Keywords: Zeolite powder, High-strength concrete, Plastic viscosity, Chloride-penetration resistance, Self-shrinkage.

Transcription

1 Advanced Materials Research Submitted: ISSN: , Vols , pp Accepted: doi: / Online: Trans Tech Publications, Switzerland Rheological Property and Durability of High Strength Concrete Using Zeolite Powder and Microsphere Yu Xin Gao 1,a, Jia Chao Lin 1,b, Bao Jun Cheng 1,c, Xiong Wu 1,d, Yuan Peng 1,e, Li Li Jia 1,f 1 Technology Center Building, South Luoshi No. 248, Hongshan District, Wuhan, Hubei,China a @qq.com, b sillybear@yeah.net, c p @163.com, d @qq.com, e @qq.com, f jiali608927@126.com Keywords: Zeolite powder, High-strength concrete, Plastic viscosity, Chloride-penetration resistance, Self-shrinkage. Abstract: The rheological property of fresh high-strength concrete (HSC)and mechanical properties, self-shrinkage and resistance to chloride ion permeability of hydrated HSC were studied on the basis of the closest packing theory. Results showed that the packing density of composite powder was the highest when the content of microsphere was 30.0%; when the content of zeolite powder added to concrete varied from 0.0% to 4.0%, the rheological and discontinuous property of concrete would be improved and its viscosity would be increased; meanwhile, compared to the standard concrete, the self-shrinkage of concrete with 2.0% zeolite powder at 1d, 3d, 7d and 28d was decreased by 77.1%, 49.6%, 44.0% and 38.1% respectively; finally, the resistance to chloride ion permeability of hydrated HSC with zeolite powder was improved with a result of 18.5% reduction of electric flux at 28d. 0 Introduction As it is known, high-strength concrete (HSC) has large percent of cementing material and low water/cement ratio, which causes its poor performance [1]. Adding superfine mineral admixture can improve the conformability between concrete and superplasticizers. Superfine power can improve the liquidity, intensity and durability of concrete by replacing clinker or cement, so it is a necessary part of HSC [2]. As a superfine powder, microsphere has not only micro-filling effect but also the plasticizing effect and pozzolanic effect [3]. However, microsphere has low density causing the bleeding cement after added to the concrete, which leads to its poor workability. Zeolite powder is a kind of pozzolanic materials grinded from natural zeolite. It has porous structure and high inner surface area. Its active effect, water absorbing and releasing characteristics can improve concrete s cohesiveness, coarse aggregate s precoating ability and workability. Meanwhile, as an autogenous curing agent, zeolite can improve HSC s long-term shrinkage [4, 5]. This paper studied the effect on fresh mixed HSC s rheological parameter and hardened HSC s mechanical property and durability of concrete containing zeolite powder or microsphere. 1 Raw Materials and Test Methods 1.1 Raw Materials Cementitious Material P Ⅱ52.5 cement produced by Hubei Yadong Cement Plant, whose basic performance is shown in Table 1. S95 mineral powder produced in Xinzhou,Wuhan and microsphere produced by Tianjin ZHUXIN New Material Technology Co., Ltd. are used. Zeolite powder is produced in Ezhou, Hubei. Their basic performance indexes and particle size distribution are shown in Table 2 and table 3. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-09/04/16,07:39:38)

