Concrete Slab Cost Guide
A concrete slab may be used by a homeowner as a foundation for erecting a shed, storage building or garage. Concrete slabs can also be used as a base for putting up a temporary swimming pool or a place to set up a picnic table or a grill. They can also be used as a recreational area for playing basketball. Large concrete slabs can act as the surface to stabilize a parked mobile home. No matter how a homeowner plans to use a concrete slab, the construction process is the same. Before undertaking the construction of a concrete slab, there are some facts homeowners need to consider.
- The average minimum cost per square foot of concrete slab is $1.36.
- The average maximum cost per square foot of concrete slab is $1.88.
In addition to the concrete used to form the slab, homeowners will face some additional costs associated with this type of residential project. Supplies such as the wood used to create the forms for the slab add an average of $3.75 per finished square foot, which is much more than the cost of the main material. The high supplies cost is due to the rebar used to add strength to the slab as well as the gravel that is laid underneath the slab for stability and enhanced drainage. Installation costs for a concrete slab average $65.50 per hour. If the terrain where the slab is to be laid has poor soil or an incline of more than 5%, this can add to the materials and labor costs. A standard concrete slab is 6" thick. Homeowners that require a thicker slab will pay more for the materials used for the project. Adding a design to the concrete, coloring the concrete or creating an unusually shaped concrete slab also add to the costs of the project.
The concrete used to make slabs is available in three different grades. The grading of concrete is based upon the strength measured in pounds per square inch (psi). Grades of concrete are achieved by adjusting the cement, water and aggregate mixture and by including different types of aggregates. The three primary grades of concrete include:
- Basic Concrete: Contractors identify this as M10, M15 and M20 concrete. This grade is the lowest strength of concrete used to make concrete slabs.
- Commercial Grade Concrete: This is the most common grade of concrete used to build concrete slabs. Contractor designations include M25, M30, M35, M40, M45, M50 and M55.
- High-Strength Concrete: This type of concrete is used in applications that must support a heavy structure. It includes contractor designations M60, M65, M70, M75 and M80.
Concrete is available in many sub-types and styles. These subtypes are based upon the aggregates used in the mix of cement, sand and water. The sub-types of concrete used in making slabs include:
- Regular Concrete: This mixture consists of Portland cement, water and sand. The sand is the aggregate. The strength of this type of concrete ranges from 1,400 psi to 5,800 psi.
- High-Strength Concrete: To make this form of concrete, the water to cement ratio is lowered to less than .35. Sand is used as the aggregate and silica fume is added for additional strength. Its strength is greater than 5,800 psi.
- Stamped Concrete: This is regular-strength concrete that has floor hardeners and pigments impregnated on the surface. Stampers create a pattern on the surface to make the slab resemble stone, brick or other materials. After stamping, the contractor seals the surface for added wear resistance.
- High-Performance Concrete: This is high-strength concrete with additional chemicals added for wear resistance and durability. The unique feature of this concrete is its fast curing time, which allows the concrete slab to be used sooner than when the slab is made of standard concrete.
- Micro-Reinforced Ultra-Performance Concrete: This concrete is high-strength and has steel fibers added to the mix. The steel fibers add to the durability and strength of the finished slab. A concrete slab made of this type of concrete exhibits high resistance to wind, water and chemicals along with high ductility and high energy absorption. It is ideal for making a concrete slab in earthquake-prone areas.
- Self-Consolidating Concrete: This concrete is growing in popularity and currently accounts for over 75 percent of precast concrete sales in the U.S. It does not require compaction and can save more than 50% on labor costs. It is used in the creation of industrial concrete slabs and other construction projects.
- Limecrete: In this type of concrete, lime replaces the Portland cement as the binder. It is an environmentally-friendly choice as the lime would otherwise be sent to a landfill. It hardens faster yet offers the same strength as standard concrete.
- Pervious Concrete: This is concrete without sand. Instead, only larger aggregates are used. This allows water to flow through the concrete slab and into the ground. It is ideal for concrete slabs to be placed in areas with high humidity and heavy amounts of precipitation.
- Glass Concrete: Recycled glass is used as the large aggregate. This type of concrete makes aesthetically pleasing concrete slabs for use under a picnic table or other recreational area. The glass adds strength and beauty to the final product.
- Asphalt Concrete: A bituminous binder is used in place of the Portland cement to hold together the aggregates.
- Rapid-Strength Concrete: This form of concrete achieves its full strength within a few hours of being poured. This allows the concrete slab to be used within a day of its creation.
- Polymer Concrete: Polymers added to the concrete mix allow for hardening within four hours to strengths of up to 5,000 psi.
- Geopolymer Concrete: Slabs made of this type of concrete feature a binder that is made of industrial waste including fly ash, slurry and slag. This type of concrete slab offers a high resistance to chemicals and heat and is environmentally friendly.
Concrete for slabs is usually mixed on-site. Most concrete contractors have a preferred type of cement mix. The sources of the aggregates used in the concrete can vary but are often derived from local quarries and sources of industrial waste.
Advantages & Disadvantages of Concrete Slabs
Concrete is inexpensive to manufacture. Concrete slabs offer a high amount of compressive strength so that heavy structures or items can be placed upon it without risk of buckling or cracking. It is highly resistant to corrosion and weathering. Concrete slabs can be created in nearly any shape or size. Concrete slabs gain in strength as they age. While there are many reasons to select concrete as the material of choice for laying a slab, there are some disadvantages to using this material. Concrete is prone to cracks in areas that experience freeze and thaw cycles. Unless concrete is reinforced with steel bars or mesh, it has a low tensile strength. Fresh concrete is prone to sinking as it dries. Expansion joints must be added into concrete to avoid cracking due to thermal cycles. Discoloration of concrete can result after years of exposure to moisture, especially in high-salt environments. Grease, oils, acids and salts also cause discoloration of concrete slabs.
Last updated on May 23, 2016
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