Chapter 4: Methods of Concrete Construction and Building Equipment
As mentioned earlier, the transportation, hauling and mixing of concrete at any given building site can depend greatly on the specific requirements of the project. Concrete, cement and other aggregate materials play a vital role in both architectural and civil projects. Construction crews frequently use concrete, the main component of paving.
However, the nature of concrete makes transport and use a very complicated process that involves various pieces of heavy equipment. Haulers transport and deliver the concrete to the building site before additional equipment can be used to mix, spread and finish the concrete at the proper height and grade. Concrete asphalt, along with other materials, also may require the use of heavy machines such as rollers and crushers for paving on roadways.
Portland cement, a commercial grade cement, needs to be mixed before spreading for building applications. Mixers can range from small mobile pieces of equipment to agitating transit trucks or even entire on-site batch plants used from the mixing to spreading stage.
How to Address the Common Problem of Setting Concrete
Unfortunately, concrete may begin to set before it can even be placed, spread or finished. Once extensive setting occurs, nothing can be done to correct the thickness. This potential issue is why agitating trucks are sometimes used to haul large quantities of the material directly to the site. Agitation helps keep the material moving so that the batch has enough integrity to do the job correctly at the desired thickness and grade.
Dry-batch concrete can help mitigate the setting problem but needs to be hauled by large dump trucks to the work site and put into the paving equipment. In the case of plant-mixed concrete, pump trucks may be used to distribute and place the concrete.
The Advantages of a Concrete Plant
For large projects, a concrete plant, or batch plant, might be one of the most useful assets for your operation. Batch plants combine all of the dry and wet ingredients that comprise concrete, which includes:
- Fly ash
A concrete plant allows for mixers, both tilt and horizontal, batchers, conveyors, stackers, bins, heaters, chillers, cement silos and more. The concrete batching plant acts as the mixer and can produce a large output with consistency, resulting in much lower labor and production costs.
In most cases, crews employ mid-sized mobile transit mixers because they offer mobility across the job site. Concrete typically is used in foundations for building projects but can be used to create entire structures like dams.
Concrete buildings, roads, walls and surfaces all offer longevity and are better suited to environmental impacts like rain and temperature than traditional building materials like wood. Depending on the amount needed, the specific design of the project, or the location of implementation, concrete demands will vary. Below we look at some of the most common pieces of equipment used to mix, spread and finish this vital building material.
1. Concrete Pumps: Distributing Liquid Concrete
Before concrete sets, its viscous, liquid-like state allows machines to pump it. Concrete pumps transport and pump high volumes of the liquid material for quicker and more efficient placement. While pump designs may vary, line pumps are some of the most common and can create:
- Concrete slabs
- Swimming pools
Line pumps are long pipes, while the pump itself pushes the amount of material through the end to be distributed. In mines and other job sites, concrete pumps may be mounted in a way to make them more flexible and maneuverable, depending on the desired application.
2. Concrete Mixers: Combining Wet and Dry Ingredients for Concrete
Concrete mixers vary in size and mobility. A concrete mixer, or cement mixer, combines all the wet and dry ingredients to prepare the concrete for placement. This includes sand, aggregate, water, fly ash and cement, which acts as the binding agent. To achieve consistency of the mixture and ensure the proper thickness of the material, a large drum rotates, providing even distribution of the ingredients. For small projects:
- A simple portable mixer may be used directly on the job site.
- Because of the need for less volume, workers can employ a small mixer to tend to the concrete before it sets.
- However, larger projects need much more working time and large volumes of the material.
Concrete begins to harden quickly. Getting it to a proper thickness and grade after spreading requires time. Finishing work cannot occur once concrete hardens, so it is important to use large transit mixers. They can be filled with batch-mixed concrete or dry material ready to be mixed on the job site.
Through constant agitation, the truck’s concrete load maintains its liquid state and allows workers to work at a reasonable pace for the more extensive areas. Workers use trowels and other tools to smooth and finish the surface once the concrete has been poured.
3. Concrete Vibrators: Reducing Air Pockets and Improving Longevity
As with compactors used to create a desired grade, concrete vibrators serve the same purpose but operate on different mechanics. Consolidating concrete helps avoid air pockets, creating a more compact and dense material for setting. This step prevents future damage to concrete and ensures the material has longevity.
When concrete is first poured, it can contain anywhere between 5 and 20 percent entrapped air. Through the proper use of concrete vibrators, you can mitigate the problem of air pockets, which can reduce the material’s strength once it hardens. Displacing any excess air that may be entrapped during the mixing and pouring phases for thinner areas of concrete can eliminate weaknesses in the material.
4. Concrete Pavers: Assisting With Grade and Surface
Depending on the project, a paver may be needed. There are different types of concrete pavers, but they are designed to travel over an area and establish the grade and surface of the pavement. Pavers often utilize steel wheels to help establish this surface profile in the case of roadways. For more specific applications, such as bridges, airports and concrete canals, traditional paving equipment may be a poor fit.
Bridge pavers and canal pavers are specifically designed to meet these needs. These specialized types of pavers are not as common on most construction sites but still play a vital role in the creation of infrastructure we utilize daily.