What is Rubblizing In Constructions?
What is Rubblizing In Construction?
Rubblization is a method used in construction and engineering to save time and reduce transportation costs by breaking down concrete into rubble on site rather than transporting it elsewhere. It is used for two main purposes: to create a foundation for new roads and to dismantle nuclear power plants.
To refurbish a worn-out Portland cement concrete road, it can be rubblized, which involves breaking it up into small pieces with specialized equipment. This rubble can then be used as a base for a new layer of pavement, typically asphalt concrete.
This method is more cost-effective than disposing of the old pavement and purchasing new base materials, and it also results in a smoother road surface compared to simply laying asphalt on top of the unbroken concrete.
Rubblization has been used in road construction since the late 1990s and has also been applied to concrete airport runways. The benefits of rubblizing a concrete surface for road rehabilitation compared to other methods, such as crack and seat or removal and replacement, are numerous.
Rubblizing is 52% cheaper than removing and replacing the concrete, it greatly reduces the time needed for road reconstruction, resulting in significant cost savings for contractors and minimal disruption to the traveling public, and it is an environmentally friendly “green” process.
Rubblization is a technique used in the decommissioning of nuclear power plants that involves the demolition of above-ground structures, including the concrete containment building, into rubble and burying it in the foundation below ground.
After the equipment is removed and the surfaces are decontaminated, the site is covered, regraded, and landscaped to allow for unrestricted use. Rubblization allows for the cost-effective decommissioning of nuclear power plants by eliminating the need to transport the demolished building pieces to another location.
The Theory Behind Rubblization
Rubblization is a method of breaking down existing concrete pavement into small fragments, typically ranging in size from sand to pieces approximately 4 to 8 inches in width.
This technique was developed as a way to address reflective cracking, which is a type of cracking that occurs in the asphalt overlay above the joints of a concrete pavement.
Reflective cracking occurs because the asphalt overlay is not strong enough to withstand the temperature fluctuations that the underlying concrete experiences on a daily and seasonal basis.
The asphalt overlay on top of an unrubblized concrete pavement primarily serves as a riding surface and does not contribute significantly to the overall structural integrity of the pavement. The concrete below remains the primary structural component.
As the concrete slabs expand and contract due to temperature fluctuations, the joints open and close. The asphalt, however, is not strong enough to handle these movements and can crack under the resulting shear stresses.
“In an effort to prevent reflective cracking, two methods called Crack & Seat and Break & Seat were developed to decrease the length of the slabs. It was thought that by reducing the size of the slabs, the movement at the joints and cracks would be minimized and reflective cracking would not occur. However, these techniques ultimately proved unsuccessful.
Despite the reduced movement of the smaller slabs, cracks still eventually appeared through the asphalt overlay.
As a result, rubblization, which involves drastically reducing the slab length, was implemented as a solution. It completely destroys the concrete’s slab action by breaking it down into crushed-stone sized fragments.
It is an attempt to turn the existing pavement into base course. However, there is one notable shortcoming to this analogy: a rubblized pavement has no gradation or density control. Specifications for base courses require both gradation and density control.
In conclusion, rubblization (as well as Crack & Seat and Break & Seat) and an asphalt overlay does not address why an asphalt overlay cracks. Instead, these procedures destroy the concrete slabs so that the asphalt does not crack.
However, this also destroys the main structural component of the pavement system and reduces its load carrying capacity.
Benefits Of Rubblizing
Rubblizing involves breaking up a concrete pavement into small pieces, and it has several potential benefits.
1. One benefit is that it allows for the reuse of existing materials, which can save on resources and transportation costs.
2. Rubblizing can also be a faster way to prepare a pavement for an overlay compared to patching.
3. Additionally, it can minimize disruptions to traffic flow and reduce the risk of reflective cracking in overlays.
4. Rubblizing is often used as a rehabilitation option for concrete pavements that have significant deterioration and require extensive patching, a structural overlay, or reconstruction.
Limitations of Rubblizing
Sometimes, when a road is being broken up and repaved (a process called rubblizing), there may be certain areas where the underlying material is too weak to handle the weight of the broken slab.
These weak spots are typically found in low-lying areas that are prone to standing water or have high water tables, as well as areas with wet clay soil containing silt.
If the resonant breaker leaves tire ruts of 2 inches or more while working on an area, it may be an indication that the area is not suitable and should be replaced.
On the other hand, if the resonant breaker is causing the slab to pump but not creating significant tire ruts, it suggests that the slab is strong enough to support traffic loads and the edge drains will be effective in draining the base and subgrade.
The weight of the resonant breaker is sufficient to test the strength of the slab without the need for a rubber tired proof roller. A heavy rubber-tired roller has the potential to cause damage to the base and interlocked rubblized concrete.
It is recommended to use a smooth drum vibratory roller to settle the surface fines into the cracks, increase the modulus of the broken concrete, fill in any voids in the base, and create a smooth surface for paving.
One pass of a water truck before the final vibratory pass can also improve the surface for paving. Although some states specify that rubblized concrete needs to be “compacted,” it is not possible or necessary to do so as the slab is only fractured, not pulverized. Using a vibratory roller can smooth and settle the surface, but true compaction is not necessary.