A Novel Method for The Determination of Direct Tensile Strength of Brittle Materials Using Expansive Cement
Sponsor: Natural Resources Canada, Newmont, Ministry of Economics and Innovation of Quebec, NSERC
MSC Thesis by Kenneth Adams
Currently, the two main testing methods available for tensile strength determination of brittle materials such as rocks and concrete are the Glued Ends Direct Tensile Strength (GEDTS) test and the Brazilian Tensile Strength (BTS) test. Although the BTS test is popularly used for indirect tensile strength measurement due to its simplicity, it suffers several validity issues that cause it to overestimate the tensile strength of the tested material. The GEDTS test, on the other hand, is a direct testing method that is internationally recognized and acknowledged as the correct method for determining the tensile strength of brittle materials. However, challenges involving eccentric loading due to the misalignment of the specimen-load axes and poor adhesive performance during hard rock tests render the GEDTS test unappealing to the research community. As a result, developing an alternative direct testing method remains an interesting research endeavor. Therefore, this thesis focuses on developing a novel testing method known as the Expansive Cement Direct Tensile Strength (ECDTS) test to directly determine the tensile strength of brittle materials. Test principle and methodology of the ECDTS test are discussed in detail and its merits over the conventional testing methods are highlighted.
This thesis is two-phase research. As part of the first phase which is the method validation phase, a simple yet effective testing system known as the Load Centering Device (LCD) is developed to eliminate eccentricity from the loading process of the conventional GEDTS test. The description and modus operandi of the LCD are outlined in detail for broader comprehension. The effectiveness of the LCD is examined and verified by conducting a series of direct tensile strength tests on Basaltic komatiite using the GEDTS test. Also, the veracity of the proposed ECDTS test is examined by conducting a series of numerical modeling analyses using Abaqus XFEM software as well as experimental studies on typical rock specimens from low-tensile marble. Comparison of ECDTS test experimental test results to the results of the conventional methods including the BTS and the GEDTS demonstrates the validity of the ECDTS test.
The second phase which is the method application phase examines the applicability of the ECDTS test on hard rocks. Sudbury breccia and Gneiss which are known to have high tensile capacities are tested using the ECDTS, GEDTS, and BTS tests. Since the bonding capacity of the glue is lower than the tensile capacity of the tested rocks, the GEDTS test failed at the glued interface and, thus, did not produce any results. As such, the applicability of the proposed ECDTS test is verified by comparing its results to the results of the BTS test. It is found that the average value of the BTS results for the two rock types is 14% higher than the average value obtained from the proposed ECDTS test. This is expected since the BTS test is known to overestimate the tensile strength of brittle materials such as rocks. This result demonstrates the effectiveness and consistency of the newly proposed ECDTS test.