Rigid and flexible waterproofing for the underground garage of the residential complex

The information is sourced from the Internet and is provided for educational purposes only: Abstract: The waterproofing of the basement in Changfu Home in Fuzhou employs a construction technique that combines self-waterproofing of the concrete structure with waterproofing using SBS polymer-modified asphalt sheets applied to the exterior walls. This article mainly discusses the construction methods for waterproof concrete, sheet-based waterproofing, as well as those related to pipes passing through walls and construction joints. Keywords: basement waterproofing, self-waterproofing concrete, membrane waterproofing. The Changfu Home in Fuzhou features a reinforced concrete frame structure with box foundations; its building plan is rectangular, with 9 floors above ground and 1 floor below ground. The area of the basement is 5,100 m2. The groundwater level within the site is approximately 2.0 meters below the surface, belonging to the category of upper phreatic water, which is mainly present in the fill soil. Its sources of recharge are surface water and rainwater. The waterproofing design grade for this project is level 2, and a waterproofing system that combines rigid and flexible waterproofing methods is employed. The floor slab and exterior walls utilize a concrete structure with inherent waterproofing properties, with the concrete’s impermeability grade specified as S6 ； The exterior wall employs a waterproofing system that combines rigid and flexible waterproofing methods. The flexible waterproofing layer consists of 4 mm thick SBS polymer-modified asphalt waterproofing membranes. For pipes passing through the wall, full welding of water-stop rings along with steel plate sealing is used for waterproofing; at construction joints, steel plate water-stop strips and rubber water-stop strips are utilized. 1 Construction of waterproof concrete in the basement 1.1 Concrete mix ratio 1.1.1 Ordinary Portland cement with a strength of 42.5 MPa is used in this project, with a cement consumption of 388 kg/M3. 1.1.2 The sand used is medium-grained sand with a fineness modulus of 2.3, a silt content of less than 3%, and a clay content of less than 2%. 1.1.3 The stones shall be crushed stones with a particle size of 5–35 mm, a mud content of 0.5%, and a clay lump content of 0.4%. 1.1.4 The admixture used is EC-l high-efficiency waterproofing agent, at a dosage of 3% of the cement amount. 1.1.5 To reduce the heat of cement hydration, an appropriate amount of fly ash with a grade of not lower than Grade 2 is added; in this project, the amount of fly ash used is 12% of the amount of cement used. 1.2 Concrete construction techniques 1.2.1 Concrete for the basement floor The concrete used for the basement floor is involved in large-scale construction over large areas; for this project, the construction method of \"segmenting the work area, using a single slope, pouring in thin layers, progressing step by step, and completing the work in one go\" is adopted. This method can adapt well to the pumping process, avoid frequent disassembly of the concrete delivery pipes, improve pumping efficiency, simplify the treatment of concrete segregation, and ensure that the concrete in the upper and lower layers does not exceed the setting time. 1.2.2 When pouring the wall concrete, it is necessary to strictly control the thickness of each layer; the thickness of each pour should be around 0.5 m, and the length of the wall that can be poured in one go should not exceed 30 m. Continuity must be ensured during pouring. 1.3 Quality assurance measures 1.3.1 Mix proportion control The concrete strength for the base slab and exterior walls of this project is specified as C35; ordinary Portland cement is used, with a strength of 42.5 MPa ； In this project, the maximum particle size of the gravel is limited to 35 mm, with a water absorption rate not exceeding 1.5% ； Medium-grit sand is used, with a sand ratio of 38% ； To reduce the heat of cement hydration, the water-cement ratio was controlled at 0.45. 1.3.2 Concrete slump: Commercial concrete will be used in this project, and it is necessary to strictly control the workability of the concrete; low-slump concrete should be employed, with the actual on-site measured slump value to be within (120 ± 20) mm ； If segregation occurs after the concrete is delivered to the site, it must be returned to the mixing plant for re-mixing ； When the concrete slump does not meet the requirements, cement slurry with the original water-cement ratio or an additional water reducer should be added and mixed; adding water directly is strictly prohibited. 1.3.3 During concrete pouring, it is necessary to ensure reasonable sectional and layered construction; the thickness of each layer should be 0.3m, and the interval between the joints of different layers must not exceed 2 hours. The temporary vertical joints created during construction should be arranged in such a way that they are offset from one another. 1.3.4 Concrete vibration: Based on the natural slope that forms during pump-driven pouring, two vibrators are placed before and after each pouring zone. The front vibrators are placed at the bottom row of rebar and at the foot of the concrete slope to ensure compactness in the lower part of the concrete ； The post-process vibrator is placed at the concrete discharge point to ensure the compaction of the upper layer of concrete. 