Fig. 2 shows the relation between the replacement ratio of BFS to OPC and the mortar
flow. The superplasticizer used was PCE and the ratio of the additive to the binder was 0.20% by mass. The fluidity of BFS alone was low; however, the fluidity tended to increase with increasing BFS4000 substitution. Thus, the amount of admixture added can be signifi- cantly reduced when using ECM.
Relation between the polymer structure and the adsorption of polymer
The adsorbed amounts of each powder per 1.0 g [3.5 × 10-2 oz.] of M23 and M9 for the
ECM admixture are shown in Fig. 3 and 4, respectively.4 For all powders, the adsorbed Table 4—Mixture proportions of concrete
W/C Cement Target slump,cm [in.] Target air,%
Unit weight, kg/m3 [lb/yd3]
W C S G
0.5
ECM6000 [7.1±1.0]18±2.5 4.5±1.0 160 [270] 320 [539] 854 [1439] 951 [1603] 0.4 160 [270] 400 [674] 740 [1247] 997 [1680]
amount of M23 increased with increasing additive but saturated at low additive amounts relative to the OPC in BFS4000 and BFS6000. The amount of M23 adsorbed was higher in ECM4000 and ECM6000 than in OPC despite the OPC replacement rate being as low as 30%; this is due to the great increase in the adsorption to the BFS component in ECM. This phenomenon is presumed to be consistent with the results of the mortar test, where Ca2+ eluted from the OPC was specifically adsorbed on the BFS surface that becomes the
adsorbing surface of the admixture.
In M9, although adsorption to the binder tended to increase with increasing additive, the amount adsorbed to the OPC reached saturation at a lower amount of addition, and the amount adsorbed for BFS4000 and BFS6000 did not change as significantly as in M23.
Fig. 2―Relation between the replacement ratio of BFS4000 and the mortar flow (20 °C, [68 °F])
Fig. 3―Adsorption of M23
Properties of a New Type of Polycarboxylate Admixture for Concrete Using High Volume Blast Furnace Slag Cement 117
However, Fig. 4 shows that the amount of M9 adsorbed in ECM4000 and ECM6000 is approximately as high as that observed in M23, as shown in Fig. 3. The phenomenon in M9 is assumed to be the same as that observed in M23, wherein Ca2+ eluted from the OPC
is specifically adsorbed on the BFS surface.
Relation between polymer structure and paste flow
The relation between the dosage of M23 and M9 and the paste flow using OPC and ECM are shown in Fig. 5 and 6, respectively. In M23, the results of the paste test demonstrated high fluidity for both OPC and ECM (especially for ECM). Moreover, a high correlation
Fig. 4―Adsorption of M9
is observed between paste flow and the amount of M23 adsorbed, as shown in Fig. 3, where both the adsorbed amount of M23 and the fluidity increased with increasing additive content. In M9, the paste fluidity of both OPC and ECM increased with increasing admix- ture content; however, the effect on OPC was small. A correlation is observed between paste flow and the amount of M9 adsorbed, as shown in Fig. 4.
Based on these results, M23 is concluded to adsorb onto both OPC and BFS in ECM and it enhances the fluidity; the adsorption of M9 to BFS also significantly contributes to fluidity enhancement.
Properties of concrete
The results for concrete at a W/C of 0.5 and 0.4 are listed in Table 5 and 6, respectively. The admixtures used were PCE, M23, M9, and M9 with GLNa.
Time Dependent slump loss behavior
The results of the slump test at a W/C of 0.5 are shown in Fig. 7. In the case of PCE or M23 added to ECM6000, the dosage was decreased and a large slump loss was observed at 30 min after mixing. However, the dosage could be maintained in M9, and a significant improvement in retention of up to 60 min was observed. In addition, further improvement of retention was obtained by adding both M9 and GLNa, which retained sufficient fluidity even after 90 min. Therefore, fluidity retention can be controlled by adjusting the ratio of M9 and GLNa.
