Name: choosing well-graded sand for concrete
Uploaded: 2024-11-07T14:48:54.000Z
Duration: 1 min 24 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Biology

BIO.2

BIO.2.D

Design Example: Aggregate Gradation

מנהל מפעל בטון צריך לבחור בין שני מתקנים לייצור חול מיוצר, A ו-B, כדי לרכוש חול העומד בדירוג הנדרש לשימוש בבטון.
דגימות של חול מיוצר מהמסועים בשני המתקנים נאספות לאחר עצירת החגורות.
שתי תבניות מרווחות, ומוכנסות לזרם החול.
החומר המלא ברווח שבין התבנית מועבר למיכל.
זה חוזר על עצמו בשני מקומות אקראיים נוספים על החגורה.
לאחר מכן מערבבים את הדגימות שנאספו ליצירת מדגם מייצג, מסמנים אותן ושומרים אותן בתנור לייבוש.
הדגימות המיובשות מפוצלות באמצעות מפצל חול לחלקים שווים, אשר לאחר מכן נתונים לניתוח מסננת על ידי מעבר דרך קבוצה של מסננות סטנדרטיות.
עקומת ההדרגתיות המתאימה משורטטת.
עקומת ההדרגתיות של החול ממתקן A נצפתה בתוך האזור התחום על ידי הגבולות שנקבעו בהתאם לתכנון תערובת הבטון.
לעומת זאת, החול ממתקן B נופל מחוץ לאזור זה. כתוצאה מכך, המנהל מחליט לקנות חול המיוצר במתקן A.

דוגמה לעיצוב: מיון אגרגטים

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סוג ואיכות האגרגטים חשובים מאוד בבטון, שכן הם משפיעים במידה רבה על תכונותיו, פרופורציות התערובת, ויעילות העלות. כאשר קיימים מקורות שונים לחול, האגרגט הדק הנפוץ ביותר בבטון, הבחירה בחול מתבצעת בעיקר על פי מיון הגרגירים שלו.
מיון הגרגירים, או חלוקת הגדלים של חלקיקי החול, נקבע באמצעות ניתוח נפה, עם גדלים סטנדרטיים הנעים בין 150 מיקרומטר ל-10 מ"מ (נפה מספר 100 של ASTM עד 9.52 מ"מ). דגימות של חול עבור מיון נאספות מזרם אגרגטים זורם, רצועות מסוע, או ממאגרי חול. דגימה יחידה מייצגת בדרך כלל כ-45,000 עד 50,000 קילוגרם של חול. בסופו של דבר, מתקבלות דגימות בדיקה לניתוח נפה מהדגימה בשטח באמצעות מפריד דגימות.
שימוש בחול עדין במיוחד יכול להיות בלתי חסכוני, וחולות גסים עלולים להוביל לתערובות פחות נוחות לעיבוד. בדרך כלל, חול המיועד לבטון צריך להיות בעל התפלגות טובה של הגדלים, מבלי שיהיה בו חוסר או עודף בולט של גודל מסוים, ובעל עקומת מיון חלקה הנמצאת בתחום שבין עקומות המיון לחול דק ולחול גס.
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מנהל מפעל בטון צריך לבחור בין שני מתקני ייצור חול מיוצרים, A ו- B, לרכוש חול העונה על הצרכים הנדרשים.

Education

JoVE Core

Civil Engineering

הנדסה אזרחית

Unit 1

יחידה 1

Design Examples

דוגמאות לעיצוב

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

choosing well-graded sand for concrete

Well-graded sand is important in concrete because aggregate choice affects strength, mix proportions, and cost. In concrete, sand is the common fine aggregate. When more than one sand source is available, its gradation often guides the selection.

Gradation means the particle-size distribution of the sand. Engineers measure it with sieve analysis, which uses standard sieve sizes from 150 μm to 10 mm, from ASTM No. 100 to the 3/8 in. sieve. This test shows how much sand stays on each sieve and helps compare one source with another.

Sand for gradation testing can be taken from a flowing aggregate stream, conveyor belts, or stockpiles. A single field sample usually represents about 45 to 50 tons of sand. The test portions for sieve analysis are then taken from that field sample with a sample splitter.

Both very fine and very coarse sands can cause problems in concrete. Very fine sands can make the mix uneconomical. Coarse sands can reduce workability, which makes the concrete harder to place and finish.

For this reason, well-graded sand is preferred. It has no major lack or excess of any size and gives a smooth grading curve between the limits for fine and coarse sand. This balance helps concrete perform better and keeps the mix practical to use.

Choosing Well-Graded Sand for Concrete

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design example: aggregate gradation

Well-graded sand is important in concrete because aggregate choice affects strength, mix proportions, and cost. In concrete, sand is the common fine aggregate. When more than one sand source is available, its gradation often guides the selection. Gradation means the particle-size distribution of the sand. Engineers measure it with sieve analysis, which uses standard sieve sizes from 150 μm to 10 mm, from ASTM No. 100 to the 3/8 in. sieve. This test shows how much sand stays on each sieve and...

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key terms and concepts

Learn how sand gradation affects concrete mix quality, workability, and cost. See how sieve analysis helps choose well-graded fine aggregate.

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Choosing Well-Graded Sand for Concrete

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