It is a known fact that the strength and durability of concrete should be guaranteed for the safety and longevity of structures. Concrete Strength testing or rebound testing is a common method that assesses the stability of concrete.
However, there are times when concrete strength fails to meet the requirement. In such cases, it is essential to look for the reasons and take immediate action to resolve them. Before that, we need to find the causes of these concrete strengths.
So, let’s examine the potential causes, recommendations, and treatment methods for concrete strength issues in this article.
Potential Causes of Insufficient Concrete Strength
Before moving on to find ways of resolving, it is best to identify the potential causes of poor concrete strength.
Poor curing or compaction
One of the most common reasons for the lack of concrete strength is poor setting during the early stages or inappropriate vibration during concrete placement. Simply when the curring is not enough, it makes it difficult for the concrete to achieve strength due to the hindering of the hydration process.
Similarly, when compaction is improper during the phase of pouring, it may leave voids within the concrete causing insufficiency in its strength.
Failure to reach design strength
There will be a standard 28-day curing period that assesses whether the concrete has reached the required strength. But if concrete fails to reach the required strength even in this period, it may point to a problem with concrete mix design or execution.
Rapid slump loss in concrete mix
During the mixing process, there are possibilities to add excess water. This may result in a quick slump loss in the concrete mix and reduce strength. Maintaining the desired consistency can also be difficult when transporting concrete over long distances.
Large batch size for small components
Concretes can lose their strength when small structural components such as columns are poured with large batches of concrete. This extends the unloading times, exposed to air for a longer time, without allowing it to fully set.
Decline in the Quality of Raw Materials
Poor-quality raw materials can greatly reduce concrete strength. Common issues include:
- High Mud in Sand and Aggregates affects binding.
- Excessive Shale in Coarse Aggregates reduces stability.
- Low-quality fly ash weakens the mix.
- Reduced water-reducing efficiency without proper dosage adjustments.
- Weak cement leads to substandard concrete.
How to Improve Concrete Strength?
Controlling Excessive Carbonation Depth
During the initial stages of concrete placement, ensuring adequate curing and compaction prevents Concrete Strength Issues. Carbonation depth of concrete over 2mm in six months or 3mm in older concrete suggests poor curing or compaction, often due to construction issues, especially in cold weather. So controlling the Excessive Carbonation Depth method can be a better way to address concrete strength issues
Enhancing Concrete Mix Design
To ensure a higher margin of safety for variations in material performance, enhancing concrete mix design is an effective way. This ensures that the concrete achieves the required strength within 28 days. The strength should meet or exceed the designed strength value, which should be calculated as the design strength plus 1.645 times the standard deviation.
Additive Testing for Each Truckload
To ensure better performance of admixtures, it is essential to test each truckload of concrete. Regular testing helps maintain consistency and quality across batches.
Limit delivery volume for small components
Overloading trucks with more than its volume can cause delays in unloading and loss of concrete strength due to exposure to air. Therefore, when pouring small components like structural columns, make sure that the pouring rate is slow while maintaining the delivery volume per truck at a range of 3 to 5 cubic meters.
Correct Raw Material Quality Issues
If there are any issues with the quality of the raw materials, it should be fixed. Whether it is sand, cement, or aggregate, you can guarantee the materials to be of good quality by working with reputable suppliers. Carrying out regular quality will also help produce long-lasting concrete.
Suggestions for Improved Concrete Strength Testing
- Identify the root cause by investigating all aspects of the concrete process including material quality, curing, pouring, and mix design. Addressing these issues in such instances will help to improve concrete strength and quality.
- Evaluate the weak components, especially when certain structural components show such signs during comprehensive strength assessment. Through repairs and reinforcements, concrete strength can be improved to ensure safety.
- It is recommended to conduct quality control programs to prevent concrete strength issues. To maintain the standards of concrete, strict inspection protocols should be implemented for materials, mix design, and pouring standards.
- To minimize mistakes during concrete pouring, curing, and mixing, it is important to provide the construction crew with proper training in concrete strength testing. This will reduce the likelihood of strength issues.
- To ensure consistent quality of raw materials, it is best to work closely with concrete suppliers, especially through regular communication.
Conclusion
The safety and longevity of a structure can be risky with inadequate concrete strength. The project’s structural integrity can be guaranteed by restoring the concrete’s strength by investigating the possible reasons, the application of corrective actions, and adherence to best practices. One essential method for assessing concrete strength is the rebound test, which measures the surface hardness and helps estimate the overall strength. It is vital that this testing is conducted properly to ensure the concrete’s durability and the safety of the structure.
All parties engaged in the construction process must work together in concrete strength testing, pay close attention to detail, and maintain quality control to solve problems with concrete strength.
