Pre-packed Concrete:

In this method, the aggregate should be wetted before placing in position. This method is also called as grouted concrete. It consists of placing the coarse aggregate only in the forms and thoroughly compacting it to form a pre-packed mass. This mass is then grouted with the cement mortar of the required proportions. The mortar that grouts the concrete displaces water and fills the voids. Dense and compact concrete should be prepared by using well graded aggregates. The maximum size of aggregate conveniently used is 80 mm. The coarse aggregate may also be allowed to fall from heights of up to 4 m, without causing any appreciable segregation. Just shutter vibrations could be used for compact the coarse aggregate. A mortar consists of fine sand, pozzlanic filler material and as chemical agent that serves the penetration, early setting of cement, and the dispersion of particles and to increase the fluidity of mortar. An air-entraining agent is also added to the mortar to entrain about 4% of air. A small variation of the procedure of preparation of the cement mortar for grouting leads to a process called colcrete. In this procedure, the mortar grout is prepared in a special high-speed mixer. No admixtures are used within this procedure. The high speed mixing produces a very fluid grout, which is immiscible with water. The maximum size of sand used is 5 mm and the sand should be well graded. Rich cement mortar is used for underwater construction and grouting of pre-stressing cables in post-tensioned bonded construction. The mix ratio ranges from 1: 1.5 to 1: 4 with a water-cement ratio of about 0.45.