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2013FallShotcreteEMag

Shotcrete Corner reaching 20 mPa (2900 psi) in 2 hours is Possible By Simon Reny and William Clements ibecomes shorter, production increases. be reviewed. Working with calcium sulfo-alu--(1000 psi) in 4 hours. But to go over this previous limit, the cement technology needed ton the mining and tunneling industries, timeis critical; and as the mining/tunneling cycle Shotcrete is often used for ground support when minate cement (CSA), a Rapidset Cement using the drill and blast method or other tun- technology from CTS Cement, King has devel- neling methods. But before reopening access oped a research program to bring early-age for the next phase of the underground heading, compressive strength gain to another level. One the applied shotcrete must reach a minimum of the challenges in shotcreting with Rapidset compressive strength to ensure the safety of the Cement, as its name implies, is that it sets workers going into the heading. To speed up almost instantly. This can prove difficult when the mining and tunneling process, King Pack- casting test specimens. Combining the use of aged Materials Company has been continually the Rapidset Cement technology with the dry- investigating different approaches to obtain the mix shotcrete process provides a solution for minimum required compressive strength as fast reducing the mining and tunneling cycle. as possible. By using high-early-strength The testing program included a first phase cement (Type III or Type HE) and a high accel- where the cement paste was optimized with the erator dosage, it is possible to provide a shot- use of different pozzolans. Following this initial crete mixture design capable of reaching testing, the target final set time was established early-age compressive strengths of up to 7 MPa to be 10 minutes after shooting. The rapid- strength-gain dry-mix shotcrete went through several levels of testing prior to its availability for commercial use. Initially, the rapid-strength- gain dry-mix shotcrete was tested internally by King in both winter and summer conditions above ground (refer to Fig. 1 and 2). Following that, the rapid-strength-gain dry-mix shotcrete was tested in both a mine training facility (to observe the effect of underground conditions) Fig. 1: Shooting test panels above ground in and at Laval University (Quebec City, QC, winter conditions Canada), where all parameters of the shotcrete application could be controlled. The final por- tion of the testing protocol involved testing the rapid-strength-gain dry-mix shotcrete under- ground at a mining facility in Northern Ontario under a cemented sand-fill section. results Shooting operations were conducted using both the Aliva 246 and Aliva 252 dry-mix shot- crete machines. Regular shooting procedures were followed as described in ACI 506, “Guide to Shotcrete.”1 During the first two phases of testing, Fig. 2: Shooting test panels and end beams on a standard mining shotcrete (produced by King) surface in summer conditions was used as a control mixture to make sure all of 26 Shotcrete • Fall 2013


2013FallShotcreteEMag
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