ASTM C109 Compressive Strength of Hydraulic Cement Mortars

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http://roadstechnology.blogspot.com/ Scope This test method covers the determination of the compressive strength of hydraulic cement mortars using 2 inch (50 mm) cube specimens. References ASTM C109 Compressive Strength of Hydraulic Cement Mortars ASTM C778 Specification for Standard Sand ASTM C150 Specification for Portland Cement ASTM C305 Mechanical Mixing of Hydraulic Cement Pastes & Mortars of Plastic Consistency ASTM C230 Specification for Flow Table for Use in Tests of Hydraulic Cements Apparatus Scale (2000 g) Specimen Molds Mixer, Mixing Bowl, Mixing Paddle, & Scraper Flow Table and Flow Mold Tamper Trowel Testing Machine, Forney 400 kip testing machine Materials Graded Standard Sand - Natural silica sand, form Ottawa, Illinois, conforming to the requirements of ASTM Specification C778. Portland Cement per ASTM C150 Mold Release Agent Procedure Mortar Composition - The proportions of materials for the standard mortar shall be one part of cement to 2.75 parts of graded standard sand by weight. Use a water cement ratio of 0.485 for all portland cements and 0.460 for all air entraining portland cements. The water cement ratio for other than portland and air entraining portland cements shall be such as to produce a flow of 110 +/- 5. Batch the following, which is sufficient for 6 samples: Cement, g 500 Sand, g 1375 Water, g Portland (w/c=0.485) 242 (Air entraining portland (w/c=0.460) 230 Non portland (As required for flow of 110)) Specimen Mold Preparation Apply a thin coating of mold release to the interior surfaces of the molds and base plates. Wipe surfaces with a cloth to remove any excess. Mortar Mixing Procedure (ASTM C305) Place dry paddle and dry bowl in the mixing position of the mixer. Introduce the materials into the bowl in the following manner: 1) Place all the mixing water in the bowl. 2) Add the cement to the water; then start the mixer and mix at slow speed (140 rpm) for 30 s. 3) Add sand slowly over a 30 s period, while continued mixing at slow speed. 4) Stop the mixer, change to medium speed (285 rpm), and mix for an additional 30 s. 5) Stop the mixer and let the mortar stand for 1.5 minutes. During the first 15 s, quickly scrape down into the batch any mortar that may have collected on the side of the bowl; then for remainder of the interval, cover with the lid. 6) Finish mixing for 1 minute at medium speed (285 rpm). 7) Determine flow of mortar as follows: a) Wipe table clean and dry and place flow mold at center b) Place a layer of mortar about 1 inch thickness in the mold and tamp 20 times. c) Then fill the mold and tamp this second layer 20 times. d) Cut mortar flush with top of mold with a trowel, held perpendicular to the mold, using a sawing motion. e) Wipe table around mold clean of all mortar and dry; then remove mold. f) Drop table through ½ inch height 25 times in 15 s. g) Use calipers to measure the diameters along the 4 scribed lines on the table. The sum of the four readings is the flow (the percent increase in the original diameter). Record this flow value. 8) Following flow test, return all mortar to the mixing bowl. Scrap down the sides and remix for 15 s at medium speed (285 rpm). Molding Test Specimens - Start molding within 2 minute and 30 s after completion of the original mixing of the mortar. 1) Place a layer of mortar about 1 in. (25 mm) (approximately one half of the depth of the mold) in all of the cube compartments. Figure 1. Order of Tamping in Molding of Test Specimens. 2) Tamp the mortar in each cube compartment 32 times in about 10 s in four (4) rounds, each round to be at right angles to the other and consisting of eight adjoining strokes over the surface of the specimen (see Figure 1).