2 1004 Materials, Transportation and Environmental Engineering II Table 1. Basic Performance of Concrete Standard Consistency/g Flexural Strength/MPa Compressive Strength/MPa 3d 28d 3d 28d Density/ g cm -3 Stability Qualified Table 2. Physical Properties of Cement and Mineral Admixtures Raw Materials Density/g cm -3 Specific Surface Area/m 2 kg Water Requirement/% -1 Fluidity Ratio/% Cement S95 Slag Powder Microsphere Zeolite Powder Table 3.Particle Size Distributionof Raw Materials 28d Compressive Strength/MPa Raw Materials D 50 /μm D 10 /μm D 25 /μm D 75 /μm D 90 /μm Cement S95 Slag Powder Microsphere Zeolite Powder Aggregate The test uses sand from Yueyang, Hunan, with 2.7 fineness modulus, 0% clay lump content, silt content of 0.8%, apparent density of 2620kg/m 3 ; Chongqin gravel, 5~16mm fully-graded gravel with a clay lump content of 0%, silt content of 0.5%, crushing value of 3.0%, apparent density of 2690kg/m 3, bulk density of 1610kg/m Admixture Polycarboxylate superplasticizer with a solid content of 25% and water-reducing rate of 28% is used. 1.2 Test Methods Concrete Compressive Strength Test Concrete strength test is performed according to the Standard for Test Method of Mechanical Properties on Ordinary Concrete (GB/T ). The concrete specimen dimensions in this paper are 100mm 100mm 100mm Concrete Rheological Properties Concrete rheometer [6] (which is produced by China State Construction Ready Mixed Concrete Co., Ltd.) is used to test rheological properties. The appearance of equipment is shown in Figure 1. Figure 1 Concrete Rheometer

3 specific surface area/ m 2 /kg Advanced Materials Research Vols Concrete Self-shrinkage Test Test is performed according to the Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete (GB/T ). A CABR-NES non-contact concrete shrinkage deformation tester is used to test self-shrinkage of HSC Concrete Anti-chloride Ion Permeability Test Test is performed according to the Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete (GB/T ). 2. The Conformation of Microsphere-cement System After making composite cement powder through mechanical pressure method, this study analyzed original particles build-up situation by testing the compacted powder s porosity based on close packing theory when microspheres replace cement in composite cementitious system [7]. This study measured composite colloid s performance density and specific surface area and the results are shown in Figure 2. According to the graph, The colloid system s performance decreases while the specific surface area increases when the content of microsphere increases density/ kg/m density microsphere ratio/ % specific surface area Figure 2.Effect of Microspheres on Density and Specific Surface Area of Composite Powder porosity/ % microsphereratio/ % Figure 3. Effect of Microspheres on Porosity of Composite Powder Figure 3 presents microsphere s effect on the porosity of composite cementitious system. As the dosage of microsphere increases, the porosity decreases first and then increases. When the mass content of microsphere is 30%, the composite colloid reaches to the closest build-up and its porosity is only 33.4%. Microsphere can fill the gap in cement paste and improve the colloid s build-up density efficiently, but if there are too many microspheres, they will have an adverse impact on the build-up structure of big particles, which leads to relaxation effect causingthe increasing of porosity of the composite cementitious system. So it shows that microsphere-cement composite reaches to the closest packing when the mass content of microsphere is 30%, which is set to be the microsphere s content of admixture in the experiment is. 3 Rheological and Mechanical Performance of HSC According to Table 3, cement, mineral powder and zeloite powder s D 50 are 15.00μm, 16.00μm and 16.19μm, so it is assumed that their mixture ratio will not influence the composite colloid s build-up density. Ternary composite of mineral powder-microsphere-cement was selected as the experimental subject. Zeloite was added into the subject with mass content of 1%, 2% and 4% to replace the same amount of cementitious material, forming the quaternary composite of mineral powder-microsphere-zeloite powder-cement. For detail information, please refer to Table 4.

