Once you’ve selected a ready-mix provider, the onus is on you to articulate your concrete’s performance requirements, encompassing both its plastic (fresh) and hardened states. Only then can your supplier collaborate effectively to formulate a mix that yields your desired outcomes.
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For instance, when pouring concrete for an extensive stamped concrete project, you might need to extend the setting time to allow ample duration for the stamping process. Your supplier also requires knowledge of the concrete’s anticipated exposure and service conditions once it’s in place. This information enables them to furnish a material robust enough for the application and to recommend suitable admixtures, such as water reducers or air entrainers, that enhance concrete performance.
Other components you might consider incorporating into your mix formulation include fiber reinforcement (ideal for slabs on grade), integral colors, decorative aggregates, or specialized admixtures like set accelerators or corrosion inhibitors. “Modern concrete can be engineered to satisfy virtually any specification, no matter how unconventional it may seem,” states Sparkman. “The critical factor is to clearly convey your needs to your supplier, empowering them to help design a solution precisely tailored to your unique situation.”
Grasping Mix Design Fundamentals, But Delegating Proportioning to Specialists
“While understanding the core principles of concrete mix design is beneficial, it’s generally best to entrust the precise proportioning to your ready-mix producer,” advises Sparkman. This approach ensures that, should your supplier err in the formula, your foundational knowledge of how mix components interact will enable you to assist in troubleshooting the issue. A reputable supplier will appreciate your input and adjust the mix to meet your specifications. Even minor modifications can, in some instances, significantly impact concrete performance.
An essential reference guide for concrete mix design is Design and Control of Concrete Mixtures, published by the Portland Cement Association (accessible at www.cement.org).
Valuable online resources include:
- The National Ready Mixed Concrete Association (www.nrmca.org/aboutconcrete)
- PCA’s Cement & Concrete Basics website (www.cement.org/basics)
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Accurately Quantifying Your Concrete Needs
After collaborating with your supplier to pinpoint the optimal mix for your application, the subsequent step involves ordering the correct volume. Errors, whether overestimating or underestimating, can be equally challenging to rectify. Procuring excessive concrete not only wastes funds but also necessitates finding an environmentally sound method for disposing of the surplus. Conversely, if your estimate is too conservative and you order insufficient concrete, you’ll be compelled to halt the project until an emergency delivery arrives – assuming you’re fortunate enough to secure one on short notice. The NRMCA suggests adding an additional 4% to 10% to your total estimate to account for potential errors, as well as spillage or over-excavation.
Ready-mixed concrete is typically sold by the cubic yard, with a standard truck mixer accommodating 9 to 11 cubic yards of material. Calculating the required yards for square or rectangular slabs is relatively straightforward (you can use a concrete calculator to assist with the math). Determining the necessary concrete volume for irregularly shaped slabs, however, presents more complexity. When in doubt, request your ready-mix supplier’s assistance with the calculations.
Utilizing a Local Supplier for Hauling Cost Savings
As you might anticipate, transportation costs generally increase proportionally to the distance of the ready-mix plant from your job site. Yet, cost efficiency isn’t the sole compelling reason to opt for a local supplier whenever feasible. A longer travel distance for the truck also increases the likelihood of a late arrival at the project.
If your job site is remote or you choose to use a supplier located further away, avoid scheduling deliveries during rush hour and consider suggesting alternative routes in case of road construction or traffic congestion.
Placing and Confirming Your Concrete Order
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Successfully Placing an Order
- Provide ample notice regarding when you’ll require the concrete, in accordance with your prior discussion with the Ready Mix Company about lead times.
- Specify the exact time you want the concrete delivered.
- Clearly state the mix number and/or type you are ordering.
- Provide the total cubic yards needed.
- Inform them of your desired spacing between trucks. For example, “I need the trucks 30 minutes apart.”
- Crucially, confirm your order the day before you want the concrete! This step is absolutely essential due to the frequent cancellation of orders. You cannot simply place an order a week in advance and then fail to follow up!
A Checklist for Ensuring Correct Concrete Ordering
- Have you utilized a concrete calculator to determine the necessary amount of concrete?
- Do you require any admixtures?
- Is the site accessible to Ready Mix trucks? Confirm this with your ready-mix supplier.
- Once you’ve chosen a Ready Mix supplier, reconfirm with them your project goals and the optimal mix to achieve the desired outcome. The details provided regarding admixtures are intended to equip you with the right questions to ask, not to transform you into an expert who requires no professional assistance.
Delivery of Ready-Mix Concrete
Determining if Concrete Can Be Placed Directly from the Truck or Requires Pumping
Can a truck get close enough to the concrete’s final placement point?
Trucks might not be able to get close enough to the pour site for four primary reasons:
- The ground surrounding the project is excessively wet, risking the truck sinking.
- The incline leading to the concrete pour is too steep for the truck.
- The access point for the truck to reach the needed concrete location is too narrow.
- The pour is extensive, and the truck’s chute cannot reach all areas where concrete must be placed.
Confirm truck access with your Ready Mix Supplier. Each Ready Mix Company maintains its own criteria for what it considers accessible for its vehicles and should be consulted.
Strategic Planning to Ensure Timely Delivery
Inquire with the ready-mix supplier about the necessary lead time for an order and whether the concrete can be delivered at your preferred time of day (such as before dawn or early evening to avoid placement during peak heat). Providing your supplier with ample notice will help ensure priority service and on-time delivery. For added assurance, always confirm your order the day before the pour.
For larger projects demanding multiple truckloads of concrete, also discuss with your supplier the most effective arrival sequence for the trucks. For example, if you anticipate your crew will take an hour to place a full truckload of concrete, then schedule subsequent trucks to arrive an hour apart. Fresh concrete is perishable and will degrade in quality if it remains in the truck for too long. ASTM C 94, “Standard Specification for Ready Mixed Concrete,” stipulates that concrete should be discharged within 90 minutes and before 300 revolutions of the mixer after water has been introduced to the cement.
Verifying You Receive What You Paid For
All components within a mix contribute to the characteristics of the concrete delivered to your job site. Some qualities, such as workability and ease of finishing, are immediately apparent during placement. However, others, like compressive strength and air content, are not directly observable. This is why onsite testing of the delivered concrete is crucial. These tests provide assurance that the material you ordered is indeed what arrives in the truck.
Slump (a measure of consistency), air content, unit weight, and compressive strength tests are the most common field evaluations for assessing the quality of freshly mixed concrete. The following ASTM standards outline procedures and acceptable timeframes for conducting these tests, which should be performed by certified technicians:
- ASTM C 172: Standard Practice for Sampling Freshly Mixed Concrete
- ASTM C 143: Standard Test Method for Slump of Hydraulic Cement Concrete
- ASTM C 138: Standard Test Method for Density (Unit Weight), Yield, and Air Content (Gravimetric) of Concrete
- ASTM C 231: Standard Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method
The unit weight test will also confirm whether you are receiving the paid-for amount of concrete because it determines the yield of a sample of the delivered ready-mixed concrete, according to the PCA. This is a straightforward calculation but requires knowing the unit weight of all batched materials. This total weight information may be included on the delivery ticket or can be obtained from your supplier.
Based on the results of these field tests or external factors, such as extended delivery times or hot weather conditions, it might become necessary to incorporate air-entraining, water-reducing, set-retarding, or other admixtures into the concrete before discharge. Allow your ready-mix supplier to advise you in such circumstances and to assume responsibility for fine-tuning the mix. Your supplier cannot be held accountable for the quality of concrete that you modify yourself, such as by adding additional water.