Mechanical and Chemical Properties of the Concrete Used in the Structures Built in Old Days

Transcription

1 Session B-3: Activation System Mechanical and Chemical Properties of the Concrete Used in the Structures Built in Old Days Daisuke Sawaki 1 Ichiro Kuroda, Dr. Eng. 2 Makoto Ichitsubo, Dr. Eng. 3 Hideaki Kitazono 4 Satoshi Tanaka, Dr. Eng. 5 Asuo Yonekura, Dr. Eng. 6 1 Section chief, Taiheiyo Consultant Co., Ltd., Ohsaku, Sakura City, Chiba Prefecture., Japan, daisuke_sawaki@grp.taiheiyo-cement.co.jp 2 National Defense Academy of Japan, Hashirimizu, Yokosuka City, Kanagawa Prefecture., Japan, ikuroda@nda.ac.jp 3 Institute of National Colleges of Technology, Higashi-asakawa, Hachioji City, Tokyo, Japan, ichitubo@kosen-k.go.jp 4 Sub manager, ABE NIKKO KOGYO Co., Ltd., 2-7 Ichigaya-sadowara, Shinjuku Ward, 5 Taiheiyo Consultant Co., Ltd., Ohsaku, Sakura City, Tokyo, Japan, kitazono@abe-nikko.co.jp Chiba Prefecture., Japan, satoshi_tanaka@grp.taiheiyo-cement.co.jp 6 Hiroshima Institute of Technology, Miyake, Saeki Ward, Hiroshima City, Hirosima Perfecture, Japan, yonekura@cc.it-hiroshima.ac.jp Keywords: Old structure, Concrete, Long term-durability, Mechanical property, Chemical analysis, Electron probe microanalyzer Abstract Performance of a concrete is changed gradually with the age by chemical and/or physical actions. Deterioration of a concrete progressed to high level may cause serious damages on the structure. Whereas there are many concrete structures durable for long term. In this research, concrete samples taken from the two structures built in 1938 and 1940 were evaluated by mechanical tests and chemical analyses. Information on the raw materials, design, and technique of construction in those days obtained by these evaluations must be valuable for considering the long term-durability. 1.Introduction Hardened concrete has toughness, but it is not permanent. Deterioration by chemical and/or physical actions may progress in severe circumstances, and it may cause serious damages on the construction. Cement and concrete consume a lot of natural earth resources and fuels for their production such as a limestone, sand, gravel, coal, petroleum, and so on. Considering the global requirements for saving the resource and energy, long life cycle is generally needed for industrial materials, and cement and concrete are not the exceptions. In Japan, there are many structures built in over fifty or one hundred years ago keeping their soundness. Actual information obtained by evaluating these old concrete structures must be useful for considering the long-term durability. However, there were not always many researches into the old structures which evaluated their materials scientifically (Yokozeki et al. 1998) (Mori et al. 2003) 291

2 (Tamai, Y et al. 2006) (Hoshino et al. 2006). In this paper, concrete samples taken from two structures built in 1938 and 1940 were evaluated by mechanical tests and chemical analyses. Necessary factors for long-term durability of concrete were considered based on the experimental information on the raw materials, design and construction about seventy years ago. 2.Experiment 2.1 Structures from Which the Samples were Taken Two concrete structures built in Japan about seventy years ago were selected. Appearances of them are shown in Fig.1. Structure (a) is a shed for watching the enemies built by the Japanese navy in Yokosuka-city (Kanagawa prefecture). It was completed in Samples for evaluation were taken from the wall facing the west side. Fig.1 shows the appearance from the east side. Structure (b) is an oil storage tank built in Kure-city (Hiroshima prefecture) in 1940 (Sawaki et al. 2007). Inner volume of it was about fifty thousands kiloliter. It was located on a coast at a distance of about 100 meters from the seashore. As shown in Fig.2, the diameter and the height of the tank was 88 meters and 10 meters, respectively. Inner side of the tank was made with cylindrical concrete of the thickness of about 30 centimeters. Cross section of the inner concrete is shown in Fig.2. Samples for evaluation were taken from this concrete. The height of the sampling point was about 6.5 meters from the bottom of the tank. Fig.1 Structure (a) Structure (b) Appearances of the structures from which the samples were taken Fig.2 Inner side of the tank of the structure (b) made with cylindrical concrete 292

