influence of selected new-generation-admixtures-on-the-workability-air-voids-parameters-of scc

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Construction and Building Materials 31 (2012) 310–319

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Construction and Building Materials
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The in?uence of selected new generation admixtures on the workability, air-voids parameters and frost-resistance of self compacting concrete
? niewska-Piekarczyk ? Beata ?az
Silesian Technical University, Faculty of Civil Engineering, Department of Building Processes, Akademicka 5 Str., 44-100 Gliwice, Poland

a r t i c l e

i n f o

a b s t r a c t
The in?uence of a new generation superplasticizer (SP) type, air-entraining admixture (AEA), viscosity modifying admixture (VMA) and anti-foaming admixture (AFA) on the air-content, workability of selfcompacting concrete (SCC) is analyzed in the paper. The purpose of this study was to examine the in?uence of the admixtures on porosity and pore size distribution of SCC at constant water on cement ratio, type and volume of aggregate and volume of cement paste. The compressive strength, frost resistance and durability coef?cient (DF), parameters of the air-voids of hardened SCC are also investigated. ? 2012 Elsevier Ltd. All rights reserved.

Article history: Received 4 October 2011 Received in revised form 31 December 2011 Accepted 31 December 2011 Available online 1 February 2012 Keywords: Self-compacting concrete Concrete admixtures Frost-resistance Durability coef?cient Air-void parameter

1. Introduction The self-compacting concrete has to ful?ll contradictory requirements of high ?owability when it is being cast and high viscosity when it is at rest, in order to prevent segregation. These requirements make use of the mineral and chemical admixtures essential for SCC. The high ?owability is achieved using superplasticizers (SPs), while stability against segregation is achieved either by using a large quantity of ?ne materials, or by using an appropriate viscosity modifying agent (VMA). EFNARC – 2002 [1] was the ?rst internationally recognized set of guidelines and speci?cations for self-compacting concrete. However, it proposed of a single range of workability for all applications. Subsequent studies from Europe indicated that different applications require the self-compacting concrete to have different ranges of ?owability and segregation resistance. This aspect has been incorporated in EFNARC – 2005 [2]. SCC is now classi?ed into different consistency classes based on its slump ?ow and ?ow time through V Funnel. Slump ?ow (SF) and T500 time (VS) is a test to assess the ?owability and the ?ow rate of SCC in the absence of obstructions. It is based on the slump test described in EN 12352. The result is an indication of the ?lling ability of SCC, and the T500 time is a measure of the speed of ?ow and hence the viscosity. The fresh concrete is poured into a cone. When the cone is upwards the time from commencing upward movement the cone to when
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the concrete has ?owed to a diameter of 500 mm is measured; this is the T500 time. The largest diameter of the slow spread of the concrete and the diameter of the spread at right angles to it are then measured and the mean is the slump-?ow. The upper and lower limits of slump-?ow classes (SF) are the following [2]: SF1 – slump ?ow from 50 to 650 mm, SF2 – slump ?ow from 660 to 750 mm, SF3 – slump ?ow from 760 to 850 mm. While the upper and lower limits of viscosity classes (VS) are the following [2]: VS1 – T500 less than or equal to 2 s., VS2 – T500 greater than 2 s. The ?owability (SF) and viscosity (VS) classes of SCC depend on the values of rheological properties of cement paste. The value of SCC ?ow diameter depends on the mix yield stress s0m, whereas SCC time ?ow depends on its plastic viscosity gpl. The cement particles are always agglomerated in water suspensions. This leads to a viscosity increase by an apparent particle volume increase. A part of water is entrapped in the porosity of the agglomerates and does not contribute to the ?owability. The role of the superplasticizers (polymers) is essentially to break down these agglomerates by modifying the balance of interparticle forces. In case of non-air-entrained SCC, achieving low air-content might became a slightly problematic task [3–6]. Certain SP of new generation produce an excessive air-entrainment remaining in the volume of the fresh mix (Table 1) and concrete [7], although the mix meets commonly accepted criteria of technical tests according to [2]. Thus, SP should be compatible with cement, but they should not increase the air content in SCC. Four mechanisms might act for the dispersion of cement particles, as well as for other powders (Fig. 1) [8,9]:

?niewska-Piekarczyk / Construction and Building Materials 31 (2012) 310–319 B. ?az Table 1 The in?uence of SP type on the concrete air-entrainment [8]. SP LS SNF SMF New generation SP PCP Air volume ++ + 0 ++ AAP ++

311

Where: LS – Lignosulfonate, SNF – Sulfonated Naphtalene Formaldehyde Condensate, SMF – Sulfonated Melamine Formaldehyde Condensate, PCP – PolyCarboxylate Polyoxyethylene, AAP – Amino Phosphonate Polyoxyethylene.

