Rheology of concrete: a study case based upon the use of the concrete equivalent mortar

ORIGINAL ARTICLE

Rheology of concrete: a study case based upon the useof the concrete equivalent mortar

F. J. Rubio-Hernandez • J. F. Velazquez-Navarro •

L. M. Ordonez-Belloc

Received: 8 February 2012 / Accepted: 13 July 2012 / Published online: 31 July 2012

� RILEM 2012

Abstract A deeper and wider knowledge of the

rheology of concrete could be obtained if a variety of

absolute rheological parameters were measured.

Although a valuable rheological classification can be

induced from concrete rheometers, they do not give

the same absolute values of the rheological parame-

ters. Moreover, rheological tests with concrete require

a large volume of material. The aim of this work is to

use the concrete equivalent mortar (CEM) method

(Schwartzentruber and Catherine, Mater Struct

33:475–482, 2000) to get concrete rheological infor-

mation with an absolute rheometer. Additionally some

graph tools that resume the results from several

rheological tests are suggested for the design of

concretes. CEM have been formulated to test concrete

formulations with an absolute rheometer. Steady flow

measurements of a CEM corresponding to a self-

compacting concrete (SCC) clearly reveal character-

istic non-linear viscoplastic behavior which it is not

shown by conventional tests used to characterize

concretes. The thixotropic behavior of a concrete is

well-established using three different rheological tests

that can be made with an absolute rheometer testing its

corresponding CEM. These tests reveal aspects of the

strength and kinetics of the micro-structure that are not

observable when thixotropy of concrete is semiquan-

tified with conventional methods. Only with a CEM is

possible to make oscillatory shear tests. In this way the

viscoelastic behavior of the concrete can be charac-

terized. Results of practical interest are so obtained.

For example, the necessity of vibration at rest

application to the fresh concrete can be established

from frequency sweep tests of CEM in the linear

viscoelastic region. The correlation between rheolog-

ical behaviors of a concrete and its corresponding

CEM has been supported. Steady flow and thixotropy

rheographs of CEM are suggested as tools for an easy

and fast determination of adequate formulation for

specific applications.

Keywords Rheology � Fresh concrete � Concrete

equivalent mortar � Rheographs

1 Introduction

1.1 State of the art

The flow behavior of fresh concrete is a matter of

interest both for its influence on the placing of the

F. J. Rubio-Hernandez (&)

Department of Applied Physics II, University of Malaga,

Malaga, Spain

e-mail: [email protected]

J. F. Velazquez-Navarro

Department of Mechanics Engineering and Fluid

Mechanics, University of Malaga, Malaga, Spain

L. M. Ordonez-Belloc

Technological Institute of Construction, AIDICO,

Paterna, Spain

Materials and Structures (2013) 46:587–605

DOI 10.1617/s11527-012-9915-1

material and for its mechanical response back when it

reaches the hardened state. Conventional techniques

(Abrams cone, L-box, etc.) can only provide semi-

quantitative knowledge of the steady flow behavior of

concrete. They have demonstrated that concrete is a

viscoplastic material that, for the case of conventional

concrete, follows the linear model due to Bingham

[1, 2]. This result has been extensively confirmed using

different concrete formulations [3–5]. The Bingham

viscoplastic behavior is described as follows. When the

shear stress (s) is higher than a threshold value (sB)

named yield stress, the material flows, i.e. ceases to

behave elastically, and Bingham linear flow model

(Eq. 1) predicts the relation between the shear stress

and the shear rate _cð Þ applied to the material,

s ¼ sB þ gp _c; s [ sB ð1Þ

In this equation gp is the plastic viscosity. Both

parameters of the model, sB and gp, have useful

practical meanings. In this way it is possible to

compare the performance of different concrete formu-

lations. The yield stress is related to the flow ability of

the material. The lower the yield stress the material will

flow more easily through very complicated formworks.

Additionally, the yield stress of the fluid phase (cement

paste or mortar) is the key parameter of the concrete

stability or rest segregation [6–8]. The plastic viscosity

is mainly related to the dynamic segregation resistance

of the material induced by flow [9]. For high-perfor-

mance concretes, it frequently constitutes the critical

parameter that controls pump ability, and ease of

finishing. With the development of new high-perfor-

mance concretes it has shown that the viscoplastic

response of these materials is more complex, i.e. it is

not necessarily linear [10–12]. This fact invalidates the

use of the Bingham model to characterize the steady

flow behavior. Fortunately there are a variety of non-

linear viscoplastic models that can be used for the

analysis of the steady rheological behavior of materi-

als. The most commonly used non-linear model is the

Herschel–Bulkley model,

s ¼ sHB þ K _cn; s[ sHB ð2ÞThis model has three rheological parameters, the

yield stress, sHB, the consistency index, K, and the flow

behavior index, n, which indicates shear-thinning if

n \ 1 shear-thickening if n [ 1, and the Bingham

model if n = 1. Although this model has been applied

to the concrete test results, it has two major

disadvantages: overestimate the yield stress value

[13] because the slope of the flow curve tends to zero at

very low shear rates, and it is difficult to interpret the

physical meaning of the parameter K, because the

dimension of this parameter is variable due to its

n-dependency(Pasn). It has been pointed out [13] that

the three following conditions must be accomplished

by a viscoplastic model: it must supply a positive yield

stress, it must have a positive linear term in the shear

rate to avoid a zero slope at low shear rates, and,

finally, all its parameters must have fixed dimensions

which traduces in a physical meaning of the param-

eters. A model that accomplishes with all those is

known as the modified Bingham model (Eq. 3) which

can be regarded as an extension of the Bingham model

with a second order term or, alternatively, as a second

order Taylor development of the Herschel–Bulkley

equation, justified by the fact that rarely n [ 2,

s ¼ sMB þ gp _cþ c _c2; s[ sMB ð3Þ

In this equation sMS is the yield stress, and c is the

second order coefficient. Comparing the second order

Taylor development of the Herschel–Bulkley equation

around a random point, a, with Eq. (3), a theoretical

relation between the quotient c/gp (modified Bingham)

and n (Herschel–Bulkley) is obtained [13],

c

gp

¼ 1

2a

n� 1

2� n

� �ð4Þ

The experimental confirmation of this relation has

been observed [13] resulting a = 7.5 s-1. Therefore

the non-linear behavior can be quantified with the

parameter c/gp. Shear-thinning is indicated if c/gp \ 0,

shear-thickening if c/gp [ 0 and the Bingham model if

c/gp = 0.

