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SUMMARY:Early-age deformations and cracking in high-performance concrete: 
 measurements\, modelling and mitigation
DTSTART:20120322T121500
DTEND:20120322T131500
DTSTAMP:20260510T062919Z
UID:e80d40361188e1d015511176f5cbee92a25ba205286a3144c29ebfb1
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Pietro Lura\nThe matrix of a high-performance concrete t
 ypically has low porosity\, typically obtained by keeping a low water-to-c
 ement ratio and by silica fume addition. High-performance concrete possess
 es advantageous properties compared with traditional concrete\, e.g. high 
 strength from early ages\, low permeability and improved durability. Howev
 er\, its practical application of faces some difficulties\, in particular 
 due to sensitivity to early-age cracking. These cracks constitute a seriou
 s problem with regard to strength and especially to durability. A main cau
 se of early-age cracking is restrained autogenous deformation\, a direct c
 onsequence of cement hydration in a low water-to-cement mixture. Another c
 ause of cracking is represented by thermal stresses that are a consequence
  of the exothermic nature of cement hydration.\nAs cement hydration procee
 ds in low water-to-binder ratio concrete\, the water becomes bound into hy
 dration products and adsorbed on their surfaces. The capillary pores are e
 mptied and the air-water menisci become progressively smaller\, the intern
 al relative humidity (RH) drops (self-desiccation) and an increasing capil
 lary tension is produced in the pore fluid. The capillary stress exerts a 
 compressive stress on the whole porous body\, resulting in bulk shrinkage.
 \nSelf-desiccation occurring in low w/c cement paste leads not only to aut
 ogenous shrinkage\, but also causes a substantial increase in the coeffici
 ent of thermal expansion in the cement paste. The latter effect is due to 
 the RH changing with temperature which causes additional expansion acting 
 in the same direction as the pure thermal dilation of a partially saturate
 d medium.\nInternal curing by means of superabsorbent polymers (SAP) is a 
 method for promoting hydration of cement and limiting self-desiccation and
  further self-desiccation shrinkage. SAP are introduced dry into the mixtu
 re and form stable\, water filled inclusions by absorbing pore solution. T
 his water is released to the cement paste during hydration\, as clearly sh
 own by neutron tomography experiments. SAP are effective in both eliminati
 ng autogenous shrinkage and decreasing the thermal expansion coefficient o
 f the cement paste\, thereby reducing the risk of early-age cracking.\nIn 
 this presentation\, our work on early-age deformation in high-performance 
 concrete will be presented\, including experiments\, poromechanical modell
 ing and mitigation techniques.\n\n\nBio: Pietro Lura is Head of the Concre
 te and Construction Chemistry Laboratory since 2008 and professor at ETH Z
 urich\, Institute of Building Materials\, since 2011. He received his MS i
 n 1998 from the University of Brescia\, Italy\, and his PhD in 2003 from t
 he Delft University of Technology\, The Netherlands. He has been assistant
  professor at the Technical University of Denmark (2003-6)\, visiting rese
 archer at the National Institute for Standard and Technology (2002) and at
  Purdue University (2005)\, and patent examiner at the European Patent Off
 ice in Munich\, Germany (2006-8).\nHis research interests include hydratio
 n and early-age properties of concrete\, in particular microstructure deve
 lopment\, shrinkage\, setting\, early-age cracking and internal curing. In
  these fields he has done important contributions to both understanding of
  the fundamental mechanisms and to advancement in the state of the art. Hi
 s work on measuring techniques of autogenous deformation earned him two aw
 ards from the Transportation Research Board\, the Bryant Mather Award in 2
 006 and the Fred Burggraf Award in 2007. For his work on internal curing h
 e received the American Concrete Institute Wason Medal for Materials Resea
 rch in 2007. He received for the second time the ACI Wason Medal in 2009 f
 or his contribution to the understanding of the mechanisms of plastic shri
 nkage cracking. In 2009 he also received RILEM L'Hermite Medal in recognit
 ion of his outstanding contribution to the study of the early-age behavior
  and volume instability of cement-based materials.\nIn addition to heading
  the Concrete and Construction Chemistry Laboratory at Empa\, Pietro Lura 
 is teaching at ETH Zurich since 2009. He is also active in teaching and or
 ganizing summer courses targeted both at students and practitioners.
LOCATION:GC C330 http://plan.epfl.ch/?room=GC%20C3%2030
STATUS:CONFIRMED
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