Utilization of beet molasses as a grinding aid in blended cements

Construction and Building Materials 25 (2011) 3782–3789

Contents lists available at ScienceDirect

Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Utilization of beet molasses as a grinding aid in blended cements Xiaojian Gao a,b,⇑, Yingzi Yang a, Hongwei Deng a a b

School of Civil Engineering, Harbin Institute of Technology, Harbin 150006, China ACBM Center, Northwestern University, Evanston, IL 60208, USA

a r t i c l e

i n f o

Article history: Received 2 December 2010 Received in revised form 24 March 2011 Accepted 14 April 2011 Available online 29 April 2011 Keywords: Blended cements Grinding aid Beet molasses Strength Microstructure

a b s t r a c t This paper investigates the viability of using beet molasses as a grinding aid for blended cements with high volumes of mineral admixtures. Different ratios of beet molasses (0.01–0.05% by weight of cement) were added into a blended cement containing 41% of fly ash and GBFS. The influence of beet molasses on performances of blended cement was studied by comparing with one commercially available, triethanolamine-based grinding aid (TA). The results show that when comparing with the blank cement mixture, the cement containing 0.02–0.03% molasses shows a higher compressive strength at 3 days and 28 days, even exceeding the TA mixture. The improved microstructure of the molasses modified cement paste was also demonstrated by the pore structure and SEM measurements. These improvements are attributed to the better particle size distribution induced by the addition of molasses, indicating the potential application of beet molasses as a good grinding aid. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction Beet molasses is a by-product of the beet sugar production. It is a thick non-transparent from brown to dark-brown liquid with particular smell and sweet taste and bitter after-taste, fully soluble in hot and cold water. The composition of molasses is variable; depending on the quality of sugar beet and processing technology, its composition varies in the following ranges: dry substances, 76– 84% (including sucrose, 46–51%); reducing substances, 1.0–2.5%; raffinose, 0.8–1.2%; inverted sugar, 0.2–1.0%; volatile acids, 1.2%; pigments, 4–8%; and ash, 6–10% [1]. China has a very large annual production of beet sugar as much as about 901,300 tons (in 2008), and more than 300,000 tons of beet molasses is discharged every year. Serious environment problems including air, soil and underground water pollution maybe happen if the untreated molasses is exhausted outside or leaks from the container. Most of sugar factories are recycling beet molasses as a raw material for ethyl alcohol production, but the distilleries produce very large amounts of vinasse and waste water, which are difficult to dispose of [2]. After a complex pretreatment to remove heavy metals, beet molasses has been used in producing pullulan and bakery yeast [3]. In Western countries, molasses has been also used as fodder for livestock without any adverse environment problem, but little amount is recycled in this way in China. In addition, a great amount of molasses has been used in cement concretes as a water-reducing and retarding admixture in several countries [4,5]. ⇑ Corresponding author. Address: P. O. Box 1430, Civil Building, Harbin Institute of Technology, 66 West Da-Zhi Street, Harbin, 150006, China. Tel./fax: +86 451 86281118. E-mail address: [email protected] (X. Gao). 0950-0618/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2011.04.041

Cement is one of the most important building materials that hold other ingredients together to produce concrete. However, the cement industry is also a significant contributor to global carbon dioxide (CO2) emissions [6]. Cement production is an energyintensive process and the production of every ton Portland cement releases approximately 1 ton of carbon dioxide [7]. It was reported that cement manufacturing is responsible for 5–7% of total worldwide CO2 anthropogenic emissions [8]. Except for energy efficiency improvement [9], new processes, a shift to low carbon fuels, application of waste fuels [10], the incorporation of mineral admixtures to partially replace cement clinker has the greater potential to reduce costs, conserve energy, and minimize industrial wastes. Many mineral admixtures, such as fly ash, calcined clay, microsilica, limestone powder, granulated blast-furnace slag, natural zeolite etc., have been used in this way to produce blended cements for many years in different countries [11–14]. And the combination of two or three kinds of mineral admixtures has emerged as a superior choice over single admixture to improve cement comprehensive properties and to increase the total replacement of mineral admixtures [15–18]. Among these blended cements with various combinations of two or three mineral admixtures, the fly ash-granulated blast-furnace slag blended cement has been the most commonly and massively produced one in China due to its lower cost and higher waste minimization. Although such blended cements present the improved longterm strength and durability [19], the strength development at early age is typically slower than that of OPC especially at a higher level of replacement of fly ash [20]. This shortcoming, to some extent, restricts the application of the blended cement. Several chemicals such as triethanolamine (TEA), diethanol-isopropanol-

