Analysis of cracks in concrete structures and treatment

Analysis of cracks in concrete structures and treatment Analysis of cracks in concrete structures and treatment Abstract: From the modern science of concrete work on the research and proved a lot of concrete work, concrete, structural cracks are inevitable, cracks that people can accept a kind of material properties, but how to harmful levels of control within the scope of a valid . Because a variety of materials used in concrete is composed of a mixture, and because is a kind of brittle materials, influenced by temperature, pressure and under the influence of external forces, there is the possibility of cracks. While, after cracks appeared, we must analyze what is harmful to crack cracks, which are harmless cracks, an analysis of the causes and harmful to the formation of cracks in how to deal with, which is proposed in this paper the key. 1 Keywords: structure analysis and processing cracks 1 Overview In today’s society as a whole building, no matter what kind of buildings are reinforced concrete structures, because the cheap building materials, construction convenient, bearing capacity, can be decorated with strong features, increasingly people are welcome. In our country, whether urban or in rural areas, the application of reinforced concrete surface can be said everywhere. However, the use of concrete at the same time, due to the performance of concrete deep understanding of the project after the 10 days, a month or a little longer time after the cracks appeared in concrete structures, or other undesirable reflected to the people heart caused by worry and 2 scared feeling. Some engage in concrete technology researchers in the formation of cracks in concrete structures to carry out a great deal of research and technology to explore ways to propose solutions to concrete cracks and comments, but also made great achievements in scientific research, so that cracks in concrete structures to reduce to a minimum range of within. Cracks in concrete structures present problem is in concrete construction projects, with a certain universality of technical problems. The destruction of concrete structures and buildings collapsed from structural cracks are also caused by the expansion of the beginning. Such as the underground works (basement, underground warehouses, underground transformer substation, underground civil air defense projects, etc.), if the cracks will have a lot of water seepage, so that the use of underground engineering performance degradation or inability to use; and factories, residential, office building The walls, panels, columns, beams, cracks after the first impact of beauty, two affect the life, there are serious cracks in the building will be a threat to people’s lives and property. Therefore, in some construction works were not allowed to acceptance of norms and concrete structure is obvious cracks. 3 However, from the modern science of concrete work on the research and proved a lot of concrete work, concrete, structural cracks are inevitable, cracks that people can accept a kind of material properties, but how to harmful levels of control within the scope of a valid . Because a variety of materials used in concrete is composed of a mixture, and because is a kind of brittle materials, influenced by temperature, pressure and under the influence of external forces, there is the possibility of cracks. While, after cracks appeared, we must analyze what is harmful to crack cracks, which are harmless cracks, an analysis of the causes and harmful to the formation of cracks in how to deal with, which is proposed in this paper the key. 2 at home and abroad on the concrete crack control requirements of Judging from the current situation, the design of concrete 4 cracks in a certain range. Judging from China’s “Design of Concrete Structures” GBJ10 - 89) “looks at the provisions in Table 3.3.4, the crack width in different environments, different cracks in concrete structures of its width is also different from the control standard that allows crack width of 0.2 ~ 0.3mm. Looking at the situation from abroad, different countries of the crack width of concrete structures have different requirements, such as the 1970 Professional Committee of the European norms of concrete collected by the various national standards designed to crack as follows: U.S. AGl specification crack for 0.108mm; France specification crack for 0.27mm; Canada specification crack for 0.064mm; the former Soviet Union specification crack for 0.12mm; Poland specification cracks of 0.182mm. From different countries of view, all countries regulate the cracks in the concrete structures of control have different scope and requirements, to ensure that there are no cracks in 5 concrete structures can be said to be impossible. In our country, right under the concrete structures in different environments in different media cases, provided the width of concrete cracks are also different. Therefore, cracks in concrete structures design our specification to allow a certain width. The international community are also in accordance with national characteristics of the concrete cracks are clearly defined, indicating cracks in the concrete structure is permitted within a certain range, in order to control cracks in concrete structures is not difficult, the key is the width of cracks should be control to what extent. Three types of cracks in concrete structures, and seepage, leakage causes Concrete seepage, leakage is mainly due to its mixture vibrated in the process of watering and vibrator vibration leakage arising from non-dense honeycomb-like pores or gaps in the external water pressure under the influence, resulting in seepage and leakage phenomenon. 