 Creating ‘‘grease’’ layer on the cement and grains of micro-?ller, decreasing internal friction of concrete mix (SMF – sulfone melamine-formaldehygenic resin).  Surrounding grains of cement with negative charge, causing their mutual repulsion (SNF – sulfonenaphtelene-formadelhygenic resins), the type of superplasticizer dictates the value of molecules dispersion force, which measure is jeta surface potential, with the value increase of this potential, the force of molecules dispersion increases.  Decreasing of surface water tension in relation to cement and micro-?llers (MLS – modi?ed lime or sodium lingisulfones; other products are: copolymers of formic acid with naphtylic-sulfone acid, copolymers of methacrylate acid with sodium salt or polyethylene glycol).  Sterole – they create long chains of polymere, physically precluding the cement’s grains to approach each other (new-second-generation of ?uxing admixtures; substances from the polycarboxylants group (PC), copolymers of acryl acid with acrylate (CAE) and not acryl resins (CLAP)). Such work results in a situation where admixtures of new generation function ‘‘preventively’’ – instead of smashing already formed cement’s grains agglomerates, they do not allow their forming. The two most important mechanisms are linked to polymer adsorption: steric hindrance through the adsorbed layer thickness and electrostatic repulsion through the induced electrical charge. In reality, once the particles are close enough for their adsorbed layers to overlap, both effects come into play. Understanding which mechanism is dominant and what parameters have an effect, is essential for the design of polymers with improved performances. It should also allow a better use of common polymers. Much has been learned from the ?eld of colloidal science, where surface forces and their role on interparticle interactions have been a subject of ongoing research for many years. The molecules of SP should also modify the surface of solid particles in order to keep its hydrophilic character. The air bubbles can adhere only to hydrophobic surfaces. The presence of listed functional groups (oxygen

in form of etheric group (–O–), hydroxyl group (–OH) and carboxyl group) produce water surface tension decrease, producing ?occulation of associated molecules and increase in moisture of not only grains of cement but also the whole mineral framework [9]. In the superplasticizers group there are ones that show only dispersion functioning not decreasing surface tension [10]. They are: hydrocarboxylen acid salts, sulfonic melamine-formaldehygenic resins, for-maldehygenic picodensats salts of beta-naphtalenesulfonic acid. Moreover, the type of new generation SP is very important to achieve stability and high level of ?uidity of SCC. Bar?eld and Ghafoori [11] study indicated that a polycar-boxylate-ester (PCE) SP needed a larger dosage to impart the same ?owability to SCC than a polycar-boxylate-acid (PCA) SP. Additionally, when using a PCE SP, VMA was always required to maintain stability. The AFA decreases effectively the air-content in SCC [12]. Such admixtures are not commonly used in the technology of SCC. The components and their proportions used in the anti-foaming admixtures, as in SP, are known only to the producers. These ingredients could be mineral oils, silicone oils, organic modi?ed silicones, hydrophobic constant molecules (silica, waxes, higher fatty acids soaps, alcohols and fatty acids), emulsi?ers, polyalcohol or alcohol derivatives of organic compounds. Mixes of the active components mentioned above could have a synergetic effect. Unfortunately, the high price and insuf?cient recognition of in?uence on the fresh mix and concrete properties do not promote wider use of the antifoaming admixtures. The mechanism of anti-foaming admixture functioning may be explained in the following way. The active components are distributed around the air bubbles, displacing surfactant molecules. As a result, the thickness of the lamella wall built of surfactant leads to its destabilization and in effect to the bubble fracture or coalescence. It is advisable to carry on proper tests for veri?cation of the in?uence of anti-foaming admixtures on the air-entrainment, rheological properties, stability of selfcompacting concrete mix, frost resistance of SCC and porosity characteristic according to EN 480-11. In case of air-entraining SCC, as with the non-entraining SCC, achieving the suitable air void characteristics is also a dif?cult task [3,4,6]. At a considerable ?uidity of self-compacting concrete mix, air bubbles, presented in the air entrained concrete mix, can be unstable because of ?oating and coalescence of the air bubbles or fading of bubbles with a diameter less than 0.10 mm [3,4]. Intentionally introduced air bubbles are unstable due to the high level of consistency of self-compacting mix. In case of too high level of mix consistency, which encourages the segregation of the mix, VMA should be used. The thixotropic property increases the stability of the concrete and reduces the risk of segregation after casting.

Fig. 1. Types of superplasticizer action: (a) creating ‘‘grease’’ layer (b) surrounding grains of cement with negative charge, (c) decreasing of surface water tension (d) long chains of polymer, physically precluding the grains of cement to approach each other [8].

