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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