低水胶比水泥浆体的力学性能与水泥石微结构
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摘要
随着工程对混凝土强度和耐久性要求的提高,混凝土材料的水胶比不断降低。低水胶比条件下,水泥基材料的力学性能、胶凝材料水化程度及孔结构特征变化规律可能出现新的特点。设计水胶比为0.13～0.21的低水胶比水泥浆体,采用标准养护和高温蒸养两种养护制度,研究了硬化浆体力学性能、水化程度和水化产物微结构变化规律。结果表明:低水胶比条件下,水泥硬化浆体的抗折强度随水胶比降低持续提升,抗压强度先提升后下降;存在极限水胶比使胶凝材料体系强度达到最高,极限水胶比取决于硬化浆体的孔隙变化规律,也受到养护温度的影响;水胶比高于0.15时,水泥水化程度与水胶比呈现严格线性;降低水胶比可有效细化毛细孔,降低硬化浆体的孔隙率;但极低的水胶比和高温蒸养会使大孔出现粗化。低水胶比条件下,硬化浆体的孔结构决定其力学性能,水泥的水化程度只起到辅助作用。
Cement ratio of concrete material decreases with the increase of the strength and durability requirements of engineering for concrete. However, some characteristics like the strength, hydration degree of cementitious materials and pore structure can appear for low water-binder ratio materials. In this work, a water-to-binder cement slurries with water-binder ratio of 0.13–0.21 were designed. The standard curing and high-temperature steam curing were selected. The mechanical properties, hydration degree and microstructure change of hydration products of hardened slurry were investigated. The results show that the flexural strength of the hardened cement paste increases, while the compressive strength first increases and then decreases with the decrease of the water-binder ratio. The cement paste has an optimum water-binder ratio, maximizing the strength of the cementitious material system. The optimum water-binder ratio depends on the variation of the pores of the hardened paste and is also affected by the curing temperature. The hydration degree of the cementitious material is linearly related to the water-binder ratio when the water-binder ratio is greater than 0.15. Reducing the water-binder ratio can effectively refine the capillary pore and reduce the porosity, while the extremely low water-binder ratio and high temperature steaming will cause macropores to coarsen. It is indicated that the refinement degree of the pore structure affects the mechanical properties of the hardened paste to some extent,while the hydration degree of the cementitious material only has a minor effect on the the mechanical properties of the hardened paste at a low water-binder ratio.
Cement ratio of concrete material decreases with the increase of the strength and durability requirements of engineering for concrete. However, some characteristics like the strength, hydration degree of cementitious materials and pore structure can appear for low water-binder ratio materials. In this work, a water-to-binder cement slurries with water-binder ratio of 0.13–0.21 were designed. The standard curing and high-temperature steam curing were selected. The mechanical properties, hydration degree and microstructure change of hydration products of hardened slurry were investigated. The results show that the flexural strength of the hardened cement paste increases, while the compressive strength first increases and then decreases with the decrease of the water-binder ratio. The cement paste has an optimum water-binder ratio, maximizing the strength of the cementitious material system. The optimum water-binder ratio depends on the variation of the pores of the hardened paste and is also affected by the curing temperature. The hydration degree of the cementitious material is linearly related to the water-binder ratio when the water-binder ratio is greater than 0.15. Reducing the water-binder ratio can effectively refine the capillary pore and reduce the porosity, while the extremely low water-binder ratio and high temperature steaming will cause macropores to coarsen. It is indicated that the refinement degree of the pore structure affects the mechanical properties of the hardened paste to some extent,while the hydration degree of the cementitious material only has a minor effect on the the mechanical properties of the hardened paste at a low water-binder ratio.
引文
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[11]韩松,刘丹,张戈,等.超低水胶比复合胶凝材料孔结构随养护制度和龄期的变化机理.硅酸盐学报,2017,45(11):1594-1604.HAN Song,LIU Dan,ZHANG Ge,et al.J Chin Ceram Soc,2017,45(11):1594-1604.
[12]王月.氯盐冻融循环与侵蚀作用下活性粉末混凝土的耐久性研究[D].北京:北京交通大学,2016.WANG Yue.Study on Durability of Reactive Powder Concrete under Chloride Salt Freeze-Thaw Cycle and Erosion(in Chinese,dissertation).Beijing:Beijing Jiaotong University.2016.
[13]KELHAM S.A.A water absorption test for concrete[J].Mag Concr Res,1988,40(143):106-110.
[14]HALL C.Water sorptivity of mortars and concrete:a review[J].Mag Concr Res,1989,41:51-61.
[2]TAFRAOUI A,ESCADEILLAS G,LEBAILI S.Metakaolin in the formulation of UHPC[J].Constr Build Mater,2009,2(23):669-674.
[3]戎志丹,虞焕新,林发彬.低水胶比条件下水泥基复合材料的微结构形成机理[J].武汉理工大学学报,2013,35(4):6-10.RONG Zhidan,YU Huanxin,LIN Fabin.Wuhan Unive Technol(in Chinese),2013,35(4):6-10.
[4]张宇,金祖权,张云升.不同方式养护高强水泥基材料孔表面积分形维数与孔结构的关系[J].硅酸盐学报,2017,45(2):249-253.ZHANG Yu,JIN Zuquan,ZHANG Yunsheng.J Chin Ceram Soci,2017,45(2):249-253.
[5]李红辉.大掺量粉煤灰高性能混凝土研究[D].北京:北京建筑工程学院,2007.LI Honghui.Research on the high performance concrete with high volume fly-ash(in Chinese,dissertation).Beijing:Beijing Institute of Civil Engineering and Architecture.2007.
[6]谭克锋,刘涛.早期高温养护对混凝土抗压强度的影响[J].建筑材料学报,2006,9(4):473-476.TAN Kefeng,LIU Tao.J Build Mater(in Chinese),2006,9(4):473-476.
[7]VERBECK G J.Structures and physical properties of cement paste[C]//5th Inter.Symp.on Chem.of Cement.1968.
[8]VANDAMME M,ULM F-J,FONOLLOSA P.Nanogranular packing of C-S-H at substochiometric conditions[J].Cem Concr Res,2010,40(1):14-26.
[9]GALLUCCI E,ZHANG X,SCRIVENER K L.Effect of temperature on the microstructure of calcium silicate hydrate(CSH)[J].Cem Concr Res,2013,53:185-195.
[10]冯竟竟,傅宇方,陈忠辉,等.高温对水泥基材料微观结构的影响[J].建筑材料学报,2009,12(3):318-322.FENG Jingjing,FU Yufang,CHEN Zhonghui,et al.J Build Mater(in Chinese),2009,12(3):318-322.
[11]韩松,刘丹,张戈,等.超低水胶比复合胶凝材料孔结构随养护制度和龄期的变化机理.硅酸盐学报,2017,45(11):1594-1604.HAN Song,LIU Dan,ZHANG Ge,et al.J Chin Ceram Soc,2017,45(11):1594-1604.
[12]王月.氯盐冻融循环与侵蚀作用下活性粉末混凝土的耐久性研究[D].北京:北京交通大学,2016.WANG Yue.Study on Durability of Reactive Powder Concrete under Chloride Salt Freeze-Thaw Cycle and Erosion(in Chinese,dissertation).Beijing:Beijing Jiaotong University.2016.
[13]KELHAM S.A.A water absorption test for concrete[J].Mag Concr Res,1988,40(143):106-110.
[14]HALL C.Water sorptivity of mortars and concrete:a review[J].Mag Concr Res,1989,41:51-61.