compatibility of ultra high performance concrete as repair material
compatibility of ultra high performance concrete as repair material
compatibility of ultra high performance concrete as repair material
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The first layer, also called penetration layer, is made inside the old cementitious <strong>material</strong>and it composed <strong>of</strong> new constituents (calcium silica hydrate with lesser amounts <strong>of</strong> AFtor calcium hydroxide) that respond chemically with active constituents in the oldsubstrate. The second layer h<strong>as</strong> <strong>high</strong> porosity and it is composed <strong>of</strong> calcium hydroxideand Aft crystals <strong>high</strong>ly oriented. The third layer approximately h<strong>as</strong> a very similar microstructure<strong>as</strong> the bulk new cementitious <strong>material</strong>. At the macro-scale, the bond-cohesiveconcept is a <strong>material</strong> property connected to the overlay transition zone <strong>of</strong> the newcementitious <strong>material</strong>.A good bond can be achieved by c<strong>as</strong>ting new <strong>concrete</strong> (rapid-hardening portland) againstold <strong>concrete</strong> with no bonding agents (Climaco and Regan 2001). Momayez et al. (2005)found that tensile bond strength for cementitious <strong>material</strong>s is approximately 40% <strong>of</strong> that<strong>of</strong> a monolithic sample and the slant shear strength is about 67% <strong>of</strong> that <strong>of</strong> a monolithicsample. In the same research, the bond strength to the <strong>concrete</strong> substrate obtained by fourdifferent sand-cement mortars containing 0%, 5%, 7% and 10% <strong>of</strong> silica fume w<strong>as</strong>compared. It w<strong>as</strong> concluded that the content <strong>of</strong> silica fume in the overlay <strong>material</strong>significantly incre<strong>as</strong>es the bond strength regardless the loading test (pull-<strong>of</strong>f, bi-surfaceshear, splitting prism, slant shear). Nevertheless, the beneficial effect <strong>of</strong> silica fumeseems to have a peak at 7% and any added silica fume content beyond this does notimprove the bond strength noticeably. Julio et al. (2005) stated that the use <strong>of</strong> bondingagent does not improve the bond strength between two cementitious <strong>material</strong>s if a surfacetreatment h<strong>as</strong> been effectively applied to the <strong>concrete</strong> substrate.2.4 SummaryThe potential use <strong>of</strong> UHPC <strong>as</strong> <strong>repair</strong> <strong>material</strong> h<strong>as</strong> been shown throughout this chapter.UHPC exhibits several properties that make it appropriate for this purpose. Its negligiblepermeability makes this <strong>material</strong> suitable <strong>as</strong> protective barrier that prevents any water orchemical penetration into the substrate. In addition, its <strong>ultra</strong>-<strong>high</strong> compressive strengthand post-cracking tensile capacity would suppose an improvement <strong>of</strong> the bearingcapacity. Its cementitious character and its ability to self-consolidate facilite itsapplication in the field. However, for extensive acceptance, it h<strong>as</strong> to be demonstrated that36
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