Construction and Building Materials 53 (2014) 488–502

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Construction and Building Materials

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The methodology for assessing the impact of new generationsuperplasticizers on air content in self-compacting concrete

0950-0618/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.conbuildmat.2013.11.092

⇑ Tel.: +48 032 2372294; fax: +48 032 2372737.E-mail address: beata.lazniewska@polsl.pl

Beata Łazniewska-Piekarczyk ⇑Silesian Technical University, Faculty of Civil Engineering, Department of Building Materials and Processes Engineering, Akademicka 5 Str., 44-100 Gliwice, Poland

h i g h l i g h t s

� Too much air is noticed in SCC that meets the requirements of EN 12350-8.� Too much air remains in the SCC despite its high liquidity.� Test compatibility of SP does not recognize the impact of SP on air content in SCC.� Foam ability, stability index and surface tension tests assess the impact of SP on air content in SCC.

a r t i c l e i n f o

Article history:Received 13 January 2012Received in revised form 17 November 2013Accepted 26 November 2013Available online 4 January 2014

Keywords:Self-compacting concrete (SCC)SuperplasticizerAir bubbleFoam ability indexFoam stability indexSurface tension

a b s t r a c t

Certain types of the new generation superplasticizers (SP) cause the rise of excessive air content in self-compacting concrete (SCC). The influence of different type of SP on air-content in cement paste and freshSCC are tested in the paper. The qualitative methods (foam ability and stability index), which serves thebest choice of SP not showing the side-effect in the form of an excessive SCC air-entrainment are pre-sented. The surface tension of SP solutions is also analyzed. The results of tests show that we can predictthe influence of SP on air-content of SCC by measuring the surface tension of SP solution, foam ability andstability index of cement paste.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Superplasticizers are the most important admixtures enhancingconcrete performance. The development of new superplasticizersduring the last decades has determined the most important pro-gress in the field of concrete structures in terms of higher strength,longer durability, lower shrinkage and safer placement particularlyin elements with very congested reinforcement [1].

First-generation superplasticizers were primarily derived fromnatural organic materials such as sugars and lignins (extractedfrom wood pulp). These products had a limited effectiveness andmay have been somewhat variable in performance, depending onthe source material. These water reducers would often retard themixture, particularly when overdosed. They are still used as TypeA, B, and D products.

Second-generation (early high-range) superplasticizers werederived from petroleum feed stocks: sulfonated naphthalene or

melamine condensates with formaldehyde. These products offergreater water reduction and are less detrimental when overdosed.

Third generations of superplasticizers often provide only about20 min of effectiveness before the concrete exhibits significantslump loss. These products can be re-dosed after this time to main-tain workability, if required. Third-generation Superplasticizers arepolycarboxylates (PC), which are copolymers synthesized fromcarefully selected monomers. These products are currently usedin mid- or high-range Superplasticizers (Type F and G; AdmixtureTypes Defined by ASTM C 494/AASHTO M 194). These admixturescan be fine-tuned for a given application, including a range of effec-tiveness and setting times [2–5]. PCEs are quite sensitive to differ-ent cement compositions (e.g. because of the sulfate effect) andthey interact strongly with clay which can occur as an impurityin aggregates and limestone. The first polycarboxylates used as dis-persants in concrete were found to be very efficient at a dosagethat was often two times lower than that of the most efficient poly-sulfonates. However, some of these first polymers were found toentrain an excessive amount of air so that an air detraining agenthad to be mixed with them. As polycarboxylates are less sensitive

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to C3A content and its reactivity, their use is very common in theEuropean precast industry, which uses fine contents rich in C3Sand C3A to obtain high early strength. Up to now, there exist somepolyacrylates with which it is not easy to develop a stable networkof air bubbles having a low spacing factor to protect concreteagainst freeze–thaw cycles and the action of deicing salt, so thattheir use is not very popular in the North American ready-mix con-crete industry. Excessive foaming needs to be controlled by theaddition of defoamers [6].

According to the standard requirements [7,8] superplasticizersshould not cause the rise of the air content in concrete mix higherthan 2%, compared to the control mix. Unfortunately, as alreadymentioned above, some types of SP increase the air-entrainment(Table 1) [9,10,4,5]. Thus in case of non-air-entrained self-com-pacting concrete (SCC), achieving low air-content might be difficult[11–15].

Thus, the compatibility test of superplasticizer with cementshould be extended to a test to assess the effect of superplasticizeron the air content in concrete. Known and used methods of testingthe air content in the paste, mortar and concrete mixture are thefollowing:

– surface tension measurement [16],– foam index test [17,18],– volume density [19],– pressure measurement of the air content [20],– Air Void Analyzer (AVA) [21–23],– laser method on frozen samples [24].

The first and second methods are used for cement paste. Forqualitative methods of air-entrainment evaluation the first twomethods are used. For quantitative assessment methods of air-entrainment evaluation other methods are used.

In the publication [16] surface tensions of the surfactants in dif-ferent solutions were measured using the Wilhelmy Plate method[14]. The test method measures the force between a probe and thesurface of a fluid. A rectangular roughened platinum thin sectionplate was used as a probe. The platinum plate was hung verticallyon a balance and lowered until it came in contact with the solutionsurface. The plate was dipped 3 mm into the liquid, and raised up1 mm. At the equilibrium point, the forces acting on the balanceare the weight of the platinum plate, the up-thrust force on thesubmerged part of the plate, and the surface tension of the liquidtouching the plate. The forces present in this situation are a func-tion of the size and shape of the plate, the contact angle of theliquid/plate interaction, and the surface tension of the liquid. Thecontact angle of the liquid/plate interface is zero underthe assumption that the solutions completely wet the plate. Conse-quently, the surface tension forces act directly downwards andin-plane on the platinum plate. The surface tension of the liquidis calculated by dividing the surface tension force (milliNewton,

Table 1The influence of SP type on the concrete air-entrainment [9].

Plasticizer or SP type Influence on air content ofconcrete

Lignosulfonate, LS ++Sulfonated Naphthalene Formaldehyde

Condensate, SNF+

Sulfonated Melamine FormaldehydeCondensate, SMF

0

Polycarboxylate Polyoxyethylenea, PCP ++Amino Phosphonate Polyoxyethylenea, AAP ++

a New generation of SP.

mN) to the wetted length of the plate (meter, m), which equalsto two times the width of the Wilhelmy thin plate [16].

