Tests, compaction

Sometimes the density of powder compacted over and above what can be achieved by tapping may be needed. There are no standard procedures for this other than the rather specialized soil compaction tests and density determinations (2.5 and 4.5 kg rammer methods) quoted in a British Standard for soils16. 

The compaction test described in the following section may also yield approximate values of compacted bulk density as it is equipped for measuring the sample height. 

The compaction characteristics of powders and granular materials also provide interesting insight into bulk behaviour of solids. Bulk materials in general are not linearly elastic and cannot, therefore, be characterized simply by Young s modulus and Poisson s ratio as solid materials can. If a powder is compressed, the deformation is primarily plastic and the elastic component is small in comparison. 

The simplest way to test the compressibility of a bed of solids (whether it is dry or wet) is by the one-dimensional compression test. A cylindrical plug of the powder is compressed axially in a cylinder which confines the sample and prevents lateral strains - 

During the test, the axial stress is increased in small increments and the axial deformation, which may be time-dependent, is recorded. The results may be plotted as an axial stress-strain relationship which is non-linear (the rate of strain increase declines with increasing stress), or as bulk density (or voidage, or void ratio) as a function of the compaction stress. 

---

Compaction tests, such as the standard Proctor, determine the maximum specific vseighi (II miiiiniiim void latio dial tan he ohiained foi a soil, painculailv a soil... 

COMPACTION TEST CURVE CUW AND SHALE CURVE KH POINT VALUE Clay and silty clay Pelagic clay Terrigenous silty clay Clay with volcanic shard relicts COMPOSITE CURVE... 

Figure 4.8 Schematic of a lateral stress compaction testing cell [2]...

Breakdown by confined compression can be tested in a compression cell similar to that in compaction tests, except that the normal forces used are greater here. A British Standard method59 packs a sample of specified quantity and size grade into a steel cylinder, 150 mm nominal diameter a plunger is inserted into the open end of the cylinder and the whole compressed in a compression testing machine. The load is slowly increased up to 400 kN and the product is then sized. A similar test has been used in assessing friability of pellets and coal. 

In understanding, the greatest question to be yet resolved is what is the best, yet simple, test to be used to monitor the cohesivity or flowability of powders There are, of course, the direct (or almost direct) ways of measuring it (the cohesion tester or the tensile testers) but neither the tests nor the equipment are really simple. Angles of repose or spatula are simple but, unfortunately, become quite meaningless as the powder gets more cohesive. I personally think that the way powders compact can be directly related to cohesivity the recent evidence of the usefulness of the Hausner ratio in many different applications points in this direction. The compaction test should also be better defined and more widely used. 

Finally, this finished compost material must be backfilled into the original excavation. Provided that the material is carefully replaced and compacted in thin lifts, a substantial reduction in the volume of the compost may be attainable. The extent of the compaction and volume reduction can be estimated by standard laboratory compaction tests conducted on representative samples of compost. Knowing this final compacted compost volume in terms of the original in-place soil volume is necessary to determine whether substantial excess compost will be created by the composting process, and whether backfilling the excavation and mounding this excess compost will be feasible for the site in question. 

In powder technology, great attention has been paid to the general behavior of powders under compression stress. Compression and compaction tests have been widely used in pharmaceutics, ceramics metallurgy, and civil engineering, as well as in the food powder field by researchers to study the mechanisms of particle interactions and to evaluate particles at a bulk level. 

The purpose of food powder compaction tests is primarily to simulate density changes during handling and transportation. Subjecting a powder to vibration or impact usually results in its compaction. During vibration of... 

Figure 4. Compaction test results. Paraho retorted shale, semiworks plant— direct heat 1.5-in. maximum size fraction.

The backfill was placed in a maximum of one-foot lifts and compacted to approximately 95% Standard Proctor Density using the track loader and rubber tired backhoe. This procedure effectively produced a 10-foot thick seal exhibiting 1.0 x 10" cm/sec permeability and precludes the possibility of appreciable settlement. Field compaction tests were performed during the backfilling to assure that proper compaction was achieved. 

Duriez Test (7). Appreciation of the mechanical property and resistance to mixture-breakdown under the effect of water, on cylindrical, compacted test samples of the mixture. The test is carried out at 18°C. 

The required compaction characteristics (maximum dry density and optimum moisture contents) are usually a function of the granular content and the moisture content. Disturbed samples obtained from source may be re-constituted, based on results of compaction tests, and be tested for shear strength. 

Proctor compaction test (modified) by American standards... 

The proctor compaction test defines the relationship between soil density and moisture content with the aim of determining the maximum density at a certain moisture content, known as the optimum moisture content. 

The modified proctor compaction test procedure in accordance with CEN EN 13286-2 (2012) slightly differs from the one described in ASTM D 1557 (2012) or AASHTO T 180 (2010). 

It may be changed after local experience and compaction tests in situ. 

---