COMPARISON OF REACTIVITY OF CEMENTITIOUS ADDITIONS ON PROPERTIES OF MICRO CONCRETE

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1 COMPARISON OF REACTIVITY OF CEMENTITIOUS ADDITIONS ON PROPERTIES OF MICRO CONCRETE M. Lanez (1), M. N Oudjit (1) and A. Bali (2) (1) USTHB, Built Environment Laboratory; Civil Engineering Faculty, BP 32 El Alia, Bab Ezzouar 16111, Algiers, ALGERIA.Phone: Fax: mohnadoudj@yahoo.fr and maadlan@yahoo.fr (2) ENP, Research Unit Engineering and Environment, Department of Civil Engineering, Algiers, Algeria. balianl@yahoo.fr Abstract Reactive powder concrete (RPC) is a new generation of concrete material which is actually a micro mortar with a maximum aggregate size not exceeding 0.630mm. It should be noted that when incorporating cementituous additions, this type of concrete shows a better homogeneity, an increased compactness of the cement matrix and an improved microstructure leading to high initial as well as final physic- mechanical performance in fresh and hardened state. The objective of this paper is to study the effect of the addition of dune sand and slag, finely ground on mineralogical, rheological and mechanical properties of RPC. The compactness of the cement matrix, principal source of strength gain, is closely linked to the consumption of portlandite occurring during hydration of cement silicates to produce new calcium silicate hydrates (C-S-H) more compact and insoluble in water. This so-called pozzolanic reactivity depends on the nature and structure of the used cimentituous additions. In order to better evaluate the gain in strength of the RPC containing finely ground dune sand (SD) and slag (S), the microstructural aspect has been examined by X-ray diffraction. The study of mixtures SD-lime and S-lime may thus be a simplified approach of that of the mixtures SD-RPC or S-RPC, in which the main reaction is the fixation of lime, resulting from cement hydration to produce additional C-S-H.In this work, the results obtained from tests carried out on RPC show that both compressive and tensile strengths increase when incorporating mineral additions in cement, thus improving the compactness of mixtures by their filler and pozzolanic effects. 1. INTRODUCTION The improvement of homogeneity, compactness and even ductility of concrete, has started in the early 90s due to the development of "Reactive Powder Concrete (RPC)," which are micro concretes characterized by a maximum particle size not exceeding 630 microns, a very low WC ratio and very high tensile and compressive strength or even greater than those of steel (350 MPa) [1,2,3]. This paper aims to elaborate micro concrete RPC based on mineral addition incorporated into Portland cement at 15% by weight. These additions are materials rich in silica such as 67

2 silica fume SF, finely ground blast furnace slag S and Dune Sand SD. The main objective of this investigation is to characterize these RPC using the compression and tension mechanical tests on specimens mixed at very low WC ratio. This has been possible through the use of a superplasticizer to maintain the workability of RPC for an easy placing. 2. MATERIALS USED The materials used in this work are: - Granular skeleton consisting of fine sand ( From Boussaâda: Southern Algeria) SS - Algerian Cement type CEM II A C - Mineral additions A: - Silica fume SF - Ground blast furnace Slag (El Hajar) S - Finely ground Dune Sand (Boussaâda) SD - Chemical Additions: - Superplasticizer based polysulfonates: SP Except Silica fume that is produced in Canada, all the other materials used are local origins 3. PROPERTIES OF USED MATERIALS The physico-chemical, mineralogical and mechanical properties of materials used are listed in tables (1, 2 and 3) respectively. Table 1: Physical characteristics of cement and addition used [4] Cement Silica fume (SF) Ground dune sand (SD) Ground slag (S) Real Density Fineness (cm 2 g) (BET) 5000 (Blaine) 6600 (Blaine) Normal 0.27 consistency Expansion in mm 0.72 Initial set 1h57mn Final set 3h47mn 68