4 1006 Materials, Transportation and Environmental Engineering II Test No. Cementitious Material Table 4. Design Proportioning of HSC (kg/m 3 ) Cement Microspheres S95 Slag Powder Zeolite Powder River Sand Gravel Water PC C % C % C % C % C % 3.1 The Rheological Properties of HSC Shear yield stress is caused by the adhesion between the particles of the constituent materials. Viscosity is an internal property of concrete structures which will impede the flow of fresh concrete. It is due to the flow of fluid between the stratosphere, which results in an opposite direction resistance to the flow (viscous resistance) of concrete. The results of rheological properties of HSC test are shown in Table 5. Compared with C0, the rheological properties of C1 which has the same amount of cementing material while with no zeolite powder, little cement and more microspheres is quite different, which is especially evident in yield stress and viscosity reduction. The yield stress of C1 is decreased by 64.3% and the viscosity is decreased by 68.0% compared with C0. This is because the microsphere as ultra-fine powder has plasticizing effect, which can dramatically reduce the viscosity of concrete. When zeolite powder content does not exceed 4%, it can be found that the yield stress and viscosity of concrete increases with the increase of content of zeolite powder through the comparison of the C1~C4 results. This is because the zeolite powder has porous lattice-like structure, which is abound of opening cavities and channels. And its large internal surface area requires more mixing water absorption, resulting in the increase of viscosity and yield stress of slurry and the decrease of fluidity. Table 5.The Rheological Properties of HSC No. Slump/mm Slump Flow/mm inverted cone/s slump yield stress /pa viscosity /pa s fitted equation C y=158.2x C y=50.4x C y=63.1x C y=90.2x C y=128.7x Figure 4-a Working Performance of C1 Figure 4-b Working Performance of C3 The real working performance of HSC is shown in Figure 4-a and Figure 4-b. Concrete of C1 presents the phenomenon of exposed rock on the surface and bleeding, while the aggregate of C3

5 Advanced Materials Research Vols was well wrapped and there is no bleeding phenomenon in concrete of C3. This is because when the zeolite powder content is under the reasonable range, although the initial work property has declined it plays the role of increasing the viscosity and plasticity, which effectively avoids the discontinuity in working performance and bleeding phenomenon. This suggests that slump and slump flow reflect the rheological properties of concrete to a certain extent in HSC. And it does not mean that the bigger slump flow is, the better it is. Concrete should have suitable viscosity to facilitate aggregate wrapping and comprehensive measure method to test the rheological properties of concrete. 3.2 Mechanical Property of HSC This research studied the mechanical property of the concrete and tested the compressive strength at 7d, 28d and 56d. The results are shown in Table 6. The correlation between zeloite powder s amount in admixture and concrete s mechanical property is shown in Figure 5. Table 6. Compressive Strength of HSC (MPa) Test No. Compressive Strength 7d 28d 56d C C C C C compressive strength /MPa B C D zeolite powder ratio/% Figure 5. Effect of Zeolite Powder on Mechanical Properties of Concrete Group C0 and C1 have the same amount of cementitious material without zeloite powder. Compared the group C0 with C1, the early strength of concrete decreases but long-term compressive strength increases a lot with the increase of microsphere content. C1 s 56d compressive strength almost equals to that of C0. Figure 5 shows that when the zeolite powder content is less than 4%, zeolite powder s addition has greater impact on compressive strength at early age but less impact at later age according to the C1~C4 s data. When the addition of zeolite is 4%, the compressive strength reduction of concrete at 3d, 28d, and 56d is 11.2%, 8.1%, and 4.5% compared with standard concrete. Zeolite powder mainly provides hydration activity of concrete in the long age and promotes increase of later strength.

