Precast Solutions - July/August 2008 - (Page 5)

UHPC mixtures contain portland cement, silica fume, quartz flour, fine silica sand, high-range water reducer, water, and steel or organic fibers. Materials are usually supplied to the precast concrete producer in three components: premix (blended, in-bulk bags); superplasticizer; and fibers. The microstructural properties of UHPC’s mineral matrix produce a highly compact, dense material within a low porosity matrix (Table 1). specimen age on the strength and durability properties of fiber-reinforced UHPC. At Michigan Tech’s Cement & Concrete Research Facilities in Houghton, four different curing regimes were tested to determine the effects of curing on UHPC’s material characteristics, including compressive strength, freeze-thaw resistance, flexural cracking strength and chloride penetration resistance. The four curing regimes tested are: 1. 48-hour thermal steam treatment at 90 degrees C With a remarkably streamlined design and light weight, this single-span UHPC pedestrian bridge girder was installed at night for minimal traffic disruption. Photo courtesy Lafarge North America RESEARCH RESULTS FOR UHPC (194 F) and 100 percent relative humidity 2. Ambient air curing 3. Delayed (10-day delay before curing) thermal steam treatment 4. Double-delayed (24-day delay before curing) thermal steam treatment CURING PROTOCOLS SIMILAR TO THOSE OF PRODUCERS Precasters and engineers need information on mechanical behavior variations for structural elements that are thermally treated at different concrete ages. Producers and specifiers also need data that are more representative of actual conditions and production techniques found in existing precast plants. Michigan Technological University (Michigan Tech) has conducted research into the effects of curing regimes and These curing regimes are representative of how precasters may manufacture products, choosing to cast products over several days and thermally treat together, or not thermally treat at all. JULY/AUGUST 2008 | PRECAST SOLUTIONS 5

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Precast Solutions - July/August 2008 Contents What You Should Know About UHPC A Winning Hand Fresno Federal Expanding U.S. Wind Power Precast Concrete Pipe

Precast Solutions - July/August 2008

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