Comparison of Durability Performance of Conventional and Air-Entrained Self-Compacting Concrete Modified by Metakaolin and Silica Fume

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1 Comparison of Durability Performance of Conventional and AirEntrained SelfCompacting Concrete Modified by Metakaolin and Silica Fume Abdulkader Ihssan El Mir 1, Salem Georges Nehme 2 1 PhD Student, Department of Construction Materials and Technologies, Budapest University of Technology and Economics, Budapest, Hungary 2 Associate Professor, Head of the Laboratory, Department of Construction Materials and Technologies, Budapest University of Technology and Economics, Budapest, Hungary Abstract: In order to obtain an adequate pore structure in selfcompacting concrete (SCC), durability indicators must be studied and analyzed to reach an optimized SCC mixture. A comparative study between non airentrained and airentrained SCC, containing metakaolin (MK) and silica fume (SF) with respect to reference mixtures is conducted. The objective of this study is to compare the effect of cement replacement by MK or SF at similar levels on durability properties. Type of cement and grading curve of aggregates were constant parameters. Water to cement ratio, limestone powder content, air entraining agent and supplementary cementitious materials type as well the content were variable parameters. Air void characteristics, resistance to water penetration, accelerated durability tests such as carbonation and chloride migration were evaluated. Also deicing salt scaling resistance test is performed. Results indicate that durability of SCC could be highly enhanced incorporating MK or SF but in selective percentages of cement mass replacement. Keywords: Selfcompacting concrete; Metakaolin; Silica fume; Fresh properties; Air void characteristics; Durability indicators. Introduction A recently new type of highperformance concrete named Selfcompacting concrete (SCC) is given more attention in terms of application and research. SCC is selected due to its ability to flow under its own weight, fill the targeted formwork and create a competent homogeneous material without any mechanical intervention [1]. K.H. Khayat, SCC th International RILEM Symposium on SelfCompacting Concrete, ISBN: RILEM

2 388 Abdulkader Ihssan El Mir, Salem Georges Nehme Fundamentally, concrete performance is based on its mechanical properties. Therefore enhancement of durability properties of concrete is taking more attention in research field. Supplementary cementitious materials (SCM) such as metakaolin (MK) and silica fume (SF) present the advanced applied materials in term of improving durability properties of concrete. Thus porosity and permeability properties are improved to obtain an extended service life for concrete [2]. Earlier studies demonstrated the positive influence of MK and SF on direct mechanical and durability properties [2, 710]. Thus the selection of appropriate combination of materials is a critical factor in SCC production. Rheological, mechanical and durability properties highly depends on SCC components. A preliminary study has been initiated where a variety of cement types, limestone powder content, a fixed water to cement ratio and high range water reducing admixtures (HRWRA) content were applied [11]. The target was to assess the optimum rheological and mechanical properties based on total fine content. Therefore according to figure 1, an investigation is performed towards understanding durability and efficiency of these mixtures. Figure 1. Effect of the dosage of limestone powder on the consistency endurance. Research Objectives Enhancement of materials properties for longer service life is one of the targets today in concrete technology. Several physical and chemical mechanisms contribute to the deterioration of concrete. Freeze and thaw cycles in presence of saltwater is a continuous damage process which ends up by surface degradation. Also frequent contact with chloride solution (eg. seawater) stimulates the corrosion of reinforcement leading to a deteriorated material. Other reactions such as carbonation which is defined by a diffusion of gas into concrete.the later can relatively result in

