22.6.c - Placing and Finishing
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Surface Preparation
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To achieve a strong bond between the polymer-modified concrete and the substrate, what should we ensure about our surface preparation?
It should be clean and free from any contaminants.
Correct! We need to ensure the surface is clean, roughened, and in a saturated surface dry state. Why do you think that state is important?
It helps improve the adhesion of the PMC to the substrate.
What contaminants are most harmful?
Great question! Dust, grease, and laitance can all interfere with the bond. Remember, we can use the acronym 'CRS' to remember: Clean, Roughen, Saturated!
Let's summarize: the key steps in surface preparation include cleaning, roughening, and ensuring a saturated surface dry condition. If we miss any of these, we may face bonding issues later.
Mixing Process
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In mixing PMC, what is the first step we should take?
We should add the polymer latex to the mixing water, right?
Exactly! This helps the polymer disperse better. After that, what do we mix next?
Then we mix the aggregates and cement together.
Correct! Following that, we add in the polymer water mix. Why is thorough mixing for 3–5 minutes important?
It ensures we achieve homogeneity, preventing weak spots in the concrete.
Very good! So remember, the steps are: add polymer to water, mix dry ingredients, then combine everything, mixing for a good 3–5 minutes!
Placing and Finishing Techniques
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Now that we have our PMC mixed, can anyone tell me about placing?
We should use conventional placing techniques.
Right! But there's a catch—what must we keep in mind about troweling and screeding?
They need to be done promptly before the polymer sets!
Exactly! Timing is crucial. If we delay, we risk having a poor finish. And how about curing? What do we need to remember?
Moist curing may not be necessary because the polymer acts like a curing membrane?
Correct! However, we should consider ambient conditions and sometimes use protective coverings for specific polymers. Was there anything else we discussed about curing?
Only when the set time comes depending on environmental conditions, right?
Very good! To conclude, the keys to successful placing and finishing are timely execution and understanding the properties of the polymer.
Introduction & Overview
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Quick Overview
Standard
The section outlines the key steps in placing and finishing Polymer-Modified Concrete (PMC), emphasizing surface preparation, mixing protocols, and the timely execution of finishing techniques to prevent issues during curing.
Detailed
Placing and Finishing
In the section on Placing and Finishing Polymer-Modified Concrete (PMC), we explore crucial steps that influence the final quality of concrete structures. Effective surface preparation is paramount, where the surface needs to be clean, roughened, and brought to a saturated surface dry (SSD) condition to ensure good adhesion and performance of the PMC. The mixing process is detailed, highlighting that polymer latex should be mixed with water before being combined with the cement and aggregates. It is essential to mix the components well for 3–5 minutes to achieve homogeneity.
When placing the PMC, conventional methods can be utilized, but the timing of troweling and screeding is critical and should occur promptly. Finishing the surface must be completed before the polymer latex begins to set, which can vary depending on the type of polymer used. Furthermore, curing is an area where PMC differs from traditional concrete; while moist curing is often not required due to the polymer acting as a curing membrane, careful attention to ambient conditions is still necessary to ensure the integrity and performance of the PMC over time. Protective coverings may be recommended for specific polymer types during the first 24–48 hours of curing.
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Surface Preparation
Chapter 1 of 4
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Chapter Content
- Surface must be clean, roughened, and saturated surface dry (SSD).
- Remove dust, grease, or laitance before placement.
Detailed Explanation
Surface preparation is a critical step before placing Polymer-Modified Concrete (PMC). A clean surface ensures that the PMC can bond effectively with the substrate. This involves removing any dust, grease, or laitance, which is a layer of weak cement paste. The surface should also be roughened to provide more grip for the concrete and be in a saturated surface dry state, meaning it's moist but not surface wet, which helps prevent excessive water absorption during curing.
Examples & Analogies
Think of surface preparation like cleaning a plate before serving food. If the plate has leftover grease or crumbs, the new food won't sit well or will mix with the remnants, affecting taste and appearance. Similarly, a clean and properly prepared surface ensures the new concrete adheres properly and performs well.
