Experimental Study On Key Technology Of Segment Concrete Of Metro Shield Without Steam Curing

In this paper,based on the existing production mix ratio of segments,a systematic optimization test was carried out based on the Chengdu Metro Line 19 project by using various chemical strengthening methods.In this study,the key technologies of segment concrete mainly include three aspects:(1)the optimization of raw materials;(2)reasonable matching of admixtures(variety and dosage matching);(3)Optimizing the mixture ratio of steam-free preserved segment concrete.The research contents and main experimental conclusions are as follows:(1)By analyzing and comparing the action mechanism of each raw material in cement-based materials,the varieties and technical indexes of each basic raw material(cement,mineral admixture,sand,stone,water)are determined.Two kinds of early strength polycarboxylic acid high performance water reducer(PEC-AY,PEC-AB)and nanometer hydration calcium silicate crystal core agent(n-C-S-H)、 lithium sulfate(LS)、 sodium thiocyanate(NS)、triethanolamine(TEA)、aluminum nitrate(AN),were screened out as the chemical admixtures used in this paper.Compatibility tests were carried out for PEC-AY and PEC-AB water reducers and concrete mixtures.The results show that the compatibility of PEC-AY and PEC-AB water reducers with segment concrete is similar.(2)Through the single mixing test of early strength agent,the influence of different types of ―water reducer-single early strength agent admixture binary system‖ on the properties of cement mortar(fluidity、mechanical properties)under two curing temperatures was obtained,and each admixture and the mechanism of action between admixtures were analyzed and summarized.Studies have shown that Under curing temperature of 10℃ and 20℃,it is advisable to select the four components of PEC-Ab(1.0%)、n-C-S-H(6.0%)、NS(0.2%)、AN(0.3%)、PEC-AY(1.0%)、LS(0.08%)、n-C-S-H(5.0%)and NS(0.3%)for early curing Compound mixing test of strong agent.(3)Test of early strength agent mixed with the orthogonal experiment method,the early compressive strength of mortar as the main evaluation criteria,the ―water reducing agent,compound early strength agent additive dual system‖ of each components of early strength agent in the mixed proportion is optimized,respectively,has been adapted to the optimum combination of two kinds of curing temperature admixture mixed {10℃: PEC-AB(1.0%)、n-C-S-H(6.0%)、NS(0.2%)、AN(0.35%);20℃: PEC-AY(1.0%)、n-C-S-H(5.5%)、LS(0.06%),NS(0.30%)}.(4)Under the curing condition of 20℃,the equivalent substitution method was used to appropriately increase the proportion of fly ash content.Through studying the influence law of different fly ash content on the related durability of segment concrete,the optimal mix ratio of non-steam cured segment concrete was obtained.The results show that when the optimal mix ratio is used,the slump、10 h demoulding strength、28 d compressive strength、impermeability grade and electric flux value of segment concrete are 51 mm、21.4 MPa、63.7MPa、P12、962C,respectively and the related performance indexes all meet the corresponding design standards of segment concrete.