1. Introduction. Yoshiharu Hosokawa 1) and Masami Shoya 2) 1) Faculty of Bio-Production & Environmental Sciences, Kitasato University, Japan

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1 EFFECTS OF RUBBING ACTION IN MANUFACTURING PROCESS OF RECYCLED COARSE AGGREGATE FROM WASTE CONCRETE ON STRENGTH AND DURABILITY OF RECYCLED CONCRETE PRODUCTS Yoshiharu Hosokawa 1) and Masami Shoya 2) 1) Faculty of Bio-Production & Environmental Sciences, Kitasato University, Japan 2) Dept. of Environmental & Civil Engineering, Hachinohe Institute of Technology, Japan Abstract In 2000, the quantity of Japan s waste concrete amounted to 35 million tons and the percentage of their recycling was 96%, as being reused mostly into lower base material in road pavements. From the effective utilization of finite resources, it is necessary to study how to reuse recycled aggregate from waste concrete into new concrete. This paper describes about effects of the rubbing action in the third manufacturing process of recycled coarse aggregate from waste concrete on the strength and durability of recycled concrete products. The recycled coarse aggregate rubbed in the third process remarkably improved their physical properties and their strength increased 42% than the coarse aggregate recycled in the second process. The strength of concrete products reused the third processed coarse aggregate increased 21% at 14-day age and 17% at 28-day age, compared with the concrete products reused the second processed coarse aggregate. The freeze-thaw durability of both concrete products was almost similar. Consequently, influencing the rubbing action in the manufacturing process improved both qualities of recycled coarse aggregate and recycled concrete products, because the rubbing action caused to make round aggregate corner while removing mortar from aggregate surface. 1. Introduction In 2000, the waste concrete quantity amounted to 35 million tons and the percentage of their recycling was 96%. It is estimated that almost all of them were reused into lower base material in road pavements. On the other hand, using better natural aggregate for concrete material is very difficult. So, we must use crushed stone, sometimes furnace slag [1], and rarely low quality aggregate. Consequently, it is important to study the effective utilization of

2 aggregate manufactured by recycling the waste concrete from standpoints of effective utilization of finite resources. The waste concrete includes various quality concrete, i.e., old construction and building concrete, and old concrete products like poles, flumes, curbs, gutters, and so on. Therefore, the recycled aggregate indicates lower quality and the recycled concrete made from reused recycled aggregate indicates much lower quality. The recycling of waste concrete into new concrete material tried to remove surface mortar of their aggregate because the recycled aggregate have high water absorption. For example, Yamada et al. [2] developed new crushing machine for waste concrete and Tatematsu et al. [3] reported the gravity concentration method. Guidebook of utilization of concrete waste in the public works was reported by Public Works Research Institute et al. [4] as the temporary recommendation of recycled aggregate utilization. In the temporary recommendation, it was described that the recycled coarse aggregate was classified by water absorption and loss in Soundness test to three kinds of aggregate quality. For example, the recycled coarse aggregate of below 3% water absorption and below 12% loss of Soundness test is classified as first class and can be reused into reinforced concrete. Concrete products are manufactured with smaller water cement ratio than general concrete under severe quality control. Recycled concrete products, reusing the recycled aggregate manufactured by the rubbing action after the second crushing, are expected to maintain better quality. This paper describes effects of the rubbing action in the third manufacturing process of recycled coarse aggregate from waste concrete on the strength and durability of recycled concrete products. 2. Materials and Method 2.1 Waste concrete and manufacturing method of recycled aggregate The original waste concrete blocks were from the reinforced concrete of some factory s building floor with 9-year age after building. The original concrete was mixed with river sand and river gravel of 25-mm maximum size but the strength of original waste concrete was not measured and the concrete mix proportion was also not clear. After the concrete blocks were crushed to make small blocks of about 500 mm size by a crushing machine at the site of the building, they were brought to the recycling plant. In the recycling plant, the waste concrete blocks were first crushed by a jaw crusher into minimum size of 30mm. The metal and other wooden chips were collected manually on a turning belt conveyer on the way to the next process. In the second process after the first crushing, the coarse aggregate was crushed by the impeller breaker into below 25 mm size and then sieved by the vibrating sieves into mm, mm, mm, 5-10 mm and below 5 mm size. The coarse aggregate of over 25 mm size was again crushed by the impeller breaker. Furthermore, about half quantities of the second crushing coarse aggregate of 5-25 mm size was crushed by the improved impeller breaker with the rubbing action and then sieved

