The effect of freeze thaw cycles on physical and mechanical properties of granitoid hard rocks

Transcription

1 Bull Eng Geol Environ DOI /s ORIGINAL PAPER The effect of freeze thaw cycles on physical and mechanical properties of granitoid hard rocks A. Momeni 1 Y. Abdilor 2 G. R. Khanlari 3 M. Heidari 3 A. A. Sepahi 3 Received: 4 March 2015 / Accepted: 21 August 2015 Springer-Verlag Berlin Heidelberg 2015 Abstract This paper presents the influence of freeze thaw cycles on physical and mechanical properties of Alvand granitoids hard rocks, in the west of Iran. For this purpose, three different types of Alvand granitoid rocks were selected and studied. For assessment of freeze thaw weathering effects, a long-term freeze thaw test was carried out for 300 cycles. P-wave velocity, porosity, water absorption, dry density, uniaxial compressive strength, and tensile strength of specimens were determined prior to doing the test and after every 50 cycles. The results of this study show that, by increases in the number of freeze thaw cycles, uniaxial compressive strength, tensile strength, dry density, and P-wave velocity decreases, whereas the water absorption and porosity increases. P-wave velocity and tensile strength were also suggested as the best indicators to assess the effects of freeze thaw cycles on the physical and mechanical properties of the studied granites. Keywords Freeze thaw Water absorption Porosity P-wave velocity Tensile strength & A. Momeni Ali_moomeni@yahoo.com Department of Geology, Faculty of Earth Sciences, Shahrood University, Shahrood, Iran Department of Geology, Faculty of Sciences, Lorestan University, Khoramabad, Iran Department of Geology, Faculty of Sciences, Bu-Ali Sina University, Hamedan, Iran Introduction Freeze thaw action is one of the most powerful physical weathering agents, which may cause a rapid change in the mechanical properties of stones, and limit their durability. Therefore, the resistance to deterioration should be evaluated before the selection of an appropriate building stone (Zappia et al. 1998). Building stones and historical monuments are prone to damage due to the natural destructive factors with instant or gradual function or by the human destructive factors. Generally, instant natural and human destructive factors for damage have been taken into consideration, but gradual natural destructive factors mostly were neglected. The one most important gradual natural destructive process is weathering due to freezing and thawing. Rock deterioration under freeze thaw cycles is a concern in many projects such as road, railroad, pipeline, and building construction in cold regions (Grossi et al. 2007; Zhang et al. 2004). Natural stones are generally used as building materials for construction, decoration, and monuments. Determining the deteriorations of stones after freeze thaw cycles is an important subject for natural building stones used in cold regions, because they are exposed to excessive freezing and thawing during the year. The stones used in cold regions are exposed to at least one freezing and thawing cycle every year (Bayram 2012). Many researchers have studied the durability, as well as the physical and mechanical properties of various rocks under freeze thaw cycles (Khanlari and Abdilor 2014; Altindag et al. 2004; Binal and Kasapoglu 2002; Karaca et al. 2010; Mutluturk et al. 2004; Nicholson 2001; Rossi-Doria Rossi 1985; Ruedrich and Siegesmund 2007; Tan et al. 2011; Topal and Doyuran 1998; Topal and Sözmen 2000; Yavuz et al. 2006). Khanlari and Abdilor (2014) studied the influence of

2 A. Momeni et al. freeze thaw on the physical and mechanical properties of sandstones. They observed that by increasing the number of freeze thaw cycles, the P-wave velocity and uniaxial compressive strength decreased, whereas the porosity values showed an increasing trend. Altindag et al. (2004) evaluated the decay function model, proposed by Mutluturk et al. (2004), for loss of integrity of ignimbrite and determined the effects of freeze thaw cycles on Isparta ignimbrite. Binal and Kasapoglu (2002) investigated the effect of freeze thaw on the uniaxial compressive strength of Selime (Aksaray) ignimbrite. Chen et al. (2004) studied the effect of water saturation on highly porous