The foam index test is the method usually employed to deter-mine the degree of fly ash interference with air entrainment agentsin concrete [25–27]. The foam index test is not a standardizedmethod. The procedure for the foam index test is similar to thatwhich others have proposed. 2 g of fly ash, 8 g of Portland cement,and 25 ml of deionized water were poured into a cylindrical glassvessel being 6 cm in diameter, which was capped and shaken ona vortex shaker for 1 min. A 5 vol.% aqueous solution of AEA wasadded in small aliquot amounts (20 ll) from a diluter and the ves-sel was shaken for another 15 s. The foam was observed for stabil-ity, i.e. defined as no bursting of bubbles within 30 s. In case thefoam was unstable, more AEA was added, and the procedure wasrepeated until the foam remained stable. The test involves theuse of commercial air-entraining agents (AEAs) and visual observa-tion of foam stability. These facts reduce the reproducibility of thetest, because commercially available AEAs vary in strength, and thecriteria for foam stability are operator dependent [28]. The paper[28] presents efforts toward the development of a new methodbased on dynamic surface tension measurements, using the bubblepressure method, on filtrate from a fly ash and cement suspension.

The purpose of the foam index test is to predict surfactant-ce-ment compatibility using a simple method and evaluation. Themodified foam index test proposed by Corr et al. [29] was deemedmore applicable to this experiment because it allows a better com-parison between the three surfactants with and without the effectof cement [16]. The absolute volume of the foam and the relativelack of change between the final and the initial volume of the foamindicate the foam stability. The compatibility between the cementand each surfactant can be implied by relative change in the foamstability between surfactant solution and surfactant solution withcement.

This paper presents efforts toward the development of a meth-od based on surface tension measurements of superplasticizer sus-pension, using the stalagmometric method, and new methodverification of foam ability and also foam stability index of superp-lasticizer suspension.

2. Study on the mechanism causing foaming behavior ofsuperplasticizer

The two most important mechanisms are linked to polymeradsorption: steric hindrance through the adsorbed layer thicknessand electrostatic repulsion through the induced electrical charge.Water-reducing chemicals belong to a group of chemicals knownas ‘dispersants’. The action of the dispersant is to prevent the floc-culation of fine particles of cement. These dispersants are basicallysurface-active chemicals consisting of long-chain organic mole-cules, having a polar hydrophilic group (water-attracting, such as–COO�, –SO3–, –NH4+) attached to a non-polar hydrophobic organ-ic chain (water-repelling) with some polar groups (–OH). The elec-trostatic attractive forces, existing among cement particles andcausing agglomeration, would be neutralized by the adsorptionof anionic polymers negatively charged, such as SNF or SMF, forthe presence of –SO3– groups on the surface of cement particles.The dispersion of cement particles would be related with the elec-trical repulsion produced by the negatively charged groups –SO3–on the other side of the main polymer chain (Fig. 1) [35].

The polar groups in the chain get adsorbed on the surface of thecement grains, and the hydrophobic end with the polar hydrophilicgroups at the tip project outwards from the cement grain. Thehydrophilic tip is able to reduce the surface tension of water, andthe adsorbed polymer keeps the cement particles apart by electro-static repulsion (The grinding of cement results in the ground

Fig. 1. Schematic picture of sulfonated polymer (SNF) and its electrostatic repulsion on the dispersion of cement particles [35].

490 B. Łazniewska-Piekarczyk / Construction and Building Materials 53 (2014) 488–502

particles having a surface charge (zeta potential). The adsorptionof the admixture leads to a decrease of the zeta potential, andeventually causes like charges (negative) on the cement particles).With the progress of hydration, the electrostatic charge diminishesand flocculation of the hydrating product occurs. Lignosulfonates(normal, and sugar-refined), SMF, and SNF based superplasticizerswork on the mechanism of lowering zeta potential that leads toelectrostatic repulsion.

The dispersion mechanism performed by the PC-based superp-lasticizers could be related more to a steric hindrance effect (pro-duced by the presence of neutral side long graft chains) ratherthan to the presence of negatively charged anionic groups (COO–) which are responsible for the adsorption of the polymers on thesurface of cement particles (Fig. 2). In other words, the graft chainsof the polymer molecules on the surface of cement would hinderby themselves from flocculating into large and irregular agglomer-ates of cement particles (Fig. 2) [35].

Fig. 2. Schematic picture of the polycarboxylate (PC) superplasticizer and i

The molecular structure of polycarboxylate (PC) superplasticiz-er admixtures is shown in Fig. 2. Their ‘comb-type’ molecule con-sists of one main linear chain with lateral carboxylate and ethergroups [30]. According to the literature [31], the carboxylategroups are instrumental in the adsorption of these admixtures tocement particles. Dispersion is due to electrostatic repulsion (asin melamine and naphthalene admixtures) owing to the carboxyl-ate groups, but primarily to the steric repulsion associated with thelong lateral ether chains. The high degree and duration of the flu-idity that this admixture affords concrete are related to structuralfactors; hence, the shorter the main chain and the longer and morenumerous the lateral chains, the greater and more long lasting isthe fluidity induced [30,32]. The molecular weight of these admix-tures likewise has a substantial effect on their performance:according to Magarotto et al. [33] adsorption and system fluidityare proportionally higher in polymers with large molecular weight[30].

ts steric hindrance effect on the dispersion of cement particles [35,31].

Fig. 3. Types of superplasticizer action: (a) creating ‘‘grease’’ layer, (b) surroundinggrains of cement with negative charge, (c) decreasing of surface water tension and(d) long chains of polymer, physically precluding the grains of cement to approacheach other [9].

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Deflocculating and dispersion of the cement particles are thenet result and allow better use of the available water for more uni-form lubrication and hydration.

Additional mechanisms of SP action include dispersion of ce-ment particles by reduction in surface tension of mixing water(Figs. 3 and 4) and a decrease in frictional resistance because ofthe line-up of linear polymers along the concrete flow directionand lubrication properties produced by low molecular weightpolymers. Unfortunately, many PC entrain as much as 2% [36].

The presence of functional groups (oxygen in form of ethericgroup (–O–), hydroxyl group (–OH) and carboxyl group) producewater surface tension decrease, producing flocculation of associ-ated molecules and increase in moisture of not only grains of ce-ment but also the whole mineral framework [38]. The research[34] results show that the surface tension changed considerablywith time depending on the combination of powder and superp-lasticizer. The change seems to be caused by the sorption, whichincludes chemical adsorption, physical adsorption and absorption.Among three kinds of sorption, the absorption of superplasticizerby powder obstructs the function of superplasticizer. The tendencywas indicated that the absorption could occur in paste according tofluidity test of paste.