312 Table 2 The main aim of the use of the admixtures. Combination of admixtures SP1 SP1 + AFA SP2 SP2 + VMA SP2 + AEA SP2 + AEA + VMA

?niewska-Piekarczyk / Construction and Building Materials 31 (2012) 310–319 B. ?az

The main aim of use the of the admixtures The air-entrained SCC (as a result of side effect of SP1) Elimination of too high air-content (as a result of side effect of SP1) in SCC Non air-entrained SCC Elimination of segregation as a result of SP2 action Intentionally air-entrained SCC Elimination of segregation as a result of SP2 and AEA action

The common VMAs in concrete include microbial polysaccharides (such as Welan gum), cellulose derivatives (methyl cellulose), and acrylic polymers [13,14]. The mechanism of action in each case is different. Some VMAs adsorb on cement particles and increase viscosity by promoting inter-particle attraction [15–17]. The mixture containing VMA exhibits shear-thinning behavior whereby apparent viscosity decreases with the increase in shear rate. Such concrete is typically thixotropic, where the viscosity buildup is promoted due to the association and entanglement of polymer chains of the VMA at a low shear rate that can further inhibit ?ow and increase viscosity. The thixotropic property increases the stability of the concrete and reduces the risk of segregation after casting [18]. An air-entraining admixture (AEA) is also required in order to produce the air bubbles dispersed throughout the concrete, which ultimately provides durability for the hardened concrete in freezing and thawing situations. The air-entraining agents are typically either surfactants that aid in bubble stabilization by reducing the surface tension of water, or substances that produce a water-repellant precipitate when mixed with concrete. It is well documented that speci?c limits on the air void characteristics can greatly improve the frost durability of concrete when exposed to water, even in self-consolidating concrete [3]. For self-consolidating concrete mixtures, past research indicates that increasing slump ?ow increases the demand for AEA to entrain a given volume of air [3,19,20]. The air bubbles can move more freely in concrete when it is highly ?uid; therefore, there is increased occurrence of bubble coalescence and rupturing. To a certain degree, a SCC mixture with a high viscosity (usually accompanying a lower slump ?ow) prevents bubbles from rupturing or coalescing by creating a ‘‘cushion effect’’ for the air voids to remain unaffected by mixing and other disturbances [21]. While the higher ?uidity of SCC can have a destabilizing effect on air voids once they are formed, the usage of admixtures such as VMA and SP can reduce the ability of the airentraining admixture (AEA) to create a proper air void system [3]. The other admixtures can interfere with the ability of AEA to stabilize air voids in concrete by the way in which they interact on a molecular level. The ?uidity of SCC affects the generation and stability of the air voids in a concrete matrix by increasing bubble

coalescence, and by increasing interaction between admixtures, which can inhibit the effectiveness of a given amount of AEA [11]. Many inorganic electrolytes and polar organic materials in?uence the foaming ability of surfactants [21]. Because of the complexity of modern AEAs and other chemical admixtures, it is impossible to generalize the effects of their interactions with surfactants on the air entrainment. The compatibility of the admixtures should be experimentally examined if the effects of such combinations are not known in advance. Most organic chemical admixtures will increase the air entrainment partly because they may reduce adsorbed AEA molecules on solid surface through competition, such as super plasticizers. In addition, macromolecular materials may help stabilize the dispersed air bubbles. Furthermore, some high-range water reducers may have the air-entraining potential themselves [21]. The VMAs in?uence the air bubbles stability too. Research results proved that VMA in?uences on air-content in SCC [4,18]. In publication [18] nine concrete mixes were tested including one mix with COM (the chemical composition of COM is a commercial patent and it is composed of a combination of SP and VMA.), one mix with Welan gum, one control mix and six mixes with various dosages of four novel polysaccharide-based VMAs. W/C of all the concrete mixes was kept constant at about 0.45 while the proportion of coarse and ?ne aggregates was kept at 1:1. The research results [18] indicated that the air content seems to decrease with the increase of VMA content in the SCC mixes. This suggests that the incorporation of VMA will probably necessitate greater additions of air entraining agents to secure a given air volume. This ?nding is consistent with that suggested by Khayat [4]. This article presents the development of SCC with two different types of new generation SP: SP1 (with air entraining side effect) and SP2 (without entraining side effect) and one type new generation of VMA, AEA and AFA. It establishes the following main aim of the use of the admixtures (Table 4). The main objective of the research is to determine the in?uence the admixtures on the rheological aspect, air-content in fresh concrete mix, porosity characteristics of hardened SCC, frost-resistance, durability coef?cient and effects of admixture source on the relationships between the air-voids parameter and frost resistance of concrete. Because the rheological properties in?uence the air-content in SCC, a study was then carried out on the fresh and hardened properties of different SCC mixtures with various dosages of admixtures to achieve the same consistency class (SF2). 2. Research signi?cance Using various admixture manufacturers available commercially will provide builders and engineers awareness and knowledge on the complexities associated with the development and production

Table 3 The chemical and physical properties of CEM II/B-S 32.5 R. Chemical analyses (%) SiO2 24.7 CaO 56.7 Al2O3 6.3 Fe2O3 2.3 MgO 2.9 Na2Oe 0.7 SO3 3.2 Speci?c surface Blaine (cm2/g) 3250 Speci?c gravity (g/cm3) 3.0 Compressive strength (MPa) 42.4 Setting time, vicat test (min) Initial setting 240 Final setting 270

