標準編號:	GB 751-1981
中文名稱:	水泥膠砂干縮試驗方法
英文名稱:	Test method for drying shrinkage of cement mortar
行業分類:	GB    國家標準
發布日期:	1981-10-01
實施日期:	1981-10-1
標準狀態:	superseded
被新標準替代:	JC/T 603-1995 水泥膠砂干縮試驗方法
被替代日期:	1996-10-1
翻譯語言:	英文
文件格式:	PDF
中文字符數:	5000 字
翻譯價格(元):	720.0
交付時間:	付款后 1 個工作日

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:

中華人民共和國國家標準 水泥膠砂干縮試驗方法 GB 751—81 國家標準總局發布 1981年10月1日實施 本標準適用干比較不同水泥的干縮性能。 本標準所測得的水泥膠砂干縮性是用兩端裝有球形釘頭的25×25×280mm的1:2.5軟練膠砂試體，在干空氣中養護后，以比長儀測量試體長度變化來確定的。 測定干縮性的試體在干空氣中放置時，溫度為20±3℃。相對濕度為60±5％，溫、濕度均應每日檢查并記錄。 一、儀 器 1.膠砂攪拌機 見GB 177—77《水泥膠砂強度檢驗方法》中第一章第1條的規定。 2.跳桌、截錐圓模及模套、圓柱搗棒、卡尺均應符合GB 2419—81《水泥膠砂流動度測定方法》中第一章的規定。 3.試模：用金屬材料制成的三聯試模(如圖1所示)，可以拆卸，模型應有編號。每聯試模內壁尺寸為25×25×280 mm。模板頂端具有安置測量釘頭的小孔，小孔位置必須保證測量釘頭在試體的中心線上。測量釘頭用不銹鋼或銅制成，其規格如圖2所示。 圖1三聯試模 圖2釘頭 測量釘頭伸入試體深度應為15±1 mm。釘頭內側之間的長度應保證試體的有效長度為250±2.5mm。 4.搗棒：包括方搗棒及缺口搗棒兩種，見圖3，均用金屬材料制成。方搗棒受壓面積為23×23mm。缺口搗棒用于搗固測量釘頭兩端的膠砂。 方搗棒 缺口搗棒 圖3搗棒 5.三棱刮平刀見GB 177—77《水泥膠砂強度檢驗方法》的規定。 6.比長儀(如圖4所示)：由百分表及支架組成，百分表刻度值最小為0.01mm，量程為10mm。 注：允許用其他型式的測長儀，但精確度必須符合上述要求，在仲裁檢驗時，應以比長儀為準。 圖4比長儀 1—百分表；2—支架 二、水泥膠砂用水量的確定 7.水泥膠砂用水量根據膠砂流動度大小來確定，水泥膠砂的制備按GB 177—77中第15條的規定進行。 8.水泥膠砂流動度的測定按GB 2419—81中第7、8、9條的規定進行。 9.膠砂底部擴散直徑，取互相垂直的兩直徑之平均值，結果如在130～140mm范圍內，則為標準稠度加水量，如小于130mm或大于140mm，則需重新增減水量再進行測定，直至擴散直徑為130～140mm時為止。 三、水泥膠砂試體的成型 10.測定水泥膠砂的干縮性需成型3條試體。每3條試體需稱取水泥試樣350g，標準砂875g。膠砂的制備按GB177—77中第15條的規定進行。 將已拌和均勻的膠砂，分兩層裝入兩端已裝有釘頭、內壁已涂上一層機油的試模內。第一層膠砂裝入深度約為試模高度的2/3，先用小刀來回劃實膠砂，尤其釘頭兩側應多劃幾次，然后用23×23mm搗棒由釘頭內側開始，即在兩釘頭尾部之間，從一端向另一端順序地搗壓10次，往返共搗壓20次，再用缺口搗棒在釘頭兩側各搗壓2次，然后裝入第二層膠砂，膠砂裝滿試模后，用小刀劃勻，刀劃之深度應透過第一層膠砂表面，再用搗棒在試體上順序地搗壓12次，往返共搗壓24次。每次搗壓時，先將搗棒接觸膠砂表面再用力搗壓。搗壓必須均勻穩定，不得打擊。搗壓完畢，將剩余膠砂填滿試模并用三棱刮平刀刮平，然后記上編號，放入溫度為20±3℃，相對溫度為90％以上的養護箱內養護。 四、試體的脫模與養護 11.試體自加水時算起，養護24±2h后脫模。然后將試體立即放入溫度為20±2℃的水中養護。對于低標號水泥，早期強度低或特種水泥不可能在24h脫模時，可酌情延長脫模時間。將所延長的時間在試驗報告中注明。 12.試體在水中養護6d后，由水中取出，擦去表面水分，用比長儀測定初始讀數，然后將試體先在成型室內放置2d，待試體稍干后再移入溫度為20±3℃、相對濕度為60±5％的干空氣中，進行養護。 五、試體長度變化的測量 13.試體自測定初始讀數后算起繼續在溫度為20±3℃、相對濕度為60±5％的干空氣中放置7d、14d、28d、2個月，3個月和6個月后，再測量其讀數。 注：測量齡期可以根據需要作必要的增減。 14.比長儀應放置在17～25℃的試驗室中，每次測量前，先校對百分表的零點。 15.測量前應將試體的釘頭擦干凈。試體放入比長儀的上下位置，每次測量時應保持一致。讀數時應左右旋轉試體，使試體釘頭和比長儀正確接觸。測量應精確至0.01mm。如指針讀數擺動時，可取擺動范圍內的平均讀數。 六、結果的計算 16.水泥膠砂試體的各齡期干縮率St(％)按下式計算： 式中 Lt——某齡期的測量讀數，mm； L0——初始測量讀數，mm； 250——試體有效長度，mm。 干縮率結果應取3條試體之平均值，計算應精確至0.01％，水泥膠砂試體干縮率以“-”號表示。 附加說明： 本標準由中華人民共和國建筑材料工業部提出。 本標準由建筑材料科學研究院起草。