Ready Mix concrete lorry
Determining if the concrete can be placed directly from the truck or will need to be pumped
Can you get a truck up close to where the concrete's final destination is?
Trucks can't get close enough to the pour for four reasons:
- The ground surrounding the project is too wet and the truck will sink.
- The slope leading to the concrete pour is too great for the truck.
- There is too narrow of an opening for where the truck would need to pass to reach where the concrete is needed.
- The pour is big and the trucks chute can not reach everywhere concrete will need to be poured.
Confirm with your Ready Mix Supplier that there is truck access. Each Ready Mix Company has their own criteria on what they feel is accessible for their trucks and should be consulted.
Plan Ahead to Ensure Timely Delivery
Ask the ready mix supplier how many days of lead time are necessary for an order and whether the concrete can be delivered at the time of day you want it (such as before dawn or early evening to avoid placements during the heat of the day). Giving your supplier ample notice will help to ensure priority service and on-time delivery. For additional reassurance, be sure to confirm your order the day before the pour.
For larger projects requiring several truckloads of concrete, also discuss with your supplier the best time sequence for truck arrival. For example, if you estimate it will take your crew an hour to place a full truckload of concrete, then schedule the trucks to arrive an hour apart. Fresh concrete is perishable and will lose quality if it sits in the truck too long. ASTM C 94, "Standard Specification for Ready Mixed Concrete, " says that concrete should be discharged within 90 minutes and before 300 revolutions of the mixer after water has been added to the cement.
Make Sure You Get What You Pay For
All the materials in a mix will contribute to the characteristics of the concrete that arrives at your jobsite. Some qualities, such as workability and ease of finishing, are readily apparent as you place the concrete. But others, such as compressive strength and air content, can't be observed. That's why onsite testing of the delivered concrete is important. These tests will assure you that the material you ordered is the same material that arrives in the truck.
Slump (a measure of consistency), air content, unit weight, and compressive strength tests are the most common field tests for determining the quality of freshly mixed concrete. The following give procedures and acceptable time frames for performing these tests, which should be conducted 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 tell whether you're getting the amount of concrete you paid for because it determines the yield of a sample of the ready mixed concrete as delivered, according to PCA. This is a simple calculation, but requires you to know the unit weight of all materials batched. The total weight information may be shown on the delivery ticket or can be provided by your supplier.
Based on the results of these field tests or external factors, such as long delivery times or hot weather conditions, it may be necessary to add air entraining, water reducing, set retarding, or other admixtures to the concrete prior to discharge. Let your ready mix supplier advise you in such circumstances and take responsibility for fine-tuning of the mix. Your supplier can't be held accountable for the quality of concrete that you alter yourself, such as by adding more water.