CN113832855A - Construction method of large-diameter steel pipe arch concrete - Google Patents
Construction method of large-diameter steel pipe arch concrete Download PDFInfo
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- CN113832855A CN113832855A CN202010580350.5A CN202010580350A CN113832855A CN 113832855 A CN113832855 A CN 113832855A CN 202010580350 A CN202010580350 A CN 202010580350A CN 113832855 A CN113832855 A CN 113832855A
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- E—FIXED CONSTRUCTIONS
- E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
- E01D—CONSTRUCTION OF BRIDGES, ELEVATED ROADWAYS OR VIADUCTS; ASSEMBLY OF BRIDGES
- E01D21/00—Methods or apparatus specially adapted for erecting or assembling bridges
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Abstract
The invention relates to the technical field of arch bridge construction, and particularly discloses a construction method of large-diameter steel pipe arch concrete, which comprises the following steps: the method comprises the following steps of working concrete selection, working concrete pump-in waiting time control, working concrete mold-in temperature control, working concrete mold-in operation and steel pipe arch external heat insulation operation. The invention provides a construction method of concrete in a large-diameter steel pipe arch, which constructs a set of construction process measures starting from factors closely related to concrete shrinkage deformation of a solid structure of the steel pipe arch, such as the performance of working concrete, the waiting time for pumping, the mold-entering temperature, the heat preservation system and the like; the construction method formed by cooperatively adopting the materials and the process measures can powerfully guarantee the construction quality of the concrete in the large-diameter steel pipe arch with the diameter of 1.0-2.0 m in the large-span steel pipe concrete arch bridge and effectively avoid the phenomena of debonding and void removal of the working concrete in the steel pipe arch caused by shrinkage deformation.
Description
Technical Field
The invention belongs to the technical field of arch bridge construction, and particularly relates to a construction method of large-diameter steel pipe concrete in an arch.
Background
In recent 20 years, the concrete-filled steel tube arch bridge is widely applied to highway and railway engineering in China. The statistics show that as long as 2017, 1 month, nearly 500 built and under-construction concrete-filled steel tube arch bridges with span of more than 50m are provided. Generally, in a steel pipe concrete structure, concrete is taken as a core, so that early local buckling of a steel pipe can be prevented when the steel pipe is stressed, the steel pipe surrounds a central column, a constraint effect is achieved on the central column, the steel pipe and the central column can work in a coordinated mode, and the structural bearing capacity is improved.
Researches show that the steel pipe concrete structure has better strength, ductility and energy absorption capacity than a single steel structure. However, once the core concrete in the steel pipe concrete structure is debonded and separated from the outer steel pipe wall, serious problems occur in terms of load bearing capacity, rigidity, and volume stability. Before that, because the core concrete and the outer steel pipe wall are seriously debonded, a certain steel pipe concrete arch bridge built in 1996 has to be dismantled and rebuilt in 2008, and the economic loss is huge.
Researches show that the main reasons for causing the debonding and even the hollowing of the steel pipe concrete structure include the bearing of excessive axial pressure, the cyclic change of seasonal temperature, the performance of the concrete material in the pipe and the poor construction process thereof, and the like. The performance of the concrete material in the pipe and the construction process thereof are not optimal and common, and the concrete material comprises the following specific components: firstly, the concrete has insufficient fluidity, is difficult to pump and compact, and cannot effectively fill the inside of the whole steel pipe arch; secondly, air bubbles contained in the concrete mixture and air which is not discharged in time in the steel pipe arch are agglomerated and float upwards, and a strip-shaped cavity area is formed at the arch top of the steel pipe; and after plastic shrinkage and hardening of the concrete, the concrete has large deformation caused by self shrinkage and temperature drop shrinkage, the volume stability of the concrete is seriously influenced, and the concrete in the pipe and the pipe wall are hollow, so that the concrete is particularly obvious in a large-diameter steel pipe arch structure of a large-span steel pipe concrete arch bridge with the strength grade of the concrete in the pipe exceeding C50.
In order to solve the problems, the following main measures are provided by the research of engineering technicians: firstly, self-compacting concrete with good fluidity and clearance passing property is adopted to pour a steel pipe arch; secondly, a vacuumizing process is adopted, air in the steel pipe arch is discharged in advance, and the phenomenon of air trapping is avoided; and thirdly, the expansion agent is doped to compensate the shrinkage deformation of the concrete in the pipe, and the volume stability of the pipe is improved. Although the measures effectively improve the construction quality of the concrete in the large-diameter steel pipe arch, the applicant finds that the phenomena of debonding and void caused by shrinkage deformation of the concrete in the pipe are relatively serious in the construction process of a plurality of large-size steel pipe concrete arch bridges.