In the SPs group there are ones that show only dispersion func-tioning not decreasing surface tension [39]. They are: hydrocarb-oxylen acid salts, sulphonic melamine-formaldehygenic resins,formaldehygenic picodensats salts of beta-naphtalensulphonicacid.

The foaming capacity of a surfactant depends primarily on itseffectiveness to reduce the surface tension of the solution, itsdiffusion characteristics, its properties with regard to disjoiningpressure in thin films, and the elastic properties it imparts tointerfaces [40]. Fig. 5 shows a free-body diagram for the right half

Fig. 4. Water conglomerates deflocculating under the influence of s

of the bubble, on which two forces act. First, there is the force dueto the surface tension in the film. This force is exerted on the righthalf of the bubble by the left half. The surface tension force pointsto the left and acts all along the circular edge of the hemisphericalfilm. The magnitude of the force due to each surface of the film isthe product of the tension c and the circumference (2pR) of the cir-cular edge, or c(2pR). The total force due to the inner and outersurfaces is twice this amount or �2c(2pR). We have included theminus sign to denote that this force points to the left in the draw-ing. We have also assumed the film to be sufficiently thin enoughthat its inner and outer radii are nearly the same. Second, there is aforce caused by the air pressure inside the bubble. At each point onthe surface of the bubble, the force due to the air pressure is per-pendicular to the surface and is directed outward. Fig. 1b showsthis force at six points on the surface. When these forces are addedto obtain the total force due to the air pressure, all the componentscancel, except those pointing to the right. The total force due to allthe components pointing to the right is equal to the product of thepressure Pi inside the bubble times the circular cross-sectional areaof the hemisphere, or Pi(pR2). Using these expressions for theforces due to the surface tension and air pressure, we can writeNewton’s second law of motion as

PF = 0, or �2c(2pP) + Pt

(pR2) = 0, where: 2c(2pR) force due to surface tension; Pi(pR2)-force due to pressure inside bubble. Solving this equation for thepressure inside the bubble gives Pi = 4c/R. In general, the pressureP0 outside the bubble is not zero. However, this result still gives thedifference between the inside and outside pressures, consequentlythat we have (see Fig. 5).

Pi � P0 ¼ 0 ðSpherical air bubbleÞ ð1Þ

This result tells us that the difference in pressure depends onthe surface tension and the radius of the sphere. What is surprisingis that a greater pressure exists inside a smaller air bubble (smallervalue of R) than inside a larger one (compare with Fig. 5c). Thus,the force due to the surface tension is only one-half as large as thatin a bubble. Consequently, the difference in pressure between theinside and outside of a liquid drop is one-half of that for a soapbubble [42].

Pi � P0 ¼ 2c=R — Laplace’slaw ð2Þ

The rate of surface tension decrease by surface active com-pounds is followed in accordance with Gibbs Eq. (3) [43]. Thisequation shows that the change of surface tension results fromsubstance absorption on given surface (Fig. 2).

� drdc¼ RT

Csi

cð3Þ

where dd is the change of surface tension; dc the change of given sub-stance concentration in the solution; Cs

i the surface concentration

uperplasticizer as the effect of surface tension diminution [37].

Fig. 5. (a) The forces pointing to the left are due to the surface tension, (b) the forces pointing perpendicular to the hemispherical surface are due the air pressure inside thebubble [41] and (c) the inner and outer pressures on the spherical air bubble ale Pi and P0, respectively [42].

Fig. 6. (a) Rapid change of surface tension over a relatively small concentration range [44]. (b) Rapid change of surface tension and foam production over a concentrationrange [42].

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(mol/m2), c the constituent concentration; R the gas constant; T isthe temperature.

The combined Gibbs–Marangoni effect is the theory derived toexplain the function that surfactant played in foam film formationand persistence. From Gibbs adsorption Eq. (3), the surface tensionof a liquid will decrease as the concentration of the monomer sur-factant in solution increases (assuming positive adsorption) up tothe point of surface saturation (Fig. 6). The instantaneous (dy-namic) surface tension at a newly formed surface is always higherthan the equilibrium value. There is a finite time requirement dur-ing which the surfactant in the solution must diffuse to the inter-face in order to lower the surface tension. The time lag in reachingthe equilibrium surface tension due to diffusion is generally knownas the Marangoni effect, which explains why the diffusion proper-ties and concentration of a surfactant is important. These twosurface tension effects are usually complementary. Because thedisturbance of air bubbles in concrete is unavoidable, the Marang-oni effect is essential to maintain the integrity of air bubbles [44].

The hydrophobic tails of surfactant molecules stick out of thesolution to reduce the distortion of water molecules by the hydro-phobic sections and thus lower the overall free energy of the sys-tem. Relationship between surface tension, solid tension andphase-to-phase voltage according to equation Younga–Dupre’awas presented in Fig. 7.

The mutual repulsion between the hydrophilic heads of surfac-tant molecules reduces the attraction of the bulk liquid phase and alower surface tension is resulted. Because of the electrostatic com-ponent of the repulsion force of ionic surfactants, their effective-ness to reduce surface tension is more significant than nonionicsurfactants. The nature and concentrations of the surfactants

determine the physical and chemical properties of the interfaceat the air bubble surfaces, including surface tension (equals to freesurface energy) and stability. The electrostatic and steric repul-sions between surfactants help stabilize air bubbles in the pastephase. Ions, organics, and polymers in the bulk solution also affectthe properties of the interfaces through complex interactions withthe orientated surfactant molecules [44]. Air-entraining admix-tures molecules in the solution help entrain air-bubbles and stabi-lize them in the fresh concrete. Most of the modern AEAs areanionic because of the stability of air voids entrained [44]. Theanionic surfactants include: n-alkylcarboxylates (n-RCOO�),n-alkylsulfonates n-RSO�3

� �and n-alkylsulfates n-RSO�4

� �, with

hydrocarbon chain lengths between C7 and C12. The two main fea-tures of the AEAs are their composition and size of hydrophobicchain and the nature and size of their hydrophilic head groupaffecting surface activity and their solubility in cement paste solu-tion. Maximum air entrainment is obtained with surfactants ofintermediate chain length because their surface activity and solu-bility vary in opposite directions. The hydrophilic head group in-creases the air entrainment in the order carboxylate, sulfonate,sulfate in line with the respective solubility of surfactants [45].Unfortunately, there is still little information on the influence ofthe type and characteristics of the new generation superplasticiz-ers on the air content of concrete.

