Low-slump concrete or low-workability concrete has its uses, but if you want medium or high workability and end up with low workability, it will become very difficult to place and handle because of its stiffness. It can even lead to project failure if you use stiff concrete where medium or high workability concrete is required. So, you should know its causes to fix it or you can order concrete mix delivery to receive concrete on your site that is manufactured in a plant according to your requirements.

Causes Of Low-Slump Concrete

Low Water-Cement Ratio

This is one of the most common reasons for low workability in concrete. If the water content ratio is low, it will not flow as required and will be stiff. Sometimes, a lower water-cement ratio is intentional for high-strength concrete, so check the requirements first to know which type of concrete you need.

If you need high-strength concrete (water-cement ratio of 0.3 to 0.4), its workability will be low. To improve its workability without compromising the strength of concrete, you can add plasticizers instead of adding water. They are chemical admixtures that lower the requirement to add water to improve concrete workability and flow.

However, if you want concrete for general construction used for standard foundations, walls, driveways, and others, you would want the water-cement ratio to be between 0.4 to 0.6. And if the concrete workability is low, you should add water cautiously because too much water will lead to many other problems like lower strength, cracking, shrinkage, etc.

Even in this case, you can add plasticizers or air entraining agents, or use fly ash or slag to improve concrete workability.

Higher Aggregate Content

Aggregate content in concrete is sand, gravel, and crushed stone. They offer strength and bulkiness in the concrete mix if you add the right amount. But they require enough cement content to coat the small stones for sufficient workability. This ensures the concrete is easy to pour and finish.

However, if the aggregate content is higher than required, there will be too much stones and much less cement to coat them. So, the concrete won’t flow as required and will be stiff.

Therefore, you can carefully add more cement or water to improve workability or use admixtures to ensure that. Another method is by using round aggregates as they will not cause as much friction as angular aggregates will.

Excess Cement

If more than required cement is added to the concrete mix, it will have low workability. Even though cement gives concrete strength and is the material that binds the aggregate in the concrete mix, too much of it won’t work in your favor because the concrete will be stiff and sticky. Because of this, the concrete, ironically, won’t be strong enough. This will lead to cracks and shrinkage.

Another interesting thing is that the concrete with higher amounts of cement will set quickly, but it won’t be durable.

To fix this problem, you can adjust the mix design by carefully adding a small amount of water, adding bigger aggregates if the required mix design allows, adding fine aggregate (sand), or using admixtures. You can also add a combination of these options.

Mix design problems commonly cause workability issues. To avoid this, consult concrete suppliers Rockville for ready-mixed concrete.

Higher Absorption of Aggregates

Aggregates absorb a small amount of water when mixed with cement and water. And workers keep this fact in mind when adding water and cement. However, if the amount of aggregates is more than required or the aggregates are porous or weren’t pre-soaked, they will absorb more water than expected. This will lead to stiff concrete.

You can avoid this problem by pre-soaking aggregates before mixing. If dry aggregates are already added and causing low workability, you should adjust the mix water or use admixtures. This advice works for any type of project whether its home construction, home improvement projects like building a pool or driveway, or commercial construction projects.

Delayed Placement

If there is a longer delay between concrete mixing and placement, the concrete will become stiffer even when it wasn’t when it was freshly mixed.

As soon as water is added to the concrete mix, the chemical reaction begins. The concrete mix starts losing water through hydration and the mix starts getting stiffer, slowly. This is why it’s critical that there aren’t delays between mixing and placement.

Commonly, if the concrete was transported from a distant plant, the on-site mixer was too far away from the area where concrete needs to be poured, or if the weather is warm, the concrete may become stiffer before pouring and placing. So, find the cause of the problem to fix it.

For example, if the cause of stiff concrete is a longer distance between the on-site mixer and the concrete placement site, adjust the concrete mix. You can add concrete retarders or water-reducing admixtures to increase the setting time of concrete, which will buy you more time to move concrete from the mixer to the jobsite.

However, what you don’t want to do is to add water when there is nothing wrong with the concrete mix design, and the issue is due to the delay in placement, because it will only make the concrete weaker.

Hot, Windy, Or Dry Weather Conditions

Concrete becomes stiffer as water keeps evaporating from the mix. If the weather condition is hot or it’s windy or there is low humidity, the evaporation process will occur at a higher rate, leading to low-slump concrete. The concrete can become stiff in this case, even if the mix design is perfect.

To avoid warm, windy, or dry conditions affecting concrete’s workability, you can use many methods:

• Add retarders, water-reducing admixtures, or superplasticizers.
• Use ice or cool water in the concrete mix to keep the concrete’s temperature lower for longer periods.
• Store aggregates and cement in a cool area. And before adding aggregates, spray them with water so they are not too warm or don’t absorb too much water.
• Reduce the time between concrete mixing and placing. Keep it between 30 and 60 minutes.
• Use shades to reduce the impact of the hot weather or wind. You can use windbreaks.
• Mist the forms and area before pouring concrete.
• Schedule work during the cool hours of the day (morning or nighttime).

Insufficient Mixing Or Overmixing Concrete

Concrete mixing time can also affect the workability of concrete. If concrete is overmixed, the aggregates may settle, and the water and cement content will stay on top. Plus, this will allow water to evaporate faster, so you will get stiff concrete. Similarly, cement may also hydrate, causing low workability.

On the flip side, insufficient concrete mixing may also create workability problems because the water and cement will not coat the aggregates properly and there will be segregation. Therefore, make sure you mix concrete for 2-5 minutes or follow the manufacturer’s recommendations or the advice of experts on-site.

Conclusion

Low workability in concrete can create durability issues, cracking, and shrinkage. Many problems can cause this and most of them can be avoided if skilled workers are hired for on-site concrete mixing and proper concrete pouring and placement rules are followed. Moreover, if on-site concrete mixing is frequently causing these errors, consider ordering ready mix concrete delivery Potomac.