3 Comparison of Durability Performance of Conventional and AirEntrained SCC 389 microstructure deterioration and decrease of ph value of cement stone leading to inadequate environment for reinforcement. The goal of this study is to investigate the influence of MK and SF on durability indicators of SCC mixtures. Experimental Procedure Materials and mixture proportions Locally collected natural quartz sand and Danube river stone were used as fine and coarse aggregates. The particle size distribution of aggregates with maximum size of 16 mm is set to be 45% (04mm), 20% (48mm) and 35% (816mm). Each had a saturated surface dry specific gravity of 2.34, 2.51, 2.56 respectively based on EN10976 standard [3]. Limestone powder (LP), MK and SF applied in this study were collected from a local producer. The corresponding specific gravities of LP, MK and SF are: 2.69, 2.6 and 2.35 g/cm 3. A total of eighteen SCC mixtures were prepared in different proportions. Mixtures were divided into two groups: Group I: nonair entrained (NAE); Group II: airentrained (AE). Each group was classified into three categories: SCC without SCM (three reference mixtures: R1, R2, R3); SCC with MK: (M1, M2, M3); SCC with SF: (S1, S2, S3). Three different water to cement ratios were adopted: 0.562, 0.5 and Constant parameters were defined as: aggregate particle size distribution, cement type, the total fine content (620 kg/m 3 ) and water content (180 kg/m 3 ). On the other hand, variable parameters were defined as: water to binder ratio (w/b), limestone powder, cement, MK and SF content. The mass of cement was substituted by MK or SF between 10 and 12.5%. Applied admixtures were air entrained and HRWRA noted as the following: Sika Aer based on a synthetic chemical blend and Viscocrete 5Neu modified polycarboxylate. It should be pointed out that HRWRA were added in different dosages to the mixtures in order to obtain the desired slump. For more information, mixture proportions are listed in table I. Specimens were stored in water for curing after batching for 7 days under laboratory conditions.

4 390 Table I. Concrete mixture proportions. Mix. ID Cement (kg/m 3 ) MK (kg/m 3 ) SF (kg/m 3 ) L.P. (kg/m 3 ) w/b Aggregates (kg/m 3 ) 04 (mm) (mm) (mm) IR IR IR IM IM IM IS IS IS IIR IIR IIR IIM IIM IIM IIS IIS IIS HRWRA (ml/m 3 ) AEA (ml/m 3 )

5 Comparison of Durability Performance of Conventional and AirEntrained SCC 391 Measurements The evaluation of fresh state deformability and viscosity is performed through the slump flow and Vfunnel tests based on EN standards [5,6]. Regarding hardened state, air void characteristics were determined according to EN480 [12]. Moreover, degradation mechanism which occurs on transport of aggressive substances is of importance to be studied by means of multiple experiments. Thus several durability tests were executed. According to EN :2009, 150 mm concrete cubes were tested under 5 bar water pressure for 72 hours [14]. The diffusion of chloride solution into SCC specimens was tested by means of a rapid electrochemical principles [16]. Accelerated carbonation test was performed for one month by means of special climate carbonation chamber of 4 vol. % CO 2. The mean penetration depth of CO 2 was calculated from the recorded measured values in perpendicular direction using phenolphthalein solution. Salt scaling tests were following the suggestions of the CEN documents [15]. It should be pointed out that Freezethaw cycles were applied at 3 levels and the scaling loss was measured after 7, 14 and 28 cycles only. All tests were carried out at the age of 28 days except of chloride migration test at the age of 56 days and air void characteristics at the age of 90 days. Results and Discussion Fresh and hardened properties Viscosity and deformability: Rheological properties of SCC highly depend on the binder type and content. Figure 2 and table 1 illustrate the rheological results obtained, as well as the applied dosages of HRWRA. It should be stated out that a range of slump flow of mm was obtained. Regarding Vfunnel results, MK mixtures showed in average a higher values of 55% for NAE and 79% for AE mixtures in comparison with their reference mixtures (R1, R2, and R3). However SF mixtures showed a slight increase in average of 6% for NAE and 10% for AE mixtures which are close to reference mixtures. Thus, MK highly effect the viscosity and cohesion of SCC mixtures in comparison with SF addition.

