a) In geology, compaction (= geological compaction) refers to the densification process caused by the gradual increase of overburden (weight) resulting from continuous deposition of sediments or by pressures from the movement of rock within the crust.

b) The geologic process of changing fine-grained sediment to consolidated rock, as in clay to shale.

c) In soils engineering, compaction is the artificial process to improve the engineering properties of a clay or soil by mechanical energy (e.g., vibration, static pressure). The clay or soil is usually partially saturated and thus contains mineral particles, air, and water. Compaction reduces the volume of air in the pores so that the dry density of the soil/clay increases. In practice, to maximize compaction, the water content is adjusted to a suitable value, called the optimal water content, so that the dry density approaches a maximum value.
See water, optimal content for compaction; consolidation, clay or soil

A complex is a dissolved or surface species that forms by association of a cation and either an anion or a neutral molecule, the latter anion or molecule is often referred to as a ligand. The complex may have an overall charge that is positive, negative, or neutral.

a) In soils engineering, compressibility is a mechanical property that defines the resistance of a water saturated clayey soil to compressional deformation under effective stress. The change in effective stress leads to the flow of porewater, resulting in the change in soil thickness or volume. Usually the compressibility of clay is measured by the one-dimensional (i.e., K0 condition) consolidation testing, and is defined by the compression index.

b) In geophysics, compressibility is defined as the reciprocal of the bulk modulus, which relates the change in volume of a material to the hydrostatic state of stress.
See also effective stress, void ratio, compression index

The ratio of change in void ratio to the change in the logarithmic effective stress when a clay is subject to consolidation.
Cf., compressibility

In clay science, the initial stage of consolidation compression of a clay, which is governed by the dissipation of excess pore water pressure (i.e., pore water pressure in excess of the hydrostatic water pressure). During this stage, the excess pore water pressure changes (usually approaching the hydrostatic water pressure), and the clay either produces pore water (in the case of positive excess water pressure) or adsorbs water into the pores (in the case of negative excess water pressure). During this stage, the effective stress changes, and the clay volume changes as well.
Cf., compression, secondary

The stage of consolidation compression occurring under an effective stress imposed after primary compression. Whereas primary compression or consolidation is mainly caused by the escape of excess pore water pressure accompanied by the change in effective stress, secondary compression occurs only under a constant effective stress.
Syn., drained creep;
Cf., compression, primary; creep.

A material property commonly determined for cements (e.g., Portland cements, also geopolymers) to evaluate their resistance to compression by a load. The compressive strength is given as the applied force at the point of failure (in Newton, N), usually at the peak force, divided by the initial area over which the force was applied (in m²). Compressive strength is measured from the amount of stress (force) that is gradually increased until the structure of the material is unable to absorb any more energy, leading to fractures, brittle failure, or excessive plastic deformation.
Cf., Portland cement, geopolymer

A building material comprised of a binder (e.g., cement, Portland cement) and aggregates (e.g., sand, gravel, crushed stone). With the addition of water to the dry binder, a hydraulic reaction causes calcium silicate hydrate (CSH) phases to form. This process is called setting or hardening and leads to the strength of the cement/concrete.
Cf., calcium silicate hydrate (CSH) phases, Portland cement, cement

See glaebule.

Although not a true equilibrium constant, a conditional stability constant describes the equilibria of complex formation at ambient solution conditions. For example, a conditional stability constant may be used when pH is fixed at a specific value; the conditional stability constant would then vary with pH. Thus, the complex will be either strong or weak depending on solution conditions, in this case with pH and possible protonation of the ligand. In other cases, temperature or ionic strength may alter metal to ligand strength, which changes the conditional stability constant. Conditional stability constants are commonly used to describe surface complexation reactions.
Syn., apparent stability constant;
See also ligand