civil test 2 outline - All concrete has some entrained air...

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All concrete has some entrained air air is for freeze thaw cycle and the salts that melt ice max size aggregate is 33% to 25% a dowel is for load transfer while a tie bar holds the joints together Mr = 2.3 Fc to the 2/3 power modulas of rupture Mr is flexural strength Fc actual compressive strength AASHTO american association of state, highway, and transportation officials A = CfLWh/24Fs drag equation A = area of steel needed per foot F = Cf = 1.5 coefficient of subgrade resistance L = space between joints w = density of concrete 12.5 psf or if W = 150 lb/ft3 h = thickness of slab Fs = tensile strength 2/3 yeald strength in Psi curing retains moisture sealing prevents foreign material and protects it salt is worst thing for concrete, corrodes steel unbonded means a chemical treatment or membrane in-between slabs to act as a bond breaker excess cement increases tempeture and spoiling and waists money vapor barrier has higher permiability than vapor retarder intermescant paint is a product that expands when heated it’s a fire retarder isotropic = material properties are the same in all directions steel anisotropic = material properties are not the same in both directions wood in wood the mod of elasticity changes the most concrete parking ppt tensile stresses most important compressive strength wont break stresses greatest at edge so thicken ½" for 18" 5" thick minimum for parking 6" for entrance 8" + for entrance drives with heavy trucks minimum slope for paved area 6" per 100' however 12" is better pavements plain unreinforced with or without load transfer devices (dowels) or reinforced with distributed steel reinforcing either WWF or small steel rebar DSR only hold cracks together from the changes in tempeture it does not prevent them the most important aspect of parking lot design is concrete quality, thickness, and the type and spacing of joints joints contraction can be sawed, hand tooled, formed (keyway), or inserts, only about 25% of slab thickness expansion includes isolation concrete expands 3/4" per 100' constuction where laying stops for the day Factors to Consider in Joint Spacing 1. Thickness of Slab 2. Base – thickness & type, load capacity 3. Subgrade
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General Guidelines 1. “Panels” to be as “square” as possible 2. If panels are rectangular – keep length to width ratio less than 1.5:1 3. For Parking Lots & Drives - spacing 15’ or less (length) (15’ x 10’) 8(A 15’ x 15’ panel is likely to crack at mid-point in one direction) 4. Do not “stagger” joints 5. WWF – Re-Bar – or plain concrete? 6. Avoid acute angles at joints (obtuse angles are o.k.) 7. Re-entrant corners 8. Joint Sealing 9. Joints placed a maximum distance of 24 – 36 x the thickness of concrete up to 30 feet use distrubuted steel reinforcing if joints are too far apart or if subgrade conditions give non uniform support WWF 6 x 6 w2.9 x w2.9 wire is 6" apart in both directions and is 2.9 one hundredths of a square inch or .029 #4 re bar is 4 eighth inches or ½" do not use WWF rolls use sheets and overlap 1 ½ times the space between wires
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