FROST RESISTANCE AND MICRO PORE STRUCTURE CHANGE OF MORTAR EXPOSED TO DIFFERENT CLIMATE CONDITIONS

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1 Cementitious Composites, April 212, Amsterdam, he Netherlands FRS RESISANCE AND MICR PRE SRUCURE CANGE F MRAR EXPSED DIFFEREN CLIMAE CNDIINS Yukio ama (1), Yoshihiko Kishimoto (1) and Mohamed Zakaria (2) (1) Architecture and Building Engineering Research Unit, College of Environmental echnology, Graduate School of Engineering, Muroran Institute of echnology, Muroran, Japan. hama@mmm.muroran-it.ac.jp & kisimoto@mmm.muroran-it.ac.jp (2) Graduate School of Engineering, Muroran Institute of echnology, Muroran, Japan, Aswan Faculty of Engineering, South Valley University, Aswan, Egypt. eng_zakaria@yahoo.com Abstract Micro pore structure is an important factor affecting the properties of mortar and concrete, such as strength and durability. For example, the frost resistance, which is quite needed for better durability performance of concrete members, is affected by the volume of micro pore with 4-2 nm diameter. It was pointed out recently that the nanostructure of C-S- and the micro pore structure of concrete are remarkably changed by drying or drying-wetting cycles, and thus the frost resistance can be consecutively degraded by those changes. owever, the clarification of the environmental action on frost damage and microporosity has not been fully understood. he aim of this study is to investigate the influence of environmental conditions (drying temperature, relative humidity, drying period and dryingwetting cycles) on the frost resistance and micro pore structure distribution. Micro pore structure of mortar specimens subjected to drying conditions in the laboratory, as one test set, and exposed to different climate conditions at three outdoor locations, as another test set, was quantified using Mercury Intrusion Porosimetry (MIP) method. RILEM CIF test was also carried out to evaluate the frost resistance of tested mortar specimens. he results of both the outdoor exposure test and the laboratory test revealed that not only the volume of 4-2 nm diameter pore but also the unconnected pore volume can be increased by high temperature drying. Furthermore, it was clarified that the drying temperature is more critical to the coarsening of micro pore structure and the degradation of frost resistance than humidity. 1. INRDUCIN Frost damage by freezing/thawing action adversely influences the durability performance of concrete in cold regions. owever, frost resistance can be affected not only by weather conditions in winter, such as freezing temperatures and freezing/thawing cycles, but also by

2 Cementitious Composites, April 212, Amsterdam, he Netherlands drying conditions in summer. ama et al. [1,2] showed that the frost resistance of high performance concrete (PC) without AE excessively decreased after several years of outdoor exposure. he increase of micro-cracks due to the higher temperature of drying-wetting cycles curing was the reason for the decrease of the frost resistance of non-ae PC. his implies that the pore structure became coarser after cycles of high temperature drying-wetting, which may affect the degradation of frost resistance. he previous study by Kamada et al. [3] concluded that the volume of 4-2 nm diameter micro pore has a significant influence on the mechanism of frost damage in concrete. he change of pore structure of hardened cement paste is probably related to the change in nanostructure of C-S- gel, which is a main constituent of the hardened cement paste. Recently, Many researchers [4,5,7] have studied the effects of drying and/or wetting cycles on frost resistance, pore size distributions and nanostructure of C-S- in hardened cement paste using Mercury Intrusion Porosimetry (MIP), Nuclear Magnetic Resonance (NMR), and 2 sorption isotherm. It was found that the nanostructure of C-S- and the micro pore structure of concrete are coarsened by drying or drying-wetting cycles and the frost resistance is degraded by those changes. he change of micro pore structure is due to the polymerization of silicate anions coordinated with Ca layer developed when C-S- was subjected to drying. In spite of these efforts, the effects of different environment conditions on the micro pore structure and frost resistance in mortar and concrete have not been clarified yet. he ambient conditions, such as temperature and humidity during drying period in the laboratory, might be different from the actual ambient conditions at the outdoor exposure environment. herefore, it is necessary to verify the relationship between the property of pore structure and the frost resistance in case of outdoor exposure tests for mortar samples. In this study, the influence of environmental conditions, which are drying temperature, relative humidity and drying period, on the frost resistance and micro pore structure changes was investigated using RILEM CIF test and MIP method, respectively. Mortar specimens were prepared and subjected to drying in the laboratory, and exposed to different climate conditions at three outdoor locations as well. he obtained results are useful for understanding the degradation of the durability performance of mortar and concrete with respect to frost damage. 2. EXPERIMENAL PRCEDURE 2.1 Materials and specimens Mortar specimens without AE were prepared using two types of cement, which are ordinary Portland cement (N) and fly ash cement (FA). Fly ash content in FA cement was 15% by weight of cement. Land sand from Noboribetsu was used as a fine aggregate with 2.69 g/cm 3 and 1.52 % for the density in saturated surface-dry condition and the percentage of absorption, respectively. Water-cement ratio (W/C) was set as.35 and.55 and the cementsand ratio was set as.5. All specimens were casted into W 4 L 16 4 mm prism size. For the laboratory test, where the effects of drying curing condition were examined, mortar specimens were demoulded and curing conditions were applied as given in able 1. he initial curing of mortar was curing in water at 2 for 4 weeks. Afterwards, drying curing and drying-wetting curing were applied at 2 and 5. In the case of drying at 5, different humidity values (5% and 6%R) were provided, and the period of drying was varied as 2 and 4 weeks as well.

