| In the application of prestressed concrete, there are concerns on severe prestress loss caused mainly by elastic shortening, shrinkage and creep of concrete, which will result in the extreme reduction of the design capacity of prestressed concrete structure, or even the premature structure failure. Hence, the values of elastic modulus, ultimate shrinkage strain, and ultimate creep coefficient of concrete have to be estimated reasonably and accurately at the production stage in order to avoid loss of structural capacity, or even unexpected structural failure caused by prestress loss.At present, the modulus of elasticity, shrinkage and creep properties of concrete that are used in structural design are either based on the arbitrary available literature or based on the limited research of the locally available materials. Thus, there is a great need for a comprehensive testing and evaluation of locally available concrete mixes to determine their mechanical and physical properties so that correct values for these properties can be used in structural design. Also, there is a great need to design a simple, effective, practical and reliable creep apparatus to carry this massive investigation on creep behavior of concrete out.In this study, a creep test apparatus was designed, and twenty four creep apparatus were constructed for use in performing creep tests. The creep apparatus was evaluated to be working satisfactorily. An effective creep testing procedure was developed and documented. Also, a gauge point position guide was designed for installing gauge point on the cylindrical mold and it was proved to be an effective tool in preparation of specimens for creep tests. In addition, an alignment frame was designed and it was proved to be a very useful tool to ensure that the specimens can be set up in the creep apparatus vertically.In this study, 14 concrete mixtures were evaluated, and replicate batches for ten of these mixes were also produced and evaluated. Three types of coarse aggregate, fly ash and ground blast-furnace slag were incorporated in the mix designs in this study. Concrete specimens were fabricated and tested for their compressive strength, splitting tensile strength, elastic modulus, shrinkage and creep. This study has generated valuable data and determined general trends on the compressive strength, splitting tensile strength, elastic modulus, drying shrinkage strains and creep coefficient of structural concretes investigated in this study. Most importantly, the inter-relationships among compressive strength, elastic modulus and shrinkage and creep properties of concrete were found through regression analysis. These relationships make the predictions of shrinkage and creep possible with the information from compressive strength and elastic modulus. |
