Joint-Free Concrete Slab Post-Tensioning Shrinkage Control
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Solution Overview
Problem
Current methods for placing concrete slabs, particularly exposed and polished concrete floors, face challenges with cracking, curling, and maintenance issues due to the need for control joints, which detract from aesthetics and functionality.
Innovation Solution
The method involves preparing a base with a flat surface, overlaying barriers, and placing a fresh concrete mixture without forming control joints, using post-tensioning cables and a high-cement, high-fiber concrete mix with large aggregates to reduce shrinkage and cracking, and sealing the side edges with a vapor barrier to minimize moisture vapor transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If control joints are formed in concrete slabs to mitigate cracking and curling, then the structural integrity is improved, but the aesthetic appearance and maintenance requirements deteriorate
Solution Approach 1:
The patent removes control joints entirely from the concrete slab system by using post-tensioning cables to apply compressive forces that counteract tensile stresses during curing, thereby eliminating the need for joints while maintaining structural integrity and achieving continuous aesthetic surfaces
Solution Approach 2:
The patent changes the stress state parameter by applying compressive forces through post-tensioning cables, which transforms the concrete from a tensile-stressed state (prone to cracking) to a compressive-stressed state (resistant to cracking), allowing joint-free construction
2Ease of manufacture
If control joints are formed and filled with caulk or other materials to smooth the surface, then the aesthetic appearance is improved, but maintenance requirements and potential aesthetic issues worsen
Solution Approach 1:
The patent eliminates control joints and their associated filling materials by preventing cracks through post-tensioning, thereby removing the maintenance burden of joint sealing while maintaining surface smoothness and aesthetic continuity
3Strength
If conventional concrete mix designs are used, then the concrete achieves adequate compressive strength, but shrinkage and low tensile strength cause cracking and curling
Solution Approach 1:
The patent modifies the stress state parameter by applying compressive forces through post-tensioning cables, which compensates for low tensile strength and shrinkage effects, allowing conventional concrete mixes to achieve crack-free performance
Solution Approach 2:
The patent creates a composite system combining concrete with post-tensioning cables, where the cables provide tensile reinforcement and compressive pre-stress, compensating for the concrete's low tensile strength and shrinkage tendencies
4Device complexity
If the concrete slab is allowed to cure without barriers, then the curing process is simplified, but moisture vapor transmission from the surrounding environment increases
Solution Approach 1:
The patent introduces vapor barriers as intermediary layers between the concrete slab and the environment, which mediate moisture vapor transmission by providing a protective barrier while allowing the curing process to proceed
Data Source
AI summary
Method of forming a concrete slab to reduce or eliminate control joints includes preparing a substantially flat base, overlaying one or more barriers on top of the base, placing a concrete mixture on top of the barrier(s) and base to form a concrete slab, and allowing the concrete to cure without forming control joints. The base is prepared with a flatness of about ±¼ inch over 10 feet. A side edge is prepared along a periphery of the concrete slab by extending a vapor barrier from a bottom surface of the slab up the side edge toward a top surface of the slab and covering the side edge. A plurality of post-tensioning cables are positioned to extend through the slab and configured to compress and assist in controlling accelerated displacement of the concrete slab during curing and shrinkage. The concrete slab is formed of an evenly gradated and low slump concrete having high fiber content, minimized cement content, and maximized size of large aggregate.