welded tuff due to the freeze thaw cycles. They found that the porosity and rock damage significantly increased when the initial degree of saturation exceeded 70 %. Hale and Shakoor (2003) reported that porosity values in the range between 2 and 7 % caused significant reduction in compressive strength of sandstones during multiple freeze thaw cycles. Topal and Sözmen (2000) investigated the changes in dry density, porosity, UCS, and P-wave velocity of the Yazilikaya tuffs after freeze thaw cycles. Yavuz et al. (2006) proposed a model equation for estimating the index properties of deteriorated carbonate rocks due to freeze thaw cycles. This model explains a decrease in the index property of a deteriorated rock depending on its initial engineering property and porosity of rock with the coefficients for a specific index property. In the freezing period, the stone is frozen and water in micropores expands about 9 % of the original volume. This expansion induces tensile stress concentration and damages the micropores, when the rock is thawed, water flows through the fractured micropores, which increase the damage (Bayram 2012; Bell 2000). Rock damage potential in cold regions is the result of freeze thaw cycle number, temperature, rock type, applied stress, and moisture content (Chen et al. 2004; Takarli et al. 2008). The durability of rocks under severe climatic conditions is a determining factor for the stability of natural stone structures used in buildings or sculptures. The response of rocks to changing temperature is also of interest in other applications where heat is a significant factor, as in geothermal energy and radioactive waste disposal (Yavuz et al. 2006). Most of the previous studies of freeze thaw effects on engineering behavior of rock were carried out on some rocks with low to medium strength. Because of high strength of hard rocks, their response to cyclic freeze thaw weathering was generally neglected. On the other hand, this test was normally done in a short period, and because of it being time consuming and other difficulties, long-term freeze thaw tests were not of interest to previous researchers. The climate of the study area is considered to be semiarid, with a mean annual precipitation of approximately 300 mm. Available data for a period of indicated that in this area the minimum temperature was C and the maximum temperature was?40 C with an average of 136 freezing days per year. Alvand batholith has around 400 km 2 outcrops and mainly is composed of porphyroid monzogranite, toalite, and hololeuco-granodiorite. These granitoid rocks are the most used stones in the construction of ancient buildings, ornamental elements, and movable stone heritage artifacts (e.g., statues, altar pieces, benches, etc.) in the west of Iran. In order to gain more knowledge of the weathering process that ice crystallization cause, laboratory freeze thaw tests are needed to evaluate the damaging dynamics. The main aim of the present work was to compare the engineering behavior of the three types of granitoid rocks against the freezing and thawing phenomenon. Materials and methods Three different types of Alvand granites were taken from different locations in southwestern Hamedan, (western Iran). Thin sections were taken and the petrographic characteristics of the samples were determined using an optical microscope. The contents of quartz, plagioclase, K-feldspars, biotite, and other minerals were distinguished. The mineral composition was also investigated by XRD analysis. Laboratory core drill and saw machines were used to prepare cylindrical samples with 54 mm diameter and a length to diameter ratio of between 2.5 and 3.0. Physical properties [dry density (c d ), the water absorption (QAI), porosity (n), and ultrasonic wave velocity (V p )] and mechanical properties [uniaxial compressive strength (UCS), and tensile strength (r t )] of all samples were determined prior to performing the cyclic physical weathering tests. It should be noted that to determine the physico-mechanical properties, ISRM (1981) suggested standard methods to be employed. For the freeze thaw test, initially the samples were saturated by submerging in water for 48 h and then placing in a freezer at -30 C for 18 h. Then, they were taken out of the freezer and placed into a water bath with rising temperature up to 40 C, where they were allowed to thaw for 6 h. These two stages are considered as one cycle, so each cycle of the freeze thaw test was completed for 24 h. The generalized temperature curve for each freeze thaw cycle is shown in Fig. 1. The freeze thaw test was carried out for 300 cycles and physic-mechanical properties of the specimens were determined after every 50 cycles. Results and discussion Petrographic studies The results of petrographic studies are given in Table 1. Mineralogical studies indicated that the studied granitoid