Studies on other rheological parameters than yield

stress and plastic viscosity of concrete are scarce. The

main reason is the geometric limitation imposed by the

size of coarse particles which makes not possible using

absolute rheometers. For example, despite its evident

practical utility [7, 14], studies on the transient

rheological behavior of concrete and its temporal

evolution during the induction period (thixotropy) are

scarce [15]. The practical utility of the transient

rheological behavior study of concrete can be illus-

trated, for example, considering that a low thixotropic

formulation, i.e., one that after being sheared, quickly

regains its initial viscosity (see later author’s opinion

588 Materials and Structures (2013) 46:587–605

about nomenclature of thixotropic concretes), it would

be useful to build high walls. This is because, being so

consistent, the pressure on the formworks [14, 16–19]

will be less and, when removed, the structure does not

collapse. If the same formulation is however intended

to produce multi-layered slabs, its high consistency

will prevent its mix with other layers, resulting in

undesirable cold joints [19]. Other interesting rheo-

logical study useful for concrete applications refers to

viscoelasticity. The scarce studies which have been

found on the viscoelastic rheological response of the

fresh cementitious materials refer only to cement

pastes [20–22]. None relationship between the values

of rheological parameters measured (loss and storage

modulus) and some practice property or application of

the material has been suggested.

1.2 Multi-scale theory and concrete equivalent

mortar

One of the main challenges facing the Rheology of

concrete refers to the possibility of obtaining, in the

most simple and convenient way, a relationship

between composition and performance of a given

formulation. Absolute rheometers are adequate to

accomplish with this objective because a variety of

rheological parameters (obtained with steady, transient

and viscoelastic studies) can be measured with small

amounts of material. Therefore, it is mandatory to face

the serious difficulty that results of the relatively large

size of coarse aggregate that form part of the concrete.

Multi-scale theory [23–26] allows, at present, to

propose a first solution to the problem. The basic

principle of the theory is to admit that the material

properties can be predicted from knowledge of both the

properties of the matrix and its inclusions. Applied to

mortar, the multi-scale theory leads to identify the

cement paste (cement, water and additives) with the

matrix and the fine aggregate with the inclusions. Thus,

the rheology of the mortar can be predicted from the

rheology of cement paste and the shape, size and

volume fraction of fine aggregate. In the case of

concrete, we would identify the mortar with the matrix

and coarse aggregate with the inclusions. Therefore the

rheology of the concrete can be predicted from the

rheology of the mortar and the nature and quantity of

the coarse aggregate. Although this scheme is attrac-

tive from an experimental point of view, it should be

taken with caution. It is not appropriate to predict the

rheology of the concrete from the rheology of cement

paste considering the fine sand and coarse aggregate as

inclusions, because as it was noted [5, 27] the rheology

of both materials differs in several aspects. To be

clearer, while in the cement paste we have a solid

concentration of about 50 %, in the concrete becomes

80 %. Moreover, whereas the rheology of cement paste

is governed primarily by colloidal forces, the rheology

of concrete is dominated by more complex processes

like friction between the aggregates and the ratio of the

aggregate solid volume fraction over the packing

volume fraction [15, 28]. Therefore, should not be

surprising to observe that today is considered the study

of the rheology of cement paste as only a way to check

what additives are suitable for a particular formulation,

or to simply compare the performance of different

formulations as a starting point for a more thorough

investigation [26] despite experiments and multi-scale

analysis have shown that the concrete rheology is

mostly governed by the cement paste behavior and the

aggregate solid volume fraction over the packing

volume fraction of the aggregates [28]. According to

what has been stated, it is obviously crucial to define

the role played by the mortar for the prediction of the

rheological behavior of concrete.

Schwartzentruber and Catherine [29] proposed the

use of the so named concrete equivalent mortar (CEM)

to study the rheology of fresh concrete with the

assumption that the rheological properties of the CEM

should be correlated with those of the corresponding

concrete. For the CEM design is considered that all

friction phenomena take place at the cement paste/

aggregate interface. Therefore the total specific area of

the aggregates is a fundamental variable to understand

the level of workability of the concrete [30]. When the

composition of the CEM is calculated the main

following relations concerning the original concrete

composition should keep:

(a) the same kind and dosage of cement and mineral

additives,

(b) the same ratio effective water-cement,

(c) similar percentages of additives and method of

addition to the mix and, finally,

(d) the use of fine aggregate amount necessary to

achieve the same total surface area of coarse

aggregate replaced.

Other geometric features like angularity of the fine

and coarse aggregates affect the rheological properties

Materials and Structures (2013) 46:587–605 589

of concrete. However, at this level of substitution of

coarse by fines this is not taken into account.

It is interesting to note that the substitution of gravel

by fine aggregates leads to a reduction of the grading

curve and an increase of the average inter-granular

distance. As the size of sand particles is smaller than

gravel, the total amount of aggregate needed to make the

CEM is less than that contained in the concrete. As a

result, the chemical inertness of the mortar is less than

that of concrete, which is advantageous, since the

induction period of the CEM will be greater and,

therefore, the lifetime of the samples will be also greater,

making more feasible the rheometric work [30].

There are several experimental studies that have

supported the CEM method [29, 31, 32]. They have

concluded that there is a certain correlation between

the rheological behavior of the CEM and the concrete.

In view of the great information we can get from the

use of absolute rheometers and considering that the

CEM is liable to be studied with this type of

rheometers and it looks to be a valid substitute of

concrete for rheological studies, the rheology of the

CEM has been analyzed in this work.

1.3 Purpose of this work

The aim of this research work is to contribute to get

experimental procedures that permit to accomplish

complete rheological studies of concretes by means of

the study of the CEM rheology. Additionally, two

rheograph tools made from the knowledge of the

rheological parameters of several CEMs and the knowl-

edge of the corresponding concrete type are presented

and discussed. These rheographs, when full developed,

presumably should serve to identify a concrete type from

the position of the corresponding CEM in the phase space

of the rheograph. The potential significance of these

outcomes is that eventually the procedures and rheo-

graphs developed with the use of CEM should be

standardized and incorporated into technical regulations.

2 Experimental

2.1 Materials

Ordinary Portland cements I 42.5R/SR and I 42.5N

(Italcementi Group) were used in this study. Table 1

shows the characteristics of the cements. While the

former is intended for the manufacture of concrete that

have to withstand aggressive media, the second is not

appropriated for this type of media. The substitution of

cement by mineral additions is recommended by three

main reasons. Firstly, from the economical point of

view if the additions have a competitive price.

