (4.1) expands and penetrates into cracks and/or voids and fills them
Data Source
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Figure 3~4
Figure 5
AI summary
The invention relates to a method for producing a concrete-steel connection in which formwork material made of steel is backfilled with concrete to form a force-absorbing and/or transferring structure, wherein an intermediate layer of a filler material is arranged between the formwork material made of steel, which is referred to as lost formwork due to its remaining in the structure to be produced after the concrete has hardened, and the concrete to be backfilled.This system is characterized by the fact that the filling material is applied as a two-component system. The first component comprises a material that expands in volume after excitation, and the second component comprises an activator to excite the material of the first component. This activator is activated, i.e., brought to reaction, 20 to 40 days after the steel formwork material has been backfilled with concrete. As a result of this activation, the filling material expands and penetrates and at least partially fills any cracks and/or voids that have formed between the steel formwork material and the backfilled concrete since the concrete was poured.