Disclosure of Invention
In order to solve the problems in the prior art, the invention adopts the following technical scheme:
a construction method of large-diameter steel pipe arch concrete comprises the following steps:
selecting working concrete: adopting self-compacting and non-shrinkage concrete added with a composite expanding agent as the working concrete;
the control step of the waiting time for the working concrete to enter the pump comprises the following steps: keeping the time interval from uniformly mixing the working concrete out of the machine to pumping the working concrete to be 45-120 min;
and (3) controlling the mold-entering temperature of the working concrete: adjusting the mold-entering temperature T of the working concrete according to the daily average air temperature T during construction0(ii) a Wherein, the average temperature in the dayWhen T is more than or equal to 25 ℃, controlling the mold-entering temperature T0Less than or equal to 28 ℃; when the daily average temperature T is more than or equal to 10 ℃ and less than 25 ℃, controlling the mold-entering temperature T0The daily average temperature is less than or equal to +8 ℃ and T0Less than or equal to 28 ℃; when the daily average temperature T is less than 10 ℃, controlling the mold-entering temperature T to be less than or equal to 10 DEG C0＜18℃；
The working concrete is put into a mould: firstly, controlling the vacuum degree in a steel pipe arch to be not lower than-0.08 MPa, and then pumping the working concrete into the steel pipe arch until the whole space in the steel pipe arch is filled;
the external heat preservation operation steps of the steel pipe arch are as follows: and carrying out external heat preservation treatment on the outside of the steel pipe arch so as to enable the average temperature drop rate v in 7d after the working concrete temperature peak in the steel pipe arch to be less than or equal to 5 ℃/d.
Further, in the step of selecting the working concrete, the working performance of the self-compacting and non-shrinkage concrete meets the requirement of the standard JGJ/T283-2012; the key control indexes of the volume stability performance of the self-compacting and non-shrinkage concrete comprise: firstly, the autogenous volume deformation (namely the vertical expansion rate) before final setting is 0.02 to 0.1 percent, and the test is carried out according to the standard GB/T50448-2015; ② the autogenous volume deformation is more than or equal to 0.02 percent at the 3d age from the final setting, and the test is carried out according to the standard GB/T50082-2009; and thirdly, the deformation of the autogenous volume is more than 0 when the fluid is at the age of 90d from the final setting, and the fluid is tested according to the standard GB/T50082-2009.
Further, in the selection step of the working concrete, the composite expanding agent comprises 0.2-2% of azodicarbonamide plastic expansion component, 30-50% of light-burned calcium oxide clinker, 10-30% of light-burned magnesium oxide clinker and the balance of fine powder, wherein the mass of the composite expanding agent is 100%; wherein the specific surface area of the fine powder is more than 200m2/kg。
Preferably, the composite expanding agent can be produced by Jiangsu Subo New Material Co., Ltd
-II high-performance concrete magnesium oxide composite expanding agent.
Further, in the step of selecting the working concrete, the addition amount of the composite expanding agent is 8-10% by mass.
Further, in the external heat insulation operation step, a heat insulation material is wound on the outside of the steel pipe arch.
Further, the thermal conductivity coefficient of the thermal insulation material is not more than 0.045W/(m.K), and meets the fireproof requirement of B1 level and above in the standard GB8624-2012, and the thickness of the thermal insulation material is not less than 20 mm.
The invention provides a construction method of concrete in a large-diameter steel pipe arch, which constructs a set of construction process measures starting from factors closely related to concrete shrinkage deformation of a solid structure of the steel pipe arch, such as the performance of working concrete, the pump-in waiting time, the mold-in temperature, the heat preservation system and the like. The construction method formed by cooperatively adopting the materials and the process measures can powerfully guarantee the construction quality of the concrete in the steel pipe arch with large diameter (1.0-2.0 m) in the long-span concrete-filled steel pipe arch bridge.
Drawings
The above and other aspects, features and advantages of embodiments of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a flow chart showing the steps of a method for constructing concrete in a large-diameter steel pipe arch according to the present invention;
FIG. 2 is a steel pipe full-scale model test overall layout view of a construction method of large-diameter steel pipe in-arch concrete according to example 1 of the present invention;
FIG. 3 is a schematic view showing the arrangement of a structural compactness testing zone of a steel pipe based on an ultrasonic method in example 1 according to the present invention;
FIG. 4 is a schematic view showing the arrangement of single measuring points for measuring the compactness of the steel pipe structure based on the ultrasonic method in example 1 of the present invention.
Detailed Description
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the specific embodiments set forth herein. Rather, these embodiments are provided to explain the principles of the invention and its practical application to thereby enable others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use contemplated. In the drawings, the shapes and sizes of elements may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or similar elements.
Aiming at the current situation that the phenomena of debonding and hollowing caused by shrinkage deformation of concrete in a pipe are serious after the measures of self-compacting concrete pouring steel pipe arches, vacuumizing processes, expanding agent doping and the like are generally adopted in the prior art, the invention provides a brand-new construction method of the concrete in the steel pipe arch with the large diameter (1.0-2.0 m). The construction method constructs a set of construction process measures starting from factors closely related to concrete shrinkage deformation of the solid structure of the steel pipe arch, such as the performance of working concrete, the pump-in waiting time, the mold-in temperature, the heat preservation system and the like.
Specifically, referring to fig. 1, the construction method provided by the present invention comprises the steps of:
the method comprises the following steps: and selecting working concrete.
Specifically, self-compacting and non-shrinkage concrete added with a composite expanding agent is used as working concrete and is used for being pumped into a steel pipe arch subsequently; wherein the addition amount of the composite expanding agent is 8-10 percent (calculated by mass percentage), namely the composite expanding agent accounts for 8-10 percent of the mass of the working concrete.
