Research On Preparation Process And Crack Resistance Of High Performance Concrete Prefabricated Cable Trench

During the past decades,the construction of urban environment has become a popular topic.Traditional cable trench is a commonly used infrastructure structure in power station to protect the cable from damaging,which is generally constructed on site by brickwork and cast-in-place concrete with the adavantages of ease construction and low cost,including brickwork and cast-in-place concrete.Due to the disadvantages of traditional cable trench,such as long construction period,low corrosion resistance and variation in quality,the construction of cable trench has been gradually transformed from the on-site construction mode into fabricated construction mode.Compared with the on-site construction mode,the fabricated construction mode has the following benefits: shorter construction period,higer quality,better safety control on site.However,current prefabricated cable trench is generally made by normal concrete,which has some drawbacks: 1)relatively low strength and low durability,making the fabricated structure too heavy to transfer and install.2)low workability and low early strength making difficult in casting and demoulding.Therefore,it is essential to develop highperformance concrete(HPC)prefabricated cable trench.However,the research about preparation of high-performance prefabricated cable trench is still lacking.In this thesis,the preparation process and crack resistance of HPC prefabricated cable trench were studied.The main work in the thesis was as follows:(1)A concrete experimental testing program was launched,wherein concrete mixes with orthogonal combinations were made for testing of their fresh and mechanical properties.The effects of total cementitious materials content,granulated blast furnace slag(GBFS)content,ultra-fine fly ash(UFFA)content,silica fume(SF)content were deeply evaluated.The test results show that: 1)SF has the highest impact on workability,UFFA comes second;2)The UFFA has the highest effect on flowability,SF comes second.3)SF has the highest effect on cohesiveness,and GBFS takes the second place.4)GBFS has the most effect on gap passing ability,UFFA takes the second place.5)regarding to strength,UFFA and GBFS play the most important roles;6)after comprehensive consideration,an optimum mix proportion of concrete mix was proposed..(2)Crack resistance test was launched,in which HPC prefabricated cable trenchs with 150 mm and 120 mm thick were made.The results indicates that: 1)the failure process of HPC prefabricated cable trench can be simplified into three stages: elastic stage,cracking stage and failure stage;2)for the 150 mm thickness HPC prefabricated cable trench,the cracking load was 195 kN,the failure load was 380 kN.whereas for the 120 mm thickness HPC prefabricated cable trench,the cracking load was 165 kN and the failure load was 361 kN.These two HPC prefabricated cable trench all meet the requirements in electric power industry specification.(3)Numerical modeling was carried out,in which ABAQUS software was applied to establish modles and the crack resistance of prefabricated cable trench with different thickness(150mm,120 mm,100mm,80mm)was analyzed.The results showed that the thicknesses used in this study have marginal influence on the crack resistance of the cable trench.Under working load,the flexural properties of prefabricated cable trench increased with the increase of side wall thickness,while the stresses of concrete and steel rebar were low enough to meet the use requirement.The crack resistance test proposed by electric power industry specification ignores the effect of working load,but numerical modeling can simulate the working load.By using ABAQUS to carry out finite-element analysis,it is found that under the working load,prefabricated cable trench can suffer higher failure load,showing that the requirements stipulated in electric power industry specification is safe and applicable.Most importantly,compared to 250 mm normal concrete prefabricated cable trench,the weight of HPC prefabricated cable trench with different thickness of 150 mm,120mm,100 mm and 80 mm was reduced by 42%,54%,62% and 70%.