3 The effect of freeze thaw cycles on physical and mechanical properties of granitoid hard rocks Fig. 1 The generalized temperature curve for the freeze thaw cycle rocks are monzogranite, tonalite, and granodiorite. The studied mozogranite is coarse grained ([5 mm) with a subhedral granular texture and porphyritic fabric (Fig. 2). Tonalite shows medium-grained (2 5 mm) intergranular texture (Fig. 2). Granodiorite samples have a fine-grained matrix that is composed mainly by feldspar and quartz. In this type of rock, plagioclase mainly appears as phenocryst. Compared to other types, mafic minerals are absent, which leads to appearing to be white in color. The XRD test results for three rock types are shown in Fig. 2 as well. As can be seen in this Fig., the results of XRD analysis confirmed the obtained mineral composition of the thin sections studies. Physical and mechanical properties The results of physico-mechanical properties for all types of Alvand granitoid rocks are given in Table 2. To determine this parameter, at least five samples of each type of rock were tested, and average values were taken. Among the studied rocks, tonalite has the higher and granodiorite has the lower dry density. This difference is attributed to their mineral compositions and the presence of mafic minerals (biotite and amphibole) in tonalite. The maximum and minimum values of Vp, QAI, and porosity were measured for granodiorite and monzogranite, respectively. This indicates that Vp and porosity are mostly dependent on each other. This trend was also seen for mechanical Table 1 The results of petrographic analysis Rock type Modal composition Qz Pl Or Bt Am Minor mineral Monzogranite Tonalite Granodiorite properties as well. As presented in Table 2, monzogranites show the lowest UCS and rt (90.65 and 8.73 MPa), whereas granodiorites are characterized with the highest strength ( and MPa). As can be seen in Fig. 2 and Table 1, monzogranite has around 23 % biotite as a weak and weatherable mineral. On the other hand, the long type of grain contact especially for plagioclase was observed as dominaant types of minerals contacts, which leads to decreases of this type of strength. In the tonalite type, mafic minerals are more than monzogranite, but the texture shows the intergranular type, which leads to increase in minerals interlocking. Compared to monzogranite, intergranular texture and finer grained minerals have a resultant higher strength for tonalite. Absent of mafic minerals and fine-grained texture for granodiorite leads to increases in strength. Generally, both mineralogical composition and textural properties lead to the lowest strength for monzogranite and the highest strength for granodiorite. For the low porosity and high strength of these rocks, it is predicted that they will be strong against freeze thaw weathering effects. Freezing thawing test As previously mentioned, 300 freeze thaw cycles were carried out for each rock type, which took about 1 year of laboratory work. After every 50 freeze thaw cycle, UCS, tensile strength, water absorption, dry P-wave velocity, dry density, and porosity were measured. The results were discussed in two sections including freeze thaw effects on physical properties and mechanical properties. Freeze thaw effects on physical and mechanical properties The physical properties of the rocks during freezing thawing tests were measured, and the results are shown in Table 3. For assessment of freeze thaw effects on engineering parameters of these rocks, a damage ratio (DRx) was calculated and used for all physico-mechanical properties using the following equation DR x ¼ 1 x C300 x C0 100; ð1þ where x are physico-mechanical properties, x C300 are the physico-mechanical properties at the end of 300 freeze thaw cycles, x C0 are the properties of rock sample prior to the cyclic test. Based on the results presented in Table 3, minimum and maximum of the porosity increase ratio (DR n ) is 1 and 7 % for granodiorites and tonalites, respectively. The results indicate that the highest increase of damage ratio for water absorption (DR QAI ) is 31 % for granodiorites, whereas the lowest is 6 % for

