INFLUENCE OF THE PROPERTIES OF SELF-COMPACTING CONCRETE ON THE EFFECT OF AIR ENTRAINMENT

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1 INFLUENCE OF THE PROPERTIES OF SELF-COMPACTING CONCRETE ON THE EFFECT OF AIR ENTRAINMENT Janusz Szwabowski 1, Beata Łaźniewska 2 1 Prof. dr hab. inŝ., Department of Building Processes, Faculty of Civil Engineering Silesian University of Technology, Akademicka, 44-1 Gliwice, Poland Janusz.Szwabowski@polsl.pl 2 Dr inŝ., Department of Building Processes, Faculty of Civil Engineering Silesian University of Technology, Akademicka, 44-1 Gliwice, Poland Beata.Lazniewska@polsl.pl Abstract. Ensuring an adequate and stable air-void system in flowable concrete is essential to guarantee proper resistance to freezing and thawing. Test results show that the air-void characteristics of self-compacting concrete (SCC) can be similar to those found for normal-slump concrete. This paper provides information regarding the effect of properties of fresh SCC on the stability of the airvoid system. In general, greater air-void stability can be obtained when the SCC is proportionated with a lower water-cementitious materials ratio (w/b). To prevent coalescence of small air bubbles during agitation, the plastic viscosity and yield stress values should not exceed 1 Nms and 2 Nm, respectively.. Keywords: self-compacting concrete, frost resistance, air-entraining admixture, porosity structure, stability of air voids 1. Introduction The key issue concerning durability of concrete is frost-resistance. Basing on the actual state of knowledge, in accordance with the PN-EN 26-1:23, using air entrainment (Fig. 1 and 2) as a basic way of assuring the frost-resistance of concrete is recommended (Fig. 3) c) a) b) Fig. 2. Diagram of influence of air-entrained admixture on selfcompacting mix stabilization of particles (C) [1] Fig. 1. Diagram of influence of air-entrained admixture on selfcompacting mix: a) reduction of surface tension, b) dispergation of particles (C) [1] According to the actual state of knowledge, concrete is frost-resistant if the values of porosity structure parameters (Fig. 4) are values presented in Table 1.

2 _ High pressure _ Sparse larger pore Frequent small pore Low pressure Fig. 3. Influence space factor on frost resistance of SCC Fig. 6. Self-compacting concrete capacity spaces without vibration void Fig. 4. Physical interpretation of space factor Table 1. Porosity structure parameter is included in precisely set limits [9] Parameter A A 3 α Unit mm % Value,2, % > 1, 1,8 mm -1 > 1-2 Self-compacting concrete (SCC) is a highly workable concrete that can flow under its own weight (Fig. 6) without segregation (Fig. ) [1], [13]. In the case of self-compacting mixture the process of its selfcompacting, depending in fact on autogenous release of random air bubbles from its volume, can significantly affect the final value of concrete porosity structure parameters. When the SCC is air entrained it can substantially affect the frost-resistance of self-compacting concrete. Fig.. Fluidity concrete mix can self-compact without segregation 2. Factors shaping the quality of air entrainment of self-compacting concrete Factors that influence the quality of air entrainment in concrete can be divided into two groups technological and material factors. Therefore, the key issue concerning the correct forming of concrete frostresistance is to answer the following questions - which factors impact the change of effect of air entrainment of concrete; to what degree they are crucial; and what the character of their impact is. The outcomes of research into the significance of chosen material factors impact conducted by the present author showed that the significant factors on account of concrete frost-resistance forming are the w/b ratio and the sort of mineral additive (Fig. 7, 8). The use of silica fume have limited effect on the formation and stability of an air-void system [9]. Zawartość powietrza volume% w m-c mieszance w % CEM I CEM I 8% 8% silica pyłu fume krzemionkowego 3% 3% fly popiołu ash lotnego 33% 33% granulated ŜuŜla blast-furnace slag,1,2,3,4,,6 Ilość AEA AEA % w m-c % m-c Fig. 7. Influence of content of cementations materials on contents of AEA in concrete [3]

