Considerable bad experience has been encountered when alkali reactive aggregates have been used. A low alkali cement is normally required to protect against disruptive expansion of concrete which usually occurs due to alkali-aggregate reaction. chemical reaction between cement alkalis and reactive aggregates. Another way to control alkali-aggregate reactions is to use suitable fly ash or natural pozzolan. If a highly reactive aggregate is to be used, then it is necessary to use an aggregate with a low alkali content. cement and pozzolan. Another design recommendation is the type of cement to use. Type 2 cement is normally used by the Bureau of Reclamation in mass concrete dams. Limits on the heat of hydration of this cement are specified where deemed necessary to minimize cracking in the concrete structure. The use of Type 2 cement will generally reduce the heat of hydration of the cement to an acceptable level, particularly when Type 2 cement is used in conjunction with other heat reduction methods. These include the use of a lower cement content. and the use of pozzolan as part of the cementitious material, the use of a pipe cooling system, and the use of a specified maximum temperature for concrete placement, which may be as low as 50 degF . Using some or all of these methods generally reduces or eliminates the need. for strict limitations on the heat of hydration of concrete. However, a 58% limitation on the content of tricalcium aluminate plus tricalcium silicate type 2 is required when the heat of hydration must be kept low. Further limitation of heat of hydration, if tighter heat control is required can be achieved with Type 2 cement by providing a maximum limitation on cement of 70 calories per gram at 7 days or 80 calories per gram at 28...... middle of paper ...... for the transport of concrete whose aggregate size is less than 7.5 cm. Pumping of concrete should be carried out in such a way that the concrete is delivered without air pockets or interruptions. Concrete Placement: Concrete should be placed at a uniform rate throughout the concrete placement. Each layer is well compacted before placing the other layer. Generally, the thickness of the layers should not exceed the following limits. Reinforced concrete: 25 cm. Vibrated concrete: 45 cm. Hand-compacted mass concrete: 30 cm. The concrete is placed vertically on top of each other. layer to avoid damage, segregation and air pockets. Compaction should be carried out as quickly as possible after placement. When concrete is placed in the forms, the temperature may increase, as some previous studies suggest, so measures should be taken to reduce such effects. They are