Housing Giants - September 24, 2008 - (Page 17)

the tensioning process is done incorrectly. The best way to ensure this doesn’t happen is to educate your construction teams on the best practices for designing and constructing posttension slabs. Otherwise, issues are likely to develop, leading to costly repairs and unhappy homeowners down the road. Some of the most common errors that cause post-tension slabs to crack are easy to prevent. Let’s look at three. concrete. There should be an even 2- to 4-inch gravel layer on top of the soil. It’s also important to ensure areas around beams are properly formed and areas where the slab thickness intentionally changes are gradual and smooth. Error no. 2: strEssing tHE tEndons too latE Tendons have to be stressed at a specific time during the curing stage. Stressing them too late allows the slab to advance significantly through the curing stage. At this point, the slab is too strong to allow the stressing operation to close any plastic cracks that opened up during curing. To prevent this problem, the stressing operation should start as soon as the concrete attains the proper strength. This strength is typically reached during the first 4 to 10 days of the curing stage. Anthony Grisolia, manager of Ibacos Homebuilding Quality Consulting in Pittsburgh, stresses watching weather. “It’s really important to take the weather conditions into consideration in order to properly time the stressing operation. You want to check the current weather, as well as keep an eye on weather in the coming days. With concrete, weather Error no. 1: inconsistEnt slab tHicknEss Making sure the slab is the proper thickness is very important. When the slab’s thickness varies, it will resist movement during the stressing operation, preventing cracks in the concrete from closing. One reason the thickness may vary is because the bearing surface hasn’t been properly leveled or compacted. When the bearing surface is uneven, it makes the bottom of the slab uneven, preventing the stressing operation from moving the slab smoothly across the ground to close any cracks that have formed. To prevent this issue, it’s best to properly level and compact the bearing soil and gravel layer prior to placing www.Housinggiants.com 9.24.08.Housing giants 17 http://jobsite.buildiq.com/articles/risk-management/concrete-slabs.aspx http://homebuildingqc.ibacos.com/bios/anthony-grisolia.aspx http://homebuildingqc.ibacos.com/ http://homebuildingqc.ibacos.com/ http://www.housinggiants.com

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