Secondly, from a rheological point of view if the use

of an adequate quantity of fines increases the paste

volume, reducing the yield stress and increasing the

consistency of the formulation [27, 33, 34]. And,

thirdly, if the use of fines increases the compactness of

the concrete and, consequently, its hard resistance at

all ages [27]. In this study commercial limestone filler

(OMYACARB 10-BE, Omya Clariana S.L., Spain)

and silica fume (Ferroatlantica, Spain) have been used

as mineral additives. Limestone filler is mainly

composed by natural calcium carbonate grounded

([99 %) and small amounts of silica and quartz

(0.05–0.5 %). It appears as a white odorless powder

non soluble in water. Its density is 2,730 kg/m3 and its

average particle size is 30 lm. The chemical compo-

sition of silica fume (Ferroatlantica, Spain) is shown in

Table 2. The particles of silica fume show an irregular

shape (Fig. 1). The average size of the particles is

300 nm, while the volume of a silica fume sample is

mainly occupied by particles with sizes 300 nm and

Table 1 Characteristics of the cements

Cement I 42.5R/SR Cement I 42.5N

Chemical composition (% w/w)

SiO2 19.40 18.80

Al2O3 4.00 4.80

Fe2O3 4.20 2.64

CaO 63.30 63.10

MgO 2.90 1.21

K2O 0.90 0.75

Na2O 0.20 0.09

SO3 3.40 2.81

LOI 1.70 5.80

Mineralogical composition (% w/w)

C3S 56.20 69.96

C2S 20.20 1.12

C3A 7.40 8.25

C4AF 16.20 8.03

Blaine surface (cm2/g) 4,900 3,079

Particle size (lm) 15 37

Density (g/cm3) 3.20 3.14


20 lm. As can be seen in Fig. 1, despite its high

polydispersity the larger particles disintegrate easily,

thus increasing the population of smaller particles.

Indeed, the beneficial effects of silica fume particles

both in the rheological and mechanical responses are

not only due to its rapid pozzolanic reaction but, as

highlighted here, to the filler effect of silica fume

particles. Because of its fineness particles of silica

fume can fill the gap between the larger cement

particles, resulting in a denser microstructure [33].

The increase in the amount of fines present in the

composition of the concrete means a greater demand

for water that decreases, however, the resistance of the

hardened material. To avoid this problem is necessary

to use superplasticizers additives [35, 36]. Superplast-

icizers increase the flowability of the material due to

the dispersion effect on the cement particles [37, 38].

Two lignosulphonate additives were used in this study.

Their properties are shown in Table 3. Moreover

acrylic additives prevent segregation. Four of these

additives were used, and their properties are also

shown in Table 3. The appropriate selection of

aggregate type and size distribution directly affects

the properties in the fresh and hardened concrete.

Table 4 shows the particle size distribution, adsorp-

tion coefficient and density of aggregates used in this

study.

2.2 Rheometers

A Gemini 150 (Malvern Inst., England) controlled

stress/rate rheometer was used to collect the rheolog-

ical data corresponding to cement pastes and mortars.

This device was equipped with a control temperature

Peltier system. Each experiment was conducted on a

fresh sample at 25.00 ± 0.05 �C.

Four serrated vane geometry was used. The diam-

eter of the rotor was 25.0 ± 0.1 mm, which was

introduced in a cup (stator) with an inner diameter of

37.0 ± 0.1 mm. The advantage of using this geometry

with cementitious materials has been extensively

justified [14, 18, 26, 39, 40]. The rheometer was

calibrated before use with a calibration oil (190104)

for continuous shear and with a reference PDMS for

oscillatory shear. These materials were supplied by the

fabricant.

To get rheological parameters directly from con-

crete samples, a 4C-Rheometer (Danish Technologi-

cal Institute) was used. This device is equipped with an

Abrams cone held by a mechanical robotic arm. In this

Table 2 Chemical composition of the silica fume

Chemical composition (% w/w)

SiO2 Al2O3 C CaO

[85 \1 \4 \1

Fig. 1 Scanning electron microscopy of silica fume

Table 3 Properties of the superplasticizers additives

Fabricant Chemical basis Aspect Density (kg/m3) Dry residue (%)

Lignosulphonates

175 SIKA Modified lignosulphonate Dark brown liquid 1,200 43

LiCa AXIM Calcium lignosulphonate Dark brown liquid 1,350 30

Acrylics

3425 SIKA Acrylic Orange liquid 1,100 26

Driver 3 AXIM Acrylic Clear liquid 1,010 35

PL-RX-HAC BASF Modified polycarboxylate Brown liquid 1,002 3

Glenium C303 SCC BASF Acrylic Green liquid 1,044 20


way the cone always rises to the same height and at the

same speed, giving the test fine reproducibility. Right

in the middle of the cone has a digital video camera to

record the time evolution of the size of the spread that

forms when the cone rises and allows the free flow

material. From this information, the device software

calculates the values of yield stress and plastic

viscosity of the sample [41].

2.3 Protocols

Due to the physical composition of concrete and its

chemical evolution just after the contact between

cement and water, it is necessary to develop a suitable

experimental protocol which minimizes the impact of

hydration on the rheological behavior of cementitious

materials. The objective is to obtain accurate and

reproducible results.

Steady flow curve (Gemini 150) for mortars was

designed starting from the higher shear rate. This

design allows minimizing cement hydration effects.

The duration of tests can increase and, consequently, it

is possible to get data at a wider number of shear rates.

The protocol is described in Fig. 2.

Hysteresis loop consists in the application of

successive shear ramps (up-down or down-up) to the

sample. The output is the instantaneous shear stress

corresponding to each shear rate applied to the

material. If the curves do not overlap a time-depen-

dence of the material is inferred. The protocol used in

this study (Gemini 150) is described in Fig. 3. Due to

the same reasons pointed out to get steady flow curves,

the decreasing ramp was first applied and the cycle

was full field with a twin increasing ramp. The area

between both flow curves is taken as a measure of the

thixotropic level of the material. The physical mean-

ing of this magnitude is the energy per time and

volume units necessary to break the rest structure of

the material. A larger value of this magnitude can be

interpreted as the manifestation of a stronger or a more

developed structure, or both. Then, a certain ambiguity

is inferred from the interpretation of the results

obtained with this thixotropic test.

Once that, eventually, the sample has shown time-

dependence of the flow behavior, just when it is

applied the protocol described in Fig. 3, the thixotro-

pic level of the material has been additionally

Table 4 Particle size distribution, adsorption coefficient and

density of aggregates

Sieve (mm) Sand

0/4

Gravel

4/8

Gravel

8/12

Gravel

11/22

0.063 3 1 1 1

0.125 9 1 1 1

0.25 23 1 1 1

0.5 38 1 1 1

1 52 1 1 1

2 69 2 1 1

4 96 11 1 1

8 100 97 15 1

10 100 100 51 2

16 100 100 100 40

20 100 100 100 79

32 100 100 100 100

40 100 100 100 100

125 100 100 100 100

250 100 100 100 100

Adsorption

coefficient (%)

0.80 1.40 1.20 0.97

Density (kg/m3) 2,650 2,600 2,610 2,610

Fig. 2 Steady flow curve protocol

Fig. 3 Hysteresis loop protocol


quantified with step-up and step-down tests. This

protocol is shown in Fig. 4. The percentage of initial

steady shear stress (first step-up from rest to _c ¼ 1 s�1)

which is recovered after 40 s of the final step-down

from _c ¼ 50 s�1 to _c ¼ 1 s�1, is taken as the thixotro-

pic index of the material (IR40). The larger this value

the quicker and higher is the initial structure

recovering.

