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2015SpringShotcreteEMag

Fig. 1: Candidate shotcrete mixtures Fig. 3: Nozzleman shooting a test panel for packaged in 66 lb (30 kg) bags later-age strengths and durability properties Fig. 4: Steel end-beam mold used for early-age strengths measurements boiled water absorption and volume of permeable voids, rapid chloride permeability, air-void system analysis (CSA-AEA mixture only), and freezing- Fig. 2: Aliva 246 dry-mix shotcrete machine and-thawing resistance. The boiled absorption and volume of permeable voids was determined in connected to a 2 in. (50 mm) hose with a hydro- accordance with ASTM C642 (2013). The rapid mix nozzle introducing pressurized water to chloride permeability was determined in accor- the material stream through a water ring located dance with ASTM C1202 (2012). The freezing- 10 ft (3 m) from the nozzle. Conventional and-thawing resistance was determined in shooting procedures described in ACI 506R-05, accordance with ASTM C666/C666M (2008). The “Guide to Shotcrete,” were followed for each air-void system analysis was only determined on dry-mix shotcrete formula tested (Fig. 3). All the CSA-AEA mixture in accordance with ASTM dry-mix shotcrete mixtures were shot using the C457/C457M (2012). The two polymer­modified “wettest stable consistency” as recommended by mixtures were air-cured only, whereas the CSA- ACI 506R-05 for steel reinforcing bar encapsu- AEA mixture was kept in wet curing conditions lation in repair applications. for 28 days prior to testing. Early-age compressive strengths were deter- mined using the end-beam test method (using Results and Discussion rectangular steel molds presented in Fig. 4), The early-age strengths and the initial set time adapted from ASTM C116 (1990), whereas the measured on the three dry-mix shotcrete mix- initial set time was obtained using a hand-held tures conformed to the results targeted during penetrometer in accordance with the test method the preliminary tests using the equivalent mortar (ASTM C1117 1994). mixtures. As expected, all shotcrete mixtures Later-age compressive strengths and certain started to set after 15 to 20 minutes and then durability properties were determined using rapidly developed compressive strength, square test panels illustrated in Fig. 3. More pre- reaching more than 3600 psi (24.8 MPa) after cisely, the compressive strength at 7 and 28 days only 2 hours and reaching more than 7300 psi was obtained in accordance with ASTM C1604 (50.3 MPa) after 28 days. The CSA-Polymer A (2012). The durability properties tested for each shotcrete mixture reached a 28-day compressive shotcrete mixture include the determination of the strength in excess of 9000 psi (62 MPa). Early- Shotcrete • Spring 2015 13


2015SpringShotcreteEMag
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