STUDY ON STRENGTH AND DURABILITY OF CONCRETE USING LOW QUALITY COARSE AGGREGATE FROM CIRCUM-PACIFIC REGION

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1 STUDY ON STRENGTH AND DURABILITY OF CONCRETE USING LOW QUALITY COARSE AGGREGATE FROM CIRCUM-PACIFIC REGION Wanchai Yodsudjai, Nobuaki Otsuki, Takahiro Nishida, Hiroyuki Yamane Department of International Development Engineering, Tokyo Institute of Technology O-okayama, Meguro-ku, Tokyo , Japan ABSTRACT This study attempts to examine the strength and durability of concrete using low quality coarse aggregates from the circum-pacific region. The research starts with the examination of the strength and durability of low quality coarse aggregates from the circum- Pacific region, and subsequently examine for the influence of the low quality coarse aggregate on the concrete characteristics. Lastly, the quality improvement methods: the coating of coarse aggregate and combined with the normal aggregate methods, for concrete using the low quality coarse aggregates are proposed. As a result, it can be concluded that the strength and durability of concrete using low quality coarse aggregate can be clarified by the strength and durability of low quality coarse aggregate. In addition, the improvement methods proposed in this study can be successfully implemented for improving the strength and durability of concrete using low quality coarse aggregate. KEYWORDS: low quality coarse aggregate, circum-pacific region, strength, durability, improvement method INTRODUCTION Since coarse aggregate in concrete occupies 4% of the volume, the coarse aggregate phase predominantly influences on characteristics of the concrete, particularly for a case of highly porous and weak aggregates. In circum-pacific region, where Japan also belongs to, it is provided with a vast supply of low quality coarse aggregate, i.e. volcanic aggregate and coral aggregate due to its geographical location surrounded by many of oceans and volcanoes. From the construction viewpoint, utilizing material resources found around or near the construction site is deemed necessary in order to effectively optimize resources. However, it is unfortunate to note there had been no research undertaken at the moment, that examine the strength and durability of concrete using these low quality coarse aggregates gathered from the circum-pacific region. Therefore, this study attempts to examine the strength and the durability of the concrete using the low quality coarse aggregates from the circum-pacific region. The research starts with an examination of the strength and the durability of the low quality coarse aggregates, and subsequently examines for the influence of the low quality coarse aggregate on the concrete characteristics. Lastly, the quality improvement methods for concrete using low the quality coarse aggregate are proposed.

2 Low Quality Coarse EXPERIMENTAL PROGRAM Table 1 Physical Properties of Coarse Name Materials Density (kg/l) Absorption Ratio (%) Fineness Modulus Solid Ratio (%) Okinawa Nicaragua Philippines Lime Stone (Coral Reef Sediment) Igneous Rock Volcano (Mt.Pinatubo) Kiribati Coral Normal Crushed Stone Four types of the low quality coarse aggregate from the circum-pacific region are examined: Okinawa aggregate (Lime Stone), Nicaragua aggregate (Igneous Rock), Philippines aggregate (Volcanic) and Kiribati aggregate (Coral). In addition, crushed stone from Oume-made (Tokyo) is used as a normal coarse aggregate serving as a control variable for the comparative study. The physical properties of the coarse aggregates are shown in Table 1. Fig. 1 shows the void structure of each low quality coarse aggregate taken from the microscope. It can be observed that the aggregates coming from the Philippines and Kiribati show continuous voids, and that from Nicaragua have separated voids. It is interesting to note that out of the four types of aggregates observed only the aggregates from Okinawa did not contain any void spaces, however, the results from porosity test shows that the aggregate from Okinawa contains many of very small voids. 2 m 2 m 2 m 1 m Philippines Kiribati Nicaragua Okinawa Fig. 1 Voids Structure of Low Quality Coarse Materials Ordinary Portland cement with 3.16 g/cm 3 density is used. Fine aggregate is river sand with 2.62 specific gravity and 2.87 fineness modulus. Mixing Proportions and Mixing Procedures Mixing Proportions are shown in Table 2. For concrete mixing procedure, the cement is sandwiched between two layers of sand in the mixer, and then the mixer rotates for 3 seconds. Water is added as the mixer rotates for 3 seconds. The mixing is stopped as soon as all water is already poured into the mixer. Finally, coarse aggregate is added and the concrete is mixed for 12 seconds.