Table 4 The chemical and physical properties of lime stone. Chemical analyses (%) CaCO3 96.00 SiO2 + NR 1.50 MgCO3 1.40 Fe2O3 0.11 Al2O3 0.08 Na2O 0.023 K2O 0037 S 0.03 43.75 2.7 Loss on ignition Speci?c gravity (g/cm3)

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313

of SCC. This research is important in cold regions where concrete must have adequate frost durability under repetitive freezing and thawing cycles. It is important to determine the effects of modi?cation of the non-air-entrained SCC and air-entrained SCC by VMA and AFA. The effects of admixtures actions may in?uence the air-voids parameters and frost resistance of concrete. The relationship between the parameters and frost resistance may be different under the in?uence of the admixtures.

Table 6 The properties of sand and gravel. Property The content of mineral dust The content of organic substances Bulk density qnz Flatness index Absorptivity Sand 0/2 mm 0.67%, category f3 Absence 1.74 kg/dm3 – – Gravel 2/8 mm 0.48%, category f3 Absence 1.69 kg/dm3 6.2%, category FI10 0.62%

3. Materials and description of the tests The experimental investigation was carried out in two phases. In Phase 1, tests were carried out on various concrete mixes with SP1, SP2 and one type of VMA, AEA and AFA. The admixtures are commercial used in Poland. The Phase 2 investigated the properties of the hardened concrete. 3.2.1. Tests on fresh SCC properties The tests were conducted to determine the consistency, workability and aircontent in SCC. The tests of fresh self-compacting mix were carried out after 20 min, because the SP liquefaction ef?ciency increases after 20 min [22]. Before the test self-compacting mix was mixed for 3 min. 3.2.1.1. Slump ?ow. The slump ?ow test [2] was used to evaluate the free deformability and ?owability of SCC in the absence of obstructions. A standard slump cone was used for the test and the concrete was poured in the cone without consolidation. Slump ?ow value represented the mean diameter (measured in two perpendicular directions) of concrete after lifting the standard slump cone. The research results of concrete mix properties are presented in Table 9. The main aim of this step of research is to compress the in?uence of admixtures with the air-content in SCC (with similar SF and VS class). Because the dosages of admixtures were conformed to the constant slump ?ow class (SF), the diameters ?ow of concrete mix are similar (Table 9). The research results in publication [23] show that SCC with slump ?ow value >700 mm might segregate. The presented research results proved that SCC incorporating new generation SP is stabile with ?ow diameter value = 740 mm. 3.2.1.2. Air content in mix. The air content was measured by the pressure method according to EN 12350-7:2001. The air content varied from 2.1% to 8.0% (Table 9). C1A, C2 and C2V mixtures are non-air-entrained concretes, C1, C2A and C2AV mixtures are air-entrained concretes. 3.2.2. Discussion of Phase 1 test results The study on fresh concrete suggests that all investigated admixtures can be used in the development of a SCC with satisfactory rheological properties (better cohesiveness and higher ?owability). Nevertheless, the type of the new generation SP in?uences essentially the air-content in the fresh concrete mix. However, overall performance of Types 1 SP was better in enhancing rheological and consistency properties of self-compacting concrete mix. The VMA decreases intentionally the air-entrainment (as a result of SP2 and AEA acting) of the self-compacting concrete mix. All investigated admixtures were chosen to develop SCC and the development of SCC is described in Phase 2 of the investigation. 3.3. Phase 2: tests on hardened SCC properties The temperature and relative humidity were respectively 20 °C and 100% (in water). After 28 days, the tests were conducted to determine the freeze–thaw resistance, durability coef?cient DF and air-voids parameters of SCC. 3.3.1. Freeze–thaw resistance The freeze-proof resistance was investigated according to PN-88/B-06250. After 28 days, concrete samples (150 ? 150 ? 150 mm) were freezing for 3 h in temp. ?20 °C and thawing in water for 3 h in temp. +20 °C. Four cycles per day were performed. After 300 freeze–thaw cycles the compressive strength and mass decrease of the concrete specimens were tested. According to this norm, concrete is frostresistant when its compressive strength decrease is lower than 20% after n cycles and weight loss is lower than 5%. The research results of the frost-resistance are presented in Table 10. The research result indicates that the type of SP is very important for frost-resistance of SCC. The air-entrained (as a result of SP1 action) SCC is frost-resistant (decrease of compressive strength after freeze–thaw cycles is lower than 20%). Because of the weight and length loss, the change measurements are the last reliable indicators of freeze–thaw damage, and the dynamic modulus test is normally speci?ed. The test is predicated on the fact that the outcome of these measurements will re?ect the damage (cracking) to the cement or aggregate caused by the expansion of water in the concrete to ice during freezing. 3.3.2. DF durability coef?cient The results of the dynamic elastic modulus test are presented in terms of the durability factor DF [24] (ASTM C666), which is de?ned by [25]:

