Construction and Building Materials

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Construction and Building Materials 35 (2012) 227 231 Contents lists available at SciVerse ScienceDirect Construction and Building Materials journal homepage: www.elsevier.

Shandong Provincial Key Laboratory of Preparation and Measurement of Building Materials, University of Jinan, Jinan 250022, China article info abstract Article history: Received 1 October 2011

1 Construction and Building Materials 35 (2012) Contents lists available at SciVerse ScienceDirect Construction and Building Materials journal homepage: Effects of slag and limestone powder on the hydration and hardening process of alite-barium calcium sulphoaluminate cement Wang Shoude, Chen Cheng, Lu Lingchao, Cheng Xin Shandong Provincial Key Laboratory of Preparation and Measurement of Building Materials, University of Jinan, Jinan , China article info abstract Article history: Received 1 October 2011 Received in revised form 2 March 2012 Accepted 7 March 2012 Keywords: Slag Limestone Barium calcium sulphoaluminate Alite Hydration For the existence of C 2:75 B 1:25 A 3 S mineral, alite-calcium barium sulphoaluminate cement has dual priming action of alkali-activated effect and sulfate-activated effect on mixed material. When the total amount of added mixed material is unchanged, the effects for ratio of slag to limestone powder on water requirement, setting time, mechanical performance, hydration products and hydration heat of alite-barium calcium sulphoaluminate cement are investigated. The experimental results show that the water requirement and setting time decrease with the decrease of the ratio of slag to limestone powder. The compressive strength of specimen cured for 90 days with 50% cement, 30% slag and 20% limestone powder is higher than that of pure cement. Slag and limestone powder prompt the second exothermic peak to appear early and shorten induction period. Furthermore, slag and limestone decrease rapidly hydration calorimetric of cement, especially for its early hydration calorimetric. Meanwhile, it is concluded that alite-calcium barium sulphoaluminate cement has dual priming action of alkali-activated effect and sulfate-activated effect. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Alite-calcium barium sulphoaluminate cement () is a new type of cementitious material, whose main minerals are alite, calcium barium sulphoaluminate (C 2:75 B 1:25 A 3 S), belite, tricalcium aluminate, and calcium aluminoferrite [1 5]. The new type of cement has not only the property of Portland cement, but also the performance of rapid hydration and hardening, higher early age strength and smaller volume shrinkage of hardening. C 2:75 B 1:25 A 3 S is a kind of sulphoaluminate mineral in the cement clinker. For the existence of C 2:75 B 1:25 A 3 S mineral, due to the high concentration of OH and SO 2 ions in its hydration circumstance, has dual priming actions of alkali-activated effect and sulfate-activated effect on industry waste. Therefore, has more advantage than ordinary Portland cement to activate the industry waste. Blast furnace slag is a by-product obtained in the manufacture of pig iron in the blast furnace and is formed by the combination of earthy constituents of iron ore with limestone flux. When the molten slag is swiftly quenched with water in a pond, or cooled with powerful water jets, it forms into a fine, granular, almost fully noncrystalline, glassy form known as granulated slag, having latent hydraulic properties. In the previous works, it was found that slag can decrease the pore size of concrete and improve the density of concrete engineering. Meanwhile, slag can decrease hydration heat of cement and reduce the creak induced by hydration heat Corresponding author. Tel.: ; fax: address: mse_wangsd@ujn.edu.cn (W. Shoude). accumulated. Limestone powder is an important material for cement manufacture. The addition of limestone powder to Portland cement may significantly improve several cement properties such as compressive strength, water demand, workability, durability [6 12], and can also decrease production costs. The effects of small limestone additions on both compressive strength and on heat of hydration are relatively well known, but less is known about the dependence of these effects on clinker properties (for example C 3 S content), fineness of cement and other factors. There is evidence that the influence of limestone depended on C 3 A content of clinker because CaCO 3 produced calcium carboaluminate hydrate during the reaction with C 3 A [6,13,1]. There is also some evidence that finely ground limestone influences C 3 S hydration [15 18]. However, to date, no much attention has been paid to the double effects of slag and limestone powder on alite-calcium barium sulphoaluminate cement. 2. Experiment 2.1. Preparation of specimens The clinker and gypsum are offered by Shandong Cement Company. The slag is given by Jinan Steel and Iron Company. Limestone powder is industry material. Meanwhile slag and limestone powder are all grounded to specific surface area exceeding 20 m 2 /kg. The chemical components (by weight) of raw materials are shown in Table 1. The specimens with different components (by weight) are named in Table 2. For instance, the component of specimen is only pure alite-calcium barium sulphoaluminate cement. The component of LS3 specimen includes 50%, 25% slag and 25% limestone powder. The water requirement and setting time of specimens are determined according to GB/ of China. All the raw material was /$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.

