标准编号:	GB 751-1981
中文名称:	水泥胶砂干缩试验方法
英文名称:	Test method for drying shrinkage of cement mortar
行业分类:	GB    国家标准
发布日期:	1981-10-01
实施日期:	1981-10-1
标准状态:	superseded
被新标准替代:	JC/T 603-1995 水泥胶砂干缩试验方法
被替代日期:	1996-10-1
翻译语言:	英文
文件格式:	PDF

Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative. Test method for drying shrinkage of cement mortar This standard is applicable to the comparison of drying shrinkage performance of different cements. The drying shrinkage of cement mortar measured in this standard is determined by measuring the length change of 1:2.5 plastic mortar specimen of 25×25×280mm (both ends are equipped with spherical nail head) with comparator after the specimen is cured in dry air. When the specimen used for determination of drying shrinkage performance is placed in dry air, the temperature is 20±3℃ and the relative humidity is 60±5%. The temperature and humidity shall be checked and recorded every day. I. Instruments 1. Mortar mixer See the requirements of GB 177-77 Test method for strength of cement mortar, clause 1, article 1. 2. Shock table, truncated-cone round mold and mold sleeve, cylindrical tamper and caliper, which shall all meet the requirements of GB 2419-81 Test method for fluidity of cement mortar, clause 1. 3. Test mold: triple test mold made of metal material (as shown in figure 1), that may be disassembled and shall be numbered. The inner wall dimension of each part is 25×25×280mm. There is small hole for installation of measuring nail head on top of mold and the position of the small hole must ensure that the measuring nail head is on the center line of the specimen. The measuring nail head is made of stainless steel or copper and has specification as shown in figure 2. Figure 1 Triple test mold Figure 2 Nail head The depth of measuring nail head into the specimen shall be 15±1mm. The distance between inner sides of nail heads shall make the valid specimen length be 250±2.5mm. 4. Tamper: there are two kinds, i.e. square tamper and notched tamper; see figure 3; both are made of metal materials. The compression area of square tamper is 23×23mm. The notched tamper is used to tamp and measure mortars on both ends of the nail head. 5. Three-edge scraper, see the requirements of GB 177-77 Test method for strength of cement mortar. 6. Comparator (as shown in figure 4): composed of dial indicator and bracket. The minimum scale value of dial indicator is 0.01mm and its measuring range is 10mm. Note: It is allowed to use other types of length measuring instruments, but the accuracy must meet the above requirements. In arbitration inspection, the comparator shall prevail. Figure 4 Comparator 1——dial indicator; 2——bracket II. Determination of water consumption for cement mortar 7. The water consumption for cement mortar is determined according to the fluidity of mortars; cement mortar is prepared in accordance with the requirements of GB 177-77, article 15. 8. The fluidity of cement mortar is determined in accordance with the requirements of GB 2419-81, articles 7, 8 and 9. 9. Take the average of two perpendicular diameters as the diffusion diameter at mortar bottom; if the average is between 130~140mm, it is the water consumption for normal consistency; if less than 130mm or larger than 140mm, it is required to add or reduce water for redetermination until the diffusion diameter is between 130~140mm. III. Molding of cement mortar specimen 10. Three molded specimens are required for the determination of drying shrinkage of cement mortar. 350g of cement specimen and 875g of standard sand shall be weighed for each 3 specimens. The mortar is prepared in accordance with the requirements of GB 177-77, article 15. Place the uniformly mixed mortar into the test mold with both ends installed with head nail and coated with a layer of machine oil on the inner wall by two layers. Fill the first layer of mortar to a depth of about 2/3 of the height of the test mold. First, scratch the mortar back and forth with a knife to make it become tight (in particular, both sides of the nail head shall be scratched for more times), and then tamp from the inner side of the nail head with a 23×23mm tamper, i.e. tamp from one end to the other sequentially for 10 times (in total 20 times when counting from both directions) between the tails of two nail heads; tamp on each side of the nail head with notched tamper for 2 times, then fill the second layer of mortar. After the test mold is filled with mortar, scrape evenly with a knife. The depth of knife stroke shall go beyond the surface of the first layer of mortar, and then tamp on the specimen with the tamper sequentially for 12 times (in total 24 times when counting from both directions). In each tamping, first make the tamper contact the mortar surface then tamp with force. The tamping must be uniform and stable and hit is not allowed. After tamping, fill the test mold with the left mortars and scrape with three-edge scraper; mark it and place it in curing box with temperature of 20±3℃ and relative humidity of more than 90% for curing.