3783

X. Gao et al. / Construction and Building Materials 25 (2011) 3782–3789 Table 1 Chemical composition of raw material (wt.%). Name

CaO

SiO2

Al2O3

Fe2O3

MgO

K2O

Na2O

SO3

LOI

Clinker Slag Fly ash Gypsum

65.3 41.85 6.26 37.6

21.99 37.65 60.74 2.41

4.81 9.83 20.55 0.98

3.66 1.0 4.78 –

0.85 6.96 1.21 0.48

0.71 0.8 2.44 –

0.24 0.18 0.94 –

0.54 1.28 0.43 34.5

1.77 0 1.21 23.47

100

1000

100

1000

Table 2 Chemical compositions of molasses. Purity (%)

pH

65.7 66.8

63.1 62.8

6.6 6.7

Invert sugar (%)

Raffinose (%)

Betain (%)

0.25 0.23

0.76 0.82

2.2 2.1

amine (DEIPA), calcium chloride (CaCl2) and sulfates (Na2SO4 or gypsum) can be used as activation agents to improve early age strength of blended cements [21–23]. Unfortunately, the addition of these ingredients will lead to a higher cement manufacturing cost or introduce a great deal of detrimental ions (Cl , Na+ and SO24 ) in cement that aggravate the durability of concrete structures [24]. On the other hand, the early age strength of the blended cement can be improved by a higher fineness of clinker or mineral admixtures [25,26]. Many chemicals called grinding aids have been researched to improve the grinding efficiency of cement. These chemicals include triethanolamine, mono- and di-ethylene glycols, oleic acid, organosilicones, organic acetates, carbon blacks and calcium sulfate [27]. Of these, triethanolamine or triethanolaminebased mixture is the most commonly used one in cement industries in China. Triethanolamine is very expensive (20,000 RMB per ton) and it seems not as effective as expected for the intergrinding production of blended cements because blast-furnace slag particle has a higher hardness and less grindability than clinker. The separate grinding maybe a good choice [28], but it needs very high investment for new milling equipments. Therefore, selecting a cheap and efficient grinding aid becomes urgent and significant for many medium-sized cement manufacturers to increase the mineral admixture replacement and improve the early age strength of blended cements. The purposes of this paper were to investigate the possibility of beet molasses used as grinding aid for fly ash-granulated blast-furnace slag blended cements. The particle distribution, setting time, mechanical strength development and microstructure of the blended cements with and without beet molasses were analyzed. And the suitable addition content of beet molasses was suggested. Therefore, the results are helpful for reducing cement production costs, decreasing the environment pollution from storage of fly ash, granulated blast-furnace slag and beet molasses. 2. Material and methods 2.1. Raw materials and cement proportions Four types of raw materials used for blended cements were: Portland cement clinker from one plant of Liaoyuan Jingang Cement Group, granulated blast-furnace slag (GBFS) from Anshan Iron and Steel Group Corporation, fly ash from Daqing

Cumulative passing (%)

A B

Brix (%)

80

Control

TA

60

40 20

0 0.1

1

10

Particle size (µm)

(b) 100 Control

Cumulative passing (%)

Molasses

(a) 100

Ma-2

80 60

40 20

0 0.1

1

10

Particle size (µm) Fig. 1. Cumulative particle size distribution curves of blended cements. (a) Control and TA samples. (b) Control and Ma-2 samples.

