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Sunnyside Gold Corp. Page 12 March 10, 1993 <br /> diameter by 12-inch long test cylinders will have to be prepared <br /> for every five yards of concrete placed. One of the test cylinders <br /> can be used for a seven-day strength test, but one must be tested <br /> to measure the 28-day strength. The test cylinders should be taken <br /> randomly and not at the start or at the completion of pour. <br /> Adjustment of the concrete mix proportions during bulkhead <br /> construction would necessitate more frequent collection of test <br /> specimens. <br /> The design concrete mix is 1 sack of Type V cement (94 lbs) , <br /> to 235 lbs of fine aggregate, sand, to 330 lbs of well graded <br /> coarse aggregate and 15 lbs of fly ash, pozzolan. The mix <br /> proportions are 1:2 .5: 3.5 (cement, sand, gravel) . One yard of <br /> concrete would contain 5.7 bags of cement (536 lbs) , 1340 lbs of <br /> sand, 1881 lbs of well graded 3/4-inch maximum coarse aggregate and <br /> 86 lbs of fly ash, pozzolan. One yard of the specified concrete <br /> would have a dry weight of 3843 lbs/yard and a mixed weight of 4085 <br /> lbs/yard when the required 29 gallons of water is added. The <br /> approximate in place density of the concrete will be 151 lb/cu ft. <br /> The specified mix would normally be considered an "oversanded" <br /> mix. However, the higher than normal sand content is designed to <br /> increase pumpability, i.e. slump, at the low water cement ratio of <br /> 0.45 required to resist the "Very Severe" design sulfate ion <br /> concentration in the mine water. High slump is necessary to <br /> facilitate the complete filling of the bulkhead forms. It will not <br /> be possible to vibrate the low water-cement ratio mix. Therefore, <br /> the concrete mix must flow easily under gravity to completely fill <br /> the space between the rebar and the face of the forms. <br /> The Standard Handbook for Civil Engineers (Merritt, 1983, <br /> Table 8-4) indicates that a well-graded aggregate with a maximum <br /> size of 2 inches can be used with the mix proportions specified. <br /> However, it is recommended that 3/4-inch maximum aggregate size be <br /> used, again to enhance pumpability and minimize voids, segregation <br /> and "honey combing" , particularly between the rebar mat and the <br /> face of the bulkhead forms. The fly ash is sufficiently fine <br /> grained that it does not occupy space in the mix, but fills voids <br /> that would otherwise be present in the concrete. Fly ash also <br /> decreases the permeability of the cast in place concrete. <br /> Reinforced concrete is not necessary for water impoundment <br /> bulkhead construction. Plain, or mass, concrete has been <br /> successfully used on many occasions. The required length of a <br /> plain concrete bulkhead to resist deep-beam bending stresses for <br /> each of the four locations in the Sunnyside Mine is shown on Table <br /> 2 . The dead or fluid load (D or F) acting on the bulkhead was <br /> multiplied by 1. 4 (ACI 318-89, Section 9.2 . 1) and the plain <br /> concrete bending strength reduction factor of 0. 65 was used. The <br /> bending strength reduction factor for plain concrete is from the <br /> 1971 ACI code, Section 9. 3 .2 and the 1977 ACI code, Section <br /> 9 . 2 . 1. 5. The 1989 ACI code does not present a plain concrete <br /> bending strength reduction factor. The actual safety factor would <br /> appear to be 2 . 15 . This higher than typical reduction factor for <br /> the bending strength of concrete may be the result of the high <br />