Usage of molasses in concrete as a water reducing and retarding admixture

Transcription

1 Indian Journal of Engineering & Materials Sciences Vol. 19, December 2012, pp Usage of molasses in concrete as a water reducing and retarding admixture Hasan Yildirim* & Baris Altun Material Science Division, Faculty of Civil Engineering, Istanbul Technical University, 34469, Maslak, Istanbul, Turkey Received 5 July 2011; accepted 28 September 2012 Molasses is a by-product material like lignosulphonate, which is obtained from paper and sugar industries. Molasses shows plasticizing effect in concrete. In this study a comparison is made between molasses with 40% purity grade and lignosulphonate with respect to the improvements in properties of concrete. Three molasses obtained from different sugar factories are used in this study at two admixture dosages, such as 0.4% and 0.7% of cement dosage. Two types of concretes are prepared with two cement dosages, such as 270 and 320 kg/m 3, respectively. The workability and setting times are determined at the fresh state and both compressive and flexural strength properties are measured on hardened concretes. Furthermore, durability properties are compared by using capillary and sulphate resistance tests. Molasses can be used as a Type D, if initial and final setting times and compressive strengths at 35 and 125 days which are measured in this work, are considered, and can be used as Type A because of reducing the dosage of admixture, in concrete in accordance with ASTM C 494 standard. Keywords: Molasses, Water reducing, Retarding admixture, Lignosulphate Molasses is a by-product of sugar industry, which uses beet in the production. Like lignosulphonate, which is a by-product of paper industry, molasses also shows plasticizing properties in concrete. Furthermore, due to the existence of sugar in molasses, it exhibits retarding effect in fresh concrete. Molasses has been used in many industries as raw material, like animal food industry, in the production of alcohol, ferment and glycerin 1-3. In Turkey there are 27 sugar factories, which process sugar beet to obtain sugar. At the end of various refining processes a dark-brown syrup, which is called molasses is obtained in sugar industry. Molasses consist of 50% sucrose, 30% of other sugars (ash and nitrous materials) and 20% water approximately. About 4-8% of beet remains as molasses after the process. The composition of molasses differs depending on the source it has been obtained, such as from reed or beet. Reed molasses, which have invert sugar, has lower nitrogenous material than molasses of beet 4. Pigments of molasses are surfactants and electronegative colloids that contain unsaturated groups, hydroxyl groups, and carboxyl groups. Pigments of beet molasses contain % products of alkaline hydrolysis of inverted sugar, % melanoidins, and % caramels 5. These *Corresponding author ( yildirimhasan63@hotmail.com) components have an important effect on the plasticizing property of molasses. Although the number of studies on the usage of molasses in concrete is limited, there are some studies about the effect of sugar on the properties of concrete. Addition of sugar in concrete in small amounts delays the hydration reaction of cement 6-8. The concretes made with sugar addition show strength reduction at early ages, but their later age strengths might be higher 9,10. For example, sucrose, which has five members ring, is classified as non-reducing sugar and may retard the initial setting of cement from 1000 to 8000 min and final setting from 1400 to min 7,8. Although there is divergence of opinion among researchers as to what cause the retardation effect, the most commonly accepted opinion is its calcium binding and complexing ability 9,11. Sucrose is produced from agricultural plants of reed and beet. Haworth formulation of the sucrose (α-d-glukopiranozido-β-dfruktofuralozid) is given in Fig Fig. 1 Haworth formulation of sucrose

