Most of the soil floor is not reinforced, or only nominal reinforcement measures are taken to control the crack width. Reinforcing steel bars placed at the top or top of the floor slab can limit the random crack width due to concrete shrinkage, temperature stress, foundation settlement, external loads, and other problems. This type of reinforcement is commonly referred to as shrinkage and temperature enhancement devices.
Shrinkage and temperature enhancement are different from structural reinforcement. Structural reinforcement is usually placed at the bottom of the concrete slab to enhance the load bearing capacity of the floor slab. Most of the soil-bearing structural floors are provided with upper and lower reinforcements at the same time, while controlling the crack width and enhancing the bearing capacity. Due to the construction feasibility and cost of the double-layer reinforcement method, the soil-bearing structure floor is not as common as the non-structure floor.
Basic principle
If the concrete slab is laid on a high quality base and ensures good support, while using low shrinkage concrete material, the joint spacing is set at 4.5 m or less and installed correctly, there is generally no need for reinforcement. In general, there is almost no cracking at random or non-seam areas. If random cracks do occur, the crack width should also be kept small due to the small joint spacing and the low shrinkage of the concrete material, thus avoiding the problem of subsequent repair or maintenance.
When concrete slabs are laid on low-quality bases with more problems, there is a risk of uneven support. When ordinary or high-shrinkage concrete materials or joint spacing exceeds 4.5 m, it is necessary to take reinforcement measures to limit the occurrence of Crack width. When the crack width develops and increases to about 0.9 mm, the load transfer effect of the aggregate locking disappears, causing vertical displacement cracking or "destruction" of the concrete slab.
Once this happens, the edges of the crack are exposed, and blasting is likely to occur; and the concrete slab is subject to wheel compaction, especially when high-level forklifts with hard wheels are crushed. Once the blasting phenomenon begins, the crack width of the surface will increase, and the damage of the concrete slab along the crack will deteriorate rapidly.
Shrinkage and temperature enhancement methods are required where shrinkage joints are not allowed on site and are not installed. Sometimes, this method is also known as continuous enhancement or seamless flooring, and a large number of closely spaced (90-180 cm) small cracks are allowed on the floor panel.
Crack control method
Generally, there are two methods for controlling the crack in the soil floor:
(1) controlling the location of the crack by installing a shrinkage joint (the crack width cannot be controlled),
(2) controlling the crack width by installing a reinforcement device (the crack position cannot be controlled).
Using Method 1, we can control the cracking position of the concrete slab; the width of the shrink joint or the crack in the joint is largely controlled by the joint spacing and concrete shrinkage. As the seam spacing and concrete shrinkage increase, the seam width also increases. Similar to the crack, if the seam width is close to about 0.9 mm, the efficiency of locking and transferring the aggregate between the aggregates and avoiding vertical displacement between the seams is greatly reduced. In view of this, many designers use load-conducting designs such as force-transmitting rods, force-transmitting sheets, or continuity-enhancing devices at the shrink seam position to ensure good load transfer and limit vertical displacement between seams.
Using Method 2, we allow random cracking of the concrete slab, but with reinforced steel or welded mesh to control the crack width. In general, this method is not used when setting a shrink seam. Cracking occurs randomly, forming numerous numerous intertwined small cracks. Due to the appearance considerations, this type of crack control method needs to communicate with the owner in advance.
