Pouring concrete for projects like fence posts or deck footings raises a common question among homeowners. They often wonder if postcrete, a quick-setting concrete mix, is as durable as standard concrete. The short answer is that when mixed and cured properly, postcrete can be nearly as strong as conventional concrete. However, when it comes to postcrete vs concrete, there are some key differences between postcrete and standard concrete that impact the final strength.
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What is Postcrete and what is it made of?
Postcrete, sometimes called fast-setting concrete, is a special concrete mix that allows you to pour concrete and allow it to cure much more quickly than standard concrete. Postcrete is generally composed of standard concrete ingredients like cement, sand, gravel, and water. However, postcrete contains additional chemicals that accelerate the curing process. It also contains a coarser gravel aggregate which allows the concrete to strengthen more quickly. The coarse aggregate used in postcrete can make it slightly less strong than standard concrete in the long run. This is a downside to consider when comparing the two.
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Is Postcrete as Strong as Concrete?
The short answer is no, Standard concrete that is properly mixed and cured will always be stronger in terms of compressive and tensile strength. However, postcrete strength can come close to standard concrete in strength if mixed and cured correctly. And for many non-structural jobs, postcrete is “strong enough” to get the job done. The convenience factor of postcrete often makes it an acceptable alternative depending on the application.
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Factors Affecting Postcrete Strength
- Mixing: It’s important to mix postcrete thoroughly and according to the manufacturer’s directions. Don’t add too much or too little water. Let the mixed postcrete slump for about 5 minutes before pouring.
- Curing: Postcrete sets up in 30-60 minutes but continues to cure and gain strength for 1-2 weeks just like standard concrete. Moist curing improves strength. Don’t stress/load the postcrete until fully cured.
- Aggregate: The coarse aggregate in postcrete makes it weaker than standard concrete in the long run. There are tradeoffs between strength and quick curing.
- Reinforcement: Adding rebar or other reinforcement increases the strength of postcrete posts and footings, just like standard concrete. Always reinforce structural elements.
- Water-Cement Ratio: The ratio of water to cement is critical for strength. More water weakens postcrete. Follow the mix directions carefully.
- Compaction: Properly compacting postcrete eliminates air pockets and improves strength. Tamp postcrete as you pour.
- Weather Conditions: Extreme cold or heat during curing impacts strength. The ideal curing temp is around 23°C.
- Pour Thickness: Pour postcrete in thin layers or lifts for proper curing rather than thick layers.
- Voids & Pitting: Too little cement paste exposes aggregates and causes surface voids, reducing overall strength.
- Age: Postcrete continues to gain compressive strength for 6+ months. Peak strength is achieved after 1-2 years.
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Explaining why ready-mixed concrete is generally superior to postcrete:
Ready-mixed concrete from a reputable local concrete supplier is almost always going to be a better choice over postcrete or other fast-setting concrete mixes. Here’s why:
- Higher Quality Ingredients: Ready mix concrete is made in controlled batches. It uses exact measurements and high-quality ingredients, such as Portland cement, coarse aggregates, sand, and admixtures. The process ensures that each batch is consistent and of high grade. This degree of quality control ensures maximum concrete performance.
- Greater Strength: Properly batched concrete has a compressive strength of 3,000 to 5,000 psi at 7 days and beyond. In comparison, postcrete typically has a lower strength of 2,000 to 4,000 psi. This allows it to withstand greater structural loads and resist cracking.
- More Durable: Ready mix concrete, thanks to precise batching methods, has minimal flaws and air pockets, resulting in higher density. This density makes it more resistant to damage from moisture, freeze-thaw cycles, and chemical exposure over many years of use.
- Customization: Suppliers can adjust concrete mix designs to meet specific performance criteria. This includes factors like achieving high-early strength, extended working time, sulphate resistance, and more.
- Assured Quality: Companies thoroughly test each batch of concrete for compressive strength, air content, slump, and temperature. These tests follow strict quality control standards to ensure the quality of the produced concrete Postcrete has no independent quality assurance.
- Professional Service: They provide valuable technical advice on concrete specifications. They also ensure highly consistent delivery of the concrete product to your work site whenever it is needed.
- Flexible Delivery: Concrete companies use large fleets of trucks that can deliver concrete to any job site in precise amounts, preventing waste. In contrast, Postcrete bags restrict flexibility in terms of delivery and may lead to limitations.
- Volume Capability: They can handle big projects, like large homes or commercial buildings, that need a lot of strong concrete. They have the capacity and inventory for such massive volumes. So, even if a project requires a huge amount of high-strength concrete, ready-mix suppliers are equipped to handle it.
- Consistent Mixing: Specialised drum mixer trucks mix concrete thoroughly while on the way to keep it consistent. Mixing postcrete by hand can lead to inconsistencies. It’s important to avoid hand-mixing postcrete to ensure a uniform result.
- Expert Finishing: Concrete suppliers can provide skilled crews to finish concrete work, saving on labour. These crews handle the placing, screeding, and finishing of concrete flatwork. However, Postcrete needs self-finishing, meaning it requires independent completion.
- Sustainability: Concrete plants continuously reuse water and ingredients wasted on-site are recycled back into aggregate stockpiles.
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Conclusion
Postcrete is helpful for small jobs. However, when you mix on site concrete, it allows you to control the quality and strength through proper mixing, pouring, and curing. It’s important to emphasise that when optimised, standard concrete consistently achieves higher strength compared to postcrete.
Ready Mix Concrete London stands out as the premier choice for the top reliable concrete supplier across the United Kingdom. Our commitment to delivering excellence at affordable prices makes us the preferred partner for diverse construction needs throughout the UK.
