ﺑﺮرﺳﯽ آزﻣﺎﯾﺸﮕﺎﻫﯽ اﺛﺮ اﻟﯿﺎف ﺷﯿﺸﻪ ﺑﺮ ﭼﻘﺮﻣﮕﯽ ﺷﮑﺴﺖ و اﻧﺘﺸﺎر ﺗﺮك ﺣﺎﻟﺖ I، ﺣﺎﻟﺖ II و ﺣﺎﻟﺖ ﺗﺮﮐﯿﺒﯽ I-II در ﺑﺘﻦ ﻣﺴﻠﺢ اﻟﯿﺎﻓﯽ

Experimental Investigating the Effect of Glass Fibre on Mode I, Mode II, and Mixed Mode (I-II) Fracture Toughness and Crack Propagation in Fibre-Reinforced Concrete

وﺟﻮد درزه، ﺷﮑﺎف و ﺷﮑﺴﺘﮕﯽﻫﺎي اوﻟﯿﻪ و از ﭘﯿﺶ ﻣﻮﺟﻮد در ﺳﻨﮓ و دﯾﮕﺮ ﻣﻮاد ﻣﻮرد اﺳﺘﻔﺎده در ﻋﻠﻮم ﻣﻬﻨﺪﺳﯽ، اﻣﺮي اﺟﺘﻨﺎبﻧﺎﭘﺬﯾﺮ ﺑﻮده و از وﯾﮋﮔﯽﻫﺎي ذاﺗﯽ ﻫﺮ ﻣﺎده اﺳﺖ. اﯾﻦ ﻣﻮﺿﻮع ﺑﺎﻋﺚ ﻣﯽﺷﻮد ﮐﻪ ﺳﺎزهﻫﺎ و ﯾﺎ ﺗﻮدهﻫﺎي ﺳﻨﮕﯽ، ﺗﺤﺖ ﺑﺎرﮔﺬاريﻫﺎي ﻣﮑﺎﻧﯿﮑﯽ ﯾﺎ ﺳﺎﯾﺮ ﻋﻮاﻣﻞ ﻣﺤﯿﻄﯽ، ﺳﺮﯾﻊﺗﺮ ﮔﺴﯿﺨﺘﻪ ﺷﻮﻧﺪ. ﺑﺘﻦ، ﺑﻪﻋﻨﻮان ﭘﺮﮐﺎرﺑﺮدﺗﺮﯾﻦ ﻣﺼﺎﻟﺢ در ﻣﻬﻨﺪﺳﯽ ﻋﻤﺮان ﺑﻮده ﮐﻪ ﻣﻌﻤﻮﻻً ارزانﺗﺮﯾﻦ و راﯾﺞﺗﺮﯾﻦ ﻣﺼﺎﻟﺢ ﻣﻮﺟﻮد را در ﺧﻮد دارد. از اﯾﻦ رو ﺑﻪ ﺳﺒﺐ ﺑﺮوز ﺗﺮك و ﺷﮑﺴﺘﮕﯽ ﻣﯽﺗﻮاﻧﺪ ﺧﺴﺎرتﻫﺎي ﺟﺒﺮانﻧﺎﭘﺬﯾﺮي را ﺑﻪ ﺑﺎر آورد. ﺑﻪ اﯾﻦ ﻣﻨﻈﻮر در ﺳﺎلﻫﺎي اﺧﯿﺮ ﺑﺎ ﺳﺎﺧﺖ ﺑﺘﻦﻫﺎي اﻟﯿﺎﻓﯽ ﻣﺴﻠﺢ، ﺗﺎ ﺣﺪود زﯾﺎدي ﺿﻌﻒﻫﺎي ﻣﺬﮐﻮر در آن ﺑﻬﺒﻮد ﯾﺎﻓﺘﻪ اﺳﺖ. در اﯾﻦ ﭘﮋوﻫﺶ ﺑﺎ اﺳﺘﻔﺎده از روش آزﻣﻮن روي دﯾﺴﮏ ﺑﺮزﯾﻠﯽ داراي ﺗﺮك ﻣﺴﺘﻘﯿﻢ ، ﭘﯿﺶﺑﯿﻨﯽ روﻧﺪ اﻧﺘﺸﺎر ﺗﺮك و ﭼﻘﺮﻣﮕﯽ ﺷﮑﺴﺖ در ﻧﻤﻮﻧﻪﻫﺎي ﺑﺘﻦ ﺑﺪون اﻟﯿﺎف و ﻧﻤﻮﻧﻪﻫﺎي ﺣﺎوي اﻟﯿﺎف ﺷﯿﺸﻪ در درﺻﺪﻫﺎي ﺣﺠﻤﯽ ﻣﺨﺘﻠﻒ 0/35 ،0/2 و 0/5 ﺑﺮرﺳﯽ ﺷﺪه اﺳﺖ. ﻋﻼوه ﺑﺮ اﯾﻦ، ﻓﺮآﯾﻨﺪ ﮔﺴﺘﺮش ﺗﺮك از ﺷﮑﺎفﻫﺎي از ﭘﯿﺶ ﻣﻮﺟﻮد در ﻧﻤﻮﻧﻪﻫﺎ و ﻫﻤﭽﻨﯿﻦ ﭼﻘﺮﻣﮕﯽ ﺷﮑﺴﺖ در ﺣﺎﻟﺖﻫﺎي II I و ﺣﺎﻟﺖ ﺗﺮﮐﯿﺒﯽ I-II ﻣﺤﺎﺳﺒﻪ ﺷﺪ. آزﻣﺎﯾﺶ دﯾﺴﮏ ﺑﺮزﯾﻠﯽ ﺑﺮ روي ﻧﻤﻮﻧﻪﻫﺎي ﻣﻮردﻣﻄﺎﻟﻌﻪ در زواﯾﺎي 75 ،60 ،45 ،28/83 ،15 ،0 و 90 درﺟﻪ ﻧﺴﺒﺖ ﺑﻪ راﺳﺘﺎي ﺗﺮك از ﭘﯿﺶ ﻣﻮﺟﻮد اﻧﺠﺎم ﺷﺪه اﺳﺖ. ﭘﺲ از ﻣﻄﺎﻟﻌﺎت آزﻣﺎﯾﺸﮕﺎﻫﯽ ﻣﺸﺨﺺ ﮔﺮدﯾﺪ ﮐﻪ ﺷﺮوع ﺗﺮكﻫﺎي ﺑﺎﻟﻪاي در زواﯾﺎي ﮐﻢﺗﺮ از 75 درﺟﻪ (0<α <75) از ﻧﻮك ﺗﺮك از ﭘﯿﺶ ﻣﻮﺟﻮد اﺗﻔﺎق ﻣﯽاﻓﺘﺪ و ﺑﺎ اداﻣﻪي ﺑﺎرﮔﺬاري ﻣﺴﯿﺮ رﺷﺪ و اﻧﺘﺸﺎر ﺗﺮك ﺑﻪ راﺳﺘﺎي ﺑﺎرﮔﺬاري ﻧﺰدﯾﮏ ﻣﯽﮔﺮدد. اﯾﻦ در ﺣﺎﻟﯽ اﺳﺖ ﮐﻪ ﺑﺮاي زواﯾﺎي 75 درﺟﻪ و ﺑﺰرگﺗﺮ از