6 392 Abdulkader Ihssan El Mir, Salem Georges Nehme Airvoid characteristics Figure 2. Slump flow and Vfunnel tests for all SCC. Figure 3 presents air void content results of all SCC mixtures. The average total air content of NAEMK, SF and reference mixture are 4.23%, 4.21% and 5% respectively. SF and MK mixtures showed similar mean values of air content relatively close to reference mixtures. Lowest air content value is recorded for highest binder content mixture NAES3 (2.46%). Regarding AE mixtures, the average total air content of AEMK, SF and reference mixture are %, 10.55% and 11.97% respectively. Similar behaviour for the effect of MK and SF on AE and NAE is noticed. Yet much higher air content is clearly noticed in AE mixtures. An average increase of 248% of air content of AE in terms of NAE references at 0.15% cement mass replacement of air entraining admixture.

7 Comparison of Durability Performance of Conventional and AirEntrained SCC 393 Durability indicators Figure 3. Air content results for all SCC. Table II summarizes all experimental results for resistance against water penetration depth, deicing salt scaling, chloride migration coefficient, and carbonation depth. All results will be discussed in the following sections. Resistance to water penetration test: According to figure 4, AE mixtures show a higher average water penetration depth value about 24% with respect to NAE mixtures. The maximum penetration depth is recorded for AER2 (16.02 mm). The lowest value corresponds to NAES3 (6.58 mm). Water penetration depth decreased in average from 8 to 41% for NAE and from 1% to 25% for AE mixtures according to their references. SF mixtures showed a more effective behaviour in comparison with MK mixtures with a higher resistance reaching more than 40% at a total bindery content of 440 kg/m 3.

8 394 Abdulkader Ihssan El Mir, Salem Georges Nehme Figure 4. Relative % of water penetration and carbonation depths based on reference mixtures. Table II. Results of water penetration depth, salt scaling, chloride migration coefficient and carbonation depth tests. Mix. ID Water Penetration depth Salt scaling Chloride migration coeffecient, D nssm (mm) (kg/m 2 ) (10 12 m 2 /s) (mm) Carbonation depth NAE AE NAE AE NAE AE NAE AE R R R M M M S S S DeIcing salt scaling test: According to table II, AE mixtures exhibit a lower average salt scaling values: a reduction about 44% with respect to NAE mixtures. The

9 Comparison of Durability Performance of Conventional and AirEntrained SCC 395 maximum scaling value is recorded for NAES1 (0.373 kg/m 2 ). The lowest one corresponds to AES3 (0.115 kg/m 2 ). Referring to figure 6, MK mixtures demonstrate a more effective behaviour rather than SF mixtures. An unfamiliar behaviour was shown by SF. In this case the scaling value increased in average by 30% (NAE S1 and S2). However MK showed a significant drop of 40.78% in case of NAEM2 with total bindery content of 400 kg/m 3. Thus it should be noted that MK mixtures were more effective in salt scaling resistance. Accelerated carbonation test: According to table II, AE mixtures showed a higher average CO 2 penetration depth value about 46% with respect to NAE SCC mixtures. The maximum penetration depth is recorded for AER1 (3.05 mm). The lowest value corresponds to NAES3 (0.756 mm). Referring to fig 4, a decrease of carbonation depth ranged between 7% to 54% for NAE and 9% to 44% for AE mixtures based on their reference mixtures. To visualize the results, an illustration is given in figure 5 that shows a comparison between AE mixtures of R1, M1, and S1, in which SF showed the highest resistance against CO 2 diffusion. Figure 5. Mean carbonation depth for AE mixtures R1, M1 and S1. Rapid chloride migration test: AE mixtures appear to have a higher average chloride migration coefficient value about 36% with respect to NAE mixtures. The highest coefficient is recorded for AER1 ( m 2 /s). The lowest value corresponds to NAES3 ( m 2 /s). Referring to figure 6, a decrease of chloride migration coefficient ranged between 15% to 88% for NAE and 13% to 88% for AE mixtures in terms of their reference mixtures. It is observed in case of highest bindery content (440 kg/m 3 ), SF tend to be more effective than MK at similar percentages of mass replacement of cement. Thus SF is more effective in chloride migration resistance between % of mass replacement of cement.