6 At the same time, the design of reasons, such as structure, form size, force, tectonic factors such as ill-considered would have caused the concrete structure of the seepage, leakage phenomenon. The actual situation from the past, concrete cracks can be broadly divided into the following categories: (1) The concrete mixture pre-condensation of settlement cracks and shrinkage cracks; (2) Concrete temperature stress cracks; (3) of concrete from the stress cracks; (4) Concrete cracks under external and load impact. From a practical point of view, underground cracks in concrete engineering structures can be divided into the 7 following areas the situation, the author shall be presented separately. 3.1 Settlement cracks in concrete mixture The occurrence of such cracks, often using a large liquid concrete mixture cracks occur from time to time, we all know, high fluidity concrete mixture in the initial setting of concrete before the concrete mixture in the coarse aggregate is always in a free verse, although the device through the vibration of the vibration, the internal porosity has been largely ruled out, but within the coarse aggregate in the concrete itself in its own slowly sinking under the action of the quality, if the plain concrete, the internal sink is uniform, in Concrete hardening process, the surface cracks in general are in operation during the construction workers left hamstring after the result of leveling with the Su-paste formed, because these cracks is a prime slurry generated in the curing shrinkage (dry) cracks; But as long as the initial setting of concrete to be pressure 8 when the light can be resolved. On the other hand is a reinforced concrete, the concrete did not meet initial setting prior to its internal state of coarse aggregate to continue in the sink, while the reinforced concrete along the bottom to continue to sink, due to the role of reinforcement of reinforced concrete has been above supporting reinforcement in the reinforced steel along the direction of the upper surface of cracks, this crack reached only reinforced the depth of the surface until the general. 3.2 Early shrinkage cracks in concrete Such cracks are usually thinner in the concrete structure; such as the in-situ concrete slabs, road concrete, floors and other concrete structural section ? 300mm, concrete slump> 100mm, the most vulnerable to such cracks. This causes cracks in the concrete mixture is poured pound after the water inside the concrete mixture secrete a loss of part of the cement hydration has been used in the other part by 9 evaporation, especially in the dry heat, wind than a big season and in the air thin-walled structure plate concrete mixture is more prone to dehydration and shrinkage cracks occur. Such cracks of time earlier, generally in the initial setting of concrete has happened before, if not addressed and conservation, local cracks throughout the concrete structure will be, some cracks will also meet the structural 1 / 3 ~ 1 / 2 the depth of . If the cracks like this have not reached the initial setting of concrete until the surface of wood trowel pressure to re-shoot disappearing, and immediately on the surface coverage of conservation, you can eliminate the kinds of cracks happen again. This crack in the actual construction process will be frequently encountered, but as long as attention, such as concrete cracks in the early stage before the initial setting can be avoided completely. 3.3 bolt reinforcement end at the phenomenon of water leakage 10 The actual project construction, the right bolt is used to a fixed template, and in pre-fixed before concreting the steel cage, and the reinforced concrete structure across the whole. During the construction, the pull bar in ? 0.00 for the following call for reinforcement in the pull-welding a steel plate in the sealing pad, to prevent the infiltration of groundwater directly from the reinforced concrete structure around the house to require sealing by welding steel plate and steel welding at least four weeks, not Youlou welding and spot welding, to ensure that the sealing bolt effect, if the sealing pad welding dissatisfaction, in the process of concrete vibrator, right below the bolt continues sinking aggregate particles in the concrete setting, the The following pairs of steel to form a pull water film, resulting in concrete cement hydration and moisture evaporation later, Bolt was formed under the surface of a cross-cutting nature of the pores, the pores in the external groundwater pressure , will produce water seepage. However, some steel sealing plate welding welding too lax or missing solder joints Youlou Department, the role of 11 external water pressure, water will leak through the seal plate welding Department, along the steel bolt penetration to the internal structures. 