ScienceDirect. Effect of incorporating blast furnace slag and natural pozzolana on compressive strength and capillary water absorption of concrete

Transcription

1 Available online at ScienceDirect Procedia Engineering 18 (215 ) th Scientific-Technical Conference Material Problems in Civil Engineering (MATBUD 215) Effect of incorporating blast furnace slag and natural pozzolana on compressive strength and capillary water absorption of concrete Walid Deboucha a,*, Mohamed Nadjib Oudjit a, Abderrazak Bouzid b, Larbi Belagraa b a Built Environment Laboratory, Faculty of Civil Engineering, University of Science and Technology Houari Boumediene, 16111, Algiers, Algeria b Laboratory of Materials and Electronic Systems, Faculty of Sciences and Technology, University of Bordj Bou Arreridj, 34, Algeria Abstract Blast furnace slag (BFS) and natural pozzolana (NP) have been widely used as a partial cement replacement in concrete construction due to their advantages including cost reduction and improvement of the ultimate mechanical and durability properties. Based on an ongoing experimental program, this research emphasizes on the effect of substituting cement with Blast furnace slag and natural pozzolana up to 4 % on compressive strength and capillary water absorption of concrete. The compressive strength was determined on prisms at the ages of 7, 28, and 9 days. Cylindrical specimens were employed for capillary water absorption test after 28 days of curing. The results show that it is possible to obtain the same or better strength grades by replacing cement with BFS up to 3% in concrete. However, the use of NP content reduced the compressive strength. Lower capillary water absorption for BFS or NP substitution is observed. 215 The Authors. Published by Elsevier Ltd. 215 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( Selection and peer-review under responsibility of organizing committee of the 7th Scientific-Technical Conference Material Peer-review Problems in under Civil responsibility Engineering. of organizing committee of the 7th Scientific-Technical Conference Material Problems in Civil Engineering Keywords: blast furnace slag; natural pozzolana; concrete; compressive strength; capillary water absorption * Corresponding author. Tel.: address: deboucha.eng34@gmail.com The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of organizing committee of the 7th Scientific-Technical Conference Material Problems in Civil Engineering doi:1.116/j.proeng

2 Walid Deboucha et al. / Procedia Engineering 18 ( 215 ) Introduction Mineral additives have become the common way used to reduce the impact environmental of cement manufacturing by reducing CO 2 emission and to increase durability of concrete [1,2,3].With the existence technologies in using the benefits of mineral additives such as blast furnace slag (BFS) and natural pozzolana (NP) in concrete increase the ultimate strength and enhance impermeability [4]. The first parameter in good concrete structural design is the compressive strength, which is usually used to estimate concrete quality. Bilim et al [5] found that the concrete mixtures containing 2% and 4% BFS have higher compressive strength compared to the control concrete at 28 days. In contrast, the compressive strength decreased when increased the natural pozzolana content [6]. In term of concretes durability, large size of capillary pores play a preponderant role in the transfer properties of the concrete, thus on the durability performances. The capillary water absorption test used to evaluate the capillary pores. A considerable number of published articles stated the effect of BFS and NP as Portland cement replacements on capillary water absorption of concrete. Hadjsadok et al [7], Alexander and Magee [8] reported that the incorporation of BFS decreased the capillary water absorption of concrete. On other hand, the incorporation of NP leads also to a decrease of capillary water absorption of concrete [9]. The main objective of this research is to investigate the effect of local materials such as BFS and NP on compressive strength and capillary water absorption of concrete. 2. Experimental study 2.1. Materials The concrete mixtures were prepared with CEM-I 42, 5 N Ordinary Portland Cement (OPC) conforming to the requirements specified in NA 442[1], with a fineness of 367 m 2 /kg, Blast furnace slag (BFS) used in this work was obtained from the iron and steel company (El-Hadjar, Algeria) and natural pozzolana (NP) was obtained from Beni Saf quarry in the west of Algeria. The two materials i.e. BFS and NP were grounded in a laboratory mill to a specific surface of 5 m 2 /kg. The Chemical and physical properties of cement and mineral additives used are summarized in Table 1. X-ray diffraction patterns and identified phases of cement, blast furnace slag and natural pozzolana are shown in Fig.1.Crushed limestone coarse aggregates with a nominal particle size of 8 mm (G1) and 15mm (G2), as fine aggregate, natural sand was used with a nominal particle size of 3mm Mix proportion and specimen preparation In order to provide an observation on the effectiveness of the replacement levels of BFS and NP, A total of 8 concrete mixtures were prepared having a constant slump of 6±1 mm and total binder of 36 kg/m 3. The control mixture included only OPC as the binder while the remaining mixtures incorporated binary cementitious blends in which the OPC was replaced with BFS or NP. The replacement ratios for BFS were 2%, 3% and 4%. While for NP were 1%, 2%, 3% and 4% by mass of total cement content. The concrete mixtures proportions are summarized in table 2.

3 256 Walid Deboucha et al. / Procedia Engineering 18 ( 215 ) Fig. 1. X-ray diffraction of a) cement b) blast furnace slag and c) natural pozzolana.

