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2015SpringShotcreteEMag

Fig. 4: Effect of RC agents and SF on the strength at 7 and 28 days However, these results show that due to their following two potential reasons. The paste content pozzolanic nature, the RC agents reacted faster of the mixtures containing the RC agents was than the SF at early ages, and still achieved lower than that of the SF mixture (as a result of comparable 28-day strength. In addition, the replacing the powder-based SF with the liquid- impact of the selected dosages and grades of the based RC agents). In general, aggregates are likely RC agents on 28-day strength was marginal. to be denser than the cement paste and have a lower permeability than the cement paste, so Durability mixtures with lower paste content tend to have Durability plays a key role in determining the lower permeability. On the other hand, the life span of structures, and it is often assessed by colloidal silica contained in the RC agents evaluating the permeability, which governs the decreases the permeability by increasing the rate of flow of a fluid (or gas) into a porous solid. density of the interfacial transition zone (the If concrete or shotcrete mixtures have high weakest phase in concrete) as a result of the permeability, deleterious substances can migrate combination of its filler effect and high pozzolanic into the structure, especially if they are exposed reactivity. SF also has pozzolanic properties, but to chemical attack or freezing-and-thawing cycles. because the reactivity and the surface area of the To evaluate the effect of the two RC agents and RC agents are higher than those of SF, the degree SF on the permeability, water penetration tests of their contribution to the permeability/durability were carried out at 28 days. will be influenced accordingly. Figure 5 shows that the water penetration depths of the mixtures containing the two RC Conclusions agents were slightly lower than those of the SF The following conclusions were drawn based mixture, as desired. This is most likely due to the on the test results obtained from the investigated shotcrete mixtures: • The SF mixture and mixtures containing the RC agents provided similar slump and were all very efficient in reducing the rebound loss to a range of 5 to 6%; • The addition of the RC agents increased the early-age strength compared to the SF mixture, and provided similar compressive strength at 7 and 28 days; • The water penetration depth of the mixtures containing the RC agents was slightly lower than that of the SF mixture, as desired; • The impact of the selected dosages and grades of the RC agent on the performance was minor for the investigated non-fiber-reinforced shotcrete mixtures; • The RC agents were more dosage­efficient than Fig. 5: Effect of the RC agents and SF on the water penetration depth at SF, as they required a much lower dosage rate 28 days to provide equivalent performance; and 30 Shotcrete • Spring 2015


2015SpringShotcreteEMag
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