3 Session B-3: Activation System 2.2 Samples Taken from the Structures Cylindrical concrete samples were taken from each structure. Appearances of them are shown in Fig.3. The diameter and the length of the sample taken from the structure (a) (sample (a)) were 45mm and 300mm, and which of the sample taken from the structure (b) (sample (b)) were 150mm and 250mm, respectively. Sample taken from the structure (a) Fig.3 Appearances of the samples Sample taken from the structure (b) 2.3 Observation on the Deterioration in Macro Area The cylindrical concrete samples were divided into two parts along the central line for the long direction Observation by naked eyes Cross section of the concrete was observed by naked eyes to check the state of the cement paste, aggregate, and the interface of cement paste and aggregate Depth of neutralization A solution of phenolphthalein in methanol was sprayed on the cross section of the concrete, and the depth of the part which was not colored red was measured Distribution of element Square sample with dimensions of 40mm by 40mm by 10mm was taken from the sample (b). The polished and carbon-deposited surface (40mm by 40mm) was subjected to elemental mapping analysis of calcium, chlorine and sulfur by electron probe microanalyzer (EPMA). The condition of measurement was as follows. Accelerating voltage : 15kV, Current : A, Time of measurement for each pixel : 40msec, Diameter of the probe : 100 m, Size of each pixel : 200 m, Number of pixels for measurement: 160,000 (400 by 400) 2.4 Estimation of Mix Proportion Estimation was carried out in accordance with Japan Cement Association s method. 2.5 Measurement of Mechanical Properties Compressive strength, Young s modulus and Poisson s ratio were measured in accordance with JIS A Measurement of Pore Size Distribution Small pieces of the concrete of about several millimeters after dehydration by immersed in acetone and drying by kept in vacuum chamber for one week was subjected to mercury intrusion porosimetry (MIP). Range of pressurizing of MIP was from 0.5 to 60,000psia. 293

4 3.Results and Discussions 3.1 Deterioration in Macro Area Observation by naked eyes Appearance of the cross sections of the concrete sample (a) and (b) are shown in Fig.4. In the both samples, coarse aggregates had round shape, so they were considered to be river gravel. Aggregates contacted with the cement well, and defects in the interface between cement paste and aggregate were not observed. Defects in the cement paste probably because of poor compacting of concrete were also not observed. They were considered to be dense concretes well compacted. Silica gel formed by alkali-silica-reaction was not observed. Sample (a) Sample (b) Fig.4 Appearance of the cross section of the samples Depth of neutralization Results are shown in Table 1. Mean values measured on the inner side of the sample (a), outer side of the sample (a), and on the inner surface of the sample (b) were 6.9mm, 6.4mm and 4.8mm, respectively. The structure (a) is located on a hill which is about 100 meters above sea level, so it has usually been exposed to the wind. The structure (b) had not been filled with oil at all time, so the upper part of its concrete had been exposed to the air when the oil level had been low. Considering the age and the conditions to be exposed, neutralization of these structures are considered to be little compared to the other structures built in the same age, for example the concrete arch bridge in Miyanoharu line (Tamai, T et al. 2006). Table 1 Depth of neutralization of the samples Sample (a) : Inner side of the wall Sample (a) : Outer side of the wall Sample (b) 294

5 Session B-3: Activation System Distribution of element Result of the mapping analysis of the sample (b) is shown in Fig.5. In the area of about several millimeters depth from the surface, the concentrations of calcium, chlorine and sulfur were lower than those in the inner area. This is considered to be due to the neutralization caused by carbonation and/or dissolution of cement paste. Its depth, about several millimeters was close to the value measured by spraying of phenolphthalein. It is well known that sulfur and chlorine transfer to the non-neutralized area due to the incline of their concentrations caused by the decomposition of sulfur or chlorine-containing hydrates in the carbonated area (Kobayashi et al. 1990). Such phenomenon could be observed in sulfur s result, but the extent of it was not large, so it suggested that the carbonation did not progress much. The concentration of chlorine in the non-neutralized area declined gradually toward the inner area. It suggests that the chloride from the ocean intrudes into the concrete. However, the concrete was not a steel-reinforced one, so the deterioration due to the chlorine was not observed. Fig.5 Distribution of Ca, S and Cl in the sample (b) (Area for analysis : 40mm by 40mm) 3.2 Mix Proportion Observation with scanning electron microscope showed that the sample (a) and the sample (b) didn t contain blending components such as blast furnace slag, therefore the kind of cement used in them was supposed to be ordinary Portland cement (OPC). Estimation was carried out under the premise that the cement was OPC. When the content of cement in the concrete was calculated, the values of ignition loss (ig.loss) and content of CaO of cement were fixed for 0.6% and 65%, respectively, they were close to the standard values of OPC in 1940 (Nakao 1968). At the calculation of content of aggregate in the concrete, the values of insoluble matter (insol.), ig.loss and content of CaO of aggregate were fixed for 95.2%, 1.2% and 0.4%, respectively, they were mean values of natural aggregates (river sand and gravel) mined in Japan. The result is shown in Table 2. Estimated unit weights of cement, water and aggregate of the sample (a) were 397kg/m 3, 263kg/m 3 and 1595kg/m 3, respectively. Ratio of water to cement (W/C), and that of aggregate to cement (A/C) were 295

