Is post-tension better than rebar? Concrete foundation - Texas Barndominiums Episode 29

Summary

In this video, the host discusses pouring a 3,100 square-foot concrete slab using a post-tensioned foundation. The method, aimed at reducing costs and minimizing hairline cracks, involves using less rebar compared to traditional methods. The process includes a pre-stress and final stress to enhance durability. The host explains the benefits and challenges of post-tensioning, sharing insights from testing it on two slabs before deciding whether to fully switch from rebar. The video offers a detailed look into the construction process, including the weather's impact and collaboration with engineers.

Takeaways

• 🏗️ The video showcases a concrete pour for a post-tensioned foundation.
• 🏠 The slab being poured is 3,100 square feet and requires around 100 yards of concrete.
• 💡 Post-tensioned foundations are being tested to reduce hairline cracking, which is important for stained concrete.
• 💰 Rising steel prices are pushing the experiment with post-tensioning as a potential cost-saving method compared to rebar.
• 🔧 Post-tensioned systems require more work after the pour, as forms can only be removed the day after due to cable brackets.
• ⚙️ The process includes a pre-stress and final stress to help minimize cracking, with pre-stressing done a few days after the pour.
• 📝 The builder is experimenting with this system and comparing it to rebar to decide on future projects.
• 🔍 Engineers have designed the foundation both with rebar and post-tension, with the post-tension slab having more beams, leading to questions about over-engineering.
• 📅 The full tensioning process takes place over a couple of weeks, with a partial stress done early and the final stress later.
• 🌧️ Weather is a concern, with an 80% chance of rain, which could impact the process.

Q & A

What is the main task being performed in the video?

The main task being performed is pouring concrete for a post-tensioned foundation.

How large is the slab being poured?

The slab being poured is about 3,100 square feet.

What is post-tensioning and why is it being used?

Post-tensioning is a method where steel tendons are used to strengthen concrete by applying tension after the concrete has cured. It is being used to see if it can minimize hairline cracking and reduce the amount of rebar required.

What are the expected benefits of using post-tensioning in concrete slabs?

The expected benefits are potentially less hairline cracking and reduced rebar usage, which can lower costs while maintaining quality.

Why is the presenter skeptical about the cost-saving claims of post-tensioning?

The presenter mentions that despite claims of cost savings, post-tensioning doesn’t seem to be much cheaper, especially given the number of beams required.

What is one of the challenges mentioned with post-tensioning compared to traditional rebar methods?

One challenge with post-tensioning is that the forms cannot be pulled off the same day as the pour, unlike with rebar. The process requires waiting until the next day.

What is the two-step tensioning process described in the video?

The two-step tensioning process involves a partial tension of the tendons a few days after the pour, followed by final tensioning about a week later. This is done to potentially minimize hairline cracking.

Why is the presenter testing post-tensioning on two slabs before making a decision?

The presenter wants to gather factual data and results from two slabs to compare post-tensioning with the traditional rebar method before deciding whether to switch permanently.

Why was the foundation in the video described as being 'over-engineered'?

The foundation was described as over-engineered because it included more beams than necessary, likely due to barndominiums being a relatively new type of structure for engineers.

How does the weather forecast impact the project?

There is an 80% chance of rain the next day, which could potentially impact the continuation of the project.