Concrete leveling
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Concrete leveling is a procedure that attempts to correct uneven concrete surfaces by altering the foundation that the surface sits upon. It is a cheaper alternative to having unlevel concrete removed and repoured. The phrase "concrete leveling" was originally coined by Randall Greene of the R. Greene Concrete Leveling Co., Inc. in 1977. Also referred to as mudjacking, slabjacking, or pressure grouting, this service is commonly performed at small businesses and private homes.
Sidewalks, patios and garage floors are most often made of concrete. When the concrete is a few inches thick and poured on insufficient foundation and/or without steel reinforcement it may crack and subside. Sometime water run off from rain or flood can wash away dirt upon which the concrete slab is resting leading to cracking and subsiding. When that happens the concrete can be demolished and removed and then re-built, however a method called mudjacking or slabjacking can both raise the old cracked slab back to its original position and create a new foundation of cement mortar or sand mix by injecting the mortar under the slab through a hole, under pressure. The viscosity of the mortar will keep it from flowing back through the hole until it sets. For a diagram see [1]
Accounts of raising large concrete slabs through the use of hydraulic pressure go back almost a century. Mudjacking or slabjacking has been in common use for about 50 years. HMI, or Hydraulic Mudjacking equipment was the first equipment used for residential concrete raising. Refinement of the process to its current state occurred about 20 years ago when Grover Miller an inventor from Peninsula, Ohio, began working on A-1’s patented Self-contained pumping trucks, which utilize a highly-dense crushed limestone material, sometimes mixed with Portland Cement.
Generally in Mudjacking or Slabjacking a portable pump is carried to the location of the block to be raised. A hole of up to 3 inches in diameter is drilled into the block. Varying combinations of soil, sand, cement, or other materials, are mixed and then injected under the sunken concrete block, causing it to rise.
Problems associated with Mudjacking involve: containment of the mess caused by excess mud or cementeous material in the area to be raised; drilling of large holes that can weaken the block, and allow material to flow too quickly causing cracking of the slabs. HMI is not conducive to filling large void areas.
Modern Concrete Leveling techniques utilize smaller holes to avoid weakening the concrete slab, or raising the blocks too quickly. A highly dense crushed limestone is sometimes mixed with moderate amounts of cement, and can be pumped slowly and safely through hoses that are connected directly to the pumping truck, with little or no destruction of landscaping or surrounding structures.
External links
[2] Generally regarded as the first true concrete leveler, Green Concrete Leveling Co., Inc. was established in 1977 under the name R. Greene Concrete Leveling Co., Inc. While other mudjacking companies can raise concrete to correct drainage problems or trip hazards, only the Green Company can both raise and lower concrete. Often, concrete sidewalks and driveway blocks are pushed upwards by tree roots and other forces. To restore its original position, the concrete must be lowered. This is what sets older, more experienced companies apart and allows this company to offer an unmatched five year warrantee. This corporation is now offering franchises nationally.
[3] The newest method (developed by URETEK) in concrete leveling utilizes two part closed cell polymer expanding foam which is injected through a hole less than one inch in diameter, typically 5/8". Although the material injected at a higher psi rate than traditional cementious grouts the pressure is not what causes the lifting. The expansion of the injected material below the slab surface performs the actual lifting action. Material injected below a slab to be lifted will first find weak soils, expanding into them in such a manner as to consolidate and cause sub-soils to become more dense and fill any voids below the slab. One inherent property of expanding foams is that they will follow the path of least resistance, expanding in all directions. Another inherent property includes reaching a hydro-insensitive or hydrophobic state when cured with 100% cure times as little as 30 minutes. Closed cell polymer foams offer benefits which go beyond the goal of leveling hard surfaces. They will not retain moisture, which in northern climates can cause frost heaving. They are not subject to erosion once in place. Their fast cure time allows for immediate use when application is complete. Their light weight, 3 to 8 lbs. per cubic ft. vs. 100 to 120 lbs. per cubic ft. for cementious grout will not cause further settlement. Foams will retain their cured shape and volume indefinitely reducing the possibility of new voids forming below grade to nearly zero unless acted upon by some outside cause. Some closed cell polymer foams have baseline lifting capabilities of 6,000 lbs per sq. ft. and leveling procedures have been performed in which loads as high as 125 tons have been lifted and stabilized in a surface area of less than 900 sq. ft.
Sources
Green Concrete Leveling Corporate Website: [4]