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2015SpringShotcreteEMag

Durability Investigation of Ultra-Rapid Strength-Gain Dry-Mix Shotcrete By Nicolas Ginouse and William Clements Ialuminate (CSA) cement and providing about designs using the equivalent mortar method. As-The first phase of the testing program consisted of selecting three candidate mixturet has already been shown that rapid strength-gain dry-mix shotcrete using calcium sulfo- 2900 psi (20 MPa) after only 2 hours can be mentioned in Lemay (2013), this method is very effectively produced and placed in mining appli- useful for conducting preliminary optimization cations (Reny and Clements 2013). As already of early-age strengths for dry-mix shotcrete for- discussed in several papers (Reny and Ginouse mulas because it allows the user to work on 2014; Lemay et al. 2014), the use of such rapid mortar mixtures having the same total specific strength-gain dry-mix shotcrete can be a very area as the dry-mix shotcrete mixtures. Because efficient and robust solution to provide ultra­ mortars do not contain coarse aggregate, the rapid support and reduce the mining/tunneling equivalent mortar method first involves calcu- cycle by reaching the re-entry criteria much faster lating the amount of surface area provided by the than with traditional portland cement-based dry- coarse aggregate in the candidate shotcrete/ mix shotcrete using set accelerators. concrete mixture design. Then the surface area In this context, the use of ultra-rapid strength- provided by the coarse aggregate is replaced by gain shotcrete appears to be a very attractive the equivalent surface area in the form of fine solution for emergency repairs in civil applica- aggregate in the equivalent mortar. Using the tions, where rapid strength-gain materials such equivalent mortar method allows for close as mortars or concretes are already employed to approximation of the early-age strength develop- meet shortened construction schedules due to ment between the candidate shotcrete/concrete restricted lane closure times on bridges and mixture design and the equivalent mortar as each roadways and restricted access time in tunnels. material maintains the same paste proportions at However, the use of rapid strength-gain repair the aggregate-binder interface. materials is still a relatively new practice, and a In this first step, the equivalent mortar method practice that has not been fully investigated with was used to select three candidate formulas respect to the durability of these repair materials presenting the most promising early-age strengths even if several papers covering this topic have among many different mixture designs in a already been published (Barde et al. 2006; Garcia relatively quick and economical fashion when 2014). To develop a durable rapid strength-gain compared to shooting all of the candidate mix- dry-mix shotcrete for emergency repairs, King tures. The three candidate shotcrete mixtures Packaged Materials Company, Burlington, ON, selected include a variation of the earlier devel- Canada (King), conducted a testing program oped rapid strength-gain dry-mix shotcrete for focused on certain durability properties of CSA mining applications (King RS-D2 Mining cement-based dry-mix shotcrete. Therefore, the Shotcrete) but including an air-entraining admix- intent of this article is to present the preliminary ture (CSA-AEA), and two shotcrete mixtures results of this investigation. combining CSA cement-based binder with a redispersible polymer (CSA-Polymer A and Materials and Methods CSA­Polymer B). During this first step, the three Even though the cement chemistry and the hydra- formulas were also adjusted to provide an initial tion process controlling the rapid strength develop- set time of 20 minutes to guarantee a minimum ment of CSA cement-based materials have been the finishing period. topic of several scientific studies (Juenger et al. 2011; For the second phase of the testing program, Pelletier et al. 2010; Bernardo et al. 2006), the dura- a full-scale shotcrete trial was conducted at King’s bility of such alternative cementitious materials is facility (Sudbury, ON, Canada) using all three still under investigation. To investigate the dura- candidate shotcrete mixtures packaged in 66 lb bility properties of rapid strength-gain dry-mix (30 kg) bags (Fig. 1). shotcrete using CSA cement-based binder further, Shooting operations were conducted using an the testing program was divided into two phases. Aliva 246 dry-mix shotcrete machine (Fig. 2), 12 Shotcrete • Spring 2015


2015SpringShotcreteEMag
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