Influence of Variety of Superplasticizer onthe Properties of Blastfurnace Slag Concrete

A. LAICHAOUI 1, 2, R. KETTAB 2, A. BALI 2

1. Civil Engineering Department, A. MIRA University, Béjaïa,Algeria.

2. Construction & Environment Laboratory, E.N.P, Algiers,Algeria.

ABSTRACT: The high performance of cementitious materials has been achieved with the use of polymer additives (superplasticizers) in the proportioning

mixtures. Superplasticizers, which are chemical products, can result in high workability of concrete and high strength, but they may produce undesirable

effects on setting and hardening of concrete if used in large amount in mixes. In this work the parameters involved are superplasticizer content and optimal

percentage of the mineral addition. The experimental study is mainly carried out using two different families of superplasticizers (Polycarboxilates and Poly-

Melamine Sulfonate) and blastfurnace slag as a mineral addition The results obtained show that the type of superplasticizer used has a great

influence on the variation of rheological parameters - plastic viscosity and shear stress – of the studied grouts. Moreover, the percentage of mineral

addition (slag) is strongly related to the type of the superplasticizer andcement.

This investigation aims also to valorize an industrial waste (slag) and to incorporate it into the concrete formulations at high proportions, without

altering the rheological properties of grouts and concretes with the presence of superplasticizers..

Keywords: superplasticizer, slag, cement grouts, viscosity, concreteproperties.

A Laichaoui is a research student in the civil-engineering Department (Ecole Nationale Polytechnique- Algiers)

R Kettab: is an assistant lecturer at Ecole Nationale Polytechnique in Algiers. His research focuses mainly on materials, waste recycling.

A Bali: is professor and head of a research laboratory at Ecole Nationale Polytechnique in Algiers. His research concentrates on materials, waste recycling, concrete at elevated temperatures, repair

of damaged structures.

.

INTRODUCTION

Engineers seek to obtain concretes with high performances without neglecting the rheology of the material, in the fresh state, which

is a very significant technological parameter.

Concrete is a composite material in which the aggregates (gravel and sand) are bound by a hydrated cement paste. The quantity of water

necessary for the reactions of hydration represents approximately 25 % by weight of cement. However, an additional quantity of water

(at least double) is necessary in order to obtain a satisfactory workability of the freshly-mixed concrete during placing. The water

excess will evaporate in the long term, leaving voids in concrete. In a Portland cement paste with Water/Cement ratio of 0.5, total

porosity represents between 25 and 30 % of the volume and the size of the pores vary from a nanometre to a few millimetres (Moranville-

Regourd, 1992, Laichaoui, 2011). Porosity in the material greatly decreases its mechanical resistance and durability. Concrete is therefore a porous composite material, whose performances vary according to its capillary porosity and thus to the water excess necessary to the workability of the fresh concrete (Pole, 2004).

Concrete making which was based on a simple ternary association: cement, water and aggregates, has gradually become more complicated

so that a current concrete actually contains currently five components: cement, water, aggregates, additions and additives

(Amouri, 2009).

The need for improving concretes performances, and reducing the quantity of mixing water to decrease porosity, implies the use of

new materials such as the superplasticizers. Added in small quantities (usually from 0.5 to 2 % of the mass of cement), the latter

make it possible to reduce considerably (30 % and more) the quantity of water necessary to obtain satisfactory rheological properties for a good placement of the concrete (P.F.G, 2003).

In this study, two types of superplasticizers of different chemical nature "Polycarboxilate (Pcx) and Poly-melamine sulphonate

(PMS) "have been chosen. For ecological concern, a mineral addition (slag), which is an industrial waste, has been incorporated, with various percentages as a substitution of a part of cement. The Pcx

and PMS point of saturation with cement CPJ has been determined, as well as the optimal slag percentage which gives the best rheological

characteristics of the grouts. For mortars, the optimal percentage of the mineral addition is considered, with an aim of checking the

capacity to relocate the results obtained for grouts with mortars; measurements of the density, spreading and time of flow have been

carried out.

CHARACTERIZATION OF CEMENT, SLAG AND SUPERPLASTICIZERS

The chemical analyses and the many tests of leaching showed that slag coming from waste dumps do not lead to any counter-indication

as for their use in the various applications in construction (Amini,2010).

Tests for the determination of the chemical composition are carried out according to standards' NF EN 196-4. The results are given in

table 1.

