【作者】 陈伟；

【导师】 钱觉时；

【作者基本信息】 重庆大学 ， 材料学， 2013， 博士

【摘要】 轻集料可以改善混凝土的轻质、抗渗、抗震等性能，饱水轻集料的“内养护”作用还可以有效地降低高性能混凝土的自收缩，但是轻集料密度较小、强度较低、吸水性较大的特点，使轻集料与基体间的作用方式与普通集料明显不同，可能会对混凝土的工作性、均匀性、强度、收缩等产生不利影响。因此，从轻集料与基体之间协同作用的角度出发，研究轻集料-基体之间的水分传输、强度协调和密度协调的作用规律与对混凝土性能的影响，有利于充分发挥轻集料在混凝土中的作用。课题主要从轻集料-基体间的水分传输、强度协调和密度协调三方面研究了对混凝土性能的影响，并针对一些不利影响提出了相应的解决技术途径。首先，研究了混凝土拌合过程中轻集料-基体之间，特别是在压力作用时，水分传输特性及混凝土工作性。试验采用压力泌水仪对混凝土拌合物施加压力作用，然后将混凝土拌合物中的轻集料和水泥浆体分离出来，测试了轻集料的含水率和水泥浆体的水灰比，通过轻集料和水泥浆体的含水变化反映轻集料-基体水分传输作用，并测试了压力下的混凝土拌合物的体积变化情况。结果显示，压力作用下轻集料-基体的水分传输更明显，同时会使混凝土拌合物存在较明显的体积压缩现象，轻集料饱水处理后，压力作用下水分传输量和体积压缩量都明显减少；压力作用后混凝土的工作性会显著降低。试验还研究了混凝土水化硬化中轻集料-基体水分传输对收缩性能的影响。在低水灰比条件下，采用饱水轻集料和膨胀剂复合使用，对比了与单独使用时的减缩效果，并结合混凝土内部相对湿度和XRD图谱分析复合使用时的减缩机理。结果表明，单独使用饱水轻集料或膨胀剂对干燥收缩的减缩效果不明显，甚至干燥收缩还会增加，通过饱水轻集料与膨胀剂复合使用，可以显著提升减缩效果；饱水轻集料和膨胀剂复合使用时，混凝土内部湿度相对较高，膨胀剂的反应程度提高。其次，研究了轻集料-基体的强度与密度协调作用对混凝土强度的影响。试验通过调整基体的水灰比控制基体强度，然后采用不同强度轻集料和不同强度基体搭配配制混凝土。结果表明，采用强度较低的轻集料时，通过提高基体强度来提高混凝土强度的方法并不可行。同时，试验在相同水灰比条件下，通过调整不同类型陶粒和陶砂的搭配，发现在基本保持混凝土同等密度下，合理协调搭配陶粒和陶砂，混凝土强度可较为明显地提高。试验还研究了轻集料-基体的密度协调作用对混凝土强度的影响，发现轻集料-基体间的密度差值越大，轻集料的上浮分层会使混凝土强度明显降低，并且在垂直方向比侧向强度降低程度更大。另外，针对超轻轻集料混凝土中轻集料-基体间的水分传输作用更明显，强度、密度差异更大，对混凝土的工作性、强度的不利影响较突出的问题，考虑轻集料-基体之间的水分传输、强度和密度的协同作用，提出高水灰比配制超轻轻集料混凝土的技术途径。试验采用不同密度的陶粒和陶砂配制超轻轻集料混凝土，研究随水灰比增加轻集料混凝土坍落度损失、轻集料分层度以及强度与密度关系的变化，并研究高水灰比对轻集料混凝土收缩和吸水性的影响。结果显示，提高水灰比能明显降低轻集料混凝土的坍落度损失与轻集料分层度；采用表观密度738kg/m~3的陶粒以及破碎后制备的陶砂，水灰比0.75时，配制了干密度低于900kg/m~3，28d抗压强度为14MPa左右的超轻轻集料混凝土；高水灰比轻集料混凝土收缩和吸水性可控制在相对较低范围内。结果还表明，采用的轻集料越轻，水灰比增加幅度应越大，不仅可以显著降低轻集料混凝土的坍落度损失和轻集料上浮，还能较大幅度降低混凝土密度下保持较高强度。实际工程应用也表明，高水灰比方法生产超轻轻集料混凝土用于楼面保温工程有较好的技术经济优势。研究结果显示，轻集料应用于混凝土时，不应仅仅着眼于某一方面性能的改善，应综合考虑轻集料-基体间水分传输、强度、密度等多因素的协同作用以及对混凝土各方面性能的影响，才能更有效地发挥轻集料的有利作用，同时降低可能带来的不利影响。更多还原

