ABSTRACT
Precast concrete is of the highest possible quality, both in terms of strength and durability. The essence where concrete is accurately delivered to every part of the mould, ensuring zero segregation, honey-combing and minimal vibration. Even the introduction of small quantities of uncontaminated recycled concrete, usually from the factory's own waste production, superplasticizers and pozzolanic materials has not reduced this standard. Concrete strengths are made to match the optimum performance of each element, such that flexural members are produced in grade C40 concrete, whilst compression members are in C50. Various methods to accelerate the early strength of concrete include rapid hardening Portland cement, chemical accelerators and by external heating, such as steam curing and electrical heating. Care must be taken in thin walled section. Where site concrete is added to precast elements to form composite sections the relative strengths and stiffness of the two materials must be considered, namely, the modular ratio method.
