Concrete leveling is a procedure that attempts to correct an uneven concrete surface by altering the foundation that the surface sits upon. It is a cheaper alternative to having replacement concrete poured, and commonly performed at small businesses and private homes. In 1977, the term concrete leveling was coined by Randall Greene in Cleveland, Ohio. http://www.greenconcreteleveling.com/home He created the phrase to convey his company's ability to both raise and lower concrete to correct the insufficent grade of a slab. http://www.greenconcreteleveling.com/concrete_repair_services

Problem cause

Sidewalks, patios and garage floors are most often made of concrete

Concrete

Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

. When the concrete is a few inches thick and poured on insufficient foundation and/or without steel reinforcement it may crack and subside. Sometimes water runoff from rain or flood can wash away dirt upon which the concrete slab is resting, leading to cracking and subsiding. In addition, tree roots and other subsurface obstructions can make concrete slabs rise, so that they no longer align to the adjacent slabs.

Slabjacking

Slabjacking can both raise the old cracked slab back to its original position and create a new foundation of cement

Cement

In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...

 mortar

Mortar (masonry)

Mortar is a workable paste used to bind construction blocks together and fill the gaps between them. The blocks may be stone, brick, cinder blocks, etc. Mortar becomes hard when it sets, resulting in a rigid aggregate structure. Modern mortars are typically made from a mixture of sand, a binder...

 or sand mix by injecting the mortar under the slab through a hole, under pressure. The viscosity

Viscosity

Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

 of the mortar will keep it from flowing back through the hole until it sets.

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. Generally a portable pump

Pump

A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...

 is carried to the location of the block to be raised. A hole of up to 3 inches in diameter

Diameter

In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...

 is drilled into the block. Varying combinations of soil

Soil

Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...

, sand

Sand

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...

, cement, or other materials, are mixed and then injected under the sunken concrete block, causing it to rise.

Problems associated with slabjacking involve: containment of the mess caused by excess mud

Mud

Mud is a mixture of water and some combination of soil, silt, and clay. Ancient mud deposits harden over geological time to form sedimentary rock such as shale or mudstone . When geological deposits of mud are formed in estuaries the resultant layers are termed bay muds...

 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 methods use smaller holes to avoid weakening the concrete slab, or raising the blocks too quickly. A highly dense crushed limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

 is sometimes mixed with moderate amounts of cement

Cement

In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...

, and can be pumped slowly and safely through hoses that are connected directly to the pumping truck, with little or no destruction of landscaping

Landscaping

Landscaping refers to any activity that modifies the visible features of an area of land, including:# living elements, such as flora or fauna; or what is commonly referred to as gardening, the art and craft of growing plants with a goal of creating a beautiful environment within the landscape.#...

or surrounding structures.

This site shows before and after pictures of slabjacking. http://www.greenconcreteleveling.com/photos__testimonials

Closed cell polymer foam

Foam leveling utilizes two part closed cell polymer expanding foam 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.