3 For mixtures with relatively low content of cementitious materials and high w/b, the air-void system stability increased when a viscosity-modifying admixture (VMA) is incorporated. On the other hand, the use of chemical admixtures including HRWR, VMA, and AEA in SCC combination, as well as supplementary cementations materials makes it complicated to produce a stable air-void system. value of concrete porosity structure parameters, and it can influence frost-resistance of self-compacting concrete. One should pay special attention to the degree of the flowability of self-compacting concrete mixture. The values of rheologic parameters should be g < 2 Nm and h < 1 Nms (Fig. 11, 12) [], [13]. Fly ash F according to ASTM Fly ash C according to ASTM Floating of large pore Comparision of the amount AEA for concrete without and with fly ash [%] ,2,4,6,8 1, 1,2 Coalescence of pores Fading of pore that are less than,1 mm in diameter Fig. 1. entrainment and SCC essence of problem [9] Fig. 8. Influence of content of carbon on contents of AEA in concrete [3] [µm] Contents of organic particles in fly ash [%] w/c=,3 w/c=,4 w/c=, w/c=,6 w/c=,7 Specific surface [mm -1 ] without AEA AEA AEA + SP Normal consistence Increase of air bells size standard deviation mean value AEA 1 + AEA 2 + SP SP Fluid consistence,1,2,3,6 Diameter of pores [mm] 1 Fig. 11. The influence of admixtures on the size of air bubbles [3] r [µm] Fig. 9. Influence of w/c on size of air-voids in concrete [3] 3. Influence of concrete mix fluidity on stability of bubbles The high flowability of SCC can destabilize entrained-air bubbles during transport, which can affect the final air-void system of the hardened concrete (Fig. 1) [7], [8]. The influence of this admixture must be particularly related to the characteristic of the cement and airentraining admixture (AEA) types [13]. As a result, selfcompacting process can significantly affect the final Diameter of spreading of SCC [mm] D = 64 cm D = 6 cm L,1,2 Spacing factor [mm] Fig. 1. The influence property of SCC on spacing factor in SCC []

4 g (Nm) 2 g (Nm) h (Nms) ,1,2,3,4 Space factor (mm) h (Nms) 4. Method and analysis results of porosity structure of self-compacting concrete In the foundation stage of investigation [9] 2 different self-compacting concrete (Tab. 2) was put to the frost resistance tests, according to PN-88/B-62. In order to check the influence of four factors (kind of mineral addition (m.a), cement paste-aggregate ratio ϕ kz (Fig. 13) dosage of air entraining admixture (%AEA) and w/b) on frost resistance of SCC a composition of 2 sorts of SCC was prepared according to the method of experimental design. After 28 days concrete samples 1x1x1 mm were freezed and thawed in water for three hours in temp. ±2 C. Since concrete samples weren t damaged after 1 cycles of freezing and thawing, the testing of the frost resistance was continued. Fig. 11. The influence of rhelogical property of SCC on spacing factor of pores in SCC [] g (Nm) g (Nm) h (Nms) Specific surface α (mm 3 /mm 2 ) h (Nms) Table. 