3.1. Examined materials 3.1.1. Cement, mineral additives and aggregates A type CEM II/B-S 32.5 R cement with speci?c gravity of 3.00 and Blaine ?neness of 3250 cm2/g was used. Chemical and physical properties of cement are shown in Table 3. The chemical and physical properties of a lime stone are shown in Table 4. Twenty-millimeter maximum size crushed limestone, local natural sand, ?ne and 8 mm maximum size gravel aggregates, were used in concrete mix, respectively. The properties of sand and gravel aggregate are presented in Tables 5 and 6. Fig. 2 presents the grading of ?ne and coarse aggregates. Water was used according to EN 1008.

3.1.2. Chemical admixtures The properties of admixtures are presented in Table 9. SP 1 and SP 2 composed of different type of polycarboxyl ether, having total solid content of 30.0% were sed. The synthetic copolymer based on VMA (suspension in water) was used (Table 7). AEA is composed of synthetic tensid. The chemical composition of SP1, SP2, VMA and AEA is a proprietary commercial patent. The percentages of VMA and SP were calculated on the basis of total solid content to achieve the same of SF2 and VS2 consistency class of SCC. All tests in this study were carried out at room temperature.

3.2. Phase 1: mix proportion and its preparation Six self-compacting concrete mixes (Tables 2 and 8) were made to study the effect of SP, VMA, AFA and AEA on the rheological properties and air-content of the mixture. The proportion of cement, lime stone, water, coarse aggregate and sand was kept constant. The following combination of the admixtures was used (Table 8): SP1 (with airentraining side effect), SP2 (without air-entraining side effect), AFA, VMA, AEA and AFA. Because the consistency of the concrete mix in?uences the air-content in SCC [22], the dosages of the SP, VMA were conformed to the same slump ?ow class (SF2) of SCC. The details of the concrete mix proportions are summarized in Table 8. AEA was conformed to the air content value 4–7%. The concrete was produced in a horizontal pan mixer with capacity of 0.070 m3. The sand and coarse aggregate were ?rst mixed for 1 min. Then, cement and ?y ash were added with the water. After mixing for 3 min, the SP was introduced and allowed to mix for an additional 3 min. Finally, remaining admixtures (according to Table 8) were added and mixed for the additional 5 min. The elapsed time of the total mixing sequence was 12 min, or 11 min following the ?rst cement and water contact.

Table 5 The chemical and physical analysis of sand 0/2 mm. Parameters SiO2 Fe2O3 Al2O3 CaO MgO Clay CaCo3 Moisture Loss on ignition pH Density Result >99.3% 300 ppm Max 2500 ppm Max 250 ppm Max 50 ppm Max 0.3% Max 0.5% Max <0.1% Max <0.3% Max Neutral 2.65 gm/cc

DF ? RDM UPTT ;n ? N=M

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?niewska-Piekarczyk / Construction and Building Materials 31 (2012) 310–319 B. ?az

100 80
98.2 76.5 53.8 41.2 26.1 6.9 0.0 0.4

100.0

[%]

60 40 20 0 0 0.125

0.25

0.5

1

2

4

8

16

[mm]
Fig. 2. The grain size distribution of aggregate. Sand content in the aggregate is 44.4%.

Table 7 The properties of admixtures. Property Main base Speci?c gravity at 20 °C (g/cm3) pH-value at 20 °C Chloride ion content (% mass) Alkali content (Na2Oeqiv.) (% mass) SP1 Polycarboxyl ether 1.07 ± 0.02 6.5 ± 1.0 60.1 1.5 SP2 Polycarboxyl ether 1.05 ± 0.02 6.5 ± 1.5 1.3 1.3 AEA Synthetic tensid 1.01 ± 0.02 8.8 60.1 61.0 VMA Synthetic copolymer 1.0–1.02 6–9 <0.1 – AFA Polyalcohol 0.95 ± 0.02 4–6 – –

Table 8 The components of SCC. Symbol of SCC CEM II B-S 32,5R (kg/m3) 442.40 442.40 442.40 442.40 442.40 442.40 w/c w/b Sand 0/2 mm (kg/m3) 693.20 693.20 693.20 693.20 693.20 693.20 Gravel 0/8 mm (kg/m3) 866.49 866.49 866.49 866.49 866.49 866.49 Volume of paste (%) 41.00 41.00 41.00 41.00 41.00 41.00 SP1 SP2 VMA AEA AFA

The dosage of admixtures by weight of total binder (%) 0.67 0.67 0.00 0.00 0.00 0.00 0.00 0.00 1.33 1.53 1.16 1.51 0.00 0.00 0.00 0.25 0.00 0.27 0.00 0.00 0.00 0.00 0.04 0.08 0.00 1.80 0.00 0.00 0.00 0.00