2 228 W. Shoude et al. / Construction and Building Materials 35 (2012) Table 1 Chemical component of raw materials (% by weight). Raw materials CaO SiO 2 Al 2 O 3 Fe 2 O 3 SO 3 BaO MgO Loss The sum Clinker AS Gypsum Slag Limestone Table 2 Components of different cement specimens (% by weight). Specimens L0 LS1 LS2 LS3 LS LS5 S0 Cement Slag Limestone mixed according their components with their water requirement and the paste was put into the 2 2 2cm 3 molds with vibration. These specimens were demoulded after being cured in moist air at (20 ± 1) C with more than 90% relative humidity after 1 day standard curing. Then the specimens were cured in water for measurement of the compressive strength for 90 days Testing The hydration of the specimens was terminated with absolute alcohol and the specimens were dried and analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry analysis (DSC). The hydration heat evolution testing of cement clinker was performed by an isothermal heatconduction calorimetry (TAM air C80, Thermometric, Sweden). Furthermore, the sulfate concentration change of hardened cement paste was characterized by barium sulfate gravimetric method. A gram cement powder was weighted accurately and was put into beaker for 300 ml. The distilled water for 0 ml and 10 ml hydrochloric acid solution with were added into beaker. The beaker was heated until the solution was boiling slightly and kept this situation for 5 min in order to let sulfate ions dissolve sufficiently. The mixed solution was filtered by moderate speed qualitative filter paper when solution was cooled. The filter residue was washed 10 times by warm water and threw away. Filtrate was heated to boiling situation and its volume was kept for 200 ml all the time. Meanwhile, BaCl 2 solution with 10% concentration was added. The mixed solution was filtered by slow moderate speed qualitative filter paper when solution was cooled for h. The second filter residue was washed until without the chloride reaction (determination by 1% silver nitrate solution). Crucible was burn until its weight was constant. Filter paper and filter residue all were put into crucible and then burn in furnace at 00 C at the atmosphere air until filter paper was burn completely. Then the crucible was taken out, cooled in drier for 30 min and weighed. So the mass of barium sulfate was calculated. Meanwhile, the sulfate mass in cement could be calculated. 3. Results and discussion 3.1. Effects of slag and limestone powder on compressive strength Water requirement and setting time of different cement specimens are illustrated in Table 3. As shown from Table 3, the water requirement of specimens increases with the ratio of slag to limestone powder rising. The reason is that limestone powder can improve the cement fluidity for its slippery surface. Meanwhile, as shown from Table 3, the initial and final setting times are at the normal level even if the amount of limestone powder changes at a wide range. Limestone powder acts as the nucleation center in cement paste, shortens the induction period of cement and promotes setting time to reduce. Although cement mixed material often increases setting time, the above effects of limestone powder would decrease this negative effect, particularly when the amount of limestone powder is high. Effects of the ratio of slag to limestone powder on compressive strength of different cement specimens are illustrated in Fig. 1. As shown from Fig. 1, the compressive strength of cement specimen with only slag or limestone powder is lower than that of bank cement specimen. The cement clinker amount decreases rapidly when the mass of slag and limestone powder is the same as cement clinker. This leads to hydration products of specimen decrease accordingly. So the compressive strength of cement specimen with slag or limestone powder is lower than that of blank cement specimen. As shown from Fig. 1, the compressive strengths of cement specimen both with slag and limestone powder are much lower than that of blank cement, except for LS specimen. The compressive strength of LS specimen for 1 or 3 curing days is relatively low. Whereas, when curing age exceeds 28 days, its compressive strength increases rapidly and is higher than that of blank cement specimen. The hydration activity of limestone powder is considerably less than slag, which should have negative effect on the early strength of cement. Although its hydration activity is low, the surface of limestone powder should adsorb aluminate anion, which can decrease the concentration of aluminate anion in solution. As a result, the hydration of C 3 A is promoted and the formation of ettringite is accelerated. This mechanism is the microcrystalline effect and catalysis. When the curing age exceeds 28 days, the potential activity of slag is activated effectively. The microcrystalline effect and catalysis of limestone power also shows fully. Therefore, the compressive strength of cement increases rapidly in the later curing age Effects of slag and limestone powder on hydration products and hydration heat The XRD patterns of hydration products of LS and blank specimens cured for 3 days, 28 days and 90 days are illustrated in Fig. 2. As shown from Fig. 2, it is seen that the main hydration products of blank cement at different ages are all ettringite (AFt) and Ca(OH) 2 (CH). Because of calcium silicate hydrate(c S H) being gel, its diffraction peak is not obvious in Fig. 2. Meanwhile, the categories of the hydration products of LS are similar to each other, including CH, CaCO 3 and C S H gel. But when curing age is 90 days, the diffraction peak of AFmc and AFtc are obvious. This indicates that CaCO 3 has reacted with cement at the later curing age. Previous studies [19 21] proved that limestone powder is harmful to concrete durability with SO 2 ions being present. The reason is that thawmasite is easily formed in above condition. The formation of thawmasite is recognized as a cause of deterioration of Portland Table 3 Water requirement and setting time of different cement specimens. Specimens L0 LS1 LS2 LS3 LS LS5 S0 Water requirement (g/ml) Initial setting time (min) Finial setting time (min)