3 Table 2 Mixing Proportions W/C s/a (%) Slump, Flow (cm) Air Conten t (%) Unit Unit Content (kg/m 3 ) Content (m 3 /m 3 ) W C SF S G Water Reducing Agent (Cx%) AE Agent (Cx%) Superplasticizer (Cx%) ±5. 4± ±2.5 4± ±2.5 4± ±2.5 4± Testing Procedures for Evaluation Low Quality Coarse Minute-Compressive Measurement Test Piece Fig.2 Test Piece Fig.3 Minute Compressive Measurement 5 mm 5m 3% 3 % NaCl Solution Saturated Ca(OH) 2 Solution Epoxy Resin Matrix Fig.4 Test Piece Test Piece setting in in Epoxy Fig. 5 Minute-Diffusion Cell A minute compressive measurement is used for evaluation a compressive strength of the low quality coarse aggregate. This method is developed originally by the authors (Yamane, 21). The low quality coarse aggregate is cut into a cube of 3 x 3 x 3 mm as can be seen in Fig.2. The compressive measurement is performed by using the universal test machine with 5 kn maximum test load. The loading of the test piece can be seen in Fig.3. In addition, this minute compressive measurement is applied to use for evaluation the mortar that taken from the concrete specimens. Minute-Diffusion Measurement A minute diffusion measurement is used for evaluation a chloride diffusion coefficient of the low quality coarse aggregates. The test piece of 5 x 5 x 1 mm is cut from the coarse aggregate and set in the epoxy resin (φ 3 x 1 mm) as can be seen in Fig. 4. The minutediffusion cell is set-up as can be seen in Fig.5. The 15 ml of 3% NaCl solution is filled one side of its container while on another side is filled with 15 ml saturated Ca(OH) 2 solution. To obtain the chloride ion diffusion coefficient of the low quality coarse aggregate, it can be

4 calculated using the Fick s first law of diffusion (Cranck, 1996) by determining the change of concentration of the chloride ion on the saturated Ca(OH) 2 side. Testing Procedures for Evaluation Concrete Compressive Strength After 28 days curing in water at 2±2 C, the compressive strength test is determined with φ1 x 2 mm cylindrical specimen. Three specimens are used in each case of the experiment. Chloride Diffusion Coefficient The diffusion coefficient ion in concrete is investigated through an electro-migration test (Otsuki, 1998). RESULTS Strength and Chloride Diffusion Coefficient of Low Quality Coarse Fig. 6 shows the strength of the low quality coarse aggregate from the circum-pacific region. It can be seen that their compressive strength is lower as compared to the normal aggregate. Particularly, the strength of the Philippines aggregate and the Kiribati aggregate is less than 1% of the normal aggregate. Fig.7 shows the chloride ion diffusion coefficient of the low quality coarse aggregate from the Circum-Pacific region. It can be seen that the chloride ion diffusion coefficient of all low quality coarse aggregates are higher than that of the normal coarse aggregate from Tokyo. Particularly, the chloride ion diffusion coefficient of the Philippines aggregate and the Kiribati aggregate are around 1 times higher than that of the normal aggregate. As a result, it can be confirmed that the low quality coarse aggregates from the circum-pacific region have lower strength and higher chloride ion diffusion coefficient than that of the normal coarse aggregate from Tokyo. 3 Compressive Strength (MPa) Philippines Kiribati Okinawa Normal Nicaragua Fig. 6 Compressive Strength of Coarse

5 1 Philippines Kiribati Chloride Ion Diffusion Coefficien (x 1-8 cm 2 /sec) Okinawa Nicaragua Normal Fig. 7 Chloride Ion Diffusion Coefficient of Coarse Strength and Chloride Ion Diffusion Coefficient of Concrete Using Low Quality Coarse s from Circum-Pacific Region Fig. 8 shows the strength of concrete using the low quality coarse aggregates from the circum-pacific region. It can be seen that when the cement-water (C/W) ratio is low the type of coarse aggregate does not much influence on the strength of concrete. On the other hand, the difference of concrete strength can be clearly seen when the cement-water ratio is high, i.e. the type of coarse aggregate influences on the strength of concrete. Fig. 9 shows the chloride ion diffusion coefficient of the concrete using the low quality coarse aggregate from the circum-pacific region. It can be seen that the coarse aggregate type does not much influence on the chloride ion diffusion coefficient of concrete in the case of.25 water-cement (W/C) ratio. On the other hand, for the case of.4,.55 and.7 water-cement ratios, the coarse aggregate type influences on the chloride ion diffusion coefficient of concrete, i.e. the concrete using the low quality coarse aggregates have higher chloride ion diffusion coefficient than that of the normal aggregate. Compressive Strength (MPa) Okinawa Nicaragua Philippines Kiribati Normal Cement-Water Ratio (C/W) Fig. 8 Strength of Concrete Using Low Quality Coarse