2. Composition of self-compacting c concrete S1-S2 [9] m.a. AEA (%) CEM II 32,R B-S CEM II 32, R B-V CEM II 32, R B-M CEM III 32, N CEM I 32, R + 1% PK S11 S1 S6 S16 S21 ϕ kz = 1. ϕ kz = 1.2 ϕ kz = 1.4 ϕ kz = 1.1 ϕ kz = 1.3 w/b =.29 w/b =.32 w/b=.3 w/b =.38 w/b =.41 S12 S2 S7 S17 S22, ϕ kz = 1.1 w/b =.32 ϕ kz = 1.3 w/b =.3 ϕ kz = 1. w/b =.38 ϕ kz = 1.2 w/b =.41 ϕ kz = 1.4 w/b =.29 S13 S3 S8 S18 S23,1 ϕ kz = 1.2 ϕ kz = 1.4 ϕ kz = 1.1 ϕ kz = 1.3 ϕ kz = 1. w/b =.3 w/b =.38 w/b =.41 w/b =.29 w/b =.32 S14 S4 S9 S19 S24,1 ϕ kz = 1.3 w/b =.38 ϕ kz = 1. w/b =.41 ϕ kz = 1.2 w/b =.29 ϕ kz = 1.4 w/b =.32 ϕ kz = 1.1 w/b =.3 S1 S S1 S2 S2,2 ϕ kz = 1.4 ϕ kz = 1.1 ϕ kz = 1.3 ϕ kz = 1. ϕ kz = 1.2 w/b=.41 w/b =.29 w/b =.32 w/b =.3 w/b =.38 Fig. 12. The influence of rhelogical property of SCC on specific surface of pores in SCC [] Moreover, the technical and technological factors are very important to ensure that this concrete can assure the proper air-void system that remains stable during agitation, placement, and setting. Adequate and stable airvoid system in SCC is guaranteed, complying following practical regulations [11]: a minimum slump flow value to guarantee is D = 74 cm; also the time of spreading t should not be higher than 3 seconds (compare with Fig. 18), 2δ n 2δ 2 2δ 1 Fig. 13. Cement paste-aggregate ratio of SCC the velocity of rising should not be higher than m/h, the concrete is not allowed to flow against the vertical wall, but placed central, to avoid segregation due to the contact of the concrete with reinforcement. If narrow moulds are used, the free height of fall should be as low as possible (at most 2 m). A laboratory test was stopped when the amount of alternate cycles of freezing and thawing of concrete amounted to 3. It was noticed that only two types of SCC (S1, S12) were not frost resistant (because the decrease of compression strength amounted to more than 2% after 3 cycles according to PN-88/B-62), Fig. 14.

5 fcm serie Fig. 14. Results frost-resistance tests according to PN-88/B-62 [9] The results of concrete research according to PN-EN showed, in case of samples S21 and S19, porosity structure parameters were adequate (compare with Fig. 16, 17) moreover quality of air entraining was the highest although concrete sample S21 contained too much air. The exemplar view of adequate concrete porosity structure is shown on Fig. 2). Unfortunately, in case of S23, S24 and S2, the quality of porosity structure was inadequate. It was noticed that sparing factor had too high value and parameters α, A 3 had too low value (Tab. 3); it may produce an evidence that porosity structure contained too large pores. Also it was noticed that content of pores with a diameter smaller than 3 µm was inadequate (particularly in case of samples S24 and S2). In the following stage of investigation, concrete samples were tested on porosity structure parameters according to PN-EN (Fig. 1). Unfortunately, because of the limited investment outlays, only eight concrete samples were tested on porosity structure parameters according to PN-EN The porosity structure research of eight concrete samples was conducted in IPPT PAN in Warsaw. Among eight concrete samples were two which were not freezeproof and six which were freezeproof, but had different decrease of compression strength amounted to more than 2% after 3 freezing and thawing cycles (compare with Fig. 14). L [mm],4,3,3,2,2,1, serie Fig. 16. Results of concrete porosity parameters tests to PN-EN [9] α [mm -1 ] Nr serie serii Fig. 17. Results of concrete porosity parameters tests according to PN-EN [9] 2 Fig. 1. Testing concrete porosity structure according to PN-EN [9] In the further part of the analysis of the research results it was perceived, that concrete which was characterized by inadequate porosity structure parameters, gets frost resistance degree of the order of F3 according to PN-88/B-62 (Fig. 2). In order to explain partial discrepancy in research results according to PN-88/B-62 and PN-EN 8-11, a problem was approached by a detailed analysis of similar researches which are available in professional literature.

