Ready Mixed Concrete or RMC is delivered to job sites in a ready-to-use manner. Traditionally, concrete is prepared at job sites. It requires a lot of labor and raises the possibility of human error. An adequately mixed batch of concrete is essential for the integrity of structures. Preparing concrete mixture at job sites cannot ensure every batch has the right proportion of cement, water, and aggregates. As a result, RMC was introduced in the construction industry as advanced technology, involving a high degree of mechanization and automation. Hence, every concrete batch has the exact proportions of ingredients certifying the best outcome.

Cement is the primary ingredient of concrete. So, concrete inhabits the properties of cement. Cement starts a hydration reaction after coming into contact with water. It is responsible for the hardening process of cement. Therefore, it is crucial to know the setting time of ready mixed concrete to work effectively. The setting time of concrete will determine how to schedule the task list in order to achieve the best results.

Setting Time of Ready Mixed Concrete

As mentioned earlier, concrete mainly consists of cement. Cement starts the hardening process when water is added to it. RMC is a mixture of cement, water, and aggregates. RMC is produced at batching plants where water is added to the dry mix of cement and aggregates. Hence, the cement is activated and starts the hardening process.

After a certain amount of time, the concrete will lose its effectiveness if not placed before it is hardened. The setting of RMC indicates its hardened state. The concrete batch will be considered waste if it gets hardened before being used on a job site. So, it is decisive to know when the concrete will be set.

However, RMC has a particular setting time compared to site mixed concrete. There are many differences between site mix concrete and Ready-Mix Concrete. The setting time can vary depending on the mixture type.

The setting time of RMC can be divided into two categories. These are 1) Initial Setting Time and 2) Final Setting Time. The concrete starts the hardening process as soon as the water is added to the cement mixture. RMC is transported via cement trucks. These trucks have rotating drums or vessels that carry the RMC. The RMC requires continual agitation and mixing while it is transported from the batch plant to the job site.

Initial Setting Time

The initial setting time of concrete is around 210 minutes. So, the RMC must be used within 210 minutes after preparing in batching plants. It becomes a race against the clock to transport the RMC in due time. Sometimes admixtures are added to the concrete mix to delay its setting time to travel further distances. That is why local Ready Mix Concrete suppliers are crucial. The concrete trucks should be able to deliver within standard time, or the concrete will lose its effectiveness. Too much delay might make it completely useless.

Final Setting Time

Technically, concrete never stops the hardening process. Concrete continually hardens forever. However, it reaches a point where further hardening becomes incredibly slow and unnoticeable after a specific time. In standard industrial cases, full-strength concrete is accepted at 28 days. After a week, concrete gains 70% of full strength when appropriately cured. After the final setting time, the concrete mixture completely loses its plasticity. The concrete hardens and takes the shape in which it is cast. Any form or scaffolding can be removed after the final setting time. Concrete’s final setting time is generally 24 to 48 hours, depending on the conditions. At this point, it is safe to walk over the concrete without worrying about footprints. However, it would help if you kept it clear of heavy equipment during this time.

Source: Power Blanket

What Factors Can Affect the Setting Time of RMC?

There are some factors you should take notice of that can influence the setting time of ready-mix concrete. These are:

• Moisture is a critical factor in the curing time for ready-mix concrete. If there is a lack of water in the mix, the concrete will cure quickly, resulting in a weaker overall strength. On the other hand, too much moisture will weaken the top layer and cause flaking.
• Hot ambient temperature or high wind can accelerate the evaporation of moisture. It can speed up the RMC setting time.
• Sometimes admixtures of accelerant types are used in the ready-mix concrete. Because some job sites require the concrete to be used as soon as possible, accelerants can quicken the setting time of concrete but also deliver a weaker overall strength in the end. However, it will still meet standard strength requirements.
• Some admixtures can delay the setting time of ready-mix concrete. Sometimes job sites are far away from batching plants. So, the trucks require additional time to deliver the mixture.
• The water to cement ratio significantly impacts the concrete’s setting time, performance, and quality. Ready Mix Concrete usually has a predetermined setting time controlled by the manufacturer. When concrete is produced at job sites manually, the setting time can vary depending on the ratio of cement and water. So, ask the manufacturer about the setting time for the Ready Mix Concrete you intend to purchase.
• Concrete mixes with lower water to cement ratios have faster setting times. It can become harder to work with these mixes as all operations need to be done faster.
• Concrete mixes with a higher water-to-cement ratio have a slower setting time. It can give you more time to work with the mixture.

Some Technical Aspects of RMC Setting Time

Here is a list of essential aspects regarding concrete setting time:

• The ready-mix concrete should be set neither too rapidly nor too slowly. Make sure it is appropriate according to your job site’s location and the nature of construction work.
• Do not confuse setting time with hardening. Hardening refers to the gain in mechanical strength after a certain amount of time.
• Initial setting time refers to the time when the concrete mix starts to lose its plasticity.
• Initial setting time is vital for transporting and placing.
• Initial setting time duration is required to know beforehand to delay the process of hydration or hardening.
• After the final setting time, the mixture loses its plasticity completely.
• Determination of accurate final setting time facilitates the removal of scaffolding or form. You can safely walk on the surface as well.

Summary

The popularity of ready-mix concrete is gaining due to its many advantages. There are many advantages of using Ready Mix Concrete in Bangladesh as well. Big construction sites rely on the accuracy and consistency of concrete mixtures to build robust structures. However, if the workers are not educated about the setting time of concrete mix, your job site will experience a lot of waste and inefficiency. Hence, consult with your contractor to inform the workers how to deal with the concrete mixture. RMC is delivered via trucks, and your job site must expedite the delivery process. It will guarantee a safer workplace and scheduled construction work.

Frequently Asked Questions (FAQs)

How long does Ready Mixed Concrete take to dry?

Ans: Typically, it takes 24 to 48 hours to dry enough for you to walk on it.

How long can concrete last in a Ready-Mix Truck?

Ans: Ready Mix Concrete should be used under 210 minutes after leaving the batching plant.

From where should I order RMC?

Ans: Ask your contractor to order from local RMC suppliers. Otherwise, a long delivery duration might weaken the integrity of the concrete.

How long does 1 inch of concrete take to completely dry?

Ans: A good rule of thumb is that concrete takes approximately 30 days to dry for every inch of poured concrete.

How much strength does Ready Mix concrete gain in a week?

Ans: Ready Mix Concrete gains around 65% – 70% strength in a week.