Cementitious Composites, 11-13 April 212, Amsterdam, he Netherlands For the outdoor exposure test, the specimens, after initial curing in water at 2 for 4 weeks, were exposed to different climate

3 Cementitious Composites, April 212, Amsterdam, he Netherlands For the outdoor exposure test, the specimens, after initial curing in water at 2 for 4 weeks, were exposed to different climate conditions for about one and a half years at three outdoor sites in Japan, which are Muroran (okkaido), Narashino (okyo) and Naha (kinawa). he climate conditions for the outdoor exposure test are shown in able 2 and Fig. 1 as well. he mortar specimen () was considered the reference mortar specimen for both the laboratory and the outdoor exposure tests. able 1: Curing conditions in the laboratory test Symbol Initial curing Drying condition Drying period Water curing at 2 No drying 2D-4W for 4 weeks Drying at 2 (6%R) 4 weeks 5DL-2W Drying at 5 (5%R) 2 weeks 5DL-4W 4 weeks 5D-2W Drying at 5 (6%R) 2 weeks 5D-4W 4 weeks 5DW-2W Drying and wetting cycles at 5 * 2 weeks (4 cycles) 5DW-4W 4 weeks (8 cycles) *: [Drying at 5 (5%R) for 3 days Wetting at 5 for.5 days] able 2: Climate condition at exposed points Symbol Exposure place Annual mean temperature ( ) Annual mean humidity (%R) Muroran, okkaido 8.6 (max 23.4, min -4.2) 77 (max 9, min 69) Narashino, okyo 15.3 (max 31., min 1.4) 69 (max 8, min 55) Naha, kinawa 23.1 (max 31.8, min 14.6) 74 (max 83, min 66) Muroran, okkaido Narashino, okyo Naha, kinawa Figure 1: Exposure test conditions 2.2 Experimental Method Frost resistance of W 4 L 16 4 mm mortar prisms was evaluated by RILEM CIF test [6]. Lateral surfaces of mortar prisms were sealed by aluminium foil tape with butyl rubber. he mass change during the isothermal capillary suction and the freezing/thawing cycles was measured. he change of relative dynamic modulus of elasticity (RDM) during freezing/thawing cycles was also recorded. MIP was used to quantify the micro pore structure of tested mortars. First, the mortar specimens were cut into 5 mm cubes, treated with acetone to stop the hydration, and then kept in D-dried condition. Finally, approximately 228 Mpa maximum pressure corresponding to 6nm of minimum pore diameter was applied to measure the pore size distributions by MIP.

4 Cementitious Composites, April 212, Amsterdam, he Netherlands 3. RESULS AND DISCUSSIN 3.1 Frost Resistance Figure 2 shows the variation of relative dynamic modulus of elasticity versus freeze/thaw cycles using the CIF test method in case of mortars dried in the laboratory. he air content of N-.35 (air content 3.7%) FA-.35 (air content 2.8%) modulud of elasticity (%) Figure 2: Results of freezing/thawing test for laboratory curing specimens N-.55 (air content 1.4%) FA-.55 (air content 1.%) 5DL-2W 5D-2W 5DW-2W 2D-4W 5DL-4W 5D-4W 5DW-4W modulus of elasticty (%) N-.35 (air content 3.7%) N-.55 (air content 1.4%) FA-.55 (air content 1.%) FA-.35 (air content 2.8%) Figure 3: Results of freezing/thawing test for outdoor exposure specimens