Roussel [19] has proposed an alternative method to

characterize and quantify the thixotropic character of a

cementitious material. The method consists into

measure the time-dependence of the static yield stress.

The static yield stress is the initial shear stress value

measured when a constant shear rate is applied just

after the sample has rested during a time interval

which is varied. The time evolution of the shear stress

is recorded, being the maximum shear stress just after

the rest state the magnitude recorded in this analysis,

as it is shown in Fig. 5. A larger sMB value is

interpreted as the development of a stronger rest

structure.

As it was before pointed out, the use of rheological

dynamic analysis to get material functions of cemen-

titious materials is not an extended experimental task.

Nevertheless, the evolution with frequency of storage

and loss modulus is a valuable information because

can be interpreted as the necessity or not of vibration

of the material to avoid segregation. Therefore,

amplitude sweep (Fig. 6) to determine the linear

viscoelastic region and frequency sweep (Fig. 7) to get

information on the necessity of vibration have been

made.

2.4 Nomenclature

Each concrete formulation was named as Ci and the

corresponding CEM was named CiEM, with i varying

from 1 to 4.

2.5 Self-compacting concrete—a need for more

precise rheological studies

The most important milestone in the history of

concrete is, probably, the appearance in 1986 of

Fig. 4 Thixotropy protocol

Fig. 5 Alternative method for thixotropic study

Fig. 6 Amplitude sweep scheme

Fig. 7 Frequency sweep scheme


self-compacting concrete (SCC). According its inven-

tor [42] SCC can be defined as a concrete that is able

to flow, without segregation separation or bleeding,

inside the casing filling the volume of it. It is also able

to pass between the bars of the reinforcement without

other means of compaction which consolidation due

to its own weight. This new material was a response to

the need in Japan of a high strength cementitious

material, but also with a sufficient fluidity to fill very

intricate formworks needed to withstand any earth-

quake so frequent in that country. With the advent of

SCC it has been made a great effort in developing

methods to obtain, with maximum accuracy and

reproducibility, quantitative data on the rheological

parameters characterizing the flow behavior of the

fresh material. However most of them are inconsis-

tent and depend on the type of test or measurement

instrument used [2, 5, 24]. As a consequence,

rheological methods have not properly been applied

to these concretes and, traditionally, workability and

other performance parameters of fresh concrete are

usually determined by semi-quantitative empirical

tests [27]. Obtaining precise numerical values for the

rheological parameters is currently a very important

topic for industry. There is also a great interest in

reducing the number of experiments required to obtain

a relation between the rheology and the design of the

mix. In this way it would be possible to obtain

concrete formulations that combine resource econom-

ics (less environmental impact) with high perfor-

mance features [36, 43]. On the other hand, to predict

the flow behaviour of fresh concrete in transport,

pumping and placement on horizontal surfaces (slabs)

and vertical (walls) would be useful to determine the

range of applicability of specific formulations [7, 14].

As a consequence of these motivations, we have

studied the rheology of intended SCC formulations.

3 Results and discussion

3.1 Design of the concrete C1

The procedure followed to get the concrete C1 which,

as the other three formulations, was intended as a SCC,

is here described. C2, C3 and C4 formulations were

obtained following the same procedure. To avoid

unnecessary reiteration, only C1-procedure will be

described.

There are two basic methods for designing a SCC

[44–46]. On the one hand, we can set the resistance to

be achieved, and after this selection, would set the

amounts of the components necessary to meet this

objective. On the other hand, we can start from a

certain standard formulation that will be corrected to

achieve the workability appropriate to the desired

application. In this work, the second option has been

used.

Independently the method used to design a SCC,

the granular skeleton must accomplishes the condition

to have the least amount of holes. In other words, the

dosage of aggregates should get the highest possible

packing. Two methods have been followed to achieve

this objective. The first one consists into use the

adequate dosage of coarse and sand in order to get a

final aggregate with a grading curve that fits to Fuller

ideal curve (Eq. 5),

Y ¼ A

ffiffiffiffid

D

rð5Þ

In this equation Y is % of aggregates passing the sieve,

d is particle size, D is the maximum particle size of the

aggregate and A is a coefficient depending on D-value.

Grading curve of each aggregate and that obtained

using this method is shown in Fig. 8. The resulting

dosage is shown in Table 5.

The second method to get maximum aggregate

pack uses an optimization algorithm implemented in

the 4C-Packing software [47]. Two different dosages

were obtained with this last method, which are shown

in Table 5. Finally, to select the best aggregate dosage

between the three options shown in Table 5, the self-

packing index of every dosage was determined

following an experimental method proposed by Niel-

sen et al. [47]. The results are shown in Table 5. F-

dosage was selected to formulate the SCC due to its

self-packing index was the higher one.

The final concrete composition is shown in Table 6.

Cement, filler and water quantities were selected to get

a good workability of concrete [48]. For the formu-

lation of the concrete C1 two polycarboxylate syn-

thetic additives were used to get lower water demand

(BASF PL-RX-HAC) and superplasticizer effect

(BASF GLENIUM C303 SCC). To obtain the best

dosage of these additives, following manufacturer

recommendation, the quantity of BASF PL-RX-HAC

was fixed to 0.2 % by weight of cement (bwc) and the


dosage of BASF GLENIUM C303 SCC was varied

(0.5–1.5 % bwc). The different concrete formulations

so obtained were studied by means of spread tests. An

adequate diameter of the spread and the absence of

segregation were the factors determining the finally

accepted BASF GLENIUM C303 SCC dosage. Sam-

ples were prepared following the protocol described in

Table 7.

3.2 Rheology of the concrete C1

Figure 9 shows the spread test results obtained with

the rheometer 4C. As it can be seen, the diameter of the

spread increases with time until a maximum value is

reached. The final value of the spread diameter is

shown in Table 8. Yield stress value has been obtained

using a version for the spread radius data of Murata

approach [49] given by Flatt et al. [24],

sC ¼qVg

2pR2ð6Þ

where sC is the yield stress value, q is the concrete

density, V the material volume, g the gravity acceler-

ation and R the spread radius. Concrete C1 is,

considering the result of this test, just in the limit to

be qualified as a SCC.