Oilfield Power Plant, gypsum from one factory in Shandong province. The chemical compositions of them are shown in Table 1. A commercially available, triethanolamine-based grinding aid (TA) was also used in the form of brown and black liquid. It has a density of 1.12–1.20 and pH value of 9.80–11.80. Its recommended dosage is 0.03–0.04% of the total raw material by weight. Two molasses samples were respectively collected from Wangkui (Ma) and Yian (Mb) branch companies of Botian Sugar Co., Ltd. in China. The chemical compositions of two molasses are given in Table 2. Chinese ISO standard sand conforming to Chinese standard GB/T 17671-1999 was used for measuring mechanical performances of cements. The control cement mixture was selected after large numbers of tests, with the weight ratio of clinker: fly ash: GBFS: gypsum: 53:26:15:6. On the basis of the control cement mixture, different amounts of TA, Ma and Mb were added as grinding aids (by weight of the total cementitious materials): 0.03% for TA, 0.1–0.5% for Ma and Mb respectively. As shown in Table 3, 12 different blended cements were prepared.

Table 3 Different amounts of grinding aids added in blended cements. Number

Control

TA

Ma-1

Aid type Amount (%)

None 0

TA 0.03

Ma 0.01

Ma-2 0.02

Ma-3 0.03

Ma-4 0.04

Ma-5

Mb-1

Mb-2

Mb-3

Mb-4

Mb-5

0.05

Mb 0.01

0.02

0.03

0.04

0.05

3784

X. Gao et al. / Construction and Building Materials 25 (2011) 3782–3789

Table 4 Particle size distribution and Blaine specific surface area. Particle size (lm)

Control

TA

Ma-1

Ma-2

Ma-3

Ma-4

Ma-5

Mb-1

Mb-2

Mb-3

Mb-4

Mb-5

<3 3–32 32–65 P65 Blaine value (m2/kg)

12.04 59.11 23.32 5.53 380

14.07 57.74 24.38 3.82 398

13.47 59.8 23.94 2.78 410

13.94 60.82 23.28 1.96 415

13.37 61.29 23.28 2.06 411

13.44 60.2 23.85 2.51 407

13.6 59.9 23.9 2.6 403

13.72 59.72 23.76 2.8 407

13.86 60.63 23.35 2.16 412

13.57 61.35 23.16 1.92 416

13.56 60.14 23.85 2.45 408

13.7 59.97 23.78 2.55 405

(a)

(c)

(e)

(b)

(d)

(f)

Fig. 2. SEM of blended cements with different grinding aids. (a) Control cement (200). (b) Control cement (1000). (c) TA cement (200). (d) TA cement (1000). (e) Ma-3 cement (200). (f) Ma-3 cement (1000). 2.2. Test methods A laboratory ball mill was used to grind blended cements containing different grinding aids as described in Table 3. Clinker, granulated blast-furnace slag and gypsum were crushed into small particles with 2–3 mm diameters prior to grinding procedure. To improve the weighing accuracy and dispersion of grinding aid in

cement mixture, every grinding aid was evenly diluted by ten times with fly ash before adding into the mill. The total feed weight was 5 kg per mill and the grinding time was kept the same as 30 min for every cement. The particle size distribution of grinded cement was tested by the means of laser granulometry. The Blaine specific surface area was also measured according to the standard method of GB/T 8074-2008. The normal consistency water require-

3785

X. Gao et al. / Construction and Building Materials 25 (2011) 3782–3789 Table 5 Normal consistency and setting time of blended cements. Number

C

TA

Ma-1

Ma-2

Ma-3

Ma-4

Ma-5

Mb-1

Mb-2

Mb-3

Mb-4

Mb-5

w/c for normal consistency (%) Setting time (min) Initial Final

31.2 204 251

32.6 195 238

32.6 220 270

33.1 231 276

33.0 261 324

32.2 267 325

32.0 275 347

32.8 241 289

32.8 214 281

33.0 226 306

31.9 255 335

31.5 295 366

(a)

10 TA-28d

Flexural strength (MPa)

9 8 7

Ma-3d

Ma-28d

Mb-3d

Mb-28d

3. Results and discussion

6 TA-3d

3.1. Particle size distribution

5 4

0

0.01

0.02

0.03

0.04

0.05

0.06

Adding content (%)