The results of the slump test at a W/C of 0.4 are shown in Fig. 8. In the case of PCE or M23 added to ECM6000, the dosage was decreased and a large slump loss was observed at 30 min, similar to that at a W/C of 0.5. In the case of M9, the improvement in retention up to 60 min was observed. However, a slight initial growth of slump and a large slump loss after 90 min was observed. Therefore, M9 and GLNa were combined with M23 for suppressing the initial growth of slump because the combination demonstrated excellent
Fig. 6―Flow of OPC paste and ECM paste with added M9
Properties of a New Type of Polycarboxylate Admixture for Concrete Using High Volume Blast Furnace Slag Cement 119
initial dispersion power. Thus, fluidity up to 90 min was ensured without the initial growth of the slump.
These results show that M9 displays better retention ability than PCE or M23. This is likely due to the maintenance of the adequate dosage and the suppression of the early
Table 5—Concrete test results
W/C Admixture type Dosage of admixture, C×% Dosage of GLNa, C×%
Slump, cm [in.] (Air content, vol%) Setting time, h 0 min 30 min 60 min 90 min initial final
0.5 PCE 0.11 - [7.7]19.5 (4.0) 9.5 [3.7] (3.3) - - 6.0 11.3 M23 0.05 - [7.3]18.5 (4.2) 5.0 [2.0] (3.0) - - 5.8 11.1 M9 0.21 - [7.5]19.0 (4.4) 19.5 [7.7] (4.4) 16.0 [6.3] (4.0) 12.0 [4.7] (3.8) 8.5 13.7 M9 0.20 0.04 [7.3]18.5 (4.1) 20.5 [8.1] (4.0) 20.5 [8.1] (4.1) 19.5 [7.7] (4.2) 9.3 14.5 0.4 PCE 0.10 - [7.7]19.5 (4.2) 11.5 [4.5] (3.7) - - - - M23 0.05 - [7.5]19.0 (4.5) 6.0 [2.4] (3.4) - - - - M9 0.20 - [7.9]20.0 (4.2) 20.5 [8.1] (4.1) 17.5 [6.9] (4.0) 11.0 [4.3] (3.3) - - M9+M23 0.13+0.04 0.04 [7.1]18.0 (4.4) 20.5 [8.1] (4.2) 20.5 [8.1] (4.2) 18.0 [7.1] (4.2) - - * % by mass of cement (C×%)
Table 6—Compressive strength
W/C Admixture type Dosage of admix-ture, C×% GLNa, C×%Dosage of
Compressive strength, MPa [psi] 24 h 7 days 28 days 0.5 PCE 0.11 - 2.7 [390] 30.9 [4480] 43.8 [6350] M23 0.05 - 2.7 [390] 31.0 [4500] 43.6 [6320] M9 0.21 - 2.5 [360] 32.8 [4760] 47.3 [6860] M9 0.20 0.04 2.0 [290] 33.3 [4830] 47.7 [6920] 0.4 PCE 0.10 - 4.1 [600] 41.0 [5950] 58.3 [8460] M23 0.05 - 4.2 [610] 40.8 [5920] 58.2 [8440] M9 0.20 - 3.4 [490] 42.9 [6220] 60.6 [8790] M9+M23 0.13+0.1 0.04 3.1 [450] 43.5 [6310] 60.9 [8830] * % by mass of cement (C×%)
admixture consumption caused by the early hydration of OPC by the small molar ratio of MAA and the short side chain length of M9.
GLNa adsorbs to ECM or OPC very easily, and the fact that it is adsorbed competi- tively is considered to be a reason for the effective functioning of GLNa for ECM, thereby suppressing the early admixture consumption.
