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Abstract: This paper introduces several chemical grouting materials with excellent performance, and illustrates through several typical engineering examples the comprehensive application of chemical grouting technology in building waterproofing and leakage sealing projects. Keywords: Chemical grouting; Building engineering; Seepage prevention and leakage sealing. Chemical grouting is one of the methods used for building waterproofing and leakage sealing. High-performance chemical grouting materials and reasonable and feasible construction grouting methods are the key to achieving chemical grouting for waterproofing and leak sealing. 1 Introduction to several chemical grouting materials 1.1 Cement-silica gel grouting material This material has a setting strength of 0.5–15 MPa, a setting rate of 98%–100%, and a gelation time of 30–120 seconds. It features low costs and good adaptability, is particularly suitable for dealing with sudden leaks as well as mud and sand, has a high slurry filling rate, and exhibits good durability in wet conditions. The characteristics of its slurry are as follows: ① The gelation time of the slurry can be accurately controlled within the range of a few seconds to several dozen minutes ； ②The compressive strength of the stone mass can reach 10–20 MPa ； ③The stone rate was 100% ； ④The permeability coefficient of the stone mass is 10-8 cm/s ； ⑤Suitable for use in sand layers with cracks larger than 0.2 mm and particle sizes larger than 1 mm ； ⑥The materials are readily available and inexpensive. 1.2 Sinochem-656 (acrylate) grout – This material is widely used to seal leaks of water and oil in various types of concrete. It features a low initial viscosity of the slurry, good pourability, and a curing time that can be adjusted arbitrarily from two seconds to several minutes, or even hours. The impermeability of the compacted material is k＜10-8cm/s, and its resistance to extrusion is 35kg/cm2 ； The compressive strength of the sand consolidation body is 3–8 kg/cm2, and the initial viscosity of the slurry at 25°C is 1.2–1.6 cp. This pulp won an award at the National Science Conference. 1.3 Modified epoxy resin paste This material has a wide range of applications, is relatively inexpensive, its strength, viscosity, and curing time can be adjusted, and it possesses good mechanical properties. The compressive strength ranges from 700 to 1200 kg/cm2, the tensile strength from 70 to 300 kg/cm2, and the flexural strength from 300 to 850 kg/cm2. The splitting bond strength is 19–31 kg/cm2 for dry cracks and 13–19 kg/cm2 for cracks with moisture. The initial viscosity of the paste at 25°C is 6–150 cp. This pulp won an award at the National Science Conference. 2 Process flow and effectiveness testing methods for seepage prevention and leakage repair in construction projects 2.1 Process flow (1) Water detection: Drain water from damp and water-accumulated areas and wipe them dry with cotton yarn; identify the cracks where water is leaking (expansion joints, contact joints, settlement joints, construction joints, stress joints, structural joints, post-cast strip joints, etc.), as well as other areas where water leaks or seeps through, such as holes, cavities in the concrete, and sand holes. (2) Grooving: U-shaped grooves are cut around the seams or spots; generally, the depth of these grooves should be 2–10 cm deep within the concrete, in addition to the thickness of the mortar protective layer ； In principle, the groove width is determined by removing the soft and leaky concrete; the standard width of such grooves (spots) ranges from 5.0 to 30 cm. (3) Cleaning: Remove the residues from the new tank and wipe it clean with dry cotton yarn; no silt or standing water should remain. (4) Pipe embedding: A piece of aluminum pipe of a certain length is placed vertically at the location of the leak hole; small gravel or cotton yarn is then placed around it. The pipe is sealed in its groove using cement-silica solution, and finally, a waterproof concrete mortar is used to cover and level the surface. (5) Grouting: Adjust parameters such as viscosity, hardness, and setting time according to the project requirements, and use a hand pump to force the grout into the structure to be grouted through the grouting nozzle. (6) Sealing: For grouting pipes that meet the grouting requirements, the part of the aluminum pipe that protrudes above the base surface must be cut off, the pipe end must be clamped with pliers, and then surface repair work must be carried out. 2.2 Effect Detection Methods (1) Casing cap inspection method. Approximately 12 hours after burying the aluminum tube, cover it with a rubber hose, then secure the hose in place using thin iron wire to prevent water leakage; this allows for an inspection of the quality of the buried tube. (2) Sensory examination method. 