Compressive strength (MPa)

(b)

Particle shapes and size distribution of grinded blended cements were observed with a scanning electron microscope (SEM). The cement paste samples with water to ratio of 0.5 were prepared for pore size distribution and microstructure measurements. A JEOL SX-4 scanning electron microscope (SEM) was used and the accelerating voltage was maintained at 25 kV for particle shape observation or 20 kV for microstructure of cement paste. Pore size distribution test was carried out by using a IV 9510 mercury intrusion porosimeter (MIP) with a pressure range from 0 to 60,000 psi (414 MPa), capable of measuring pore size diameter down to 3.0 nm.

55 TA-28d

45

35

Ma-3d

Ma-28d

Mb-3d

Mb-28d

TA-3d

25

15

0

0.01

0.02

0.03

0.04

0.05

0.06

Adding content (%) Fig. 3. Influences of molasses content on strength of blended cement. (a) Flexural strength. (b) Compressive strength.

Table 6 Strength of molasses modified cements and standard requirements. Cement No.

P.C42.5R Control TA Ma-2 Ma-3 Mb-2 Mb-3

Flexural strength (MPa)

Compressive strength (MPa)

3d

28d

3d

28d

P4.0 4.3 4.8 5.1 5.0 5.0 5.1

P6.5 8.5 8.8 9.2 9.1 9.0 9.1

P19.0 18.2 19.8 21.5 21.3 20.8 20.6

P42.5 46.5 47.8 50.7 50.5 49.3 50.0

ment and setting time were examined according to the standard method of GB/T 1346-2001. Mortar prisms (40  40  160 mm) were cast according to the same weight ratio of cement:sand:water: 1:3.0:0.5. After 24 h in a moist cabinet, they were removed from the mould and cured in water at room temperature (20 ± 2 °C). At the ages of 3 and 28 days, flexural strength of every mixture was measured on three prismatic specimens and then the compressive strength test was conducted on six pieces of prisms according to the Chinese standard GB/T 17671-1999.

The cumulative particle size distributions of the control, TA and Ma-2 samples are given in Fig. 1. Other molasses samples have particle size distribution curves similar to that of Ma-2. To further demonstrate the effects of different dosages of molasses on the particle size distribution of blended cement, the mass percent in four selected particle size ranges and Blaine specific surface area of every sample are also given in Table 4. GBFS is harder than clinker and fly ash and therefore more difficult to grind [29]. Thus, when clinker, fly ash and GBFS are interground, the finer portion of the blended cement is mostly ground clinker and fly ash whereas the coarser portion is mostly GBFS. For the control blended cement, it is observed that there are 71.15% of particles by weight below 32 lm and 5.53% above 65 lm. Many irregular coarse particles (bigger than 50 lm) like GBFS can be easily found in the control cement (shown as in Fig. 2a and b). Both particle size distribution test and SEM observations demonstrate that the blended cement was poorly ground without any additives. The addition of 0.03% amount of TA evidently increased the percentage of very fine particles (less than 3 lm) and decreased the coarse particles bigger than 65 lm as shown in Fig. 1a and Table 4. It can also been observed from SEM photos in Fig. 2 that the overall cement particles became finer due to the addition of TA. Compared with the control cement, the weight percentages of particles, smaller than 32 lm, increased to the maximum values (74.5–75.0%, over 3.0% higher than the control cement and much higher than TA sample) as the addition of molasses increased up to an optimum point (0.02% for molasses A and 0.03% for B), after which the weight percentages of particles in this range decreased a little. At the same time, the percentages of particles coarser than 65 lm were decreased to about 2.0% when 0.02 or 0.03% of molasses were added. It is shown in Fig. 2e and f that there is few big particles in cement with 0.02% molasses and recognizable GBFS particles are much smaller than those in the control cement, and even smaller than those in TA mixture. The same tendency can be found in the results of Blaine specific surface area in Table 4. Therefore, the addition of suitable amount of molasses (0.02– 0.03%) shows a better role to improve the grindability of blended cement, especially to reduce the GBFS particle size, than the addition of TA. In GBFS-fly ash blended cement systems, besides clinker, finely ground GBFS particles contribute to the early age strength development [30], whereas fly ash hydrates very slowly and is mostly beneficial to the long-term strength. Therefore, the addition of molasses is beneficial to improve the hydration reactivity of GBFS and consequently to increase the strength development of blended cements.