6 Table. 3. Results of SCC testing according to PN-EN and PN-88/B-62 [9] α A A No Serie L 3 f cm [mm -1 ] [%] [%] [%] [mm] 1 1,22 2,47 4,86 1, ,22 27,98 3,69 1, ,21 21,93 7,4 1, ,2 32,2 3,72 1,18 21,13 36,14 7,19 2, ,36 19,4 3,49, ,31 16,7,82, ,33 14,24 7,3 1,18 Suggested [1]:,2,22 > > 1,-1,8 < 2 The reasons of partial discrepancy of research results according to PN-88/B-62 and PN-EN 8-11 are caused by complying with requirements for porosity structure parameters regarding the whole kind of concrete. Fagerlund [3] considers that critical value, which was calculated in order to protect concrete from freezing and thawing, in reality depends on cement-water ratio (Fig. 18). [µm] 1 2 DF > 9% DF < 9%,2,3,3,4,4,, w/c Fig. 18. and w/c influence on frost resistance of concrete according to ASTM C 666-A [12] In order to verify the w/c influence on critical value, the author of publication [4] presents the results of laboratory research of freezing and thawing cement paste waterlogged in critical degree as well as the results of porosity parameters research. The results of this research enabled it to estimate the theoretical and practical value of porosity structure parameter (Tab. 4). Moreover, it was noticed, that common concrete with w/c of the order of,4,4 and of the order of,4 mm can withstand a test of 3 cycles of freezing and defrosting. Whereas, in case of high performance concrete w/s <,36 and <,2 mm ensures, as it was shown [4], adequate frost resistance of concrete. Table. 4. Theoretical and practical value of [4] Freezing Critical value [mm] theoretical practical in water,22,2,3,4 with critical salt concentration in water,16,2,22,2 The residual criteria, in respect of critical value in dependence on w/c of high performance concrete, are presented in table. On the basis of the research results [4], it was concluded, that in case of high performance concrete with silica fume and w/c =,3, practical value amounts to,4, mm, and by w/c =,2, without silica fume =,7 mm. Further research [4] lead to a conclusion that concrete with compression strength of about 1 MPa, w/c =,33, with silica fume 7,% m.c., by of the order of,8 do,8 mm, withstand a test of 112 cycles of freezing and defrosting in the presence of salt. Whereas concrete with w/c =,3, with silica fume 6%, without air entrainment admixture, possessed a remarkable scaling resistance, and was of the order of as much as,9 mm. Table.. Suggested criteria according to w/c high performance concrete [9] Proposed Freeze w/c Critical resistance >,4 23 µm,4-,3 3 µm 26 µm (scaling resistance) 4 µm (scaling resistance),3-,3 4 µm µm <,3 3 cycles ASTM C666 cycles ASTM C672 3 cycles ASTM C666 cycles ASTM C672 cycles ASTM C666 No data available, above criteria are accepted Apart from the shown research results and the visual observation of freezing and defrosting concrete constructions [4], which prove that critical value can be of the order of,4 or higher, it is still recognized that values in respect of porosity structure are always right.

7 w Value a rtość. Influence of concrete mix composition on quality of porosity structure One should pay special attention to the degree of the liquidity of self-compacting concrete mixture (Fig. 19) [6]. It was noticed that content of pores with a diameter smaller than 3 µm was inadequate (particularly in case of samples S24 and S2), whereas in case of samples S1 and S1 pores which weren t formed in consequence of purposeful air entraining were identified, though they were formed as a result of high flowability of concrete mix, which is necessary for self-compacting (Fig. 2) D 1 [cm] t [s] 1-1 [mm] Series nr serii Rhelogical characteristic of series of SCC with the best porosity structure: D 74 cm t > s Series of SCC with the best porosity structure Along with the w/c value increase, the adverse increase in the rate of air pores spacing was observed (Fig. 21). Similar tendency was observed when the mixtures containing fly-ash or clay dust were applied (Fig. 22, compare with Fig. 8). L [mm] L [mm],3,3,2,2,1,1, R 2 =,3,29,29,32,32,3,38,38,41 w/b w/s Fig. 21. The influence of cement-water ratio on increase of spacing factor L [9],4,3,3,2,2,1,1, Fig. 19. Diameter D and time t of spreading of SCC compared to CEM I + PK CEM I + PK CEM I + PK CEM I + PK CEM II B-M CEM II B-V CEM II B-S CEM III a) Fig. 22. The influence of cement-water ratio on increase of spacing factor L [9] 6. Conclusions b) Defect of porosity structure Inadequate Fig. 2. Comparison of inadequate (a) and adequate (b) porosity structure of SCC [9] Ensuring the adequate air-void system in concrete is essential