Scholarly article on topic 'Stability of Air-content in the Case of Innovative Air-entraining Portland Multicomponent Cement'

Stability of Air-content in the Case of Innovative Air-entraining Portland Multicomponent Cement Academic research paper on "Civil engineering"

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{"air-entraining cement" / "fly ash" / "air-entraining admixture" / superplasticizer / air-content / temperature / mortar}

Abstract of research paper on Civil engineering, author of scientific article — Beata Łaźniewska-Piekarczyk, Janusz Szwabowski

Abstract The research results of the stability of air-entrainment in the case of innovative air-entraining multi-component CEM II/B-V are presented in this paper. Compatibility with innovative cement air-entraining CEM II/B-V plasticizers and superplasticizers were evaluated in terms of stability of air entrainment and maintenance of consistency for one hour of mortar according to PN-EN 480-1. The research results indicated that in case of a significant increase in the degree of liquidity of the air-entrained mortar or concrete made of participation of the innovative, air-entraining multi-component cement CEM II/B-V, first and new generation superplasticizers based on modified naphthalene, and then modified phosphoramidate should be used. The new generation superplasticizers based on polycarboxylate, polycarboxylic ether and acrylate cause a significant increase in the air-content of the air-entrained mortar and concrete.

Academic research paper on topic "Stability of Air-content in the Case of Innovative Air-entraining Portland Multicomponent Cement"

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Procedía Engineering 108 (2015) 559 - 567

Procedía Engineering

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7th Scientific-Technical Conference Material Problems in Civil Engineering (MATBUD'2015)

Stability of air-content in the case of innovative air-entraining Portland multicomponent cement

Beata Lazniewska-Piekarczyka*, Janusz Szwabowskia

aSilesian University of Technology, Akademicka 5, 44-100 Gliwice, Poland

Abstract

The research results of the stability of air-entrainment in the case of innovative air-entraining multi-component CEM II/B-V are presented in this paper. Compatibility with innovative cement air-entraining CEM II/B-V plasticizers and superplasticizers were evaluated in terms of stability of air entrainment and maintenance of consistency for one hour of mortar according to PN-EN 480-1. The research results indicated that in case of a significant increase in the degree of liquidity of the air-entrained mortar or concrete made of participation of the innovative, air-entraining multi-component cement CEM II/B-V, first and new generation superplasticizers based on modified naphthalene, and then modified phosphoramidate should be used. The new generation superplasticizers based on polycarboxylate, polycarboxylic ether and acrylate cause a significant increase in the air-content of the air-entrained mortar and concrete.

© 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review underresponsibilityof organizing committee of the 7th Scientific-Technical Conference Material Problems in Civil Engineering Keywords: air-entraining cement; fly ash; air-entraining admixture; superplasticizer; air-content; temperature; mortar

1. Introduction

The results of studies conducted by Mosquet, [1], Sakai et al. [2], Szwabowski and Lazniewska-Piekarczyk [3] have shown that the use of a new generation of superplasticizer with the previously air-entrained concrete mixture causes a problem of maintaining the proper air-entrainment. The air content in the hardened concrete, which is a side effect of superplasticizer (SP), may be higher than 8% [2]). In case of previously air-entrained concrete that is

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

1877-7058 © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of organizing committee of the 7th Scientific-Technical Conference Material Problems in Civil Engineering doi:10.1016/j.proeng.2015.06.178

made with an air-entraining cement, after the addition of new generation SP a very large increase in air entrainment occurs. The air-content of mixture may be higher than 13%. A behavior problem of required air-content of mixture appearance refers specifically to supplementary cementing materials (Ponikiewski et. al. [4]). The use of supplementary cementing materials (SCMs) in concrete has become practically the rule, and not the exception, due to enhanced durability, long-term strength, improved workability, and reduced cost (in most cases). The SCM particles usually have higher surface areas than Portland cement grains. Replacing cement with SCMs improves the fineness of the cementitious materials which stabilizes the air bubbles better according to research results from Lianxiang and Folliard [5], Yang [6].

