Roller-compacted concrete (RCC) is rapidly becoming a popular material for dam construction, heavy-duty paving, and mass fill applications. Its economy comes primarily from being able to transport and place it in large quantities with minimal time and labor by using earthmoving or conveyor equipment. The no-slump mix is spread with bulldozers and compacted into a solid mass with large vibratory rollers. The effect of compaction methods, water content, and other variables on density, pore pressure, practical construction problems, and permeability are discussed.

A brief discussion of consolidation of concrete aimed toward the users of concrete is presented to encourage the use of vibration in improving the quality of the finished product. Significant points leading to successful consolidation of quality concrete include the interrelationship of proportioning, mixing, placement, and application of the vibrator to break down mechanical stacking, eliminate unintentional air voids, reduce residual water content, and achieve densification and enhancement of the micro-structure of the concrete.

Fiber reinforced concrete is reinforced by a small amount of short fibers randomly dispersed into cement concrete, and this composite material is superior to normal plain concrete, with respect to flexural strength, impact resistance, and ductility. But the consistency of fiber reinforced concrete is extremely decreased by adding fiber so that, in some cases, it becomes difficult to place and mold by the ordinary method. These phenomena are observed irrespective of kinds of fibers used. The effects of compaction methods on the strength of fiber reinforced concrete with poor consistency and containing a fairly large amount of fibers were investigated. Conventional steel fiber and alkali-resistant glass fiber were used. Test specimens (10 x 10 x 60 cm) of plain and fiber reinforced concretes were compacted by external vibration with temporary or continuous compressive loading, and were tested in flexure. The mechanism of compaction effects was discussed. Test results indicate that the compaction with compressive loading increases the flexural strength of both types of fiber reinforced concretes and also does extensibility of glass fiber reinforced concrete, although the improvement is made within a certain limit of compaction loading.

Industrial and mining wastes, often extremely fine-grained, are being used as fillers and binders in structural concrete and consolidation by compaction, as opposed to high-frequency vibration. Impact and static compaction can be industrially used for the automatic production of such building elements as bricks and blocks, whereas roller-compacted concrete is more suitable for field applications. Compressive strength characteristics under air-dry, sealed, and soaked conditions of portland cement mixtures containing a complete range of combinations of dihydrate phosphogypsum (by-product of the phosphate fertilizer industry) and fine aggregate (crushed lime rock) are presented. Cylindrical specimens were prepared according to the Modified Proctor procedure (impact compaction). Based on these results, strength comparisons are made for selected constituent proportions in the cases of: 1) consolidation by static compaction; 2) consolidation by high-frequency vibration; 3) site consolidation by vibratory roller compactor; and 4) substitution of the dihydrate phosphogypsum with the hemihydrate form (other available by-product). It is shown that consolidation by compaction is advantageous because of the contribution of phosphogypsum to strength development. Laboratory-compacted samples of the by-product alone indicate that strengths of over 1000 psi (6.89 MPa) can be achieved. In addition, low-cement (7.5 percent) mixtures using hemihydrate gypsum waste exceed the 4000 psi (27.56 MPa) mark.

The main purpose of concrete consolidation is to reduce the amount of entrapped air and densify the concrete. This can be accomplished by subjecting the concrete to vibration. A recently completed laboratory and field investigation to determine the movements occurring in the fresh concrete during the consolidation process is reviewed and data is presented regarding the relationship between energy level in the concrete and the degree of consolidation achieved. Accelerometers were used to measure the movement of the fresh concrete as a function of time. For the particular concrete mixes tested, a minimum energy of approximately 300 ft-lb (407 N-m) has been found to result in a degree of consolidation of 97 percent or more.