10 396 Abdulkader Ihssan El Mir, Salem Georges Nehme Figure 6. Relative % of salt scaling and RCM results based on reference mixtures Conclusions This study aimed to investigate the effect of air entraining admixture and cement substitution by MK or SF independently but at similar levels. Based on experimental analysis conducted on fresh and durability properties of SCC, the following can be concluded: Based on Vfunnel results, MK have a higher viscosity effect and HRWRA demand in comparison with SF mixtures. The addition of 0.15% cement mass of air entraining admixture highly increased the air content of SCC with respect to their NAE mixtures. The addition of MK or SF noticeably decreased air void content at high level of binder substitution (440 kg/m 3 ) in case of NAE mixtures. The addition of MK and SF improved the resistance of SCC against water penetration under pressure, carbonation, salt scaling and chloride migration with respect to both NAE and AE reference mixtures. Carbonation diffusion resistance is more enhanced on average of all NAE and AE mixtures by 35% applying SF in comparison with MK by 12.54% The scaling resistance property is mostly enhanced by incorporating MK rather than SF. At same level of replacement of cement by 10%, MK had a lower weight per surface reduction by 30 to 36% for NAE and AE respectively according to reference mixtures. SF mixtures shows a more effective behaviour in comparison with MK in terms of chloride migration coefficient

11 Comparison of Durability Performance of Conventional and AirEntrained SCC 397 References [1] ACI Committee 237. (2007), SelfConsolidating Concrete, 237R07 Self Consolidating Concrete. RILEM Publications, Bagneux [2] Hassan, AAA.,Lachemi, M. and Hossain, KMA. (2012). In: Effect of metakaolin and silica fume on the durability of selfconsolidating concrete. Cement Concrete Composites, 34(6): [3] BS EN (2013), Tests for mechanical and physical properties of aggregates. Determination of particle density and water absorption. BSI. [4] CEN, EN (2009), Testing hardened concrete Part 8: Depth of penetration of water under pressure, CEN/TC 104 Concrete and related products. [5] BS EN (2010), Testing fresh concrete, Part 8: Selfcompacting concreteslumpflow test. BSI. [6] BS EN (2010), Testing fresh concrete, Part 9: Selfcompacting concretevfunnel test. BSI. [7] Khayat, K., De Schutter, G. and Sonebi, M. (eds). (2014). In: Mechanical Properties of SelfCompacting Concrete: StateoftheArt Report of the RILEM Technical Committee 228MPS on Mechanical Properties of SelfCompacting Concrete. RILEM StateoftheArt Reports, vol. 14, Springer, / [8] Nehme, S. G. (2015). In: Influence of supplementary cementing materials on conventional and self compacting concretes Part. 1. Literature review, Építőanyag Journal of Silicate Based and Composite Materials, Vol. 67. No. 1, pp (In Hungarian). [9] El Mir, A. Nehme, S. G. (2015). In: Porosity of SelfCompacting. Procedia Engineering, Vol. 123, p. [10] Borosnyói, A. (2015). In: Development of compressive strength of HPC with the use of supplementary cementing material (SCM) combination. EpitőanyagJournal of Silicate Based and Composite Materials, Vol. 67, No.3, ptests, Építőanyag Journal of Silicate Based and Composite Materials, Vol. 67. No. 2, pp.7178, (In Hungarian). [11] Zsigovics, I. (2005), In: Effect of limestone powder on the consistency and compressive strength of SCC, Proceedings of the 4 th international RILEM Symposium on SelfCompacting Concrete, vol. I, pp , Shah, S. (Ed.), Hanley Wood Publication, U.S.A. [12] BS EN 48011, (2005). Admixtures for concrete, mortar and grout. Test methods. Part 11: Determination of air void characteristics in hardened concrete.

12 398 Abdulkader Ihssan El Mir, Salem Georges Nehme [14] CEN, EN , (2009). Testing hardened concrete Part 8: Depth of penetration of water under pressure, CEN/TC 104 Concrete and related products, [15] CEN, CEN/TS , (2006). Testing hardened concrete Part 9: Freezethaw resistance Scaling. [16] Nordtest. (1999): Concrete, Mortar And CementBased Repair Materials: Chloride Migration Coefficient From NonSteadyState Migration Experiments.