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twenty-five (25) per cent or more than sixty (~0) per cent, by weight, will pass a screen <br /> having three-fourths (~) inch round openings. <br /> <br />_,iCTION 4. MIXING WATER. <br /> The water used in mixing all concrete and mortar shall be reasonably free from <br /> alkali, silt or other impurities, and in no case shall the amount of solids exceed three <br /> grams per litre. Where alkali predominates in the solid matter, the solids shall not exceed <br /> one and one-half (1~) grams per litre. <br /> <br />Par III. <br /> <br />Concrete and Mortar. <br /> <br />SECTION 1. CONCRETE PROPORTIONS. <br /> All concrete shall be mixed in the proportions of one (1) bag of Portland Cement, to <br /> not more than two (2) cubic feet of concrete sand, to not more than four (4) cubic feet of <br /> either crushed stone or gravel or both, and in no case shall the volume of the fine aggre- <br /> gate be less than one-half (~i) the volume of the coarse aggregate. <br /> <br /> The voids in the concrete shall be completely filled with mortar. If voids appear, <br /> this condition shall be remedied by reducing the proportion of coarse aggregate and not <br /> by increasing the. amount of fine aggregate. <br /> The amount of mixing water used shall be the least quantity that will produce a <br /> workable mix. <br /> <br /> A cubic yard of concrete in place shall contain not less than six (6) bags of Portland <br /> Cement. <br /> <br />SECTION 2. MIXING CONCRETE. <br /> <br /> The concrete shall be mixed either by machine or by hand as hereinafter specified: <br /> (a) MACHINE MIXING. If a machine mixer is used, the Contractor shall mix, <br /> without spilling, such quantity of aggrgeates, as will be within thc capacity of the mixer, <br /> and in no case shall the quantity be such as to require the splitting of a sack of cement. <br /> <br /> The mixer drum shall have a speed of not less than thirteen (15) revolutions, nor more <br /> than twenty (20) revolutions per minute and every batch of concrete shall be mixed in <br /> the drum of the mixer not less than sixty (60) seconds before any portion of the batch <br /> is discharged. The drum shall not be charged while the mixer is discharging. <br /> <br /> (b) HAND MIXING. Where concrete is mixed by hand, one (1) box of rock shall <br /> be placed on a tight platform, not less than ten (10) feet wide and twelve (12) feet long. <br /> Upon the rock shall be placed one (1) box of sand and upon this shall be placed the <br /> requisite number of sacks of cement. The inspector shall be given the opportunity to <br /> check the number of sacks of cement on each batch before the sacks are opened. <br /> <br /> The mass shall then be turned with shovels two (2) times dry and two (2) times wet, <br /> not including shoveling into wheelbarrows. The requisite amount of water shall be <br /> supplied in a spray during the wet turns. <br /> <br /> (c) REMIXING CONCRETE. No concrete shall be used which has partially set <br /> and no concrete shall be retempered or remixed. <br /> <br />SECTION 3~ FINISH MORTAR PROPORTIONS. <br /> <br /> The mortar shall consist of one (1) part of Portland Cement to one and one-half (1~) <br />parts of concrete sand, as hereinbefore specified, excelrt that the sand must all pass a one- <br />fourth (~) inch screen. Unless otherwise specified, lamp black shall be used for coloring <br />in the proportion of one.fourth pound to each sack of cement used. <br /> <br />314 <br /> <br /> <br />