【Abstract】 A lighter, less water-permeable and higher earthquake-resistant concrete can beproduced by using light weight aggregate (LWA). Meanwhile, the autogenous shrinkageof high performance concrete can be mitigated by the internal curing effect induced bysaturated LWA. However, the interaction between LWA and concrete matrix in LWAconcrete is obviously different from that in concrete made of ordinary aggregatebecause of the lower density, lower mechanical property and high water-absorbingcapacity of LWA, leading to adverse influences on the workability, homogeneity,strength development and volume stability of concrete. Therefore, a study ofwater-transfer, mechanical property coordination and density coordination betweenLWA and concrete matrix based on the interaction of the two is of great importancewhen making good use of the advantages of LWA on concrete. The influence ofwater-transfer, strength coordination and density coordination between LWA andconcrete matrix on the performance of concrete was studied in this work and sometechniques were proposed to tackle with the adverse influences.Firstly, the water-transfer action between LWA and concrete matrix, as well as theworkability of concrete mixture was studied under normal and extra-pressure. LWA andcement paste of LWA-concrete were separated by using pressure bleeding instrumentand the water-transfer action between LWA and concrete matrix was illustrated by thealternation of water content of LWA and cement paste. The volume variance of concretemixture under pressure was measured as well. It is shown that more water transfersfrom concrete matrix to LWA under pressure and concrete volume has been remarkablyreduced as well, but the variations are less noticeable when LWA is pre-saturated. It isalso shown that concrete workability is remarkably reduced when extra-pressure isapplied.The influence of water-transfer action between LWA and concrete matrix on thevolume stability of concrete during hydration and hardening processes was studied. Andthe shrinkage-reducing effects of saturated-LWA and expanding agent were investigatedunder the unique and combined usage at a low water-to-binder ratio. Furthermore, theshrinkage-reducing mechanism was analyzed through concrete internal humiditymeasurement and XRD spectrum investigation. It reveals that no good drying shrinkage-reducing effect is seen when the saturated-LWA and expanding agent is solelyused if no increase in drying shrinkage is shown, however, the shrinkage-reducing effectis remarkably improved when the two are incorporated together, which leads to a higherinternal humidity of concrete and a greater hydration degree of expanding agent.Secondly, the coordination effects of mechanical property, as well as bulk densityof LWA and concrete matrix was studied. Concrete matrixes with various mechanicalproperties were made by altering water-to-cement ratio, and then they were mixed withLWAs of various mechanical properties. Results show that it is not practicable toimprove the mechanical property of concrete by increasing the mechanical property ofconcrete matrix when LWA of low mechanical property is used. It also shows that themechanical property of concrete can be significantly improved by optimizing thecompatibility of coarse and fine expanded shale under a comparable density when aconstant water-to-cement ratio is applied. Effect of density coordination of LWA andconcrete matrix on the compressive strength of concrete was also studied and it revealsthat a greater variance of bulk density of LWA and concrete matrix results in a moresignificant reduction of compressive strength resulting from segregation of concretecomponents and the strength loss is more significant in the vertical direction than that inthe lateral direction.Considering a greater water-transfer action between LWA and concrete matrix inthe ultra-light LWA concrete and greater variances of the strength and bulk density ofthe two will induce greater adverse side effects on the workability and mechanicalproperty of ultra-light LWA concrete, a new technical way was proposed to produceultra-light LWA concrete, in which a high water-to-cement ratio was used byconsidering the synergic actions of water-transfer, mechanical property and bulk densityof LWA and concrete matrix. Various types of LWA were used to prepare concrete.Variations of the slump loss, segregation of LWA, relationship between strength anddensity of the concrete with the water-to-cement ratio were investigated. The shrinkageand water absorption of the concrete with higher water-to-cement ratio were tested. It isshown that increasing the water-cement ratio reduces the segregation of lightweightaggregate and slump loss of the concrete; when W/C is0.75, a lightweight aggregateconcrete with bulk density of less than900kg/m~3and compressive strength of14MPa isobtained by using a coarse expanded shale with apparent density of738kg/m~3andresulting fine aggregate by crushing. The shrinkage and water absorption of lightweight aggregate concrete, prepared by using higher W/C, are within an acceptable range. It issuggested that the lighter the lightweight aggregate, the higher the W/C, the less thesegregation of the aggregate and slump loss of the concrete, and the higher the retainedstrength. It has been proved that there are great technical and economic advantages ofutilizing ultra-light LWA concrete on floor insulation works in practical engineeringapplications.It is concluded from the results that the advantages of LWA on concrete can bemore effectively achieved by considering both the coordination actions of water-transfer,strength and bulk density between LWA and concrete matrix and their influences on theperformance of concrete, rather than a mere focus on one certain property. Moreover,the disadvantages can be mitigated as well.更多还原