4 A. Momeni et al. Fig. 2 Petrographic images and XRD results of the Alvand granitoid rocks; M monzogranite, T tonalite and G granodiorite (Qz quartz, Pl plagioclase, Or orthoclase, Bt biotite, Am amphibol, Sp sphene) monzogranites. Based on the results of Vp presented in Table 3, monzogranites show the highest decrease in P-wave velocity (8 %), whereas the lowest is 5 % for tonalites. The damage ratio for dry density shows that this parameter in practice was not affected by freeze thaw cycles, and there is no obvious weight loss. The used damage ratio (DRx) only considered cycles 0 and 300. So, variation trends of the properties between the cyclic tests (0 300 cycles) must be considered as well. In fact, this parameter gives valuable information regarding interaction of freeze thaw cycles and the properties. For this reason, variations of the used physical properties are

5 The effect of freeze thaw cycles on physical and mechanical properties of granitoid hard rocks Table 2 Mean values of physical and mechanical properties of fresh granites Rock type c d (gr/cm 3 ) n (%) QAI V P (m/sec) UCS (MPa) r t (MPa) Number of tests Monzogranite Tonalite Granodiorite c d dry density, n porosity, QAI quick water absorption, Vp P-wave velocity, rt tensile strength, UCS uniaxial compressive strength Table 3 The physical properties values during 300 freeze thaw cycles Parameter Rock type Cycle number DR x n (%) Monzogranite Tonalite Granodiorite QAI (%) Monzogranite Tonalite Granodiorite Vp dry (m/s) Monzogranite Tonalite Granodiorite Dry density (gr/cm 3 ) Monzogranite Tonalite Granodiorite shown in Fig. 3. As shown in this Fig. 3, the variations of porosity and water absorption values exhibit an increasing trend with increasing the freeze thaw cycles. An exponential function was developed as the best function for variation of QAI, whereas the best function for porosity changes was adopted with a linear function. When making a close inspection of Fig. 3a, b, it can be realized that variation limits of these parameters are very low, which can support high resistance of the studied rocks against cyclic freeze thaw weathering. In contrast, the rocks exhibit a sensible decrease of Vp in linear function. The high determination coefficient (R2) and relatively high slope of Vp variation for these rocks indicate that these physical properties are more sensitive to freeze thaw effects and will be used as a damage indicator. Monitoring the dry density variation, indicates that this parameter decreases very slowly and insensibly, and it can be said that dry density was more or less unaffected during 300 cycles of the freezing thawing test. The results of mechanical tests on the rocks during 300 cycles of freeze thaw test are given in Table 4. The results indicate that the freeze thaw treatments induced a considerable reduction in both UCS and r t for all types of granitoid rocks. In this study, the damage ratio was also used to indicate the effects of freeze thaw cycles on the strength of studied rocks. As shown in Table 4, granodiorites indicate the highest deterioration with 33 % reduction in UCS. The lowest deterioration was experienced by tonalite with 25 % reduction in UCS at the end of 300 freeze thaw cycles. Based on the results presented in this table, the minimum and maximum decreases in tensile strength were obtained for granodiorites and monzogranites with 13 and 32 % reduction, respectively. The variation of UCS and tensile strength with freeze thaw cycles is given in Fig. 4. Figure 4 shows that by increasing the freeze thaw cycles, UCS and tensile strength of studied rocks linearly decrease. As is clear from Fig. 4, the obtained variation slope and determination coefficient for UCS test are higher than tensile strength