混杂纤维增强PCM（相变）混凝土冻融断裂性能及微观力学模型研究

With rapid development of technology and the common sense on the energy shortage, the PCMs (Phase Change Materials) have been applied in many fields. Recently, many foreign researches focused on the application in the engineering field, with a little research work on the fundamental and technology section. Thus, it is highly urgent to conduct fundamental and intensive research on the durability and micromechanical behavior of the concrete structure with PCMs.. The study is based on our premier project “Micro- Mechanical Behavior of High Performance Hybrid Fiber Reinforced Concrete with PCMs” Sponsored by UCLA (University of California, Los Angeles，America) ongoing advance project under the U.S. NSF), and now focus on the “Micro-Mechanical and Fracture Behavior of High Performance Hybrid Fiber Reinforced Concrete with PCMs under Low Temperature Environment, especially in Freezing Environment Outside.”. For this study, our primary research work and innovative points are summarized as:. Reference on the ASTM 666 Standard, we conduct the Freeze-Thaw testing in the freezer cabinet for 3 types concrete, including hybrid fiber reinforced concrete with PCMs, plain concrete, and the hybrid fiber reinforced concrete. Testing the mass loss and the loss of the young's modulus (Ep). After 300-500 Freeze-thawing cycles, we carry out the three-point bending fracture tests for the plain concrete, fiber (PVA fiber and hook-end steel fiber) reinforced concrete and the hybrid fiber reinforced concrete with PCMs. Then, the full curve of Load-Crack Tip Opening Displacement (P-CTOD) will be obtained by laboratory testing.. With different interface constitutive models for the PVA fiber and the hook-end steel fiber across the matrix fracture panel, we can derive the corresponding micro-mechanical fracture models, respectively. Subsequently, the micro-mechanical fracture energy models of the hybrid fiber reinforced concrete with PCMs are developed, aiming at the direct tension fracture and the three-point flexural bending fracture.. On the basis of our micro-mechanical fracture energy models for the PVA fibers and the hook-end steel fibers bridging the fracture panel of concrete, we develop the ultimate combined micro-mechanical fracture energy model for the PCM concrete reinforced by the PVA fibers and steel fibers, separately, under the condition of the direct tension fracture and the three-point flexural bending fracture.. Finally, we estimate the micro-mechanical fracture energy model parameters by coupling the interface stresses of the PVA fibers and the steel fibers across the fracture panel of concrete, and then compute the fracture energy of the hybrid fiber reinforced concrete with PCMs. Thus, to perform validation of the applicability and accuracy of the proposed micro-mechanical models for the hybrid fiber reinforced concrete with PCMs.

随着对建筑能耗增加而能源缺乏的共识，建筑节能材料开发应用已成为当前研究热点。一些发达国家已开始将相变材料PCM（Phase Change Materials）应用于建筑领域，PCM混凝土在工程应用中愈来愈受提倡和重视，对PCM混凝土的研究也逐渐兴起。本项研究拟在本人前期所做“高性能PCM混杂纤维混凝土断裂性能及微观力学模型研究” （UCLA在研NSF项目）课题基础上，对掺入PCM的普通混凝土和混杂纤维混凝土试件进行冻融试验，测其对应的质量及动弹性模量（EP）损失、在冻融循环完成后，对各类混凝土试件进行基本力学性能及三点弯曲断裂试验，测绘对应的荷载-位移（P-δ）曲线、及荷载-裂缝嘴张开位移（P-CMOD）全曲线，据此计算混杂纤维增强PCM混凝土在冻融循环下的断裂能、并尝试建立微观力学模型，最后对模型进行数值计算验证，为PCM混凝土更好地应用于工程中提供实践基础和理论依据。

PCM相变储能材料 掺入混凝土中不仅能节省能耗、提高建筑物温度调节能力，还可减小结构自重、增加其有效使用面积。继续在PCM混凝土中加入增强纤维可提高其强度、韧度及阻裂性能，使混杂纤维增强PCM混凝土兼具结构性及功能性特点，能更广泛地应用于建筑工程中。混杂纤维增强PCM混凝土的基体组分及微观构成与普通混凝土有较大差别，对其力学行为、断裂机理、以及低温耐久性能的研究已成为亟待解决的问题。. 基于PCM相变储能材料不具有水化胶结性能，其掺入普通混凝土势必会降低基体材料的受力性能，所以本项研究着重对功能性混杂纤维增强PCM相变储能混凝土常温及低温环境下的物理化学性能、基本力学性能、以及断裂力学性能进行详细研究，并与普通混凝土和混杂纤维增强混凝土常温及低温下基本力学性能及其断裂力学性能进行对比研究。具体研究内容概括如下：. 1）对普通混凝土、混杂纤维（PVA纤维与弓形钢纤维）增强混凝土、以及PCM（体积掺量5％、7％、9％）混杂纤维混凝土两类试件进行400个慢速冻融循环试验，每50个循环测质量损失及动弹性模量（EP）损失。. 2）对冻融循环前后的各类试件进行圆柱体抗压及劈拉强度实验、以及自行设计单边预留切缝三点弯曲断裂试验，测得荷载-位移（P-δ）曲线、荷载-裂缝嘴张开位移（P-CMOD）全曲线，用简化方法计算得出对各类混凝土的三点弯曲断裂能。对比各类混凝土强度及断裂能试验值，得出PCM对纤维混凝土早期抗压强度影响较大、而对（冻融前后）断裂能影响相对较小的结论；根据PCM对纤维混凝土抗压强度的影响程度，初步确定混凝土中PCM体积掺量不宜超过10%。. 3）用微观力学分析方法，尝试建立混杂纤维PCM混凝土断裂机理和微观力学断裂能模型。分别对混凝土断裂面处PVA纤维与弓形钢纤维拔出过程中的断裂能耗分别建立微观力学计算模型。随后利用能量叠加原理，对两种纤维增强作用下PCM混凝土在直接拉伸、及三点弯曲情况下的断裂能建立微观力学理论模型.4）依据试验结果，对混杂纤维增强PCM混凝土断裂能微观力学模型参数进行耦合确定，采用所建模型进行值计算，将结果与三点弯曲断裂能试验值对比，验证所建模型正确与合理性。