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OCR for page 20
20 4 3.5 Surface Too Soft for Chip Seal Above this Line 3 Above Line C Ball Penetration, mm Correction = 2.5 -0.06 gal/yd2 B From Line B to C C A (-0.30 L/m2) 2 Correction = From Line A -0.04 gal/yd2 1.5 to B Correction = (-0.20 L/m2) -0.02 gal/yd2 No Correction Needed (-0.1 L/m2) 1 this side of Line A 0.5 0 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Traffic, Veh/day/lane Figure 4. Correction factors for chip penetration into substrate (Austroads 2006). d) Absorption of Emulsion into Aggregate Chips, Aaa 6.3 Time Until Sweeping and Traffic Absorption of emulsion into the chips requires a cor- The time required before sweeping or before traffic can be al- rection of +0.02 gal/yd2 (+0.1 L/m2) for each 1% of water lowed on the fresh chip seal is related to the moisture content in absorption. the chip seal (Shuler 2009). The laboratory test method in NCHRP Project 14-17 may be used to determine when the chip seal can withstand sweeping and traffic stresses. In this method, 6.2 Aggregate Application Rate test specimens of the emulsion and chips are fabricated in the The aggregate application rate is determined based on ALD, laboratory and tested at three moisture contents. The moisture traffic volume, and chip size. at which less than 10% of the chips are dislodged during the test The aggregate spread rate for 3/8-in. (10-mm) and larger is the target moisture content to be achieved in the field before chips depends on the traffic. sweeping or traffic operations should commence. a) For pavements with less than 200 vehicles/day/lane: 6.4 Other Considerations Aggregate spread rate, lbs yd 2 = [ ALD, in. W ] 27.0 08 6.4.1 Chips Required to Avoid Roller Pickup Aggregate spread rate, m 2 m3 = 750 ALD, mm Additional aggregates than are actually estimated to pro- duce a one-stone layer should be spread during chip-seal con- Where W is loose unit weight, lb/yd3. struction to aid in reducing the potential for embedded chips to be picked up by pneumatic rollers. The amount of addi- b) For pavements with more than 200 vehicles/day/lane: tional material will vary, but generally is between 5% and 10%. Aggregate spread rate, lbs yd 2 = [ ALD, in. W ] 25.2 27 6.5 Example Design Aggregate spread rate, m m = 700 ALD, mm . 2 3 An example of how to use the design method to determine the binder and aggregate spread rates follows. The range of spread rates for 3/8-in. (9-mm) and smaller If chips depends on whether there are one or two layers of chips placed. It ranges from 0.104W to 0.093W (290 to 260 m2/m3) Maximum aggregate size = 1/2 in.; for a single layer to 0.089 W to 0.072W (250 to 200 m2/m3) for Median aggregate size = 3/8 in.; two layers. Flakiness index = 30%;
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21 Loose unit weight, W = 110 lbs/ft3; ALD = 0.328 in.; Traffic = 1,500 veh/day/lane, channelized, with equivalent EF = 1.2, from Section 6.1.5; heavy vehicles, EHV%=16; PF = 1.1, from Table 10; Polymer modified emulsion binder with 70% residue; As = 0.02 gal/yd2, from Figure 3a; Sand patch diameter for texture = 18 in.; Ae = 0, from Figure 4; Ball penetration = 0.5 mm; Aas = 0, from Section 6.1.7c; and Substrate is old chip seal with no expected absorption poten- Aaa = +0.02 gal/yd2, from Section 6.1.7d. tial; and Chip-seal aggregate has 1% water absorption Bd = [( 0.85 - 0.028 - 0.112 ) 0.328 1.2 1.1] Design binder application rate (from Section 6.1) is: 2 + 0.02 + 0 + 0 + 0.02 = 0.35 gal yd Bd = [(Vf + Va + Vt ) ALD EF PF ] + As + Ae + Aas + Aaa Aggregate spread rate (from Section 6.2) Vf = 0.85 gal/yd /in., from Figure 2b; 2 = [ ALD, in W, lbs yd 3 ] 25.27 Va = -0.028 gal/yd2/in., from Table 8; Vt = -0.112 gal/yd2/in., from Table 9; = 0.328 110 27 25.27 = 38.5 5 lbs yd 2 .