Concrete 101: Understanding the Concrete Mix – What’s in the Bag?

New to concrete? No problem. Whether you're pouring a slab for a shed or managing a new driveway install, it helps to know what’s actually in a concrete mix—and why it matters. At its core, concrete is a simple recipe: cement, aggregates, and water—but slight changes to that recipe can have a big impact on how your project performs.

Let’s break down what goes into a standard mix and what each ingredient can do for your concrete.

🧪 The Basic Ingredients

1. Cement

Cement is often confused with concrete, but it’s just one part of the mix. It's the binding agent—when combined with water, it reacts chemically (a process called hydration) to create a paste that hardens and glues everything together. Most mixes use Portland cement, which is widely available and compatible with a variety of applications.

2. Aggregates (Sand and Gravel)

Aggregates give concrete its volume and strength. These can be a mix of fine material (like sand) and coarse material (like gravel or crushed stone). The type, size, and cleanliness of your aggregates can influence both workability and durability.

• Grading (distribution of particle sizes) can affect how tightly the materials pack, which influences strength.

• Clean aggregates (free from silt, clay, or organic material) can help improve bond and reduce the risk of long-term deterioration.

3. Water

Water activates the cement and gives the mix its initial plasticity. But here’s the kicker: not all water amounts are equal. The water-to-cement ratio plays a critical role in performance.

A higher water-to-cement ratio can lead to weaker concrete, while a lower ratio can improve strength but reduce workability.

This means if you add too much water to make the mix easier to work with, you can weaken the finished product. On the flip side, using too little water can make the mix difficult to place and finish.

⚗️ Optional Additions: Admixtures

Admixtures are chemical or mineral additives that can modify the properties of concrete. Depending on the needs of the project, these can:

• Accelerate or slow down set time (helpful in cold or hot weather)

• Improve freeze-thaw resistance

• Enhance workability without changing the water content

• Reduce shrinkage or cracking potential

Common admixtures include air-entraining agents, plasticizers, retarders, and accelerators. These should be selected carefully, as they can interact differently depending on mix design and jobsite conditions.

🚚 Ready-Mix vs. Custom Batching

You’ll often hear about ready-mix concrete, which is batched at a plant and delivered by truck. This option can offer consistency, especially for large or time-sensitive pours. However, custom batching on-site can give more control for small jobs, specialty applications, or remote locations.

Each approach has its place. If you're using ready-mix, communicating your needs to the supplier (like slump, strength requirements, or additives) is key.

📌 Final Thoughts

Concrete might seem simple, but the chemistry behind it is anything but. By understanding how each component in the mix can affect the end result, you’re one step closer to making smarter decisions for your project.

No two jobs are exactly the same, and conditions like weather, subgrade, and usage all play a role. But with a solid grasp on the basics of the mix, you're better prepared to ask questions, spot red flags, and ultimately get the results you want.

⚠️ Legal Disclaimer:

This blog post is intended for informational purposes only and should not be taken as professional, legal, or construction advice. Every project is unique, and conditions may vary. RLW Concrete LLC is not liable for any actions taken based on this information. Always consult with a qualified professional for your specific needs.