Mixing
Chapter 2 of 4
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Chapter Content
- Add polymer latex to mixing water.
- Mix aggregates and cement first, then add polymer water mix.
- Mixing should be done for at least 3–5 minutes for homogeneity.
Detailed Explanation
Mixing the ingredients for PMC is a systematic process. First, the polymer latex should be added to the water to create a polymer solution. Then, the dry components like aggregates and cement should be mixed together before the polymer solution is included. This sequence ensures an even distribution of the polymer throughout the mix. A minimum of 3 to 5 minutes of mixing is necessary to achieve homogeneity, meaning all components are well-mixed and consistent in texture.
Examples & Analogies
Imagine making a cake. You wouldn't just dump all ingredients in at once; you would first mix the dry ingredients (like flour, sugar, and baking powder) and then gradually add in the wet ingredients (like eggs and milk). Likewise, proper mixing of concrete ensures that the final product has a uniform consistency, resulting in better performance.
Placing and Finishing
Chapter 3 of 4
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Chapter Content
- Use conventional placing methods.
- Troweling and screeding should be done promptly.
- Finishing should be completed before polymer starts to set.
Detailed Explanation
Once the mixing is done, the concrete can be placed using conventional methods, similar to traditional concrete placement. Troweling and screeding—the processes of smoothing and leveling the surface—must be done quickly because PMC has a limited working time before it starts to set due to the polymers. It's crucial to finish these tasks before the mix begins to harden to ensure a smooth and durable surface.
Examples & Analogies
Placing and finishing PMC can be compared to icing a cake. After you've baked your cake (mixed the ingredients), you need to spread the icing on promptly while the cake is still warm and easy to work with. If you wait too long, the icing won't adhere well, and the result will be messy.
Curing
Chapter 4 of 4
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Chapter Content
- Moist curing may not be necessary as polymer acts as a curing membrane.
- Air curing at ambient temperature is often recommended.
- For some polymers, protective coverings are advised for first 24–48 hours.
Detailed Explanation
Curing is essential for concrete to reach its maximum strength, but with PMC, the presence of polymers can eliminate the need for constant moisture. Polymeric materials can act as a barrier, holding moisture in. Generally, air curing at ambient temperatures is sufficient. However, for some types of polymers, using protective coverings for the first 24 to 48 hours may be advisable to prevent premature drying and ensure optimal curing conditions.
Examples & Analogies
Consider how a plant needs water to grow. When it rains, the soil is moist, allowing strong roots to develop. Similarly, the curing process ensures that the concrete remains adequately hydrated to gain strength while the polymers help retain this moisture. Protective coverings are like a greenhouse for plants, shielding them from the harsher conditions until they are well established.
Key Concepts
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Surface Preparation: Ensuring surfaces are clean, roughened, and SSD is vital for adhesion.
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Mixing Process: Combining polymer latex with water followed by aggregates and cement ensures a uniform mixture.
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Placing Technique: Timely execution of placing and finishing will ensure high-quality results in PMC applications.
Examples & Applications
Before placing PMC, ensure the substrate is prepared adequately by removing dust and grease to enhance bonding.
In the process of making PMC, start by mixing polymer latex with water, then blend with the dry components for a homogeneous mix.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
For PMC that's the best, clean and dry is the test; roughened surface is key, skip this and you'll see.
Stories
Imagine a sculptor preparing a statue; they clean and smooth the stone to ensure the finest detail. Similarly, we must clean and prepare our concrete surfaces for the best results.
Memory Tools
Remember 'CST' for surface preparation: Clean, Smooth, Trowel.
Acronyms
Think 'CMR' for the placing sequence
Clean
Mix
Repair (screen/trowel).
Flash Cards
Glossary
- Saturated Surface Dry (SSD)
A condition of the concrete surface where it is wet but there is no standing water, ensuring optimal adhesion.
- Troweling
The process of smoothing wet concrete by using a flat tool to create a level surface.
- Screeding
The action of leveling and finishing wet concrete to the desired thickness and smoothness using a straightedge.
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