3.4 penetrating the pores and micro-cracks In general high fluidity concrete engineering structure prone to penetrating the pores. Because of pumping concrete mobility, with a corresponding concrete unit of water consumption is also to be more water than ordinary concrete. Pound in the concrete pouring finished, part of the water, bleeding out, part of the evaporation part of the cement in the cement hydration was absorbed, the remaining part of the concrete mixing water existed within a certain period of time, the water slowly evaporate the water share of the original the size of the pores formed a gap in the concrete structure under the pressure of external ground water, this linking of the pores is very prone to leakage. 12 Micro-cracks mainly reflected in the high fluidity concrete house, due to vibration or vibrated vibrated when the leak is not enough, in the concrete to harden before, especially in the steel beneath the aggregate continued to sink, while the reinforced concrete top of the bone has been reinforced by the support material can not be sinking, in the reinforcement of the lower surface formed a fine water film in the future it will be the formation of a porous, underground water will leak from cracks inside the concrete structures. 3.5 concrete stress cracks 3.5.1 Concrete Temperature Stress cracks The concrete hardening process of concrete structures may be subjected to various temperature and humidity, and other 13 causes deformation resulting from stress cracks, because concrete inner and outer restraint stress circumstances, the concrete elements of self-restraining stress is due to non-linear deformation caused by the uneven, it produced a partial fracture, while the concrete structures (structures) in the external stress due to the constraint structure and the structure of mutual constraints, such constraints may make concrete structures on the deformation (structural) produces cross-cutting faults and partial cracks . According to Professor Wang Tiemeng’s theory, especially the large volume of concrete poured concrete pound exhausted, the cement hydration has already begun, its maximum temperature of concrete inside the peak of the experience can be the following formula, namely: T0 = T C * α Where T0 - Concrete internal peak temperature (C ?); 14 T - concreting into the mold when the temperature (C ?); C - amount of cement per cubic meter of concrete (kg/m3); α - the experience factor; when using slag cement, pozzolanic cement, fly ash cement pm; α = 0.1; when using ordinary Portland cement, when α = 0.105. When the stress is greater than the internal temperature of concrete tensile stress of concrete, the concrete structure cracks will appear, so in the “concrete structural engineering construction and acceptance of standard” GB50204 - 92 ““ in Section 4.5.3 stipulates, “The large volume concrete curing, should be taken according to climatic conditions, temperature control measures, as required, after pouring the concrete determination of surface and internal temperature, the temperature control in the context of the design requirements; when the design is no specific request, the temperature should not exceed 25C ? “. While in a large 15 volume of concrete construction, are often designed without clearly defined, can only rely on the experience of construction control. Because the concrete mixture within the cement hydration, we should generate a lot of hydration heat, when the temperature difference between inside and outside of concrete exceeds a certain limit, the concrete tensile stress is less than concrete heating or stress, it will generate temperature stress cracks. Such cracks occurred mainly in the large volume of concrete or concrete construction in the winter period. For example: We have a large equipment-based Baoshan Iron and Steel concrete construction, concrete strength is designed to C30 grade, amount of cement per cubic meter of concrete for the 360kg/m3, then temperature of 33C ?, in order to understand the internal concrete temperature peak, 16 we have taken thermocouple temperature and the temperature inside the hole way to determine the temperature of concrete and concrete surface temperature to calculate the temperature difference between inside and outside of concrete, after the measured temperature and calculate the temperature of view, both more or less. Temperature between the two results: (1) The actual test the temperature of peak 71.3C ?; (2) The calculation of temperature: T0 = 34.5 (360 × 0.1) = 70.5C ?; From both the temperature situation, the temperature difference of only 0.8C ?. Shows calculated temperature and measured the temperature difference is not entirely possible to calculate the temperature of the concrete for insulation measures. The project was the maximum concrete temperature of concrete when the measured temperature of 17 the outer surface of 44C ?, internal and external temperature of 27.3C ?, larger than the specification of the 25C ? requirements, and therefore to take immediate and concrete surface of the insulation measures to improve the concrete surface temperature, reduce the temperature difference between inside and outside the , so that there is no concrete, cracks due to thermal stress and ensure the quality of the concrete foundation. Thermal stress cracks in the concrete case there is a general tend to occur in concrete structures and concrete cross-section of variable cross-section of smaller parts, for which the construction of mass concrete or a thick concrete wall version, the construction units should be Note. 3.5.2 Stress cracks in concrete self - In the concrete to harden, even without any load in the concrete at the top of the role, but also because of its own contraction cracks. Especially in the summer of concrete construction, more prone to crack in this area. Such cracks are 18 often prone to the concrete wall panels, its form is generally run through the cracks from top to bottom, throughout the concrete wall showing regularly at the crack, generally 1.8 ~ 2.2m 1. As we said in the basement of a Shanghai Institute of concrete wall construction, concrete curing and 7 days, the watering basement concrete roof, the construction finished, found in the basement walls showing the regularity of crack, the crack width of about 0.15mm length of the entire wall height. The requested part of the expert analysis, the kinds of cracks are caused by self-stress concrete, because concrete in the cement hydration heat reaches a certain temperature, when the expansion of concrete stress begin to disappear at a time when the concrete beginning to shrink. This contraction is uniform contraction, so in these circumstances, the concrete wall cracks showing regularly at the cracks. However, if the load-bearing wall and the basement is linked tread place, often at the intersection of column and wall cracks and in the wall of variable cross-section cracks occur. 3.6 load-deformation crack 19 Such cracks usually can be divided into two situations resulted: First, the concrete structure has not yet reached the design requirements of strength when he was crushed vehicles or heavy loads, or hit, smashing a result of deformation crack; Second, even if the concrete has reached the design strength, and in the concrete walls or thin-walled structures or super-loads stacked on the impact caused by the cracks. The latter cracks were generally more obvious, are cross-cutting cracks. 3.7 of water leakage in concrete structures Concrete water leakage tends to occur in the following areas: (1) cellular surface water leakage in the Ma Cellular Pock directly related to concrete construction. The 20 emergence of these cellular Pock The main reason is the leakage vibration or vibration during the construction of the shortage of time to happen, such a honeycomb textured structure, either in the concrete existence of an independent group of films, while others showed coherence. Therefore, in the event of seepage, leakage, when it is not a point of seepage, leakage, but rather into the film permeability and leakage phenomenon. (2) the expansion joints, settlement joint seepage, leakage In large mass concrete and concrete structures rather long, the larger difference between high and low structures projects, the requirements of due process generally are equipped with expansion joints and settlement joint to ensure that the deformation of concrete structures without affecting the other parts of the overall deformation of the needs of . These sites are often at work for some reason to make joints and settlement joint can not fully guarantee its quality, resulting in these parts of the seepage, leakage, it is in dealing with often 21 than in other parts of the seepage, leakage should be much more intractable. (3) new and old concrete Jiecha (seam) and seepage, leakage In the original concrete structure to continue watering concrete, the original surface of the concrete foundation no treatment or cutting of hair cutting hair does not clean up after, or did not wash with water, on the basis of the original concrete pour concrete mixture. This will result in new and old concrete Jiecha (slit) formed between a doped and leakage gap. Such leakages on the actual project construction will be frequent, especially in the concrete slump is small (usually 50mm or less) Jiecha (seam) is not yet even more prone to laying cement mortar. This gap in the concrete construction of particular attention, attention. Reposted elsewhere in the paper for free download 22 4 cracks seepage, leakage approach According to concrete seepage, leakage characteristics, to conduct analysis of the seepage, leakage and seepage of the reasons for the formation of the site, as well as seepage, leakage level, according to different forms can be taken to plugging a different approach, our actual plugging is as follows : Method of plugging of concrete is generally used four kinds of approaches, in the daily implementation of these four methods are more appropriate and feasible, these methods are: (1) chemical grouting method; (2) filleting plugging method; (3) block letters plugging method; (4) Tu-mode (Brazzaville), plugging method. 23 Plugging the above four kinds of methods is based on different seepage, leakage case may choose different ways to solve the concrete Pei-drain seepage, leakage problems, the following author according to different permeability, leakage of plugging in different ways to be introduced. 4.1 Chemical grouting method Chemical grouting Sealing is the use of a chemical grouting material to address the formation of linear mixed concrete, leakage of the site, it typically seepage, leakage is a line to be taken when plugging the chemical grouting material and rapid condensation of cement and no shrinkage cement mortar used in conjunction, can we truly achieve the plugging effect; chemical grouting materials are generally divided into four kinds of models, their technical specifications in Table 1. 