Question
In General Specification for Civil Engineering Works, designing of roadbase material is based on recipe approach. Give reason.
Answer
Designing of roadbase material is based on recipe move towards, as Hong Kong government follows the traditional British practice by adopting recipe plan in which aggregate grading envelope, quantity and grade of bitumen are specified in bituminous mix. This recipe of bituminous mix is derived based on precedent experience and first-rate workmanship during construction. In information, several countries now adopt special design mix of roadbase that proves to produce satisfactory bituminous mixes to suit different site and design situation.
In real, recipe specification of bituminous materials does suffer from quite a lot of drawbacks. Firstly, conditions of traffic and climate of newly constructed bituminous road possibly will differ from conditions on which recipe design is based. In case regulation has to be made to recipe design, it is extremely difficult to determine and assess modifications required. Secondly, it creates intricacy to site engineers to assess effects of minor non-compliance if recipe specification is adopted. At last, recipe mix might not be most economical design that is dependent on site conditions.