There are many different ways to mix and pour concrete, and this guide will teach you how to sample from all types of containers, from small stationary mixers that batch on site to large concrete trucks that pump concrete down a chute. In all cases, the time between receiving the first and last parts of the sample should not go over 15 minutes. Also, if you are making cylinders, you need to start molding them within 15 minutes after you have mixed the composite sample, and your sample should be at least 1 cubic foot in volume. Whatever container you use to collect the concrete must have a nonabsorbent surface. When sampling from a truck mixer, you must take your sample from the middle portion of the batch. ASTM C Procedure Sampling From Stationary Mixers Take two or more portions at regularly spaced intervals during the discharge of the middle portion of the batch, and mix them up into one composite sample with a shovel.

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A number in parentheses indicates the year of last reapproval. No other units of measurement are included in thisstandard. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Referenced Documents2. Significance and Use3. Themixer shall have a minimum of two controlled speeds. Rheo-stat adjustment of speed is not acceptable. The mixer shall beequipped with either an adjustment screw which is an integralpart of the mixer or a clearance adjustment bracket such as theone shown in Fig.

NOTE 1—When the bracket is in the proper position beneath the motorhousing, the lugs are to the front and facing upward and the heads of theadjustment screws are to the rear and facing downward in the path of thesliding frame that holds the bowl.

It is intended that the bracket befastened at the front housing connection by inserting replacement screwson an appropriate size upward through the opening in each lug and into theexisting threaded holes in the bottom of the motor housing. The originalstops for the sliding frame are to be filed down if they prevent the framefrom coming in contact with the adjustment screws.

The dimensions of the paddle shall be such that whenin the mixing position the paddle outline conforms to thecontour of the bowl used with the mixer, and the clearancebetween corresponding points on the edge of the paddle and theside of the bowl in the position of closest approach shall beapproximately 4.

The bowl shall be so equipped thatit will be positively held in the mixing apparatus in a fixedposition during the mixing procedure. Provide an enclosurearound the mixing bowl or a lid to minimize evaporation ofwater during periods of rest of the mixture. The enclosure or lidshall be made of non-absorbing material that is resistant todeterioration from the alkaline environment of cement pastesand mortars.

Current edition approved Aug. Published September Originallyapproved in Last previous edition approved in as C - United States The blade shallbe about 75 mm long, 50 mm wide, and tapered to a thin edgeabout 2 mm thick. NOTE 3—A kitchen tool known as a plate and bowl scraper conforms tothese requirements. Temperature and Humidity5. Materials, Proportioning, and Consistency6.

Procedure for Mixing Pastes7. Then introduce the materials for a batchinto the bowl and mix in the following manner Procedure for Mixing Mortars8. During the first 15 s of this interval, quickly scrape down intothe batch any mortar that may have collected on the side of thebowl; then for the remainder of this interval, close the mixerenclosure or cover the bowl with the lid.

Warning—The clearances between the paddle and the bowlspecified in this practice are suitable when using mortar madewith standard sand as described in Specification C Topermit the mixer to operate freely and to avoid serious damageto the paddle and bowl when coarser aggregates are used, itmay be necessary to set the clearance adjustment bracket toprovide greater clearances than those specified in 4. Approved Aug. ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard.

Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility. This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn.

Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.


ASTM C305-06

A number in parentheses indicates the year of last reapproval. A superscript epsilon e indicates an editorial change since the last revision or reapproval. It is the responsibility of the user of this standard to establish appro- priate safety and health practices and determine the applica- bility of regulatory limitations prior to use. Apparatus 4. Rheostat adjustment of speed will not be acceptable. The mixer shall be equipped with either an adjustment screw which is an integral part of the mixer or a clearance adjustment bracket such as the one shown in Fig.


ASTM C305 - 14


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