3. Experimental

The experimental investigation was carried out in three phases. In Phase 1, testswere carried out on various aqueous plasticizers and SP solution. Phase 2 investi-gated the properties of the cement paste with SP. In Phase 3, tests were carriedout on self-compacting concrete mixes.

Fig. 7. Relationship between surface tension, solid tension and phase-to-phase voltage according to equation Younga–Dupre’a [42].

Table 3The composition of SP aqueous solution.

Type of SP SP (%m.c.)

PCP 1 0.77PCP 2 0.77PCP 3 0.77PCE 1 0.77PCE 2 0.56PCE 3 0.16AP 0.77SF 0.77

m.c. – In relation to mass of cement.

Table 4Standard properties of applied cement.

Properties CEM III/A 42.5N-HSR/NA

Le Chatelier, mm 0.3Beginning of setting time, minutes 229Compressive strength after 2 days, MPa 17.5Compressive strength after 7 days, MPa 32.7Compressive strength after 28 days, MPa 55.1Specific surface, cm2/g 4205Water demand, % 32.1Loss on ignition, % 0.4Insoluble residue, % 0.5SO3, % 2.5CL�, % 0.050

Table 5The composition of cement paste.

CEM III/A 42.5N – LH/HSR/NA (kg/m3) w/c Type ofSP

Dosage of SP(%m.c.)

510 1.0 PCP 1 0.77510 1.0 PCP 2 0.77510 1.0 PCP 3 0.77510 1.0 PCE 1 0.77510 1.0 PCE 2 0.56510 1.0 PCE 3 0.16510 1.0 AP 0.77510 1.0 SF 0.77

m.c. – In relation to mass of cement.

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3.1. Materials

In Phase 1, the surface tension of aqueous plasticizers and SP solution wasdetermined (Tables 2 and 3). It should be noted that the exact composition of testedplasticizer and SP and the presence of other possible compounds is not well known,because it is restricted by the manufacturer.

Phase 2 investigated the properties of the cement paste with SP. For cementpaste and concrete manufacturing, the following materials were used: CEM III/A42.5N-HSR/NA, gravel aggregate 2/8 mm and 8/16 mm, pit sand 0/2 mm, tap waterand chemical admixtures (Table 3). Standard cement properties determined usingEN standard methods are presented in Table 4.

In Phase 2, the effect of SP type on air-entrainment of cement paste was verified(Table 5). Because the author’s research methodology of paste requires it to behighly liquid, w/c = 1.0 was intentionally used.

In Phase 3, tests were carried out on self-compacting concrete mixes. The mixdesign of concrete, according to requirements of [47] is given in Table 6. A principalcriterion for applied dosage of SP was its ability to provide a maximum slump flowwithout segregation of self-compacting mixture (SCC). Since the effectiveness of theplasticizers and SP used is varied, in order to obtain self-compacting mix, their var-ious quantities should be used. SP was introduced after approximately 30 s, aftermixing the dry ingredients with water. The ingredients of the mixture were mixedfor 5 min.

The doses of admixtures in the aqueous solution and in cement pastes (Tables 3and 5) correspond to doses of superplasticizer used in the SCC (see Table 6). Alter-natively, the same manufacturer’s recommended dosage of superplasticizers can beused to verify the effect on the air content in the SCC.

3.2. Test methods

3.2.1. Test methods of surface tensionThe stalagmometric method (drop counting method) is one of the most com-

mon methods for measuring surface tension. The principle is to measure the weightof the drops of the fluid falling from the capillary glass tube, and then calculate thesurface tension of the specific fluid which we are interested in. We know the weightof each drop of the liquid by counting the number of the drops falling out. From thiswe can determine the surface tension [43].

There are two line marks on the stalagmometer: top line above the wide partand bottom line bellow it (Fig. 8). The volume between these two lines is V, and li-quid with density q contained in this volume has a mass m

m ¼ V � q ð4Þ

Such a volume V corresponds to n drops, which are released from the stalag-mometer upon the decrease of liquid level from top to bottom line mark. Here,the average mass of one drop is

mn¼ V � q

nð5Þ

surface tension of the other liquid can be calculated from the equation

Table 2Type of plasticizers and SPs.

Symbol The basic polymers included in the content ofSPs

Form

PCP 1 PCP, polycarboxylates Liquid formPCP 2 PCP, polycarboxylates Liquid formPCP 3 PCP, polycarboxylates and modified

phosphatesLiquid form

PCE 1 PCE, polycarboxylic ethers Liquid formPCE 2 PCE, polycarboxylic ethers Liquid formPCE 3 PCE, polycarboxylic ethers Solid form/

powderAP AP, acrylates Liquid formSF SF, modified phosphonates compounds Liquid form

Table 6Self-compacting concrete mixture design (kg/m3).

CEM III/A42.5N – LH/HSR/NA(kg/m3)

w/c Sand (kg/m3) Gravelaggregate (kg/m3)

Typeof SP

Dosageof SP(%m.c.)

0/2 mm 2/4 mm 4/16 mm

510 0.38 800 400 505 PCP 1 0.77510 0.38 800 400 505 PCP 2 0.77510 0.38 800 400 505 PCP 3 0.77510 0.38 800 400 505 PCE 1 0.77510 0.38 800 400 505 PCE 2 0.56510 0.38 800 400 505 PCE 3 0.16510 0.38 800 400 505 AP 0.77510 0.38 800 400 505 SF 0.77

m.c. – In relation to mass of cement.

Fig. 8. Schematic picture of stalagmometer.

Table 7The test results of foam formation of examined plasticizers and SPs.

SP type rR

(mN/m)p0

(mm)h0

(mm)p45

(mm)h45

(mm)FA FS

Distilled water 72 – – – – – –PCP 1 41 7 59 4 60 10 6PCP 2 48 7 58 3 63 10 4PCP 3 42 8 66 2 65 11 3PCE 1 45 6 61 5 62 8 6PCE 2 42 9 64 3 64 13 4PCE 3 45 9 65 1 65 13 1AP 53 4 54 4 60 6 6SF 39 8 66 3 66 12 4

Table 8Tests results of mixtures properties.