More specifically, the working performance of the self-compacting and non-shrinkage concrete should meet the requirements of the standard JGJ/T283-2012, and key control indexes of the volume stability performance of the self-compacting and non-shrinkage concrete include: firstly, the autogenous volume deformation (namely the vertical expansion rate) before final setting is 0.02 to 0.1 percent, and the test is carried out according to the standard GB/T50448-2015; ② the autogenous volume deformation is more than or equal to 0.02 percent when the self-setting is started at the 3d age, and the test is carried out according to the standard GB/T50082-2009; and thirdly, the autogenous volume deformation is larger than 0 at the age of 90d from the final setting, and the test is carried out according to the standard GB/T50082-2009.
The composite expanding agent in the invention comprises0.2 to 2 percent of azodicarbonamide plastic expansion component, 30 to 50 percent of light-burned calcium oxide clinker, 10 to 30 percent of light-burned magnesium oxide clinker and the balance of fine powder (the specific surface area is more than 200 m)2Kg) of the components, wherein the mass percentages of the components are based on 100 percent of the total mass of the composite expanding agent.
Preferably, the composite expanding agent can be produced by Jiangsu Subo New Material Co., Ltd
-II high-performance concrete magnesium oxide composite expanding agent.
The self-compacting and non-shrinkage concrete adopted by the invention can compensate shrinkage deformation of the self-grouting forming by stages and in the whole process from the beginning of the pouring forming by adding the composite expanding agent, and when the self-compacting and non-shrinkage concrete is applied to a large-diameter steel pipe arch, the close adhesion between the concrete in the steel pipe arch (namely, working concrete pumped into the steel pipe arch in the mould entering operation step) and the outer steel pipe wall (namely, the outer wall of the steel pipe arch) and the cooperative stress can be ensured. Specifically, firstly, the azodicarbonamide plastic expansion component is continuously decomposed in an alkaline environment of a working concrete plastic stage to continuously generate micro bubbles with the particle size not more than 0.2mm, so that the volume of the mixture of the working concrete is expanded, the syneresis of the working concrete in the plastic stage before hardening is compensated, and the working concrete in the steel pipe arch is free of shrinkage in the plastic stage; secondly, the light-burned calcium oxide clinker has fast hydration reaction, high activity and large expansion energy, can effectively store expansion pre-pressing stress in the working concrete in the steel pipe arch during the heating period and compensate the shrinkage deformation during the cooling period by a small amount; thirdly, the light-burned magnesia clinker has the advantages of delayed expansion characteristic and long expansion course, and mainly compensates the temperature reduction shrinkage and self-shrinkage of the working concrete in the steel pipe arch in a longer age. The light-burned calcium oxide clinker and the light-burned magnesium oxide clinker are compounded and added, so that the working concrete in the steel pipe arch can have no shrinkage in the hardening stage, and the action effect is better than that of singly adding calcium oxide or magnesium oxide.
Step two: and controlling the waiting time of the working concrete in the pump.
Specifically, the time interval from uniformly mixing the working concrete out of the machine to pumping the working concrete is kept to be 45-120 min.
In this step, the above time is designed mainly based on the following reasons: firstly, working concrete is generally stirred uniformly within half an hour, because water reducing agent molecules are gradually adsorbed and cementitious material particles such as cement are gradually dispersed, the working performance of the concrete mixture is greatly changed and mainly shows the characteristics of increased fluidity and enhanced segregation tendency in self-compacting concrete, so that the pouring time is prolonged, the influence of the factor can be avoided, the mixture with relatively stable working performance in the following long time is obtained, and the quality control of a construction site is facilitated; even if the air content of the self-compacting concrete, namely the working concrete in the steel pipe arch, is strictly limited, a large number of small bubbles with the diameter of 0.5-5 mm are gathered and floated within a long period of time after uniform mixing, and the condition that the arch top of the steel pipe is possibly hollowed is still existed, especially within a half hour after uniform mixing and discharging, the phenomenon is most severe, so that the pouring time is prolonged, the concrete mixture is fully cured, a large number of internal bubbles are discharged, and the bad influence of floating and gathering of the internal bubbles on the pouring compactness of the steel pipe arch can be effectively improved; the gas evolution process of the azodicarbonamide plastic expanding agent adopted in the working concrete can usually exceed 4h, even if the working concrete in the steel pipe arch can not be poured in a short time after being uniformly mixed, the subsequent complete compensation of the plastic shrinkage of the mixture can not be influenced, and the plastic stage can be realized without shrinkage. Therefore, the influence factors of the working performance and the volume stability of the working concrete in the subsequent steel pipe arch are comprehensively considered, and the invention provides the construction factor limit that the time interval from uniform mixing and discharging to pumping is not less than 45min and not more than 120 min.
Step three: and controlling the mold-entering temperature of the working concrete.