24 hours after grouting, the dryness of the grouted area can be visually inspected or felt by hand, allowing for a qualitative assessment of the quality of the grouting. 3 Comprehensive Application of Chemical Grouting in Building Waterproofing and Leak Sealing Projects 3.1 Chemical Grouting for Leak Sealing of the Pond in the Rockery of Guangzhou Southern Theatre This project is located at the intersection of Xihu Road and Jiyu Road. Since the bottom of the rockery pond in the ornamental garden is 1.00 m below the ground level, there are multiple scattered springs that cause water to accumulate in large quantities, affecting the surrounding area. At the request of the hospital, Sinochem-656 was used as a water-blocking agent to keep the bottom of the rockery pond dry. Sinochem-656 is a chemical grouting material composed primarily of acrylamide, with methylenebisacrylamide as a crosslinking agent, along with other materials. Each component has excellent water solubility; it is a colorless and transparent true solution with very low viscosity, close to that of water, allowing it to penetrate into extremely small pores. Under the action of an oxidation-reduction initiation system, aqueous solutions can polymerize rapidly to form rigid gels with a three-dimensional polymer structure that are elastic and insoluble in water and common solvents. This rigid, continuous gel can seal off the pathways of water in the pores of soil and sand or in the fine cracks in rocks, preventing water from passing through. It also binds together loose soil and sand, thus serving both to prevent water infiltration and to strengthen the material. Typically, acrylamide grouting material is an aqueous solution with a concentration of 5% to 30%. This slurry has stable properties, and its two components can be stored separately for a long time. Adding potassium ferrocyanide to the slurry can delay the onset of coagulation and slow down the polymerization rate, with significant effects even at small amounts. The containers used for measuring components A and B as well as the slurry should not be shared, as this may alter the properties of the slurry or even render it unusable. The formula (mainly the slurry concentration, setting time, and amount of slurry used) is determined based on the results of on-site investigations (including the purpose of grouting, the soil properties at the grouting site, water flow, water quality, temperature, pressure, and the quality of raw materials), and then confirmed through formulation tests in the laboratory using the data collected on site. In this project, the slurry concentration is generally set at 10% (with the ratio of acrylamide to N,N’-methylenebisacrylamide fixed at 95:5; changing the concentration only alters their total content in water). In special cases, it may be appropriate to consider adjusting the slurry concentration. For individual spring sites with high water discharge rates, in order to counteract the dilution of the slurry by groundwater, it is necessary to increase the slurry concentration to 12%–15%, or even to 20% ； On the contrary, in fine crack points, the amount of slurry injected is very low due to the presence of saturated water, and this water is sufficient to dilute the slurry; therefore, it is also necessary to increase the concentration to 12%, and for particularly fine crack points, the concentration must be raised to 15%. The slurry is prepared in batches; for two-component systems, it is best to mix the two liquids in a 1:1 ratio and pour them simultaneously, carrying out the grouting work while mixing – this streamlining approach yields better results. Through random sampling tests, the compressive strength of the gel sand control bodies with 10% acrylamide concentration ranges from 0.2 to 0.8 MPa; they can withstand high hydrostatic pressures and exhibit good impermeability, with a permeability coefficient of 2×10-10 cm/s. Although both the slurry raw materials and the prepared slurry are somewhat toxic, posing a hazard to humans before gelation and being corrosive to metals, the dissolved metal ions also affect the properties of the slurry; however, they are basically harmless after gelation. At the same time, since slurries with a concentration higher than 5% (as concentrations below 5% do not allow gelation) form a translucent gel upon solidification, this gel is insoluble in solvents such as water, kerosene, and gasoline (no solvent capable of dissolving this gel has been found yet) ； Resistant to corrosion by dilute acids, gases, and fungi ； Once the gel dries, it can swell again when exposed to water; therefore, it can be considered a semi-permanent material. It can be used with confidence, as its quality is guaranteed and it has strong resistance to aging. 