Pros and Cons of Precast concrete VS Cast In place

Available methods of concrete constructions are quite limited. You can use cast in place concrete or precast concrete. Which method is better? Let’s try and figure it out.

To begin with, we should compare the methods in several aspects: the production process, labor costs, logistics, and quality. Then it will be possible to see the whole picture and understand which of the methods of providing your project with concrete will be optimal.

Production and quality of materials

For a construction project, the quality of the components used is important. Concreting is just one of the main stages of any construction project and strict requirements are imposed on it.

One of the advantages of precast concrete is its manufacturing conditions. All concrete elements of the future building are produced in a location isolated from weather conditions and atmospheric influences, the process itself is under strict supervision of specialists. The production of precast concrete products cannot be influenced by weather conditions – unlike concrete production on site – the quality will be confirmed and the concrete structures for construction will be certified by a laboratory in cooperation with this precast factory. Therefore, there seems to be no cause for concern here.

But still, several factors raise questions by construction specialists about this advantage of reinforced concrete. First, precast factories usually have their own laboratories that prepare product certificates, and you cannot be completely sure that there are no “special” arrangements between the factory and the laboratory so that concrete products are always certified. You also have no control over the aggregate quality used for precast concrete. Real construction experts always ask for how long inert materials and cement were stored in the warehouse of the plant and under what conditions. Thus, you remain uncertain about what the reinforced concrete products delivered to you are made of.

Now let`s see how things look with cast in place concrete on a construction site? With this approach, an important aspect is going to be related to the concrete source you are going to choose:

• delivery of concrete mix from a nearby concrete plant
• independent production of concrete on your construction site

When it comes to ordering concrete from concrete plants there may be problems similar to the shortcomings of cooperation with precast concrete factories, which we talked about earlier. Firstly, again you will have certificates and confirmation of quality, but you will not be confident in the accuracy of the documentation.

Secondly, the delivery of concrete mix to the construction site is immediately associated with underfilling of truck mixers that arrive from the batch plant. Companies are already accustomed to ordering more concrete from suppliers than what is calculated according to construction estimates. Why? Because a small part of the concrete mix in mixers remains at the bottom of the mixer or is smeared on the walls. Representatives of concrete plants sometimes like to exaggerate the volume of concrete lost during the delivery or discharge process.

It is unlikely that you will have a measuring tank of similar volume to a mixer truck to check the delivered volume of concrete. It’s not always possible to organize such a check at a construction site.

Producing your concrete on construction site become more common over the past years since in this way you are in control of all the stages from the selection of aggregates to the concreting of the project. Another aspect in favour of setting up your own concrete production at the jobsite is related to a change in machinery available as with new self-loading mobile concrete mixers, large volumes of concrete usually required by big industrial projects are not a problem any more!

There are various types of equipment, which may satisfy the needs of a certain construction project. The first solution: stationary concrete batching plants, which are installed directly on site. However they are difficult to assemble and maintain. The installation of such a concrete plant will take a long time compared to the self loading mobile concrete mixers, as well as its transportation to the site being quite difficult to organise. Together with a stationary concrete batching plant, you will have to purchase supporting construction equipment: at least 1 mixer and one wheel loader, which will transport the concrete mix from the plant to the pouring area and the loader will be occupied with feeding the plant with aggregates. It will take 5-10 workers to run and service these construction equipment. Therefore, this solution is more suitable for multi-year projects that require large volumes of concrete all the time.

More mobile solutions are available to construction companies. They can not only move around the jobsite, but also reduce the labor costs of concrete production, which is the main disadvantage of the cast in place concreting method.

Carmix self-loading concrete mixers are among such multifunctional solutions. Special equipment not only mixes concrete, but also independently loads all the components of the concrete mixture thanks to a bucket and on board water tanks and pump, drives up to any pouring site using an all-wheel drive transmission and all-terrain wheels and unloads concrete to the right place with the help of extension chutes.
If it is impossible to drive close enough to the pouring place, mobile concrete plant can turn the mixing drum 300 degrees for convenient unloading of the mixture. The concrete mixer has a clear and simple control system that requires only one trained individual to fully operate it. Labor costs for the production of concrete are reduced significantly compared to the use of other equipment or special machinery.