Specifically, the mold-entering temperature T of the working concrete is adjusted according to the time-day average air temperature T during construction0(ii) a Wherein, when the daily average temperature T is more than or equal to 25 ℃, the mold-entering temperature T is controlled0Less than or equal to 28 ℃; when the daily average temperature T is more than or equal to 10 ℃ and less than 25 ℃, controlling the mold-entering temperature T0The daily average temperature is less than or equal to +8 ℃ and T0Less than or equal to 28 ℃; when the daily average temperature T is less than 10 ℃, controlling the mold-entering temperature T to be less than or equal to 10 DEG C0＜18℃。
Preferably, the working concrete can be cooled by at least one of the modes of sun-shading storage of raw materials, prolonging of storage time, air cooling, mixing by adding cold water or flake ice, liquid nitrogen cooling and heat preservation of a loading pump of a transport vehicle; or heating the working concrete by adopting at least one mode of heating raw materials, mixing with hot water and insulating the loading pump of the transport vehicle.
In the construction method, the mold-entering temperature of the working concrete in the steel pipe arch is controlled, because the mold-entering temperature of the working concrete in the steel pipe arch is not too high, and the mold-entering temperature of the working concrete in the steel pipe arch cannot be too low to be not lower than 10 ℃ in order to prevent possible frost damage during low-temperature construction. Specifically, thermal expansion and contraction are inherent properties of concrete materials, when the mold-entering temperature of working concrete in a steel pipe arch is higher, the temperature peak value reached in the hydration temperature rise stage of the working concrete is correspondingly increased, but the temperature peak value is finally reduced to a level close to the ambient temperature in the subsequent temperature reduction stage, so that the mold-entering temperature and the temperature peak value are higher, the subsequent temperature reduction and the shrinkage deformation caused by the subsequent temperature reduction are larger, and the risk of void is increased. Although the composite expanding agent adopted in the construction method can effectively compensate the self-shrinkage, the temperature shrinkage and the like of the working concrete in the steel pipe arch, the compensation effect has the limit, so that under the key control index of the volume stability performance of the working concrete provided by the invention, the requirement on the mold-entering temperature of the working concrete is also required to be provided so as to effectively ensure the no shrinkage of the working concrete in the solid structure of the steel pipe arch. The inventor of the invention puts forward the requirement of controlling the mold-entering temperature of the working concrete in the steel pipe arch at the air temperature of different days during construction on the basis of experimental research and finite element simulation calculation, so that the working concrete can be fully hydrated at the proper temperature, and the phenomena of debonding and void of the solid structure of the steel pipe arch caused by excessive temperature reduction shrinkage can be avoided.
Step four: and (3) a working concrete mold entering operation step.
Specifically, the vacuum degree in the steel pipe arch is controlled to be not lower than-0.08 MPa, and then working concrete is pumped into the steel pipe arch until the whole space in the steel pipe arch is filled.
Before the steel pipe arch is filled, a vacuumizing process is adopted, and the operation of discharging air in the steel pipe arch in advance can be carried out, so that the adverse influence factor of 'air pocket' in the steel pipe arch can be avoided.
Step five: and (3) performing external heat preservation operation on the steel pipe arch.
Specifically, the outer part of the steel pipe arch is subjected to external heat preservation treatment, so that the average temperature reduction rate v in 7d after the working concrete temperature peak in the steel pipe arch is less than or equal to 5 ℃/d.
If the method can be carried out by winding heat insulation materials on the outer part of the steel pipe arch, the heat insulation materials with the heat conductivity coefficient not exceeding 0.045W/(m.K) and meeting the fire protection requirements of B1 level and above in the standard GB8624-2012, such as rock wool and the like, are generally selected. The thickness of the heat-insulating material is generally controlled to be not less than 20 mm.
In the construction method, the outer heat preservation is carried out on the steel pipe arch, so that the temperature reduction rate of the working concrete in the steel pipe arch is not more than 5 ℃/d, one is that the hydration activity of the calcium oxide clinker in the composite expanding agent adopted by the invention is high, the hydration temperature rise of the working concrete in the steel pipe arch is increased by the outer heat preservation measure, and meanwhile, the expansion efficiency of the calcium oxide clinker in the temperature rise stage is obviously improved, so that the working concrete in the steel pipe arch generates larger expansion deformation, and the storage of the expansion pre-stress is facilitated. And secondly, because the magnesium oxide clinker in the composite expanding agent has the characteristic of delayed expansion, the hydration rate of the working concrete in the steel pipe arch can be improved by maintaining a higher temperature level for a longer time, and the full play of the expansion efficiency is facilitated. The inventor of the invention discovers through a great deal of research that the heat dissipation condition of the steel pipe arch structure is good, the temperature drop rate of the working concrete in the steel pipe arch after the temperature peak is usually very large, and the instantaneous value can exceed 12 ℃/d, so the average temperature drop rate in 7d after the temperature peak is reduced to be below 5 ℃/d by carrying out external heat preservation to a certain degree, which is beneficial to fully utilizing the compensation shrinkage effect of the magnesium oxide clinker in the temperature drop stage, reducing the temperature drop shrinkage deformation of the working concrete in the steel pipe arch and realizing the non-shrinkage of the working concrete in the solid structure.
Therefore, the construction method of the concrete in the large-diameter steel pipe arch provided by the invention has the advantages that the materials and the process measures are cooperatively adopted, and the construction quality of the concrete in the large-diameter steel pipe arch in the field of large-span steel pipe concrete arch bridges is powerfully guaranteed.
