How to test water reduction rate of mortar?

1. Subject content and scope of application

This method specifies the apparatus and operation steps for the determination of fluidity of cement mortar.

This method is applicable to the determination of mortar fluidity of volcanic ash Portland cement, composite Portland cement, ordinary Portland cement mixed with volcanic ash, slag Portland cement and other types of cement designated to use this method.

2. Reference standards

GB177 Cement mortar strength test method

GB178 Standard sand for cement strength test

JBW 01-1-1 Standard sample for fluidity of cement mortar

3. The detection method of water reduction rate of mortar is as follows:

3.1 Instruments and equipment

A. Mortar mixer;

B. Jump table (5mm thick glass plate must be added);

C. Cylindrical ramming bar: made of metal material, diameter 20mm, length about 185mm;

D. truncated cone circular mold and mold cover: truncated cone circular mold size, height is 60±0.5mm, upper diameter φ 70±0.5mm, lower diameter 100±0.5mm, the mold cover must be matched with truncated cone circular mold, truncated cone mold and mold cover made of metal materials;

E. Ruler (measuring range 300mm) or calipers with measuring range 300mm;

F. spatula.

G. Drug balance (weighing 1000g, sensing 1g).

3.2. Test procedure

3.2.1 Measure the water consumption of reference mortar

A. Weigh 300g cement and 750g standard sand and pour them into a mixing pot, start the mixer, add water slowly after mixing for 5s, and add them within 30s. Stop stirring for 3min after starting the machine. Scrape the mortar off the blades and remove the stirring pan.

B. In mixing mortar at the same time, with wet cloth wipe jump table table, ramming rod, cut cone round mold and mold cover inner wall, and put them in the center of the glass plate, covered with wet cloth.

C. The mixed mortar is quickly divided into two layers into the mold, the first layer is installed to the cone mold about two-thirds high, with the ramming bar from the edge to the center evenly inserted ramming fifteen times, then loaded with the second layer of mortar, installed to about two centimeters higher than the round mold, the same cylindrical rod ramming fifteen times. When loading sand and ramming, press the truncate cone die by hand to avoid movement.

D. After tamping, take off the mold cover, use a spatula to scrape off the mortar which is higher than the truncated cone circular mold and wipe it flat, then gently lift the circular mold vertically upward. Shake hands with the crank of the wheel to make the jumping table jump thirty times at a rate of one per second.

E. After beating, use calipers to measure the diffusion diameter of mortar bottom, and take the average value of two diameters perpendicular to each other as the diffusion of mortar when the water is used, expressed in mm. When mortar reference diffusivity is 140±5mm, water consumption is the water consumption of reference mortar diffusivity.

3.2.2 According to 3.2.1 method, the water consumption of mortar with water-reducing agent reached 140±5mm.

3.3. The water reduction rate of treated mortar is calculated as follows:

Water reduction rate of mortar (%) = (W0-W1)/ W0 ×100

Where, w0 — water consumption (g) when the diffusion of reference mortar is 140±5mm;

W1 — Water consumption (g) when the diffusion of mortar with water-reducing agent is 140±5mm.

The value of water reduction rate is the arithmetic mean value of three samples.

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