Name: concrete mixer types and capacity
Uploaded: 2024-11-07T14:48:34.000Z
Duration: 1 min 30 s
Channel: JoVE

המטרה העיקרית של ערבוב בטון היא לערבב את מרכיביו, להבטיח שהאגרגטים מצופים באופן שווה במשחת מלט, והתוצאה היא תערובת אחידה.
בדרך כלל, בטון מעורבב באמצעות מערבלי אצווה או מערבלים רציפים.
מערבלי אצווה מעבדים אצווה שלמה אחת בכל פעם, מערבבים את המרכיבים ואז משחררים אותם לפני הצגת האצווה הבאה. ישנם ארבעה סוגים של מערבלי אצווה: מערבלי תופים הטיה, מערבלי תופים ללא הטיה, מערבלים מסוג מחבת ומיקסרים עם תוף כפול.
מערבל תוף הטיה משתמש בלהבים פנימיים כדי לערבב בטון, ומשחרר את התערובת על ידי הטיית התוף. לעומת זאת, מערבל תופים שאינו נוטה משחרר את המיקס דרך מצנח או על ידי היפוך סיבוב התוף.
ערבוב בטון בקבוצות יכול להיעשות במיקסר מסוג מחבת באמצעות משוטים או במערבל תופים כפול הכולל תהליך ערבוב דו-שלבי בתוך מערך טנדם של תופים.
מיקסרים רציפים מקבלים מרכיבים באופן אוטומטי ורציף, אשר לאחר מכן משולבים באופן אחיד באמצעות מיקסר מסוג תוף או בורג הנע בתוך בית נייח, וכתוצאה מכך זרימה מתמדת של בטון מעורב.
לבסוף, כדי להבטיח את יעילות המיקסר ביצירת תערובת אחידה, דגימות בנקודות פריקה ספציפיות נאספות ומוערכות לעקביות.

ערבול בטון

Mixing Concrete

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ערבול בטון מבטיח תערובת הומוגנית שבה האגרגטים מצופים היטב בתערובת הצמנט. ערבוב הבטון מתבצע בדרך כלל באמצעות שני סוגים עיקריים של מערבלים: מערבלי אצוות (batch) ומערבלים רציפים (continuous). מערבלי אצוות מטפלים במנה אחת בכל פעם, מערבבים את החומרים בצורה יסודית לפני הפריקה ומקבלים את המנה הבאה. לעומתם, מערבלים רציפים מקבלים זרימה קבועה של מרכיבים, מערבבים אותם באופן מתמשך ופורקים ללא הפסקה.
בתוך מערבלי אצוות, קיימים מערבלי תוף נטוי, המערבבים בעזרת להבים פנימיים ופורקים את התערובת על ידי הטיית התוף, בעוד שמערבלי תוף שאינו נטוי משתמשים במגלשה או על ידי סיבוב התוף לשם פריקה. מערבלי מחבת (pan) בעלי להבים המסתובבים סביב ציר אנכי, ומערבלי תוף כפול, המאפשרים ערבוב רציף בשני תופים, נפוצים גם הם בשימוש במערכות סדרתיות.
מערבלי בטון זמינים בטווח רחב של קיבולות, הנעות בין 0.04 מ"ק ל-12.99 מ"ק. ערבוב נפח שהוא רק חלק קטן מהקיבולת הכוללת של המערבל נחשב לבלתי יעיל ועלול להוביל לתערובת לא אחידה. באותו אופן, העמסת יתר של המערבל מעבר ל-10% מהקיבולת המומלצת עלולה גם היא לגרום לתערובת לא אחידה.
כדי לוודא את יעילות המערבל בהפקת תערובת אחידה בין המנות השונות, מבצעים דגימות בנקודות פריקה שונות ובודקים את העקביות שלהן בהתאם לקריטריונים שנקבעו, כגון צפיפות, תכולת אוויר, חמיטה, וחוזק לחיצה. פעולות אלו מבטיחות שבסופו של דבר יתקבל בטון איכותי התואם לדרישות הפרויקט.
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המטרה העיקרית של ערבוב בטון היא לערבב את מרכיביו, להבטיח את האגרגטים מצופים באופן שווה עם דבק מלט, וכתוצאה מכך אחיד ...

