FUNDAMENTAL PROPERTIES OF CONCRETE WITH CEMENT DISPERSING AGENT FOR RETEMPERING K. Tokuhashi, Tsuruga Cement Co. Ltd., Japan M. Shoya, Hachinohe Institute of Technology, Japan M. Aba*, Hachinohe Institute of Technology, Japan T. Kamata, Taiheiyo Soil Corporation, Japan D. Mito, MM Shokai, Japan 31st Conference on OUR WORLD IN CONCRETE & STRUCTURES: 16-17 August 2006, Singapore Article Online Id: 100031051 The online version of this article can be found at: http://cipremier.com/100031051 This article is brought to you with the support of Singapore Institute www.scinst.org.sg All Rights reserved for CI Premier PTE LTD You are not Allowed to re distribute or re sale the article in any format without written approval of CI Premier PTE LTD Visit Our Website for more information www.cipremier.com
31 st Conference on OUR WORLD IN CONCRETE & STRUCTURES: 16 17 August 2006, Singapore FUNDAMENTAL PROPERTIES OF CONCRETE WITH CEMENT DISPERSING AGENT FOR RETEMPERING K. Tokuhashi, Tsuruga Cement Co. Ltd., Japan M. Shoya, Hachinohe Institute of Technology, Japan M. Aba*, Hachinohe Institute of Technology, Japan T. Kamata, Taiheiyo Soil Corporation, Japan D. Mito, MM Shokai, Japan Abstract In recent years, it has been pointed out that many concrete structures are likely to be due to the structural defects in construction work because of the massive and complicated configuration and function of concrete structures. Therefore, the service life of concrete structures and the structural performance will be lowered by loading action and environmental attack such as carbonation, frost action and drying action. On the other side, in the last few decades, various types of chemical admixture have been developed, with emphasis on making the highly durable concrete and on producing the highly flowable concrete for self-compacting. In this paper, one kind of negative ion type cement dispersing agent for retempering, denoted as CDA, was examined to confirm its effect on fundamental properties of concrete. The efficacy of the agent was confirmed for the improvement of vibrating compaction of fresh concrete dependent on the elapsed time for adding after mixing, by the test using vibrating table-type consistency meter. From the tests for bleeding, setting, mechanical properties and micro structures of concrete such as Vickers hardness and pore size distribution, the effect of CDA was also confirmed promising for use. Keywords: Cement dispersing agent, fleshly mixed concrete, micro structure of concrete 1. Introduction In recent years, the various types of chemical admixture have been developed, with emphasis on making the high performance concrete such as high strength concrete, highly durable concrete and self-compacting concrete. There has been strong concern about enhancing factors to lower the durability of many existing concrete structures. Especially in Japan, one of the reasons is believed to be due to the insufficient practice in placing and compaction of fleshly mixed concrete. Therefore, the 1
technique to improve the workability of concrete will be very important to secure the performance in service life of concrete structures. The authors have developed one kind of cement dispersing agent for retempering of concrete, denoted as CDA with a new concept that this type of agent has the function not only to improve the performance on vibrating compaction of fresh concrete, but also to increase the resistance of segregation of concrete, due to the dispersion of cement particles and the reduction of bleeding of concrete by the addition. The CDA is negative ion type cement dispersing agent having main component of Polyester fiber. The efficacy of CDA is attracted by the dosage of a bit of agent (0.5g ~1.0g/m 3 ). In this study, the properties of freshly mixed concrete were examined by the slump test, air content test, bleeding test and test correspondingly applied by using vibrating table-type consistency meter. Then, the mechanical properties, the micro structure, compressive strength and the resistance to the frost action of hardened concrete were also investigated to examine the applicability of CDA. 2. Materials Used and Mixture Proportions of concrete Materials used in this test were shown in table-1. An ordinary