SP type Ac (%) SF (mm) T500 (sec.) q (kg/m3)

PCP 1 4.5 630 3.0 2.216PCP 2 4.0 750 3.0 2.264PCP 3 3.0 700 2.0 2.288PCE 1 6.0 730 6.0 2.190PCE 2 4.0 710 5.0 2.261PCE 3 0.9 700 2.0 2.310AP 5.6 620 3.0 2.201SF 3.5 630 3.0 2.283

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r ¼ rw �m

mwð6Þ

Substituting the mass m in the Eq. (6) with the mass of one drop then yields

r ¼ rw �qqw� nw

nð7Þ

Finally, the solution surface tension was measured using the dependence (8). Amodel liquid used in the measurements was distilled water, which surface tensioncalculated from the formula (9).

rR

rW¼ nWqR

nRqWð8Þ

r ¼ ½72:9� 0:155ðt � 18Þ� � 10�3 ð9Þ

where is the rR is the paste surface tension (N/m); rW the water surface tension (N/m); nR the waste drops amount; nW the water drops amount; qR the density of testedpaste (kg/m3); qW the water density (kg/m3); t the environment temperature (�C).

3.2.2. Test methods of foam ability index and stability indexIn order to determine the effect of the plasticizer or SP type on the quantity and

stability of foam generated by its operations, the author adopted the following val-ues: FA – foam ability index (10) and FS – foam stability index (11).

FA ¼ p0

hp� 100 ð10Þ

FS ¼ p45

hp� 100 ð11Þ

where p0 is the difference in the levels of paste and the top surface of the foam in theflask (after 60 s of vigorous mixing) (mm), (Fig. 9); p45 the difference in the levels ofpaste and the top surface of the foam in the flask (after 45 s from stopping the pastemixing). The higher p45 value, the higher foam formation is, (mm), (Fig. 9); FA thefoam ability index of plasticizer or superplasticizer. The higher the FA value, themore plasticizer or superplasticizer has the ability to foam generation; FS is the foamstability index of plasticizer or superplasticizer. The higher the FS value, the morestable foam is.

Pastes were shaken vigorously for 60 s in a closed glass flask with internaldiameter 3.0 cm and a volume of 100 cm3 (Fig. 9), volume of the grout (Table 5)in the flask was always 65 cm3. Immediately after the cessation of mixing the levels

Fig. 9. The method of indicating the parameter values of hp, h0, h45, p0, p45.

of paste and foam were reported, using millimeters located on the surface of theflask. Differences in the levels were marked as p0 After 45 s the paste and foam lev-els located on the surface determined and differences in levels were marked as p45.

3.2.3. Test methods of fresh self-compacting concreteThe flow test of mixtures (Table 5) was carried out according to [50], density

according to [19], the air content in the mixture according to [20].

4. Test results

The results of the SP water solutions and cement pastes proper-ties are summarized in Table 7. While the research results of mix-tures properties are presented in Table 8.

5. The analyze of the research results

5.1. The influence of surface tension of water solution ofsuperplasticizer on foam ability index

The surface tension of pure water was found at 72 mN/m(Table 7), which is close to the literature value of water at 23 �C.The research results indicate that investigated superplasticizer de-crease the surface tension of the water. In Fig. 10 the relationshipbetween the surface tension of aqueous solution of SPs and foamability index is presented. Considering the results shown inFig. 14 it can be concluded that the superplasticizers cause exces-sive increase in the air content in concrete because they reduce thesurface tension of water.

With the addition of polycarboxylic ethers (PCE) much morewater can be bound to the solid particles (Fig. 11). The moleculesof the PCE contact the particles with their backbone and adsorbwater molecules at their side chains [49]. With this effect the filmof bound water around the particles becomes thicker, the propor-tion of bound water increases and the remaining cross-sectionfor the flow of unbound water decreases. The back pressure rises.A similar effect can be achieved by the addition of very fine parti-cles. Due to their immense largeness of surface they can bind a lotof water and they down size the remaining cross-section for waterflow, too [49].

Fig. 10. The effect of surface tension of SP solution on the air content in the freshself-compacting concrete.

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Another possibility to bind the water is the use of organic stabi-lizers. These are large organic molecules. They can adsorb a lot ofwater molecules. These emerging molecule packages are more in-ert and immobile. If their long molecule chains intertwine they caneven evolve into a sort of net-structure, which limits the mobility

Fig. 11. Options to contr

Fig. 12. Model of the influence of different components of ce

of both the bound and the free water molecules. As a result of allthese three effects the drainage cannot be stopped completely,but it can be significantly slowed down [49]. This is the basis fora foamed cement paste being stable until hardening with minimalsymptoms of decline. The before mentioned ideas are combinedand illustrated in Fig. 12.

On the basis of the research results [49] it becomes apparentthat the type and dosage of the organic stabilizer decide aboutthe foam stability. It is obvious that the dependency is not linear.There is a material related marginal dosage which is necessary tokeep the foam stable. The influence on the density of the freshand hardened (stable) foamed cement pastes is small. This sort ofanalysis does not detect changes of the pore structure inside thefoam. They were reviewed by means of fracture surfaces [49].

In the study [48], the mechanism behind the foaming action ofan allyl ether-based polycarboxylate was investigated. Allyl ether-based PCE was chosen because it possesses a well defined chemical

ol the drainage [49].

ment paste on foam processing and foam stability [49].

Fig. 13. Chemical structures of PC and EPBE-PC [46].

PCP1PCP2

PCP3

PCE1

PCE2

PCE3

AP

SFR² = 0.6417

0

123

456

7

0 2 4 6 8 10 12 14

Ac,%

FA

Fig. 14. The effect of FA index on the air content in the mixture.

PCP1

PCP3

PCE1

PCP2; PCE2

PCE3

AP

SF

R² = 0.9351

0

1

2

3

4

5

6

7

0 1 2 3 4 5 6 7

Ac,%

FS

Fig. 15. The effect of FS on the air content in the mixture.

496 B. Łazniewska-Piekarczyk / Construction and Building Materials 53 (2014) 488–502

structure with a fairly narrow molecular weight distribution [11].At first, the foaming action of the PCE as obtained from the synthe-sis was compared to that of the PCE after purification which re-moved unreacted monomers and impurities. Foaming tendencyof PCE was determined by measuring surface tension and foam de-cay times of aqueous PCE solutions and the air void content of astandard mortar formulation. It was found that both purified allylether-co-maleic acid PCE and individual allyl ether macromono-mer possess moderate surfactant properties but do not cause theexcessive foaming known from industrially manufactured PCEs.Whereas, a mixture of purified PCE polymer and only smallamounts (P10%) of allyl ether macromonomer shows very strongfoaming. This combination exhibits similar foaming action likeindustrially manufactured PCE superplasticizers. Apparently, theallyl ether macromonomer acts as a co-surfactant (foam stabilizer)to PCE which already presents a macro tenside. Minimizing theamount of unreacted allylether monomer in commercial PCEs pro-vides a solution to obtain a less foaming product.

