FREEZE-THAW RESISTANCE OF WATER PERMEABLE CONCRETE

Transcription

1 FREEZE-THAW RESISTANCE OF WATER PERMEABLE CONCRETE Z. Wang, N. Saeki, T. Horiguchi and Shimura Hokkaido University, Graduate School of Engineering, Hokkaido, Japan Abstract In this research, it is supposed that water permeable concrete is being used in several environments. For example, it is being used on the ground, near lakes or in river. In these humid conditions, the permeable concrete will reach a degree of saturation. In the winter, concrete is subjected to freeze-thaw attack, damage to the internal structure of the concrete as well as to its surface can occur. The degradation is enhanced if a de-icing agent attacks at the same time. Therefore it is necessary for us to discuss about the resistance against freeze-thaw attack. In general, when the permeable concrete is set up on the permeable back-filling material, water is not retained in the continuous-void, but retained in the void of matrix due to capillary suction. This action is an important reason that the freeze-thaw attack occurs. The correlation between the water permeability and the resistance of permeable concrete against freeze-thaw attack will be mainly discussed in this paper. RILEM TC-117 CIF/CDF is adopted as the testing method for the resistant against freeze-thaw. The water permeability of the test specimens is varied from 2 to.1cm/s in the range of normal permeable concrete. Keywords: Water Permeable concrete, RILEM TC-117CIF/CDF test, FREEZE-THAW 1 Introduction In recent years, the multi-property of concrete has been studied in many research departments. The permeable concrete is a kind of concrete which has the properties (high air permeability and high water permeability), its application becomes active as harmonic material in nature. In some fields, the properties of permeable concrete are not understood clearly. In a cold region, freeze-thaw damage in practice occurs rarely, but the freeze-thaw resistance of permeable concrete by ASTM666A is weak. So it is necessary to discuss the mechanism of permeable concrete within these different conditions. 33

2 In the experiment, the experimental method is based on the RILEM TC-117CIF. CIF means Capillary suction, Internal damage and Freeze-thaw test. It is considered as the main reason that the resistance against freeze-thaw of concrete is connected with the capillary suction and internal damage. In this experiment, the method of measurement is adopted by determination of surface scaling, evaluation of the inner damage with ultrasonic method. 2 Test Specimens and Test procedure 2.1 Materials and mix proportion of specimens As specimen materials, the mixed materials are made up with ordinary portland cement and three kinds of coarse aggregates. The coarse aggregates are all crushed stone and divided into three kinds (maximum sizes of 2mm, 13mm and 5mm). Two kinds of chemical admixtures are used by air entrained agent (AE-A) and AE water reducing agent (AEWR-A). Mix proportion of specimens is shown in Table1. Table 1: Mix proportion of concrete Specimens Gmax Void p/a W C G AE-A AEWR-A mm % % kg/m³ cc/m³ V2B wc =,25 The specimens are divided into three kinds,, V2B6 and. The types of the specimens are decided by the different factors with maximum size of coarse aggregate, with the volume ratio of cement paste to aggregate. 2.2 Preparation of experiment (1) Specimens For the mixing procedure, the cement and aggregate were mixed for 1.5 minutes, then water and chemical admixtures were added and mixed for 3 minutes with a double shaft pug-mill mixer. The mixed materials were cast into a mm mould on which the inner surface had been covered with a teflon plate, then compacted on a vibratory table. After the age of 14 days, using a concrete cutter, mm specimens were made. The concrete surface of the teflon plate is the test surface. (Fig.1) 34

3 saw cut casting 75mm 75mm in mould, 1 day 15mm 15mm 15mm 15mm 1mm 55mm water curing (2 C, 3 days) air curing (2 C, 65%RH, 14 days) 15mm 75mm Pre-suction (2 C, 65% RH, 7 days) Fig. 1 Specimen Fig. 2: Flow chart of curing (2) Preparation of specimens The procedure of the preparation of specimens is shown in Fig.2. After 24h of curing in mould the specimens were removed from the mould and stored for 13 days (until the age of 14 days) in tap water at 2 C. Then the concrete specimens were stored in the climate chamber (2 C, 65% RH) for surface drying for 14 days. During the dry storage course, the specimens were sealed on their lateral surfaces with aluminium foil with butyl rubber. Before sealing, the lateral surfaces, the specimens had been cleaned and kept dry. Following dry storage the specimens were placed in the test containers on the 1 mm high spacers with the test surface underneath (Fig.3). lid of the chest next container lateral sealing test liquid cooling liquid reference point air layer as thermal isolation mm specimens test surface spacer 5 mm high 1 mm 5 mm Subsequently, the test liquid was filled into the container to a height of 15mm. Presaturation of test liquid by capillary suction was 7 days at a temperature of 2 C. During capillary suction, the liquid level was checked and adjusted, the weight gain of the specimens was measured. Fig.3: Container and specimen 2.3 Freeze-thaw testing In this experiment 56 cycles were adopted with 12h a cycle. Staring at +2 C the temperature was lowered in 4h with a constant cooling rate of 1 K/h. It was kept constant for 3h at 2 C and increased in 4h with a constant heating rate of 1 K/h. It is kept con- 35