3 by the vibrating sieves into mm, mm, mm, 5-10 mm and below 5 mm size, as the third crushing coarse aggregate. In this process by the improved impeller breaker, the mortar and the rough jag on the surface of second crushing aggregate were rubbed off as the coarse aggregate run against each other inside the machine, as shown in Fig. 1. This process is important to manufacture the recycled coarse aggregate to remove mortar on aggregate surface. Lastly, the aggregate of below 5 mm was divided into recycled fine aggregate of mm size and dust under 0.15 mm size by the air separator s strong wind at 1,200 r.p.m. while using their density difference. The second and third crushing (recycled) coarse aggregate were brought to the laboratory in order to analyze the aggregate properties and the shape, and to require the point load strength of coarse aggregate. 2.2 Properties, point load strength and shape of coarse aggregate Generally, using recycled coarse aggregate into concrete products is necessary to compare with crushed stone. The properties of crushed stone and recycled aggregate were tested for density, water absorption, fineness modulus, unit weight, solid content, losses in Abrasion, Washing and Soundness tests, by Japanese Industrial Standards (JIS). The point load test [5] to require the point load strength is to press coarse aggregate between the upper and the lower steel sticks attached on the same axis in the compressive test machine, and its phenomenon is to tension inside coarse aggregate between two points on the same axis. 20 coarse aggregates with mm size were required for the point load strength. The point load strength is calculated by the following equation. S = 0.9 F / (d 2 ) where, S: Point load strength (N/mm 2 ) F: Breaking loads at the test (N) d: Minimum distance of stone at the breaking (mm) Moving of whole aggregate Moving of rubbing board Moving of each aggregate Fig. 1: Mechanism of the improved impeller breaker with the rubbing action. On the other hand, the aggregate shape was studied by the Zingg s shape judgment and the spherical shape rate. After measuring the shape of 20 pieces of mm size of crushed stone and recycled coarse aggregate, the Zingg s shape judgment, introduced by Ito [6], classifies the pieces into spherical, club, slab and slender sheet shapes, depending on the

4 following properties: Spherical shape: M/L>0.667 and S/M>0.667 Club shape: M/L<0.667 and S/M>0.667 Slab shape: M/L>0.667 and S/M<0.667 Slender sheet shape: M/L<0.667 and S/M<0.667 where, L, M and S: long-axis, middle-axis and short-axis lengths (mm) Furthermore, the spherical shape rate of coarse aggregate is calculated by next equation, using the same three axis lengths of shapes as above. Spherical shape rate = 3 M/L S/L 2.3 Concrete mix proportion using crushed stone and recycled coarse aggregate Table 1 shows the concrete mix proportion for concrete product using crushed stone and for recycled concrete products using recycled coarse aggregate. The concrete materials used Ordinary Portland cement with 3.16 g/cm 3 density, the aggregate shown in Table 2 included crushed sand, and ground water in the concrete product plant. Fresh concrete for concrete Table 1: Concrete mix proportion * of concrete products Concrete W/C (%) s/a (%) Quantity per unit volume (kg/m 3 ) Water Cement Fine aggr. Coarse aggr. H.W.R.A. ** A.C.A. *** Crushed stone Recycled 2nd crushing concrete 3rd crushing * : Target of slump and air content of fresh concrete is 5.0±1.0 cm and 5.0±1.0%, respectively. ** H.W.R.A: High-range water-reducing agent, *** A.C.A: Air control admixture. Table 2: Properties of aggregate Aggregate Coarse Crushed stone Recycled aggregate Density (g/cm 3 ) Water absorption (%) Fineness modulus Unit weight (kg/l) Solid content (%) Loss in Washing test (%) nd crushing rd crushing Fine Crushed sand Loss in Soundness test (%) products was compacted in the test pieces molds by the table vibrator with each 2,850 r.p.m. under cm steel boards. All of test pieces were cured in the water with 20 temperature, because steam curing sometimes has strength difference relative to curing conditions, like the time difference in the pre-steam curing of each concrete batch. 2.4 Evaluation of recycled concrete products Test pieces were tested for compressive and bending strengths at the ages of 7, 14 and 28 days,