6 Chloride Ion Diffuision Coefficient 1-8 cm 2 /sec Okinawa Nicaragua Philippine Kiribati Normal Compressive Strength of Concrete (MPa) Water- Cement Ratio W/C Fig. 9 Chloride Ion Diffusion Coefficient of Concrete Using Low Quality W/C =.25 6 W/C =.4 W/C =.55 4 W/C = Compressive Strength of Coarse (MPa) Fig. 1 Relationship Between Compressive Strengths of Coarse and Concrete Compressive Strength of Concrete (MPa) Philippines Kiribati Okinawa Nicaragua Normal Lightweight Compressive Strength of Coarse (MPa) Fig. 11 Compressive Strength of Concrete Using Different Strengths

7 a) Strength of Coarse is Lower than that of Mortar 8 b) Strength of Coarse is Higher than that of Mortar Fig. 12 Fracture Surface of Concrete Cl- Diffusion Coeffficient of Concrete ( 1-8 cm 2 /sec) Cl- Diffusion Coefficient of Coarse ( 1-8 cm 2 /sec) W/C =.25 W/C =.4 W/C =.55 W/C =.7 Fig.13 Relationship Between Chloride Ion Diffusion Coefficients of Coarse and Concrete Influence of Low Quality Coarse on Concrete Strength and Chloride Diffusion Coefficient Fig. 1 shows the influence of the strength of the coarse aggregate on the strength of the concrete. It can be seen that the strength of the concrete increases as the strength of the coarse aggregate increases, however, the strength of the concrete trends to be steady after reach the peak for all cases of water-cement ratios. The reason can be explained from Fig. 11 that when the strength of the coarse aggregate is lower than that of the mortar the strength of coarse aggregate influences on the strength of concrete, i.e. the strength of concrete increases as the strength of coarse aggregate increases because the cracks develops in both mortar and coarse aggregate. Fig. 12(a) shows the fracture surface of the concrete in the case of the strength of the coarse aggregate is lower than that of the mortar (Philippines aggregate). It can be seen that the cracks propagate not only on the mortar portions but also throughout the coarse aggregate. On the other hand when the strength of coarse aggregate is higher than that of the mortar, the strength of coarse aggregate does not influence on the strength of concrete, i.e. the strength of the concrete is steady even the strength of the coarse aggregate increases. It can be confirmed by the cracks pattern as can be seen in Fig. 12(b). Fig.12(b) shows the fracture surface of the concrete in the case of the strength of the coarse aggregate is higher than that of the mortar (Normal aggregate). It can be seen that the cracks propagates only in the mortar portion. Fig. 13 shows the influence of the chloride ion diffusion coefficient of the