Table 1 Chemical composition of the CPJ and Slag

OXIDES CPJ (%) SLAG (%)

CaO 59.24 45SiO2 18.99 34Fe2O3 4.2 2.5Al2O3 5.78 12.4MgO 3.9 8.6MnO 0.09 0.29SO3 1.74 0.097

Superplasticizers

The superplasticizers are organic polyelectrolyte, belonging to the category of the polymeric dispersing. In this investigation, two types of superplasticizers, the polycarboxilates (Pcx ) and

Poly-melamine Sulfoate (PMS) have been used their chemical formulas are illustrated on figure 1.

(a) (b)

Figure 1 (a) Pcx, (b) PMS

EXPERIMENTAL STUDY

Cement Grout

Material

In this part, rheological measurements were carried out using a viscometer with rotary cylinders in permanent mode (HAAKE - Viscotester VT550 with the device of measurement SV DIN). It is

connected to a cryostat controlled by a computer, which maintains the temperature of the sample of the experiment to 20°C. The

acquisition of the data by computer generates curves of flow (shear stress) and of viscosity for a rate of shear given (gradient of

speed).

Figure 2. Device SV DIN and viscometer VT550 used

The principle consists of shearing the suspension between a surface at rest and a mobile surface. The fluid to be analyzed is placed

between two coaxial cylinders. The laminar movements of shearing are obtained by communicating to one cylinder (interior cylinder) a

uniform rotational movement, the other cylinder remaining motionless (Figure 2).

Design mixes studied

The description of the studied proportioning and mixtures is asfollows:

- CPJ a grout of CPJ without superplasticizer or mineral addition

- CPJ+ X %Pcx a grout of CPJ + X % of Polycarboxilates - CPJ+ X %PMS... a grout of CPJ + X % of PMS - CPJ+1%Pcx+ y %Slag: a grout of CPJ + 1 % of Polycarboxilates +y % of slag

- CPJ+1.2%PMS+ y %Slag: a grout of CPJ + 1.2 % of PMS + y % of slag W/C Ratio used in the presence of the superplasticizers is 0.35

Mortars

Material

The density of mortars is measured using the weighing values difference of the mould 4×4×16 cm 3

over the volume of the mould. Spreading is measured using the vibrating table and the workability

is measured with the mortar maniabilimeter LCL (NF P 15-437) where the time of flow of a fresh mortar subjected to vibrations is

measured.

Design mixes studied

The mortar pilot 0 made according to standard NF EN196-1, is constituted (by weight) from one part of cement and three parts of

standardized sand and of a half-part of water. The mortar pilot 1 is of the same composition than mortar 0 with a ratio W/C of 0.35 with 1% of Pcx. The mortar pilot 2 is of the same formulation than mortar 0

with a ratio W/C of 0.35 with in more 1.2% of PMS. For the other mortars the percentage used of slag in the formulations of grouts is

that which gave the best rheological performances and thus the addition contents concerning Pcx 40, 45 and 50%, and 25, 30 and 35%

for the PMS have been retained.

RESULTS AND DISCUSSIONS

Cement Grout

The first part of the tests consists of the determination of the optimal percentage of the superplasticizers offering to cement

grouts the best rheological characteristics.

It can be noticed, according to figures 3 and 4 that for three cement grouts (CPJ alone, CPJ + Pcx and CPJ + PMS) the rheological behaviour

is well a Binghamien behaviour for the fluids with CPJ alone and CPJ + Pcx, and Newtonian for the fluid CPJ + PMS.

0.1

1

10

0 50 100 150 200 250 300 350 400Rate of shear (1/s)

Plas

tic visco

sity (P

a.s) CPJ

CPJ+0.8% PM SCPJ+1.2% PM SCPJ+1.6% PM S

Figure 3 Plastic viscosity according to the rate of shear for a CPJ without and with various percentages of PMS with W/C = 0.35

It is also noticed that the polycarboxilate has a dispersing action more effective than that of the PMS, and this is influenced

(Uchikawa, 1994) by the capacity of adsorption of the polycarboxilate on the anhydrous and the hydrates of cement.

0.1

1

10

0 50 100 150 200 250 300 350 400Rate of shear (1/s)

Plastic viscosity (P

a.s) CPJ

CPJ+0.5% PcxCPJ+1% PcxCPJ+1.5% PcxCPJ+2% Pcx

Figure 4 Plastic viscosity according to the rate of shear for a CPJ without and with various percentages of Polycarboxilate with W/C =

0.35

It can be noted from the curves of figures 3 and 4 the points of saturation for the two organic additions used. It is 1 % for the

polycarboxilate (Pcx) and 1.2 % for the PMS.