X. Gao et al. / Construction and Building Materials 25 (2011) 3782–3789

Incremental pore volume (mL/g)

(a) 0.160

361.3nm

0.140 0.120

112.8nm

0.100 0.080 0.060 0.040 0.020 0.000 100000

10000

1000

100

10

(b)

0.160

Incremental pore volume (mL/g)

3786

0.140

5.2nm

0.120 0.100

112.6nm

0.080 0.060 0.040 0.020 0.000 100000

1

298.7nm

10000

0.180

Incremental pore volume (mL/g)

0.160

(d)

113.1nm

Incremental pore volume (mL/g)

(c)

0.140 0.120 0.100 0.080

5.2nm

0.060 0.040 0.020 0.000 100000

10000

1000

100

1000

100

10

1

10

1

Pore diameter (nm)

Pore diameter (nm)

10

Pore diameter (nm)

1

0.180

113.1nm

0.160 0.140 0.120 0.100

299.8nm

0.080 0.060 0.040 0.020 0.000 100000

10000

1000

100

Pore diameter (nm)

Fig. 4. Pore size distribution of hardened cement pastes at 28 days. (a) Control. (b) TA. (c) Ma-2. (d) Ma-3.

3.2. Setting time and normal consistency The experimental results of normal consistency and setting time are shown in Table 5. The water-to-cement ratio (w/c) required for normal consistency of the cement paste increased with the addition of TA or molasses. And the water requirement reached the maximum values when the addition of two molasses was 0.02% or 0.03%; beyond these dosage points, the water requirement did not increase but decreased quickly with the increasing addition of molasses. This tendency can be explained by the development of cement particle fineness and specific surface with dosage of molasses. It was reported that sugar and molasses show some water-reducing effect in concrete [4], but the dosages of molasses in that study was as high as 0.25% or 0.50% of binder by weight. In another research [31], 4% and 5% water reductions were reported for the sugar dosages of 0.03% and 0.06%, respectively. Because the molasses contains high percentages of sugar, the abrupt decreasing water requirement should be partly attributable to the molasses water-reducing effect when the dosage of molasses is higher than 0.03%. As shown in Table 5, the initial and final setting times of blended cement were shortened by 9 and 13 min respectively when 0.03% of TA was used, being attributable to the increased fineness of cement. For the molasses cement mixtures, two opposite factors should be considered: the fineness improvement tends to reduce setting time; the addition of molasses prolongs the setting time due to its evident retarding effect [32]. The retarding effect showed more significant than fineness improvement, and both initial and final setting times of blended cement were delayed with the increasing addition of molasses. However, the most extended

finial setting time (366 min, 115 min longer than the control cement), when 0.05% of molasses B is used, is still much below 600 min as required by the cement standard. 3.3. Strength development The strength development is the most important property of cements and concretes. According to the Chinese standard GB/T 17671-1999, the test results of compressive and flexural strength at 3 days and 28 days are given in Fig. 3. The flexural strengths of blended cement at 3 days and 28 days were increased by 0.5 MPa and 0.3 MPa respectively and the compressive strengths were increased by 1.6 MPa and 1.3 MPa respectively when 0.03% of TA was added as a grinding aid. Both flexural and compressive strength of cement were increased as the addition of molasses increased to one threshold value (0.02% for molasses A and 0.03% for B), and then were decreased by the further increasing addition of molasses. When the addition of these two molasses were 0.02% or 0.03%, the cement flexural strengths at 3 days and 28 days were 0.7–0.8 MPa and 0.5–0.7 MPa higher than those of the control cement respectively; the compressive strengths were increased by 2.4–3.3 MPa and 2.8–4.0 MPa respectively. When the further higher content of molasses (0.04% and 0.05%) were added, both 3 days and 28 days strength were decreased, but the early age strength reduction was more pronounced than the later age strength due to the retarding effects of molasses. Therefore, a suitable content of molasses (0.02–0.03% by weight) is a more effective method than TA to improve the strength of blended cements. As shown in Table 6, the molasses modified cements have very satisfactory strengths, exceeding the requirement of the high early age strength