C1 C1A C2 C2V C2A C2AV

0.45 0.45 0.45 0.45 0.45 0.45

0.31 0.31 0.31 0.31 0.31 0.31

Table 9 Test results of SCC mix. Symbol C1 C1A C2 C2V C2A C2AV Slum ?ow (mm) 730 705 715 710 640 690 T500 (s) 3 2 2 4 2 4 Ac (%) 8.0 2.7 2.1 2.5 5.0 5.0

If RDMUPTT,n (measured according to (CEN/TR 15177, 2006) on 100 ? 100 ? 400 mm concrete specimens) falls to a value lower than 60% of its pre-freeze–thaw value, then the test is terminated and DF is calculated. If the number of the freeze– thaw cycles reaches 300 before RDMUPTT,n falls to less than 60% of its pre-freeze– thaw value, then the test is stopped and DF is calculated. If there is no change in the dynamic elastic modulus, then DF = 100%. If P falls to less than 60% of its prefreeze–thaw value, then DF = 60%. Any concrete test specimen with a DF = 60% is often considered nondurable or frost-damage susceptible. However, other higher levels of DF may be more desirable as critical values. The concrete test specimen with a DF P 80% is often considered durable [24]. The research results of DF coef?cient durability testing are presented in Table 11. The SCC with SP2 is frost-resistant until 250 cycles (DF P 80%). After 300 cycles the SCC with SP2 is not frost resistant (DF < 60%).

Table 10 The decrease of the mass and compressive strength of SCC after 300 freezing–thawing cycles of SCC. Symbol C1 C1A C2 C2V C2A C2AV Decrease of mass after 300 freeze–thawing cycles (%) 0.5 1 4 3 0.1 0.3 Decrease of fcm after 300 freeze–thawing cycles (%) ?3.0 (increase) ?0.4 (increase) 49.3 32.6 ?3.3 (increase) 3.1

3.3.3. The air-voids parameters The entrained air void distribution in hardened concrete was determined using a computer-driven system of automatic image analysis. Tests were performed using polished concrete specimens 100 ? 100 ? 20 mm cut from cube specimens. The testing procedure and estimation method of air-voids parameters were described in publication [26]. The automatic measurement procedure was designed to comply with the requirements imposed by EN 480-11. Results of measurements were available as a set of standard parameters for air void microstructure characterization: – – – – – Spacing factor (mm). Speci?c surface a (1/mm). Air content A (%). Content of air voids with diameter less than 0.3 mm A300 (%). Air void diameters distribution.

where RDMUPTT,n is the relative dynamic modulus (the measured value divided by the value determined before any freeze–thaw cycling); N is the number n of freeze–thaw cycles for RDMUPTT,n; M is the total number of freeze–thaw cycles.

In Table 12 and in Figs. 3–14 the air voids parameters research results are presented. The research results proved that SP type is very important to values of airvoids parameters of SCC. VMA does not in?uence the parameters of the air-entrained SCC.

?niewska-Piekarczyk / Construction and Building Materials 31 (2012) 310–319 B. ?az Table 11 The research results of DF coef?cient measurements after freezing–thawing cycles (%). Symbol C1 C1A C2 C2V C2A C2AV 0 cycles 99 102 99 100 100 100 25 cycles 104 101 102 101 102 103 75 cycles 104 98 102 100 103 104 100 cycles 107 99 103 99 101 103 150 cycles 104 101 100 101 103 105 250 cycles 107 100 81 99 106 103

315

300 cycles 107 101 65 101 105 103

Table 12 The air-voids characteristics of SCC. Symbol C1 C1A C2 C2V C2A C2AV A (%) 4.47 2.10 1.86 3.14 3.80 3.72 L (mm) 0.29 0.58 0.84 0.99 0.33 0.32

a (mm?1)
20.83 15.04 10.88 7.16 20.21 20.71

A300 (%) 1.55 0.25 0.22 0.16 1.39 1.54

4. Discussion of research results 4.1. The effect of the admixtures on the fresh SCC properties The analysis of data presented in Table 9 results in the following discussions. The SP type signi?cantly in?uences the air-content in self-compacting mix with similar slump ?ow value (a measure of ?owability). The air-content amounts to 8% in spite of the fact that the ?ow diameter amounts to 730 mm. Deliberate air entraining contributes to the decrease of diameter ?ow of self-compacting concrete mix (Table 9) more than the air-content as a result of SP side effect. It should be emphasized that in the same publications are decreased contradictory conclusions concerning the