2 422 INDIAN J ENG. MATER. SCI., DECEMBER 2012 Experimental Procedure Materials Cement Ordinary Portland cement (OPC) was used for the concretes. The properties of CEM I 42.5 are given in Table 1a-1c. The tests were carried out according to the EN 196 standard. Aggregates Crushed limestone with maximum aggregate size of 16 mm was used as coarse aggregate. Sea sand and crushed stone sand were used as fine aggregates. The grading of the aggregate mixture is presented in Table 2. Admixture A lignosulphonate-based water reducer (ASTM C 494 Type A) and molasses from three different sources, such as Konya, Susurluk and Bor sugar factories of Turkey, were used as plasticizer admixture. All three of molassesbased and lignosulphonate-based admixtures were including 40% efficient material by weight. Density of the lignosulphonate and molasses-based admixtures were 1.19 g/dm 3 and 1.20 g/dm 3, respectively. Sucrose ratios of Table 1a The physical properties and chemical analysis of cement Density (g/cm 3 ) 3.18 Specific surface area (blaine) (cm 2 /g) 3030 Initial setting time (h:min) 3:00 Final setting time (h:min) 3:45 Le Chatelier opening (mm) 1.0 Table 1b Norm compressive strength of cement Age (day) Concrete code Compressive strength (MPa) ,2 Cement (kg/m 3 ) Water (kg/m 3 ) Table 3 Mixing proportions of the concretes Aggregate (kg/m 3 ) Water reducing capacity (%) the molasses were 51.2% and 47.3% and 48.4% for Konya, Bor and Susurluk molasses, respectively. Mix design Fourteen series of concretes were prepared. Two different cement dosages were used in the concretes, such as 270 kg/m 3 and 320 kg/m 3. A series of concretes without admixture were produced as control mixtures. Two different admixture ratios, 0.4 and 0.7% of the cement by weight, were used in the production of admixture concretes. Lignosulphonate-based plasticizer and Konya molasses were used as admixtures for the concretes having cement dosage of 270 kg/m 3. Three types of the molasses with 40% purity grade and lignosulphonate were used with two different dosages in the concretes having the dosage of 320 kg/m and 320 kg/m 3 cement dosages were selected in the experiments because they are the most common dosages used in the production of C25 and C30 classes. Constant slump values were aimed. Water content was changed according to workability. The mixing proportions of the concretes are shown in Table 3. The code of concrete Table 1c Chemical composition of cement Component % SiO Insoluble residue 0.21 Al 2 O Fe 2 O CaO MgO 1.66 SO Cl Ignition loss 0.37 Table 2 Grading of the aggregate mixture Sieve size (mm) ,5 0,25 Passed (%) Admixture (%) Admixture (kg) Slump (cm) Base of admixture 270C ,0 0,00 16 Control specimen 270L ,4 1,08 14 Lignosulphonate 270K ,4 1,10 15 Konya molasses 270L ,7 1,89 15 Lignosulphonate 270K ,7 1,90 17 Konya molasses 320C ,0 1,00 13 Control specimen 320L ,4 1,29 15 Lignosulphonate 320K ,4 1,30 15 Konya molasses 320B ,4 1,30 15 Bor molasses 320S ,4 1,29 14 Susurluk molasses 320L ,7 2,26 16 Lignosulphonate 320K ,7 2,27 15 Konya molasses 320B ,7 2,27 16 Bor molasses 320S ,7 2,25 14 Susurluk molasses

3 YILDIRIM & ALTUN: USAGE OF MOLASSES IN CONCRETE 423 indicates the dosage, the type of admixture (L: lignosulphonate; B: Bor, K: Konya, S: Susurluk molasses) and the usage ratio of admixture, respectively. As an example 270L04 shows; the concrete produced with cement dosage of 270 kg/m 3 and with lignosulphonate dosage of 0.4%. Water reducing capacity, which is shown in the fourth column of the Table 3, is the ratio of reduced water to the initial water for the admixtured mixtures at the same workability. Figure 2 shows that for the concrete of 320 dosages LBA reduces more water than MBA. However, for the concrete of 270 dosages MBA is better water reducer than LBA. Because of water requirement (5% limit), all of mixtures with molasses conformed to the EN and ASTM C494. Test procedure Prismatic specimens with the dimensions of cm and cube specimens with the dimensions of cm were prepared for the tests. Compressive strength, flexural strength, ultrasonic pulse velocity and according to DIN standard method, capillarity tests were carried out on the specimens at 35 and 125 days. Vicat setting time tests were also applied on the pastes, which were including the admixtures. All the concrete specimens were cured in 23±2 C lime saturated water during 35 days after casting. After 35 days some of the specimens were transferred into 10% Na 2 SO 4 solution (by weight) and stored there up to 125 days. According to ASTM C 1012, standard test method for length change of hydraulic-cement mortars exposed to a sulphate solution, sulphate attack test takes longer time with sulphate solution with 5% concentration. In this study, solution concentration was determined as 10% to decrease the test time. The ph value of solution was kept constant at 9.5~11.5. Results and Discussion Fresh properties For the same workability, water reducing capacity of the molasses-based admixture (MBA) is higher than the lignosulphonate-based admixture (LBA) for 270 kg/m 3 dosage concrete. Konya MBA reduces 9-13% water when LBA 4-11% for 270 content concretes at the admixture dosage ratios of 0.4 and 0.7, respectively. However, for the concretes with the cement dosage of 320 kg/m 3, MBAs are not as efficient as those for the lower dosage concretes. It is known that when aggregate concentration decreased, increase in cement dosage increases the compressive strength less than high aggregate concentration. MBAs at 0.4% dosage reduced the water 5-7% when LBA 11% for the same workability of 320 kg cement contents. The higher ratios of admixtures have caused the higher water reducing as expected. When the admixtures are used as 0.7%, the water reductions of admixtures are 7-10% and 13% for MBAs and LBA, respectively. Test results show that the molasses are different from each other for water reducing capacity. Setting times of the cement pastes, which were produced with dosages of 0.4% and 0.7% for four types of admixtures, are given in Table 4. Paste codes indicate the type of the admixture and the dosage respectively. Normal consistency water of the cement was taken into consideration in preparation of the pastes for setting time test. Setting times tests were applied by vicat needle apparatus in accordance with ASTM C191. All the admixtures, which were used in the concrete mixtures, cause the retardation on setting times. Setting times are getting longer with increase of admixture ratio in cement paste. Retardations in setting times of concretes having sucrose are well known 8,9, The same retardation effect is expected from molasses due to its sucrose content. Molasses-based admixtures are delaying final setting times up to 16:30 h while control paste has only 5 h. Fig. 2 Water reducing capacities