The solution to the present problem is the condition of system compatibility: innovative aeration cement and superplasticizer, due to the presence of the air in the mixture and its consistency. Importantly, the condition of system compatibility to be verified is not for any admixture of cement separately, but together, to determine the impact of their interactions with each other and cement, taking into account the impact of the order of dosing due to the air content and consistency. This can be accomplished only by experimentation, by selecting the type and quantity of the first air-entraining admixture (AEA) for the type of cement, because of the required air-entrainment. Then, the SP should be selected due to the maintenance of the air entrainment and to obtain the required consistency over time.

The present study is an experimental analysis of the impact of the type of plasticizing (P) and superplasticizing (SP) admixtures on the air content and consistency of cement based mixtures made with the participation of the air-entraining innovative cement. The scope of these studies is based on cement with fly ash. As a model cement based mixture, which allows the elimination of the effect of variation of the aggregate and the drastic reduction of employers and material research, adopted the reference cement mortar according to PN-EN 480-1 [7]. In the next step of the study compatibility with innovative air-entraining cement plasticizers and superplasticizers was evaluated in terms of stability of the air entrainment and maintenance of the consistency of mortar for one hour. In the next stage of the study the impact of w/c (0.45 and 0.55) and temperature (12.0 ± 1 °C and 29.0 ± 1 °C) were examined for the stability of air entrainment and consistency of mortar with of the most compatible superplasticizing admixture.

2. Experimental procedure

Materials used to prepare mixtures of cement based mortars, which were the subject of the study were: CEM II/B-V, air-entraining innovative CEM II/B-V (Tables 1, 2 and 3), normalized sand, distilled water and different types of plasticizing (P) and superplasticizing admixtures (SP) (Tables 4, 5 and 6). The content of siliceous fly ash cements V in all cements was 30%. With these materials, standardized cement mortar with w/c = 0.50 was prepared, in accordance with the recommendations of PN-EN 480-1[7]. Reference mortar is also made, i.e. air-entraining and superplasticizing without admixtures. PN-EN 206 [8] for XF classes (exposure classes for freeze/thaw attack) has specified ranges of air content between 4% and 7%. The most effective air content in concrete mixes containing aggregate grains of diameter dmax=16 mm is 5-6% (according to PN-EN 206, the minimum value is 4%). However, the amount of air in the mortar is not specified. The air content in the frost resistant mortar may be assumed to be equal to about 10% (twice as much as in concrete), as the content volume of mortar in concrete mix is about 50% (Piasta and Marczewska [9]).

Table 1. The air-entrainment of CEM II/B -V.

Cement Established air content in the mortar, % Air-entraining admixture type Amount of air-entraining admixture, % mass of cement Air content acc. PN-EN 1015-7 of mortar acc. PN-EN 480-1, %

Air-entraining CEM II/B-V 10.0 natural 0.060 10.0

Table 2. The properties of CEM II/B-V.

Cement

Specific surface

Setting time

SO,, %

LOI, %

Air-entraining CEM II/B-V

Table 3. The properties of components of air-entraining CEM II/B-V.

Properties

CEM I 52.5R, % mass of cement

Silica fly ash, % mass of cement

Loss on ignition 0.64 2.26

SiO2 20.8 54.20

Al2O3 5.18 26.81

FezO, 2.94 5.62

Ca0 63.9 3.03

MgO 1.38 0.82

SO3 4.61 0.34

K2O 0.73 2.92

Na2O 0.12 0.61

The aim of the first stage of the study is to match the type and the quantity of plasticizers and superplasticizers to the air content of mortar which was approximately similar to that of the reference mortar, i.e. without plasticizing and superplasticizing admixtures. The liquid plasticizing and superplasticizing admixture dosed with the mixing water, in accordance with the recommendation of PN-EN 480-1 [7]. While plasticizing and superplasticizing admixture in powder form were dispensed with cement, according to the manufacturer's recommendations. Table 7 summarizes the required amounts of admixtures necessary to fluidity of the mortar at a comparable degrees. In most cases the greatest degree of fluidity of mortars was obtained which is important, maintaining the stability of the mortar.

In the second stage of the research, compatibility with cement plasticizers and plasticizing admixtures in the highest degree among the analyzed SPs in the first stage the research was evaluated in terms of stability of the air entrainment and maintenance of the consistency of mortar for one hour.