Fig. 8 Aggregate grading. As can be seen Fuller fits the experimental data

Table 5 Aggregate optimal dosages and self-packing indexes

Aggregate Method of

Fuller

4C-packing software [47]

F-Dosage (%) A-Dosage

(%)

B-Dosage

(%)

Sand 0/4 41.8 48.0 42.4

Gravel 4/8 16.1 12.0 10.6

Gravel 8/12 17.7 30.0 1.0

Gravel 11/22 24.5 10.0 46.0

Self-packing

index

0.749 0.727 0.710

Table 6 Compositions of dries C1 and C1EM

Component C1 C1EM

Quantity

(kg/m3)

Quantity

(kg/m3)

Cement I 42.5N 400.0 400.0

Limestone Filler 150.0 150.0

Water 212.9 201.7

Sand 0/1 – 506.8

Sand 0/4 713.7 –

Gravel 4/8 264.0 –

Gravel 8/12 292.3 –

Gravel 11/22 405.8 –

BASF PL-RX-HAC 0.8 (0.2 %

bwc)

0.8 (0.2 %

bwc)

BASF GLENIUM

C303 SCC

4.0 (1.0 %

bwc)

4.0 (1.0 %

bwc)


Thixotropic behavior of the concrete C1 was

quantified measuring the yield stress dependence on

the rest time of the sample just before the spread test

starts [19]. The results obtained with the rheometer 4C

are shown in Fig. 10.

A linear function was fitted to experimental data.

The result was,

sC ¼ 27� 9ð Þ þ 0:72� 0:08ð Þtr2 ¼ 0:9663

ð7Þ

According to Roussel’s criterion [19] this material is

thixotropic, so that it will probably give rise to cold

joints if layers of material are deposited in different

time intervals. It is considered in concrete science and

technology that a material is more thixotropic as faster

is the recovering of its rest structure. Roussel’s

criterion is based upon this idea. However, the authors

prefer other terminology. Thixotropy is defined as the

reversible and time-dependent viscosity variation of

the material when alternative shear-up and shear-

down (to rest) is applied. According with this defini-

tion, no time-dependence should be interpreted as the

absence of thixotropy and, oppositely, the slower

structure recover at rest the more thixotropic must be

considered the material. Really, the ultimate conclu-

sion does not change but the material should be

qualified as less thixotropic when the slope of the

curve shown in Fig. 10 is higher. A faster rest structure

formation (less thixotropic according with definition)

gives rise, of course, to the formation of cold joints,

being the same our conclusion than Roussel’s one.

No more rheological information can be currently

obtained from direct concrete measurements. This is

clearly a problem because, as it was before pointed

out, feasible formulations must be supplied for the

customer satisfaction. In order to obtain a deeper

understanding of the rheological behavior of concrete,

Schwartzentruber and Catherine’s CEM model [29]

must be used. These authors proposed to replace the

coarse aggregate present in the concrete by an

adequate amount of fine aggregate. In this way, the

resulting material, the CEM, is liable to be studied

with absolute rheometers so, in addition, permits to

Table 7 Parameters resulting from oscillating experiments

C1EM C2EM C3EM C4EM

Amplitude sweep

cL 0.01 0.01 0.01 0.001

G0VELðPaÞ 90 ± 1 17 ± 2 91 ± 8 2,400 ± 200

G00VELðPaÞ 25 ± 1 29 ± 3 45 ± 2 1,060 ± 90

cC 0.48 – 0.26 0.48

Frequency sweep

fC1 (Hz) – 0.41 0.30 –

fC2 (Hz) – 23.66 – –

Gp (Pa) 490 ± 80 – – –

Fig. 9 Test results corresponding to C1 obtained with the

rheometer 4C

Table 8 Slump test results

of the concretes and

modified Bingham model

parameters of the CEMs

Cementitious

phase

Slump

(mm)

Yield

stress (Pa)

Plastic viscosity

(Pa s)

c/gp (s)

C1 645 – – –

C1EM – 53.3 ± 0.8 2.47 ± 0.04 0.006 ± 0.002

C2 690 – – –

C2EM – 6.6 ± 0.3 7.49 ± 0.09 0.0176 ± 0.0005

C3 680 – – –

C3EM – 5.9 ± 0.5 6.48 ± 0.12 0.025 ± 0.001

C4 530 – – –

C4EM – 188.7 ± 0.4 3.20 ± 0.03 0.00078 ± 0.00007


extend the range of rheometric tests, providing

feasible information on a greater number of rheolog-

ical parameters.

3.3 Design of C1EM

To design a CEM the following conditions relating to

the original concrete should be maintained:

• same type and dosage of cement and mineral

additives,

• same effective water/cement relationship,

• same proportion of additive and mix method,

• to use the fine aggregate amount necessary to

obtain a specific surface equal to the total surface

area of the coarse aggregate replaced from the

original concrete composition.

It is noted that the two critical steps in designing a

CEM is the calculation of the specific area of the

aggregates present in the concrete and to determine the

actual amount of water corresponding to the original

w/c ratio.

Table 9 shows the data and calculations needed to

get the specific surface area of the sand 0/1 used in this

study to formulate the C1EM, i.e., the equivalent

mortar of concrete C1.

Spherical shape of the sand particles is assumed.

Two first columns are obtained from grading curve.

Column I is the percentage of sand accumulated on

each sieve. Column II is the percentage of sand

retained on each sieve and is calculated subtracting the

percentage accumulated onto the following sieve to

Fig. 10 Rest time dependence of the yield stress value of C1

Table 9 Specific surface area of the sand 0/1

Sieve (mm) % I II III IV V VI VII

% Accumulated % Retained Equivalent

particle

diameter (mm)

% Vol N S Weighted

surface

(m2/kg)

