ELAZIG GUNISIGI NEWSPAPER - December 2010
READY-MIX CONCRETE OR SITE-MIXED CONCRETE?
Some issues are tough to solve, some questions have no definitive answers, and some priorities remain unchanged. Urban transformation is one of the country’s most significant challenges because, without eliminating the stock of buildings that are not earthquake-resistant, it will be impossible to breathe freely. The situation worsens when newly constructed buildings also lack proper earthquake resistance.
Endless questions exist: Is ready-mix concrete better quality? Or is on-site mixed concrete the way to go? This question will continue to be asked, and we will keep answering it. Without a doubt, ready-mix concrete should always be used for concrete pouring. On-site mixed concrete is both weaker in strength and more expensive.
Our unwavering priority is life safety. Economy has always been secondary in engineering. When considering the operational costs of buildings, on-site mixed concrete becomes economically impractical.
Why would anyone prefer a method that is both weak and expensive? Sometimes, rural construction projects are cited as a justification. Ready-mix plants may not be able to deliver concrete to more remote locations. However, there are trucks (transmixers) that can mix and transport concrete to such areas. In these cases, on-site mixed ready-mix concrete should still be used.
Speaking of rural areas, you know that after the earthquake in Kovancılar District, earthquake-resistant housing is being built in the villages there. Everyone involved has a legal and moral responsibility towards these buildings. Using any concrete other than ready-mix concrete in these earthquake-resistant houses means the project won’t achieve its intended goal.
The rural conditions of our country and region are well-known. Projects and solutions should be tailored to these conditions. Even in what are considered perfect projects, implementation issues arise. When these issues are shared with relevant institutions and individuals, I believe suitable solutions can be found. It is impossible for one person to know everything. But those who know that there is someone out there who can solve every problem are the true wise ones.
When concrete is first mixed, it has a fluid consistency and is known as fresh concrete. Over time, the concrete hardens, becomes shapeable no longer, and takes on its final form as hardened concrete.
Characteristics of Fresh Concrete:
- Workability and consistency
- Appropriate water/cement ratio
- Temperature of fresh concrete
- Maximum aggregate particle size
- Homogeneity, slump loss, air content
- Unit weight
Characteristics of Hardened Concrete:
- Strength (compressive, tensile, and shear strength)
- Impermeability, abrasion resistance
- Freeze-thaw resistance
- Heat and sound insulation
- Aesthetic (appearance of the surface)
- Economy
It’s nearly impossible to consistently achieve these properties with on-site mixed concrete. With ready-mix concrete, all materials are weighed to prepare the mix. This means the production follows precise calculations. In on-site mixed concrete, no weighing is performed. How can we claim the mix is made according to specifications if there is no weighing involved?
One of the most critical strength characteristics of concrete is the water/cement ratio. It’s impossible to properly control this ratio with on-site mixed concrete, especially since only visual inspection is used, and the effectiveness of this is yet to be proven.
On-site mixed concrete is typically produced in batches of up to 250 cubic decimeters. Ready-mix concrete, on the other hand, is produced in minimum batches of 8 cubic meters (8000 cubic decimeters). Just considering the production volume, the margin of error for ready-mix concrete is 32 times smaller than for on-site mixed concrete.
In conclusion, the superiority of ready-mix concrete is undeniable, especially in housing projects where life safety is at stake. Therefore, under no circumstances should on-site mixed concrete be used in the structural elements of buildings.
What’s done is done. Let’s ensure we pay attention to this issue going forward. I hope those who are aware of this matter will inform those who are not.