<p><p><strong>Reference(s):</strong></p><p><em>Byrne et al. (1998)<br>Lazarte et al. (2015)<br>Porterfield et al. (1994)<br>Rogbeck et al. (2003)<br>SHRP2 Phase I Technology Assessment (2008)</em></p><p><strong>Method Summary</strong></p><p>The cube test can be performed on grout samples while cores are typically taken for shotcrete strength verification. Byrne et al. (1998) Appendix C 2.2.3 describes how to extract core samples from shotcrete walls to be tested for compressive strength. Cores from non-reinforced shotcrete test panels are tested for compressive strength while cores from reinforced test panels are inspected for air pockets and quality in comparison with photographs. According to Byrne et al. (1998), three cores are tested at three days and three cores are tested at 28 days in accordance with AASHTO T24/ACI C 42. Lazarte et al. (2015) and Rogbeck et al. (2003) mention testing sample grout cubes for strength.</p><p><strong>Accuracy and Precision</strong></p><p>Confirming the unconfined compressive strength of the grout for use in the project is a straightforward but not always precise process. The results of cube testing are influenced by the technician’s ability to make a cube, the mold type, and the end conditions of the sample at the time of testing.</p><p><strong>Adequacy of Coverage</strong></p><p>Tests are representative of each batch of grout or shotcrete, and each shooting position (for shotcrete).</p><p><strong>Implementation Requirements </strong></p><p>Measuring unconfined compressive strength of the grout and shotcrete is a simple procedure. However, the time required for the sample to set up needs to be considered in the timeframe of construction processes.</p><p><strong>General Comments</strong></p><p>Testing shotcrete cores can be both a preconstruction test on cores from test panels and a post‑construction quality assurance measure from cores on the shotcrete wall according to Byrne et al. (1998). Measuring the unconfined compressive strength of the grout verifies the acceptability of the grout mix design, which is critical to successful micropile implementation. Quality grout allows the micropile to satisfactorily support the anticipated service load. Because cube testing is a retrospective test, specific gravity testing is typically preferred. Great debate exists as to the accuracy of cube testing. The ability of the nails to successfully pass the load testing requirements is the best indication of their adequacy. Cube testing is applicable to performance and method approach specifications.</p></p>