Slab tips - Pt 2 - how to build driveways, patios, house slabs, and roads - reinforcing and slope
Introduction and Importance of Reinforcement in Slabs
In this section, Tyler Light introduces himself and discusses the importance of reinforcement in slabs to prevent cracks and faulting.
Why do we put reinforcement inside slabs?
- Reinforcement helps keep cracks small and prevents slabs from faulting.
- Faulting occurs when one side of the slab drops compared to another, leading to potential hazards and an unsightly appearance.
Overview of Slabs and Cracks
This section provides an overview of slabs and explains why it is crucial to control crack size.
How do cracks affect slabs?
- Large cracks can cause faulting, which poses safety risks.
- Faulted slabs can lead to tripping hazards, damage to vehicles, and an unappealing appearance.
Methods of Reinforcing Slabs
This section explores different methods for reinforcing slabs, including rebar, wire mesh, rebar mats, and fibers.
Rebar
- Rebar is typically tied in mats or a crossing pattern using chairs to ensure proper placement.
- A common practice is using 3/8 inch diameter bars at 18 inches on center for slabs on grade.
Wire Mesh and Rebar Mats
- Wire mesh and rebar mats are alternatives to traditional rebar placement.
- They are pre-welded or pre-fixed together for ease of installation.
- Wire mesh is less expensive but not as strong or stiff as rebar mats.
Fibers
- Fibers are materials added to fresh concrete during mixing.
- They help keep cracks small by dispersing throughout the concrete matrix.
- Fiber-reinforced concrete can significantly reduce crack sizes by more than 50%.
Can Fibers Replace Rebar?
This section discusses the possibility of using fibers as a replacement for rebar in slabs.
- Macro synthetic fibers can be used instead of mesh, typically at a rate of four pounds per cubic yard.
- The use of fibers as a complete replacement for rebar depends on the structural requirements and specific project needs.
- In heavy-use industrial slabs, five to seven pounds per cubic yard of macro synthetic fibers without rebar have shown excellent performance.
Design Considerations for Re-entrant Corners
This section focuses on design considerations for re-entrant corners in slabs.
What are re-entrant corners?
- Re-entrant corners are corners located on the inside of a slab.
- Examples include holes, penetrating columns, and internal corners.
Importance of addressing re-entrant corners
- Neglecting to address these corners can lead to issues such as cracking and structural problems.
The transcript ends here.
Common Problems with Slabs
In this section, the speaker discusses common problems that can occur with slabs in construction projects.
Cracked Slab and Re-entrant Corner
- A cracked slab can be caused by various factors.
- One problem area is the re-entrant corner, which is a corner on the inside of the slab.
- Reinforcement is necessary to prevent cracks in these areas.
Preventing Cracks in Re-entrant Corners
- To prevent cracks in re-entrant corners, two additional rebars should be tied out at the corner.
- These rebars should be placed at the halfway point or upper third of the slab to help keep cracks small.
Sloping Slabs Away from Structures
- It is important to ensure that slabs slope away from any adjacent structures.
- Flat slabs can lead to water accumulation and potential damage to buildings.
- A slope of greater than 2% is recommended for effective water drainage.
Calculating Slope
- The slope of a slab can be calculated using the formula: change in height over change in length times 100.
- For example, if there is a half-inch change in height over 10 feet in length, the calculated slope would be 2%.
In summary, reinforcement is essential for preventing cracks in slabs. Pay attention to re-entrant corners and use proper reinforcement techniques. Additionally, ensure that slabs are sloped away from structures to control water drainage effectively.