24 Table 1 Specifications of chemical grouting materials No. Material name 25 Bond strength (MPa) Compressive Strength (MPa) Swelling with water (%) 1 26 LW water-soluble polyurethane 1.70 -- 27 273 2 HW water-soluble polyurethane 2.70 28 19.8 -- 3 29 LW: HW = 60:40 1.86 11.8 30 30 4 Low Viscosity Epoxy Resin 5.10 31 82.4 -- Chemical grouting plugging in general is a more serious leakage of the site, they generally are penetrating cracks, and in stopping leaks is more difficult to deal with a kind of seepage, leakage, for which the need for chemical grouting approaches to plugging , and stopping leaks, the first seepage and leaking cracks in part be determined, research treatment methods, and then determine the plugging program, the kinds of cracks and leaking approach is as follows: (1) leaks carved into a “V” groove, with the incorporation 32 of quick-setting agent for the laying of cement grout filling the mouth with a polymer cement mortar PCCM Sealing; (2) on the concrete surface with wire brush clean-up grassroots floating dust, and rinse with water; (3) in the concrete surface, no floating grass-roots level, the spraying 5mm thick PCCM - polymer cement mortar. PCCM main mechanical properties of polymer cement mortar in Table 2; Table 2 PCCM main mechanical properties of polymer cement mortar 33 Performance Bond strength (MPa) Tensile (MPa) 34 Ultimate tensile value (Eu) Tensile elastic modulus (E) Crack factor (k) 35 Impermeability pressure (MPa) Indicators 3.5 ~ 4.2 36 3.7 ~ 4.7 700 ~ 800 × 10-6 700 ~ 800 (MPa) 5.5 ~ 7.5 × 10-4 37 > S1.2 (4), after spraying of polymer 5d conservation, using water-soluble polyurethane grout LW chemical grouting, pressure grouting is generally 0.3 (MPa), to prevent excessive pressure during filling, resulting in burst into the plastic tube. Plugging in the actual processing, the use of linoleum, or aluminum foil is intended to prevent water slurry into the metal valve (metal valve to connect one end of transparent plastic grouting hose as water pipes, in the concrete surface after a certain strength as a chemical grouting pipeline) and grouting holes to plug. With asphalt or aluminum foil to trap the metal valve, and then in aluminum foil around the linoleum, or with rapid coagulation of cement grout to be 38 sealed, and then use the above described surface treatment materials. 4.2 filleting plugging France Used by the plugging method is generally the concrete surface Ying-water phenomenon appeared only in the long run, the can into a large concrete wall mapping wet tracks and underground water are filled with water, if not addressed, will affect the entire surface of the beautiful and indoor use of results, this end, this approach should be adopted for the handling of water seepage filleting methods, filleting approach is: (1) carved into the gap along the seepage of concrete “v” groove, clear the tank of debris, then rinse with water; (2) in a clean, dry surface of the seam even brushing SR 39 plastic sealing material dedicated base fluid; (3) in the base fluid solid work before the SR embedded filled plastic sealing material; (4) repair and protection: the surface sealant dry before smoothing with a small scraper tools will be repaired surface smooth; (5) After filleting seam spray bottle with the withdrawal of the surface of the Sheung Shui to keep sewing surface wet; (6) The preparation of the PCCM will be proportional with the scraper be embedded in mortar crevices, and use spatula to smooth out their; (7) Subject to the PCCM mortar condensation, the use of wet approaches for the conservation 3 ~ 5d; 40 (8) in proportion to the preparation of HK - 964 thickened epoxy paint, repeatedly stir well before use; (9) in the dry, flat seam surface, even brushing 964 elastic coating 2, to a brush a brush pressing operation, to prevent the leakage brush; (10) after the completion of the whole plugging on the use of SR, 964 paint tools, must be promptly cleaned with solvent inactive. 4.3 Sealing Sealing Method Plugging in the kinds of ways, primarily used in underwater or underground concrete water gushing under the conditions of the pores, holes and cracks fast block. Parts of such a leakage in the Blocking often than other seepage, leakage is much more difficult, and the water shut-off effect has to be 41 slightly worse some, but as long as required in the processing operation can ensure the concrete surface is not watered. Some of this material is called fast-blocking agent, also known as the PBM and some polymers, the polymer concrete underwater performance in Table 3. Table 3 PBM-7 underwater performance of polymer concrete 42 Age performance Bond strength (MPa) Tensile (MPa) Flexural strength 43 (MPa) Compressive strength (MPa) 1d 2.0 44 5.2 13.7 42.6 45 30d 2.1 5.9 46 15.1 56.4 When used in this way plugging a certain base treatment should first clean the concrete surface shall not be left in the debris of concrete and powder, if the point of gushing water, first leaks chisel with a diameter of 80 ~ 150mm depth 50 ~ 80mm working pit in the pit leaks in the aqueduct at a pre-amplifier, as a drainage purposes, be the first to cast polymer concrete (or mortar), after a certain intensity, and then forced to stuffed polymer mortar. In dealing with leakage, generally according to the size of the amount of leakage of water to adopt different ways of plugging, if there is water out leap can be taken to