Sixty years of layers, and the cracks underneath all of them

A section built once and added to ever since

A great deal of the commercial paving on the south side went in with the buildings, and a large share of those buildings date from the 1960s. Almost none of that original surface is still doing the work on its own.

What is there instead is a stack. An original surface over whatever base was considered adequate at the time, then an overlay when that surface got tired, then patches cut into the overlay, then in many cases another overlay placed over the patches. Every one of those was a defensible decision in the year it was made. The result, six decades on, is a pavement section that nobody designed and nobody has a record of.

The stack does not behave like a thick pavement, which is the part that surprises owners. Thickness accumulated in separate lifts placed years apart, over cracking that was never treated, is a different object from the same thickness placed as one structure on a sound base. It is heavier and stiffer on top of the same tired ground, and every old crack is still down there waiting.

Why the same cracks return through new asphalt

Reflective cracking is the mechanism, and it is the most common reason an owner feels cheated by a resurfacing that looked flawless in October and was lined again by the following summer.

A crack in an old layer is a discontinuity, and the two sides of it move relative to each other. They move with temperature, since asphalt contracts as it cools and the movement concentrates at the opening. They move under load, since a wheel crossing the crack deflects one side before the other. New material placed on top is thin compared with the layer underneath and it cannot bridge that movement indefinitely, so a crack works its way upward until it appears at the new surface directly above the old one.

The geometry gives it away. A reflected crack reproduces the map of the crack beneath it: same spacing, same direction, often the same small jog around an old patch outline. Cracking from a new cause does not arrive pre-drawn.

There are ways to slow it. Routing and sealing the worst of the old cracking before placing, milling the old surface off rather than covering it, an interlayer, more thickness. They slow it down. None of them repeals it, and where the movement underneath is structural rather than thermal, the only honest answer is to deal with the layer that is moving.

Telling an overlay stack from a sound structure

From a car window the two look identical. The evidence is at the edges and wherever the pavement has already broken open.

• Curb reveal. If the curb face is much shallower than it ought to be, or the gutter line is now nearly level with the surface, the lot has been raised repeatedly.
• Castings and drains sitting low relative to the pavement, often inside a ring of patch material added to make up the difference.
• Layer lines visible where a pothole or a broken edge exposes a cross section, showing as distinct seams rather than one homogeneous depth of material.
• Rectangular crack patterns that do not correspond to how anyone drives, which are old patch outlines telegraphing upward.
• Door thresholds, aprons and walk transitions where the pavement now sits awkwardly close to the finished floor level inside.
• Edges with no confinement at all, where the stack simply ends and crumbles away into soil or mulch.

Why a core is worth more than an opinion

A core is a cylinder cut down through the entire section and lifted out. It answers the questions the surface cannot: how many layers there are, how thick each one is, whether they have separated from one another, what the base is made of, how deep the base goes, and what the ground below it is doing.

Specifying work without that information is estimating, and on a lot of this age the estimates tend to be optimistic in a particular direction. They assume there is a stone base, that it is the depth that would have been standard, and that the existing asphalt is one or two lifts rather than four. Where those assumptions are wrong, the scope written on them is wrong by a large margin and the discovery happens after the work has started, which is the most expensive time to find out.

A handful of cores across a large property is a small cost measured against the size of the work they inform. They are the difference between a proposal that describes this pavement and a proposal that describes a pavement.

They also settle disagreements. Bidders working from the same core information tend to converge on a similar scope. Bidders guessing tend to produce numbers that differ by several times, which leaves the owner comparing confidence rather than comparing work.

The point where another overlay stops being the cheaper answer

An overlay is usually the least costly thing that can be done to an entire lot in one season, which is exactly why it keeps getting chosen. It stops being the least costly thing at the moment it has to be removed again.

The rough test is how much of the area has failed structurally as opposed to superficially. Where failures are localised, full-depth repair of those areas followed by a surface course across the property is sound engineering and sound spending. Where the failures are distributed, the structure is telling you something different: interconnected cracking over much of the surface, depressions that hold water in several unrelated places, edges gone all round, fine material pumped up through the cracks after a rain. At that point another overlay is a season of appearance placed on a section that is no longer carrying its load.

Full-depth reclamation is the option that usually goes unmentioned. The existing asphalt is ground up together with part of the base and recompacted in place as a new base layer. The old cracks stop existing because the material containing them has been destroyed, which is the one claim an overlay can never make. It costs more than an overlay and considerably less than excavating the whole section and hauling it away, and it reuses what is already on the property rather than paying to remove it and paying again to replace it.

The comparison worth asking for is not the price of each option. It is the price of each option set against the number of years before the next intervention. An overlay that has to be repeated, over a base that is still losing material, loses that comparison decisively even though it wins on the day the proposals are opened.

The drainage an overlay stack quietly destroyed

Every overlay raises the pavement. Curbs do not grow, and drainage structures only move if somebody pays to adjust them, which on a maintenance budget they rarely are.

After several rounds the curb reveal that used to contain runoff and carry it along the gutter line has largely disappeared, so water that once travelled to an inlet now spreads across the surface or spills over into the landscaping. Castings left at their original level sit in a dish of successive patch material, which is why so many of them have a ring of broken asphalt around them.

Grade gets blurred as well. An overlay placed at a uniform thickness reproduces whatever shape was underneath it, including every settled area. A low spot is not corrected by being covered. It is covered.

On an older strip property this is frequently the largest item that nobody has quoted. Standing water is the input to almost every other failure described on this page, and on a lot with this history it is usually a consequence of the maintenance record rather than of the original design.

One lot, several tenants, several sets of opening hours

A multi-tenant strip complicates the programme in a way a single-occupant building does not. The owner holds the pavement, but the businesses standing on it open at different times, take deliveries at different times, and have very different tolerance for losing the frontage outside their own door for two days.

There is rarely an hour when everybody is shut. There is almost always a window when each one individually is, and a workable programme can be assembled from those windows if the lot is divided into small enough sections and the sequence is planned around the tenants rather than around the paving.

• Collect each delivery window before the sections are drawn, not after somebody complains about the one they got.
• Keep one entrance and one continuous route through the property open at every stage of the work.
• Take the areas serving the earliest-opening businesses first in the day, or overnight, and leave the late traders for afternoon work.
• Issue notice in writing with dates, and expect to reissue it, because one rain day moves every phase behind it.
• Treat the areas no tenant claims, the shared corral and the rear service aisle, as the responsibility of the owner. Nobody will raise them and they are usually the worst pavement on the site.

What phasing actually costs

Splitting a property into six sections is not the same job done in six pieces. It is six setups, six sets of protection, six joints between areas placed on different days, and more days on site overall.

Those joints matter beyond the price. A joint between two days of paving is a visible line and it is a place water can find later, so a surface placed in fewer and larger pieces is a better surface as well as a cheaper one.

None of which argues for closing a strip property for a fortnight, because the cost of that falls on the tenants and eventually returns to the owner in a different form. It argues for making the trade knowingly. Decide how much disruption the property can absorb, price the phasing that matches it, and stop treating the phasing plan as an administrative detail to be settled on the first morning.

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