3 W. Shoude et al. / Construction and Building Materials 35 (2012) Compressive strengh (MPa) 100 LS 90 LS5 80 LS2 LS3 70 LS1 60 S0 L Hydration period (days) Fig. 1. Effect of slag and limestone powder on compressive strength of cement. hydration heat liberation rate (mw/g) LS LS Hydration age (hour) Fig. 3. Rate curves of heat liberation and hydration heat of specimens. hydration heat (J/g) LS LS LS CH C E E E E CH C C C CH-Ca(OH) 2 E AFt C CaCO 3 90days cement based products. It has been identified as a deterioration compound in historical buildings and as the last stage of deterioration in marine structures. Limestone powder is the source of CO 2 3 ions which is required component in formation of thawmasite. SO 2 ions are created in hydration surrounding of alite-barium calcium sulphoaluminate cement. So it is possible that thaumasite is formed when limestone powder is mixed into alite-barium calcium sulphoaluminate cement. However, there is no diffraction peak of thaumasite in XRD pattern when curing age is 90 days. Therefore, limestone powder is safe to alite-barium sulphoaluminate cement. The long term effect of limestone powder requires furthermore observation. In experiment the hydration heat liberation rate curves and hydration heat of LS and blank specimens within 55 h are illustrated in Fig. 3. As shown from Fig. 3 it is seen that two thermopositive peaks appear in blank specimen. One sharp peak appears in a few minutes at the beginning of the hydration process. Another peak appears from 6 h to 20 h. Similarly, there are two thermopositive peaks in LS specimen. But the two peaks all come earlier than that of blank specimen. This indicates that slag and limestone powder shorten the induction period and promoted final setting time. C 3 S hydration will release plenty of Ca 2+ ions, and transportation velocity of Ca 2+ ions is higher than that of SiO 2 ions group. According to the principle of absorption, the physical adsorption appears when the Ca 2+ ions spread to surface of CaCO 3 and slag gain. For the physical adsorption, Ca 2+ ions concentrating in the vicinity of C 3 S grain decreases. This will promote C 3 S hydration. Meanwhile, the physical adsorption of CaCO 3 and slag gain will promote the formation of CH crystal nucleus. That is to say, the CH Fig. 2. XRD patterns of the hardened cement pastes. 3days 28days 90days AS-28days LS2-28days AS-3days LS2-3days Temperature ( ) Fig.. DSC curves of hardened cement pastes. LS2-3days LS2-28days -3days -28days formation velocity of CH increases, so the cement induction period is shortened. As shown from Fig. 3, the hydration heat of LS specimen is much lower than that of blank specimen. Slag and limestone powder decrease sharply the hydration heat of cement, especially for the early hydration heat Activated mechanism slag and limestone powder in cement For the existence of C 2:75 B 1:25 A 3 S mineral, due to the high concentration of OH and SO 2 ions in its hydration circumstance, has dual priming action of alkali-activated effect and sulfateactivated effect on slag. Alkaline activated mechanism is described as follows. Ca(OH) 2 (CH) is formed firstly, which is one of important hydration products for C 2 S and C 3 S. Slag particle surface would absorb much of OH ions. This results in the damage of oxygen silicon tetrahedron skeleton for slag and the release of SiO, AlO 2 and Ca 2+ ions from slag. Secondly, Ca 2+, SiO and OH ions in water solution will react and form calcium silicate gel. Ca 2+, AlO 2 and OH ions in water solution will react and form calcium aluminate gel. In addition to alkaline activated mechanism, sulfate activated is another activated mechanism for slag. The earlier stag of sulfate activated mechanism is the same as that of alkaline activated mechanism. In the later stage, Ca 2+, AlO 2, OH and SO 2 ions in solution will form ettrigate. These two activated effects are connected with the amount change of SO 2 ions and CH. If the amounts of SO 2 ions and CH for specimen with slag are much lower than that of blank specimen in the later hydration