\0.063 0 100 4 0.03 4 22.9 9 109 71.34 2.85

0.063 4 96 12 0.09 12 86.1 9 107 23.91 2.87

0.125 16 84 26 0.19 26 10.9 9 107 11.99 3.12

0.25 42 58 30 0.38 30 13.6 9 106 5.99 1.80

0.5 72 28 28 0.75 28 17.0 9 105 3.00 0.84

1 100 0 0 1.50 0 21.2 9 104 1.50 0

2 100 0 0 3 0 26.5 9 103 0.75 0

4 100 0 0 6 0 33.1 9 102 0.38 0

8 100 0 0 9 0 981 0.25 0

10 100 0 0 13 0 326 0.17 0

16 100 0 0 18 0 123 0.13 0

20 100 0 0 26 0 41 0.09 0

32 100 0 0 36 0 15 0.06 0

40 100 0 0 82.5 0 1 0.03 0

125 100 0 0 187.5 0 0 0.01 0

250 100 0 0 250 0 0 0.01 0

Total 11.48

Density 2.67 kg/m3. See text


the value shown in column I. Column III is the

equivalent particle diameter (D) of the sieve. It is the

average of the consecutive two sieve sizes (the first

and last one are exceptions, they are calculated as

0.063/2 and 250 mm, respectively). Column IV is the

volume percentage occupied by particles of diameter

shown in column III. Its value coincides with that

shown in column II. Column V is the number of

particles per kg of sand. It is calculated from Eq. (8),

N ¼ Total volume

Particle Volume¼

1Sand density

43p Equivalent particle diameter

2

� �3

ð8Þ

Column VI is the specific surface corresponding

to each particle size. Its value is obtained from

Eq. (9),

S ¼ NpD2 ð9Þ

Column VII is the weighted surface in m2/kg for each

particle size. It is obtained multiplying columns IV

and VI and dividing by 100. The specific surface is the

sum of the elements of column VII. Finally, the mass

of sand 0/1 that substitutes all aggregates in the C1EM

will be calculated by using Eq. (10),

M0=1 ¼M0=4S0=4 þM4=8S4=8þM8=12S8=12 þM11=22S11=22

S0=1

ð10Þ

The result obtained with Eq. (10) corresponds to wet

sand. The dry sand mass must be obtained with Eq.

(11),

Mdry0=1 ¼M0=1

1þ Absorption coefficient100

ð11Þ

To determine the actual amount of water correspond-

ing to the original w/c ratio we proceed as follows. To

the initial amount of water obtained from w/c ratio, the

water absorbed by the aggregate must be added, and

the amount of water provided by the additives must be

subtracted. Equation (12) is used to get the actual

amount of water,

Mwater ¼ Mwaterw=cþMwater absorbed by aggregates

�Mwater in additives ð12Þ

Each term in Eq. (12) is calculated as follows,

Mwaterw=c ¼ w

cMcement ð13Þ

Mwater absorbed by aggregates ¼ Mdry 0=1

Absorption coefficient

100

ð14Þ

Mwater in additives ¼MPL�RX�HAC

1�Dry residue

100

þMGLENIUM C303 SCC

1�Dry residue

100

ð15Þ

The final composition of the C1EM is shown in

Table 6 and the mixing protocol of the different

components is shown in Table 10.

3.4 Rheology of C1EM

A Gemini 150 rheometer was used to accomplish this

task. As a preliminary study step-up tests from a

reference shear rate (1 s-1) were performed to deter-

mine the reversibility limit when a growing shear rate

is applied to CEM samples. The rheological protocol

is shown in Fig. 11.

After shear stress reaches the equilibrium value (se)

every time the sample returns to the reference shear

rate, the material is forced to a higher shear step-up

and, after that, is again returned to the reference shear

rate. If the subsequent equilibrium stress values differ

less than a pre-fixed value (20 %) respect to the first

Table 10 Mixing protocol of C1 and C1EM

Step Time (s)

Aggregate enter into the mixer

Add 50 % water (65 rpm) 120

Let stand 120

Add cement and limestone filler (65 rpm) 30

Add 50 % water with BASF PL-RX-HAC (65 rpm) 150

Add BASF GLENIUM C303 SCC (65 rpm) 120

Fig. 11 Shear reversibility analysis


measured equilibrium shear stress, a reversible behav-

ior is accepted, i.e., it will be assumed that the micro-

structure reversibly breaks when that shear rate is

applied to the sample. In Fig. 12 the results corre-

sponding to C1EM are shown.

As can be seen, it can be accepted that the C1EM

recovers its internal structure when the shear rate is

less that 150 s-1. This is a much more high value of

shear rate normally experienced by concrete and

mortar in actual processes (lower that 50 s-1).

In Fig. 13 the steady flow curve of C1EM in the

shear rate interval between 1 and 100 s-1 is shown. As

can be seen, a non-linear behavior is observed. At the

higher shear rates the apparent viscosity slightly

increases (shear-thickening). Note that conventional

method used to get rheological direct information

from C1 could not reveal this behavior, despite the fact

that it has been documented this is a behavior observed

in self-compacting formulations [11, 50]. Shear-

thickening in self-compacting formulations can be

predicted because the two necessary conditions to

observe this rheological behavior, i.e., high particle

concentration and non-aggregating particles [51], are

clearly accomplished. Due to the non-linear steady

flow behavior observed in C1EM samples, the mod-

ified Bingham model has been fitted to the experi-

mental data. The parameters of the model are shown in

Table 8. Relatively low yield stress indicates the

material can easily start to flow, although the plastic

viscosity is not enough high to be sure the material will

not segregate. In other words, like with conventional

methods used to study the concrete C1, we can

conclude studying C1EM that this is a very limited

SCC formulation.

To study the thixotropic behavior of C1EM, three

different tests have been made. The result of applying

a hysteresis loop to the C1EM is shown in Fig. 14. Due

to the protocol here used (see Fig. 3), the initial

structural state in the sample is relatively weak. This is

because the higher shear rate (100 s-1) is first applied

just before starting the decreasing ramp. When shear

rate decreases structural build-up progressively over-

comes structural break-down, being the first mecha-

nism which dominates at the lower shear rates. On the

way back the break-down progressively dominates

onto build-up but, now, during the increasing ramp, the

starting point is a strong structural state. This can justify

why the back curve is above the outward curve. The

area between booth curves, A = (9.1 ± 0.4) kW/m3,

represents the work per unit time and volume neces-

sary to break internal structure of the material. The

Fig. 12 Reversibility results for C1EM

Fig. 13 Steady flow curve of CEMs Fig. 14 Hysteresis loops


higher the area between curves, the stronger the

structure is and/or faster building at rest of the

structure. With this test we cannot discriminate which

of these two possibilities must be chosen. To decide

between both options another thixotropic test should

be done. Step up-down tests were performed with this

objective. The results (Fig. 15) show that a high IR40

index is observed for the C1EM. In other words, the

rest structure of the material quickly builds-up, which

is a result coincident with that inferred from direct C1

measurements. Therefore, of the two possibilities

suggested by the loop test result, the step up-down test

supports the second one, i.e. the structure quickly

builds at rest. Additionally, the rest-time evolution of

the static yield stress of C1EM has been also

measured. The results are shown in Fig. 16. A linear

curve has been fitted to the experimental data. As it

was before pointed out, the thixotropic index is the

slope of the straight line that, for C1EM was

Athix = (0.15 ± 0.01) Pa/s. According to Roussel’s

criterion before pointed out, this is a thixotropic

material. We have confirmed the structure at rest

quickly builds. With the use of C1EM instead of C1 it

has been possible to combine three different tests that

confirm, in an unambiguous way, the thixotropic

nature of C1 formulation.