5 Cementitious Composites, April 212, Amsterdam, he Netherlands each specimen case is described in Fig. 2. It is obvious from the figure that the frost resistance, represented by RDM, significantly decreased with drying or drying-wetting cycles at 5 C (5DL, 5D, 5DW) regardless of the drying period and cement type used, except specimen N-.35. In case of N-.35, all mortar specimens showed high frost resistance because of the great air content (3.7%) of specimens compared to other cases. n the other hand, no difference in frost resistance between the reference specimen without drying () and the specimen dried at 2 C (2D) was observed. hus, it can be clarified that the influence of drying temperature is relatively larger on the frost resistance degradation than humidity. he change of relative dynamic modulus of elasticity during freezing/thawing cycles based on the CIF test, where mortars exposed to outdoor conditions for one and half years, is presented in Fig. 3 including Ref. specimen. he frost resistance of outdoor exposure mortars tested at three different sites was decreased in a similar way to that of the laboratory test. 3.2 Pore Structure Change Figure 4 shows the volume of micro pore with 4-2 nm diameter, which has the influence on the frost resistance, for all mortar samples in this study. he pore volume (4-2 nm diameter) for both mortar samples tested outdoors, and dried in the laboratory at 5 C (5DL, 5D, 5DW), regardless of the type of cement used, increased compared to specimen. Also, the change of the pore volume for the outdoor exposure mortar specimens was almost the same to that of 5DW mortar specimens tested in the laboratory. It was found that the influence of drying at 5 C on the pore structure change was more severe than that of the outdoor exposure for one and a half years. his is the reason for the sudden degradation of frost resistance of mortars in case of drying curing in laboratory. Pore volume from 4 to 2nm in diameter (cc/g) N-.35 2D-4W 5DL-2W 5DL-4W 5D-2W 5D-4W 5DW-2W 5DW-4W Pore volume from 4 to 2nm in diameter (cc/g) N-.55 2D-4W 5DL-2W 5DL-4W 5D-2W 5D-4W 5DW-2W 5DW-4W Pore volume from 4 to 2nm in diameter (cc/g) FA-.35 2D-4W 5DL-2W 5DL-4W 5D-2W 5D-4W 5DW-2W 5DW-4W Pore volume from 4 to 2nm in diameter (cc/g) D-4W 5DL-2W 5DL-4W 5D-2W 5D-4W 5DW-2W 5DW-4W FA-.55 Figure 4: Volume of micro pore with 4-2 nm diameter

6 Cementitious Composites, April 212, Amsterdam, he Netherlands Laboratory Exposure Pore volume from 4 to 2nm in diameter (cc/g) Pore volume from 4 to 2nm in diameter (cc/g) Figure 5: Relationship between volume of 4-2 nm diameter pore and disconnected pore volume N emperature ( ).8 FA emperature ( ) Pore volume from 4 to 2nm in diameter (cc/g) Pore volume from 4 to 2nm in diameter (cc/g) N emperature ( ) FA emperature ( ) Laboratory (6%R) Exposure Figure 6: Relationship between volume of pore with 4-2 nm diameter and temperature

