Light Compaction Equipment About compaction Welcome remarks TBD.

History of compaction Ancient technique: Herds of cattle or sheep were used to compact soil for road construction. Their weight on small hoof used to make an effective compaction. 18th century Horses or oxen drawn rollers 19th century First steam roller in France 1905 First sheep foot roller for dam construction in California Light Construction Utility Equipment

History of compaction 1930’s First use of vibratory compactors in Germany for highway construction. 1940’s Tow behind vibratory roller in the USA. 1950 – 1960’s First self-propelled units. Fast development started by the end of the 60’s because of the popularity of self-propelled units in highway construction. Light Construction Utility Equipment

What is compaction? Rearranging the particles. Removing voids (increasing the density [kg/dm³]). Interlocking the particles. Compacting freshly dropped soil will generally double its density. The action of compacting can be measured by The density increase. The soil hardness increase. The particles arrangement on a sample. Light Construction Utility Equipment

Compaction objectives Reducing soil compressibility and therefore reducing further deformation: Increasing soil strength Improving stability and load bearing capacity Reducing water absorption Increasing impermeability: no erosion due to sweeping water No soil swelling and contraction due to water seepage Reducing frost damage Hardening and flattening the surface Reducing erosion Improving the grip Light Construction Utility Equipment

Importance of ground compaction The building itself can be as strong as possible. If the ground below cannot bear the building weight, serious problems will arise! Light Construction Utility Equipment

Why does efficient compaction make the difference? Poor compaction leaves voids in the ground that will either: Let water come in the ground, create cavities and destroy it when freezing. Be weaknesses in case heavy loads are coming over: collapsing. A quality work requires performing proper compaction at all levels of the layers structure. Light Construction Utility Equipment

Materials: usual road layers Shear resistance Asphalt wearing course Asphalt binder course Asphalt base course Subbase Capping layer Loam Bearing capacity Pavement Different materials require different compaction parameters. For light compaction, asphalt can be seen like a material mix + a binder. Ground Light Construction Utility Equipment

Soil and Asphalt In the prospect of light compaction, asphalt can be seen as a particular case. Asphalt: On low traffic ways: Small stones – High sand content – Liquid bitumen On high traffic ways: Large aggregates – Low sand content – Thick bitumen Asphalt specificities: Must be worked when hot. Water is necessary to prevent bitumen from sticking to the compacting machine Compaction control is performed by core sampling. The information that follows is focused on soil compaction + + Light Construction Utility Equipment

Frequency effect High frequencies are suitable for compacting a thin layer of asphalt* or small particles granular soil. Small particles also require more energy as more particles mean more friction. Lower frequencies will work best to put big aggregates into motion on a thicker layer. Ideal soil frequency: 2450 RPM (32 Hz) Light Construction Utility Equipment

Material parameters Particle size Coarse granular soil Fine sands & silts. Coarse grains can be seen. Feels gritty when rubbed between fingers. When moist, very little or no plasticity. Little or no cohesive strength when dry.  Soil sample will crumble easily. Relatively easy to compact Fine cohesive soil Mixes & Clays Particles stick together Grains cannot be seen by naked eye. Feels smooth and greasy when rubbed between fingers. When moist, Plastic and sticky. Can be rolled. Has high strength when dry. Crumbles with difficulty. Slow saturation in water. Requires high compaction energy Light Construction Utility Equipment

Material parameters Particle shape Rolled aggregates Compaction properties of granular soils will vary as according to their particle shape. Rolled aggregates E.g.: River gravel Particles easily slide on each other. Low shear resistance. Relatively easy to compact Static compaction can be enough. Crushed aggregates E.g.: Crushed granite Lots of grip on the particle contacts: they don’t move easily. High shear resistance. Requires high compaction energy Requires vibration Light Construction Utility Equipment

Material parameters Size mix The size distribution of the particles has a strong effect over the long term stability of the compacted soils. Mixed aggregate sizes allow to achieve better mechanical properties of the compacted layer because of better interlocking more contact points fewer voids It is not allowed to backfill trenches or road support with any kind of soil. Poor mix Good mix Light Construction Utility Equipment

Material parameters Water content There is an optimum water content that will reduce aggregate friction and therefore maximize the compaction ability: ~11% Dry Ideal moisture ~11% High water pressure Hand test: Pick up a handful of soil, squeeze it in your hand and open. If the soil is powdery and will not retain the hand shape, it is too dry: add water. If the soil is moldable and breaks into only a couple of pieces when dropped, it has the right moisture content for compaction. If the soil is plastic in your hand and stays in one piece when dropped, it is too wet for compaction. Light Construction Utility Equipment