4 Walid Deboucha et al. / Procedia Engineering 18 ( 215 ) Test procedure Compressive strength of concrete was measured according to NF EN [11] by means of a 3 KN capacity testing machine. The test was conducted on 1 mm cubes at the ages of 7, 28 and 9 days. The compressive strength value was determined as the average of three specimens test. Capillary water absorption test measures the rate at which water is drawn into the pores of concrete. For this test, three specimens having dimensions of ø1 6 mm cut from ø1 2 mm cylinder specimens were employed [12]. After twenty eight days, the specimens were removed from the water curing medium and kept in a drying oven at 15 C until getting a constant weight. The specimens were coated with the paraffin on their lateral surfaces in order to ensure uni-axial water absorption and immersed in water such that their cut surfaces would be submerged in water at a depth of 5 mm. The concrete specimens were weighted before and after submerging for 5, 1, 15, 3, 6, 9,12 and 15 minutes. The capillary water absorption coefficient was calculated from the following formula Q/A= S t, where Q/A is the amount of absorbed water per unit surface (kg/m 2 ); A is the area of the specimen in contact with water in (m 2 ); t is the time elapsed; S is the capillarity water absorption coefficient (kg/m 2 /min 1/2 ). Table 1. The chemical composition and physical characteristics of the cement and mineral additions. Chemical composition (%) OPC BFS NP SiO Al 2O Fe 2O CaO MgO / So K 2O Na 2O / LOI Physical characteristics Specific gravity Blaine (cm2/g) Initial setting time (min) Final setting time (min) Expansion (mm) Results and discussions 3.1. Compressive strength Effect of blast furnace slag The influence of BFS on the compressive strength of Portland cement concrete is shown in Table.3. A decrease in compressive strength with increased slag content at early age was observed, this reduction is more pronounced for mortar mixture containing 3% and 4% of BFS as cement replacement. However, at 28 and 9 days, compressive strength of concrete containing 2% BFS was higher ( 5%) than that of control concrete. In addition, the concrete containing 3% BFS exhibited an equivalent or a greater final strength than that of control concrete. For example, when the concrete made with 3% BFS as cement replacement, the compressive strength loss at 7 days was 8%. However, the strength at 28days increased by 3% compared to the control concrete.

5 258 Walid Deboucha et al. / Procedia Engineering 18 ( 215 ) Table 2. Mix proportions concrete. Concrete W/B Binder (kg/m 3 ) Aggregates (kg/m 3 ) Cement Slag Pozzolana Sand(/3) G1 3/8 G2 8/15 C-PC BFS BFS BFS NP NP NP NP Table 3. Effect of blast furnace slag and natural pozzolana on the compressive strength of concrete at various ages. Concrete Compressive strength (MPa) 7 days 28 days 9days C-PC BFS BFS BFS NP NP NP NP The results obtained in this study show that the use of BFS decreased the strength of concretes at early ages compared to the control concrete. This decrease observed at the beginning, due to the relatively slower rate of pozzolanic hydration process [13]. But at later ages, blast furnace slag, which is latently hydraulic, undergoes hydration reactions in the presence of water with calcium hydroxide Ca(OH) 2. This secondary pozzolanic reaction yields a denser microstructure because the Ca(OH) 2 was consumed and C S H paste is formed [14], and thus leads to enhance the later strength Effect of natural pozzolana The compressive strength of the concrete containing natural pozzolana is presented in Table 3. NP induced reductions in the compressive strength of concrete at all levels of replacement at 7, 28 and 9 days. The compressive strength for control concrete after 28 and 9 days of curing was found and MPa. Water absorption (kg/m 2 ) C-PC 2BFS 3BFS 4BFS Time (Min 1/2 ) Water absorption (kg/m 2 ) C-PC 1NP 2NP 3NP 4NP Time (Min 1/2 ) Fig. 2. Water absorbed per unit area of a) blast furnace slag and b) natural pozzolana concretes at 28 days.

6 Walid Deboucha et al. / Procedia Engineering 18 ( 215 ) Mix Mix Fig. 3. Capillary water absorption coefficient of a) blast furnace slag and b) natural pozzolana concretes at 28 days. Respectively.Similarly to the compressive strength measurement for concrete containing 4% NP was found MPa and MPa respectively at 28 and 9 days of curing. This decrease of compressive strength in NP concrete was attributed to the increasing water to binder ratio by increasing NP content, which was.56 for the concrete containing 4%NP, whereas the water to cement ratio was.53 for control concrete Capillary water absorption Effect of blast furnace slag Capillary water absorption results of BFS concrete mixtures at the age of 28 days are presented in Fig. 2.a. It is noticeable from the figure that, the highest capillary water absorption of 3.32 kg/m 2 was observed at the control concrete mixture. The incorporation of BFS were remarkably effective when decreasing the capillary water absorption in concrete mixtures, particularly, concrete with a 4 % of BFS decreased the capillary water absorption by 4 % compared to the concrete mixture without BFS. Fig.3.a presented the evolution of capillary water absorption coefficient of concretes containing different amounts of BFS. The capillary absorption coefficient results were also significantly influenced by the binder combination used. In the comparison to the control concrete, capillary water absorption coefficient was improved through the use of a 4% BFS as cement replacement. This improvement of the capillary water absorption due to the more pore structure refined,the distribution and dimension of the capillary porosity which is mainly due to the formation of the secondary C-S-H gel issued from the pozzolanic reaction of BFS [15] Compressive strength (MPa) Compressive strength (MPa) Fig. 4. Correlation between capillary water absorption coefficient and compressive strength of a) blast furnace slag and b) natural pozzolana concretes.

