1.1 本试验方法测量密封水泥浆或砂浆试样（包括含有外加剂、各种辅助胶凝材料（SCM）和其他精细材料的试样）的体积应变，在恒定温度下，从最终凝固到规定龄期，不受外力作用。这种菌株被称为 自体应变 . 自生应变在水胶比较低的混凝土中最为显著( 宽/厘米 )（参见 注1 ). 注1: 低水胶凝材料比( 宽/厘米 )对于本试验，可以认为水灰比为0.40或更低。 1.2 以国际单位制表示的数值应视为标准值。本标准不包括其他计量单位。 1.3 本标准并非旨在解决与其使用相关的所有安全问题（如有）。 本标准的用户有责任在使用前制定适当的安全和健康实践，并确定监管限制的适用性。 ( 警告 -新鲜的水硬性胶结混合物具有腐蚀性，长时间接触可能会导致皮肤和组织化学烧伤。 2. ) ====意义和用途====== 5.1 自生应变是水泥浆、砂浆或混凝土在恒温硬化过程中自行产生的体积应变。在传统混凝土中，自收缩应变通常可以忽略不计，但在水胶比较低的混凝土中( 宽/厘米 )或者对于硅粉，这可能是相当可观的( 1. ). 5. 骨料或相邻结构构件对自生应变的约束可能导致形成微观和宏观裂纹，从而影响强度、耐久性和美观性。 裂纹也可能是表面卫生清洁方面的问题。 5.2 低应力水泥混合料自应变的精确测量 宽/厘米 对于评估混凝土结构早期开裂的风险很重要。使用体积法或线性法测量自应变。这两种方法都可能显示出明显的伪影( 1. ); 因此，如果执行不当，这两种方法的结果可能相差很大。 5.3 密封、柔性波纹模具系统( 2. )结合了自应变线性和体积测量的优点，同时避免了它们的大多数缺点。该模具有效防止水分损失，并将硬化过程中对体积变化的限制降至最低。此外，在体积法中消除了一些伪影，特别是通过用于容纳试样的膜的吸水性后，使用波纹模具系统获得的结果与体积法的结果一致( 3. , 4. ). 与体积法相比，波纹模具系统更易于使用，并显示出更好的重复性( 3. , 4. ). 波纹模具系统的测量值与使用试验方法获得的无约束长度变化测量值非常一致 C157/C157M 密封试样( 5. ); 然而，试验方法 C157/C157M 不允许在24小时前测量收缩( 5. ). 5.4 本试验方法可用于评估胶凝材料、外加剂和混合物比例对糊料或砂浆试样自收缩应变的影响。 5.5 相同条件下，砂浆试样的自收缩应变将小于糊状试样的自收缩应变 宽/厘米 . 相同条件下，混凝土的自收缩应变将小于砂浆的自收缩应变 宽/厘米 . 本试验方法中使用的砂浆标称最大骨料粒径为4。 75毫米。

1.1 This test method measures the bulk strain of a sealed cement paste or mortar specimen, including those containing admixtures, various supplementary cementitious materials (SCM), and other fine materials, at constant temperature and not subjected to external forces, from the time of final setting until a specified age. This strain is known as autogenous strain . Autogenous strain is most significant in concrete with low water-cementitious materials ratio ( w/cm ) (See Note 1 ). Note 1: A low water-cementitious materials ratio ( w/cm ) can be considered to be a water to cement ratio of 0.40 or lower for this test. 1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. ( Warning —Fresh hydraulic cementitious mixtures are caustic and may cause chemical burns to skin and tissue upon prolonged exposure. 2 ) ====== Significance And Use ====== 5.1 Autogenous strain is the self-created bulk strain of cement paste, mortar, or concrete during hardening at constant temperature. In conventional concrete, autogenous shrinkage strain is generally negligible, but in concrete with low water-cementitious materials ratio ( w/cm ) or with silica fume it may be considerable ( 1 ). 5 Restraint of the autogenous strain by aggregates or adjoining structural members may result in formation of micro and macro cracks that impair strength, durability and aesthetics. Cracks may also be a problem with regard to hygienic cleaning of surfaces. 5.2 An accurate measurement of the autogenous strain of cementitious mixtures with low w/cm is important for evaluating the risk of early-age cracking of concrete structures. Measurements of autogenous strain have been carried out using either volumetric or linear methods. Both methods may show evidence of significant artifacts ( 1 ); therefore, results of the two methods may disagree considerably if not carried out properly. 5.3 A sealed, flexible corrugated mold system ( 2 ) combines the advantages of linear and volumetric measurement of autogenous strain, while avoiding most of their disadvantages. The mold effectively prevents moisture loss and minimizes restraint to volume change during hardening. Moreover, results obtained with the corrugated mold system agree with those from the volumetric method, once some artifacts, in particular water absorption through the membrane used to contain the test specimen, have been eliminated in the latter ( 3 , 4 ). The corrugated mold system is easier to use and shows better repeatability than the volumetric technique ( 3 , 4 ). Measurements with the corrugated mold system are in good agreement with unrestrained length change measurements obtained using Test Method C157/C157M with sealed specimens ( 5 ); however, Test Method C157/C157M does not allow measurement of the shrinkage occurring before 24 h ( 5 ). 5.4 This test method can be used to evaluate the effects of cementitious materials, admixtures, and mixture proportions on autogenous shrinkage strain of paste or mortar specimens. 5.5 The autogenous shrinkage strain of mortar specimens will be less than that of paste specimens for the same w/cm . The autogenous shrinkage strain of concrete will be less than that of mortar for the same w/cm . The nominal maximum aggregate size for mortar used in this test method is 4.75 mm.