Introduction - Introduction to Polymeric Composites with Rice Hulls - page 6

1.3.7 Concrete
Concrete is probably the most common artificial composite material and typically
consists of loose stones (aggregate) mixed with a matrix of cement. Concrete is a
very robust material (much more robust than cement) and will not shatter even under
quite a large compressive force. However, concrete cannot survive tensile loading
(will breakdown under stretching). Therefore, to give concrete the ability to resist
stretching, steel bars (which can resist high stretching forces) are often added to
concrete to form 'reinforced concrete'.
1.3.8 Shape-polymer Composites
Shape-polymer composites are high-performance composites formulated using fibre or
fabric reinforcement and shape-memory polymer resin as the matrix. Because a shape-
memory polymer is used as the matrix, these composites can be manipulated easily
into various configurations if they are heated above their activation temperatures, and
exhibit high strength and stiffness at lower temperatures. They can also be re-heated
and re-heated repeatedly without losing their material properties. These composites are
ideal for application as lightweight; rigid; deployable structures; rapid manufacturing
processes; and dynamic reinforcement.
1.3.9 Metal Fibre Composites
Composites can also use metal fibers, reinforcing other metals. Ceramic matrix
composites are built primarily for fracture toughness, not for strength. Organic
matrix-ceramic aggregate composites include asphalt concrete, mastic asphalt, mastic
roller hybrids, dental composites and syntactic foams. Certain types of composites
are used in special military applications.
1.3.10 Thermoplastic Composites with Metal Powders
Thermoplastic composites can also be formulated with specific metal powders,
resulting in materials with high densities (e.g., composites with the same density as
lead). The most common name for this type of material is 'high-gravity compound'
(though 'lead-replacement compound' is also used). These materials can be used in
place of traditional materials such as aluminium, stainless steel, brass, bronze, copper,
lead and even tungsten in weighting and balancing, vibration damping and radiation-
shielding applications. High-density composites are an economically viable option if