Education

JoVE Core

Civil Engineering

הנדסה אזרחית

Unit 1

יחידה 1

Mixing, Placing and Curing Concrete 

ערבוב, יציקה וריפוי בטון

KEY TERMS AND CONCEPTS

מונחי מפתח ומושגים

concrete mixer types and capacity

Concrete mixing creates a uniform blend of cement, aggregates, and paste. The goal is to coat the aggregates evenly with cement paste. Mixers used for this job are usually grouped into two main types: batch mixers and continuous mixers.

Batch mixers handle one load at a time. They mix the materials thoroughly, discharge the batch, and then receive the next one. Continuous mixers work differently. They take in a steady flow of ingredients, mix them at a constant rate, and discharge the concrete without stopping.

Several batch mixer designs are common. Tilting drum mixers use internal blades and empty by tilting the drum. Non-tilting drum mixers discharge through a chute or by reverse rotation. Pan-type mixers use paddles that rotate around a vertical axis. Dual drum mixers allow the material to pass through two drums in sequence.

Mixer size also matters. Concrete mixers come in many capacities, from 1.5 cubic feet to 17 cubic yards. Using only a small part of the mixer can be inefficient and may lead to an uneven mix. Overloading the mixer by more than 10% can also reduce uniformity.

To check mixer performance, samples are taken from different discharge points. These samples are tested for consistency using measures such as density, air content, slump, and compressive strength. This helps show whether the mixer produces the same quality mix across batches.

Concrete Mixer Types and Capacity

mixing concrete

Concrete mixing creates a uniform blend of cement, aggregates, and paste. The goal is to coat the aggregates evenly with cement paste. Mixers used for this job are usually grouped into two main types: batch mixers and continuous mixers. Batch mixers handle one load at a time. They mix the materials thoroughly, discharge the batch, and then receive the next one. Continuous mixers work differently. They take in a steady flow of ingredients, mix them at a constant rate, and discharge the concrete...

mixing time

Concrete Mixer Charging and Timing

Concrete mixer charging and timing are key to making a uniform concrete mix with the needed strength. Mixing begins only after all ingredients are inside the mixer. The usual charging order starts with 10% of the water, then the solid materials are added steadily, followed by 80% of the water. The last portion of water is added later, within the first quarter of the total mixing period. The minimum mixing time depends on mixer capacity. Mixers with up to 1 cubic yard of capacity need at least...

ready mixed concrete

How Ready-Mixed Concrete Is Delivered

Ready-mixed concrete is prepared at a centralized plant and then delivered by truck to a construction site. It arrives ready for placement, which makes it different from concrete mixed entirely on site. Ready-mixed concrete includes three main forms: central-mixed, truck-mixed, and shrink-mixed. Central-mixed concrete is fully mixed at the plant and carried to the site in agitator trucks. These trucks rotate at 2 to 6 rpm, which helps keep the concrete in motion during transport. Truck-mixed...

pumped concrete

Concrete Pumping for Hard-to-Reach Sites

Concrete pumping moves large amounts of concrete through pipes to places that are hard to reach. It is used for sites such as deep foundation pits and other inaccessible locations. The system includes a hopper, a pump, and pipelines that carry the concrete to the placement point. Direct-acting pumps use a piston to move the concrete. Concrete enters the pump through the inlet valve by gravity and by suction created as the piston moves. The forward movement of the piston then pushes the...

placing concrete

Concrete Placement Methods and Compaction

Concrete placement methods focus on keeping the mix in a uniform shape and position. The concrete is placed as close as possible to its final location to reduce segregation, which is the separation of ingredients. It is then fully compacted to remove trapped air. The next layer is added while the layer below is still plastic, or soft enough to shape. The rate of placing and compacting concrete is kept equal. Concrete is laid in uniform layers, and hand shoveling is avoided. Moving concrete...

