Prestressed channel grouting, prestressed post tensioning construction, requirements for grouting

After the prestress tension, the cement slurry is pressed into the prestressed tendon hole by grouting. The grouting pump is used to press the cement slurry into the prestressed tendon hole, so that it fills the gap between the prestressed steel strand and the hole, so that the prestressed steel strand and the concrete are firmly bonded as a whole.

Construction process: preparation before grouting work.

Flush the orifice. The hole should be flushed with pressure water before grouting to eliminate the powder and slag and other debris in the hole, ensure that the hole is unblocked, and blow off the water in the hole with an air compressor after washing, but to keep the hole moist and make the cement slurry and the hole wall well combined, in the washing process, if there is water and leakage, the hole should be plugged in time for treatment.

Cement slurry mixing.

The cement slurry should have sufficient fluidity, and the fluidity of 150-200mm can meet the grouting requirements.

The water used for water mortar should be clean water, free of substances harmful to cement or prestressed steel strands, and each liter of water should not contain more than 500mg of chloride ions.

Admixture: In order to prevent the volume shrinkage of the cement slurry in the pores, the infiltration of the expansion agent (aluminum powder) into the cement slurry The infiltration of aluminum powder is the amount of cement, or the infiltration of UEA expansion agent, the infiltration of UEA is 10%-12% of the cement amount.

Mixing of cement slurry:

The mix ratio of cement slurry is determined by trial matching before mixing, and can also be determined according to the previous mix ratio re-inspection. For the mixing of cement slurry, first add water to the mixer, start the mixer, and then add cement and expansion agent, and the material measurement should be based on the weight of cement to calculate the amount of water and admixture. The mixing time should ensure that the cement slurry is mixed evenly, generally it takes about 3min, in the grouting process, the mixing of the cement slurry should be uninterrupted, when the grouting process is stopped for a short time, the cement slurry should be circulated in the mixer and grouting machine to prevent the blockage of the pipeline and the switch valve after precipitation.

Main technical indicators of cement slurry:

The water-cement ratio is. The water secretion rate was controlled at 2% for 3 hours after the cement slurry was mixed, and all the water secretion was absorbed by the slurry within 24 hours.

The cement slurry is mixed with expansion agent, and its free expansion rate should be less than 10%.

The consistency of the cement slurry is controlled between 14-18s.

There should be no chloride ions or any other organic matter of more than 500mg per litre of water.

First of all, the strength should be high, and secondly, the liquidity should be good.

Prestressed post-tensioning construction, requirements for grouting:

1. The channel grouting is mixed with ordinary Portland cement and water. The quality of the cement should be in accordance with the provisions of the General Portland Cement (GB175).

2. The water-cement ratio of cement mortar for grouting is generally not greater. After stirring, the water secretion rate should not be greater than 1, and the water should be able to be fully absorbed by the cement slurry within 24 hours. The free expansion rate should not be greater than 10.

3. High-performance admixtures should be mixed into cement slurry. It is strictly forbidden to mix with various chloride-containing salts or admixtures that have a corrosive effect on prestressed tendons. After being mixed with admixtures, the water-cement ratio of cement slurry can be reduced to.

Ideal grout material:

1. Early strength, high strength: the strength can reach more than 60MPa a day, and the equipment can be operated and produced one day after installation.

2. Self-flowing state: only need to add water and stir on site, and then directly pour into the equipment foundation, and fill all the gaps of the equipment foundation without vibration.

3. Micro-expansion: to ensure close contact between the equipment and the foundation.

4. No rust effect: no rust hazard to steel bars, steel plates, etc.

5. Anti-oil seepage: after soaking in oil for 30 days, its strength is more than 10% higher than that before oil immersion.

6. Durability: 30 fatigue tests, 50 freeze-thaw cycle tests with no obvious change in intensity.

7. Good weather resistance - 40 600 long-term safe use.

1. After the tensioning of the prestressed tendon is completed and passed the inspection, the hole grouting should be carried out in time, and the cement slurry in the hole should be full and dense.

2, the exposed part after the anchorage of the post-tensioned prestressed tendon should be cut by mechanical method, and can also be cut by the oxyacetylene flame method, and its exposed length should not be less than the times of the diameter of the prestressed tendon, and should not be less than 30mm.

3. The following preparations should be carried out before grouting:

It should be confirmed that the orifice, exhaust and drainage pipes and grouting holes are unblocked; For the forming hole of the embedded pipe, compressed air can be used to clean the hole; The excess prestressed tendons outside the anchor should be removed, and cement slurry and other materials should be used to seal the anchor clamp gaps and other possible slurry leakage, and the anchor cover can also be used to close the end anchor; When using the vacuum grouting process, the tightness of the orifice should be confirmed.

2 is wrong, do you think it is appropriate from the perspective of practical life alone, not from the technical aspect? The grouting at both ends will be that the air in the hole is not easy to exclude, which will cause the paddles on both sides to be unable to bond and leak ribs; and so on, there is no point in doing so.

1. The function of post-tensioning channel grouting is to protect the prestressed steel bar and make the prestressed steel bar effectively bonded with the concrete.