4 424 INDIAN J ENG. MATER. SCI., DECEMBER 2012 Hardened concrete properties Strength results Compressive strength test results are given in Fig. 3. All the concretes having admixture except 320 dosages and 0.4% MBA has higher compressive strengths than the control specimens for 35 days. Increase in compressive strength is due to decreasing of w/c ratios of the concretes with admixture. The usage of MBA causes to decrease of compressive strengths with respect of LBA for 320 dosage concretes. As mentioned above, molasses does not decrease the w/c ratio for 320 kg/m 3 dosage concrete as much as 270 kg/m 3 one especially at the lower usage dosage. Additionally, LBA is more effective Table 4 Setting times of the pastes Paste Code Initial setting (h:m) Final setting (h:m) Control 3:15 5:00 L04 3:40 6:00 K04 10:00 16:10 B04 8:30 16:30 S04 9:45 15:30 L07 5:10 9:30 K07 12:00 16:30 B07 11:50 16:30 S07 11:50 15:30 Fig. 3 Compressive strength test results than MBA for the concretes of 320 dosages. This could be the cause for strength loss of MBA concretes according to LBA concretes. The compressive strengths are not changed significantly at 125 days with respect of 35 days test results for 320 dosages with 0.4% usage MBA concrete mixtures. They are showing the same trend with the results of 35 days water cure. Flexural strength test results are shown in Fig. 4. All the concrete mixtures produced with admixtures have higher flexural strengths than the control specimens. Concretes with MBA have also displayed higher strengths than the specimens with LBA. As a difference from the compressive strength test results, flexural strengths at 125 day for water cure showed increase with respect to 35 day test results. Sulphate attack The strengths of concretes stored in sulphate solution are given in Figs 3 and 4. It seems that the compressive strengths do not show any deterioration in 125 day storage period in sulphate solution. Similarly, it was reported that any damage has not been observed at the end of 19 weeks storage time in sulphate solutions When the flexural strengths are considered even sulphate solution-stored specimens exhibited higher strengths than those of water-cured specimens for the same period of time. This behavior may be due to the filling effect of sulphate salts in the pores before ettringite formation. When the ultrasonic pulse velocities, which are presented in Fig. 5 are studied, it is seen that there is not a significant difference between the admixturedconcretes and control specimens. Capillary results Coefficients of capillary of the concretes are given in Fig. 6. The coefficients of the control specimens Fig. 4 Flexural strength test results Fig. 5 Ultrasonic pulse velocity test results

5 YILDIRIM & ALTUN: USAGE OF MOLASSES IN CONCRETE 425 are much greater than the admixture-concrete specimens as shown in Fig. 6. Although usage of water reducing admixtures decreases the capillary due to lower w/c ratio, the reduction in capillary is higher for the molasses added concretes than those of lignosulphonate concretes. The coefficients of the capillary for MBA concretes are 40-45% lower than those of control mixtures while 10-14% lower for LBA concretes. The relations of coefficients of capillary with setting times are given in Figs 7 and 8, for 270 and 320-dosage concretes, respectively. It seems that for admixture added concretes longer the setting time, lower the coefficient of capillary. The decrease of capillaries with increase in setting times can be due to the slow hydration process and formation of more homogeneous internal structure, hence modification of capillary pores in MBA concretes. Conclusions The following conclusions can be drawn from this study: (i) Fig. 6 Capillary test results Fig. 7 Coefficient of capillarity and setting times for 270 dosage concrete Usage of molasses as a plasticizer in concrete is satisfying the ASTM C standard for water reduction criteria. Fig. 8 Coefficient of capillarity and setting times for 320 dosages concrete (ii) Molasses can be used as a Type D and by reducing the dosage of admixture it can be used as Type A in concrete in accordance with ASTM C 494 standard. (iii) Usage of lignosulphonate and molasses-based plasticizers causes to reduction of the coefficient of capillary due to increase in setting times as well as decrease in w/c ratios. (iv) Molasses-based plasticizers are more effective on reducing of capillary coefficient than lignosulphonate-based plasticizers. (v) Some strength difference among samples is far from the w/c development trend. In this study, molasses with 40% purity grade was used to prevent the other interaction. 0.7% is high amount and molasses, which is used to obtain this amount, can cause to harmful effects like air entrainment. To prevent decrease of the strength because of these effects, using of some chemicals in producing of molasses can be effective. (vi) Molasses are effective on retarding of setting times. The high retarding effect should be taken into consideration for molasses concretes. (vii) Molasses added concretes do not show any different behavior than lignosolphonate concretes in sulphate solution for 125 days storing time. (viii) According to these results, it s clear that molasses has water reducing and retarding effect on concrete. To use molasses as water reducing and retarding admixture, some additives like triethylamine, can be added to molasses. References 1 Gorgulu F, Beet Paste and Molasses in Feeding Animals (Guven Press, Ankara), 1967, (in Turkish). 2 Leblebici M J & Kavas M F, Handbook of Quality Control Laboratory, (Turkey Sugar Factories Co. Analytical Branch Press, Ankara) 2000), (in Turkish).

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