Bonded deck overlays: latex-modified, silica fume, UHPC and polymer

How bridges get built · Finishing, articulation and maintenance · Bonded deck overlays: latex-modified, silica fume, UHPC and polymer

Also called: LMC overlay, silica fume overlay, UHPC overlay, UHPFRC overlay, polyester polymer concrete overlay, epoxy thin overlay, deck preservation overlay

How it is done

Survey the deck: delamination (sounding, GPR, infrared), chloride profile, cover and half-cell potentials; decide whether an overlay is enough or the deck needs cathodic protection or replacement.
Remove the top of the deck by scarifying or milling (typically 6–13 mm), or by hydrodemolition to sound concrete and below the top bars where chloride or delamination require it; break out and patch deeper defects.
Blast or hydro-blast to a clean, rough profile; pre-wet to saturated surface dry for cementitious overlays, or dry the deck thoroughly for polymer overlays.
Place the overlay: latex-modified or silica fume concrete from a mobile mixer, scrubbed in and struck off by a deck finishing machine on screed rails; UHPC as a thixotropic mix placed and levelled with a vibrating screed; polymer binders mixed, spread and seeded with aggregate.
Cure as the material requires: wet burlap for 24–48 h then air drying for latex-modified concrete, about 7 days wet for silica fume, sealed curing for UHPC, a few hours for polymers. Control evaporation; plastic shrinkage cracking is the commonest failure.
Texture for skid resistance (tining or grinding for concrete, broadcast aggregate for polymers), seal joints and cracks, and reopen once strength is reached.
Test bond by pull-off, sound for hollows, check thickness and chloride permeability on cores, and record the overlay in the deck history.

Key numbers

Thicknesslatex-modified and silica fume concrete 30–50 mm; UHPC 25–50 mm; polyester polymer concrete about 20–25 mm; multi-layer epoxy 6–10 mm
Latex-modified concreteabout 15 % latex solids by mass of cement
Silica fume concreteabout 7–10 % silica fume by mass of cementitious material
Bond acceptancepull-off typically about 1.0–1.7 MPa depending on system, or failure in the base concrete
Closurepolymer overlays reopen in a few hours; latex-modified concrete after about 2–4 days (rapid-set versions in hours); silica fume after about 7 days of wet cure

Where it fits

Concrete decks with surface wear, cracking or chlorides in the cover zone but sound below.
Bare decks in de-icing climates without membranes.
UHPC where capacity must also be added or the deck slab is thin.

Where it does not

Decks with active corrosion below the overlay depth (add cathodic protection or replace).
Placing in hot, windy or freezing weather without curing control.
Polymer overlays on wet, cracked or very flexible decks.

Choosing it

Choose a polymer overlay over a concrete overlay when the deck is sound, closures must be overnight and dead load must not rise; it seals but adds no strength.
Choose latex-modified or silica fume concrete over polymer when the top of the deck must be removed and rebuilt and a 30–50 mm structural wearing course is wanted.
Choose UHPC over latex-modified or silica fume concrete when the overlay must also add capacity (reinforced UHPC acts as a tension or compression layer) or near-zero permeability is worth the material cost and specialist placement.
Prefer deck replacement over an overlay when chloride at bar level is high over most of the deck or delamination is widespread; the overlay would seal the corrosion in.

Plant, pace and money

PlantMilling or scarifying machines, hydrodemolition robots, shot blasters, mobile volumetric mixers, bridge deck finishing machines, UHPC mixers and vibrating screeds, polymer overlay distributors.

ProductivityIndicative: polymer overlays of several thousand square metres in a night or weekend closure; concrete overlays a stage of a deck per pour, with curing governing the closure.

CostIndicative: polymer overlays USD 40–100 per m²; latex-modified and silica fume overlays USD 100–250 per m² including surface preparation; UHPC overlays USD 200–400 per m².

Risks and controls

What goes wrong

Debonding from poor surface preparation or a dry substrate.
Plastic and drying shrinkage cracking.
An overlay hiding active corrosion below.
Wrong thickness from uneven milling, adding dead load.

Quality assurance

Surface profile and cleanliness checks, pull-off bond tests, thickness checks, curing records, chloride permeability on cores, sounding for hollows after cure.

Origins

Low-slump dense concrete (the 'Iowa method') and latex-modified concrete overlays were developed in the US in the 1960s and 1970s against de-icing salt damage, and silica fume overlays followed in the 1980s. UHPFRC overlays were developed in Switzerland at EPFL and codified in SIA 2052 (2016); the first UHPC deck overlay in the US was placed in Iowa in 2016.

Examples

Latex-modified and silica fume overlays are standard deck preservation in many US states; thin epoxy overlays seal sound decks overnight; UHPC overlays are used in Switzerland and increasingly in the US to strengthen and waterproof in one layer.

Case studies

Chillon ViaductsSwitzerland · 2014–15About 52,000 m² of the twin 2.1 km box-girder viaducts of 1969 overlaid with 40–50 mm of reinforced UHPFRC, strengthening and waterproofing the deck slabs in one operation.

Mud Creek Bridge, Buchanan County, IowaUSA · 2016First UHPC deck overlay in the United States, about 38 mm thick.

San Mateo–Hayward BridgeUSA · 2015The original epoxy asphalt on the orthotropic deck was replaced with a polyester polymer concrete overlay.