in all types of Alvand granitoid rocks. It means that this parameter was affected more than tensile strength due to the freezing thawing test. Figure 5 shows the rock samples in different freeze thaw cycles. As shown in Fig. 5, macroscopic damage in these samples not was observed. It seems that very low porosity of studied granitoids plays a main role in this issue. The results from other studies indicate that if the porosity is too low (\1 %), then water cannot enter the rock to degrade it (Hale and Shakoor 2003). Thin section studies after 300 freeze thaw cycles indicated that some small cracks were created (Fig. 6). The generated cracks were not developed because of low

6 A. Momeni et al. Fig. 3 Variations of a porosity, b water absorption, and c P-wave velocity vs. freeze thaw cycles for studied rocks Table 4 The mechanical properties values during 300 freeze thaw cycles Parameter Rock type Cycle number DR x UCS (MPa) Monzogranite Tonalite Granodiorite r t (MPa) Monzogranite Tonalite Granodiorite Fig. 4 The variations of a UCS-values and b r t values vs. freeze thaw cycles

7 The effect of freeze thaw cycles on physical and mechanical properties of granitoid hard rocks Fig. 5 The studied rocks in different freeze thaw cycles induced stress or number of cycles. If the number of cycles increases, not only the rocks were weakened, but also the induced stress increased as well. So, it is predicted that macroscopic damage features will emerge in a high number of freeze thaw cycles for the studied rocks. The damage mechanism of the cyclic freeze thaw test is related to the fatigue process. This process occurs as a consequence of any type of cyclic loading. It is well known that rock strength decreases due to the phenomenon of rock fatigue. The fatigue process consists of three stages: fatigue crack formation (initiation phase I), stable crack propagation (uniform velocity phase II), and unstable crack propagation resulting in a sudden breakdown (accelerated phase III) (Xiao et al. 2010). During the freezing thawing test on the studied rocks, cracks were nucleated, but the fatigue process remained in the initiation phase. In fact, low porosity of the rocks decreases the induced stress. On the other hand, the relatively high strength of these rocks results in resistance against crack development. That is why fatigue damage of the cyclic freeze thaw test remained in the initial phase. This leads to the created cracks being separated from each other and some physical parameters such as porosity, which is needed for connected cracks, was not sufficiently affected. Comparing to Fig. 6 Petrographic images of the Alvand granitoid rocks after 300 cycles of freeze thaw test; M monzogranite, T tonalite and G granodiorite (Qz quartz, Pl plagioclase, Or orthoclase, Bt biotite, Am amphibol) porosity, Vp is more sensitive to any type of crack (connected or separated cracks) and shows clearly a decrease by increasing cycle numbers. Moreover, these cracks nuclei during mechanical loading cause stress concentrations and lead to effective decreases in mechanical properties.

8 A. Momeni et al. If the number of cycles increased, then consequently the freeze thaw fatigue process will pass the initial phase and move to the other phases. On the basis of the results of this paper, the effects of freeze thaw weathering on deterioration behavior of granitoid hard rocks, especially when they used in ancient monuments, should be considered. Conclusions The degradation in the engineering properties of Alvand granitoid rocks under freeze thaw cycles was investigated by a series of physico-mechanical tests including porosity, quick water absorption, dry density, ultrasonic wave velocity, Brazilian tensile strength, and uniaxial compression tests. According to the present study, the conclusions can be summarized as follows: It was found that by increasing the number of freeze thaw cycles, the P-wave velocity, tensile strength, and uniaxial compressive strength decreases, whereas the porosity and water absorption values show an increasing trend. Ultrasonic wave velocity (Vp) was found to be a sensitive physical parameter and sufficient to detect the beginning of fabric deterioration before a macroscopic decay be observed. Also, this parameter is