230 W. Shoude et al. / Construction and Building Materials 35 (2012) 227 231 Fig. 5. SEM EDS analysis of LS specimen. age, SO 2 ions and CH will react with slag.

4 230 W. Shoude et al. / Construction and Building Materials 35 (2012) Fig. 5. SEM EDS analysis of LS specimen. age, SO 2 ions and CH will react with slag. It is concluded that slag is activated effectively in hydration surrounding. After the examination, the sulfate amount of LS specimen for 1 day and 90 days are 3.65 mg/g and mg/g. Meanwhile, the sulfate amount of blank specimen for 1 day and 90 days are mg/g and 3.83 mg/g. Therefore, the sulfate amount of LS specimen is comparable to that of blank specimen when hydration age is 1 day. But the sulfate amount of LS specimen is much lower than that of blank specimen when curing age is 90 days. Furthermore, the amount of CH for LS specimen decreases sharply in the later curing age. The DSC curves of LS and blank specimens curd for 3 days and 28 days are shown as Fig.. From Fig. it can be seen that the DSC curves of LS and blank specimens curd for 3 days and 28 days are almost the same. These two specimens cured for 3 days and 28 days all have two obvious endothermic peaks. The first peak is the dehydration peak of C S H gel and AFt at C, which is usually formed by adsorption water and combined water. The second peak is the dehydration peak of CH at C. As shown from Fig. 3, the endothermic peak area of CH of LS specimen cured for 3 days is larger than that of LS specimen cured for 28 days. Undoubtedly, this reason is that slag has reacted with CH and decreases the amount of CH. Some studies [6,13 15] suggested that limestone powder has possibility to react with C 3 A to form calcium carboaluminate hydrate when it is mixed with cement for a long time. Calcium carboaluminate hydrate had two crystalline forms (C 3 A3Ca CO 3 32H 2 O and C 3 ACaCO 3 11H 2 O). Whereas, the diffraction peak of calcium carboaluminate hydrate of LS specimen with 90 days curing age is not found in XRD pattern. The reason is that the amount of calcium carboaluminate hydrate was small. Its diffraction peak is not obvious in XRD pattern. The SEM EDS analysis of LS specimen is illustrated in Fig. 5. As shown from Fig. 5, limestone powder and hydration products are closely linked. It indicates that limestone powder with filling effect and tiny aggregate effect can improve the mechanical performance of concrete.. Conclusions The experimental results show that the water requirement and setting time of alite-calcium barium sulphoaluminate cement decrease when the ratio of slag to limestone decreases. The compressive strength of cement specimen cured for 90 days is higher than that of pure cement, when the added mixed material ratio of slag to limestone powder is 3:2. Slag and limestone powder prompt the second exothermic peak to appear beforehand and shorten induction period. Slag and limestone powder decrease rapidly hydration calorimetric of cement, especially for its early hydration calorimetric. Alite-calcium barium sulphoaluminate cement has dual priming action of alkali-activated effect and sulfate-activated effect on slag. Acknowledgments This work is supported by National Natural Science Foundation of China (No and ), Science and Technology Plan for Shandong Province College (J11LD01) and School Key Foundation of University of Jinan (XKY1002). References [1] Cheng X, Lu L, Wang L, Chang J, Liu F, Chen Y, et al. Study on mineral system of alite calcium barium sulphoaluminate with good binding characteristic. J Chin Ceram Soc 200;32: [2] Lu L, Chang, Shen Y, Yu L, Cheng X, Liu H, et al. Research on preparation technology of alite-c 2:75 B 1:25 A 3 S cement material. Bull Chin Ceram Soc 200;5: [3] Lu L, Chang J, Shen Y, Cheng X, Liu H, Yuan R. Synthesis and mechanical performance of alite-calcium barium sulphoaluminate cement. J Chin Ceram Soc 2005;33: [] Wang L, Lu L, Cheng X. Development of composite cement materials on Portland and sulphoaluminate minerals. J Jinan Univ 200;18:2 7. [5] Cheng X, Chang J, Lu L, Liu F, Teng B. Study on the hydration of Ba-bearing calcium sulphoaluminate in the presence of gypsum. Cem Concr Res 200;3: [6] Cochet G, Sorrentino F. Limestone filled cements: properties and uses. In: Sarkar SL, Ghosh SN, editors. Mineral admixtures in cement and concrete, vol.. ABI Books; p [7] Neto C, Campiteli V. The influence of limestone additions on the rheological properties and water retention value of Portland cement slurries. ASTM 1990;106:2 9. [8] Livesey P. Performance of limestone-filled cements. In: Swamy RN, editor. Blended cements in construction, London: Elsevier; p [9] Bertrandy R, Poitevin P. Limestone filler for concrete, French research and practice. In: Swamy RN, editor. Blended cements in construction, London: Elsevier; p [10] Sprung S, Siebel E. Assessment of the suitability of limestone for producing Portland cement (PKZ). Zem Kalk Gips 1991;:1 11.

