Properties of Fresh ConcreteSlgnlñcance • The first 48 hours are very important for the performance of the concrete structure. • It controls the long term behavior • It controls the long-term behavior, influence fc, Ec, creep, and durability. Þroperues aL Larly Age Workability • Workability • Slump Loss • Segregation/Bleeding • Plastic Shrinkage Plastic Shrinkage • Time of Set Temperature • Temperature -Curing Þroperues of fresh concreLe • WorkablllLy – ease of placemenL – reslsLance Lo segregauon – homogeneous mass • ConslsLency – ablllLy Lo ßow Semng and Pardenlng Slump 1esL • lnverLed cone • ñll lL up wlLh Lhree layers of equal volume • rod each layer 23 umes • scrape oñ Lhe surface 8” 4” 12” Slump 1esL slump cone rod concrete Slump LesL Slump Ruler Slump 1esL Slump LesL resulLs • suñ 0-2" – masslve secuons, llule relnforcemenL – use vlbrauon • medlum 2-3" – columns, beams, reLalnlng walls • lluld 3-7" – heavlly relnforced secuon, ßowable concreLe lacLors añecung slump • waLer cemenL rauo – w/c = welghL of waLer / welghL of cemenL example: welghL of waLer mlxed aL Lhe planL 292 lbs. welghL of cemenL 683 lbs./cu. yard w/c = 292/683 = 0.43 waLer cemenL rauo lf you add 10 gallons of waLer per cublc yard aL [ob slLe, Lhen: exLra waLer 10 gallons/cublc yard * (3.8 llLers/gallon) * (2.2 lbs./kg) * ( 1kg/llLer) = 83.77 lbs. LoLal waLer 282 + 83.77 = 363.77 new w/c = 363.77 / 683 = 0.334 >> 0.43 lacLors añecung slump- pasLe conLenL • consLanL waLer cemenL rauo – lncrease pasLe conLenL • lncrease slump • nC CCCu • consLanL cemenL conLenL – lncrease waLer conLenL • lncrease slump • nC CCCu lacLors Añecung Slump- WaLer ConLenL • Add waLer aL Lhe consLanL cemenL conLenL, w/ c lncreases, slump lncreases. • Add waLer aL a consLanL waLer cemenL rauo, have Lo lncrease cemenL as well, slump lncreases. AdmlxLures • seL reLardlng admlxLures • seL acceleraung admlxLures • waLer reduclng admlxLures • superplasuclzers • alr enLralnlng admlxLures lacLors añecung slump • AggregaLes – gradlng Lhe larger Lhe parucle slze, Lhe hlgher Lhe slump for a glven pasLe conLenL 8leedlng and Segregauon • Segregauon: coarse aggregaLe Lends Lo segregaLe due Lo gravlLy. 1yplcal of dry mlxes. • 8leedlng: waLer rlslng Lo Lhe surface. 1yplcal of weL mlxes. • When excesslve, cemenL parucles and waLer go Lo Lhe surface poroslLy goes up - pasLe can easlly be abraded --> dusung. Segregauon 8leedlng and lLs conLrol • CreaLes problems: – poor pumpablllLy – delays ln ñnlshlng – hlgh w/c aL Lhe Lop – poor bond beLween Lwo layers ! causes ! lack of fines ! too much water content ! Remedies ! more fines ! adjust grading ! entrained air ! reduce water content Alr ConLenL Larly-Age volume Change (Larly Cracklng) lree Shrlnkage, causes volume change, buL no sLresses before shrinkage After Shrinkage 8esLralned Shrlnkage- creaLes sLresses, whlch may cause cracklng 8esLralned shrlnkage cracklng Parallel cracking perpendicular to the direction of shrinkage Causes of Þlasuc Shrlnkage Cracklng • waLer evaporaLes fasLer Lhan lL can reach Lhe Lop surface • drylng whlle plasuc • cracklng Þlasuc Shrlnkage Cracklng-8emedles • ConLrol Lhe wlnd veloclLy • reduce Lhe concreLe's LemperaLure – use lce as mlxlng waLer • lncrease Lhe humldlLy aL Lhe surface – fogglng – cover w/polyeLhylene – curlng compound • llber relnforcemenL Curlng • 1he ume needed for Lhe chemlcal reacuon of porLland cemenL wlLh waLer. • Clue ls belng made. • concreLe aûer 14 days of curlng has compleLed only 40° of lLs poLenual. • 70 ° aL 28 days. Curlng ups • ample waLer • do noL leL lL dry • dry concreLe = dead concreLe, all reacuons sLop • can noL revlLallze concreLe aûer lL drles • keep LemperaLure aL a moderaLe level • concreLe wlLh ßyash requlres longer curlng 1emperaLure eñecLs on curlng • 1he hlgher Lhe LemperaLure Lhe fasLer Lhe curlng • besL LemperaLure ls room LemperaLure • sLrongesL concreLe ls made aL LemperaLure around 40 l.(noL pracucal) • lf concreLe freezes durlng Lhe ñrsL 24 hrs., lL may never be able Lo aualn lLs orlglnal properues. 1emperaLure eñecLs on curlng • real hlgh LemperaLures above 120 l can cause serlous damage slnce cemenL may seL Loo fasL. • acceleraLed curlng procedures produce sLrong concreLe, buL durablllLy mlghL suñer. • auLoclave curlng.