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compatibility of ultra high performance concrete as repair material

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ond and UHPC strengths exhibit an important incre<strong>as</strong>e at 2-3 days. The minimum bondcapacity achieved at the age <strong>of</strong> 2 days is substantially lower than that <strong>of</strong> 3 days, while thestrength obtained at 8 days is slightly greater than that <strong>of</strong> 3 days. This h<strong>as</strong> a similarparallelism with the UHPC hydration process, defined in 2.1.3: there is a dormant periodfollowed by a strong energy rele<strong>as</strong>e (Morin et al. 2002; Morin et al. 2001) and thehydration progress is narrowly <strong>as</strong>sociated to the compressive strength development(Kamen 2006). It seems re<strong>as</strong>onable to state that with this kind <strong>of</strong> UHPC formulation andunder ambient condition the threshold to achieve excellent bond occurs at 3 days. Aswell, it is appropriate to spotlight that the bond capacity <strong>of</strong> B-60-3d is lower than that <strong>of</strong>B-55-3d.Bond capacoty (psi)300025002000150010005000At 8 daysAt 3 daysAt 2 daysBrushed, 60° Grooved, 70° Rough, 70° Brushed, 70° Brushed, 55° Rough, 55°Figure 4.14 Evolution <strong>of</strong> the bond strength per c<strong>as</strong>e study obtained in the slant-shear test4.2.2 DiscussionThe results from this loading configuration show that the bond between UHPC and NSCh<strong>as</strong> an excellent <strong>performance</strong> under a state <strong>of</strong> shear and compression stresses regardlessthe surface treatment applied in the <strong>concrete</strong> substrate. The bond capacity at 8 dayslargely exceeds with the requirements specified by ACI 546.3R-06 at 7 days and alsosatisfies the minimum bond requirements for 28 days.89

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