In the third stage of the study the influence of w/c (0.45 and 0.55) and temperature (12.0 ± 1 °C and 29.0 ± 1 °C) on the stability of the air entrainment and consistency of mortar with of most compatible SP was tested.

Table 4. Properties of admixtures.

Technical data PCE-1 PCE-2 PCE-3 PCE-4 PCP-2

Main chemical base Form Density (at 20°C), kg/dm3 pH (at 20°C): polycarboxylate ether liquid 1.06 6.0 ± 1.0 polycarboxylate ether liquid 1.07 6.5 ± 1.5 polycarboxylate ether liquid 1.09 5.5 ± 1.0 polycarboxylate ether liquid 1.08 4.5 ± 1.0 polycarboxylates liquid 1.06 7.5 ± 1.0

Cl- % of mass < 0.1 < 0.1 < 0.1 < 0.1 < 0.1

Na2O % of mass < 0.6 < 1.7 < 0.5 < 0.8 < 1.5

ASTM C494 [10] type Type of admixture acc. PN-EN 934-2 [11] Conventional dry F and E SP 37.0 ± 1.5 G SP 38.0 ± 1.2 F and E SP 39.0 ± 1.9 G SP 36.0 ± 1.7 G SP 36.0 ± 1.6

material content

Table 5. Properties of admixtures.

Technical data PCP-1 PC CLAP AAP MN

Main chemical base polycarboxylates modified polycarboxylates cross-linked polymers, acrylic modified amino phosphonates modified naphthalene

Form liquid liquid liquid liquid powder

Density (at 20°C) , kg/dm3 1.04 1.10 1.07 1.06 0.60

pH (at 20°C): 6.5 ±1 6.0 6.0 ± 1.0 4.0 ± 0.5 5.0

Cl-, % of mass < 0.1 < 0.1 < 0.1 < 0.1 < 0.1

Na2O, % of mass < 1.0 < 3.0 < 3.0 < 3.0 < 3.0

ASTM C494 [10] type G A and F F and E G F

Type of admixture acc. SP SP and P SP SP SP

PN-EN 934-2[11]

Conventional dry material content 37.0 ± 1.5 33.0 ± 1.6 35.0 ± 1.7 31.0 ± 1.5 100.0

Table 6. Properties of admixtures.

Technical data SNF-1 SNF-2 SMF MGL-1 MGL-2

Main chemical base sulfonated naphthalene-formaldehyde resins sulfonated naphthalene-formaldehyde resins sulfonated melamine formaldehyde lignosulfonates lignosulfonates/car bohydrates of natural origin

Form Liquid Liquid Liquid Liquid Liquid

Density (at 20°C) kg/dm3 1.17 1.19 1.13 1.13 1.17

pH (at 20°C) 6.5 6.0 7.0 10.0 ± 1 .0 4.5 ± 1.0

Cl-, % of mass < 0.1 < 0.1 < 0.1 < 0.1 < 0.1

Na2O, % of mass < 4.5 < 4.5 < 5.0 < 6.5 < 0.8

ASTM C494 [10] type D and F A. and F A and F A A

Type of admix [11] SP and P SP and P SP and P P P

Conventional dry material content, % 34.5±1.7 30.0 ± 1.5 28.0 ± 1.6 27.0 ± 1 .4 36.0 ± 1.8

Table 7. The type and amounts of admixtures used in the research; % mass of CEM II/B-V.

Temperature w/c Symbol % mass of cement

21.0±1°C 0.50 PCE-1a 0.870

21.0±1°C 0.50 PCE-2 2.000

21.0±1°C 0.50 PCE-3 1.620

21.0±1°C 0.50 PCE-4 2.740

21.0±1°C 0.50 PCP-1 1.250

21.0±1°C 0.50 PCP-2 1.630

21.0±1°C 0.50 MN 1 b 0.620

12.0±2°C 0.50 MN 1 b 0.222

29.0±2°C 0.50 MN 1 b 0.738

21.0±1°C 0.45 MN 1 b 0.667

21.0±1°C 0.55 MN 1 b 0.222

21.0±1°C 0.50 PC 1.000

21.0±1°C 0.50 CLAP a 1.640

21.0±1°C 0.50 AAP a 3.110

21.0±1°C 0.50 SNF-1 2.190

21.0±1°C 0.50 SNF-2 a 1.900

21.0±1°C 0.50 SMF a 3.450

21.0±1°C 0.50 MLG-1 a 4.080

21.0±1°C 0.50 MLG-2 4.710

a - admixture used in second stage of the research, b - admixture used in third stage of the research

