墙体材料热湿膨胀机理与实验方法研究

Nowadays the wall cracking phenomenon is very common, which is caused by thermal and moisture expansion, water expansion, and drying shrinkage of the masonry materials. However, the complicated principle and experiment methods of thermal and moisture expansion result the lack of effective measures which is used to control the wall cracking for expansion-shrinkage deformation. Drying shrinkage test method as a common way of the thermal and moisture expansion research is actually not accurate and effective enough. Because of this, a principle model of wall material moisture expansion and drying shrinkage, as well as an exact and standardized experimental method are proposed to resolve the wall cracking problems.The main researches are as follows: 1. By analyzing the process and principle of the wall material thermal and moisture expansion, a dynamic measurement model of water absorption and expansion will be developed, and then a new experimental method to realize dynamic water expansion measurement standardization will be presented. 2. A solution to key points such as measuring the gauge length positioning system will be proposed by researching the method of dynamic measurement of water-absorption. And base on that, a dynamic water expansion measuring equipment will be developed which achieves the measurement of continuity, automaticity, accuracy and steady. 3. A standardized experimental method to measuring moisture expansion and drying shrinking dynamic will be proposed, by analyzing the deformation law of wall material with a small alteration of environment humidity. As well, a dynamic measuring equipment of moisture expansion and drying shrinking will developed, and the tendency of wall material deformation in dry-wet environment will be found.The achievement of this research will provide cracking control theoretical basis for novel design of wall structure.

目前新型墙体因砌筑材料热湿膨胀、吸水膨胀和干燥收缩而引起的开裂现象十分普遍，因热湿膨胀机理和相关实验方法复杂性，墙体的胀缩开裂控制措施和方法缺乏，现阶段以测量干缩值为实验方法的防治手段效果也不佳，因此，要从根本上防治开裂，首先应提出适用于墙材湿胀干缩变化机理模型，并建立精确测量的标准化实验方法。本课题重点研究内容包括：1.分析墙材热湿膨胀过程及机理，建立吸水膨胀过程的膨胀值和吸水率瞬态计算模型，提出全新的动态吸水膨胀测量标准化实验方法；2.探索墙材在水中吸水量的连续测量方法，提出测量标距定位等关键问题和解决方案，进而建立具备连续、自动、精确和稳定测量功能的动态吸水膨胀测量装置；3.研究环境湿度小范围变化条件下墙材的变形规律，建立动态吸湿干缩测量的标准化实验方法，研制动态干缩湿胀循环过程测量装置，并确定墙体在干湿循环状态下的变形发展规律。本课题成果将为新型墙体构造设计提供开裂控制理论依据。

墙体开裂严重影响建筑耐久性和居住质量。目前裂缝防治多集中在对墙体材料的干燥收缩控制上，墙体干湿交替诱发的湿涨变形一直未给予充分重视。由于缺少专门的实验方法，国内外学者研究湿胀问题时不得不选用干缩实验方法替代，既不符合膨胀发展规律，测量精度也不高。因此，本课题对建筑材料湿胀性能测量装置和标准化实验方法进行了系统研究，包括以下内容：1.分析了墙材湿胀过程、机理及现有实验方法，建立了动态吸水膨胀实验方案；通过探索墙材在水中吸水量的连续测量方法和解决测量标距定位等关键问题，推导吸水膨胀过程的膨胀值和吸水率瞬态计算模型，建立了具备连续、自动、精确和稳定测量功能的动态吸水膨胀测量装置；2.通过典型墙材的动态吸水膨胀实验，检验了测量装置和实验方法的准确性，进而提出了全新的墙体材料动态吸水膨胀标准化实验方法，并分析了典型墙材的吸水膨胀规律，建立了其吸水膨胀实验模型，分析了尺寸效应对其吸水膨胀规律的影响；3.基于准静态吸湿条件下膨胀完全与含湿量变化相适应的假设，提出了用动态方式依次测量多个相对湿度由低到高的小范围变化区间内的瞬时膨胀量和吸湿量来获得等温状态下墙体材料吸湿膨胀曲线的新方法，并研制了动态湿胀干缩测量装置，确定了准静态吸湿成立条件，进而建立了动态吸湿测量的标准化实验方法；4.基于典型墙材实验数据，分析了其吸湿膨胀规律，建立了相关实验模型。5.首次定义了墙体材料动态湿胀系数及其计算方法，获得了加气砖和灰砂砖的动态湿胀系数。