It should be noted that the descriptions of the steps one to five are not absolute limitations on the sequence of the steps, but are merely used to distinguish different operations and different angles of the control process parameters. In the first to third steps, the first step is not limited to be performed before the second step, and the second step is performed before the third step, but the plurality of raw materials of the working concrete and a part of the temperature adjusting material (such as cold water, ice flakes, hot water, and the like for mixing) in the third step may be mixed in the concrete mixer, and only the kind and ratio of each raw material in the first step and the performance parameters in the second step/the third step need to be controlled. If the operation in the step five is performed on the steel pipe arch, the operation in the step five can be performed simultaneously when the step one to the step three are performed. By analogy, only the logic sequence is required to be satisfied among the steps, and the corresponding steps without the logic sequence are specifically selected according to the actual situation.
The construction method will be described below with reference to fig. 2 to 4 by specific examples, specifically, a steel pipe full-scale model test simulating an actual project is performed, and the implementation effect of the construction method provided by the present invention is evaluated.
Example 1
As shown in FIG. 2, the steel pipe full scale model 1 is in the shape of a hollow pipe, and has a size of phi 1.2m (outer diameter L1) × 8.0 m (L2), and a pipe wall L3 thickness of 2.0cm, and is made of Q345 steel. One end of the steel pipe full-scale model 1 is provided with a slurry inlet 11, a concrete pump pipe 21 for slurry inlet is welded on the slurry inlet 11, and the concrete pump pipe 21 is connected with a concrete pump truck (not shown in the figure) for loading working concrete; the concrete pump pipe 21 is provided with a check valve 22 for preventing the concrete slurry from flowing back after the slurry is fed. A slurry outlet 12 is arranged on the side wall close to the other end of the steel pipe foot model 1, a slurry observation column 23 for displaying the slurry outlet degree is communicated with the slurry outlet 12, the slurry observation column 23 is made of transparent materials such as transparent organic glass and is connected with a vacuum pump (not shown in the figure) for evacuating the air in the steel pipe foot model 1. A concrete strain gauge 24 produced according to GB/T3408 plus 2008 is embedded in the middle part of the steel pipe full scale model 1 along the radial direction of the steel pipe, and the concrete strain gauge 24 is arranged on the central axis in the steel pipe full scale model 1 along the radial direction; the concrete strain gauge 24 is used for testing the temperature and the strain history of the working concrete in the steel pipe foot rule model 1. Rock wool with the thickness of 20mm is used for wrapping the outer surface of the whole steel pipe full-scale model 1 for external heat preservation and maintenance.
In this embodiment, the steel pipe full scale model 1 is placed horizontally, the distance L4 between the slurry inlet 11 and the lowest end of the side wall of the steel pipe full scale model 1 is 0.3m, and the distance L5 between the slurry outlet 12 and the top of the end face of the steel pipe full scale model 1 far from the slurry inlet 11 is 0.5 m.
According to the construction method of the large-diameter steel pipe arch concrete provided by the invention, the composite expanding agent with the mass ratio of azodicarbonamide, light-burned calcium oxide clinker, light-burned magnesium oxide clinker and fine powder material of 1:40:20:39, cement, water reducing agent and other raw materials are selected and mixed to produce about 10m3The C60 self-compacting and non-shrinking concrete with working performance and volume stability meeting the requirements is used as working concrete.
The test season is summer, the daily average temperature is about 30 ℃, cold water and flake ice are added for mixing, the mold-entering temperature of the working concrete is controlled to be 27.4 ℃, and the limitation of 28 ℃ is not exceeded.
After the production of the working concrete is finished, waiting for about 1h in a concrete pump truck, namely keeping the time interval from the uniform mixing and discharging of the working concrete to the pumping of the working concrete to be 60 min; then, pumping and filling into the steel pipe full-scale model 1; and opening a vacuum pump about 10min before the beginning of the pouring to pump out air, and maintaining the vacuum degree in the steel pipe full-scale model 1 to be not lower than-0.08 MPa in the whole pouring process. Observing the slurry observing column 23, when the liquid level of the working concrete rises to about 1m height in the slurry observing column 23, stopping pumping and closing the vacuum pump and the check valve 22 at the concrete pump pipe 21. The whole perfusion process takes about 20 min.
After the working concrete in the steel pipe full scale model 1 is poured, the temperature and the strain history of the working concrete are continuously monitored. Ultrasonic velocity at different sections (test areas) is tested by an ultrasonic method according to technical rules for detecting concrete defects by an ultrasonic method in CECS 21:2000, 90d age, and the distribution conditions of the sections and the test points are shown in figures 3 and 4.
Example 2
In the description of embodiment 2, the same points as those in embodiment 1 are not repeated herein, and only the differences from embodiment 1 are described, the differences between this embodiment and embodiment 1 are: in the composite expanding agent in the embodiment, the mass ratio of azodicarbonamide, light-burned calcium oxide clinker, light-burned magnesium oxide clinker and fine powder is 0.2:50:30:19.8, and the C60 self-compacting and non-shrinkage concrete prepared by adopting the composite expanding agent is used as working concrete.