Compressive strength and setting time
As shown in Table 6, M9 and M9 + GLNa, although the compressive strength at 24 h was slightly reduced, the compressive strength subsequently increased as compared to PCE or M23. Fig. 9 shows the relation between the compressive strength (at 28 days) and the setting time (final) at a W/C of 0.5. The observed increase in the compressive strength with
Fig. 7―Slump retention behavior (W/C of 0.5)
Fig. 8―Slump retention behavior (W/C of 0.4)
Properties of a New Type of Polycarboxylate Admixture for Concrete Using High Volume Blast Furnace Slag Cement 121
delay in the setting time when using ECM has already been shown, as will be discussed shortly, and this was probably the effect.
Fig.10 shows the relation between the setting time (final) and the compressive strength
of concrete (W/C of 0.38) that used ECM4000. This is an experimental verification. The setting time had been adjusted by changing the admixture and the amount of the admixture (by changing the unit volume of water), and by using retarders. The compressive strength of the concrete using ECM was shown to improve by delaying the setting time of the concrete.
Although the definite potential for enhancing compressive strength using ECM has been verified, further studies considering workability are necessary.
Fig. 9―Relation between 28-d compressive strength and setting time (W/C of 0.5)
Fig. 10―Relation between 28-d compressive strength and setting time (W/C of 0.38)
CONCLUSIONS
This study is summarized as follows.
1. M23 and M9, with varying methacrylic acid ratio and side chain lengths, demon- strated different adsorption behavior for OPC.
2. M23, which has a longer side chain length and a larger amount of carboxylic acid than M9, demonstrated sizable absorbance to both OPC and ECM. In addition, on the basis of the fluid tendency of the paste, M23 adsorbs to both the OPC and BFS components in ECM and enhances fluidity.
3. M9, which has a shorter side chain length and a smaller amount of the carboxylic acid than M23, exhibited a smaller absorbance to OPC, whereas a significant amount absorbed to ECM. Additionally, on the basis of the fluid tendency of the paste, M9 is found to adsorb to the BFS component of ECM, thereby enhance fluidity.
4. M23 and M9 impart high fluidity to the concrete made with ECM. In addition, fluidity retention can be controlled using M23, M9, and GLNa.
5. M9 and GLNa improve the compressive strength of concrete made with ECM. However, the early strength was found to decrease slightly. Further study is required to overcome this problem.
Standards cited
Japanese Industrial Standards
JIS R 5201 Physical testing methods for cement JIS A 1150 Method of test for slump flow of concrete
JIA A 1147 Test method for time of setting of concrete mixtures by penetration resistance JIS A 1108 Method of test for compressive strength of concrete
JIS R 5211 Portland blast-furnace slag cement JIS R 5213 Portland fly-ash cement
AUTHOR BIOS
Shinji Tamaki is a Research Engineer of R&D, Construction Chemicals Division,
Takemoto Oil & Fat Co., Ltd., 2-5 Minatomachi, Gamagori, Aichi, Japan. His current research interests are chemical synthesis of water-soluble functional polymers and mate- rials science.
Kazuhide Saito is a Research Engineer of R&D, Construction Chemicals Division,
Takemoto Oil & Fat Co., Ltd., 2-5 Minatomachi, Gamagori, Aichi, Japan. His current research interests include fluidity, strength, and durability development for concrete using high volume blast-furnace slag cement.
Kazuhisa Okada is a Research Engineer of R&D, Construction Chemicals Division,
Takemoto Oil & Fat Co., Ltd., 2-5 Minatomachi, Gamagori, Aichi, Japan. His current research interests are chemical synthesis of water-soluble functional polymers and mate- rials science.
Daiki Atarashi is an assistant professor of metallurgy and ceramics science, Graduate
School of Science and Engineering, Tokyo Institute of Technology, Japan. He received
Properties of a New Type of Polycarboxylate Admixture for Concrete Using High Volume Blast Furnace Slag Cement 123
his B.S. in 2001, M.S. in 2003, and Dr. Eng. in 2006 from Tokyo Institute of Technology. His research interests include the action mechanisms of chemical admixtures, fluidity of cement paste, and material design of high-recycled-content and low-CO2-emission
cements.