X. Gao et al. / Construction and Building Materials 25 (2011) 3782–3789

(a)

(c)

3787

(b)

(d)

Fig. 5. SEM photos of fractured surface of the control cement paste at 28 days. (a) Interface around big GBFS particle. (b) Fly ash sphere with smooth surface. (c) Sheets of Ca(OH)2 crystals. (d) Needle-like hydrates.

composite cement with strength grade of 42.5 (P.C42.5R) in the Chinese standard GB175-2007. 3.4. Pore size distribution Relationships between pore diameter and incremental pore volumes of the control, TA, Ma-2 and Ma-3 cement pastes at 28 days are shown in Fig. 4. For the control cement, there are two peaks of capillary pores locating at 361.3 nm and 112.8 nm. The TA cement paste has three peaks lower than those of the control paste which are 298.7 nm, 112.6 nm and 5.2 nm. The pore content and median pore diameter are 0.1662 ml/g and 216 nm for the control paste, and 0.1624 ml/g and 136 nm for the TA cement paste. These results suggest that the addition of TA effectively decreases the content of big capillary pores and improves the density of cement paste. The addition of 0.02% or 0.03% molasses by weight decreased the highest peak from 361.3 nm of the control paste to 113.1 nm, which was also much lower than the TA cement paste. And their median pore diameters are 114 nm and 129.6 nm, showing the significantly improved pore size distribution. Therefore, it can be suggested that molasses is more effective than TA for reducing the pore diameter of the paste. The decreased pore diameter is favorable to the strength development (as shown in Section 3.3) and the durability improvement of cements and concretes [24]. The reduction of pore size is due to the gradual filling of large pores from factors such as hydration reaction, packing effect and pozzolanic reaction of different components in blended cement. The hydration reaction occurs from the chemical constituents in clinker and water while the pozzolanic reaction occurs from the reaction of Ca(OH)2 with SiO2 and Al2O3 from GBFS and at late ages also from fly ash. The addition of molasses enhances the fineness of blended cement more effectively than the addition of TA as shown in Section 3.1, contributing to the higher hydration reaction of

clinker and pozzolanic reaction of GBFS particles. The packing of the fine, solid and spherically shaped fly ash particles, which are little reacted at early ages, fill the voids and allow denser packing within the particle of materials and matrix phase [33]. 3.5. SEM observations SEM micrographs of the fracture surface of the control cement paste specimen cured for 28 days are shown in Fig. 5, while those of the Ma-2 cement paste specimen at 28 days are presented in Fig. 6. The overall microstructure looks very dense for the control cement paste, some big GBFS particles as shown in Fig. 5a, however, are found to induce weak and porous interface zones around them due to the low reactivity. Although no big hexagonal plates of portlandite (Ca(OH)2) crystal was found due to the high replacement of clinker by mineral admixtures and pozzolanic reactions [34], some deformed portlandite crystals with sheet shapes were detected in the control paste ash shown in Fig. 5c. At the same time, a great quantity of needle-like hydrates grows on the clinker and small GBFS particles and fills in pores as shown in Fig. 5d. The pastes prepared from molasses or TA cements appeared to have a denser microstructure as shown in Fig. 6a, and no distinct difference can be found among them, hereafter only one typical molasses cement paste is discussed. As molasses was added in the blended cement, obvious pozzolanic reactions happened around the better grinded GBFS particles as shown in Fig. 6b. Several fly ash particles with a dissolved surface or a covering layer of pozzolanic reaction products were observed in this paste as shown in Fig. 6c, indicating an increased pozzolanic reactivity when molasses was added. No typical portlandite crystals were found in this paste. On the other hand, a denser and interconnected network of needle-like hydrates formed in the molasses cement paste as shown in Fig. 6d. Besides the improved particle size