Despite valuable information could be obtained

from dynamic mechanic analysis of the concrete, only

the cement paste phase has been object of this study

and in a very limited number of works [20, 52]. The

objective pursued with dynamic mechanic analysis is

to get information about the viscoelastic properties of

the material and to determine its flow behavior at short

and long time intervals. With this information, appro-

priated applications of the concrete could be otherwise

inferred. Again is the coarse size the reason by which

dynamic mechanic analysis cannot be directly made.

The absolute rheometers cannot support these kinds of

systems. Instead the viscoelastic properties of the

CEM can be determined using an absolute rheometer.

Firstly, an amplitude sweep with a fixed frequency

(1 Hz) was applied to a sample of C1EM to determine

the linear viscoelastic region. It can be seen in Fig. 17

that the linear viscoelastic region extend to a defor-

mation of approximately 1 %. On the other hand, the

storage modulus (G0) is higher than the loss modulus

(G00) in this linear region, which means that the

concrete will show a great structural strength in

conditions near to rest, which is consistent with the

conclusion obtained from the thixotropy study. After a

certain amplitude critic value (48 % for C1EM) has

Fig. 15 Step-up and step-down results Fig. 16 Rest time dependence of the yield stress value

Fig. 17 Generic amplitude sweep curve


been achieved the viscous component dominates over

the elastic component (gel–sol transition). From this

result we can infer that when the amplitude of the

deformation is lower than the critical value, the

material will show consistent, while at higher defor-

mations the behavior of the mortar will resemble to a

particle sol [53].

Once the linear viscoelastic region has been

determined, a frequency sweep is applied to the

sample maintaining constant the amplitude of the

deformation. With a frequency sweep test it is possible

to determine the behavior of the material both at short

(high frequency) and long (low frequency) time

intervals [54]. The results are shown in Fig. 18. In

the case of C1EM the amplitude of deformation was

fixed to 1 % and the frequency was varied between

0.15 and 11 Hz. With this so low amplitude value

simulating rest conditions is possible. It is observed

that for C1EM the storage modulus is higher than the

loss modulus in the frequency interval studied. The

high G0-values and the parallelism between both

material functions suggest that this slurry has devel-

oped a strong internal structure. As a consequence, we

can conclude that the gravel will not segregate from

the concrete, although its self-leveling capacity will

not be as good as it would be desirable. It is interesting

to note that after three thixotropic studies it was

concluded that the structure builds fast instead of

assume the structure finally formed is strong. How-

ever, oscillatory tests can add valuable information on

this subject: the area observed in the hysteresis loop

test is actually the consequence of the combined effect

of both, a strong structure and a fast build of it.

3.5 Rheology of the other concrete and CEM

formulations

Following the same procedure three other concrete

formulations and their corresponding CEMs were

obtained. Table 11 shows the composition of these

concretes and CEMs.

Steady flow curves of CiEM (i = 1, 2, 3, 4) are

shown in Fig. 13. Modified Bingham model has been

fitted to each experimental data series. The parameters

Fig. 18 Generic frequency sweep curve

Table 11 Compositions of dries (a) C2 and C2EM, (b) C3 and

C3EM, and (c) C4 and C4EM

Component Ci CiEM

Quantity (kg/m3) Quantity (kg/m3)

Panel a

Cement I 42.5 R/SR 873.5 873.5

Silica Fume 87.3 87.3

Water 361.5 367.0

Sand 0/1 – 970.6

Sand 0/4 820.0 –

Gravel 4/8 545.0 –

Gravel 8/12 433.0 –

Gravel 11/22 391.0 –

SIKA 175 4.4 (0.5 % bwc) 4.4 (0.5 % bwc)

SIKA 3425 26.2 (3.0 % bwc) 26.2 (3.0 % bwc)

Panel b

Cement I 42.5 R/SR 906.4 906.4

Silica Fume 85.5 85.5

Water 350.8 357.3

Sand 0/1 – 885.8

Sand 0/4 773.0 –

Gravel 4/8 430.0 –

Gravel 8/12 375.0 –

Gravel 11/22 250.0 –

AXIM LiCa 3.6 (0.4 % bwc) 3.6 (0.4 % bwc)

AXIM Driver 3 18.1 (2.0 % bwc) 18.1 (2.0 % bwc)

Panel c

Cement I 42.5 R/SR 873.5 873.5

Water 341.6 345.1

Sand 0/1 – 1203.9

Sand 0/4 1052.0 –

Gravel 4/8 544.0 –

Gravel 8/12 482.0 –

Gravel 11/22 392.0 –

SIKA 175 5.5 (0.9 % bwc) 5.5 (0.9 % bwc)

SIKA 3425 2.4 (0.4 % bwc) 2.4 (0.4 % bwc)


of the model are shown in Table 8. As can be seen the

yield stresses of C2EM and C3EM are similar and

appreciably lower than the yield stress of C1EM and

much lower than the yield stress of C4EM. This result

suggests that specifically the fluidity of C4EM will be

less than the corresponding to the other formulations.

On the other hand, a higher plastic viscosity is shown

by C2EM and C3EM. This result suggests these two

mortars will flow without segregation. However the

plastic viscosity of C1EM and C4EM is low, which is

an indication of possible segregation of the material.

An additional information that we can get from steady

flow curves of the CEMs, after fitting modified

Bingham model, is obtained from the value of the

quotient c/gp. As can be seen this parameter is positive

in all cases being an indication of shear-thickening

behavior, which is, as it was before pointed out, a

feature of self-compacting material. However, this

parameter is practically zero for C4EM which means

that this is not a self-compacting CEM. Summarizing

we can conclude from the analysis of steady flow

curves that C2EM and C3EM correspond to self-

leveling concretes without segregation (SCC), while

C1EM corresponds to a segregating self-leveling

concrete and C4EM is the equivalent mortar of an

essentially conventional concrete. These consider-

ations are consistent with the yield stress values

obtained from the spread values obtained with

concretes (Table 8) and the direct observation of the

existence or absence of segregation during the tests

made with the 4C-rheometer. Therefore, it can be

conclude a certain correlation exists between concrete

rheology and CEM rheology. However, a deeper and

systematic study on these two systems (concrete and

its corresponding equivalent mortar) is necessary to

affirm that the rheology of both is really linked.

Thixotropic behavior of C2EM, C3EM and C4EM

equivalent mortars has been studied. The results are

shown in Figs. 14, 15, and 16. While C1EM, C2EM

and C3EM have shown a similar thixotropic behavior

when analyzed by the three different methods, C4EM

shows that recovers more quickly its structure after

shearing. As a practical conclusion, this last formula-

tion will be more adequate for vertical applications

while the other ones will be more useful for horizontal

applications.

To complete the time-dependence characteristics of

the equivalent mortars and, consequently, those of the

corresponding concretes, information obtained from

mechanical dynamic analysis has been also analyzed.