1.3.5 High-frequency mechanical vibration must be used during the construction of waterproof concrete, with strict control over the vibration interval and duration. For each vibration point, the vibrating time should be such that the concrete is compacted to the point where the surface shows only a thin layer of slurry, no bubbles appear, and further settlement ceases; the vibrating time should be 20–30 seconds, in order to avoid insufficient vibration, inadequate vibration, or excessive vibration. 1.3.6 Treatment of concrete bleeding: During the pouring and vibration of large-volume, highly fluid concrete, the bleeding water and floating slurry that rise to the surface flow down along the slope of the concrete to the bottom of the pit, and move forward together with the concrete. When setting up the formwork, holes should be left at the bottom of the formwork on both sides in the pouring direction to allow excess water and slurry to drain out. When the concrete at the foot of the slope approaches the formwork at the end, the direction of concrete pouring must be changed immediately, with pouring done from the end backwards. Additionally, pouring of concrete on both sides should be intensified so that the final pouring forms a convergence from all four sides, thereby allowing excess water and slurry to be removed more effectively. 1.3.7 Surface treatment of concrete: In the case of mass-poured concrete, after removing excess water and slurry, a thick layer of cement slurry remains on the surface. 4–5 hours after pouring, this surface should be leveled using a long straightedge. Before the concrete begins to set, it should be rolled back and forth several times with a roller. As the concrete gets close to its final setting stage, it should be polished once more with a wooden tool in order to close any cracks that may have formed. 1.3.8 Concrete curing: Due to the large temperature difference between the interior and exterior of mass concrete, proper curing is essential. The temperature during the pouring of this project was as high as 35 degrees. Only perform moisturizing care. Watering maintenance should be employed along with the use of plastic film to prevent water evaporation from the concrete and surface dehydration, which could lead to shrinkage cracks; the maintenance period should be no less than 14 days. There are basically two methods for applying waterproof membranes made of 2SBS polymer-modified asphalt in basement areas: the external application method and the internal application method. This project adopts the external application method: after the construction of the wall enclosure structure is completed, the vertical membrane waterproofing layer is directly applied to the outer surface of the enclosure structure, followed by the implementation of protective measures. 2.1 Construction process flow: Inspection and cleaning of the substrate, application of a substrate treatment agent, additional reinforcement for detailed structures (joints), marking with string lines for layout, laying of the waterproof membrane, sealing of edges and handling of detailed structures (joints), inspection for sealing, trimming, and application of the protective layer. 2.2 Key construction techniques: 2.2.1 Before starting construction, the substrate must be cleaned thoroughly. When applying the substrate treatment agent, the substrate should be flat, solid, clean, and dry. The substrate treatment agent should be compatible with the properties of the membrane, and it should be applied evenly. 2.2.2 After the surface preparation is dried, additional waterproofing layers should be applied to areas with special requirements as specified in the design; for example, corners should be made into arcs or at a 135-degree angle. (45. ) Fold it over and attach 1–2 layers of sheeting with the same material, with a width of not less than 500 mm. 2.2.3 The laying of membrane sheets is carried out using the full-adhesion hot-melt method, that is, a construction technique in which a torch is used to melt the hot-melt adhesive on the bottom surface of the membrane sheets for bonding. During construction, the distance between the flame nozzle and the bottom surface of the membrane should be appropriate; heating should be uniform across the entire width, until the asphalt on the bottom surface of the membrane melts and becomes shiny. Overheating or burning through the membrane must be avoided. Once the asphalt on the bottom surface has melted, the membrane should be rolled out immediately, followed by air removal, rolling, and bonding. The edges of the seam should be sealed using a spade, and then the area should be heated evenly and thoroughly with a flame. 2.2.4 When laying the membrane, start with the horizontal surfaces first and then move on to the vertical surfaces; the joints should overlap at right angles. Where it transitions from the horizontal surface to the vertical surface, it should be temporarily attached to that wall or to the formwork. 