3788

X. Gao et al. / Construction and Building Materials 25 (2011) 3782–3789

(a)

(b)

(c)

(d)

Fig. 6. SEM photos of fractured surface of Ma-2 cement paste at 28 days. (a) Dense microstructure. (b) Pozzolanic reaction of GBFS particle. (c) Pozzolanic reaction of small fly ash sphere. (d) Mutually connected needle-like hydrates.

distribution and pozzolanic reactivity, other factors may also work in the molasses cements that need further studies. In any case, the improved microstructure by addition of molasses results in the better strength development and long-term durability, and it will consequently accelerate the actual application of blended cements with high volume of mineral admixtures. 4. Conclusions The possibility of using beet molasses as a grinding aid for blended cements has been investigated in this study. It has been found that the addition of 0.01–0.05% molasses by cement weight can improve the particle size distribution and strength development of the blended cement. When comparing with the blank cement mixture, the cement containing 0.02–0.03% molasses shows a higher compressive strength at 3 days and 28 days, even exceeding those of the cement with TA as the grinding aid. However, the further higher content of molasses had no better improvement on the cement strength development due to the retarding effects on cement hydration. The results of pore structure and SEM observations show that the addition of suitable content of molasses decreases the pore size and improve the microstructure of the cement paste. These performance improvements are attributed to the better particle size distribution induced by molasses, and are favorable to the application of blended cements with high volume of fly ash and GBFS. On the other hand, the utilization of molasses as a grinding aid provides a new method to minimize the environment impacts of sugar industry. Acknowledgments This work was supported by a grant from the Innovative Talent Research Program of Harbin Science and Technology Bureau, China

(No. 2006RFQXG039). And the authors also thank the Cement Company, Kunlun Corporation Limited Company of Daqing Oil Field, China for the mechanical measurement. References [1] Bolobova AB, Kondrashchenko VI. Use of yeast fermentation waste as a biomodifier of concrete (review). Appl Biochem Microbiol 2000;36:205–14. [2] Vaccari G, Tamburini E, Sgualdino G, Urbaniec K, Klemes J. Overview of the environmental problems in beet sugar processing: possible solutions. J Cleaner Prod 2005;13:499–507. [3] Roukas T. Pretreatment of beet molasses pullulan production to increase. Process Biochem 1998;33:805–10. [4] Jumadurdiyev A, Ozkul MH, Saglam AR, Parlak N. The utilization of beet molasses as a retarding and water-reducing admixture for concrete. Cem Concr Res 2005;35:874–82. [5] Liu W, Liu Y, Liu S, Jiang X. The progress of research on treating molasses waste water and resources. China Res Compr Util 2009;27:39–41 (in Chinese). [6] Rehan R, Nehdi M. Carbon dioxide emissions and climate change: policy implications for the cement industry. Environ Sci Policy 2005;8:105–14. [7] Worrell E, Price L, Martin N, Hendriks C, Meida LO. Carbon dioxide emissions from the global cement industry. Ann Rev Energy Environ 2001;26:303–29. [8] Chen C, Habert G, Bouzidi Y, Jullien A. Environmental impact of cement production: detail of the different processes and cement plant variability evaluation. J Cleaner Prod 2010;18:478–85. [9] Worrell E, Martin N, Price L. Potentials for energy efficiency improvement in the US cement industry. Energy 2000;25:1189–214. [10] Walker N, Bazilian M, Buckley P. Possibilities of reducing CO2 emissions from energy-intensive industries by the increased use of forest-derived fuels in Ireland. Biomass Bioenergy 2009;33:1229–38. [11] Pandey SP, Singh AK, Sharma RL, Tiwari AK. Studies on high-performance blended/multiblended cements and their durability characteristics. Cem Concr Res 2003;33:1433–6. [12] Malhotra VM, Hammings RT. Blended cements in North America – a review. Cem Concr Compos 1995;17:23–35. [13] Poon CS, Lam L, Kou SC, Lin ZS. A study on the hydration rate of natural zeolite blended cement pastes. Constr Build Mater 1999;13:427–32. [14] Tsivilis S, Chaniotakis E, Kakali G, Batis G. An analysis of the properties of Portland limestone cements and concrete. Cem Concr Compos 2002;24:371–8. [15] Shehata MH, Thomas MDA. Use of ternary blends containing silica fume and fly ash to suppress expansion due to alkali–silica reaction in concrete. Cem Concr Res 2002;32:341–9.

