Ready mix concrete is concrete that is manufactured at a batching plant, mixed to a precise specification, and delivered to a job site in a freshly mixed state, ready to pour. Unlike concrete mixed by hand or in a portable mixer on site, ready mix is produced under controlled conditions using computer-calibrated equipment that measures materials to within 1-2% accuracy. It accounts for the vast majority of concrete used in construction today, from residential driveways to commercial foundations.
What Goes Into the Mix
Every batch of ready mix concrete contains four core ingredients: cement, water, fine aggregate (sand), and coarse aggregate (gravel or crushed stone). The aggregates make up the bulk of the mixture by weight. In a standard mid-strength mix, a single cubic meter contains roughly 315 kg of cement, 1,879 kg of aggregate in various size fractions, and 180 kg of water. The ratio between water and cement is one of the most important variables in the entire mix. A shift of just 0.1 in the water-to-cement ratio can change the final strength by 15-20%.
Beyond these basics, producers often add chemical admixtures to fine-tune performance. Water reducers allow the concrete to flow more easily without adding extra water, preserving strength. Accelerators speed up setting time, which is useful in cold weather or when a project needs to move fast. Retarders do the opposite, slowing the set so crews have more working time in hot conditions. Air-entraining admixtures create tiny, evenly spaced air bubbles throughout the mix, which help concrete resist cracking from freeze-thaw cycles.
How It Gets Mixed
There are three primary methods for producing ready mix concrete, and the difference comes down to where the mixing happens.
- Transit mixed (truck mixed): All raw materials are loaded directly into the truck’s rotating drum at the plant, and mixing occurs during transport. The drum spins at a fast “charging” speed during loading, then slows to an agitating speed for the drive. This is the most common method.
- Central mixed: The concrete is fully mixed in a large stationary mixer at the plant before being loaded into a truck for delivery. About 20% of concrete plants in the U.S. use this approach. It offers faster production, better consistency, and less wear on truck drums.
- Shrink mixed: A hybrid of the two. Concrete is partially mixed at the plant, then transferred to a truck mixer to finish the job. Generally, about 30 turns in the truck drum (roughly two minutes at mixing speed) is enough to complete the process.
The Batching Process
At the plant, materials are weighed and loaded in a specific sequence. First, a portion of water and coarse aggregate go into the drum. Then aggregates and cement are “ribboned” together, meaning they’re fed in simultaneously so the cement doesn’t clump. A final charge of water flushes any cement clinging to the hoppers and chutes. Getting this sequence right matters more for truck mixing than central mixing, because the truck drum is less efficient at breaking up poorly loaded materials.
All weighing and measuring equipment is regularly calibrated. Materials are batched in three groups: aggregates, cement (and any supplementary powders), and liquids (water plus admixtures). The plant operator controls the proportions for each batch based on the mix design ordered by the customer.
The 90-Minute Clock
Once water hits cement, a chemical reaction begins. That reaction doesn’t wait for the concrete to arrive at your project. Industry standards set a 90-minute window from the time of batching to the time of discharge. After that, the concrete may lose too much workability to place and finish properly.
This time limit is strictly enforced. A significant volume of concrete gets sent back to batching plants every year because of excessive slump loss during transport, overproduction, or simply traffic delays. In some cases, producers add high-range water reducers or retarding admixtures during transit to extend workability without changing the water-to-cement ratio. But the 90-minute rule remains the default threshold, and hot weather, long haul distances, or high-strength mixes can shorten that window further.
Why It Outperforms Site-Mixed Concrete
The core advantage of ready mix is consistency. Computer-controlled batching eliminates the guesswork of shoveling ingredients by hand. Properly produced ready mix concrete can be up to 40% stronger than site-mixed concrete, largely because the proportions are exact and the mixing is thorough. On a construction site, it’s nearly impossible to replicate that level of precision with a portable mixer and bags of cement.
Ready mix also reduces waste. Because each load is mixed to the volume you order, there’s far less over- or under-ordering compared to buying raw materials in bulk and estimating on site. You’re not stuck with leftover bags of cement hardening in a shed, and you’re not dumping excess mixed concrete. The materials arrive, get placed, and the truck leaves.
Speed is another factor. A single truck can deliver several cubic meters in one load, work that would take hours with a small site mixer. For anything larger than a fence post or a small pad, ready mix is faster, stronger, and more economical per cubic meter.
How It Gets Placed
Once the truck arrives, the concrete needs to go from the drum to its final location. For simple pours like slabs or footings close to the truck, concrete flows down a chute directly from the back of the mixer. The chute can typically reach about 3 to 4 meters from the truck.
For harder-to-reach areas, elevated pours, or large-volume jobs, a concrete pump is used. Boom pumps are truck-mounted with an articulating arm that can reach over obstacles and place concrete precisely. Line pumps push concrete through a pipeline along the ground for longer horizontal distances. The choice depends on the pour location, volume, and access. Proper pump selection and setup are critical because pumping can affect the concrete’s properties. For instance, when a boom pump has a long vertical drop, the air content in the concrete at the discharge point can fall to less than half of what went into the pump hopper.
Environmental Considerations
Cement production is carbon-intensive, and the ready mix industry is one of the largest consumers of Portland cement. The National Ready Mixed Concrete Association adopted the Architecture 2030 Challenge in 2012, setting goals to reduce embodied carbon from concrete to net zero by 2050. In 2021, the association reaffirmed that commitment by supporting the Portland Cement Association’s roadmap to carbon neutrality.
In practice, producers reduce their carbon footprint by partially replacing Portland cement with supplementary materials like fly ash (a byproduct of coal power plants) or ground slag (from steel production). These substitutions can lower the cement content per cubic meter while maintaining or even improving long-term strength and durability. The trade-off is that these mixes often set more slowly, which may not suit every project timeline.