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3.2 Pumping <br />Concrete was pumped into the adits using a Schwing piston pump, at a nominal <br />pressure at the pump of 250-300 bar (3675 - 4410 psi). <br />• <br />Some pumpability problems were encountered on the first day, as the concrete <br />mix with the specially imported flyash was behaving differently than the vendor <br />expected. The first two "test" truckloads did not meet an acceptable spread <br />index, and there were persistent problems pumping the mixture. <br />After consultation between the vendor, MES superintending engineer Willis <br />Beach, P.E. and Stephen Phillips, P.E., the proportion of cementitious materials <br />was raised, improving pumpability and allowing the work to progress normally. <br />Compressive strength samples were taken by CTL Thompson, and appear under <br />Tab 10. For the Steve Adit, the actual minimum 28-day compressive strength <br />achieved was 6390 psi, vs. a design strength in the initial calculations of 3000 <br />psi. <br />For the Pierce adit, the actual minimum 28-day compressive strength achieved <br />was 5330 psi, versus a design strength in the initial calculations of 3000 psi. <br />3.3 Curing and Shrinkage <br />• The MES construction specifications and plans followed the recommendations of <br />PMGG in that there was a minimum 28-day lag period between the pumping of <br />Figure 7: Concrete pumping operations <br />