Example 3
In the description of embodiment 3, the same points as those in embodiment 1 are not repeated herein, and only the differences from embodiment 1 are described, the differences between this embodiment and embodiment 1 are: in the composite expanding agent in the embodiment, the mass ratio of azodicarbonamide, light-burned calcium oxide clinker, light-burned magnesium oxide clinker and fine powder is 2:50:30:18, and the C60 self-compacting and non-shrinkage concrete prepared from the composite expanding agent is used as working concrete.
Example 4
In the description of embodiment 4, the same points as those in embodiment 1 are not repeated herein, and only the differences from embodiment 1 are described, the differences between this embodiment and embodiment 1 are: in the composite expanding agent in the embodiment, the mass ratio of azodicarbonamide, light-burned calcium oxide clinker, light-burned magnesium oxide clinker and fine powder is 0.2:30:30:39.8, and the C60 self-compacting and non-shrinkage concrete prepared by adopting the composite expanding agent is used as working concrete.
Example 5
In the description of embodiment 5, the same points as those in embodiment 1 are not repeated herein, and only the differences from embodiment 1 are described, the differences between this embodiment and embodiment 1 are: in the composite expanding agent in the embodiment, the mass ratio of azodicarbonamide, light-burned calcium oxide clinker, light-burned magnesium oxide clinker and fine powder is 0.2:50:10:39.8, and the C60 self-compacting and non-shrinkage concrete prepared by adopting the composite expanding agent is used as working concrete.
Example 6
In the description of embodiment 6, the same points as those in embodiment 1 are not repeated herein, and only the differences from embodiment 1 are described, but the differences from embodiment 1 are: in the embodiment, the construction season is autumn, the daily average temperature is about 18 ℃, the mold-entering temperature of the working concrete is controlled to be 23.0 ℃ by adding cold water for mixing, and the limitation that the daily average temperature is not higher than +8 ℃ and not higher than 28 ℃ is met; the rest of the procedure was carried out with reference to the procedure described in example 1.
Example 7
In the description of embodiment 7, the same points as those in embodiment 1 are not repeated herein, and only the differences from embodiment 1 are described, the differences between this embodiment and embodiment 1 are: the construction season of the embodiment is winter, the daily average temperature is about 8 ℃, the mold-entering temperature of the working concrete is controlled to be 15.5 ℃ by taking a measure of fully reducing the temperature by prolonging the storage time of powder materials such as cement and the like, and the limitation of 10-18 ℃ is met; the rest of the procedure was carried out with reference to the procedure described in example 1.
In order to demonstrate the importance of the parameter control of each step of the construction method of the present invention, the inventors of the present invention also conducted the following comparative experiment.
Comparative example 1
In the description of comparative example 1, the same points as those of example 1 described above will not be described again, and only the differences from example 1 will be described. This comparative example differs from example 1 in that: in the comparative example, a composite expanding agent is not used, and only C60 self-compacting concrete with working performance and volume stability meeting requirements, which is composed of other raw materials such as cement, a water reducing agent and the like, is used as comparative working concrete; the rest of the procedure was carried out with reference to the procedure described in example 1.
The volume stability of comparative working concrete obtained in this comparative example and the first comparative full-scale model concrete obtained were tested with reference to the test method of example 1.
Comparative example 2
In the description of comparative example 2, the same points as those of example 1 described above will not be described again, and only the differences from example 1 will be described. This comparative example differs from example 1 in that: in the comparative example, the pouring of the working concrete is started only after the working concrete waits for about 10min in the transport vehicle, namely, the time interval from the uniform mixing and discharging to the pumping of the working concrete is only 10 min; the rest of the operations were carried out with reference to the procedure described in example 1.
The second comparative full-scale model concrete obtained in this comparative example was also tested with reference to the test method of example 1.
Comparative example 3
In the description of comparative example 3, the same points as those of example 1 described above will not be described again, and only the differences from the examples will be described. This comparative example differs from example 1 in that: in the comparative example, the working concrete is kept to be poured after waiting for about 150min in the transport vehicle, namely, the time interval from uniformly mixing and discharging the working concrete to pumping the working concrete is kept to be prolonged to 150 min; the rest of the procedure was carried out with reference to the procedure described in example 1.
The third comparative full-scale model concrete obtained in this comparative example was also tested with reference to the test method of example 1.
Comparative example 4
In the description of comparative example 4, the same points as those of example 1 described above will not be described again, and only the differences from example 1 will be described. This comparative example differs from example 1 in that: in the comparative example, the mold-entering temperature of the working concrete is not controlled, namely the daily average temperature in the test of the comparative example is about 30 ℃, and the mold-entering temperature reaches 36.2 ℃ after the concrete is stirred in a concrete mixer; the rest of the procedure was carried out with reference to the procedure described in example 1.
A fourth comparative full-scale model concrete obtained in this comparative example was also tested with reference to the test method of example 1.
Comparative example 5
In the description of comparative example 5, the same points as those of example 6 described above will not be described again, and only the differences from example 6 will be described. This comparative example differs from example 6 in that: in the comparative example, the mold-entering temperature of the working concrete is not controlled, namely the daily average temperature in the test of the comparative example is about 18 ℃, and the mold-entering temperature reaches 30.2 ℃ after the working concrete is mixed in a concrete mixer; the rest of the operations were carried out with reference to the procedure described in example 6.
