How sealcoating works and how it can save you money.
Courtesy of the Pavement Pro's of the National Pavement
Contractors Association

Research has demonstrated that properly applied (and
properly timed) sealcoat can save the owner of a property
$100,000 or more — over the life of a hot mix asphalt
pavement. But what does seal-coat actually do that results
in this substantial savings?

To understand how sealcoating works, it is necessary to
understand the nature of the asphalt pavement itself.
Because of its excellent waterproofing, flexibility, and
adhesive properties to bind and hold the aggregates in the
pavement, asphalt has been used extensively for paving
and road construction. Prior to the advent of asphalt as a
paving material, roads were constructed by spreading
graded aggregates over a road bed. These roads worked
well as long as the stones remained in place and stayed
dry. Naturally, these roads needed constant repair. Stone
would shift under the traffic and the road’s load carrying
capacity was severely damaged when it rained. The stone
would absorb water, swell and lose its strength. But
spraying asphalt on the surface overcame this problem
somewhat. Asphalt paving technology gradually evolved
and today the vast majority of all roads are constructed
using asphalt as the binding material for the aggregates.
Due to its waterproofing properties, asphalt protects the
aggregates from absorbing water, thus preserving their
strength and load-carrying capacities. Today’s asphalt
pavement is a mixture of stone aggregate and mineral filler
combined with 4.5% to 12% (average of 6%) asphaltic
binder (asphalt cement). The strength of an asphalt
pavement is directly related to the pavement design from
the ground up. The asphalt pavement people see is only the
"roof," so to speak, of the entire pavement. This "roof"
covers a bed of graded stone aggregates of varying depths
according to ground conditions as well as traffic
requirements. This base of aggregate is what really carries
the load of the traffic. The same theory applies to off-street
parking lots or drive-ways. A firm resilient surface that
provides a roof over the stone base will keep the pavement
bed dry. It is important to have an elastic characteristic in
this pavement so that it can expand and contract and still
remain intact.
Knowing Your Asphalt