Concrete Construction Practices Concrete Technology Concrete Construction Practices Lecture 13 Eng: Eyad Haddad

Chapter 7: Concrete Construction Practices Batching and mixing. Transportation. Placement of concrete. Finishing concrete. Special aspects of handling concrete. The production of high-quality concrete does not rest solely on proper proportioning. The concrete placed in a structure must be of : (1. uniform quality, 2. free of voids and discontinuities, 3. adequately cured) Lack of sufficient attention to mixing, handling, and placing can result in poor concrete from a well-designed mix.

Batching of aggregates and cements is best done by weight, since Batching and mixing A) Batching: Batching of aggregates and cements is best done by weight, since dispensing of solids on a volume basis can lead to gross errors. Only water and liquid admixtures can be measured accurately by volume. Look at Figure 11.1 of your text book for handling and storing of aggregates, figure 11.2 for methods of batching.

Cement is preferably batched separately, but aggregates may be batched separately or cumulatively. Available materials handling equipment can be divided into three general categories: Manual semi-automatic and fully automatic. Manual batching is generally only acceptable for small jobs (up to 400 m3 or 520 yd3) and low output requirements (15 m3fh or 20 yd3/h); otherwise, semiautomatic should be used in semiautomatic arrangements, the charging and discharging of the batchers are activated manually, but are automatically terminated. In a fully automatic system a single starter switch activates the batching sequence.

The optimum mixing time depends on: The type of mixer. b) Mixing: Thorough mixing is essential for the complete blending of the materials that are required for the production of homogeneous, uniform concrete. The optimum mixing time depends on: The type of mixer. The condition of the mixer. The speed of rotation. The size of the charge. The nature of the components. Lean, dry or harsh mixes require more mixing than those made with rounded gravels.

a horizontal shaft with spiral blades may be rotated in the drum. Type of Mixer: a horizontal shaft with spiral blades may be rotated in the drum. Tilting drums: which are commonly used for small jobs, are also available in large sizes. They have the advantage of a quick, clean discharge even of dry mixes. Horizontal drums: are discharged by inserting a chute to intercept the concrete as it is mixing or by reversing the direction of rotation, which forces the concrete out of the mixer. C) Transportation There are many different ways of handling concrete, it depend mostly on : the amount of concrete involved. the size and type of construction. the topography of the job site. the location of the batch plant, and the relative costs.

Methods of transportation can be assigned to four general categories: wheeled transports. Buckets. conveyors and chutes. pumps. Transport of concrete from the batching plant to the job is generally by ready mixed trucks equipped with a revolving drum for agitation. The use of dumpsters should not involve long trip times to avoid excessive slump loss or segregation. Buckets, overhead cableways, or trucks can be used to transport concrete from an adjacent batch plant.

See table 11.1 in the text book (Methods of transportation concrete) TRANSPORTATION (pumping)

Placement of Concrete

Placement of Concrete

Placement of Concrete

Placement of Concrete

Placement of Concrete

Placement of Concrete

Placement of Concrete

Placement of Concrete