8/21/2019 Cement and Concrete – an Introduction
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Cement and concrete – an
introductionBede Andrea - Technical University of Cluj-Napoca
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Overview
2
Concrete concrete properties
Mortar
Aggregates
Hydraulic cement properties
production hydration phases + hydration reactions
hydration products
Admixtures classifcation
eects
Supplementary Cementitious Materials (SCMs) classifcation
eects
Silica ume silica nanoparticles
!urther possi"le research
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Concrete
#
Concrete is an artifcial roc$%li$e material& a mixture ocoarse aggregate (gra'el or crushed stone)& fne aggregate(sand)& cement& air& and ater
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Concrete properties - part 1
*
he density o cement can "e determinedusing a ,e Chatelier -as$ and $erosene or "yusing a helium pycnometer
Crac$ing& .oint closing& spalling and lateraloset are caused "y se'ere al$ali%silicareacti'ity in this parapet all
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Concrete properties - part 2
/
Air%entrained concrete ("ottom "ar) ismore resistant to damage romrepeated ree0e%tha cycles
ime o set& determined "y the 1ilmoreneedle
elationship "eteen total atercontent and drying shrin$age 3ithinthe shaded area o the cur'es arerepresented se'eral mixtures ith'arious proportions
Measuring the coe4cient o thermalexpansion
Measuring concrete slump ith a slumpcone
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Concrete properties - part 3
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Concrete properties - part 4
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he measured heat o hydration can "eillustrated either as a temperature cur'e or asa heat -o7cumulati'e heat -o cur'e8p9 temperature cur'e dierences "eteensimple cement paste and cement paste ith
*:; -y ash
he heat -o cur'e has a 'ery distinct shape and it can"e replicated or the same cement paste ormulation!or dierent cement compositions& the second mainpea$ may mo'e according to the speed o hydration
reactions
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Concrete properties - part 5
• o the let& an example o
mercury porosimetry on
cements prepared ith three
dierent silanes
•
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Mortar
Mortar is a $ind o concrete made only ith small aggregates(sand)Mortars are mostly used to9• "ind together "uilding "loc$s9 "ric$s& cut roc$s andconcrete masonry units• fll and seal the irregular gaps "eteen them
•add decorati'e colors or patterns in masonry alls
he dierent uses o concrete (let) and mortar (right)
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Aggregates
D:
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Hydraulic cement - properties
DD
Eefnition (
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Hydraulic cement production -from extraction to dispatch
D2
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Cement composition
D#
he mainchemicalconstituents oortland cement9 alite
"elite
tricalcium aluminate(celite)
errite
gypsum& plaster oranhydrite
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Cement hydration phases
D*
Stage 1: Mixing
(t < 15 min)
Stage 2: Dormancy
(15 min < t < 2 h)
Stage 3: Hardening
(2 h > t < 12 h)
Stage 4: Cooing
(12 h > t < 2! h)
Stage 5: Den"i#ication
(t > 2! h)
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Cement hydration reactions
D/
• frst reactions9 calcium hydroxide dissol'es in the solution&the calcium aluminate and gypsum orm ettringite
• next& the alite reacts ith ater once the solution is saturatedin calcium hydroxide
• "elite is sloer to react and ill continue to hydrate or along time
• gi'en an excess o calcium aluminate& ettringite ill react toorm monosulphate• ith an excess o calcium sulphate rom the en'ironment&secondary ettringite ill orm and maniest itsel as sulphateatac$
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Hydrated cement composition
D5
•CSH % calcium
silicate hydrate
•ettringite % C%A%S%
H
•monosulphate
•calcium
hydroxide
•hydrated !e and
Al hydroxides
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Admixtures - classification
D6
Admixtures can "e used hile mixingthe concrete and or fnishing theconcrete suraces
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Admixtures - effects
D=
S l C
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Supplementary CementitiousMaterials
D
S@M image o microsilica (a)& calcined $aolin (")& "lasturnace slag (c)& -y ash (d) and natural 'olcanic ash (e)
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SCMs - effects
2:
Compressi'e strengthde'elopment at D& #& 6& 2=and : days o concretemixtures containing a -y ashdosage o 2/;
Change in rate o heat e'olution o cement%silica umepastes ith time
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Silica fume & silica nanoparticles
2D
Comparison "eteen porositiesdetermined "y He pycnometry andHg porosimetry on cement%silicaume pastes
Fn-uence o nanosilica on the hydrationtemperature o cement pastes % dierent
concentrations (up) and dierent particlesi0e at the same concentration ("elo)
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Silica fume & silica nanoparticles
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he e'olution o the hydration ogray cement pastes ith :* 7cratio and /; addition o colloidalnanosilica& simple and suracemodifed nanosilica
Heat o hydration or cement pastesith dierent ?uantities o =5 nm
nanosilica
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Conclusions & possible research
2#
• Hydration o cement pastesith dierent concentrations onano silica % treated or untreatedith dierent $inds oorganosilanes
• Hydration o cement pastesith untreated nanosilica andseparate addition oorganosilanes• Hydration o cement pastesith untreated nanosilica and
superplastici0ers• Hydration o cement pastesith treated nanosilica&superplastici0ers and a really lo7c ratio % :2/• At the same time& using othertechni?ues to measure9temperature& resisti'ity&
A comparison "eteen 2 relaxation times o silicananoparticles& compressed& saturated ith ater&"eore and ater urther compressing them
Some possi"le research ideas9
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