3.2 Chemical grouting for seepage prevention of the roof beams and slabs at the main factory building of Guangzhou Baihua Spice Factory This project is located in Fangcun; due to various reasons, multiple cracks have appeared in the roof beams and slabs, with some areas also showing honeycombing. It leaks when it rains, and it also causes weathering and corrosion of the rebar, affecting the load-bearing capacity of the building structure. Commissioned by the factory, chemical grouting was used for seepage prevention and reinforcement. Epoxy resins possess a series of advantages such as high strength, strong adhesion, good stability, and the ability to cure at room temperature, and are widely used in electrical insulation materials, reinforced plastics, coatings, adhesives, and electronic potting materials. Bisphenol A-type epoxy resins are generally used, with E-44 (6101) epoxy resin being the most common choice; fatty amines or modified amines such as T31 are used as curing agents. Since the viscosity of conventional epoxy resins is usually above 2000 centipoise, an appropriate diluent must be added in order to pour the slurry into small gaps. At the same time, due to reasons such as the brittle nature of epoxy resins after curing, tougheners, accelerators, and surfactants are usually added to accommodate various situations; this is why modified epoxy resin grouting materials are developed and used. In special geotechnical engineering, various special additives can be added to epoxy resin to endow the grout with properties such as high permeability and wettability, in order to meet the grouting requirements of special applications. For this project, the FYZ material and a furfural-propane dilution system are used. Since both furfural and propylene have low viscosities, adding them to epoxy gives the slurry good pourability, allowing it to be poured into water-containing cracks, and it is also inexpensive. Furfural and propylene oxide, upon the addition of a curing agent, form imines that slowly cure the epoxy resin; the free furfural and propylene oxide also gradually form their oligomers, which eventually result in furan resin. Thus, after the slurry cures, it becomes a composite system with the following characteristics: ① High strength, with a compressive strength of over 60 kg/cm2 ； Tensile strength of over 70 kg/cm2 ； The bending strength is over 250 kg/cm2. ②It has strong adhesion; it exhibits excellent bonding properties, especially with concrete, where the bonding strength in dry joints is over 17 kg/cm2 and in wet joints it is over 12 kg/cm2. ③It has good corrosion resistance and aging resistance. ④The compacted body has good impermeability. The construction procedure for this project is: (1) Cleaning the joints: Removing the plaster and protective layer until the structural layer is exposed. (2) Brushing and blowing: Use a wire brush to remove loose debris and silt, and use a high-pressure blower to eliminate dust. (3) Foundation liquid ； Permeation treatment is carried out using 1∶1 FYZ. (4) Grouting boxes: Use FYZ in a ratio of 1:1.75 to fill the grouting boxes, which are generally installed on the top surface at a rate of about 3 per meter. For individual thick beams, double-sided grouting is required; that is, an additional grouting box is placed on the bottom surface, positioned offset from the box on the top surface to create a staggered pattern, which facilitates even grouting. (5) Sealing: Use FYZ in a ratio of 1:1.75 for sealing; if there are seams on the bottom surface, an additional seam needs to be sealed as well. Generally, 2 to 3 small vents or drainage holes (?0.5–?1.0 cm) are left in each seam to facilitate grouting. (6) Grouting: Use FYZ for grouting. Diethylenetriamine or ethylenediamine is used as the curing agent, accounting for approximately 5% to 16% of the main component; for particularly fine cracks, FEZ paste with better penetration properties must be used for mechanical injection (the other properties of FEZ are essentially the same as those of FYZ material). In the case of larger cracks, construction can be carried out by manually feeding grout to allow it to seep in freely. Through several years of continuous observation, it has been confirmed that the modified epoxy resin material exhibits stable performance and good waterproofing effects. 