确定砂浆的水保留性[IS：2250-1981]

目的

Water retentivity of mortar is the ability of mortars to retain water against suction and evaporation in general. It is indirectly a measure of the workability of mortars.

仪器

The apparatus used for this test consists of a water aspirator or other source of vacuum controlled by way of a three way stopcock to a funnel upon which rests a perforated dish. The perforated dish shall be made of metal, not attacked by masonry mortars. The metal in the base of the dish shall have a thickness of 1.7 to 1.9 mm and shall conform to the outline shown in figure below. The bore of the stopcock shall have a minimum inside diameter of 4 mm.

A mercury manometer, connected as shown in Fig, indicates the vacuum. A synthetic rubber gasket shall be permanently sealed to the top of the funnel and shall be lightly coated with petroleum or light cup grease during the test to ensure a seal between the funnel and the dish. Care shall be taken to ensure that none of the holes in the perforated dish is clogged from the grease used on the rubber gasket. Hardened filter paper of a grade equivalent to Carl Schleicher and Schuell filter paper No.576 or to Whatman No.50 filter paper shall be used. It shall be of such diameter that it will lie flat and completely cover the bottom of the dish.

Adjust the mercury relief column so as to maintain a vacuum of 5cm as measured on the manometer. Seat the perforated dish on the greased gasket of the funnel. Place a wetted filter paper in the bottom of the dish. Turn the stopcock to apply the vacuum to the funnel and check the apparatus for leaks and to determine that the required suction is obtained. Then turn the stopcock to shut off the vacuum from the funnel.

程序

1. Mix the mortar to a consistency to give a flow of 110 to 115.
2. 进行流程测试后，立即将流桌上的砂浆返回到搅拌碗中，并以中等速度将整个批次重新搭配15秒。
3. Immediately after remixing of the mortar, fill the perforated dish with the mortar to slightly above the rim. Tamp the mortar 15 times with the tamper. Ten of the temping strokes shall be applied at approximately uniform spacing adjacent to the rim of the dish and with the long axis of the tamping face held at right angles to the radius of the dish. The remaining five tamping strokes shall be applied at random points distributed over the central area of the dish. The tamping pressure shall be just sufficient to ensure filling of the dish.
4. 完成她难的顶部应稍微延伸到盘子的边缘上方。通过在盘子顶部绘制直边的平坦侧（略微升高），使砂浆平滑。然后将砂浆切成平面表面与盘子的边缘一起用直缘，用两条切割的笔触在盘子的顶部穿过锯子运动，从盘子中心附近开始每次切割。
5. If the mortar is pulled away from the side of the dish during the process of drawing the straight edge across the dish, gently press the mortar back into contact with the side of the dish using the tamper.
6. 将挡块旋转以将真空应用于漏斗。从混合水泥和水的开始到施用油酸的时间的时间不得超过8分钟。
7. After suction for 60 sec quickly turn the stopcock to expose the funnel to atmospheric pressure. Immediately slide the perforated dish off from the funnel, touch it momentarily on damp cloth to remove droplets of water and set the dish on the table.
8. 然后，使用碗刮刀，流动并混合盘中的砂浆15秒。
9. Upon completion of mixing, place the mortar in the dish for 15 sec. Upon completion of mixing, place the mortar in the flow mould and determine the flow.
10. 整个操作应在不中断的情况下进行，并尽快进行，并应在混合水泥和水混合后的11分钟内完成，以进行首次流动测定。

Calculation

Calculate the water retention value for the mortar as follows;

Water retention value = A/B x 100

Where,

A = flow after suction and

B =混合后立即流动

Reference

IS：2250 - 1981年 - 准备和使用砖石砂浆的实践守则