the above-mentioned methods. If the leakage is very small, you can approach the above leaks before plugging chisel addition to a working pit, rinse with water 47 immediately after the polymer concrete or a block polymer mortar, and force the polymer concrete or aggregate material mortar compaction (polymer mix concrete or cement mortar, its setting time is generally 3 to 5 minutes) until the condensation hardened concrete or mortar after mortar smeared on its surface with high-grade, in the 5d to maintain surface of moisture can be. Note that, when there is gushing water plugging process, be sure to steel or concrete or mortar in the hardened bamboo (condensation) before the rotation, to prevent the concrete or mortar can not be removed after the hardening, resulting in the final block flow phenomenon occurs when the difficulty or rework . In addition, if leakage brought to the next crack in the block this form of cracks, we should pay attention to operate from top to bottom, in relatively easy-to-height settings drains, wait 48 until the crack of the sealing materials to meet the design requirements, and then the location of drainage blocking. Can also be sub-block, method, ibid. 4.4 coating (Brazzaville) plugging method Sealing is coating the surface of concrete structures where leakage processed directly on the waterproofing treatment on its surface. This method generally applicable to vibrated concrete structure during construction is not dense, and some leakage of internal concrete vibration is not formed by compacting a large area of water seepage caused by the situation, which generally can not use the water leakage and the embedding method to deal with pressure grouting, the surface coating method can only waterproofing treatment. This approach is relatively simple, but the more stringent requirements in operation, generally do not require the surface of concrete structures floating ash and debris, otherwise it will affect the concrete surface and the coating 49 bond strength, impact waterproofing effect. Coating (Brazzaville) waterproof material used in HK - 96 Series thickened epoxy paint, which uses the performance are as follows: 961 - used to dry the concrete surface; 962 - for the wet concrete surface; 963 - used for underwater concrete or surface structures; 964 - for the elastic coating. In the selection of the above four kinds of coating materials, must be based on leaks of different ways to select a different coating materials. If a continuing structure of the settlement, but the settlement is very small, then to choose a flexible coating, can not select the hard and brittle nature of the coating material, to prevent the structures do not occur in the settlement of the waterproofing effect of brittle fracture, but 50 pleasant. 5 on the work of plugging a few comments After a Baosteel I, II and III of the underground concrete structure works were seepage, leakage post-processing view, plugging of concrete is only an ex post solution, first in the concrete construction of concrete construction is necessary to strengthen management, to reduce and eliminate cracks in the concrete structure, this is our only objective. Plugging plugging, no matter how, it is nothing but a negative approach, it is not only wasteful, but also putting in a lot of manpower and material resources, the project will be put into place after use all kinds of unexpected problems. To this end, first of all our energies should be focused on concrete construction management, strictly good concrete construction quality. However, because concrete is formed by a variety of materials, a kind of brittle material, in the construction process is often difficult to ensure that there are no cracks in concrete structure, but be sure to control concrete cracks appeared as 51 little as possible. As a last resort when the cracks, further sealing of cracks or leakage to pressure grouting approach. Following in Baosteel I, II and III of the leakage of underground concrete works deal with situation, the effect is obvious, to achieve the desired purpose, for which we recognized that: (1) To determine the concrete seepage, leakage parts, determine plugging the program, select a reasonable plugging materials to avoid plugging achieving the desired results. (2) plugging the former, whether it is making a hole or a chisel “V” groove depth must be reinforced over the following, generally the depth of digging 50 ~ 80mm, so shallow and then prone to leakage phenomenon. (3) All have been digging the hole or “V” groove, all use 52 clean water rinse, the hole and the tank shall not be there floating dust, or after a period of time, around the hole will be re-seepage and leakage. (4) using PBM - 7-speed gel polymer clay, make the existing service is now available, to prevent a preparation too much, too long storage time expired and wastage. (5) If the water-soluble polyurethane grout using LW as a blocking agent, we must pay attention to kept under seal to prevent exposure, and mixed with water and the chemical reaction caused the solution and to maintain pressure pump clean, pump container shall not mixed with debris to prevent clogging, use of solvents used at any time after wash. (6) in the actual plugging operation, must be individual 53 responsibility and personal action to ensure the quality of plugging. Reposted elsewhere in the paper for free download 54