Portland cement was used, and its density, specific surface area by Blaine, 28 days compressive strength and Na 2 Oeq were 3.16g/cm 3, 3350 cm 2 / g, 42.5 N/mm 2 and 0.75 %, respectively. The fine aggregate used in the test was the crushed limestone with fineness modulus of 2.70, density of 2.69 g/cm 3 and water absorption of 0.27 %. The coarse aggregate used in the test was crushed limestone with maximum size of 20mm, all of passed though 5 mm sieve with a fineness modulus of 6.55, density of 2.71 g/cm 3 and water absorption of 0.97 %. One kind of commercial chemical admixtures was used for air-entraining and water-reducing. The main component of CDA was a polyester fiber, and the cement dispersing effect was demonstrated by late addition for retempering of concrete. According to the record on working site, the remarkable effect of CDA for concrete is attracted by the dosage of only 0.5 ~ 1.0 g per 1 m 3 of fresh concrete. Table-2 shows the mixture proportions of concrete when making concrete. Water cement ratios of 40, 50 and 60 % were adopted in this test. The target value of slump and air content Table-1 Material used in the test Cement Ordinary portland cement Water Ordinary water ( tap water ) Fine Aggregate Crushed sand (Density 2.70g/cm 3 ) Coarse Aggregate Crushed limestone (Density 2.71g/cm 3 ) Maximum size of 20mm Chemical Admixture Air-entraining water reducer Main component of lignosulfonic acids and ethers Air entraining agent Main component of natural resin Cement dispersing agent (CDA) Main component of polyester fiber 2
Table-2 Mixture proportions of concrete W/C s/a Slump Air Unit content (kg/m 3 ) Air-entraining water reducer C (%) AE agent W C S G (%) (%) (cm) (%) C (%) 40 42.0 393 761 1059 0.006 0.10 50 44.0 8.0 4.5 157 314 827 1060 0.007 0.10 60 46.0 261 885 1047 0.008 0.08 Non addition (N) First mixing 90 sec Mixed up 15 min 30 min 45 min 60 min Setting Retempering Setting Retempering Setting Retempering Setting Retempering 14 min 30 sec 30 sec 14 min 30 sec 30 sec 14 min 30 sec 30 sec 14 min 30 sec 30 sec Addition at first mixing of concrete (AD-0) 60 sec 30 sec 14 min 30 sec 30 sec 14 min 30 sec 30 sec 14 min 30 sec 30 sec 14 min 30 sec 30 sec Addition at retempering of concrete in the elapsed time After 15 min (AD-15) 90 sec 14 min 30 sec 30 sec After30 min (AD-30) 90 sec 14 min 30 sec 30 sec 14 min 30 sec 30 sec After 45 min (AD-45) 90 sec 14 min 30 sec 30 sec 14 min 30 sec 30 sec 14 min 30 sec 30 sec After 60 min (AD-60) 90 sec 14 min 30 sec 30 sec 14 min 30 sec 30 sec 14 min 30 sec 30 sec 14 min 30 sec 30 sec Masurement Masurement Masurement Masurement Masurement Measurment :Slump value, Air content, Midified VB consolidation factor (Vibrating frequency of 500 rpm) Fig-1 Measurement of properties of fresh concrete in elapsed time of fresh concrete were fixed with 8.0 ± 1 cm and 4.5 ± 0.5 %, respectively. Mixing of flesh concrete was done using the double shaft pugmill mixer. 3. Testing method 3.1 Test method for fresh concrete 3.1.1 Slump test, air content test and test using vibrating table-type consistency meter The performances of fresh concrete were examined by the slump test, the air content test and the vibrating table-type consistency meter to confirm the effect of the existence of CDA. The slump test and the air content test were conducted in Japan Industrial Standards whose regulations were JIS A 1101 and JIS A 1128, respectively. Test using vibrating table-type consistency meter was performed for the evaluation of compaction performance of fresh concrete. However, the vibrating frequency of consistency meter (VB testing) was modified to 500 rpm from 1,500 rpm after several attempts. This reason is that the test was done using fresh concretes other than those of dry and stiff consistency. These tests were conducted after the addition CDA at first mixing of concrete and after the late adding CDA for retempering of concrete as shown in Fig-1. 3.1.2 Bleeding test Bleeding tests of concrete was also conducted to confirm the improvement of segregation resistance for the bleeding of concrete by the addition. Test was made with JIS A 1123 using 250mm diameter by 285mm high cylindrical container. 3