I. Instruments II. Determination of water consumption for cement mortar III. Molding of cement mortar specimen VI. Demolding and curing of the specimen VII. Measurement of specimen length change VIII. Result calculation Additional explanation:

中华人民共和国国家标准 水泥胶砂干缩试验方法 GB 751—81 国家标准总局发布 1981年10月1日实施 本标准适用干比较不同水泥的干缩性能。 本标准所测得的水泥胶砂干缩性是用两端装有球形钉头的25×25×280mm的1:2.5软练胶砂试体，在干空气中养护后，以比长仪测量试体长度变化来确定的。 测定干缩性的试体在干空气中放置时，温度为20±3℃。相对湿度为60±5％，温、湿度均应每日检查并记录。 一、仪 器 1.胶砂搅拌机 见GB 177—77《水泥胶砂强度检验方法》中第一章第1条的规定。 2.跳桌、截锥圆模及模套、圆柱捣棒、卡尺均应符合GB 2419—81《水泥胶砂流动度测定方法》中第一章的规定。 3.试模：用金属材料制成的三联试模(如图1所示)，可以拆卸，模型应有编号。每联试模内壁尺寸为25×25×280 mm。模板顶端具有安置测量钉头的小孔，小孔位置必须保证测量钉头在试体的中心线上。测量钉头用不锈钢或铜制成，其规格如图2所示。 图1三联试模 图2钉头 测量钉头伸入试体深度应为15±1 mm。钉头内侧之间的长度应保证试体的有效长度为250±2.5mm。 4.捣棒：包括方捣棒及缺口捣棒两种，见图3，均用金属材料制成。方捣棒受压面积为23×23mm。缺口捣棒用于捣固测量钉头两端的胶砂。 方捣棒 缺口捣棒 图3捣棒 5.三棱刮平刀见GB 177—77《水泥胶砂强度检验方法》的规定。 6.比长仪(如图4所示)：由百分表及支架组成，百分表刻度值最小为0.01mm，量程为10mm。 注：允许用其他型式的测长仪，但精确度必须符合上述要求，在仲裁检验时，应以比长仪为准。 图4比长仪 1—百分表；2—支架 二、水泥胶砂用水量的确定 7.水泥胶砂用水量根据胶砂流动度大小来确定，水泥胶砂的制备按GB 177—77中第15条的规定进行。 8.水泥胶砂流动度的测定按GB 2419—81中第7、8、9条的规定进行。 9.胶砂底部扩散直径，取互相垂直的两直径之平均值，结果如在130～140mm范围内，则为标准稠度加水量，如小于130mm或大于140mm，则需重新增减水量再进行测定，直至扩散直径为130～140mm时为止。 三、水泥胶砂试体的成型 10.测定水泥胶砂的干缩性需成型3条试体。每3条试体需称取水泥试样350g，标准砂875g。胶砂的制备按GB177—77中第15条的规定进行。 将已拌和均匀的胶砂，分两层装入两端已装有钉头、内壁已涂上一层机油的试模内。第一层胶砂装入深度约为试模高度的2/3，先用小刀来回划实胶砂，尤其钉头两侧应多划几次，然后用23×23mm捣棒由钉头内侧开始，即在两钉头尾部之间，从一端向另一端顺序地捣压10次，往返共捣压20次，再用缺口捣棒在钉头两侧各捣压2次，然后装入第二层胶砂，胶砂装满试模后，用小刀划匀，刀划之深度应透过第一层胶砂表面，再用捣棒在试体上顺序地捣压12次，往返共捣压24次。每次捣压时，先将捣棒接触胶砂表面再用力捣压。捣压必须均匀稳定，不得打击。捣压完毕，将剩余胶砂填满试模并用三棱刮平刀刮平，然后记上编号，放入温度为20±3℃，相对温度为90％以上的养护箱内养护。 四、试体的脱模与养护 11.试体自加水时算起，养护24±2h后脱模。然后将试体立即放入温度为20±2℃的水中养护。对于低标号水泥，早期强度低或特种水泥不可能在24h脱模时，可酌情延长脱模时间。将所延长的时间在试验报告中注明。 12.试体在水中养护6d后，由水中取出，擦去表面水分，用比长仪测定初始读数，然后将试体先在成型室内放置2d，待试体稍干后再移入温度为20±3℃、相对湿度为60±5％的干空气中，进行养护。 五、试体长度变化的测量 13.试体自测定初始读数后算起继续在温度为20±3℃、相对湿度为60±5％的干空气中放置7d、14d、28d、2个月，3个月和6个月后，再测量其读数。 注：测量龄期可以根据需要作必要的增减。 14.比长仪应放置在17～25℃的试验室中，每次测量前，先校对百分表的零点。 15.测量前应将试体的钉头擦干净。试体放入比长仪的上下位置，每次测量时应保持一致。读数时应左右旋转试体，使试体钉头和比长仪正确接触。测量应精确至0.01mm。如指针读数摆动时，可取摆动范围内的平均读数。 六、结果的计算 16.水泥胶砂试体的各龄期干缩率St(％)按下式计算： 式中 Lt——某龄期的测量读数，mm； L0——初始测量读数，mm； 250——试体有效长度，mm。 干缩率结果应取3条试体之平均值，计算应精确至0.01％，水泥胶砂试体干缩率以“-”号表示。 附加说明： 本标准由中华人民共和国建筑材料工业部提出。 本标准由建筑材料科学研究院起草。