7 26 Walid Deboucha et al. / Procedia Engineering 18 ( 215 ) Effect of natural pozzolana The results for capillary water absorption test of the concrete mixtures with NP addition are shown in Fig. 2.b. A reduction of the capillary water absorption is noticed for concrete containing different amount of NP, particularly for concrete mixture containing 4% NP where the value of capillary water absorption was 2.38 kg/m 2 compared to 3.32 kg/m 2 for control concrete. Fig. 3.b illustrated the capillary water absorption coefficient of NP concretes. Again, a comparison of the concrete containing pozzolana with control concrete showed a decrease in capillary water absorption coefficient at 28days.This could be due to the pores in the bulk paste or in the interfaces between aggregate and cement paste are filled by these mineral admixtures. The capillary pores are reduced by the formation of secondary C S H gel due to the pozzolanic reaction, and hence the reduction in the capillary absorption coefficient of concrete Correlation between capillary absorption coefficient and compressive strength The correlation between capillary water absorption coefficient and compressive strength of BFS or NP concretes is given in Fig.4. Irrespective of mixture composition, it can be noticed that an increase in capillary absorption coefficient is associated with an increase in compressive strength. Irrespective of strength, the higher value of capillary absorption coefficient was measured in the control concrete. The addition of BFS or NP as cement replacement exhibited an improvement in capillary water absorption coefficient of the concrete. 4. Conclusion The following conclusions could be drawn from the results obtained in this investigation: 1. Incorporation of blast furnace slag up to 3% enhanced compressive strength at medium and long term of concretes. In contrast, concrete containing natural pozzolana reduced the compressive strength at all tested ages up to 9 days as results of water to binder ratio. 2. The use of BFS or NP as cement replacement decreased the capillary water absorption by the most compared to the control concrete mixture. 3. In this work, it can be concluded that blast furnace slag and natural pozzolana can be used to improve properties of concretes mixtures. References [1] Bassuoni, M.,T., Nehdi, M.,L. Resistance of self-consolidating concrete to sulfuric acid attack with consecutive ph reduction, Cem & Conc Res, 27 ;37: [2] Senhadji, Y., Escadeillas, G., Khelafi, H., Mouli, M., Benosman, A.S., Evaluation of natural pozzolan for use as supplementary cementitious material, Eur j of Env & civ eng, 212;16: [3] Hewayde. E., Nehdi. M.L., Allouche, E., Nakhla. G. Using concrete admixtures for sulphuric acid resistance, Proc of Institution of Civil. Engineers: Const Mat, 27;34: [4] Ramachandran, V.S., Concrete Admixture Handbook:Properties, Science and Technology, Noyes Publications, [5] Bilim, C., Atis, C. D., Tanyildizi, H., Karahan, O. Predicting the compressive strength of ground granulated blast furnace slag concrete using artificial neural network, Adv in Eng Sof, 29;4: [6] Belaidi, A.S.E., Azzouz, L., Kadri, E., Kenai, S. Effect of natural pozzolana and marble powder on the properties of self-compacting concrete, Const & Buil Mat, 212;31: [7] Hadjsadok,A., Kenai, S., Courard, L., Michel, F., Khatib, J. Durability of mortar and concretes containing slag with low hydraulic activity Cement & ConcrCom, 212; [8] Alexander, M.G., Magee, B.J. Durability performance of concrete containing condensed silica fume. Cem & Conc Com 1999;29: [9] Ghrici, M., Kenai, S., Said-Mansour, M. Mechanical properties and durability of mortar and concrete containing natural pozzolana and limestone blended cements, Cem & ConcCom,. 27;29: [1] NA 442, cement: Composition, specifications and conformity criteria for common cements, Algerian standard, Algeria, 25. [11] NF EN ,, Compressive strength of test specimens, Franch standard, France,23. [12] Gesoğlu, M., Güneyisi, E., Kocabağ, M.E., Bayram, V. and Mermerdaş, K. Fresh and hardened characteristics of self-compacting concretes made with combined use of marble powder, limestone filler, and fly ash, Const& Buil Mat, 212;37: 16 17

8 Walid Deboucha et al. / Procedia Engineering 18 ( 215 ) [13] Bougara, A., Lynsdale, C., and Mileston, N.B. Reactivity and performance of blast furnace slags of differing origin. Cem& and Conc Com, 21;32: [14] Černý, R., Rovnaníková, P. Transport processes in concrete,spon Press, London, 22. [15] Jiang, S.P. and Grandet, J., Evolution comparée des porosités des mortiers de ciment au laitier et des mortiers de ciment Portland, Cem& Conc Res, 1989 ;19 :