آن، ﺷﺮوع ﺗﺮك ﺑﺎ ﻓﺎﺻﻠﻪ d از ﻧﻮك ﺗﺮك آﻏﺎز ﻣﯽﮔﺮدد. اﯾﻦ ﻓﺎﺻﻠﻪ در ﻧﻤﻮﻧﻪﻫﺎي ﻓﺎﻗﺪ اﻟﯿﺎف ﺑﯿﺸﺘﺮ از ﻧﻤﻮﻧﻪﻫﺎي ﺣﺎوي اﻟﯿﺎف اﺳﺖ. ﻫﻤﭽﻨﯿﻦ ﻧﺘﺎﯾﺞ ﻧﺸﺎن ﻣﯽدﻫﺪ ﭼﻘﺮﻣﮕﯽ ﺷﮑﺴﺖ ﻣﻮد II I و ﺗﺮﮐﯿﺒﯽ I-II ﺑﺎ اﺳﺘﻔﺎده از ﻣﻘﺎدﯾﺮ 0/2 درﺻﺪ اﻟﯿﺎف ﺷﯿﺸﻪ ﺑﯿﺶ از ﭼﻘﺮﻣﮕﯽ ﺷﮑﺴﺖ ﻧﻤﻮﻧﻪﻫﺎي ﻓﺎﻗﺪ اﻟﯿﺎف ﻣﯽﺑﺎﺷﺪ.

Concrete is the most widely-used material in civil engineering and often contains the cheapest and most common matter. It can therefore cause irreparable damages due to cracks and fractures. The creation of fibre-reinforced concrete in recent years has largely rectified the aforementioned shortcomings. This study uses the direct crack Brazilian disk test to evaluate fracture toughness and crack propagation in fibre-free and glass fibre concrete samples in 0.2, 0.35 and 0.5 volume percentages. Moreover, fracture toughness and crack propagation from pre-existing cracks were calculated for samples in mode I, mode II, and mixed mode (I-II). The samples were subjected to the Brazilian disk test at 0, 15, 28.83, 45, 60, 75 and 90-degree angles relative to the pre-existing crack’s trajectory. Laboratory investigations showed that the wing crack at sub 75-degree (0<α <75) angles was initiated from the pre-existing fracture’s tip and approached loading trajectory as the load on the crack growth and propagation trajectory continued. At the same time, crack initiation at 75-degree angles and above begins at a distance of d from the tip, which is greater in fibre-free samples. The results also showed that using 0.2% glass fibre in mode I, II and mixed mode (I-II) resulted in a higher fracture toughness than fibre-free samples.