8 coarse aggregate on the chloride ion diffusion coefficient of concrete. It can be seen that the chloride ion diffusion coefficient of the concrete increases as the chloride ion diffusion coefficient of the coarse aggregate increases. This can be explained that when the high chloride ion diffusion coefficient coarse aggregate is used the chloride ion penetrates not only into the mortar portion but also into the coarse aggregate portion. On the other hand, when the low chloride ion diffusion coefficient coarse aggregate is used the chloride ion can penetrates into only the mortar portion. Improvement Methods for Concrete Using Low Quality Coarse s Type Table 3. Comparison Between Concrete Using Low Quality and Normal Coarse s Compressive Strength Chloride Ion Diffusion Coefficient Water-Cement Ratio Water-Cement Ratio Philippines X X X X X X X Kiribati X X X X X X X Nicaragua X X X Okinawa X X X X = Better than Normal = Same as Normal X = Worse than Normal The concrete using the low quality coarse aggregates from the circum-pacific region have almost lower strength and higher chloride ion diffusion coefficient than that of the concrete using the normal coarse aggregate as can be seen in Table 3. If the designed strength of concrete is less than the result shown in Fig.8, these low quality coarse aggregates can be used without any improvement. However, in order to utilize these low quality coarse aggregates in the better quality concrete, it is necessary to find the appropriate improvement methods. One example is the Nicaragua aggregate, the concrete using the Nicaragua aggregate have the strength almost equivalent to the concrete using the normal coarse aggregate. However, the chloride ion diffusion coefficient of the concrete using the Nicaragua aggregate is higher than that of the concrete using the normal coarse aggregate. Therefore, the coating of coarse aggregate (Nathaniel, 1999) is thought as the method for improving the concrete using the Nicaragua aggregate. The Nicaragua aggregate is coated with the cement paste of.25 water-cement ratio prior to concrete mixing. The coating of coarse aggregate method leads the concrete using the Nicaragua aggregate more permeable because of the chloride ion can penetrate into only the mortar portion but cannot penetrate into the coarse aggregate due to the protection of coated cement paste. As can be seen in Fig. 14, the coating of coarse aggregate method can lower the chloride ion diffusion coefficient of the concrete using the Nicaragua aggregate around 45%. In addition, it can be seen that the coating of the coarse aggregate can also improve the strength of the concrete using the Nicaragua aggregate around 5%. For other types of the low quality coarse aggregates, the improvement methods and the results after the improvement are shown in Table 4. It can be seen that the improvements in strength and chloride ion diffusion coefficient of the concrete using the low quality coarse aggregates from the circum-pacific region can be achieved by using the proposed improvement methods.

9 Chloride Ion Diffusion Coefficient ( 1-8 cm 2 /sec) Before Improvement 45% Down After Improvement Compressive Strength % Up Before Improvement After Improvement Fig. 14 Improvement of Strength and Chloride Ion Diffusion Coefficient of Concrete Using Nicaragua by Coating of Coarse Table 4. Improvement Method for Using Low Quality Coarse in Concrete Types Nicaragua Okinawa Philippines Improvement Methods Coating of Coarse Coating of Coarse Combine with Normal Improvement of Compressive Strength Improvement of Chloride Ion Diffusion Coefficient 5% Improvement 45% Reduction 15% Improvement 7% Reduction 45% Improvement 4% Reduction CONCLUSIONS 1. The methods for evaluating the strength and the chloride ion diffusion coefficient of the low quality coarse aggregate from the circum-pacific region have been established quantitatively. 2. The strength and the chloride ion diffusion coefficient of the concrete using the low quality coarse aggregate from the circum-pacific region can be examined. 3. The influence of the coarse aggregate on the strength and the chloride ion diffusion coefficient can be clarified as follow. When the strength of the coarse aggregate is lower than that of the mortar the strength of the coarse aggregate influence on the strength of the concrete, on the other hand, when the strength of the coarse aggregate is higher than that of mortar the strength of the coarse aggregate does not influence on the strength of the concrete. The chloride ion diffusion coefficient of the coarse aggregate influences greatly on the chloride ion diffusion coefficient of the concrete. 4. The improvement in strength and chloride ion diffusion coefficient of the concrete using the low quality coarse aggregates form the circum-pacific region can be achieved by using the proposed improvement methods.

10 REFERENCES Cranck, J. (1996) The Mathematics of Diffusion. 2 nd ed., Clarendon Press, New York. Nathaniel, B.D., Otsuki, N. and Miyazato, S. (1999) The Use of Coated Coarse and Double Mixing in Making Concrete. Proc. of the 1 st International Summer Symposium, JSCE, pp , Tokyo, Japan Otsuki, N., Hisada, M., Otani, M. and Maruyama T. (1998) Theoretical Assessment of Diffusion Coefficient of Chloride Ion in Mortar by Electro-Migration Method. Journal of Materials, Concrete Structure and Pavements, No.592/V.39, pp (in Japanese). Yamane, H., Otsuki, N., Nishida, T. and Yodsudjai, W. (22) Development of Measuring Methods to Evaluate Tensile and Compressive Strength of Minute Regions in Concrete. Proc. of the 4 th International Summer Symposium, JSCE, pp , Tokyo, Japan Yodsudjai, W., Otsuki, N., Nishida, T. and Onitsuka, R. (22) Study on Strength and Durability of Concrete Using Low Quality Coarse from Circum-Pacific Region. 27 th Conference on Our World in Concrete & Structure, Singapore, pp