Sieve Analysis of Aggregates

Transcription

1 Revised 2007, WKS Datasheet No. 30 MOHAWK COLLEGE OF APPLIED ARTS AND TECHNOLOGY BUILDING AND CONSTRUCTION SCIENCES DEPARTMENT Sieve Analysis of Aggregates INTRODUCTION The evaluation of the distribution of particle sizes or gradation is a very important step in the process of developing mix designs for Portland cement concrete. Different communities will require the use of local aggregate sources to keep the price of the concrete mix reasonable. Since the raw materials and even the crushing equipment used at the source (pit) will be different in each community, there are no absolute recipes for producing concrete mixes. Usually, concrete mixes are manufactured using a coarse and fine aggregates coming from different sources, all bound together by a paste of Portland cement. The physical properties of the concrete mix can also be affected by the inclusion of additives in the mix. In this laboratory procedure a sieve analysis will be conducted on the stock aggregates that will be used to manufacture Portland Cement Concrete (PCC) mixtures. The resulting gradations for each material, i.e., coarse aggregate (CA) and fine aggregate (FA) will then be compared to standards set by the Canadian Standards Association (CSA). The fine aggregate (sand) will be evaluated (pass or fail) based on the CSA grading criteria for air-entrained concrete (FA1) and non-air-entrained concrete (FA2) shown in Table 1. The fineness modulus (a parameter used in some mix design methods) will also be evaluated using the range specified in the Ontario Provincial Standards 1. For the coarse aggregate (stone) the nominal size will be determined by comparing the gradation results to the CSA grading specifications for various sizes of coarse aggregate shown in Table 2. One of the most critical stages in the process is to acquire samples of the materials that truly represent the materials (i.e., representative samples). If 1 and select Online Standards or click on the OPS link on the instructor s homepage. 1

2 the material has been exposed to extensive rainfall or vibration, certain sizes of particles can be segregated or can collect together in pockets. The samples selected for analysis must be produced by the proper use of sample splitters. If the original sample is not representative of the material that will ultimately be used to manufacture the concrete mixtures, all the care in the world in carrying out the sieve analyses will not make the results valid. Every mistake made from this point on in the process will affect the quality of the concrete mix. Table 1: Grading Limits for Fine Aggregate (FA) after CPCA Acceptable Ranges of % Sieve Size Passing by Mass FA1 FA2 10 mm mm mm mm µm µm µm Table 2: CSA Grading Specifications for Selected Sizes of Coarse Aggregate Percent of Sample Mass Passing Sieves Sieve Sizes Nominal Size of Aggregate (mm) mm mm mm mm mm mm

3 EQUIPMENT 1. balances sensitive to 0.1 and 1 gram, 2. Coarse Sieves: 20 mm, 14 mm and 10 mm, 3. Fine Sieves: 5 mm, 2.5 mm, 1.25 mm, 630 µm, 315 µm and 160 µm 4. Sample splitters, 5. Gilson Screen Shaker 6. Miscellaneous pans, brushes, scoops, etc. PROCEDURE A: Sieve Analysis of Fine Aggregate 1. From the air dry sand select a representative sample of about 4 kg and, using the small splitter, reduce this to 500 ±50 g. The sample should be weighed to the nearest 0.1 g. 2. Nest a 10 mm sieve in a sieve pan and place the sample in the sieve. In all probability all the material will pass through it with little or no agitation. If any material is retained on the sieve, weigh it, record the mass and set it aside. 3. Repeat the previous step using a 5, 2.5, 1.25 mm, 630, 315, and 160 µm sieve, recording the masses of the material retained on each sieve. As the sieves become finer, more and more effort will be required to insure that all the material that will pass a sieve actually does. The recommended procedure is as follows: The sieve is nested in the pan and a lid is placed on the sieve. It is held, slightly inclined, in one hand. Then strike the side of the sieve sharply against the heel of the other had at a rate of about 150 times a minute. Turn the sieve about 1/6 of a revolution every 25 blows. This is continued until no more than 1% additional material passes in one minute of sieving. Usually about one minute of such sieving is adequate with the finest two sieves and somewhat less with the others. 4. Total the masses retained on the sieves and pan. This mass should agree within ±1% of the original mass of the sample. If it does not, it will be necessary to repeat the test. 3

4 B: Sieve Analysis of Coarse Aggregate 1. Select about 12 kg of the coarse, air dried aggregate. 2. Using the large or medium sample splitters, reduce the sample to 3 ± 0.5 kg and record the mass. 3. Arrange the 20, 14, 10, 5, 2.5 mm screens in the Gilson shaker and shake for 4 to 5 minutes. Weigh the residue retained on each sieve to the nearest gram. Continue sieving the material from the pan of the Gilson with the brass 1.25 mm, 630, 315, and 160 µm sieves. 4. The total of the material retained on the sieves and the pan should agree within ±1% of the original mass of the sample. If it does not, it will be necessary to repeat the test. CALCULATIONS: Dry Sieve Analysis 1. Calculate the cumulative mass retained on each sieve and the pan. 2. Calculate the cumulative percent retained on each sieve and on the pan as a percent of the original sample mass. NOTE: The % retained on the pan would work out to 100% if there was no sieving error. The value calculated should equal 100% plus the % sieving error.) 3. Calculate the percent passing each sieve by subtracting the % Retained from 100%. 4. Calculate the fineness of each material by summing the % Retained values (excluding the pan) and dividing by 100% REPORT: 1. Visit the website for the Ontario Provincial Standards: and select Online Standards or click on the OPS link on the instructor s homepage. Using the standards indicated on the Report Form, fill in the required information for the report and evaluate the suitability of the aggregate tested for the applications indicated. 4

5 2. Evaluate the fine aggregate according to the FA1 and FA2 grading specification shown in Table 1. Plot the FA gradation curve on the semilogarithmic paper provided with the datasheets on the website or use Excel to plot a scatter type chart (instructions are posted under Graphing Standards ). Also plot the grading specification(s) that the material passes (or comes closest to passing) on the same graph, labeling each curve. 3. Evaluate the coarse aggregate according to the grading specifications shown in Table 2 for 4 different Nominal Sizes. Select the Coarse Aggregate Nominal Size that the CA meets or comes closest to meeting. Plot the CA gradation curve on the semi-logarithmic paper provided with the datasheets on the website or use Excel to plot a scatter type chart (instructions are posted under Graphing Standards ). Also plot the grading specification that the material passes (or comes closest to passing) on the same graph, labeling each curve. 4. Report the fineness modulus of each aggregate and evaluate its suitability as indicated by the OPS Spec