In the aforementioned stages of the research, the amount of plasticizing or superplasticizing admixture (Table 7) was in each case adjusted to achieve a similar propagation of mortar, because the rheological properties of the mortar affect the air-content. Whereas variation in w/c values corresponds to the recommendations of PN-EN 2061 [8], as the minimum recommended values for the XF1-XF4 class of aggressiveness of the environment.

The consistency of the mortars was determined according to PN-EN 1015-3 [12], while the air-content according to PN-EN 1015-7 [13].

3. Test results and discussion

Fig. 1 shows the results of measurements of the air content in mortars. This results in compatibility with cements that have extremely different properties and compositions, including air-entraining cements. The analyzed results show that the PCE, PCP, PC, CLAP based superplasticizers increase significantly the air-content of the previously air-entrained mortars. Generally, most organic chemical admixture can enhance the air entrainment. The test results from Szwabowski and Lazniewska-Piekarczyk [3] show that the superplasticizer can reduce the surface tension of water in a similar way to admixture (AEAThe research results from Kucharska [15] indicate that the different types of high-range water-reducing admixtures influence surface tension, foaming, and the stability of air bubbles in a different way. Some types of superplasticizers have an effect on the surface tension of the liquid phase of the cement paste. The presence of functional groups (oxygen in the form of etheric group (-O-), hydroxyl group (-OH) and carboxyl group) produce a decrease in water surface tension, producing flocculation of associated molecules and an increase in moisture of not only grains of cement but also the whole mineral framework [15]. The research results from Ley et al [16] show that the surface tension changed considerably over time depending on the combination of powder and superplasticizer. The action of modified amino phosphonate involves only the steric dispersion - and so the "natural" blockade of polymer without using the deflocculating electrostatic phenomena.

The addition of anti-admixtures in SPs compositions not always prevents excessive increase in the air-entrainment of mortar. Thus, it would increase the amount of antifoaming admixture in composition of superplasticizer or another type must be used. The influence of the type of anti-foaming admixture was analyzed in Lazniewska-Piekarczyk's publication [14].

The analysis results shown in Fig. 1 indicate that, as recommended admixtures for the mortar or concrete with air-entraining CEM II/B-V are admixtures based on: the modified naphthalene, modified amino phosphonate, sulfonated naphthalene-formaldehyde sulfonated melamine formaldehyde resins and lignosulfonates.

The comparison of the results from Fig. 1 demonstrates that SPs based on modified naphthalene (MN) and amino phosphonate (AAP) provide a very good workability of the mortar, not worse than SPs on the basis of a polycarboxylate, polycarboxylate ether, acrylate, or a phosphoramidate.

In Fig. 1, test results of stability of the air-entrainment and maintenance of the consistency of mortar depending on the type plasticizers or superplasticizers are presented. Research results show that all types of investigated admixtures, selected on the basis of an earlier stage of research, provide stability of the air bubbles in mortars with air-entraining CEM II/ B-V. Admixtures based on modified naphthalene (MN) and lignosulfonates (MGL) stabilize the best the air-entrainment. Admixtures based on amino phosphonates (AAP) and naphthalene (SNF) reduce the flow of mortar after the time the least. Moreover, in case of the air-entrained mortar with traditional naphthalene (SNF) there is an increase in workability over time.

■ 5 min., w/c=0.50, 21.0±1°C «60 min., w/c=0.50, 21.0±1°C

■ 5 min., w/c=0.50, 21.0±1°C «60 min., w/c=0.50, 21.0±1°C

*<5 20 &

Fig.1. The comparison of a) air-content and b) diameter flow of the air-entrained mortar with different type of plasticizers and

superplasticizers after 5 and 60 min.