5 W. Shoude et al. / Construction and Building Materials 35 (2012) [11] ZelicÂ J, KrstulovicÂ R, TkalcÏec E, Krolo P. Durability of the hydrated limestone silica fume Portland cement mortars under sulfate attack. Cem Concr Res 1999;29: [12] Sawicz Z, Heng S. Durability of concrete with addition of limestone powder. Mag Concr Res 1996;8: [13] Negro A, Bachiorrini A, Cussino L. Interazione carbonato di calcio Ð alluminati. In: Murat M, Bachiorrini A, Guilhot B, Negro A, Regourd M, Soustelle M, editors. Alluminati di calcio, Seminario Internazionale; p [1] Tsivilis S, Chaniotakis E, Badogiannis E, Pahoulas G, Ilias A. A study on the parameters affecting the properties of Portland limestone cements. Cem Concr Compos 1999;21: [15] Ramachandran V, Chun M. Influence of CaCO 3 on hydration and microstructural characteristics of tricalcium silicate. II Cem 1986;83: [16] Ramachandran V. Thermal analyses of cement components hydrated in the presence of calcium carbonate. Thermochim Acta 1988;127: [17] Chloup-Bondant M, Edvard O. Tricalcium aluminate and silicate hydration. Effect of limestone and calcium sulfate. In: Colombet P, Grimmer A-R, Zanni H, Sozanni P, editors. NMR spectroscopy of cement-based materials. Springer Verlag; p [18] Pera J, Husson S, Guilhot B. Influence of finely ground limestone on cement hydration. Cem Concr Compos 1999;21: [19] Irassar E, Bonavetti V, Trezza M, et al. Thaumasite formation in limestone filler cements exposed to sodium sulphate solution at 20 C. Cem Concr Compos 2005;27:77 8. [20] Irassar E, González M, Rahhal V. Sulphate resistance of type V cements with limestone filler and natural Pozzolana. Cem Concr Compos 2000;22: [21] Persson B. Sulphate resistance of self-compacting concrete. Cem Concr Res 2003;33:

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