5 while measuring the dynamic modulus of elasticity (Ed) and the static modulus of elasticity (Es). The ratio of bending strength versus compressive strength and Ed/Es were also calculated to compare the properties among concrete products. To grasp the concrete durability, the freezing and thawing test, by ASTM C 666 B: freezing up to 18 C of test piece s center in the air and thawing up to 5 C of them in the water, was started for cm test pieces of 14 days age until 300 cycles, while measuring the weight and Ed of test pieces in each 30 cycles. 3. Results and Discussion 3.1 Properties of recycled coarse aggregate Table 2 shows the properties of aggregate for concrete products. Both recycled coarse aggregate have lower density, higher water absorption, larger loss in Abrasion test and larger loss in Soundness test, as compared with crushed stone. River sand and gravel was used in the original concrete, the density was 2.46 in the second crushing recycled aggregate and 2.50 in the third crushing recycled aggregate. However, the water absorption was 6.04% and 4.83% respectively. Fig. 2 indicates the relationship 3.0 Density (g/cm 3 ) Crushed stone Recycled aggregate of 2nd crushing Recycled aggregate of 3rd crushing Crushed sand R=-0.991** Water absorption (%) Fig. 2: Relationship between water absorption and density. between water absorption and density. There is a significant difference at 1% level in this relationship and it is clear that the larger the water absorption, the smaller the density. The recycled coarse aggregate in the third process was improved by the standard for concrete, i.e., more than 2.5 density, below 3% water absorption, more than 59% solid content, below 40% loss in Abrasion test and below 12% loss in Soundness test. Concerning with loss in Soundness test, % of recycled aggregate was twice as large as 8.8% of crushed stone, since the chemical action by using Na 2 SO 4 solution attacks against the recycled coarse aggregate composed with the original river gravel and the mortar and then lost their weights rather than crushed stone without mortar. By the temporary recommendation of recycled aggregate utilization [4], first class is classified