increase of the air-entrainment on modi?cation of the ?ow diameter of concrete mix. The character of the in?uence of the air-entrainment depends on the amount of introduced AEA into self-compacting concrete mix. Initially, a small dosage of AEA may results in increase of the ?ow diameter of SCC as a result of AEA acting. However, the successive addition of AEA into selfcompacting concrete mix causes the decrease of the ?ow diameter due to the interaction between the air bubbles and concrete mix particles [22]. The research results of publication [18] and research results in Tables 9 and 12 indicate that VMA decreases the air-entrainment (as a result of AEA action). The air-content in C2A and C2AV is the same because the dosage of AEA was twice bigger in case of C2AV. The application of AFA causes a considerable decrease of the aircontent in SCC. The use of higher dosage of SP causes mix segregation. The introduction of AFA does not result in segregation of concrete mix. In this case, the dosage was decreased to achieve the SF2 class ?ow of SCC. Normally, the ?ow diameter of SCC incorporating AFA is higher than the ?ow diameter not incorporating AFA and the same amount of SP. The T500 time ?ow of concrete mix that contains AFA is similar to the time ?ow of concrete mix without AFA. Moreover, mix with AFA adheres less to Abram’s cone while conducting the slump-?ow test [2].

10 20 30 40 50 60 80 100 120 140 160 180 200 220 240 260 280 300 350 400 450 500 1,000 1,500 2,000 2,500 3,000 4,000

1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0

6.0 5.0 4.0 3.0 2.0 1.0 0.0

[?m]
Fig. 3. The air void diameters distribution in C1.

0.6

2.5 2.0 1.5 1.0 0.5 0.0 10 20 30 40 50 60 80 100 120 140 160 180 200 220 240 260 280 300 350 400 450 500 1,000 1,500 2,000 2,500 3,000 4,000 -0.5

Air content [%]

0.5 0.4 0.3 0.2 0.1 0.0

[?m]
Fig. 4. The air void diameters distribution in C1A.

Cumulated air content [%]

Cumulated air content [%]

Air content [%]

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?niewska-Piekarczyk / Construction and Building Materials 31 (2012) 310–319 B. ?az

0.01 0.02 0.03 0.04 0.05 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0.22 0.24 0.26 0.28 0.30 0.35 0.40 0.45 0.50 1.00 1.50 2.00 2.50 3.00 4.00

0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0

1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -0.2

[mm]
Fig. 5. The air void diameters distribution in C2.

1.4

Air content [%]

1.2 1.0 0.8 0.6 0.4 0.2 10 20 30 40 50 60 80 100 120 140 160 180 200 220 240 260 280 300 350 400 450 500 1,000 1,500 2,000 2,500 3,000 4,000 0.0

3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 -0.50

[?m]
Fig. 6. The air void diameters distribution in C2V.

0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 10 20 30 40 50 60 80 100 120 140 160 180 200 220 240 260 280 300 350 400 450 500 1,000 1,500 2,000 2,500 3,000 4,000

3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -0.5

[?m]
Fig. 7. The air void diameters distribution in C2A.

0.7

Air content [%]

0.6 0.5 0.4 0.3 0.2 0.1 10 20 30 40 50 60 80 100 120 140 160 180 200 220 240 260 280 300 350 400 450 500 1,000 1,500 2,000 2,500 3,000 4,000 0.0

3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -0.5

[?m]
Fig. 8. The air void diameters distribution in C2AV.

VMA results in increase of the time ?ow of SCC (compare C2, C2V and C2A, C2AV, Table 9). Fortunately, the previously decreased air-content as a result of AFA acting is not signi?cantly increased. The self-compacting mix incorporating AFA is more resistant to segregation.

4.2. The effect of the admixtures on the hardened SCC properties The comparison of data in Tables 9 and 12 suggest that it is possible to predict the air-content in SCC on the basis of the air-content in self-compacting concrete mix. However, there are

Cumulated air-content [%]

Cumulated air content [%]

Air content [%]

Cumulated air content [%]

Cumulated air content [%]

Air content [%]

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317

Fig. 9. The view of the air voids in C1.

Fig. 10. The view of the air voids in C1A.

Fig. 11. The view of the air voids in C2.

Fig. 12. The view of the air voids in C2V.

Fig. 13. The view of the air voids in C2A.

signi?cant differences between the air-content in concrete mix, such as air-entraining side effect of SP and the air-content in hard-

ened SCC. It indicates that the air-content as a side effect of SP is very instable.

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Fig. 14. The view of the air voids in C2AV.

