In cement concrete projects, sand should be clean, hard, in accordance with the provisions of the grading, fineness modulus of 2.5 or more grit or sand. When coarse sand or medium sand cannot be obtained, after the mix ratio design test is required, it is considered that when fine sand is available, fine sand with less than 3% of sand and mud impurities can be used. Sand technical requirements are shown in Table 1. Sand Technical Requirements Table 1 project skills requirement One grain level Match Screen size (mm) Square hole sieve Round hole sieve 0.16 0.315 0.63 1.25 2.5 5.0 Cumulative screening the amount(%) District I 100~90 95~80 85~71 65~35 35~5 10~0 District II 100~90 92~70 70~41 50~10 25~0 10~0 District III 100~90 85~55 40~16 25~10 15~0 10~0 Soil debris content (punching method) (%) ≤3 Sulfide and sulfate content (converted to SO3) (%) ≤1 Other sundries Do not mix lime, cinder, grass roots and other debris Note: 1. The sand in Area I basically belongs to coarse sand. Zone II sand belongs to medium sand and a part of coarser sand with moderate grain size and best gradation. Zone III sand belongs to fine sand and partially fine sand; 2. Preparation method of organic substance content standard solution: Take 2g tannin powder dissolved in 98mL of 10% alcohol solution to obtain the required tannic acid solution, then take this solution 2.5mL to inject 97.5mL of 3% concentration of hydroxide The sodium solution was shaken vigorously after stoppering and allowed to stand for 24 hours to obtain a standard solution. In cement concrete, gravel (gravel) stones should be hard, clean, free of debris, weathering and other stones, and should meet the requirements of the grading requirements, the maximum particle size should not exceed 40mm. The technical requirements for gravel are shown in Table 2. Crushed stone technical requirements Table 2 project skills requirement Particles Grading Mesh size (round hole sieve)(mm) 40 20 10 5 Accumulated sieve residue (%) 0~5 30~65 70~90 95~100 strength Stone saturated with compressive strength and concrete Design compressive strength ratio (%) ≥200 Stone strength classification ≥3 level Needle particle content (%) ≤15 Sulfur and sulfate content (converted to SO3) (%) ≤1 Soil debris content (extraction method) (%) ≤1 Note: Stone strength classification should comply with the provisions of the "Highway Engineering Stone Test Regulations". For gravel and gravel aggregates, non-active aggregates should be used instead of high-activity aggregates. Gravel Technical Requirements Table 3 project skills requirement Particles Grading Mesh size (round hole sieve)(mm) 40 20 10 5 Accumulated sieve residue (%) 0~5 30~65 75~90 95~100 Voidage (%) ≤45 Soft particle content (%) ≤5 Needle particle content (%) ≤15 Soil debris content (preparation method) (%) ≤1 Sulfur and sulfate content (converted to SO3) (%) Organic matter content (colorimetric method) Color is not darker than standard solution Stone strength classification ≥3 level Note: Stone strength can use crush index value (%). About the plastic prepared Microscope slides, we have 4 colores for choosered ,yellow ,green ,blue which have 12 types each colores.Includes 48 specimens of animals insects plants. Get children excited about science by viewing these microscope prepared slides under a microscope.Labeling provides specimen identification. These slides are well labeled with name and drawing. Kids can easily identify what they are observing.The slides are made of acrylic material without sharp edges. They are safer for kids to use than glass slides.This slide set is good for educational purpose for kids, entry-level students or home school programs. Mostly recommended for kids age 5 years and up. Plastic Slide,Small Plastic Slide,Plastic Slide For Sale,Pre Prepared Microscope Slides Xinxiang Vic Science&Education Co.,Ltd. , https://www.hnhumananatomymodel.com