3.2 Test method for hardened concrete 3.2.1 Measurement of micro structure of concrete The micro structure of concrete was investigated from the pore structure in mortar and the weakness zone of coarse aggregate interface. The measurement of the pore structure was made by mercury intrusion test (measured within the pore diameter : 0.006 μm~500 μm). The samples of mortar of 4 g harvested in the concrete at the depths of 5, 30 and 50mm from the surface were tested. Then, the properties of weakness zone of coarse aggregate interface in concrete were examined by Vickers hardness using micro hardness meter. The test was performed to investigate the weakness zone around the coarse aggregate at the depth in 5 and 50 mm from surface of placed concrete. The measuring location was selected around the aggregate interface in direction of perpendicular to placing direction of concrete with interval of 10 μm from aggregate interface. And the portion lower than Vickers hardness of the bulk division were defined as weakness zone. 3.2.2 Compressive strength test Test for compressive strength of concrete was made in accordance with JIS A 1108. The compressive strength was tested using 100 by 200mm cylindrical specimen at the age of 7, 14, 28 and 91 days. 3.2.3 Freezing and Thawing test Freezing and thawing test of concrete was conducted in accordance with ASTM C 666 procedure A (Freezing and thawing in water). The test started at an age of 28 days using 100 by 100 by 400mm prisms. Three specimens were tested simultaneously representing each mixture and testing conditions. The change in the relative dynamic modulus of elasticity was measured every 30 cycles up to the 300 cycles. 4. Experimental Results and Considerations 4.1 Tests results of fresh concrete Table-3 shows the measured result of slump value, air content and modified VB consolidation factor (sec) by the existence of CDA at the first mixing of concrete. From this table, it could be seen that the slump value increased about 2.0 cm by CDA addition regardless of water-cement ratio of the concrete. Large change in the slump value could not be found with the addition of three times of normal dosage of CDA. The modified VB consolidation factor of the concrete using the admixture (CDA) was lower than that of controlled plane concrete without CDA. On the other side, air content of W/C (%) Table-3 The test result of slump value, air content and modified VB consolidation factor Modified VB consolidation Slump value (cm) Air content (%) factor (sec) without CDA of three times without CDA of three times without CDA 40 8.0 10.0 9.5 4.7 4.7 4.7 28.23 19.06 50 8.5 10.5 10.0 4.5 4.6 4.8 21.79 13.15 60 8.5 10.5 10.5 4.6 4.5 4.4 17.42 10.24 4
Slump value (cm) 10 8 6 4 2 0 without CDA The addition CDA at first mixing of concrete The addition CDA at the retempering of concrete in the elapsed time 0 15 30 45 60 Elapsed time(min) 5.0 Air content (%) 4.0 3.0 2.0 1.0 VB consolidation factor (sec) 0.0 100 80 60 40 20 0 15 30 45 60 Elapsed time(min) 0 0 15 30 45 60 Elapsed time(min) Fig-2 Properties of fresh concrete with elapsed time (W/C 50%, Air 4.5%, Slump 8.0 cm) concrete was almost conformed to that of the controlled concrete. From these results, the addition of CDA was confirmed to contribute for the improvement of the vibrating compaction performance of concrete. Fig-2 shows the change in slump value, air content and modified VB consolidation factor of the 5
fresh concrete with elapsed time. The concrete using CDA showed the larger slump value about 2.0 or Amount of bleeding (cm 3 /cm 2 ) 0.50 0.40 0.30 0.20 0.10 0.00 Concret without CDA of three times 35 45 55 65 W/C (%) Fig-3 Relationship between W/C and final amount of bleeding 3.0 cm than that of controlled concrete without CDA regardless of elapsed times. In the retempering concrete by the addition of CDA, the modified VB consolidation factor significantly decreased to the same level in case of the addition CDA at first mixing of concrete. Especially, the modified VB consolidation factor showed the remarkable efficacy of late addition at the time of 60 min. But, large change in air content could not be found in the passage times by the addition. Fig-3 shows the test result of bleeding of concrete. From this figure, the final amount of bleeding of concrete using CDA decreased when water-cement ratio increased. Then, the bleeding of concrete was improved by the addition of CDA. The effect of addition of CDA will be considered by both improvement of dispersing effect of flocculated cement particles and water retentivity of cement particles. Vickers hardness, HV 60 40 20 0 (5mm) (50mm) Weakness zone Weakness zone Bulk division without CDA(50mm) without CDA(5mm) Bulk division 0 20 40 60 80 100 Distance from the coarse aggregte interface (μm) Fig-4 Relationship between distance from the coarse aggregate interface and Vickers hardness (W/C 50%, Air 4.5%, Slump 8.0 cm) 6
