clay

• Clay is made of clay minerals, produced from chemical weathering of minerals like feldspar. Water is incorporated into the chemical structure of the clay. 
• Plasticity:

  • When deformed clay keeps its new shape. It can be deformed without breaking. Adding water to dry clay increases plasticity. 
• Cohesion:

  • How well clay is held together due to electrostatic force and by cementation. 
  • High cohesion when wet 
  • Cohesion can be lost when clay is weathered. 
• Porosity:

  • Clay has a high porosity, absorbing water and swelling. 
• Structure:

  • Clay is made of layers of silica and layers of alumina. 
  • Kaolinite has alternating layers held together by strong bonds. Low plasticity and does not shrink or swell 
  • Smectite contains layers separated by water, weak hydrogen bonds so a high porosity, plasticity and shrinkage and swelling. 
• Smectite is used for cat litter because its high porosity, but is unsuited to build upon. 
• Properties involved in building:

  • Swelling 
  • Shrinkage 
  • Low compressive strength 
  • Poor shear strength 
• Shrink swell:

  • Swelling lifts paving slabs or foundations, flood basements 
  • Shrinking when trees take water from clays causing subsidence 
  • Alternating shrinking and swelling can cause fractures - weakening pipes and tunnels 
• Mitigation of shrink swelling:

  • Deep foundations below water table 
  • Effective drainage systems to keep water table low or keep high by irrigation 
  • Remove trees, although re-saturation swells anyway. 
  • Bacteria that reduce iron ions reduces tendency to swell 
• Clay can remove harmful cations from environment to counteract soil pollution.