6 by the aggregate condition with below 3% water absorption and below 12% loss of Soundness test, and the second class is similarly with below 5% absorption and below 12% loss of or with 3% absorption and below 40% loss of. Both recycled coarse aggregate were classified into third class with below 7% absorption, and can be reused into lower compressive strength concrete, without requiring high durability, of below 16 N/mm Point load strength and shape of recycled coarse aggregate The point load strength of crushed stone and recycled coarse aggregate are shown in Table 3. The point load strength of the recycled coarse aggregate was 8.2±5.8 N/mm 2 in the second crushing and 11.7±9.5 N/mm 2 in the third crushing against 17.9±11.6 N/mm 2 of crushed stone, and there is a significant difference at 5% level among them. The point load strength of the recycled coarse aggregate after rubbing action increased 42% than the recycled aggregate of second process. It is estimated that the point load strength of recycled coarse aggregate was strongly influenced by the river gravel used in the original building concrete, and the third crushing coarse aggregate was improved more than the second by the rubbing action in the Table 3: Point load strength and shape of crushed stone and recycled coarse aggregate Item Crushed stone Recycled coarse aggregate 2nd crushing 3rd crushing Point load strength (N/mm 2 ) 17.9±11.6 a 8.2±5.8 c 11.7±9.5 b [Ratio of average] [100] [46] [65] M/L * 0.68±0.09 a 0.73±0.11 ab 0.75±0.10 b Shape S/M * 0.65±0.15 a 0.77±0.13 b 0.79±0.11 b Zingg's judgment Slab shape Spherical shape Spherical shape Spherical shape rate 0.66±0.10 a 0.74±0.06 b 0.76±0.08 b * : L.,M and S: Long, middle and short axis length, respectively. a, b, c : Significant difference at 5% level between different letters in the same line. recycling process. Thus, as reported about the effects of rubbing action to the recycled coarse aggregate by Hosokawa [7], the rubbing action caused round corners of coarse aggregate while removing the mortar from aggregate surface. The most interesting point between both coarse aggregate is in their shape. As shown in Table 3, both recycled coarse aggregate indicated Spherical shape but crushed stone indicated Slab shape. Both recycled coarse aggregate had no significant difference in M/L and S/M, and indicated clearly a round shape rather than crushed stone. However, between both recycled coarse aggregate, there is no significant difference. Furthermore, spherical shape rate of recycled coarse aggregate were larger than 0.66 of crushed stone, there is a significant difference at 5% level. The recycled coarse aggregate showed a near sphere shape rather than crushed stone. Since M/L, S/M and spherical shape rate of the recycled coarse aggregate in the third process indicated slightly larger values than in the second process, it is influenced by the rubbing action in the third process.

7 3.3 Strength of recycled concrete products Fig. 3 shows the comparison of compressive strength of concrete products. In general, the standardized age for the concrete strength of test pieces is 28 days, i.e., wet curing. In this concrete products plant, the designed compressive strength of crushed stone concrete is 30 N/mm 2 at 14-day age in steam curing (by the concrete mix proportion in Table 1), and then in case of wet curing the designed compressive strength is nearly 30 N/mm 2 at 28-day age and also it is expected the target strength is 35 N/mm 2. As a result, the compressive strength of crushed stone concrete products and recycled concrete product of third crushing coarse aggregate attained the target strength. However, recycled concrete product of second crushing coarse aggregate did not reach with the 30 N/mm 2 designed compressive strength. Comparing with the concrete products reused second crushing coarse aggregate, the compressive strength of concrete products of the third crushing, treated the rubbing action, and was increased 21% at 14-day age and 17% and 28-day age. Effect of the rubbing action in the manufacturing process of recycling waste concrete was recognized as a difference in compressive strengths. Furthermore, in addition to the rubbing action, the concrete mix proportion with smaller W/C like 44.5% and larger cement-quantity per unit volume like kg/m 3 is important and effective, when reusing recycled coarse aggregate into new concrete products. Compressive strength (N/mm 2 ) Crushed stone concrete products Recycled aggr. of 2nd crushing concrete products Recycled aggr. of 3rd crushing concrete products Concrete age (days) Fig. 3: Comparison of compressive strength of concrete products. Other strength elements are shown in Table 4. The ratios of bending strength versus the compressive strength at 28-day age were 1/6.5-1/7.1 and these ratios indicate a standard ratio of 1/5-1/8 generally. Ed, Es and Ed/Es indicated N/mm 2, N/mm 2 and , respectively. The relationship between Ed and the compressive strength was in a correlation but the relationship between Es and the compressive strength was not in a correlation, and here is a difficulty of obtaining an exact measurement of Es. Ed/Es indicates about 1.1 in case of the ordinary concrete and becomes a larger value in case of lightweight concrete, therefore, of Ed/Es in this experiment indicated slightly larger than a general value.