We can find that the effect of superplasticizers with a lowmolecular weight on the reduction in surface tension is not strong.In accordance with the results [40] lignosulfonate has a character-istic of being strong hydrophilic. Its hydrophobic skeleton appearsspherical in shape, so it cannot form a regular arrangement at theinterfacial phase. This is common with certain surfactants of lowmolecular weights. The surface tension of calcium lignosulfonatesolutions decreases with increasing molecular weight. This maybe related to the fact that the charged hydrophilic groups decrease,relatively, with a molecular weight increase. The adsorptionamount thus increases leading to that calcium lignosulfonate witha high relative molecular weight has higher surface activity, i.e.,lower surface tension [40]. The lower surface tension of the liquidsolution is, the easier the wetting of solid particles may be becausethis helps the cement particles more readily disperse into water.Sugiyama et al. [46] synthesized a new series of superplasticizersin which functional groups of EPBE acting as shrinkage reducingagent (SRA), capable of reducing surface tension, were attachedto the structure of various polycarboxylate polymers (Fig. 13).

5.2. The influence of foam ability index and stability index on air-content in SCC

Figs. 14 and 15 show the relationship between FA index and FSindex and the content of the air in the mixture. Research results,presented in these figures show that FA and FS index correlate wellwith air-entrainment of mixture.

Interesting that the value of the FS index corresponds to the aircontent in concrete mix (see Fig. 15). However, this observation re-quires further study, because it deepens on composition of SCC.

Reassuming, there is good correlation between these test re-sults of surface tension of different type of superplasticizers solu-tion and air-content in SCC. The influence of plasticizer and SP onair-content in SCC can be quickly and easily verified on the basisof FA index or FS index tests, which correlate well with the air con-tent found in the self-compacting mixture. The foam ability andstability index test is not a standardized method. The describedmethod is at present stage not a finished procedure, but needs fur-ther work to fulfill our goal of having a reproducible method. Thesetests should be based on using a pure surfactant instead of asuperplasticizer, where commercial products show variation inchemical nature and concentrations. In the next stages of research,the effect of cement type, temperature and modifications SCC byadmixtures on the air content will also be taken into account.

5.3. The influence of SP type on rheological properties of SCC

Analyzing the effect of the SP type on the air content in concretemix, one should keep in mind that in case of self-compacting mix-ture the air content remains in its volume and it depends on its rhe-ological properties. Each type of the SP effects differently on themodification of SCC rheological properties, and moreover its imple-mentation may be different, therefore the analysis of the effect ofthe SP type on the air content in SCC is very complicated. Due tothe varying effectiveness of SP, in order to obtain the minimum flowof the mixture according to [50], i.e. 550 mm, it was necessary touse substantially different amounts of SP. Due to different SP typeused in the research, it is not possible to analyze directly the effectof the flow of mixture diameter or the flow time on the air contentin its volume. Fig. 16 shows the effect of the amount and type of SPon the flow of mixture. Barfield and Ghafoori’s [51] study indicatedthat a polycarboxylate-ester (PCE) SP needed a larger dosage to im-part the same flowability to SCC than a polycarboxylate-acid (PCA)SP. The research results presented in Fig. 16 indicate that it is some-times otherwise. This depends on the type of SP. More effective inrealization of the mixture used with a small amount of admixture,are SPs characterized by sequence based on acrylates, modifiedphosphates (AP and PCE3). However, the most effective in this areaare SPs characterized on the basis of polycarboxylates (PCP2). Be-sides a lower slump loss, AP-based superplasticizers perform betterthan the traditional sulfonated polymers even in terms of either

PCP 1

PCP 2

PCP 3

PCE 1PCE 2PCE 3

APSF

550

600

650

700

750

800

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

SF,m

m

SP, % m.C.

Fig. 16. The effect of the amount and the type of SP on the flow of mixture.

B. Łazniewska-Piekarczyk / Construction and Building Materials 53 (2014) 488–502 497

higher reduction in the w/c at a given workability or higher slumplevel at a given mixture composition. However, the AP superplast-icizers appear to be more expensive than others [52].

Hanada et al. [53] developed a new family of acrylic polymersbased on the following changes with respect to the PC-basedsuperplasticizer [35]:

– a polyether (PE) based superplasticizer with much longer sidechains of ethylene oxide (EO): 130 moles of EO instead of 10–25 moles as in traditional PC-based superplasticizer (Fig. 17);this change produces a lower adsorption speed and reducesthe typical retarding effect related to the early adsorption;

Fig. 17. The chemical structure of polycarboxylate type (PC), polyether type (PE)and slump-loss-controlling agent superplasticizer (SLCA); q and p are the number ofmoles of EO in PC and PE or SLCA polymers [35].

Fig. 18. The schematic molecular structure of polycarboxylate type (PC), polyeth

– a modified PE-based superplasticizer where a great number ofcarboxylic groups are replaced by a slump-loss controllingagent (SLCA) to achieve a still higher slump retention with min-imal setting retardation: indeed, due to the relatively low num-ber of carboxylic groups in SLCA (Fig. 18) the initial adsorptionand dispersing effect are negligible as well as the setting retar-dation; however, subsequently to the hydrolytic effect relatedwith the OH– presence in the aqueous phase of the cementpaste, the number of carboxylic units increases and the slumpcan still increase by prolonging the mixing time due to theincreasing adsorption of the polymer on the surface of thecement particles.

The behavior of fresh concrete in the presence of PC and SLCA-based superplasticizers is schematically shown in Fig. 19.

Polymers with backbone and graft chains, such as PCEs, acrylicesters, and cross-linked acrylic polymers, cause dispersion of ce-ment grains by steric hindrance [54–56]. This phenomenon relatesto the separation of the admixture molecules from each other dueto the bulky side chains. Steric hindrance is more effective mecha-nism than electrostatic repulsion. The side chains, primarily ofpolyethylene oxide extending on the surface of cement particles,migrate in water and the cement particles are dispersed by the ste-ric hindrance of the side chains. Electrostatic repulsion depends onthe composition of the solution phase and adsorbed amount of theSP (greater the adsorption, better the repulsion) [57]. On the otherhand, steric repulsion depends on the length of main chain, lengthand number of side chains [58]. In case of PCE based admixtures,for fluidity retention, the main chain should be short, with largenumbers of long side chains [58]. Because of the steric repulsionmechanism, PCEs are generally more effective than the sulfonatebased admixtures, and generally do not experience much problemsat low water to cement ratios. However, they are more sensitive tooverdosing, and can lead to problems like excessive air entrain-ment and retardation.