Just with the help of self-production of concrete, you can control the quality of your concrete structure at every stage:

• choose high quality aggregates and cement at reasonable prices
• monitor the process of mixing concrete and pouring it
• monitor the conditions in which manufacturing and concreting takes place

Then you will definitely be sure that your project has been carried out at the highest quality level. Cast in place concreting may have one more significant drawback in the production process – the effect of weather conditions on concrete production. We will consider it in more detail when we talk about storage and the construction process.

Versatility

When we talk about the versatility of concrete construction, precast concrete looks less favourable compared to cast in place method as the second one is not limited to pre sets of forms that are used at a precast factory.

Typically, factories produce concrete products that are more in demand. They are suitable for many projects, but still not for all. Therefore, you may be faced with a problem of not being able to find precast parts that suit your construction project design. Of course, you can make a preliminary order according to your specifications, but:

• Not all factories are engaged in the manufacture of concrete products according to the customer’s design
• this will further increase the cost of the production
• ordering precast products according to your specific design will take more time and will require detailed advance planning

On the other hand, cast in place concrete will give you much more flexibility. With this method, you can build the formwork of the desired shape and size. Everything will depend only on architectural design, surface pattern and special equipment required for pouring. For example, if you are constructing a building in a mountainous area, the pouring areas will be difficult to access and you will need to use a concrete pump to pour.

Transportation and storage

Concrete panels and other precast transportation can be a big problem for industrial facilities. Some parts of the concrete structure may require special, more expensive means of transportation. As a contrary, cast in place concreting method does not face transportation difficulties as aggregates are more easy to transport compared to complete precast parts.
In both situations logistics and deliveries will need special attention, but in our experience, delivery of aggregates is way easier to organise compared to large, bulky precast parts.

Speaking of storage at a construction site, precast concrete is very convenient, as it has already gained it`s strength and is very difficult to damage or spoil. And yet, with improper storage, mechanical damage can be caused to reinforced concrete products: cracks, chips etc. The deformed slab will have to be disposed of. For all its strength, reinforced concrete products can suffer from moisture and even become moldy, which will disrupt the structure of concrete. Storage of precast concrete requires a dry, covered space that will protect it from any precipitation.

When making concrete on site, storage is important for each component of the future concrete mix and for the already concreted structure.

Firstly, storage of aggregates has to be properly organized.A covered area or silo are going to be appropriate solutions. In this way the materials will not be affected by weather conditions, which can reduce their quality characteristics or make them unsuitable for concrete production.

Secondly, after mixing, the concrete mixture itself is viable for pouring for a very short period of time. Depending on the temperature outside, the use of various additives and plasticizers, the usable life span of concrete mix can be up to three – four hours. During this time, it is necessary to place the fresh concrete. Therefore, it is best to make concrete directly on the construction site so that the concrete mix does not deteriorate during delivery from the concrete plant if your construction site is located in a hard-to-reach area.

Thirdly, when setting the poured concrete, it is also necessary to withstand all the necessary conditions. In rainy weather, cover with a plastic so that moisture does not violate the water-cement ratio. In hot weather, pay attention to how wet the concrete is, as water evaporates, the mixture sets faster and the structure may not gain planned strength. At low temperatures, the poured concrete is heated in various ways so that the water in it does not crystallize.

Construction process and labor costs

Let us now move on to the most important matter – the construction process. Precast concrete, as mentioned, is a completely ready-to-use material.Bring it, install it right away. Sounds pretty easy. Compared to cast in place concreting, it takes less labor. To build a precast concrete structure you will need:

• several dozen workers
• heavy special equipment such as crane, a telescopic loader etc.
• a qualified team of assemblers and welders who will deal with metal bolted joints of reinforced concrete parts of the structure

With precast concrete, construction time is reduced, due to the fact that there is no need to allocate time for the construction of formwork, reinforcement structures, for pouring and hardening of concrete.