A fifth comparative full-scale model concrete obtained in this comparative example was also tested with reference to the test method of example 6.
Comparative example 6
In the description of comparative example 6, the same points as those of example 7 described above will not be described again, and only the differences from example 7 will be described. This comparative example differs from example 7 in that: in the comparative example, the mold-entering temperature of the working concrete is not controlled, namely the daily average temperature in the test of the comparative example is about 8 ℃, and the mold-entering temperature reaches 23.2 ℃ after the mixing in a concrete mixer; the rest of the procedure was carried out with reference to the procedure described in example 7.
A sixth comparative full-scale model concrete obtained in this comparative example was also tested with reference to the test method of example 7.
Comparative example 7
In the description of comparative example 7, the same points as those of example 1 described above will not be described again, and only the differences from example 1 will be described. This comparative example differs from example 1 in that: in the comparative example, rock wool is not used for wrapping the outer surface of the whole model so as to carry out external heat preservation and maintenance; the rest of the procedure was carried out with reference to the procedure described in example 1.
A seventh comparative full-scale model concrete obtained in this comparative example was also tested with reference to the test method of example 1.
Testing the autogenous volume deformation before final setting according to the standard GB/T50448-2015, and testing the autogenous volume deformation at 3d and 90d ages from the beginning of final setting according to the standard GB/T50082-2009; the self-compacting, non-shrinking concrete obtained in examples 1 to 5 above and the self-compacting concrete obtained in comparative example 1 were respectively tested for their volume stability performance, and the results are shown in table 1.
TABLE 1 volume stability Performance test results for self-compacting, non-shrinking concrete and self-compacting concrete
×10-4
According to the data in the table 1, comparing examples 1 to 5 with comparative example 1, the volume of the concrete sample without the composite expanding agent continuously shrinks before final setting and at 3d and 90d after final setting, and the volume stability performance requirement proposed by the invention can not be met; after the expanding agent is used, the volume deformation of the concrete sample before final setting and at 3d and 90d after final setting is shown as expansion, and the higher the dosage of the azodicarbonamide plastic expansion component is, the larger the expansion deformation before final setting is; the higher the usage amount of the light-burned calcium oxide clinker, the larger the expansion deformation in 3d from the final setting test, which shows that the light-burned calcium oxide has obvious early expansion compensation shrinkage effect; the higher the usage amount of the light-burned magnesium oxide, the smaller the volume deformation drop from 3d to 90d in the final setting test, which shows that the light-burned magnesium oxide has obvious effects of delaying expansion and compensating shrinkage.
The results of measuring the temperature and strain history of the concrete for steel pipe full-scale model obtained in examples 1, 6 and 7 and comparative examples 1 to 7 are shown in Table 2, and the results of measuring the ultrasonic velocity are shown in Table 3.
TABLE 2 monitoring results of temperature and strain history of concrete of steel pipe full scale model
TABLE 3 ultrasonic velocity measurement of steel pipe full-scale model concrete at 90d age
Unit: m/s
According to the data in tables 2-3, comparative example 1 and comparative example 1, steel pipe full-scale models were poured with self-compacting, non-shrinking concrete and ordinary self-compacting concrete, respectively. It is clear that although the mold-entering temperature, the temperature peak value and the average temperature reduction rate in 7d after the temperature peak are all similar, the expansion deformation of the former in the temperature rise stage is increased by about 56 percent compared with the latter, and the contraction deformation of the former in the temperature reduction stage (basically when the temperature is reduced to the air temperature) is reduced by about 24 percent compared with the latter. Thus, when the self-compacting, non-shrinking concrete of example 1 was used as the working concrete, about 76. mu. epsilon. of expansion deformation remained when the temperature of the working concrete in the steel pipe arch was substantially lowered to the atmospheric temperature, whereas about 161. mu. epsilon. of shrinkage deformation occurred when the ordinary self-compacting concrete of comparative example 1 was used as the comparative working concrete. Meanwhile, the same rule is reflected by the ultrasonic speed test result, and the ultrasonic speed value of the steel pipe structure poured by the common self-compacting concrete in the comparative example 1 is obviously lower than that of the steel pipe structure poured by the self-compacting and non-shrinking concrete in the embodiment 1. Therefore, the composite expanding agent adopted by the invention has obvious effect on inhibiting debonding and void phenomena of the working concrete in the steel pipe arch caused by shrinkage deformation after construction.
According to the data in tables 2-3, compared with the working concrete in example 1 and comparative example 2, the pouring construction is performed after the working concrete is mixed for 1 hour and 10 minutes respectively, namely, the time interval from the mixing of the working concrete out of the machine to the pumping of the working concrete is kept to be 60 minutes and 10 minutes respectively. Obviously, although the temperature and the deformation process of the steel pipe structure are similar and have no obvious difference, the ultrasonic velocity value of the 1# measuring point of the steel pipe structure poured in the waiting time of the latter is obviously lower than that of the steel pipe structure poured in the waiting time of the former for 1h, because the 1# measuring point is the ultrasonic velocity along the vertical direction, when the waiting time is short, a large amount of bubbles in the concrete mixture (namely the working concrete in the steel pipe arch) are gathered and float upwards, and the phenomenon of void of the top in the steel pipe is generated in the plastic stage; and the 3# measuring point test values along the horizontal direction have small difference because no bubble aggregation phenomenon exists on two sides of the horizontal direction, and the concrete is closely contacted with the inner wall of the steel pipe. Therefore, the time interval from the uniform mixing and discharging of the working concrete to the pumping of the working concrete adopted in the invention is not too short, and the effect of inhibiting the vertical debonding and the hollowing of the working concrete in the steel pipe arch caused by shrinkage deformation after construction is obvious.