5.4. The influence of rheological properties of SCC type on air-contentof mixture with different SP type

The determining factor for the bubble-stability in a fluid is thebalance between the internal pressure of the bubble, being alwaysa bit higher than the ambient pressure, and tensile stresses ab-sorbed by the bubble shell (Fig. 20). The maximum size of thesetensile stresses depends on the inner cohesion of the fluid andinterfacial tension [49].

The stability of foams depends not only on the stability of itssingle bubbles but also on other effects. The most important one,especially for the production of cement-bound foams, is drainage.This means that air and fluid separate. The air bubbles up whilethe fluid flows out under the influence of the gravitation

er type (PE) and slump-loss-controlling agent superplasticizer (SLCA) [35].

Fig. 19. Schematic trend in the slump loss behavior with different acrylicsuperplasticizers (PC, PE, SLCA, PE + SLCA) in concrete mixtures with CEM II A/L32.5R (340 kg/m3), w/c = 0.45 [35].

Fig. 20. Schematic diagram of a bubble [49].

Fig. 21. Schematic diagram of drainage and coalescence [49].

498 B. Łazniewska-Piekarczyk / Construction and Building Materials 53 (2014) 488–502

(Fig. 21). The most important influences on the drainage are thedensity and viscosity of the fluid. If the fluid film between two bub-bles thins out so far that the tensile stresses corresponding to theinternal pressure can no longer be absorbed, the fluid film breaksand the bubbles affiliate. This is called coalescence [49]. Providedthat the air entrainment works as well as possible, the maximumair content of the foam depends on geometrical aspects, like bubblediameter distribution and the minimum thickness of the fluid filmsbetween the bubbles. For this a higher viscosity of the fluid wouldbe better. Nevertheless, the viscosity has to be limited, because ahigh viscosity interferes with the air entrainment and the disper-sion of the air in the fluid [49].

On single bubble located in cement paste the following forcesact [65]: the force of gravity G, the buoyancy force, the force causedby the fluid vortex C, the force caused by the existence of the elec-tric field E. Resultant of these forces is thus equal to S: [59]:

S ¼W þ Gþ C þ E ð12Þ

When a mixture of self-compacting concrete is already at rest,for a single air bubble forces act: gravity G and buoyancy Wforces. Thus, the resultant will be equal: S = G + W. If the force Sis larger than zero, the particle begins to move relative to thestationary fluid at a certain flow velocity w. Then drag forceformed center R in the same direction and opposite to theresultant force S. The balance of forces acting on a single bubbleis shown in Fig. 22.

Flow speed of bubbles in the cement grout can be described byrelationship [59,60]:

w ¼d2ðqz � qpÞg

18gzð13Þ

when w is the bubble flow velocity; d the diameter of the bubble; qz

the density of the grout; qp the air density; gz the viscosity of thegrout.

Thus, the bubble outflow velocity increases with increasingbubble volume, and decreases with increasing viscosity of thegrout. However, for describing the behavior of the bubbles, thephysical and chemical interactions between the components ofthe concrete mix must be taken into account, modified by chemicaladmixtures. The molecules of SP should also modify the surface ofsolid particles in order to keep its hydrophilic character. Air bub-bles can adhere only to hydrophobic surfaces. The surfactant mol-ecules in the solution help entrain air bubbles and stabilize them inthe fresh concrete (Fig. 23a) if cement paste does not implicatesanother admixtures, especially superplasticizers (Fig. 23b) [61–63]. The effect of superplasticizers on air content of the mixturescan be estimated using FA and FS indexes.

The SP type significantly influences the air-content in self-com-pacting mix with similar slump diameter and time flow value (forexample, SF = 700, T500 = 3.0: PCP2, PCE1, PCE2, PCP3 and PCE3).The air-content amounts to 6.5% in spite of the fact that the flowdiameter amounts to 750 mm (Fig. 24). Viscosity also slows downthe potential coalition of adjacent air bubbles by working as a bar-rier [44]. The yield stress of cement paste prevents the escape ofsmall air bubbles whose buoyancy forces are not large enough tobreak the bulk paste phase. The viscosity of the paste and diameterof bubbles determine how fast the air bubbles move upwardaccording to Stokes’ law. High viscosity can provide a cushion ef-fect for air bubbles to absorb shocks from disturbances. The effectof viscosity of the mixture on air-content depends on the type of SP(Fig. 25). The superplasticizer type significantly influences the air-content in self-compacting mix, regardless of the yield stress andviscosity of SCC. Therefore, it is difficult to create a statistical modelthat describes the influence of the rheological properties of SCC onthe effect of the self-compaction, finally air-content, regardless ofthe superplasticizer type. Due to the volume of air voids, the typeof SP is essential [2,8]. FA index and FS index.

The foaming behavior of PCs was investigated by the foam vol-ume, the surface tension of PCs aqueous solution, and the air con-tent of concrete were analyzed in the research [48]. According tothe results, the hydrophobic side chains of PCs may affect thehydration reaction of cement resulting in better workability. InSPs group, which action was caused by the flow over 60 cm(Fig. 24), acrylate SP (AP) characterizes with the greatest side air-entraining effect, involving the formation of an excessive amountof the air in the mixture. SPs based on the modified phosphate(SF) did not cause an excessive air-entrainment although the mix-ture also achieved the flow over 600 mm. The smallest side effect

Fig. 22. Schematic of the balance of forces acting on a single bubble [59].

Fig. 23. (a) Adsorption of the flux molecules framework in the grains of cement and the negative effect of the anion final group; (b) diagram of arrangement of cement–waterand aggregate–cement–water arrangement, with the use of air-entraining mean (surface active anion substance) [64].

Fig. 24. The effect of mixtures flow volume, considered in terms of the type andamount of SP used, on the air content in its volume.

Fig. 25. The effect of mixtures flow time, considered in terms of the type andamount of SP used.

B. Łazniewska-Piekarczyk / Construction and Building Materials 53 (2014) 488–502 499

in the form of the excessive air-entrainment of the mixture(Fig. 24), and liquidizing the mixture in the greatest degree, is aSP based on polycarboxylates and modified phosphates (PCP3).Without a doubt it is the most effective SP from the tested ones.In case of the SP based only on the polycarboxylates (PCP1 andPCP2), the effect of the excessive air-entrainment of the mixtureoccurs.