3 Table 2: Chemical, mineralogical and mechanical properties of cement and addition [4] Content percent Oxyde Cement SF SD S SiO 2 Al 2 O 3 Fe 2 O 3 CaO MgO SO 3 Na 2 O K 2 O Cl - Free CaO R, Ins Loss on ignition Table 3: Mineralogical composition and Mechanicals properties of cement used [4] Mineralogical composition of cement (BOGUE) C 3 S βc 2 S C 3 A C 4 AF CŠH 2 C l Mechanical properties of cement Compressive strength (MPa) Tensile strength (MPa) 2d 2d The mineralogical nature of the materials was highlighted with the help of an X-ray diffraction analysis. The XRD patterns obtained show that [4,5,6,7]: - Silica fume SF has an amorphous structure similar to that of the Cristobalite. - Blast furnace slag S also has an amorphous structure. - Ground Dune sand SD has a well crystalline structure of the type of Low Quartz. 69

4 4. TEST PROCEDURE ON RPC In this section the various additions (SF, S, and SD) were incorporated in Portland cement at different contents. Two WC ratios (0.27 and 0.20) were chosen for which the behavior of RPC in a fresh and hardened states are examined. The evolution of compressive and tensile strength at different ages 7, 28 and 90 days respectively was assessed. The test specimen mixtures were prepared as follows: - RPC without additions (Control: T): C = 1, SS = 1.1, SP = 2% WC = 0.27 and RPC with additions: C = 1, A (SF, S, SD) = 0.15, SS = 1.1, SP = 2%, EB = 0.27and The formulation for 1 m 3 of RPC (with and without addition) is given in Table 4 Table 4: Proportioning of studied RPC with and without addition [4] RPC with and without additions T, SF, S or SD WB SP40 (Kgm 3 ) C (Kgm 3 ) SS (Kgm 3 ) A(SF,S,SD) (Kgm 3 ) TESTS ON FRESH CONCRETE The characteristics of freshly made RPC depend on the water content used in mixtures. The workability of RPC was measured by the LCPC maniabilimeter test. The results of this measurement as well as that of the density are given in Table 5 Table 5: Workability and density of the studied RPC [4] WB = 0.27 WB = 0.20 t (s) ρ (kgl) t (s) ρ (kgl) RPC (T) > RPC SF RPC S > RPC SD > It should be noted that for EC 0.20, flow time increased significantly (t> 60 s) the studied RPC except for concrete containing silica fume (SF) (t=16s). This result is in accordance with that reported in the literature [8,9] and clearly reflects the superplasticizer role played by the Silica Fume. For all RPC, the time measured during LCPC maniabilimeter tests and the density fresh RPC increased when the EB ratio decreased. 70

5 RILEM International workshop on performance-based specificationn and controll of concretee durability a The shortest time recordedd when using LCPC maniabilimeter test was obtained with RPC containing FS addition for EB ratios. Due to its amorphous structure and its fineness, the SF particles will contribute to the lubrication of other particles inn the same RPC by filling the smallest remaining voids, and therefore they releasee some water molecules which themselves contribute to increase the workability of concrete [4, 8,9]. For other RPC (control-(t)) and that incorporating S) batchedd with EB= =0.27, the measured times were identical. On the other hand, for RPC-based to the high fineness of ground dune sand (SD) SD addition, an improvement in workability was noticed and which is due (6600cm 2 g) comparatively to that of slag (5000cm 2 g). This allows to conclude that in the presence of superplasticizers, the increase in the fineness contributes s to improving the workability of RPC [4,5,6,7]. 6. TESTS ON HARDENED RPC 6.1 Compressive strength The compressive strength determined on prismatic specimens (4x4x16), WB of 0.20 and 0.27 as a function of time is given in Table 6 and Figure 1. Table 6: Compressive strength of RPC for WB=0.27 and 0.20 [4][ Age (d) RPC T RPC SF RPC S RPC SD Compressive strength (MPa)) EC = EC = Compressive strength (MPa) b)compressive strength of studied RPC WB=0.20 RPC RPC SF Figure 1: RPC compressive strength for WB=0.27 andd 0.20 respectively [4]. Day 71

