Page 16

2015SpringShotcreteEMag

and later-age compressive strengths obtained for the three candidate mixtures are illustrated in Fig. 5. Once the ultra-rapid strength development was confirmed for the three mixtures (refer to Fig. 5), the next step consisted of analyzing certain dura- bility features and indicators. The boiled water absorption and the volume of permeable voids were the first durability prop- erties analyzed, as these tests are typically per- formed in the shotcrete industry to provide an indication of the quality of the in-place shotcrete. The absorption results obtained for the three CSA cement-based dry-mix shotcrete mixtures and the associated shotcrete quality indicators proposed in the literature and generally accepted in the industry (Austin and Robins 1995) are presented Fig. 5: Early- and later-age compressive strengths obtained with the in Fig. 6. candidate CSA cement-based dry-mix shotcrete mixtures As shown in Fig. 6, in addition to very rapid strength development, the placed shotcrete quality was good to excellent (CSA-Polymer B mixture) for the mixtures shot according to the suggested indicators. The rapid chloride penetration test (RCPT) results presented in Fig. 7 with the chloride ion penetrability index mentioned in ASTM C1202 also confirm a low to almost negligible (CSA­ Polymer B mixture) chloride ion penetrability obtained with the rapid strength-gain dry-mix shotcrete mixtures tested. Even if the absorption (ASTM C642) and the RCPT (ASTM C1202) tests present some limits to characterize shotcrete durability exclusively (Bolduc 2009; Bolduc and Jolin 2010), the excel- lent results obtained with the three mixtures under consideration demonstrate the high quality of the shotcrete produced with this alternative Fig. 6: ASTM C642 results obtained on the three CSA cement-based cementitious material. dry-mix shotcrete mixtures In addition to the outstanding results presented previously in terms of strength development, material quality, and chloride ion penetrability, Table 1 confirms that the mixtures tested also possess excellent freezing-and-thawing resistance. The air void system characteristics measured for the CSA-AEA mixture are presented in Table 2 and explain the excellent freezing-and-thawing resistance obtained with this mixture. Based on the results obtained during this testing program, it is possible to produce a CSA cement-based dry-mix shotcrete that provides ultra-rapid compressive strength development, a good-to-excellent in-place material quality, a low- to almost-negligible chloride ion penetra- bility, and an excellent freezing-and-thawing resistance. Based on these very promising test results, the next step will consist of selecting one Fig. 7: RCPT (ASTM C1202) results and the associated chloride ion candidate shotcrete mixture to determine addi- penetrability index obtained with the CSA cement-based dry-mix tional mechanical and durability properties shotcrete mixtures required for materials used in repair applications. 14 Shotcrete • Spring 2015


2015SpringShotcreteEMag
To see the actual publication please follow the link above