Research results presented in Fig. 24, SPs based on polycarbox-ylate ethers (PCE1, PCE2 and PCE3) were characterized with a rad-ically different effect on the ‘‘air-entrainment’’. The type ofsuperplasticizer is crucial regarding the size and proportions ofthe air pores participation, gained as a result of its functioning,although the time of concrete hardening is of no importance onfurther changes of these proportions [27]. The publication [66]indicates that the superplasticizer causes reduction in total air-void surface areas and increases in air-void spacing factors. Thebubbles are slightly bigger than those formed as a result of air-entraining admixture functioning, but their stability is lower. Airbubbles formed as a result of air-entraining admixtures function-ing, reach the size of 20–250 lm. Moreover, they adhere to the sur-face of particles of cement (Fig. 19a) [4]. During concrete’shardening, formed pores are not fulfilled with the products ofhydration. With the use of polycarboxylate superplasticizers, theair pores characterize with smaller diameters than pores formedas a result of lignosulphonic or naphthalene superplasticizers func-tioning [67]. The inclusion of SP (sodium salt of a sulfonated nap-thalene-formaldehyde condensate) in cement paste, leads to areduction in the total pore volume and to a refinement of the porestructures [68]. The dominant pore size is unaffected and thethreshold diameter is reduced in the presence of SP. According toSakai et al. [67], superplasticizers type is crucial regarding the sizeand share of air pores trapped under their influence (Fig. 26),although with time of concrete hardening further changes of theseproportions mainly take place (Fig. 27). The addition of polycar-boxylate superplasticizers, the air pores have smaller diametersthan pores trapped in case of lignosulfonate or naphthalenesuperplasticizers addition. The research results [69] indicate thattotal air content, the content of micropores less than 0.3 mm indiameter, total porosity, specific pore volume and specific pore sur-face in concrete modified with superplasticizer based on polycarb-

Fig. 26. Influence of some SP, namely; naphthalene sulfonate (b-NS), refined ligninsulfonate (LS) and polycarboxylate (P32, S34) on pore structure in 28-days oldconcrete [67].

Fig. 27. Influence of the same superplasticizers as in Fig. 26 but after 90 days ofcuring [67].

Fig. 28. Chemical structure of main dispersant of PC-based superplasticizer(Molecular model was drawn with CS Chem. 3D; hydrogen (gray) and oxygen(dark gray) over carbon.) [73].

500 B. Łazniewska-Piekarczyk / Construction and Building Materials 53 (2014) 488–502

oxylans are considerably lower than in concrete modified withsuperplasticizer based on polycarboxylic ether. Whereas air voidsspacing factor L, average pore radius and specific air pore surfaceare higher for concrete with superplasticizer based on polycarb-oxylans. It can be concluded from the results that the polycarboxy-lic ether contained in superplasticizer based on polycarboxylicether causes considerable aeration of the self-compacting concrete.

Research results [70] indicate that the air-content in hardenedSCC, as a side effect of PCE acting, may amount to 5.0%, and in somecases of PCP, even 8.0% [71]. Therefore, it is important to studytheir compatibility, also because of the air content in the concrete.From the point of view of mechanical self-compacting concretecharacteristics (SCC), the most favorable situation is when themix characterizes with the lowest air content. The problem oftoo high air content becomes more fundamental when the con-crete’s design class is higher, because with the cement content inconcrete mix the content of the caught air increases. Research re-sults [67,71,70,72] proved that size of pores arising from the actionof SP in hardened concrete are characterized with overly largediameters. In effect, concrete’s mechanical parameters are sub-jected to considerable deterioration �1% of air-entrainment,depending on its type, may reduce up to 5% of concrete’s compres-sion strength.

The side effect of some type of SPs on air content in concretewas used in case of air-entraining superplasticizers (high rangewater reducers) in Japan. Polycarboxylic acid based superplasticiz-ers (Comb-type polymers with grafted pendant polyethylene oxi-des) influence on air content of concrete. The air entraining high-range water reducing agents (AEHRWRAs), which boast excellentwater reducing ratios and slump retention abilities, were devel-oped in the mid-1980s, and first marketed in 1987 [73]. The maincomponent of AEHRWRA is a copolymer with grafted pendantgroups of polyethylene oxide. Because these have a carboxyl groupin the main chain, they are generically called polycarboxylic acid-based superplasticizers. Fig. 28 shows a typical chemical structureof PC-AEHRWRA (PC-based superplasticizers). AEHRWRA ad-vanced rapidly in association with the development of high-perfor-mance concrete (self-compacting concrete) as proposed byProfessor Okamura in 1986 [74] and high-strength concrete wasapplied to New RC (New reinforced concrete) projects between1988 and 1992. AEHRWRA containing retarded and standard typeswere added in the JIS revision of 1995. AEHRWRA is especially use-ful for producing self-compacting and high-strength concretes. On

the other hand, the worsening situation with respect to aggregateresources has tended to increase the water demand of concrete,comb-type polymers, which are also the main component of AEHR-WRA, are used to reduce the contents of water for secure durabilityof ordinary concrete. The development of many types of comb-typepolymers that enable better performance has also continued,resulting in highly durable and high strength concretes [75].

6. Conclusion

On the basis of the scope of the research it can be concludedthat:

1. SCC characterized with to excessive air content, which was theeffect of functioning of superplasticizer despite fulfilling therequirements according to EN 12350-8. The effect of type ofsuperplasticizer is essential because of its ‘‘air-entraining’’effect of the self-compacting concrete. Therefore, the necessarycomplement of superplasticizer compatibility test is to verifythe effect of ‘‘air-entrainment’’.

2. The superplasticizer type significantly influences the air-con-tent in self-compacting mix, regardless of the yield stress andviscosity of SCC. Therefore, it is difficult to create a statisticalmodel that describes the influence of the rheological propertiesof SCC on the effect of the self-compaction, finally air-content,regardless of the superplasticizer type.

3. The influence of SP on air-content in SCC can be verified on thebasis of FA foam ability index or FS foam stability index tests,which correlate well with the air content found in the self-com-pacting mixture.

4. There is good correlation between these test results of surfacetension of different type of superplasticizers solution of superp-lasticizer and air-content in SCC. When surface tension of aque-ous solution of superplasticizer is low then FA foam abilityindex has high value. In turn, high value of FA foam ability indexcauses high volume of air-content in SCC.

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