Project Highlights

Four Seasons Hotel & Tower - Miami, Florida

A ready-mixed, cast-in-place, silica fume SCC application, utilizing the silica fume to boost modulus of elasticity performance with local limestone and achieve high strength concrete versus a mix design with imported granite aggregate.  At 750 feet height (230m) this building became the tallest structure in the USA south of Atlanta.  In Florida to-date, this is one of the leanest mass-produced high strength concrete designed around desirable engineering characteristics of minimum creep and shrinkage by employing optimized alternate cementitious materials.

With extremely dense reinforcement and a high modulus of elasticity requirement this building was designed to withstand high category hurricane-force wind loads.  Placing concrete in the dense reinforcement environment, particularly the core or elevator shaft portion of the building, required high concrete flowability of 20 to 25 inches (510 - 635 mm) spread.  Such plastic concrete characteristics were applied on this project in the year 2000 before SCC became a household name in the US.  Furthermore the high strength silica fume concrete design employed 10-15% less total cementitious quantity than similar high performance concrete produced locally, benefitting the desirable engineering characteristics through minimized total cementitious contents.

    
Extremely dense reinforcement necessitated self consolidating high performance concrete

Often impractical to consolidate by conventional means due to extreme rebar density it was critical to provide SCC characteristics and maintaining such workability with concrete temperatures close to 100° F (38ºC) and for up to 2 hours from time from batching.   Silica fume’s viscocity modifying properties enhanced the SCC consistency in controlling segregation even under free-fall situations of heights up to 20 feet (6.5 m).  Concrete was pumped through a 5 -inch (12.7 cm) diameter line the entire building height with a single-stage pump.  The various concrete mix designs employed an approximate 6% silica fume addition rate across the board to a 50/50 blend of slag and Portland cements.  

Approximately 20,000 cubic yards (15,000 m3) of HPC with a 5 to 6 million psi (34.5 – 41.4 Gpa) modulus of elasticity requirement and an 8,000-10,000 psi (55 - 69 Mpa) compressive stgrength specification utilized imported granite.  15,000 cubic yards with a 4 to 5 million psi (27.6 - 34.5 Gpa) modulus of elasticity requirement and also an 8,000-10,000 psi (55 - 69 Mpa) compressive strength specification could forgo the imported granite aggregate through the use of silica fume in conjunction with local Florida limestone pearock and an HPC savings of approximately $ 150,000.00.  Historically Florida limestone capacity to reach higher modulus of elasticity values diminishes at approximately ±4 million psi (27.6 Gpa)

Concrete Mix Design & Performance
Four Seasons, Miami, FL -2000

Four Seasons Hotel & Tower
Miami, FL

Extremely dense reinforcing steel requried, self consolidating high performance silica-fume concrete