(2) Stabilization With Liquid Asphalt. For an estimate of liquid asphalt

requirements, use the following expression:

where:

p

=

.02(a) + .07(b) + .15(c) + .02(d)

p

=

percent of residual asphalt by weight of dry aggregate.

a

=

percent of aggregate retained on No. 50 sieve.

b

=

percent of aggregate passing No. 50 and retained on No. 100 sieve.

c

=

percent of aggregate passing No. 100 and retained on No. 200

sieve.

d = percent of aggregate passing No. 200 sieve.

over effective areas much larger than tire contact areas, greatly reducing

stress intensity on subgrade and eliminating the need for high quality bases.

While bases normally are not required for structural reasons, they usually are

required for other reasons.

every point proportional to vertical deflection of the slab at the point and

elastic pavement. Assume subgrade support is continuous with no areas where

slab has deflected away from the subgrade.

(1) Analysis. Stress analysis utilizes a basic relationship between

bending moment and radius of curvature at any point:

EI

M = ))))

r

where:

r

=

radius of curvature of the pavement,

M

=

bending moment of the pavement,

E

=

modulus of elasticity of the pavement,

I

=

moment of inertia of the pavement.

(2) Maximum Stress. Maximum pavement stresses occur when wheel loads are

near joints and exterior edges of slabs.

subgrade interfere with pavement expansion and contraction, often resulting in

pavement cracking. Design properly spaced contraction joints to control crack-

ing caused by contraction. Excessive expansion and blowups occur infrequently

because most pavements are laid in warm weather. However, expansive aggregates

or wide temperature variations can cause blowups.

(1) Vertical Temperature Gradients. Vertical temperature gradients in

slabs cause warping. If the top of a slab is cooler than the bottom, the slab

tends to curl up at the edges because of tension in the top surface. Tension

is an additive to tensile stresses caused by external load applied to slab

edges.

(2) Stress Analysis. Analysis for warping stresses usually is not consi-

dered in pavement design; use an adequate factor of safety instead.

constant modulus of subgrade reaction. Local variations in subgrade modulus

cause increased stresses with possible pavement overstressing and decreased

life; therefore, provide a uniform subgrade.

(1) Pavements. Pavements perform better where construction traffic can

be kept off the subgrade.

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