3.3 Chemical grouting treatment for leakage in the ceiling of the dance hall in the basement of Guangzhou Xindadi Hotel Due to rainwater accumulation in the cable trenches along the street and water used for watering plants in front of the hotel, intermittent leaks occurred in the concrete ceiling of the dance hall in the basement, appearing as spot-like and linear leaks. At the owner’s request, chemical grouting was used for remedial treatment. First, the soft concrete in the areas where water is leaking must be completely removed. Then, at the points where water leakage is severe, wedge-shaped holes (grooves) with a diameter of 3–5 cm and a depth of 5–8 cm are drilled. One end of the grout pipe is placed inside these wedge-shaped holes, leaving a space of 0.5–1.0 cm at the bottom of the pipe; gravel or cotton yarn is then placed around it to facilitate the spread of the grout. The length of the slurry inlet pipe depends on the actual conditions, usually ranging from 8 to 30 cm. However, the opening of the slurry inlet pipe must be aligned with the outlet hole, so that water can flow into the pipe. The area around the pipe is then sealed with quick-setting cement powder mixed with sand (usually cement and sodium silicate), and the mortar is compressed using fingers or the palm to ensure that no water seeps around the buried pipe. On the day after sealing the pipe openings, Zhonghua-656 grouting can be applied under pressure to achieve water stoppage. Secondly, within the area where water seeps in, apply modified epoxy resin 1–2 times, with a thickness of 1.00–1.50 mm. Once it is almost dry, use cement-silica gel as the final waterproofing layer as well as a protective layer. Finally, grouting treatment is still required for the two cracked floors. One of the thin cracks is sealed directly by filling it with a mixture of modified epoxy resin and cement powder, without the need to create U-shaped or V-shaped grooves. Once the cement-modified epoxy paste has dried, grouting is carried out using a gear pump or a hand pump; after 2–3 days, the surface can be repaired and made ready for use ； The other larger crack can be enclosed with a cement mortar channel, 1–2 cm wide, to collect grout for grouting by infiltration (using thin grout). For sections where it is difficult to introduce slurry, propylene is first used to penetrate and open the path. Once the mixed slurry has dried to about 50-60% of its original consistency, dry cement powder is used to mix with the remaining slurry; this mixture is then removed using a trowel together with the cement mortar in the surrounding trench, so as to prevent the solidified slurry within the cracks from being pulled out during surface cleaning once it has dried. Then, use a small gray trowel (1 cm wide) to carry out supplementary reinforcement grouting repair on the surface of the seam. It can be put into use within 1 to 2 days. 4 Conclusion Chemical grouting has many advantages such as simplicity, speed, low cost, and effectiveness. For different grouting, waterproofing, leak sealing, and water-stopping projects, the construction plans also need to have distinct focuses. The general principles are as follows: (1) The diameter d of the aluminum tube is 1 cm; at the bottom of the buried tube, it is appropriate to wrap cotton yarn to form a flared shape with a diameter of 2–3 cm. The end of the aluminum tube should be 3–5 cm above the base surface. (2) The setting time of the grout is about 1′30″; assuming a diameter of 30–50 cm per point, the amount of grout required per tube (point) is 600–1000 mL, and it is advisable that the final pressure in the hole after grouting be ≤ 2 kg/cm2. (3) The grouting principle is to first apply grout at a fast rate, and then at a slow rate ； It is better to follow the pattern of low pressure first, then high pressure. (4) The irrigation process involves irrigating the holes with low leakage first, and then those with high leakage ； Fill the outer holes first, then the inner holes. (5) For structures that leak water only due to rainfall, modified epoxy resin can be applied for treatment ； For projects with continuous water exposure, Sinochem-656 (acrylate-based) grout is used ； For intermittent water seepage, Sinochem-656 or a combination (composite) of modified epoxy resin and cement-silica gel grouting can be preferred. (6) In natural environments, many substances directly or indirectly affect the gelation time and gel strength of grout; therefore, it is necessary to select different grout formulations and grouting techniques based on the soil and water conditions, as well as various construction projects and types of grout.