concrete slab on grade

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Concrete Slab on Grade Reported by Sarah Jane S. Pahimnayan

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Page 1: Concrete Slab on Grade

Concrete Slab on GradeReported by

Sarah Jane S. Pahimnayan

Page 2: Concrete Slab on Grade

Concrete Slab on GradeSlab-on-grade foundations are concrete slabs poured

directly on the ground with

no space between the ground and

the concrete.

Page 3: Concrete Slab on Grade

Concrete Slab on Grade

On site concrete slab on grade construction

Page 4: Concrete Slab on Grade

Concrete Slab on Grade

This most often occurs in areas where the ground is not subject to freezing and therefore not likely to heave. This type of foundations are commonly used in areas with expansive clay soil. There are derivations of this where frost underneath the structure is controlled with foam insulation or hydronic (hot-water) heating systems incorporated into the slab to prevent the ground below from freezing. However, it is usually not typically economically favourable to use the slab-on-grade in very cold climates.

Page 5: Concrete Slab on Grade

Concrete Slab on Grade Slab-on-grade foundations are a structural engineering practice

whereby the concrete slab that is to serve as the foundation for the structure is formed from a mold set into the ground. The concrete is then placed into the mold, leaving no space between the ground and the structure. This type of construction is most often seen in warmer climates, where ground freezing and thawing is less of a concern and where there is no need for heat ducting underneath the floor.

While elevated structural slabs actually perform better on expansive clays, it is generally accepted by the engineering community that slab-on-grade foundations offer the greatest cost-to-performance ratio for tract homes. Elevated structural slabs are generally only found on custom homes or homes with basements.

Page 6: Concrete Slab on Grade

Advatages of Concrete Slab on Grade

relative inexpensive form of residential foundation

cheap and very sturdy when properly designed and constructed

helps obstruct termites from entering the house there are no hollow spaces or wood channels

leading from the ground to the structure (assuming wood siding, etc., is not carried all the way to the ground on the outer walls).

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Advantages of Concrete Slab on Grade

Example of termites found under paving.

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Advantages of Concrete Slab on Grade

all pipe penetrations are properly sealed with stainless steel wool or adequate caulk to prevent their passage.

Page 9: Concrete Slab on Grade

Advantages of Concrete Slab on Grade

It also reduces the amount of perimeter crack that is vulnerable to infestation making treatment easier in the event that termites do get into the house.

Page 10: Concrete Slab on Grade

Advantages of Concrete Slab on Grade

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Disdvantages of Concrete Slab on Grade

lack of access from below for utility linespotential for large heat losses where ground

temperatures fall significantly below the interior temperature

very low elevation that exposes the building to flood damage in even moderate rains

Remodelling or extending such a structure may also be more difficult

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Disdvantages of Concrete Slab on Grade

Flood damage Marikina, City

Page 13: Concrete Slab on Grade

Structural Characteristics

Page 14: Concrete Slab on Grade

Structural CharacteristicsSlab-on-grade design calls for a slab thickness

a minimum of 4" thickening to a minimum of 6" within about 16" of the perimeter for additional reinforcing steel to support exterior wall loads. If there is to be a interior bearing wall, the engineer will also call for this area to be thickened and more reinforcing to compensate for these loads.

Page 15: Concrete Slab on Grade

Structural Characteristics Perimeter footers and interior footers or rafts are typically

reinforced with steel bars called re bar. This adds tremendous strength to the concrete by compensating for the concretes poor tensile strength. By combining steel with concrete, you combine two incredibly strong materials in a way that compensates for the weak characteristics of each.

You will also see what is called WWF (welded wire fabric) also called as reinforcing in concrete but its true purpose is to distribute temperature changes in the concrete more evenly to prevent cracking, the proper term is controlling cracking. I say prevent cracking, but you will still have cracking in concrete, it is the nature of concrete to crack, so another step taken to minimize the effect of cracking is the process of placing control joints at specified intervals to guide the cracks to the bottom of the crack where they will not be seen and to minimize the travel of any one crack.

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Proper Construction / Curing

The key to a good slab-on-grade foundation that has been properly designed is to allow time to wet cure the concrete. Concrete is poured as liquid, but begins to harden immediately. It should not be built on for a minimum for seven days and you must take care that the temperatures are not too cold or too hot when you pour it. The benefits of proper curing are:

Page 17: Concrete Slab on Grade

Proper Construction / Curing

Increased strength gain Increased abrasion resistance on the surfaceLess permeable concrete with increased

resistance to chloride penetration and freeze/thaw damage

Increased resistance to early cracking-slabs gain strength before drying out and have more resistance to shrinkage forces.

Page 18: Concrete Slab on Grade

Proper Construction / Curing

Well in warm climates, it entails keeping the concrete damp for a minimum of 7 days. This is accomplished by spraying water on the slab every day (twice a day if needed) spraying the concrete and covering it with plastic sheeting to retain the water within or using some other medium (kept wet) such as sand, straw, or blankets to do this function for at least 7 days.

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On Plan Details

Page 20: Concrete Slab on Grade

On Plan Details

Page 21: Concrete Slab on Grade

On Plan Details

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On Plan Details

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References

http://en.wikipedia.org/wiki/Shallow_foundation#Slab-on-grade_foundation

http://EzineArticles.com/358700http://cadlibrary.comhttp://solardynamicsnc.comhttp://energysavers.gov

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Thank You For Listening ! ^_^