Long Term Deformation Of Limestone Sand Concrete

With the development of the world economy, the demand of civil engineering construction materials, including concrete aggregate, correspondingly increased dramatically. As a commonly used fine aggregate, natural sand is a short-term non-renewable resource and reserves are limited. In many regions of China, the natural sand resource has been a serious shortage. In recent years many countries including China limit the exploitation of natural sand for the protection of the environment. As the most promising alternative to one of the natural sand, manufactured sand (MS) is applied more and more widely in many fields, with the in-depth study on the mechanisms of its physical and mechanical properties. There are many differences between MS and natural sand in appearance, chemical composition, particle shape, particle size distribution and content of ultrafine particles (<75μm) and other characteristics. These differences will inevitably lead to discrepancies on physical and mechanical properties of concrete. So far, the studies about the conventional physical and mechanical properties of MS concrete, has already been conducted extensively, but relevant researches on its mechanisms of shrinkage and creep properties has rarely been reported. Therefore, a relatively comprehensive study was conducted on shrinkage and creep properties of the limestone sand concrete materials and components through test research and theoretical analysis, based on the project "limestone aggregate concrete and Beipanjiang Bridge long-term performance studies", which is the part four of the Ministry of Communications and Guizhou Province Transportation Department projects’Beipanjiang Bridge key technologies’. The main research contents and results are as follows:(1) Physical and mechanical properties of the limestone sand made in the west of Guizhou Province, where Beipanjiang Bridge is in, were investigated and tested systematically. The results show that the limestone rock in this region is dense limestone or micritic limestone, as its average saturated uniaxial compressive strength reaches114.5 MPa. The MS made of this limestone rock has no reactivity with alkali silicate and alkali carbonate. The production process has a great influence on the quality of limestone sand. The limestone sand made in this region generally has a high content of ultrafine particles and coarse particles, and is not continuous in gradation. Therefore in practical engineering applications, the characteristics of limestone sand should be fully considered in the process of concrete mix design, preparation and construction.(2) Limestone sand concrete prism standard specimens with strength gradation C50were designed and manufactured according to China specifications. The shrinkage and creep tests of the limestone sand concrete specimens and river sand concrete specimens with the same proportions, were carried out under standard ambient conditions. The comparison of test results showed that the creep and shrinkage development law of both kinds of concrete are similar, meanwhile the shrinkage strains and creep coefficients of limestone sand concrete are higher than that of river sand concrete. The calculation results show that creep and shrinkage values of the limestone sand concrete specimens are overestimated by the five commonly used shrinkage and creep prediction models (i.e.: CEB-FIP90model, CEB MC90-99model, ACI209model, B3model and GL2000model). Using experimental results, shrinkage and creep prediction formulas of limestone sand concrete were modified based on ACI209model.(3) Four creep simple supported beams and two shrinkage beams with limestone sand concrete with strength gradation C30were made. The long-term loading experiments of this beams were conducted in natural environmental conditions, and long-term deformations of the beams were studied theoretically. The experimental results show that creep deflections of beams increase with the ambient temperature, and decrease with the environment humidity, but the impact of environment humidity on the creep has a certain lag. According to statics mechanical theory, the formulas of simply supported beams was deduced from the prediction model. Based on this, the mid-span deflections of test beams were calculated using the concrete creep coefficient predicted by the CEB-FIP90, ACI209 and B3models respectively. The calculated results were compared with measured values, and the comparison shows that calculated accuracy of ACI209model is the best in the three models. Thus, based on the measured mid-span creep deflection, creep coefficient formula of the tested limestone sand concrete under natural environmental conditions was proposed by inverse derivation.(4) Using of the creep and shrinkage prediction models obtained by experiment in this paper and China Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridge and Culverts (JTG D62-2004), the long-term deformations of the Beipanjiang Bridge were analysis by the finite element software MIDAS/Civil2012. The results show that the development of bridge vertical displacement increment caused by concrete creep and shrinkage is fast in the early age and slow in the late age. And at the stage of the bridge being completed for30years, the deflection increments are still relatively small and meet the Code requirement. This indicates that limestone sand concrete has no adverse effects on the long-term deformation of Beipanjiang Bridge, and can be applied in similar projects. Through the comparison of results calculated by the three models, it can be seen that displacement increments calculated using the Code(JTG D62-2004) model are maximum, which indicates that predicting the long-term deformation properties of limestone sand concrete bridges in accordance with the Code(JTG D62-2004) model is safe and feasible.