Key Factors for Producing High-Quality Concrete
A Wide Range of Quality Control Factors for Sound Concrete Construction
Proper vibration consolidation can be a decisive factor in producing high-quality concrete structures. At the same time, numerous construction processes and time-dependent factors are involved from the mixing of fresh concrete to the completion of the structure. To achieve high-quality concrete, careful control is required throughout every stage of the construction process, including the following:
- Quality control of constituent materials, including cement, aggregates, water, and admixtures, as well as their handling prior to mixing
- Quality of the mixing operation.
- Transportation time and quality control during delivery to the placement site.
- Structural design, including factors such as concrete cover thickness.
- Accuracy and quality of reinforcing bar placement.
- Quality of formwork construction and the strength of supporting structures.
- Selection and quality of form-release agents.
- Placement methods.
- Weather conditions and worksite environment.
- Selection and proper use of vibrators.
- Curing methods and quality.
- Timing and procedures for formwork removal.
Lessons from Failure: How to Make Bad Concrete
Although somewhat paradoxical, let us examine how poor-quality concrete can be produced even when following the principles listed above, as evidenced by actual experiences we have encountered in the field.
- Used the remains of a previously opened and improperly stored bag of cement that had already begun to deteriorate and partially set.
- Used dried-out gravel that had been exposed to sunlight, mixing it with normal water volume and highly saline well water.
- Added water later because the slump of the fresh concrete left in the mixer during lunch break appeared too low when work resumed.
- Concrete cover was insufficient, and the selected vibrator could not fit between the reinforcing bars due to inadequate spacing.
- Improper spacer placement allowed reinforcing bars to sag and contact the formwork.
- The formwork bulged under pressure.
- Forgot to wet the plywood formwork before concrete placement.
- Poured concrete from a height of approximately 2 meters because no chute was prepared.
- Continued concrete placement despite heavy rain.
- Prepared three vibrators but kept one as an unused spare even though two pump trucks were operating.
- Removed the curing sheet to accelerate drying in direct sunlight, or used jet heaters in cold weather without water curing.
- Prematurely removed the formwork the day after placement due to pressure from the MEP contractor to proceed.
As you can see, no matter how good our vibrators are, it is impossible to produce a high-quality concrete structure under certain circumstances. Fortunately, thanks to ready-mixed concrete, successful outcomes in the first three examples listed above are now virtually guaranteed in most cases. However, there are still many areas where the expertise of vibration specialists can make a significant difference. From ensuring adequate concrete coverage in complex structural designs, to formwork configurations around openings and beneath windows, it is imperative that the challenging flow characteristics of fresh concrete be taken into account. In such situations, the experience and know-how of EXEN's vibration experts can help improve concrete quality and construction performance.
Relative Influence on Concrete Strength and Surface Finish (Based on Field Experience)
The key point of this chapter is that high-quality concrete can only be achieved through careful management of the entire construction process. Based on our field experience, the relative influence on concrete strength and surface finish can be roughly divided as follows:
- Design, materials, mixing, and transportation: 20%
- Placement and compaction (vibrator operation): 50%
- Curing and formwork removal: 30%
However, if any one of these areas is deficient, the final result can be seriously compromised.