Cement and Concrete - An Introduction

Cement and concrete an
introduction
Bede Andrea - Technical University of Cluj-Napoca
Overview
Concrete
Mortar
Aggregates
Hydraulic cement
classification
effects
Supplementary Cementitious Materials (SCMs)
properties
production
hydration phases + hydration reactions
hydration products
Admixtures
concrete properties
classification
effects
Silica fume & silica nanoparticles
Further possible research

2
Concrete
Concrete is an artificial rock-like material, a mixture of
coarse aggregate (gravel or crushed stone), fine aggregate
(sand), cement, air, and water.
Concrete properties - part 1
The density of cement can be determined

using a Le Chatelier flask and kerosene or by
using a helium pycnometer.
Cracking, joint closing, spalling and lateral

offset are caused by severe alkali-silica
reactivity in this parapet wall.
Air-entrained concrete (bottom bar) is

more resistant to damage from
repeated freeze-thaw cycles.
Time of set, determined by the Gilmore

needle.
Relationship between total water

content and drying shrinkage. Within
the shaded area of the curves are
represented several mixtures with
various proportions.
Measuring concrete slump with a slump

cone.
Measuring the coefficient of thermal

expansion.
The measured heat of hydration can be

illustrated either as a temperature curve or as
a heat flow/cumulative heat flow curve.
Up: temperature curve differences between
simple cement paste and cement paste with
40% fly ash
The heat flow curve has a very distinct shape and it can
be replicated for the same cement paste formulation.
For different cement compositions, the second main
peak may move according to the speed of hydration
reactions.

To the left, an example of
mercury porosimetry on
cements prepared with three
different silanes.
Below, an example of the
pore size distribution
evolution over 8 hours, as
seen from NMR data.
Nitrogen adsorbtion equipment (left) and a

SEM photo (at 92 days) for porosity
Mortar
Mortar is a kind of concrete made only with small aggregates
(sand).
Mortars are mostly used to:
bind together building blocks: bricks, cut rocks and
concretemasonryunits
fill and seal the irregular gaps between them;
add decorative colors or patterns in masonrywalls.
The different uses of concrete (left) and mortar (right)

9
Aggregates
10
Hydraulic cement - properties
Definition (BS ISO 197-1:2000): a hydraulic binder - a finely ground

inorganic material which, when mixed with water, forms a paste
which sets and hardens (by means of hydration reactions and
processes) and which, after hardening, retains its strength and
stability even under water.
Raw materials, clinker and finished Portland cement powder

11
Hydraulic cement production from extraction to dispatch
12
Cement composition
The main
chemical
constituents of
Portland cement:
13
alite
belite
tricalcium aluminate
(celite)
ferrite
gypsum, plaster or
anhydrite
Cement hydration phases
Stage 1: Mixing
(t < 15 min)
14
Stage 2: Dormancy
(15 min < t < 2 h)
Stage 3: Hardening
(2 h > t < 12 h)
Stage 4: Cooling
(12 h > t < 20 h)
Stage 5: Densification
(t > 20 h)
Cement hydration reactions

first reactions: calcium hydroxide dissolves in the solution,
the calcium aluminate and gypsum form ettringite
next, the alite reacts with water once the solution is saturated
in calcium hydroxide
belite is slower to react and will continue to hydrate for a

long time
given an excess of calcium aluminate, ettringite will react to
form monosulphate
with an excess of calcium sulphate from the environment,
secondary ettringite will form and manifest itself as sulphate
atack
15
Hydrated cement composition

CSH - calcium
silicate hydrate
ettringite - C-A-SH
monosulphate
calcium
hydroxide
hydrated Fe and
Al hydroxides
16
Admixtures - classification
Admixtures can be used while mixing

the concrete and for finishing the
concrete surfaces.
17
Admixtures - effects
18
Supplementary Cementitious
Materials
19
SEM image of microsilica (a), calcined kaolin (b), blast

furnace slag (c), fly ash (d) and natural volcanic ash (e)
SCMs - effects
Compressive strength
development at 1, 3, 7, 28
and 90 days of concrete
mixtures containing a fly ash
dosage of 25%.
20
Change in rate of heat evolution of cement-silica fume

pastes with time.
Comparison between porosities

determined by He pycnometry and
Hg porosimetry on cement-silica
fume pastes
21
Influence of nanosilica on the hydration

temperature of cement pastes - different
concentrations (up) and different particle
size at the same concentration (below)
The evolution of the hydration of

gray cement pastes with 0.4 w/c
ratio and 5% addition of colloidal
nanosilica, simple and surface
modified nanosilica.
22
Heat of hydration for cement pastes

with different quantities of 86 nm
nanosilica.
Conclusions & possible research

Some possible research ideas:
Hydration of cement pastes
with different concentrations of
nano silica - treated or untreated
with
different
kinds
of
organosilanes
with untreated nanosilica and
separate
addition
of
organosilanes
with untreated nanosilica and
superplasticizers
with
treated
nanosilica,
superplasticizers and a really low
w/c ratio - 0.25
At the same time, using other
techniques
to
measure:
23
temperature,
resistivity,
A comparison between T2 relaxation times of silica

nanoparticles, compressed, saturated with water,
before and after further compressing them.

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Cement and concrete an

Supplementary Cementitious Materials (SCMs)

Further possible research

Concrete properties - part 1

The density of cement can be determined

Cracking, joint closing, spalling and lateral

Concrete properties - part 2

Air-entrained concrete (bottom bar) is

Time of set, determined by the Gilmore

Relationship between total water

Measuring concrete slump with a slump

Measuring the coefficient of thermal

Concrete properties - part 3

Concrete properties - part 4

The measured heat of hydration can be

Concrete properties - part 5

Nitrogen adsorbtion equipment (left) and a

The different uses of concrete (left) and mortar (right)

Hydraulic cement - properties

Definition (BS ISO 197-1:2000): a hydraulic binder - a finely ground

Raw materials, clinker and finished Portland cement powder

Hydraulic cement production from extraction to dispatch

Cement hydration phases

Cement hydration reactions

belite is slower to react and will continue to hydrate for a

Hydrated cement composition

Admixtures can be used while mixing

SEM image of microsilica (a), calcined kaolin (b), blast

Change in rate of heat evolution of cement-silica fume

Silica fume & silica nanoparticles

Comparison between porosities

Influence of nanosilica on the hydration

Silica fume & silica nanoparticles

The evolution of the hydration of

Heat of hydration for cement pastes

Conclusions & possible research

A comparison between T2 relaxation times of silica

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