In some way the frequency sweep test is similar to the

vibration process. Both of them consist of apply an

oscillating deformation to the material with a deter-

minate frequency keeping a constant amplitude, while

the material is at rest. From Table 11 it can be

observed that each formulation shows a very different

behavior under oscillatory shear. In one hand, formu-

lations C2EM and C3EM present two crossover points

between the storage module curve (G0) and the loss

module curve (G00), in such a way that G00 is larger than

G0 at low frequencies. This means that these materials

will have a dominant liquid-like behavior so, even

being at rest, they will work filling the empty spaces

spontaneously under the action of their own weight. In

the other hand, in C1EM and C4EM formulations G0 islarger than G00 practically in the whole range of

frequencies, so a external source of energy must be

provided in order to reach a liquid-like character for

fitting completely any hollowness in the volume of the

casting form. From these results, the general form that

a frequency sweep curve corresponding of a SCC

equivalent mortar should have, Fig. 18, can be

suggested.

3.6 Rheograph tools

Very recently [55], the advantage to use rheographs as

a tool to attain the optimization of fresh concretes has

been pointed out. The effect, single or combined, of

additions on the rheological behavior of the material is

quickly shown in rheographs that, in Wallevik and

Wallevik version [55] consist in yield stress/plastic

viscosity (Bingham model) of concrete plots. As a

contribution to the development of the use of

rheographs in concrete science, we suggest the build

of 3D yield stress/plastic viscosity/second order

coefficient (modified Bingham model) of CEM plots.

This plot will be named steady flow rheograph.

Additionally, the three thixotropic parameters used

in this study to characterize the thixotropic behavior of

the CEM (thixotropic area from hysteresis loop, slope

from rest time dependence of the initial shear stress,

and the percentage of structure recovered after 40 s of

shear) give place to the second rheograph here

proposed, which characterizes the thixotropic behav-

ior of the CEM. This plot will be named thixotropy

rheograph.


In Fig. 19 the steady flow rheograph of the CiEM

(i = 1, 2, 3, 4) is shown. The three parameters of the

modified Bingham model have been represented in a

contour graphic which is divided in four zones. The

shaded one is the zone where plastic viscosity is high,

yield stress is low and the second order parameter

value suggests a shear-thickening behaviour of the

CEM that helps to prevent the segregation, because

increasing shear rate a growth in the apparent viscosity

will be induced. In other words, a formulation having a

flow curve which yield stress, plastic viscosity and

second order term fall into that zone (C2EM and

C3EM) could be considered self-compacting. In the

other cases, the formulation could not be considered

self-compacting, either because the yield stress is too

high and then the material does not be able to flow

under its own weight effect (C4EM), or its plastic

viscosity is so low (C1EM and C4EM), thus the coarse

aggregate will segregate, or the second order term is

zero (C1EM and C4EM), which represents a floccu-

lated dispersion. In a first approximation, we suggest

the limits of 50 Pa for the yield stress and 3.5 Pa s for

the plastic viscosity. However, this should be

improved studying more concrete formulations. As a

conclusion, according with Fig. 19, C2EM and C3EM

are self-compacting formulations, while C1EM could

appears, in principle, as one of this kind because its

low yield stress, although, based upon the low plastic

viscosity and second order coefficient, the risk of

segregation is clear. Finally, C4EM is a conventional

concrete formulation.

To complete the idea of the utility of the rheo-

graphs, the thixotropy rheograph obtained with the

four formulations here studied is shown in Fig. 20. In

this contour graphic, the main thixotropic parameters

for each formulation have been plotted. It can be seen

that the high-thixotropic materials fall on close to the

left side (low Athix and IR40 but high A). These

materials are recommendable for walls and tall pre-

cast forms. On the other hand, low-thixotropic mate-

rials (high IR40 and Athix) have a more spread location

in the graph. These kinds of materials are adequate for

floors and slabs. Because of this is more difficult find

out a practical limit, but we can estimate or recom-

mend values of IR40 and Athix over 75 % and 0.15 Pa/s

to considered a material as low-thixotropic. On the

other side, high A values determine a strong internal

structure, it means that is necessary make it flow. This

effect is positive in some cases because can prevent

aggregate separation during casting process. We can

conclude, from the interpretation of this thixotropy

rheograph that C2EM and C3EM are materials with a

strong structure that build-up after a long time, C1EM

has a less strong structure that builds-up faster and,

finally, C4EM is a mortar with a weak structure that

builds-up faster and faster.

A word of caution must be made respect to both key

maps. At this time they only pretend be only a start

point for SCC formulations designing from CEMs. In

order to achieve a more general rule for different cases

more materials must be studied.

4 Concluding remarks

C1–C4 formulations were designed following a pro-

cedure that intended to get SCC.

Fig. 19 Steady flow rheograph Fig. 20 Thixotropy rheograph


From the analysis of the steady flow curves of

C2EM and C3EM is concluded that C2 and C3 are

SCC without segregation. On the other hand, the

results obtained with C1EM leads us to conclude that

C1 is a segregating self-leveling concrete. Finally, the

steady flow curve of C4EM corresponds to a conven-

tional concrete C4. Spread tests made with concretes

basically agree with these conclusions. The presumed

correlation between concrete and CEM looks to be

supported by this study, although more systematic

studies must be made before to get a conclusive result.

From transitory studies it has been observed that

C1EM, C2EM and C3EM show a similar thixotropic

behavior, while C4EM recovers more quickly its

structure after shearing. Therefore, it is suggested that

C4 concrete is useful for vertical applications while

C1, C2 and C3 are more appropriated for horizontal

applications.

From the use of oscillatory rheological tests it has

been concluded that C2EM and C3EM will have a

dominant liquid-like behavior so, even being at rest,

C2 and C3 concretes will work filling the empty spaces

spontaneously under the action of their own weight.

On the other hand, an external source of energy must

be provided in order to reach a liquid-like character for

fitting completely any hollowness in the volume of the

casting form if C1 or C4 formulations are used.

Oscillatory tests made with equivalent mortars have

lead us to conclude that a SCC requires its equivalent

mortar frequency sweep response was like that shown

in Fig. 18.

Finally, two CEM rheographs that can help to get a

more detailed design of concrete formulations with

low cost and time consumption have been proposed.

However, at the present state of research they must

only be considered as a starting point for the devel-

opment of more complete rheographs after more

concrete formulations were studied.

Acknowledgments The authors whish thank to one of the

reviewer for valuable comments and to suggest us a future

research line.

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2. Tattersall GH, Banfill PFG (1983) The rheology of fresh

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3. Ferraris CF, Larrard F, Martys N (2001) Fresh concrete

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Documents

Rheology of concrete: a study case based upon the use of the concrete equivalent mortar