Analysis of the results in Fig. 2 which relate to the influence of temperature on the properties of the air-entrained mortar leads to the conclusion that increasing temperature decreases the air content in air-entrained mortar, as well as air-entrained and then plasticized mortar. In the case of air-entrained and then plasticized mortar the final flow is the result of two variables: the temperature and the amount of superplasticizing admixture. The increase in temperature causes a reduction in propagation of mortar and an increase in the air content of its volume. To counter this it is recommended to increase the amount of compatible with cement superplasticizing or plasticizing admixture.

■ Air-entrained mortar ■ Air-entrained mortar with MN 20 [].0

1 II il I

w/c=0.45, 21.0±1°C w/c=0.55, 21.0±1°C w/c=0.50, 12.0±1°C w/c=0.50, 29.0±1°C

■ Air-entrained mortar ■ Air-entrained mortar with MN

w/c=0.50, 21.0±1°C w/c=0.55, 21.0±1°C w/c=0.50, 12.0±1°C w/c=0.50, 29.0±1°C

Fig. 2. The influence of w/c and temperature on a) air-content and b) flow diameter of the air-entrained and the air-entrained and then

plasticized mortar.

Analysis of the results of the w/c ratio influence on air entrainment mortars (Fig. 2) shows that an increased water to cement ratio causes a noticeable increase in the air content and propagation of the air-entrained mortar. Predominantly with increasing w/c ratio increases the amount of air in the air-entrained and then plasticized mortar. However, in the case of mortar with w/c = 0.55 the same amount of air was obtained as in the case of mortar with w/c=0.45, although the mortar with w/c = 0.55 was characterized by a lower flow. In the case of the air-entrained and then plasticized mortar the flow is also the result of two variables: w/c and the amount of superplasticizing admixture.

Finally it can be added that it is impossible to speculate the effects of admixture interactions with surfactants on the air-entrainment of mortar or concrete. Recent results from Lazniewska-Piekarczyk [17] indicate that most organic chemical admixtures, such as superplasticizer can enhance air entrainment since it can slightly reduce the absorbed AEA molecules on the solid surface by competing with them Mather [18], Saucier et al. [19]. As presented by these research the addition of superplasticizers to the air entrained concrete enhances the spacing factor and reduces the specific surface area of the air void system. In-plant testing is highly recommended to verify the effect of a given combination of cement-air-entraining agent-SP [19]. Other admixtures like retards, accelerators, etc., have a negligible effect on air entrainment. Yet, today there are many types of AEAs such as wood-derived acid salts AEA, vegetable oil acids AEA and synthetic detergents AEA, which may react with chemical admixtures (Kobayashi et al. [20]). This adds to the difficulty of studying the impact of chemical admixtures on air entrainment [20]. The compatibility of the admixtures should be experimentally tested if the effects of such combinations are unknown in advance. The compatibility of admixtures SP and AEA with cement and another admixtures, as for example viscosity modifying admixture, can be checked only when they occur together Lazniewska-Piekarczyk [21]). Checking each individual admixture does not take into account their interaction.

4. Conclusions

Within the scope of the research it was found that:

• Recommended admixtures for the mortar or concrete with air-entraining CEM II/B-V are admixtures based on: modified naphthalene, modified amino phosphonate, sulfonated naphthalene-formaldehyde sulfonated melamine formaldehyde resins and lignosulfonates. In the case of a significant increase in the degree of liquidity of the air-entrained mixture made of participation of the innovative, air-entraining multi-component cement CEM II/B-V, first and new generation superplasticizers based on modified naphthalene, and then modified amino phosphonate should be used. The new generation superplasticizers based on: polycarboxylate ether, polycarboxylate, cross-linked polymer, acrylic, increase air-content of previously air-entrained mortar. In certain cases of cement mortars and a smaller dosage of SP, up to half as much.

• Compatible admixtures with air-entraining CEM II/B-V provide stability of air bubbles in mortars. Admixtures based on modified naphthalene and lignosulfonate have the best stabilizing effect on air-entrainment. Admixtures based on amino phosphonates and naphthalene reduce the flow of mortar after time the least. Moreover, in the case of the air-entrained mortar with naphthalene there is an increase in workability over time.

• Increasing the temperature causes a decrease in the air content of air-entrained mortar, as well as air-entrained and then plasticized mortar.

Acknowledgements

The present study was funded by the National Centre for Research and Development Project PBS1/A2/4/2012 "Innovative Cement Concrete Air-entraining".

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