2. Requirements for grouting materials:

1) Conveying grouting is mixed with water with ordinary Portland cement. The quality of cement should be in accordance with the provisions of "Ordinary Portland Cement" (GB175).

2) The water-cement ratio of cement mortar used for grouting is generally not greater than 0 4. After stirring, the oil yield should not exceed 1, and the oil output should be completely reabsorbed by the cement slurry within 24h. The free expansion rate should not be greater than 10.

3) Cement slurry should be mixed with high-performance admixtures. It is strictly forbidden to add any additives containing chloride salts or corrosive to the prestressed tendons. After adding admixtures, the cement-water ratio can be reduced to 0 35 0 38.

4) The filling capacity of the cement slurry is controlled by the fluidity: the diameter is not less than 150mm in the flow method, and the diameter is 12 18s in the flow cone method.

5) The cement slurry should be mechanically stirred, and the grouting material should be stirred evenly. During the grouting process, it should be stirred constantly to prevent precipitation of water secretion. When the retention time of cement slurry is too long and segregated, secondary grouting should be carried out.

3. The grouting hole can be arranged on the anchor plate or guided to the outside of the component by the grouting plate pipe. The spacing of the core-pulling forming holes should not be greater than 12m, and the hole diameter should ensure that the slurry is smooth and should not be less than 20mm. At the peak of the curve, there is an exhaust pipe and a vent pipe.

If necessary, a drainage hole can be set at the lowest point. The height of the top surface of the drainage pipe suspension member should not be less than 0 5m.

The grouting function is to transfer the stress of the steel strand to the beam body and protect the steel strand from corrosion.

The grouting operation is in accordance with the requirements of the specification, first of all, the ratio of the grout, the pressure of the grouting, and the cleaning of the hole before grouting the grouting operation.

Nothing special!

Answer]: a, b, c, e

Textbook, pp. p73-p76

The post-tensioning method prestressed channel grouting should be made of ordinary Portland cement or cement prepared by slag Portland cement that has been tested to meet the requirements; For pores with large voids, cement mortar can be used for grouting. The strength of cement slurry and cement mortar shall not be less than 20MPa.

The water-cement ratio of cement slurry for grouting is not greater than 045. The water secretion rate should be within 2% for 3 hours after stirring, and the maximum maximum should not exceed 3%.

The grouting should be carried out slowly and evenly without interruption, and exhaust channels should be set.

When the cement slurry or cement mortar strength in the channel does not meet the design requirements, the components shall not be moved, the main reinforcement hole shall be cut, and the anchor shall be dismantled.

During the grouting process and 48h after grouting the structure, the structural temperature shall not be lower than 5. Otherwise, thermal insulation measures should be taken.

<> What are the key points of grouting construction of prestressed hole of reinforced concrete cap beam?

After the completion of prestress tensioning, grouting should be carried out in time, and generally should not exceed 14d

The prestressed tendon cutting should be done with a portable grinding wheel cutting machine, and it is strictly forbidden to use electric welding or oxygen-acetylene cutting.

The strength of the cement slurry should be in line with the design regulations, when there are no specific provisions in the design, it should not be less than 30MPa, and the cement slurry can be mixed with an appropriate amount of fine sand for the hole with a larger cross-section; Portland cement or ordinary cement should be used for cement, and its strength grade should not be lower than the grade.

The water-cement ratio of cement slurry should be reduced, and when an appropriate amount of superplasticizer is added, the water-cement ratio can be reduced to.

The maximum water leakage rate of cement slurry shall not exceed 3%, and the water leakage rate should be controlled at 2% for 3 hours after mixing, and the water should be re-absorbed by the slurry within 24 hours.

After passing the test, the cement slurry can be mixed with an appropriate amount of expansion agent, but its free expansion rate should be less than 10%.

The consistency of cement slurry should be controlled between 14 and 18s.

If there may be oil and other dirt in the hole, the neutral washing liquid or soap solution that does not corrode the prestressed tendon and the hole can be diluted with water, and then the water can be washed out with compressed air without oil.

When grouting with ballast spike, the curved hole should be pressed from the grouting hole at the lowest point, and the exhaust hole at the highest point should be used to exhaust and leak water; When there are multiple layers in the channel, the grouting sequence should be pressed into the lower pipe first.

The grout should be pressed into the grouting hole and should reach the other end of the hole until the slurry with the same consistency as the specified consistency flows out of the exhaust hole.

The grouting should be carried out slowly and evenly, without interruption and should be vented smoothly, and the exhaust hole and grouting hole should be closed after the hole is filled.

For cement slurry without expansion agent, it is advisable to use secondary grouting to improve the compactness of the grouting after the first grouting interval of about 30min and then carry out secondary grouting by the other end.

When the temperature is higher than 30, the hole grouting should be carried out at night.

When grouting is carried out, each team shall retain no less than 3 groups of cubic specimens, and shall be maintained and tested in accordance with relevant regulations.

Other requirements for channel grouting shall be implemented in the current "Technical Code for Highway Bridge and Culvert Construction" JTJ 041