【Daily Discussion】Utilities - Civil Engineering - 20210516

Hole grouting is an important step in the post-tensioning prestress process; it should be carried out immediately after the prestressing tendons have been tensioned. The purpose of grouting is to prevent steel reinforcement from rusting, enhance the integrity and durability of the structure, and improve its crack resistance and load-bearing capacity. The cement slurry used for grouting should have sufficient strength and adhesion, as well as good fluidity, low shrinkage, and low bleeding. The strength grade of cement should generally be no less than 42.5; the water-cement ratio should be maintained between 0.4 and 0.45. The bleeding rate within 3 hours after mixing should be controlled at 2%, with a maximum of 3%. The consistency of the cement paste should be between 14 and 18 seconds. For channels with larger pores, mortar grouting can be used. To increase the density of pore grouting and reduce the shrinkage of the cement slurry, 0.05%–0.1% defatted aluminum powder or other types of expansion agents can be added. Admixtures that do not cause corrosion to the prestressed tendons can be incorporated into the cement paste or mortar, such as calcium lignosulfonate at 0.25% of the cement mass, or aluminum powder at 0.05% of the cement mass. When no admixtures are used, the secondary grouting method can be employed. Before grouting, flush and moisten the holes with pressurized water. Grouting is carried out using an electric or manual grout pump. The grouting work must be carried out continuously without interruption, and measures must be taken to prevent air from entering the holes, as this could affect the quality of the grouting. The grouting pressure should be controlled at 0.3–0.5 MPa. The grouting sequence should be from bottom to top to prevent grout leakage from upper holes from blocking the lower ones. An exhaust hole should be provided at the end of the tunnel. During grouting, the exhaust hole can be sealed only after thick grout begins to flow out of it; thereafter, pressure can be increased to 0.5–0.6 MPa and maintained for 2 minutes. The control valve should then be closed to keep the pressure inside the tunnel. Each channel should be filled in one go without interruption; otherwise, the already poured cement slurry will be washed away, and filling must start over from the beginning. After grouting, cut the exposed portions of the prestressed steel strands (leaving 30–50 mm) and disperse them; the anchorages should be protected with concrete caps. The dimensions of the head concrete should be larger than those of the embedded steel plates, with a thickness of 100 mm or more; rebar mesh should be included within the head, and the strength grade of the fine aggregate concrete should be C30–C40. After channel grouting, the components can be moved only when the strength of the mortar reaches 15 N/mm2 ； Lifting is permitted only when the mortar strength reaches 100% of the design strength.

Protect the prestressed steel bars and ensure effective bonding between them and the concrete.

It prevents steel reinforcement from rusting, enhances the integrity and durability of the structure, and improves its crack resistance and load-bearing capacity.

Hole grouting is an important step in the post-tensioning prestress process; it should be carried out immediately after the prestressing tendons have been tensioned. The purpose of grouting is to prevent rusting of the rebar and to enhance the integrity and durability of the structure.

Hole grouting is an important step in the post-tensioning prestress process; it should be carried out immediately after the prestress tendons have been tensioned. The purpose of grouting is to prevent steel reinforcement from rusting, enhance the integrity and durability of the structure, and improve its crack resistance and load-bearing capacity.

Hole grouting is an important step in the post-tensioning prestress process; it should be carried out immediately after the prestressing tendons have been tensioned. The purpose of grouting is to prevent steel reinforcement from rusting, enhance the integrity and durability of the structure, and improve its crack resistance and load-bearing capacity. The cement slurry used for grouting should have sufficient strength and adhesion, as well as good fluidity, low shrinkage, and low bleeding. The strength grade of cement should generally be no less than 42.5; the water-cement ratio should be maintained between 0.4 and 0.45. The bleeding rate within 3 hours after mixing should be controlled at 2%, with a maximum of 3%. The consistency of the cement paste should be between 14 and 18 seconds. For channels with larger pores, mortar grouting can be used. To increase the density of pore grouting and reduce the shrinkage of the cement slurry, 0.05%–0.1% defatted aluminum powder or other types of expansion agents can be added. Admixtures that do not cause corrosion to the prestressed tendons can be incorporated into the cement paste or mortar, such as calcium lignosulfonate at 0.25% of the cement mass, or aluminum powder at 0.05% of the cement mass. When no admixtures are used, the secondary grouting method can be employed. Before grouting, flush and moisten the holes with pressurized water. Grouting is carried out using an electric or manual grout pump. The grouting work must be carried out continuously without interruption, and measures must be taken to prevent air from entering the holes, as this could affect the quality of the grouting. The grouting pressure should be controlled at 0.3–0.5 MPa. The grouting sequence should be from bottom to top to prevent grout leakage from upper holes from blocking the lower ones. An exhaust hole should be provided at the end of the tunnel. During grouting, the exhaust hole can be sealed only after thick grout begins to flow out of it; thereafter, pressure can be increased to 0.5–0.6 MPa and maintained for 2 minutes. The control valve should then be closed to keep the pressure inside the tunnel. Each channel should be filled in one go without interruption; otherwise, the already poured cement slurry will be washed away, and filling must start over from the beginning. After grouting, cut the exposed portions of the prestressed steel strands (leaving 30–50 mm) and disperse them; the anchorages should be protected with concrete caps. The dimensions of the head concrete should be larger than those of the embedded steel plates, with a thickness of 100 mm or more; rebar mesh should be included within the head, and the strength grade of the fine aggregate concrete should be C30–C40. After channel grouting, the components can be moved only when the strength of the mortar reaches 15 N/mm2 ； Lifting is permitted only when the mortar strength reaches 100% of the design strength.