proposed as the best engineering (physico-mechanical) parameter to indicate cyclic freeze thaw damage. UCS was found to be the best mechanical parameter to show cyclic freeze thaw damage. The induced fatigue damage due to 300 cycles of the freeze thaw test was in the crack nucleation phase. This leads to the created cracks being separate from each other and some physical parameters such as porosity were not obviously affected. Moreover, during mechanical loading, these cracks nuclei cause stress concentrations and lead to decreases in mechanical properties. It seems that the very low porosity and the high strength of studied granitoid rocks play a main role in low damage due to the freeze thaw cycles. Acknowledgments This work was supported by the Bu-Ali Sina University. The authors are grateful to Mr. M. Samadi and Mr. E. Bazvand for their help during laboratory work. References Altindag R, Alyildiz IS, Onargan T (2004) Mechanical properties degradation of ignimbrite subjected to recurrent freeze thaw cycles. Int J Rock Mech Min Sci 41: Bayram F (2012) Predicting mechanical strength loss of natural stones after freeze thaw in cold regions. Cold Reg Sci Technol 83 84: Bell FG (2000) Engineering properties of soils and rocks, 4th edn. Blackwell, London Binal A, Kasapoglu KE (2002) Effects of freezing and thawing process on physical and mechanical properties of Selime ignimbrite outcrops in Aksaray Ihlara valley [in Turkish]. In: Proceeding of 6th regional rock mechanic symposium, Konya, pp Chen TC, Yeung MR, Mori N (2004) Effect of water saturation on deterioration of welded tuff due to freeze thaw action. Cold Reg Sci Technol 38: Grossi CM, Brimblecombe P, Harris I (2007) Predicting long term freeze thaw risks on Europe built heritage and archaeological sites in a changing climate. Sci Total Environ 377(2): Hale PA, Shakoor A (2003) A laboratory investigation of the effects of cyclic heating and cooling, wetting and drying, and freezing and thawing on the compressive strength of selected sandstones. Environ Eng Geosci 9: ISRM (1981) Rock characterization testing and monitoring. In: Brown ET (ed) ISRM suggested methods. Pergamon Press, Oxford Karaca Z, Deliormanli AH, Elci H, Pamukcu C (2010) Effect of freeze thaw process on the abrasion loss value of stones. Int J Rock Mech Min Sci 47: Khanlari GH, Abdilor Y (2014) The influence of wet dry, freeze thaw and heat cool cycles on physical and mechanical properties of upper red sandstones, central part of Iran. Bull Eng Geol Environ. doi: /s Mutluturk M, Altindag R, Turk G (2004) A decay function model for the integrity loss of rock when subjected to recurrent cycles of freezing thawing and heating cooling. Int J Rock Mech Min Sci 41: Nicholson D (2001) Pore properties as indicators of breakdown mechanisms in experimentally weathered limestone. Earth Surf Process Landf 26: Rossi D (1985) Laboratory tests on Artistic stonework. Stu Doc Cult Herit 16: Ruedrich J, Siegesmund S (2007) Salt and ice crystallization in porous sandstones. Environ Geol 52: Takarli M, Prince W, Siddique R (2008) Damage in granite under heating/cooling cycles and water freeze thaw condition. Int J Rock Mech Min Sci 45: Tan X, Chen W, Tian H, Cao J (2011) Laboratory investigations on the mechanical properties degradation of granite under freeze thaw cycles. Col Reg Sci Technol 68: Topal T, Doyuran V (1998) Analyses of deterioration of the Cappadocian tuff, Turkey. Environ Geol 34:5 20 Topal T, Sözmen B (2000) Freeze thaw resistance of the Yazilikaya tuffs. In: 9th international congress on the deterioration and conservation of stone, p Xiao JQ, Ding DX, Jiang FL, Xu G (2010) Fatigue damage variable and evolution of rock subjected to cyclic loading. Int J Rock Mech Min Sci 47: Yavuz H, Altindag R, Sarac S, Ugur I, Sengun N (2006) Estimating the index properties of deteriorated carbonate rocks due to freeze thaw and thermal shock weathering. Int J Rock Mech Min Sci 43: Zappia G, Sabbioni C, Riontino C, Gobbi G, Favoni O (1998) Exposure tests of building materials in urban atmosphere. Sci Total Environ 224: Zhang SJ, Lai YM, Zhang XF, Pu YB, Yu WB (2004) Study on the damage propagation of surrounding rock from a cold-region tunnel under freeze thaw cycle condition. Tunn Undergr Space Technol 19: