Tiêu chuẩn Việt Nam TCVN 7572 12 2006

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

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

1 Application scope

This standards stipulates method to evaluate the resistance to degradation of coarse aggregate by abrasion and impact in the Los Angeles Machine

2 Reference documents

TCVN 7572-1: 2006 - Aggregate for Concrete and Mortar - Test Methods – Part 1: Sampling

3 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

4 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

5 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 1

Table 1: Weight of massive aggregae samples for abrasion and impact test

Sieve mesh size, mm

Weight based on grain size, g

Grading

Total 5000 ± 10 5000 ± 10 5000 ± 10 5000 ± 10

Sample shall be washed and dried until achieving a substantial constant mass, then sieved to classify grading in accordance with Table 1

6 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 2

Table 2 Number of steel ball used in Los Angeles machine Grading Number of steel ball Weight of steel ball, g

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 big-size 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%

7 Calculation

Percentage of wear (P) :

In which:

W1 – Weight of primary sample, g;

W2 – Weight of sample after test, g;

8 Report test result

Test result report should include following contents:

- Type and source of aggregate;

- Name of construction work, sampling location;

- 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)