X. Gao et al. / Construction and Building Materials 25 (2011) 3782–3789 [16] Menéndez G, Bonavetti V, Irassar EF. Strength development of ternary blended cement with limestone filler and blast-furnace slag. Cem Concr Compos 2003;25:61–7. [17] Li G, Zhao X. Properties of concrete incorporating fly ash and ground granulated blast-furnace slag. Cem Concr Compos 2003;25:293–9. [18] Chindaprasirt P, Rukzon S. Strength, porosity and corrosion resistance of ternary blend Portland cement, rice husk ash and fly ash mortar. Constr Build Mater 2008;22:1601–6. [19] Plowman C, Cabrera JG. The use of fly ash to improve the sulphate resistance of concrete. Waste Manage 1996;16:145–9. [20] Poon CS, Lam L, Wong YL. A study on high strength concrete prepared with large volume of low calcium fly ash. Cem Concr Res 2000;30:447–55. [21] Riding K, Silva DA, Scrivener K. Early age strength enhancement of blended cement systems by CaCl2 and diethanol-isopropanolamine. Cem Concr Res 2010;40:935–46. [22] Qian J, Shi C, Wang Z. Activation of blended cements containing fly ash. Cem Concr Res 2001;31:1121–7. [23] Xu A. Microstructural study of gypsum activated fly ash hydration in cement paste. Cem Concr Res 1991;21:1137–47. [24] Glasser FP, Marchand J, Samson E. Durability of concrete—degradation phenomena involving detrimental chemical reactions. Cem Concr Res 2008;38:226–46. [25] Chindaprasirt P, Jaturapitakkul C, Sinsiri T. Effect of fly ash fineness on microstructure of blended cement paste. Constr Build Mater 2007;21:1534–41.

3789

[26] Lawrence P, Cyr M, Ringot E. Mineral admixtures in mortars effect of type, amount and fineness of fine constituents on compressive strength. Cem Concr Res 2005;35:1092–105. [27] Sohoni S, Sridhar R, Mandal G. The effect of grinding aids on the fine grinding of limestone, quartz and Portland cement clinker. Powder Technol 1991;67:277–86. [28] Öner M. A study of intergrinding and separate grinding of blast furnace slag cement. Cem Concr Res 2000;30:473–80. [29] Binici H, Aksogan O, Cagatay IH, Tokyay M, Emsen E. The effect of particle size distribution on the properties of blended cements incorporating GGBFS and natural pozzolan (NP). Powder Technol 2007;177:140–7. [30] Kumar S, Kumar R, Bandopadhyay A, Alex TC, Kumar BR, Das SK, et al. Mechanical activation of granulated blast furnace slag and its effect on the properties and structure of Portland slag cement. Cem Concr Compos 2008;30:679–85. [31] Tuthill LH, Adams RF, Hemme JM. Observations in testing and use of waterreducing retarders. ASTM Spec Tech Publ 1990;266:97–117. [32] Kavas T, Olgun A, Erdogan Y. Setting and hardening of borogypsum–Portland cement clinker–fly ash blends. Studies on effects of molasses on properties of mortar containing borogypsum. Cem Concr Res 2005;35:711–8. [33] Isaia GC, Gastaldini ALG, Moraes R. Physical and pozzolanic action of mineral additions on the mechanical strength of high-performance concrete. Cem Conc Compos 2003;25:69–76. [34] Katsioti M, Giannikos D, Tsakiridis PE, Tsiboukic Z. Properties and hydration of blended cements with mineral alunite. Constr Build Mater 2009;23:1011–21.