مطالعه‌ي‌ آزمايشگاهي هم‌بستگي بين نتايج روش‌ هاي مختلف در اندازه ‌گيري مقاومت الكتريكي بتن

Experimental study on correlation between the results of different methods of measuring the electrical resistivity of concrete

هدف اين تحقيق،ارائه‌ي روابطي براي پيش بيني نتايج اندازه‌گيري مقاومت الكتريكي با روش استانداردASTM C1760 به كمك نتايج روش‌هاي ديگر است. روش طيف نگاري مقاومت ظاهري، رايج‌ترين در مطالعات آزمايشگاهي،روشASTM C1760،تنها مورد داراي دستور استاندارد، روش يك الكترودي، تكنيك جديدي در اندازه‌گيري‌هاي كارگاهي و روش چهار الكترودي،متداول‌ترين روش كارگاهي است.به اين منظور،49 طرح مخلوط بتن با مقاومت‌هاي الكتريكي پايين تا بسيار بالا در نظر گرفته شده و براي هر طرح،4 آزمونه‌ي استوانه‌اي و يك آزمونه‌ي دال مسلح ساخته شده و اندازه گيري مقاومت الكتريكي با روش‌هاي مذكور در سن28 روزه انجام شده است. بررسي‌ها نشان مي‌دهد كه اختلاف قابل اغماضي بين نتايج روش‌هاي طيف نگاري مقاومت ظاهري وASTM C1760 وجود دارد؛ اما به طور معناداري، مقاومت‌هاي الكتريكي اندازه‌گيري شده با روشASTM C1760،كمي بيشتر از نتايج روش طيف نگاري مقاومت ظاهري در همان بتن است.در روش چهار الكترودي،عوامل متعددي از جمله عدم رعايت تناسب بين فاصله الكترودها و ابعاد سازه مي‌تواند موجب بروز خطاهاي سيستماتيكي در نتايج باشدكه به همين علت،نتايج اندازه گيري با اين روش در حدود 140 درصد از روش استاندارد بزرگ‌تر است.در روش يك الكترودي نيز به علت عدم وجود رابطه‌ي جامعي براي محاسبه‌ي ثابت سلول،ابتدا مقدار اين ثابت در مقايسه با نتايج روش استاندارد به دست آمده و سپس مقادير مقاومت ويژه‌ي الكتريكي محاسبه شده است.نتايج اندازه‌گيري مقاومت الكتريكي با اين روش نيز اختلاف ناچيزي با روش استاندارد دارد.از آن‌جا كه امكانات و شرايط اندازه‌گيري با روش استاندارد در همه‌ي پروژه‌ها فراهم نيست،دست‌آورد اين تحقيق مي‌تواند در پيش بيني آن از نتايج ساير روش‌ها موثر باشد.

The purpose of this research is to develop relationships to predict the results of measuring the electrical resistivity of the standard test method ASTM C1760 with assistance of other methods’ results. Comparative Methods in this paper are Impedance spectroscopy method , one electrode method and four electrode method. Impedance spectroscopy method is the most common in laboratory studies , ASTM C1760 method (Standard Test Method for Bulk Electrical Conductivity of Hardened Concrete) only has a standard rule and use in laboratory , one electrode method is a new technique in field and it’s application is in the reinforcement structures , and four electrode measurements are more common in field. In laboratory methods, bulk electrical resisitivity measured but in field , usually surface electrical resisitivty evaluated , that is why several source of errors affecting on the results of this test methods. To reach the aim of this research , 49 mix designs with a vast domination of electrical resistivity from about 40 (Ωm) to 290 (Ωm) was intended and for each of mix designs , 4 cylindrical and one reinforced slab specimen were made. reinforced slab specimen for one electrode measurement and cylindrical specimens for the other test method measurments were considered. Moreover , the electrical resistance of the aforementioned methods was measured at 28 days age. The results showed that there is a negligible difference between the results of impedance spectroscopy and ASTM C1760 methods; however , the electrical resistivity measured by ASTM C1760 method was slightly higher than the results of impedance spectroscopy method in the concrete. As a result , we can use the results of the impedance spectroscopy method instead of standard test method results in the lack of facilities with accepting about 5% of error. In the four electrode method , a number of factors including the imbalance among the distances between electrodes and structure dimensions can result systematic errors. That is why the measurements’ results with the method is approximately 140% larger than the standard test method results. Due to the lack of a comprehensive relationship for calculating the cell constant in the one electrode method , the value of this constant was obtained by comparing the results of the standard test method. After that , the electrical resistivity values were calculated. Electrical resistivity measurement results which was obtained by this method had also little difference with the standard test method results. Finally 3 relationships separately developed for predicting the result of standard test method from results of the each other test methods. Since the features and conditions of measuring by the standard test method are not available in the entire projects , the current results are capable to predict the standard method’s results with assistance of other methods’ results.