Figures 5 and 6 allow determining the maximum percentage of cement which can be substituted by slag, with preserving the rheological

properties of cement grouts incorporating slag.

Figure 5 Plastic viscosity according to the rate of shear for a CPJ with 1 % of Pcx and various percentages of slag (with W/C = 0.35)

The percentages of slag which can be used without changing the rheological properties of the grouts are 45 % by weight of cement for

the polycarboxilate and 30 % for the PMS.

CPJ+1%Pcx+10%SlagCPJ+1%Pcx+15%SlagCPJ+1%Pcx+20%SlagCPJ+1%Pcx+25%SlagCPJ+1%Pcx+30%SlagCPJ+1%Pcx+35%SlagCPJ+1%Pcx+40%SlagCPJ+1%Pcx+45%SlagCPJ+1%PcxCPJ+1%Pcx+50%Slag

Rate of shear (1/s)

Viscos

ity

(Pa.s)

Figure 6 Plastic viscosity according to the rate of shear for a CPJ with 1.2 % of PMS and various percentages of slag (with W/C = 0.35)

The rheological behaviour is Newtonien in the presence of slag and polycarboxilate and Binghamien in the presence of PMS and slag.

Mortar

Figure 7 illustrates the variation of the density according to slag content as a substitute of cement.

It can be seen in Figure 7 that the density decreases with the substitution of cement by slag. This is explained by the fact that

the mineral addition has a real density lower than that of cement.

200020502100215022002250230023502400

Density (kg/m3)

with Pcx

M ortar 0 M ortar 1 40% 45% 50%2000

2050

2100

2150

2200

2250

2300

2350

2400

Density (kg/m3)

with PM S

M ortar 0 M ortar 2 25% 30% 35%

Figure 7 Variation of the density according to slag content

Figures 8 and 9 show the characteristics of placing (rheological) of the mortar for various superplasticizers and percentages of slag.

CPJ+1.2%PMS+10%SlagCPJ+1.2%PMS+15%SlagCPJ+1.2%PMS+20%SlagCPJ+1.2%PMS+25%SlagCPJ+1.2%PMSCPJ+1.2%PMS+40%Slag CPJ+1.2%PMS+35%SlagCPJ+1.2%PMS+30%Slag

Rate of shear (1/s)

Vi

scosity

(Pa.s)

0

24

68

10

1214

16

Spreading out (cm

)

0

2

4

6

8

10

12

Time of flow (s)

Spreading out PcxFlow Pcx

M ortar 1 40% 45% 50%

Figure 8 Variation of the spreading and the time of flow for mortars containing slag with 1% of Pcx

0

2

4

6

8

10

12

14

16

Spread

ing ou

t (cm

)

0

2

4

6

8

10

12

Time of flow

(s)

Spreading out PM SFlow PM S

M ortar 2 25% 30% 35%

Figure 9 Variation of the spreading and the time of flow for mortars with the slag with 1.2% of PMS

The results given in figures 8 and 9 show that spreading decreases for the PMS mortars, when the percentage in slag increases, whereas

spreading for Pcx mortars increases with the percentage of substitution. These tendencies would be due to the fact that Pcx is

more fluidising in the presence of slag than the PMS.

Moreover, the time of flow contrary to spreading increases with the PMS and decreases with Pcx, this result consolidates that of

spreading (figures 8 and 9).

CONCLUSION

The results obtained highlight the dispersing effect of the superplastifiants. Indeed, we could lower the ratio W/C of 0.5

(without additives) to 0.35 (with additives) while keeping comparable rheological properties. It is clear that by decreasing

mixing water while preserving good rheological characteristics of cement grout (which means good handiness and workability of fresh

concrete) we obtain a concrete of good mechanical characteristics because it will be less porous thus more compact, and more durable.

The results show that superplasticizers based on polycarboxilates has more significant fluidising and dispersing

effects than those based on poly-melamine sulphonate.

The very fluidising properties of Polycarboxylates are very useful for making high performance concretes.

The obtained results show that cement can be substituted by slag at very significant and encouraging quantities, 45 % by weight of

cement with the polycarboxilates and 30 % with the PMS; this substitution has been made without losing too much from the

rheological side.

Incorporating slag in the formulations of grouts and concretes, leads in fact to the valorisation of an industrial waste, and with

high percentage of replacement the environmental benefit isconsiderable.

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