6 self-shrinkage/ppm 1008 Materials, Transportation and Environmental Engineering II 4 Durability of HSC Using Zeolite Powder and Microsphere 4.1 Self-shrinkage of HSC The results of self-shrinkage testing on the groups C0, C1and C3 which had better workability and mechanical properties are shown in Figure C C1 C age/d Figure 6. Self-shrinkage Performance of Concrete Figure 6 shows that, with the same amount of cementitious materials, the self-shrinkage was reduced with the decrease of cement ratio compared C1 with C0. With the proper addition of zeolite powder, HSC s shrink performance was effectively improved. When the ratio of zeolite powder is 2% (C3), the self-shrinkage reduction of group C1 at 1d, 3d, 7d and14d is 77.1%, 49.6%, 44.0% and 38.1%respectively. When zeolite powder content is added, the early shrinkage of low water binder ratio concrete reduces obviously (1d and 3d). There is two reasons for the improvement on concrete s self-shrinkage performance by using zeolite powder. On one hand, concrete chemical shrinkage is suppressed due to delay in hydration; on the other hand, concrete drying shrinkage and internal capillary shrinkage are reduced due to the water retention performance of zeolite powder. 4.2 Chloride-penetration resistance of HSC The results of electric flux testing on the groups C0, C1and C3, which were formed by a cylinder of φ = (100 ± 1) mm, h = (50 ± 2) mm and cured for 28d, are shown in Table 7. Table 7. Electric Flux Test of HSC Test No. Zeolite Powder Ratio/% Cement Ratio/% Electric Flux /C C C C Table 7 shows that HSC s electric flux decreased significantly by lower cement ratio compared C0 with C1. It is because morpha effect and micro aggregate effect of the microsphere improve the density of concrete. The reduction electric flux of group C3 at 28d is 18.5% of that of group C1, showing that the effect of zeolite powder s self-curing can improve the chloride-penetration resistance of concrete. This is because the porous structure of zeolite powder absorbs mixing water in concrete mixing process, and releases water in the later hydration period. This has resulted in more hydration products forming and thereby increased the degree of compactness of concrete. 5 Conclusions (1)From the overall perspective, the porosity of composite powder compacts presented the upward trend after downward trend with increasing microsphere content; (2)When the cementitious content was in a certain value, the viscosity of concrete could be greatly decreased with the increase of microsphere content, which meant that the performance of

7 Advanced Materials Research Vols concrete was improved. And the concrete's poor performance (like its discontinuous and bleeding) could be avoided if the content of zeolite powder was not more than 4.0%, which resulted from that the yield stress and viscosity of concrete were increased with the help of the viscosity increasing and maintaining plasticity effect of zeolite powder; (3)When the microsphere content was increased, the early strength of concrete would be decreased, but its later strength would be changed a little. And the early strength of concrete decreased but its later strength increased with zeolite powder content increasing, when the content of zeolite powder varied from 0% to 4.0%. Meanwhile, the compressive stress of concrete with zeolite powder (4.0%) at 56d is 4.5% smaller than that of concrete without zeolite powder; (4)By decreasing the cement content in the cementitious system, the self-shrinkage of concrete was effectively decreased, and this phenomenon would be more apparent if zeolite powder was added into concrete. Compared to the standard concrete, the self-shrinkage of concrete with 2.0% zeolite powder at 1d, 3d, 7d and 28d decreased by 77.1%, 49.6%, 44.0% and 38.1%, respectively; (5)The chloride-penetration resistance of concrete would be increased by decreasing the cement content in cementitious system or adding zeolite powder into concrete, and it was more obvious with more content of zeolite powder and its electric flux at 28d decreased by 18.5%. Acknowledgements The corresponding author of this paper is Jiachao Lin. This paper is supported by Cscec Fund Project(cscec-2010-z-01). References [1] Michael Schmidt.:Ultra-high performance concrete high-tech material of the future. Betonwerk+Fertigteil. (2004),vol70(2): 90~91. [2] Li Chongzhi Feng Naiqian Li Yongde: study on and development of modern high performance concrete.architecture Technology.(2003),vol01: [3]C S Poona,U L Lama,S C Koua,Z S Linb:A study on the hydrationrate of natural zeolite blended cement pastes.construction and Building Materials.(1999),vol13:427~432. [4] Shujin Li, Keru Wu.:Zeolite powder and its application in high performance concrete. Shandong Building Materials. (2004), vol25(1): [5] Hui Wang, Chun Gao, Bin Chen, Naiqia Feng, Qingxia Gu.:A preparation method of self-compacting concrete contains zeolite powder. Chinese Patent. (2009), [6] Yuxin Gao,Jiachao Lin,Baojun Cheng,etc.:A concrete rheometer. Chinese Patent. (2014), [7] Yang Wen, Chen Baojun, Liu Xiaoqin: Research on the effect of beads on properties of cementing materials. Concrete.(2013),vol (5): 104~109.

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