Sarah Mildred Long Bridge project is an important regional crossing linking Maine and New Hampshire across the Piscataqua River. The existing steel, vertical-lift bridge, originally built in 1940, needed replacing. This renovation was part of the “Three Bridge Agreement” between Maine and New Hampshire.

THE CHALLENGE

• The new 2,800 foot concrete, vertical-lift bridge needed to allow larger ships to access the nearby port while hitting safety, performance, durability, economic and aesthetic goals.
• 88 tower segments, needed for the four towers, were precast on-site, each weighing 80 tons.

THE SOLUTION

• Concrete mixtures containing NewCem slag cement were used to increase the strength and durability of the new bridge. The use of NewCem in the concrete mix improved the workability of the low water-cementitious material ratio, while also reducing permeability for durability concerns. Placed during the hot summer months, ice was used with the slag cement to help mitigate thermal cracking concerns. At 28 days, compressive strengths exceeded design strengths and used less cementitious factors than a typical mix.
• Using NewCem also helped plastic concrete temperatures stay within tight specification during slower placements involving cranes and buckets. Once the bridge was completed, the four towers reached a height of 215 feet and were erected in post-tension, increasing its vertical resting position by 56 feet which allowed for 68 percent fewer bridge openings, and the passing of larger ships were accommodated by increasing the span to 300 feet.