Hole grouting is an important step in the post-tensioning prestress process; it should be carried out immediately after the prestressing tendons have been tensioned. The purpose of grouting is to prevent steel reinforcement from rusting, enhance the integrity and durability of the structure, and improve its crack resistance and load-bearing capacity. The cement slurry used for grouting should have sufficient strength and adhesion, as well as good fluidity, low shrinkage, and low bleeding. The strength grade of cement should generally be no less than 42.5; the water-cement ratio should be maintained between 0.4 and 0.45. The bleeding rate within 3 hours after mixing should be controlled at 2%, with a maximum of 3%. The consistency of the cement paste should be between 14 and 18 seconds. For channels with larger pores, mortar grouting can be used. To increase the density of pore grouting and reduce the shrinkage of the cement slurry, 0.05%–0.1% defatted aluminum powder or other types of expansion agents can be added. Admixtures that do not cause corrosion to the prestressed tendons can be incorporated into the cement paste or mortar, such as calcium lignosulfonate at 0.25% of the cement mass, or aluminum powder at 0.05% of the cement mass. When no admixtures are used, the secondary grouting method can be employed. Before grouting, flush and moisten the holes with pressurized water. Grouting is carried out using an electric or manual grout pump. The grouting work must be carried out continuously without interruption, and measures must be taken to prevent air from entering the holes, as this could affect the quality of the grouting. The grouting pressure should be controlled at 0.3–0.5 MPa. The grouting sequence should be from bottom to top to prevent grout leakage from upper holes from blocking the lower ones. An exhaust hole should be provided at the end of the tunnel. During grouting, the exhaust hole can be sealed only after thick grout begins to flow out of it; thereafter, pressure can be increased to 0.5–0.6 MPa and maintained for 2 minutes. The control valve should then be closed to keep the pressure inside the tunnel. Each channel should be filled in one go without interruption; otherwise, the already poured cement slurry will be washed away, and filling must start over from the beginning. After grouting, cut the exposed portions of the prestressed steel strands (leaving 30–50 mm) and disperse them; the anchorages should be protected with concrete caps. The dimensions of the head concrete should be larger than those of the embedded steel plates, with a thickness of 100 mm or more; rebar mesh should be included within the head, and the strength grade of the fine aggregate concrete should be C30–C40. After channel grouting, the components can be moved only when the strength of the mortar reaches 15 N/mm2 ； Lifting is permitted only when the mortar strength reaches 100% of the design strength.

Hole grouting is an important step in the post-tensioning prestress process; it should be carried out immediately after the prestress tendons have been tensioned. The purpose of grouting is to prevent steel reinforcement from rusting, enhance the integrity and durability of the structure, and improve its crack resistance and load-bearing capacity.

It prevents steel reinforcement from rusting, enhances the integrity and durability of the structure, and improves its crack resistance and load-bearing capacity.

Hole grouting is an important step in the post-tensioning prestress process; it should be carried out immediately after the prestressing tendons have been tensioned. The purpose of grouting is to prevent steel reinforcement from rusting, enhance the integrity and durability of the structure, and improve its crack resistance and load-bearing capacity. The cement slurry used for grouting should have sufficient strength and adhesion, as well as good fluidity, low shrinkage, and low bleeding. The strength grade of cement should generally be no less than 42.5; the water-cement ratio should be maintained between 0.4 and 0.45. The bleeding rate within 3 hours after mixing should be controlled at 2%, with a maximum of 3%. The consistency of the cement paste should be between 14 and 18 seconds. For channels with larger pores, mortar grouting can be used. To increase the density of pore grouting and reduce the shrinkage of the cement slurry, 0.05%–0.1% defatted aluminum powder or other types of expansion agents can be added. Admixtures that do not cause corrosion to the prestressed tendons can be incorporated into the cement paste or mortar, such as calcium lignosulfonate at 0.25% of the cement mass, or aluminum powder at 0.05% of the cement mass. When no admixtures are used, the secondary grouting method can be employed. Before grouting, flush and moisten the holes with pressurized water. Grouting is carried out using an electric or manual grout pump. The grouting work must be carried out continuously without interruption, and measures must be taken to prevent air from entering the holes, as this could affect the quality of the grouting. The grouting pressure should be controlled at 0.3–0.5 MPa. The grouting sequence should be from bottom to top to prevent grout leakage from upper holes from blocking the lower ones. An exhaust hole should be provided at the end of the tunnel. During grouting, the exhaust hole can be sealed only after thick grout begins to flow out of it; thereafter, pressure can be increased to 0.5–0.6 MPa and maintained for 2 minutes. The control valve should then be closed to keep the pressure inside the tunnel. Each channel should be filled in one go without interruption; otherwise, the already poured cement slurry will be washed away, and filling must start over from the beginning. After grouting, cut the exposed portions of the prestressed steel strands (leaving 30–50 mm) and disperse them; the anchorages should be protected with concrete caps. The dimensions of the head concrete should be larger than those of the embedded steel plates, with a thickness of 100 mm or more; rebar mesh should be included within the head, and the strength grade of the fine aggregate concrete should be C30–C40. After channel grouting, the components can be moved only when the strength of the mortar reaches 15 N/mm2 ； Lifting is permitted only when the mortar strength reaches 100% of the design strength.