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What is Rolling resistance?
a measure of the force (lb/ton) that must be overcome to rotate a wheel over the surface on which it makes contact.
What causes rolling resistance?
- -Internal friction
- -Tire flexing
How does the road condition affect productivity?
If haul roads are well maintained, rolling resistance is less and production improves.
What is the coefficient of traction?
- the ratio between the maximum amount of pull a machine exerts before slippage and the total weight on the drivers.
- i.e. required rimpull/total weight
How can you tell if the coefficient of traction is sufficient for the machine?
- Look at table 6.4, if numbers listed are greater than the coefficient of traction that was calculated, then it is ok.
- Ex. Wet Clay has .4, but was calculated to be .15, so it's ok
How does altitude affect machine power?
- If equipment works at higher altitudes, where the air is less
- dense, the engine may produce at a reduced power output.
What are the 7 operations in the production of concrete?
- 1. Batching the materials
- 2. Mixing
What are the 5 different types of cement?
- Type I is a general-purpose cement; it is typically intended for concrete that is not subject to sulfate attack.
- Type II is cement modified to resist moderate sulfate attack.
- Type III is a high-strength early-strength cement. It usually produces design strengths at seven days or less.
- Type IV is a special cement with low heat of hydration. Its strengthdevelops at a slower rate.
- Type V is sulfate resistant; it reaches its design strength in 60 days.
What are benefits of concrete crane-bucket formations?
- Using multiple buckets can shorten the construction time.
- With loading time decreased, this is beneficial for low to mid-rise construction, where bucket loading make up the better part of the overall cycle time.
What are chutes and drop pipes used for?
Chutes are used for direct placing of the mix when the concreting location is within chute reach.
Drop pipes are used to transfer the concrete vertically down for walls or columns.
Why is a pump and boom combination effective?
It's efficient and cost-effective in saving labor and eliminating the need for pipelines to transport the concrete.
What are the 3 tpes of concrete pumps?
- 1) stationary pump - suitable for large coverage areas
- 2) Trailer pump - suitable for mainly spread-out sites
- 3) Truck pump - used for one-time concrete operations when a long reach is needed
What is the main benefit of concrete pumping?
High placing rates, work convenience, and ability to deliver concrete while bypassing obstructions
In what situations is concrete pumping preferable? (4)
- 1 - Projects on which concrete is the primary material imported
- 2-Large concrete structural elements (dam, raft construction)
- 3-Sites with accessibility limitations (rough terrain, bodies of water, existing buildings)
- 4-Increased production / reduce transportation equipment
What does vibration accomplish?
Removes entrapped air in the concrete
What advantage does a crawler crane have over a truck crane?
It has a higher contact area with the ground, and therefore has the ability to travel and hoist a load at the same time.
What is the advantage of telescoping boom truck cranes?
Its ease of movement and setup, its ability to travel on highways . Can change boom length easily during construction.
What is the advantage of a rough terrain crane?
- "Cherry Pickers"
- -These units are equipped with unusually large wheels and closely spacedaxles to improve maneuverability at the job site.
- -Their high ground clearance, as well as the ability of some models to move on slopes of up to 70%.
- -Joystick Control
What is advantage/disadvantage of all-terrain crane?
- -Designed for Long-Distance travel
- -Doesn't need extra equipment to be set up
Disadvantage - expen$ive
What 3 systems are used for cranes needed for heavyweights?
- 1. Trailing counterweight
- 2. Extendable counterweight
- 3. Ring System
What is the advantage of tower cranes?
They provide high lifting height and good working radius, while taking up a very limited area.
What are the disadvantages of tower cranes?
Low lifting capacity and limited mobility
What is the advantage of bottom-slewing tower cranes?
They are smaller and can be towed between most job sites. They erect themselves with their own motors in a relatively short time.
What is a disadvantage of bottom-slewing tower cranes?
They do not have as high of a service height.
What are disadvantages to top-slewing cranes?
Transporting, set up, and dismantling require more time, are more complicated, and more costly.
What is the advantage to top-slewing cranes?
It has a higher service height.
What are the selection factors for mobile cranes? (5)
- Height of reach required
- Working envelope
- Maximum load
- Duty cycle
What heights need to be considered in crane height design? (4)
hook block, slink, material, height load is lifted
What are 3 selection factors for tower cranes?
- Operating radius
- lifting capacity
- lifting speed