6 RILEM International workshop on performance-based specificationn and controll of concretee durability a 6.2 Tensile strength Table 7 and figure 2 show the t RPC tensile strengths in function of time [4]. Table 7: RPC tensile strengthss WB=0.277 and 0.20 ratio [4] Tensile strength (MPa)( WB = 0.27 EB = 0.20 Age (d) RPC T RPC SF RPC S RPC SD Figure 2: RPC tensilee strength for WB=0.27 and WB= =0.20 respectively [4]. 6.3 Fragility index IF In order to highlight the evolution of fragility index of the elaborated RPC, the values of If =RcRt as a function f of time are determined and given in Table 8 and plotted in Figure 3. With: Rc: Compressive strength of RPC and Rt: Tensile strength of RPC. Table 8: RcRt ratio of the studied RPC [4]. Fragility Index RcRt WB = 0.27 Age (d) RPC RPC SF RPC S RPC SD WB =

7 RcRt ratio of studied RPC 12,5 11,5 10,5 9,5 8,5 7,5 6,5 a) RcRt ratio of studied RPC WB=0.27 RPC RPC SF RPC S RPC SD Day RcRt ratio of studied RPC 12 11, ,5 10 9,5 9 8,5 8 b) RcRt ratio of studied RPC WB=0.20 RPC RPC SF RPC S RPC SD Day Figure 3: RcRt ratio of the studied RPC [4]. 7. CONCLUSION Independently of the WB ratio and the mineral additions used, the compressive and tensile strength of RPC increases with time (, and ). Independently of the additions, the RPC mechanical strengths made with WB =0.20 are higher than those of the RPC with WB=0.27, this increase results in a decrease of pores in the RPC by the low content of water and consequently, a densification of the latter leads to high strengths. The RPC mechanical strengths with additions (SF, S, SD) and mainly the RPC (SF) are clearly higher than those of RPC (control) without additions, For a given addition, the RcRt ratios substantially increase with time, which indicates that additions weaken the RPC considering the slow evolution of tensile strengths compared compressive ones. REFERENCES [1] Richard, P. Cheyrez, M., 'Les bétons de poudres réactives'. ITBTP Annales. Concrete series 320. (1995). [2] Aitcin,P-C., 'Bétons hautes performances'. Edition Eyrolles. (2001). [3] Gatty.L,. 'Caractérisations microstructurales et microanalytiques des Bétons de Poudres Réactives par microscopies électroniques'. Thèse de doctorat (Nantes, 1996). [4] Lanez.M., 'Contribution à l étude des bétons de poudres réactives'. Master thesis. USTHBFGC. (Algiers. Algéria, 2005). [5] Oudjit, M.N, Arroudj, K, Bali, A., 'Pozzolanic reactivity of the dune sand'. International Conference on Structural & Geotechnical Engineering and construction Technology (IC- SGECT 04). (Mansoura. Egypt. 2004). [6] Arroudj,K. Oudjit, M.N. Lanez, M. Carayon.M,T., 'Mise en évidence par diffractométrie aux rayons X des C-S-H de seconde génération'. 1erSéminaire sur les technologies du béton. Le béton, perfection et incertitudes. (Alger, 2004). [7] Lanez, M. Oudjit, M,N. Zenati, A. Arroudj, K. Bali,A., 'Micro Environmental Concrete'. Elsevier. Physics Procedia 21 (2011) [8] De Larrard, F., 'Formulation des bétons à très hautes performances'. Thèse de Doctorat de l ENPC, (rapport de recherche LPC N 149, 1988). [9] Oudjit.M.N., 'Réactivité des fumées de silice condensées en présence de chaux ou de ciment portland'. thèse de Docteur-Ingénieur. (INSA-Toulouse. France, 1986). 73