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Tiêu chuẩn kỹ thuật TCVN 7572 122006: Cốt liệu cho bê tông và vữa Phương pháp thử Xác định độ hao mòn khi va đập của cốt liệu lớn trong máy Los Angeles Bản dịch tiếng Anh của đội dịch dự án cầu đường
TCVN 7572 - 12 : 2006 Vietnam standard Aggregate for Concrete and Mortar - Test Methods Part 12: Determination of Resistance to Degradation of Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine Application scope This standards stipulates method to evaluate the resistance to degradation of coarse aggregate by abrasion and impact in the Los Angeles Machine Reference documents TCVN 7572-1: 2006 - Aggregate for Concrete and Mortar - Test Methods – Part 1: Sampling Term and definition Loss by Abrasion and Impacting - Quantity loss of aggregate by abrasion and impact in drum containing aggregate sample and steel balls, calculated by quantity percentage Device and instruments - Los Angeles machine: Steel structure; cored cylinder; completely sealed at two ends; firmed plug at cylinder body for imputing aggregate; cylinder length of 500mm; inside dimeter of 700mm; thickness cylinder cover of 12mm; machine on a lateral axle, rotating around the axle with a determined velocity - Steel balls of 390 – 445kg for each; - Technical balance with accuracy of 1%; - Sieve set with sieve mesh size (mm): 37.5; 25; 19; 12.5; 9.5; 6.3; 4.75; 2.36 and 1.7; - Drying cabinet with temperature correction device to ensure stable drying temperature from 105 – 110oC Sample preparation Take massive aggregate samples in accordance with TCVN 7572-1: 2006 It is verified based on grading and sample weight stipulated in Table Table 1: Weight of massive aggregae samples for abrasion and impact test Weight based on grain size, g Sieve mesh size, mm Grading A B C D From 37.5 to 25 1250 ± 25 - - - From < 25 to 19 1250 ± 25 - - - From < 19 to 12.5 1250 ± 10 2500 ± 10 - - From < 12.5 to 9.5 1250 ± 10 2500 ± 10 - - From < 9.5 to 6.3 - - 2500 ± 10 - From < 6.3 to 4.75 - - 2500 ± 10 5000 ± 10 From < 4.75 to 2.36 Total 5000 ± 10 5000 ± 10 5000 ± 10 5000 ± 10 TCVN 7572 - 12 : 2006 Vietnam standard Sample shall be washed and dried until achieving a substantial constant mass, then sieved to classify grading in accordance with Table Test performance Sample and steel balls are loaded into cylinder Number of steel ball for each test depends on grading of aggregate in accordance with Table Table Number of steel ball used in Los Angeles machine Grading Number of steel ball Weight of steel ball, g A 12 5000 ± 25 B 11 4584 ± 25 C 3330 ± 20 D 2500 ± 15 Rotate the cylinder for 500 revolutions at a speed of 40 to 45 rpm Remove from the machine and make a preliminarily separation of the sample on a sieve coarser than 1.7mm to remove bigsize grain Sieve the fined portion on a 1.7mm sieve The material retained on 1.7mm sieve shall be washed and dried to a substantially constant mass and accurately weighed to 1g The screening portion through 1.7mm sieve is considered as the loss in mass of the sample after the test To evaluate the uniform of aggregate, it can determine the loss in mass of the sample after 100 rpm Then the sample, including the screening portion through 1.7mm sieve, shall be loaded into the cylinder (be careful to avoid scattering) Then the machine is set to rotate 400 rpm additionally to determine the loss of mass after 500 rpm as the above mentioned procedure The aggregate is considered to have a consistent hardness if the ratio between the loss of mass after 100 rpm and that after 500 rpm not over 0.2% Calculation Percentage of wear (P) : In which: W1 – Weight of primary sample, g; W2 – Weight of sample after test, g; Report test result Test result report should include following contents: - Type and source of aggregate; - Name of construction work, sampling location; Vietnam standard - Name of stockyard or construction site; - Date of sampling and testing; - Weight sample after 100 rpm and 500 rpm; - Uniform coefficient of hardness of big-size aggregate; - Percentage of wear by abrasion of big-size aggregate (P); - Name of person and agency in charge of the test; - Applied standard (TCVN 7572- 12: 2006) TCVN 7572 - 12 : 2006