vibrating concrete

Concrete Compaction with Vibrators

Concrete compaction with vibrators helps newly poured concrete settle inside formwork and around reinforcement bars. The goal is to remove trapped air pockets and create a dense concrete mass. Mechanical vibration is a key part of that process. One common method uses an internal vibrator, also called a poker vibrator or immersion vibrator. It is quickly inserted through the full depth of the fresh concrete and slightly into the layer below, which is still in a plastic state. The vibrator is...

shotcrete

Shotcrete for Vertical and Overhead Surfaces

Shotcrete is a concrete spraying method used on vertical and overhead surfaces. It uses mortar or small aggregate concrete with a high cement content. The material is sprayed at high velocity, and the impact helps compact it so it can cling without sagging. Builders place shotcrete in layers until it reaches about 4 inches thick. The quality depends strongly on the operator’s skill in managing the nozzle. Careful nozzle control helps the material land evenly and build up properly. Shotcrete...

preplaced aggregate concrete

Concrete Placement for Tight Spaces

Preplaced aggregate concrete is used when a construction site is hard to reach. The process starts by wetting gap-graded coarse aggregates. This helps remove dirt from the stones. The aggregates are then placed in the form and compacted. Next, a mortar mix is pumped under pressure through slotted pipes to fill the spaces between the aggregates. The mortar usually contains Portland cement, pozzolan, fine aggregates, water, and a fluidizing aid. The pozzolan reduces bleeding and segregation and...

finishing concrete

Concrete Surface Finishing Steps

Concrete surface finishing begins right after the concrete has been placed and consolidated. The first step is screeding, which levels the surface by removing extra material until it is even with the top of the formwork. A screed is a straight edge used for this leveling step. After screeding, a bull float or darby is used to smooth the surface further. These tools help lower high spots, fill low areas, and push larger aggregate particles deeper into the concrete. This preparation should...

curing of concrete

How Curing Improves Concrete Strength

Curing helps concrete gain strength after it has set. It keeps the concrete moist and at the right temperature so cement hydration can continue. Hydration is the process where cement reacts with water in the water-filled capillary pores and forms the products that fill spaces in the paste. Dry air can interrupt this process by pulling water from the concrete surface. Concrete with a water-cement ratio below 0.5 can also lose water through self-desiccation, which means internal water is used up...

curing methods

Concrete Curing for Moisture Retention

Concrete curing for moisture retention helps fresh concrete keep the water it needs as it hardens. For members with a small surface-to-volume ratio, the forms are often oiled and moistened before the concrete is placed. These forms may stay in place for a long time to reduce moisture loss. If the form material can be wetted, it can also be kept damp. When forms are removed early, the concrete member is moistened and then covered with polythene sheets. Large horizontal concrete surfaces in dry...

accelerated curing of concrete

How Concrete Gains Strength Faster

Concrete can gain strength faster when heat and extra moisture speed up cement hydration. This faster hydration helps the concrete build early strength sooner than normal curing. The process is used when quicker hardening is needed after casting. One common method is steam curing. Concrete products may move through a chamber on a conveyor belt, or they may be encased in plastic so steam at atmospheric pressure can circulate around them. Steam curing starts with moist curing for about 3 to 5...

key terms and concepts

Learn how batch and continuous concrete mixers work, why mixer capacity matters, and how sample tests check for uniform concrete quality.

Concrete Mixer Types and Capacity | JoVE K12

JoVE Core Civil Engineering provides a foundational exploration of essential construction materials in civil engineering, focusing on bricks, stones, steel, wood, and concrete through easy-to-understand animated videos. This collection covers the properties, manufacturing processes, and practical applications of these materials. Additionally, the accompanied science-in-action videos demonstrate the research experiments performed in laboratories.

civil engineering

Concrete Mixer Types and Capacity

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