8 3.4 Durability of recycled concrete products Fig. 4 shows the result of freezing and thawing test for 300 cycles. At 300 cycles, the relative dynamic modulus of elasticity was 92-96% in all concrete products. The lowest was 92% from concrete products of second crushing coarse aggregate, and there was no crack and no popout until 300 cycles. Regardless of their high water absorption and larger loss in Soundness test, these concrete products maintained enough durability. It is assumed the enough durability was influenced by enough air contents in fresh concrete of 4.7% (in case of second crushing aggregate) and of 5.1% (in case of third), by high compressive strength of about 30 N/mm 2 at 14-day age, and by severe-less method by ASTM C 666 B: freezing in air and thawing in water rather than the method of both freezing and thawing in water. Therefore, the recycled coarse aggregate from the waste building concrete mixed with river sand and gravel can be reused into the concrete products designed by smaller W/C and larger cement-quantity per unit volume under improved quality control. Table. 4: Bending strength vs. compressive strength, Ed, Es and Ed/Es of concrete products Concrete products Crushed stone Recycled coarse aggregate Bending strength vs. compressive strength at 28-day age Ed (kn/mm 2 ) Es (kn/mm 2 ) Ed/Es 1/ ± ± ±0.04 2nd crushing 1/ ± ± ±0.02 3rd crushing 1/ ± ± ± Relative dynamic modulus of elasticity (%) Crushed stone concrete products Recycled aggr. of 2nd crushing concrete products Recycled aggr. of 3rd crushing concrete products Freezing and thawing cycles Fig. 4: Result of freezing and thawing test. 4. Conclusion An experimented study on recycled coarse aggregate and recycled concrete products was carried out to grasp effects of the rubbing action in the manufacturing process of recycling waste concrete. Major findings of this study include the following:

9 1) The recycled coarse aggregate, after rubbing action in the third manufacturing process, improved the aggregate properties like density, water absorption and unit weight, indicating that the larger the water absorption, the smaller the aggregate density. The point load strength of recycled coarse aggregate of third process increased 42% more than the second. The shape of recycled coarse aggregate had a near sphere shape rather than crushed stone, and the spherical shape rate of the third processed coarse aggregate was slightly larger than the second. 2) The recycled concrete product reusing the second processed coarse aggregate did not reach the 30 N/mm 2 designed compressive strength. However, the compressive strength of concrete products reusing the third process increased to 21% at 14-day age and 17% and 28-day age more than the second, and the effect of rubbing action in the manufacturing process was recognized. 3) From the result of freezing and thawing test until 300 cycles, all concrete products kept enough durability, regardless of high water absorption and larger loss in Soundness test in the recycled coarse aggregate. The durability is estimated to be influenced by adequate the air contents in fresh concrete and by higher compressive strength at initial stage of the freezing and thawing test. 4) Consequently, the rubbing action in the process of manufacturing the recycled coarse aggregate obviously influenced and improved both qualities of aggregate and concrete products. Only in case of smaller W/C and larger cement-quantity per unit volume under improved quality control, reusing the recycled coarse aggregate into new concrete products is recommended. References [1] Shoya, M., Aba, M. and Sugita, S., A study on the effects controlling the concrete bleeding by mineral fine powders, Technology of Cement and Concrete, 53 (1999) (in Japanese with English summary). [2] Yamada, M., Kawamoto, T., Hasegawa, T. and Honda, A., Recovery of aggregate from waste concrete, J. Construction Materials, 3(1) (1993) (in Japanese). [3] Tatematsu, K., Yamazaki, J., Ito, N. and Shibatani, K., Production of high quality recycled aggregate by gravity concentration method and properties of concrete using its recycled aggregate, Cement Concrete, 634 (1999) 8-14 (in Japanese). [4] Public Works Research Institute of Ministry of Construction, Advanced Construction Technology Center, and 12 construction companies, Guidebook of utilization of concrete waste in the public works, Report No.166 (1997) 3-4 (in Japanese). [5] Editing committee of Investigation and Test for Rock -Test of point load, Soil test method, (J. Soil Engineering Society, 1990) (in Japanese). [6] Ito, S., Concrete Engineering, New Edition (Morikita-shuppan, 1972) (in Japanese). [7] Hosokawa, Y., Properties of concrete product using recycled coarse aggregate from waste flumes, Transactions of JSIDRE, 227 (2003)

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