Etsuo Sakai is a professor in metallurgy and ceramics science, Graduate School of
Science and Engineering, Tokyo Institute of Technology. He received his Dr. Eng. from Tokyo Institute of Technology in 1979. His research interests include construction chem- istry, material recycling, and material design for low-carbon cement.
ACKNOWLEDGMENTS
This research was conducted under a grant for “Strategic Development of Energy Use Rationalization Technology / Leading Research and Development of Fundamental Tech- nologies for Efficient Energy Use / Research and Development of ‘Energy CO2, Minimum’
(ECM) Cement-Concrete System” from the New Energy and Industrial Technology Devel- opment Organization (NEDO).
REFERENCES
1. Yonezawa, T.; Sakai, E.; Koibuchi, K.; and Kinoshita, M., High-Slag Cement and Structures for Substantial Reduction of Energy CO2, Proceedings of the fib Symposium, Stockholm, Sweden, pp. 463-466 (2012)
2. Nito, N.; Osawa, T.; Koibuchi, K.; and Miyazawa, S., Heat and shrinkage of concrete by slag gain and SO3 of blast-furnace slag cement (in Japanese), Proceedings of the Japan Concrete Institute, Japan, Vol. 30, No.2, pp. 121-126(2008)
3. Tsuji, D.; Wachi, M.; Inoue, K.; Mitsui, K.; Yonezawa, T.; and Kanda, T., Properties of Concrete using High Slag Cement, Proceedings of the First International Conference on Concrete Sustainability, Tokyo, Japan, pp. 139-144 (2013)
4. Sasabe, T.; Atarashi, D.; Tamaki, S.; and Sakai, E., Adsorption Mechanism of Super- plasticizer on High Volume Blast Furnace Slag Cement (in Japanese), Cement Science and Concrete Technology, Japan Cement Association, Japan, No. 65, pp. 27-32 (2011)
In this study, the polycarboxylate superplasticizers (PCs) with solid content up to 80% were synthetized using special redox initiator at 318K. In the radical polymerization reac- tions, combining with Fourier Transform Infrared Spectroscopy (FTIR) and Gel Perme- ation Chromatograph (GPC), the initiator dosing dosage, reaction temperature, reaction time and the concentration of system in the copolymerization reaction were systematic investigated through orthogonal design experiments. The performances of new PCs in cement paste were tested by measuring the fluidity and fluidity retention. The slump and the compressive strengths of concrete were also determined. Compared with traditional PC, the new PC has a better advantage in workability of fresh concrete and mechanical properties of hardened concrete.
Keywords: polycarboxylate; high solid-content; workability. INTRODUCTION
Polycarboxylates are commonly used as superplasticizers to disperse cement particles in concrete and mortar. They are usually stored, packed and transported as 20%~40% aqueous solutions, which increase the costs of transportation.1,2 It is necessary to research
the synthesis and application of high solid-content polycarboxylates. If the concentration of monomer in traditional synthesis is simply changed, the content of free water is less simple; because the viscosity in the system becomes higher. Then the self-acceleration in polymer- ization might be occurred and part of polymer chains increases abnormally, resulting in the decreasing of water-reducing rate of polycarboxylates.2,3 There are two common methods
to control the self-acceleration in polymerization: one is increasing the temperature of synthesis system, the other is adding a good solvent.4 Both methods contribute to rearrange
the chain segment of polycarboxylates. Increasing the temperature of synthesis system can accelerate the molecular thermodynamic movement, and adding a good solvent can reduce the viscosity of synthesis system. Because the synthesis of polycarboxylates takes place in water solution, the temperature of synthesis system is no more than 373 K.5 Increasing the
temperature needs changing the medium of the synthesis, so the costs could increase. Most of good solvents are more or less toxic. They are not only harmful to the builders, but also