Table-4 The measurement result of pore structure (W/C 50%, Air 4.5%, Slump 8.0 cm) The distance from surface without CDA Total pore volume Average pore diameter Concrerte Total pore volume Average pore diameter ( mm ) ( cc/g ) ( mm ) ( cc/g ) ( mm ) 5 0.070 0.0604 0.066 0.0493 30 0.055 0.0398 0.058 0.0398 50 0.051 0.0327 0.060 0.0327 Average 0.059 0.0443 0.061 0.0406 Standard deviation 0.00019 0.000415 0.00004 0.000139 Compressive strength (N/mm 2 ) 60 50 40 30 20 10 0 without CDA 0 10 20 30 40 50 60 70 80 90 100 Age (days) Fig-5 Results of compressive strength (W/C 50%, Air 4.5%, Slump 8.0 cm) 4.2 Tests results of hardened concrete Fig-4 shows the relationship between distance from the coarse aggregate interface and Vickers hardness. From this figure, the weakness zone with lower strength along the coarse aggregate interface was confirmed to reduce by the addition of CDA. Because of cement dispersing effect of CDA, the amount of free water traveling to the coarse aggregate interface in the fresh concrete was decreased, and the bleeding of concrete was considered to the controlled. Table-4 shows the pore structure of concrete. From this table, the standard deviation in every depth from surface of placed concrete tended to reduce by the addition of CDA. It was confirmed that the cement dispersion effect of CDA contributed to improve the segregation of concrete, and the uniform structure of internal concrete was formed by the addition of CDA. Fig-5 shows the results of compressive strength of concrete at a fixed water-cement ratio of 50% and slump value of 8 cm. From this result, the development of compressive strength of concrete could be judged as almost the same as that of controlled concrete without CDA. 7
Relative dynamic modulus of elasticity (%) 100 90 80 70 60 without CDA W/C:50%, s/a:44%, Slump:8.0cm, Air:4.5% 0 30 60 90 120 150 180 210 240 270 300 Freeze-thaw cycle Fig-6 Results of freezing and thawing test Fig-6 shows the results of freezing and thawing test of concrete at a fixed water-cement ratio of 50 % and air content of 4.5%. Based on this test results, it was recognized that the addition of CDA did not affect to resistance to freezing and thawing of concrete. 5. Conclusions Experimental examinations of fundamental properties of concrete with cement dispersing agent (CDA) for retempering of concrete were made in this study. The test results were summarized as follows. (1) In case of the addition of CDA at the first mixing of concrete, the slump value of concrete increased about 2.0 cm regardless of water-cement ratio. The addition of CDA was controlled to contribute for the improvement of the vibrating compaction performance of concrete. (2) In the retempering concrete by the addition of CDA, the modified VB consolidation factor significantly decreased to the same level in case of the simultaneous addition CDA at first mixing of concrete. Especially, the modified VB consolidation factor showed the remarkable efficacy of CDA addition by the late addition at the elapsed time of 60 min. (3) The final amount of bleeding of concrete using CDA showed the decrease when water-cement ratio increased. (4)The micro structure of concrete such as the weakness zone with lower strength along the coarse aggregate interface and the variation of pore structure were improved by addition of CDA. (5) The development of compressive strength and resistance to frost action of concrete could be judged as almost the same as those of concrete without CDA. (6)The use of this type of cement dispersing agent was judged promising for the improvement of concrete performance such as consistency, bleeding and micro structure. 8