Ready mix concrete, also known as ready mix or concrete, refers to concrete that is manufactured in a batch plant according to a set engineered mix design and then delivered to a work site by truck mounted transit mixers. This results in a precise mixture that allows for minimal adjustment of water at the jobsite. Ready mix concrete is an alternative to on-site concrete batching and mixing.
Some key advantages of ready mix concrete include:
- Consistency – Ready mix concrete is manufactured under controlled conditions in a concrete batching plant according to a precise engineered concrete mix design. This allows for consistency in concrete quality and workability.
- Convenience – Ready mix concrete is delivered to the work site by truck mounted transit mixers in a plastic state. This allows construction crews to focus on placement rather than mixing concrete onsite.
- Efficiency – Batching plants are automated which increases concrete production efficiency. Transit mixer trucks also allow for efficient delivery to work sites.
- Quality Control – Concrete is batched and mixed under controlled conditions allowing for easy quality control and adjustment at the batching plant if needed.
Some key components in the ready mix concrete production and delivery process include:
Batching Plant
Ready mix concrete is manufactured in batching plants. A ready mix batching plant has silos that contain aggregates like sand, gravel and crushed stone. It also has cement and other admixtures stored in silos, bins or tanks.
The batching plant combines the required raw materials in the necessary proportions according to the mix design. The batching process can be automated with computer controlled systems that batch to the specified design.
Weighing tolerances in batching plants are tightly controlled. The amount of water added at the plant is minimized so that only minor adjustments are required at the job site.
Transit Mixers
Once batched and mixed, the concrete is discharged from the batching plant into a transit mixer truck. Transit mixers are truck mounted concrete mixers with a revolving drum that keeps the concrete plastic and in a homogenous state during transportation to the work site.
Transit mixer drums are coated with hardened steel or plastic to resist abrasion and prevent reaction with concrete ingredients. Blades are fitted inside the drum to assist with mixing during transport.
Transit mixers may have capacities between 5 to 12 cubic yards of concrete. The drum rotates at a speed of about 6-18 revolutions per minute during transportation. The drum mixing action provides the final mixing stage.
Delivery
Once loaded, transit mixer trucks deliver the concrete to work sites in a plastic condition allowing for efficient pumping and placement. Delivery tickets with information like batch time, quantity and mix design details accompany each load.
Dispatching ready mix trucks is timed such that they arrive as needed for continuous concrete pouring. Modern fleet tracking allows suppliers to monitor location and schedule trucks efficiently.
The plastic concrete is discharged at a high speed directly into the forms, pump or conveyor. Discharge typically takes under 2 minutes per truck.
On-site Adjustments
Minor adjustments like addition of water or admixtures may be made at the job site to achieve the required mix consistency.
The concrete’s slump, which indicates workability and consistency, is tested onsite. Concrete with slump outside the acceptable range is rejected. Re-tempering, which is the addition of water to concrete after it has started setting, is prohibited.
Quality Control
Ready mix concrete manufacturers are responsible for quality control both during batching and delivery. Each plant has an onsite laboratory for testing mix designs and raw materials.
Concrete samples are taken during batching and tested for slump, air content, unit weight and temperature. Additional samples are taken at job sites for confirmation. Records of production and delivery are maintained.
Custom Mix Design
Ready mix concrete is made to order using a custom engineered mix design for each construction project. The mix design specifies the proportions of ingredients like cement, aggregates, water, admixtures etc. required to meet the performance criteria for the concrete’s plastic and hardened properties.
Mix designs account for the characteristics of the raw materials, project requirements like strength, placement method, exposure conditions, cost optimization and local building codes.
Trial testing is conducted to arrive at the final optimized mix. Ready mix suppliers work with contractors to formulate, test and deliver custom concrete mixes for every job.
Concrete Mix Design Factors
Some key factors considered during ready mix concrete mix design include:
Strength
Compressive strength is the primary requirement that influences the proportions of cement and water in the mix. Higher strength typically requires higher cement content and lower water to cement (w/c) ratio.
Strength is specified at different ages like 7 days, 28 days and 56 days depending on the application.
Workability
Workability refers to the ease with which concrete can be placed, consolidated and finished. It is measured by slump tests. Mix designs aim for optimal workability.
Using plasticizers and air entraining agents can improve workability at lower water contents to provide strength.
Durability
Durability considerations account for the exposure environment of the finished concrete structure. Maximum w/c ratios and air entrainment requirements are specified for freeze-thaw resistance.
Mix designs also account for sulfate resistance, corrosion protection and limiting permeability based on service conditions.
Cement Type
The type of cement – Ordinary Portland, blended, high alumina, etc. is selected based on availability, cost and structural requirements.
Blended cements with fly ash, slag, silica fume etc. are increasingly used to improve concrete properties.
Aggregate Properties
The shape, texture, strength, size gradation, etc. of aggregates influence fresh and hardened concrete properties. Well graded aggregate mixtures optimize packing density.
Local aggregate availability and cost are considered. Testing helps optimize aggregate proportions.
Admixtures
Chemical admixtures like water reducers, retarders, accelerators etc. are used to achieve the desired placing and setting characteristics.
Mineral admixtures like fly ash and silica fume are added to improve strength and durability properties.
Placement Method
The concrete placement method – pumping, pouring, spraying etc. influences the mix design. Pumpable concrete requires higher coarse aggregate content.
Pumped concrete may also require air entrainment and higher cementitious material content.
Local Standards
Ready mix concrete mixes must conform to local building standards, construction specifications, strength requirements and exposure conditions.
Regional materials availability, weather and accepted best practices also influence mix designs.
Advantages of Ready Mix Concrete
Some of the major advantages of using ready mix concrete include:
- Ensures consistent quality since concrete is batched and mixed under controlled conditions to precise mix designs.
- Minimizes effort needed for mixing, allows focus on proper placement.
- Facilitates speedy construction with continuous supply to job site as needed.
- Custom engineered mix designs provide specialized concrete mixes tailored to project requirements.
- Eliminates space needed to store and handle raw materials.
- Allows for flexibility – mix designs can be adjusted quickly based on performance.
- Economical for medium to large projects due to precise batching, rapid construction and efficiency.
- Reliable delivery service and minimal wastage.
- Technical expertise from ready mix supplier assists selection of materials, mix proportions and quality control.
The controlled conditions and precision of ready mix concrete make it an excellent choice for most construction projects today.
Conclusion
Ready mix concrete provides an efficient and versatile building solution by combining the benefits of precise automated batching plants, specialized mix design, and accurate blending. This allows for customized concrete that can meet the performance requirements of almost any construction application.
With ready mix concrete, contractors can focus on proper placement and fabrication rather than spending time and effort on batching and mixing concrete. Ready mix delivery allows for continuous concrete placing for faster construction schedules. The end result is high quality, durable concrete structures that are built right the first time.