4 stant for 1h at 2 C. The temperature cycle was monitored at the reference point in the freeze-thaw equipment. (Fig.4, 5) temperature 2 C C -2 C h 4 h 7 h 11 h 12 h time Fig.4: Control temperature cycle air layer as thermal isolation cooling liquid test liquid Fig.5: Freeze-thaw set up specimen 2.4 Method of Measurement (1) Ultrasonic transit time To evaluate the internal damage of the permeable concrete the movement of ultrasonic transit time was measured (shown as Fig.6). transducer axis of transit Specimen path 35mm test surface container Fig.6 Ultrasonic test The transducers are mounted on the sides of the container so that the transit path axis is parallel and 35mm from the test surface. (2) Determination of surface scaling The surface scaling was measured while the temperature was above 15 C. To remove loose adhering scaled material from the test surface, the test container was dipped into the contact liquid of an ultrasonic bath and subjected to ultrasonic cleaning for 3 minutes. The solution containing the scaled material was filtered. Then the paper filter was subsequently dried at 11 C for 24h. 36

5 3 Test results 3.1 Mechanical Properties of the permeable concrete (1) Tensile strength and compression strength Tensile strength and compression strength were taken at the age of 28 days. It is shown as Table2 and Table3. Table2: Tensile strength Table3: Compressive strength Specimens Tensile strength (N/mm 2 ) Average (N/mm 2 ) Compressive strength (N/mm 2 ) Average (N/mm 2 ) V2B (2) Coefficient of permeability and continuous void content Measurement of coefficient of permeability was investigated at the age of 28 days. The specimen has a highly porous structure, the measurement was based on JIS A 1218 (Fig.7). The result is shown as Table4. Measurement of continuous void content is based on JIS A 116. The results are shown in Fig.8. Table4: Coefficient of Water permeability water Water permeability Average Specimens water (cm/s) (cm/s) V2B flowingoutwater specimen Fig.7: Measurement of water permeability Fig.8: Total air void Total air void V2B Average 3.2 Capillary suction In Fig. 9 the transfer of capillary suction during the presuction and freeze-thaw cycles are described. The quantity of the capillary suction of the specimen was very remarkable on the first day in the course of presuction. After that, remarkable transfer was not 37

6 clearly recognizable, but the quantity of capillary suction increased with freeze-thaw cycles beginning at the seventh day again. This is considered that the water penetrated Absorption (g) V2B Scaling (g/m²) a -b -c Fig.1: Scaling () Scaling (g/m²) a -b -c Time (Day) Fig.9 Absorption Freeze-thaw cycles Fig.12 Scaling () the capillary because the pump suction and the capillary suction were effected with the freeze-thaw. As the coefficient of permeability is larger, the quantity of capillary suction is grows. On the other hand, with the coefficient of permeability being small, volume ratio of cement paste to aggregate being large, the amount of capillary suction increased. This is considered as one of the capillary suction reasons in the course of freeze-thaw cycles. 3.3 Quantity of surface scaling In Fig.1, 11, 12 and 13 the transfers of scaling are shown. According to these, it is admitted that the quantity of scaling increased with the progression of freeze-thaw. The difference of scaling is not large with changing the coefficient of permeability. It is shown that the quantity of scaling becomes larger as the coefficient of permeability becomes larger. So the relativity between the movement of capillary suction and a quan- Scaling (g/m²) V2B6-a V2B6-b V2B6-c Fig.11 Scaling (V2B6) Scaling (g/m²) V2B Fig.13 Scaling (average) 38

7 tity of scaling is considered. It can be observed when the coefficient of permeability is higher, but not distinguished when the coefficient of permeability is lower. 3.4 Evaluation of internal damage In Fig.14, 15 the measurements of the ultrasonic transit are shown. According to this, ultrasonic propagation velocity is slow when the freeze-thaw cycles progress and the difference by specimen did not appear definitely. Accordingly, it is necessary to discuss the size of transducer and the measurement of position. Velocity (m/s) V2B Fig.14 Velocity (ultrasonic test) Velocity ratio v t /v V2B Fig.15 Velocity ratio (Vt/V ) Fig.16 Condition of scaling () Fig.17 Condition of scaling (V2B6) 4 Conclusion Fig.18: Condition of scaling () (1) The quantity of capillary suction of permeable concrete became larger when the coefficient of permeability was lower, it is found that the pump effect occurs. The quantity of capillary suction increases when the freeze-thaw cycles begin. (2) The transfer of the quantity of scaling becomes larger when the coefficient of permeability is low as the same as the 39

8 transference of the quantity of capillary suction. Also the relativity between the movement of capillary suction and quantity of scaling is considered. (3) Although the result of internal damage with ultrasonic propagation velocity was observed, but is not remarkably distinguishable. Furthermore, it is necessary to investigate. 5 References 1 IS 117 FDC, Draft recommendation for the freeze-thaw resistance of concrete-tests with water (CF) or with sodium chloride solution (CDF). Materials & Structures.(1995) 2 Setzer, M.J. and Auberg, R, Freeze thaw and deicing salt resistance of concrete testing by CDF method-cdf resistance limit and evaluation of precision. Materials & Structures, Vol. 28, pp (1995) 3 Setzer, M.J. and Auberg, R, Evaluation of the precision of freeze thaw and deicing salt:testing by the CDF procedure. Proc. Intern. Conf. On Concrete under severe conditions, environment and loading Sapporo, (1995) 31