2.2.5 After the enclosure structure is completed, and before laying the membrane on the vertical wall surfaces, the joints of the membranes in each layer within the temporary protective wall section should be separated, and their surfaces cleaned thoroughly. If there is local damage to the membrane, it must be repaired before work can proceed. When laying the membrane, full-adhesion installation must be used. 2.2.6 After the membrane waterproofing layer has passed the inspection, a protective layer should be applied promptly. The thickness of the fine aggregate concrete protective layer for the waterproofing layer on the bottom slab should not be less than 50 mm, while the waterproofing layer on the side walls is covered with a protective layer of 20 mm thick cement mortar in a 1:3 ratio. 2.3 Quality assurance measures 2.3.1 Material requirements SBS polymer-modified asphalt waterproofing membranes should possess good water resistance, durability, puncture resistance, and corrosion resistance. The thickness of the waterproof layer should not be less than 3 mm; when used as a single layer, the thickness should not be less than 4 mm ； When used in two layers, the total thickness shall be no less than 6 mm. 2.3.2 Construction requirements: (1) The overlap width of the long sides of the membrane on the basement floor slab shall be not less than 100 mm, and the overlap width of the short sides shall be not less than 150 mm. (2) When laying two adjacent sheets on the same layer, the overlapping portion of their short sides should be offset by more than 1500 mm. The upper and lower layers of roofing material must not be laid vertically, and the overlap seams should be spaced at least 1/3 of the width apart. (3) When laying double-layer membranes on the side walls of the basement to extend them, cross-seam joining should be used, with the seam of the upper layer overlapping the lower layer by more than 150 mm. (4) At the corners where the elevation meets the plan, the seams of the membrane should be located on the plan, at a distance of not less than 600 mm from the elevation. 3 Detailed construction (node) treatment 3.1 Pipes passing through walls 3.1.1 Construction treatment (1) When the structural deformation or the expansion/contraction amount of the pipes is small, fixed waterproofing methods involving embedding the pipes directly in concrete can be used; the main pipe should have a water-stop ring welded around it completely. (2) When the structural deformation or pipe expansion/contraction is significant, or when replacement is required, a sleeve-type waterproofing method should be employed, with the sleeve and the water-stop ring being fully welded together. (3) When there are many and dense pipes passing through the wall, it is advisable to concentrate them relatively, using wall penetration boxes; the sealing steel plate of the box should be welded tightly to the embedded angle steel in the wall, and sealing material should be injected through the pouring holes in the steel plate. 3.1.2 Quality assurance measures: (1) The positions of various pipes passing through walls and embedded components must be determined accurately; such pipes and components should be installed before concrete is poured. (2) The distance between wall-penetrating pipes and interior wall corners sowie uneven surfaces shall be no less than 250 mm. (3) The metal water-stop ring shall be fully welded and sealed to the main pipe. When a sleeve-type pipe for passing through walls is used for waterproofing, the wing ring and the sleeve shall also be fully welded and sealed, and the inner surface of the sleeve shall be cleaned thoroughly before construction. 3.2 Construction Joints 3.2.1 Structural Treatment (1) For horizontal construction joints, such as those between the floor slab and the exterior walls, a steel water-stop strip with a width of 200 mm should be installed at the joint. (2) For vertical construction joints, those between exterior walls, a vertical steel water-stop strip with a height equal to that of the wall and a width of 200 mm can be installed at the joint. 3.2.2 Quality assurance measures (1) The construction of waterproof concrete should ensure continuous pouring, with as few construction joints as possible. When retention is necessary, horizontal construction joints in the wall should not be placed at the points where shear and bending forces are greatest, or at the junction of the base slab and the side walls; instead, they should be located on the wall at a height of not less than 300 mm above the surface of the base slab ； When the wall has pre-existing holes, the construction joint should be at least 300 mm away from the edge of the hole. Vertical construction joints should be avoided in areas with high levels of groundwater and fissure water, and they should be combined with intersecting joints. (2) When pouring concrete for horizontal construction joints, the surface scum and debris should be removed first; a layer of clean paste should be applied, followed by a 30–50 mm thick layer of 1:1 cement mortar, or a concrete interface treatment agent should be applied, after which the concrete should be poured promptly. (3) When pouring concrete for vertical construction joints, their surfaces should be cleaned thoroughly, a concrete interface treatment agent should be applied, and the concrete should be poured promptly. (4) When using water-swelling rubber putty seal strips for construction joints, the seal strips must be firmly installed in the grooves prepared on the surface of the joint.