7 Cementitious Composites, April 212, Amsterdam, he Netherlands In this study, the volume of disconnected pores, namely ink-bottle shape pores, which is the difference of hysteresis between first and second measurement by MIP was also analyzed. he disconnected pore volume showed an increase by drying at 5 C and exposure compared to specimen, regardless of cement type used. Figure 5 presents the relationship between the micro pore volume and the disconnected pore volume. It is clear that the connectivity of pore structure became lower than that of specimen, while the the micro pore volume (from 4-2 nm diameter) increased due to drying or drying-wetting cycles and exposure. he relationship between the micro pore volume (4-2 nm diameter) and drying temperature is given in Fig. 6, which shows that higher temperature can cause the increase of micro pore volume. While, no correlation was found between the pore volume with 4-2 nm diameter and the ambient humidity. herefore, it can be said that the influence of drying temperature on the micro pore structure change is larger than that of humidity. 3.3 Relationship between Pore Structure and Frost Resistance Figure 7 shows the relationship between the micro pore volume and the durability factor. he durability factor of CIF test was calculated by the modified ASM C666 equation, Eq. 1. DF = PN/M (1) where, DF: durability factor of the test specimen, P: relative dynamic modulus of elasticity at N cycles, %, N: number of cycles at P reaches 8% or 56 cycles (smaller value), M: 56 cycles Durability factor Pore volume from 4 to 2nm in diameter (cc/g) N Dulability factor :.35: Laboratory.35: Exposure.55: 2.55: Laboratory.55: Exposure Pore volume from 4 to 2nm in diameter (cc/g) Figure 7: Relationship between volume of 4-2 nm diameter pore and durability factor It can be inferred from Fig. 7 that the durability factor due to freeze/thaw cycles test sharply decrease, i.e. frost damage occurs shortly, when there is an increase of micro pore volume for both mortars of the laboratory and exposure tests, except in case of N-.35 specimen. N-.35 was durable to frost damage because of its high air content. Although the difference of air content could influence the adequate evaluation of the results, it is clear that the frost resistance of mortar can be degraded by the increase of the volume of pore with 4-2 nm diameter due to drying at high temperature or outdoor exposure. Moreover, the connectivity of pore structure would affect significantly the frost resistance and the micro pore volume. he change of frost resistance and pore structure in the specimens exposed to different climate conditions has the same tendency with that of the laboratory test specimens. FA

8 Cementitious Composites, April 212, Amsterdam, he Netherlands 4. CNCLUSINS Both results of the laboratory and outdoor exposure tests revealed that the pore structure of mortar was coarsened and the volume of 4-2 nm diameter micro pore, which has a significant influence on the frost resistance and frost damage of mortar, increased regardless of the cement type or drying period. Moreover, the frost resistance of mortar drastically decreased by drying or drying-wetting curing in the laboratory at high temperature and outdoor exposure conditions as well. Not only the volume of pore with 4-2 nm diameter but also the disconnected pore volume were increased by drying effects. his implies that the connectivity of pore structure would become smaller by drying or drying-wetting curing at high temperature or exposure conditions. Also, this connectivity of pore structure would influence significantly the frost resistance as well as the volume of 4-2 nm diameter pore. he drying temperature was more critical to the coarsening of micro pore structure and the degradation of frost resistance than humidity conditions. he influence of drying at 5 C on the pore structure change was more severe than that of one and half years outdoor exposure test for mortar specimens. ACKNWLEDGEMENS he authors would like to express their deepest appreciation for the grant provided by the Special Coordination Funds for Promoting Science and echnology of the Ministry of Education, Culture, Sports, Science and echnology, Japan, to accomplish this study. REFERENCES [1] ama, Y., Senbu,. and omosawa, F., Effect of Curing Condition before Freezing and hawing est to Frost Resistance of igh Performance Concrete Proceedings of 6th International Symposium on igh Strength/igh Performance Concrete, (22) [2] ama, Y., Aono, Y. and Shibata, S., Influence of Micro-cracks on Frost Resistance of igh Performance Concrete Proceedings of International Conference on Durability of PC and Final Workshop of CNLIFE, AEDIFICAI, (Essen, ) [3] Kamada, E., Senbu,., abata, M. and anaka,. Statistical Investigation Concerning Effects of Pore Structure on the Frost Resistance of Concrete (in Japanese) Journal of Structre Construction Engineering, AIJ, No.487, (1996) 1-9. [4] Aono, Y., Matsushita, F., Shibata, S. and ama, Y., Study on Frost Resistance and its Degradation Mechanism of Cement Paste Subjected to Drying and Wetting Cycles Proceedings of 5th International Essen Workshop ransport in Concrete: Nano- to Macrostructure (RANSCN7), (27) [5] Aono, Y., Matsushita, F., Shibata, S. and ama, Y., Nano-structural changes in C-S- during drying at 5C Journal of Advanced Concrete echnology, 5(3), (27) [6] RILEM C 176-IDC, Final Recommendation of RILEM C 176-IDC Internal Damage of Concrete due to frost action est methods of frost resistance of concrete: CIF-est (Capillary suction, internal damage and freeze thaw test)- Reference method and alternative methods A and B Materials and Structures, [37], (24) [7] Galle, C., Effect of Drying on Cement-based Materials Pore Structure as Identified by Mercury Intrusion Porosimetry A Comparative Study between ven-, Vacuum-, and Freeze-drying Cement and Concrete Research, 31(1), (21)

Effect of application timing of silicate-based surface penetrants on the mass transport properties of concrete

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