6 calculated as 0.66 and W/C was relatively large, and A/C is small, so it was supposed that a concrete with good fluidity was used in the structure (a) in order to fill up them fully around the steel for reinforcement. Estimated unit weights of cement, water and aggregate of the sample (b) were 236kg/m 3, 139kg/m 3 and 2013kg/m 3, respectively. W/C and A/C were calculated as 0.59 and 8.52, they were lower and higher compared to those of the sample (a). It is known that unit weight of water is needed to be 147 kg/m 3 on average to prepare a concrete with 4cm slump using river sand and river gravel. Unit weight of water of the sample (b) was approximate to this value. So, the sample (b) is supposed to be prepared as a relatively hard concrete. Whereas, it was confirmed that the sample (b) had almost no defects. From these results, sample (b) is supposed to be filled up fully by careful compacting. Table 2 Estimated mix proportion of the samples 3.4 Mechanical Properties Results of compressive strength, Young s modulus and Poisson s ratio are shown in Table 3. The mean value of compressive strength of two test piece of the sample (a) was 41.6N/mm 2. That of the sample (b) was 40.6N/mm 2. These values are considered to be sufficiently high as the concrete prepared about seventy years ago. As shown in Fig.6, which illustrates the relationship between the ratio of cement to water (C/W) and the compressive strength of the several long-aged concretes, the strength of the sample (a) and (b) are not inferior to those of the concrete having a similar C/W, and it suggests that the mechanical properties of these structures have not been deteriorated seriously. Table 3 Results of compressive strength, Young's modulus and Poisson's ratio 296

7 Session B-3: Activation System Fig.6 Relationship between the ratio of cement to water and the compressive strength 3.5 Pore Size Distribution Pore size distribution of the sample (a) and the sample (b) are shown in Fig.7. For the comparison, result of a concrete passed about twenty years since it was prepared is also shown in Fig.7. Pores which have the diameter from 1 to 10 m in the sample (a) and (b) were more than that in the comparative concrete. But the pores smaller than 0.1 m, which are so-called capillary pore and relate closer to the mechanical properties and durability of the concrete, in the sample (a) and (b) are less than those in comparative concrete. Pores smaller than 0.01 m are mainly gel pore, which are the inner space of calcium silicate hydrate. Gel pore in the concrete increases as the hydration of the cement proceeds. Gel pore in the sample (a) and (b) were more than that in comparative concrete. From these results, it is supposed that the sample (a) and (b) have dense texture and the hydration of their cement proceed to high extent. Fig.7 Pore size distribution of the samples 297

8 4.Conclusion Concrete samples were taken from two structures built in 1938 and 1940, and their mechanical and chemical properties were evaluated. In both concretes, serious deterioration with the age was not observed. Mechanical properties were good, and macro and micro texture suggested that careful construction was carried out on these structures. These results certify that the structures built with good construction can keep a long-term durability. References Hoshino, T., M. Tsuji, S. Takahashi, K. Asaga, Y. Nakata, and K. Uomoto.K Analytical research on dockyard concrete built over one hundred years ago. Midterm report of committee on assessment and repair of historical structures, Kobayashi, K., R. Shiraki, and K. Kawai Migration and concentration of chlorides, sulfides and alkali compounds caused by carbonation. Concrete Research and Technology. Vol.1. No Mori, Y., Y. Uno, and K. Kobayashi Research on freight ship TAKECHI-MARU built with steel-reinforced concrete. Proceedings of the Japan Concrete Institute. Vol.25. No Nakao, T Quality of Japanese cement. CEMENT CONCRETE. No Sawaki, D., S. Tanaka, I. Kuroda, and A. Yonekura Mechanical and chemical properties of concrete taken from an oil storage tank built in the early year of Showa Period. Submitted to Cement Science and Concrete Technology. No.61. Tamai, T., I. Kobayashi, H. Watanabe, and H. Kasami Investigation of concrete arch bridges in existence in Miyanoharu line. Proceedings of the Committee on Historical Studies in Civil Engineering held by Japan Society of Civil Engineers Tamai, Y., T. Sasaki, T. Morikawa, S. Yoshida, H. Nishizawa, and Y. Tanigawa,Y Analytical research on underground concrete pillar and foundation built ninety years ago, Midterm report of committee on assessment and repair of historical structures, Yokozeki, Y., J. Nakasone, K. Kakizaki, and K. Watanabe Durability of underground concrete structure built over one hundred years ago. Proceedings of the Japan Concrete Institute. Vol.20. No