The type of superplasticizer is crucial regarding the size and proportions of the air pores participation, gained as a result of its functioning, although the time of concrete hardening is of no importance on further changes of these proportions [27]. With the use of polycarboxylate superplasticizers, the air pores characterize with smaller diameters than pores formed as a result of lingosulfonic or naphthalene superplasticizers functioning. The inclusion of SP (sodium salt of a sulphonated napthalene-formaldehyde condensate) in cement paste, leads to a reduction in the total pore volume and to a re?nement of the pore structures [28]. The dominant pore size is unaffected and the threshold diameter is reduced in the presence of SP. Research results cited in publication [22], indicate that the air-content in hardened SCC, as a side effect of SP acting, may amount to even 8.0%. The publication [29] indicates that the superplasticizer causes reduction in total air-void surface areas and increases in air-void spacing factors. The test results (Table 12) suggest the signi?cantly in?uence of SP on the values of porosity parameters too. The SP type signi?cantly in?uences the values of the air-voids parameters. The air-void factor in case of SP2 is almost three times bigger than SCC with SP1. The speci?c surface of the air-voids in case of SCC with ‘‘air-entraining’’ SP is almost twice bigger than in case of SCC with SP without air-entraining side effect. The volume of the air-voids with diameter smaller than 300 lm is seven times bigger in case of SCC with the ‘‘air-entraining’’ SP. The VMA in?uences the air-content in SCC. The total air-content in SCC is higher in case of SCC with VMA. Other parameters of the air-voids of SCC with and without VMA are slightly different. The research results in Table 12 indicate that adding AFA into SCC results in signi?cantly decreases the air-content in SCC. The air-voids parameters research results suggest the adverse effect of AFA on frost-resistance of SCC. The application of VMA into SCC with SP and AFA does not result in changes in values of the air-voids parameters apart from the volume of the smallest air-voids (Table 12). Only the content of the air voids with diameters smaller than 300 lm is increased. This rise is bene?cial to the frost resistance of SCC. Polycarboxylate superplasticizers usually have an air-entraining effect, but some types of PC drastically reduce the freezing– thawing resistance [30]. The research results in Tables 10 and 11 showed that the air-content, as a side effect of SP based on polycarboxyl ether, secures the frost-resistance of SCC. However, the research results analyzed in publications [5,7] indicate that the ‘‘air-entrained’’ SCC, as a result of side effect of SP acting, was not frost-resistant. There must be an explanation for such a different in?uence of SP on frost-resistance of SCC. Probably, various types of SP cause different resistance of SCC to freeze–thaw cycles. The DF coef?cient research results in Table 11 suggests that the VMA in?uences frost resistance of SCC. The research results, indicated in publication [31], suggest that the same admixtures in?uence bene?cially the relationship between the frost-resistance of concrete and air voids spacing factor. It should be remembered, however, that research results in Table 10 suggests that VMA does

not in?uence compressive strength decrease after freeze–thawing cycles. This question needs a further research. The non air-entrained SCC with VMA retains the DF = 100% after 300 freeze–thawing cycles. The research results also indicate the bene?cial in?uence of VMA to frost-resistance of concrete and value of the air-voids spacing factor. However, the data in Table 12 indicates the negative in?uence of VMA on values of the air-voids parameters regardless of concrete frost-resistance. On the other side, the decrease of the compressive strength after 300 freeze– thawing cycles of SCC with VMA is smaller than SCC without VMA. Nevertheless, SCC is frost-resistant, which is also indicated by the DF research results. The unexpectedly positive in?uence of AFA on frost-resistant needs further research. According to European standards (EN 206-1, Austrian Standard ?NORM B 4710-1, Danish Standard DS. 2426, German Federal Ministry of Transport ZTV Beton-StB 01) recommended values of airvoids parameters are following: A = 3.5–5.5%, L = 0.18–0.20 mm, A300 = 1.0–1.8%. The research results in Tables 10–12 indicate that SCC is frost-resistant even though the values of the parameters of air voids are different from recommendations of these standards. 5. Conclusions In the range of investigation of the SCC, used admixtures and received research results it was indicated that: (1) The examined admixtures signi?cantly affect the properties of fresh and hardened self-compacting concrete. (2) The type of SP in?uences signi?cantly the values of air-voids parameters and frost-resistance of SCC. The ‘‘air-entrainment’’, as a result of side effect of SP1 acting, secures the frost-resistance of SCC, which is also indicated by DF research results. The SCC made of ‘‘not air-entraining’’ SP2 is not frost-resistant, also according to DF research results. Nevertheless, the air-entrainment of SCC, because of AEA acting, results in the best values of air-voids parameters regardless of frost-resistance of SCC. (3) The application of VMA results in increase of air content in non-air entrained SCC, particularly the volume of air voids with diameter smaller than 300 lm. The VMA cause the improvement of non-air entrained SCC frost-resistance after DF research results. However, compressive strength decrease after 300 freeze–thawing cycles does not con?rm the conclusion. (4) Adding of VMA causes the decrease of the air volume as a result of AEA acting. Nevertheless, the air-entrained SCC with VMA is still frost-resistant. (5) AFA effectively decreases the air-content in SCC. Unfortunately, the use of AFA results in adverse effect on values of air-voids parameters of SCC, regardless of frost-resistance of SCC. Nevertheless, SCC is frost-resistant, which is also indicated by DF research results. The unexpectedly positive in?uence of AFA on frost-resistant needs further research.

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(6) The research results also indicate that SCC is frost-resistant even though the values of air-voids parameters are different from recommendations of European standards.

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