Construction with monolithic concreting is considered to be extremely labor-intensive, because many skilled workers are needed for the stages with the setting up of formwork, production and pouring of concrete mixture. However, we want to draw your attention to the technological progress in the field of construction. Automated special equipment can reduce the number of workers at times for various stages and reduce labor costs at times.

For example, operating a self-loading concrete mixer on site can replace 10-15 workers who are dedicated to concrete production. It only takes one mixer operator to produce concrete. Then other workers can be redistributed to formwork for other pouring areas. Thus, you can shorten the construction time for monolithic concreting.

Also, the performance of special equipment affects the speed of construction. One Carmix 3500TC concrete mixer can produce up to 4 cubic yards of concrete in 20 minutes, so the process will not be interrupted for a second by on-site concrete mixing.
If you choose Carmix as a supplier of concrete to your project, you will not only control the quality of aggregates and mix, but also produce the volume that you need for pouring areas exactly when you need it according to the construction schedule.
In this way, you avoid many problematic situations with concrete plants. For example, the formwork has not yet been assembled at the facility, but the mixer is already on the way. Surely the batching plant will be able to reschedule your order, but only during free time slot in their schedule. Then the opposite situation will arise: everything on your construction site is ready for concreting, but the mixer will not arrive any time soon.
As mentioned earlier, the effects of the weather conditions can greatly slow down the concreting process. However this happens very rarely. With proper storage of construction materials and aggregates and protection of newly poured concrete slabs from heat / cold, construction will not be stopped during the construction season. When the work is going on in the autumn-winter and winter-spring periods, the weather conditions will have to be accounted for more thoroughly.

The most optimal temperature range for monolithic concrete construction is from 41°F to 70°F. When the temperature drops or rises, there are many ways to in order to maintain the quality of concrete.

Quality and durability

What is still better in terms of quality: precast concrete or cast in place concrete with concrete production on site?

Monolithic concrete walls have a higher density and therefore have higher compressive strength than precast concrete structures. Also, with monolithic concreting, there are no joints, as opposed to using precast concrete elements, therefore, the integrity, fire resistance and water resistance of the monolithic structure increase. With the correct production of the concrete mix and setting of concrete, a high level of durability can be achieved.

The high quality of reinforced concrete products depends entirely on the manufacturer, if your supplier is conscientious, then precast concrete products will not be inferior in durability to structures concreted directly at the facility. However due to the fact that a sealant is used when constructing from precast elements, there is a chance that after 15-20 years, reapplication of the sealant will be required to maintain uniformity of the structure. At the same time, maintenance is practically not required for monolithic concrete objects.

Each of the methods has advantages and disadvantages that significantly influence the choice in one direction or another. To fully use the precast concrete construction, your project must be within standards. This is due to the fact that precast factories do not have such a wide selection of shapes and sizes, and not all precast concrete factories make concrete parts of structures according to customer`s specifications.

There are often situations when an architect designs a building or structure using atypical forms. Only with the help of cast in place concreting it is possible to achieve the desired results. After all, with the correct calculations and a professional workforce, you can concrete an object of any shape and size.

There are also a number of structures that cannot be built in any other way than by concreting on site. For example, retaining walls, which are mandatory for objects under construction in the mountains and in areas with uneven terrain. Also, the foundation of bored piles is poured right on site, and is commonly used in wetlands or steep slopes or even during construction on permafrost soils. Such structures require pouring concrete mix directly on site.

What if we tell you that there is a way to combine both methods and make it cheaper compared to working with external suppliers? With Carmix self-loading concrete mixers, the choice in favor of on-site concreting will allow you not only to pour monolithic concrete structures but also the production of precast parts according to your personal specifications, right at the construction site itself.

This option is extremely valuable when the distance is substantial between your jobsite and precast concrete facility or batching plant. In addition to all this, you avoid all the disadvantages mentioned before that are related to working with external suppliers:

• control the quality of aggregates, the process of producing concrete mix, pouring prefabricated concrete parts
• you reduce your concrete and overall construction costs, as you work without an intermediary. Produce mix at prime cost, do not overpay for precast fabrication and on-site delivery