CIP 31 - Ordering Ready Mixed Concrete

1 CIP 31 - Ordering Ready Mixed ConcreteWHATis Ready Mixed Concrete ?WHYUse Ready Mixed Concrete ?HOWto Order Ready Mixed Concrete ? Concrete is a mixture of cementitious materials, water, aggregate,usually sand and gravel or crushed stone. There is a commonmisunderstanding that cement and Concrete are one and the is a powdered ingredient that provides the glue that bindsthe aggregates together in a mass called Mixed Concrete is that which is delivered to the customer ina freshly Mixed and unhardened state. Due to the ability to cus-tomize its properties for different applications and its strengthand durability to withstand a wide variety of environmental con-ditions, Ready Mixed Concrete is one of the most versatile andpopular building mixtures are proportioned to obtain the required prop-erties for the application.

2 It should have the correct consistency,or slump, to facilitate handling and placing and adequate strengthand durability to withstand applied loads in the anticipated envi-ronment and service conditions. The design quantities of concreteingredients are accurately weighed and Mixed , either in a mixer atthe Concrete plant or in a Concrete truck mixer. It is delivered in atruck mixer or agitation unit, which keeps the Concrete uniformlymixed until it is discharged at the placement location. Concreteremains plastic for several hours depending on the type of mix-ture and conditions during placement so that there is sufficienttime for it to be placed and finished. Concrete normally sets orhardens within two to twelve hours after mixing and continues togain strength for months or even years if it is properly curedduring the first few , in its freshly Mixed state, is a plastic workable mixturethat can be cast into virtually any desired shape.

3 The propertiesof Concrete can be customized for almost any application to servein a wide variety of extreme environments. Concrete is a veryeconomical building material that can serve its function for severalyears with minimum maintenance, provided the proper mixturerelative to the application and established construction practicesare used. A wide variety of options with color, texture and archi-tectural detail are available to enhance the aesthetic quality of theconcrete key to placing an order for Ready Mixed Concrete is to provideall the basic detailed information and to keep the requirements assimple as possible and relevant to the application. The readymixed Concrete producer has several mixture formulations for awide variety of applications and can help with deciding the re-quired mixture of the basic requirements to keep in mind when placing aconcrete order are as follows:Size of coarse aggregate - the important information is the nomi-nal maximum size required, which should be smaller than thenarrowest dimension through which Concrete should flow, suchas the thickness of the section and spacing of the reinforcing steel,if any.

4 For most applications, nominal maximum size of coarseaggregate is 3/4 or 1 inch ( or mm).Slump - Concrete slump, a measure of its consistency, should beindicated. A stiffer mixture will have a low slump value. Typicalslump range for most applications is 3 to 5 inches (75 to 100mm). For slip-form construction a maximum slump of 2 inches(50 mm) is required, while higher slump to a maximum of 7 inches(175 mm) is typical for basement walls. The tolerance on theslump as delivered is 1 to 11/2 inch (25 to 38 mm). Addition ofwater at the jobsite to increase slump is permitted, provided it isnot excessive enough to cause segregation and reduce strength air - Air entrained Concrete should be used if concretewill be exposed to freezing temperatures in service, or even duringconstruction.

5 In many locations air-entrained Concrete is the de-fault option. When non air-entrained Concrete is required thisshould be clearly stated at the time of Ordering . Target air contentdepends on the size of the coarse aggregate and the typical rangeis 4 to 6% of the Concrete volume. The tolerance on air content asdelivered is The Concrete supplier is permitted to make anadjustment for air content at the jobsite if, when tested it is lowerthan the required level required - The purchaser specifies the concretequality, in terms of its properties or preferred method for Ordering Concrete is by specifying per-formance requirements, which is generally the Concrete performance characteristics, such as permeability, shrink-age or various durability requirements, may be specified whenrequired.

6 The producer should be made aware of anticipated ex-posure and service conditions of the structure. The Concrete pro-ducer is best equipped to proportion, mix and furnish concretefor the desired performance. The strength level is generally dic-tated by the design of the structure to withstand anticipated loadsduring construction and in service. A minimum strength of 35002000 WHATare the Responsibilities?to 4000 psi (25 to 28 MPa) may ensure durable Concrete , such asresistance to wear, abrasion, and freezing and thawing option is to order Concrete by specifying prescriptiverequirements. The purchaser specifies limits on the quantities andtypes of ingredients in the mixture. In this case the purchasershould generally accept responsibility for Concrete strength andperformance.

7 The prescriptive limits may indicate minimum ce-ment content, maximum water-cement ratio, and limits on thequantities of pozzolans, slag or admixtures. Frequently, this ap-proach is used when a particular prescriptive mixture formulationhas worked well in the past. This approach does not allow theproducer much flexibility on the economy of the mixture or toaccommodate changes in material sources or characteristics thatmay affect Concrete s performance and prescriptive requirements is discour-aged as the performance requirements may conflict with the pre-scriptive of Concrete - Concrete is sold by volume, in cubic yards(cubic meters), in a freshly Mixed unhardened state as dischargedfrom the truck mixer. The delivered volume, or yield, is calculatedfrom the measured Concrete density or unit weight.

8 One cubicyard of Concrete weighs about 4000 lb. (2 short tons). One cubicmeter (approximately cubic yards) weighs about 2400 kg. Thetypical capacity of a truck mixer is 8 to 12 cubic yards (5 to 9cubic meters).Order about 4% to 10% more Concrete than is estimated from avolumetric calculation of the plan dimensions. This will accountfor waste or spillage, over-excavation, spreading of forms, loss ofentrained air during placement, settlement of a wet mixture, truckmixer holdback and change in volume - hardened Concrete volumeis 1% to 2% less than that of the fresh Concrete . Reevaluate theneeds during placement and communicate any changes to the con-crete of returned Concrete has environmental and economicalimplications to the Ready Mixed Concrete producer.

9 Make a goodestimate of Concrete required for the job before placing an Ordering small clean-up loads, less than 4 cubic yards ( meters).Additional Items - A variety of value-added options are availablefrom the Ready Mixed Concrete producer. Chemical admixtures canaccelerate or retard the setting characteristics of Concrete to aid inplacing and finishing during hot or cold weather. Water reducingadmixtures are used to increase Concrete slump without addingwater to the Concrete . Synthetic fibers can reduce the potential forplastic shrinkage cracking. Using color or special aggregates canenhance aesthetic characteristics. The Concrete contractor can alsobe a resource for innovative finishes and textures to delivery - Schedule the delivery of Concrete to accom-modate the construction schedule.

10 Inform the producer of thecorrect address, location and nature of the pour, and an estimateddelivery time. Call the Ready Mixed Concrete producer well inadvance of the required delivery date. Concrete is a perishableproduct and the construction crew should be Ready for concreteplacement when the truck arrives. Notify the producer of anyschedule changes or work stoppage that the truck mixer has proper access to the placementlocation. The Concrete truck weighs in excess of 60,000 lbs. (27,000kg) and may not be able to maneuver on loose dirt and residentialcurbs and responsibilities of the various parties involved in the con-struction process should be addressed at a pre-construction meet-ing, especially on a large job.