for obtaining proper resistance to freezing and thawing. With the increasing usage of highly flowable concrete and SCC, it is important to ensure that this concrete can provide the proper air-void system that remains stable during agitation, placement, and setting. This paper provides information regarding the effect of mixture composition on the stability of the air-void system. Greater of air-voids system stability can be obtained when the SCC is proportionated with a lower watercementitious materials ratio []. Conversely, for mixtures with lower binder content, the L can be lower in case of VMA concrete of higher w/b. To prevent coalescence of small air bubbles during agitation, the plastic viscosity and yield stress values should not exceed 1 Nms and 2 Nm, respectively. This values where found to be necessary to maintain a stable air-void system. Moreover, the technological factors are very important to ensure that

8 this concrete can assure the proper air-void system that remains stable during agitation, placement, and setting. The results of frost resistance research of air entrained self-compacting concrete according to PN-88/B-62 and PN-EN were shown in this paper. On the basis of the presented analysis, it can be noticed, that concrete which is not characterized by adequate values of porosity structure can be freezeproof of the order of F3. Therefore, it can be said that prevalent values of concrete porosity structure are too severe. Moreover, the requirements related to porosity structure parameters are determinated for all kinds of concrete. However, different series of concrete (series of concrete is understood according to PN-EN 26-1: one kind of cement, aggregate, addition type II and admixture) differ from each other for the sake of their porosity structure. Therefore, do requirements related to porosity structure parameters concern the whole series of concrete Moreover, frost resistance of concrete is estimated on the basis of laboratory research results. Thus what is the procedure to determine critical value to adequate degree of frost resistance of particular concrete (Fig. 23) Different questions concerning critical value of porosity structure and frost resistance of concrete were brought up in this paper. However the problem which was raised is more complicated. In order to find the solution, an adequate laboratory research should be conducted in order to estimate practical values of the porosity structure parameters and advisable frost resistance concrete degree. Amount of freezing and thawing series W/B =,3 W/B =,4 Results of research Hypothesis W/B =, [3] Fagerlund G.: Durability of concrete structures, Arkady, Warsaw, 1999 (in polish). [4] Grodzicka A. Frost resistance of high performance concrete. Publication of ITB, Warsaw 2, (in polish). [] Kamal H., Khayat and Joseph Assaad: -Void Stability in Self Consolidating Concrete. ACI Materials Journal, V. 99, No. 4, July-August 22, pp [6] Khayat K. H.: Optimization and performance of the airentrained, self-consolidating concrete. ACI Materials Journal, Vol. 97, No., 2. [7] Kobayashi M., Nakakuro E., Kodama K., Negami S.: Frost resistance of superplasticized concrete, ACI SP-68, 1981, pp [8] Litvan G.: entrainment in the presence of superplasticizers, ACI Journal, Vol. 8, No. 4, 1983, pp [9] Łaźniewska B.: Modeling of frost-resistance of selfcompacting concretes, doctor s thesis, Gliwice 26 (in polish). [1] Okamura H., Ouchi M.: SCC. Development, present use and future, 1 st It. RILEM Symp. on SCC, Stockholm, Sep , ed. RILEM Publ. S.A.R.L., [11] Proske T.: Self-Compacting Concrete pressure on formwork and ability to deaerate. Darmstadt Concrete 17, 22. [12] Rusin Z. The frost resistance concrete technology. Polish Cement Sp. z o.o., Krakow 21, (in polish). [13] Szwabowski J.: Rheology of self-compacting concretes. IV Sympozjum Naukowo-Techniczne Rheology in concrete technology, Gliwice 22, publication GóraŜdŜe Cement, pp (in polish). [14] Szwabowski J. The rheology and workability of self-compacting concrete. Cement Lime Concrete 1/24, p (in polish). [1] Wawrzeńczyk J. The diagnostic of cement concrete frost resistance. Publication of University of Technology, Kielce 22 (in polish). [µm] Fig. 23. Relationship between concrete frost resistance and [4] References [1] Collective work. Diagnostic methods of high performance concrete on the basis on structural research. Publication of IPPT PAN, Warsaw 23, (in polish). [2] De Larrard F., Bosc F., Catherine C., Deflorenne F.: The AFREM method for mix-design of high performance concrete. Materials and Structures, Vol. 3, pp , 1997.