According to the data in tables 2-3, compared with the working concrete in example 1 and comparative example 3, the pouring construction is performed after the working concrete is mixed for 1 hour and 150 minutes respectively, namely, the time interval from the mixing of the working concrete out of the machine to the pumping of the working concrete is kept to be 60 minutes and 150 minutes respectively. Obviously, although the temperature and the deformation processes of the two are close and no obvious difference is seen, the ultrasonic velocity value of a measuring point of a part of the steel pipe structure poured in the waiting time of the latter is greatly lower than that of the steel pipe structure poured in the waiting time of the former for 1h, because the flow property of concrete is greatly lost when the waiting time is too long, the self-compaction requirement cannot be met, and the concrete cannot be completely filled in the structure after being pumped into the steel pipe structure, so that the phenomenon of void of a part of area is caused. Therefore, the time interval from uniformly mixing and discharging the working concrete to pumping in the invention is not suitable to be too long, and the effect of inhibiting the phenomenon that the working concrete in the steel pipe arch cannot be densely filled due to the obvious loss of the flowing property in the construction process is obvious.
According to the data in tables 2 to 3, the working concrete injection temperatures of comparative example 1 and comparative example 4 were 27.4 ℃ and 36.2 ℃, respectively. Obviously, the temperature peak value of the latter is also increased by 9.7 ℃, thereby causing the expansion deformation in the temperature rise stage and the shrinkage deformation in the temperature drop stage (basically when the temperature is reduced) to be respectively increased by about 5 percent and 23 percent compared with the former, so that the negative effect of the increase of the temperature drop shrinkage is obviously greater than the positive effect of the increase of the temperature rise expansion, and finally, the residual expansion deformation of the working concrete in the steel pipe arch is only about 22 mu epsilon when the temperature is basically reduced to the temperature. Meanwhile, the test result of the ultrasonic velocity also reflects the same rule, and the ultrasonic velocity value of the steel pipe structure poured by the working concrete with the mold-entering temperature not controlled in the comparative example 4 is obviously lower than that of the steel pipe structure poured by the working concrete with the mold-entering temperature controlled in the example 1. Therefore, the method has obvious effect of inhibiting the phenomena of debonding and hollowing of the working concrete in the steel pipe arch caused by shrinkage deformation after construction by controlling the mold-entering temperature according to the daily average air temperature during construction.
According to the data in tables 2 to 3, the temperature and strain history development rules of the working concrete in the steel pipe arch during autumn and winter construction are substantially the same as those during summer construction in comparative example 6 and comparative example 5, comparative example 7 and comparative example 6, and the test result of the ultrasonic velocity also reflects the same rules. Therefore, the method has obvious effect of inhibiting the phenomena of debonding and hollowing of the working concrete in the steel pipe arch caused by shrinkage deformation after construction by controlling the mold-entering temperature according to the daily average air temperature during construction.
According to the data in tables 2-3, example 1 and comparative example 7 were compared with and without external heat-insulating measures. Obviously, although the mold-entering temperatures of the two are similar, the temperature peak value of the former is higher than 9.6 ℃ of the latter, and the expansion deformation is greatly increased by 115 mu epsilon in the temperature rise stage; the average temperature drop rate in 7 days after the temperature peak is only about 38 percent of the latter; although the latter has a smaller total shrinkage deformation in the temperature drop phase (when the temperature is substantially reduced), the specific shrinkage deformation per temperature drop is increased by about 11%. Therefore, according to the volume deformation test result of the concrete in the pipe in the stages of temperature rise and temperature drop, when the heat preservation measure is not adopted, the residual expansion deformation of the working concrete in the steel pipe arch is greatly reduced to only about 12 mu epsilon when the temperature of the working concrete is basically reduced to the air temperature. Meanwhile, the same rule is reflected by the test result of the ultrasonic velocity, and the ultrasonic velocity value of the steel pipe structure poured when the heat preservation measure is not adopted in the comparative example 7 is obviously lower than that of the steel pipe structure poured when the heat preservation measure is adopted in the embodiment 1. Therefore, the method for externally insulating the outer part of the steel pipe arch to slow down the temperature drop rate of the working concrete in the steel pipe arch has obvious effect on inhibiting the phenomena of debonding and void of the working concrete in the steel pipe arch caused by shrinkage deformation after construction.
It should be noted that the construction method provided by the present invention is not limited to concrete in a large-diameter steel pipe arch with a diameter of 1.0m to 2.0m, and as understood by those skilled in the art, the risk of shrinkage and void of a steel pipe arch with a diameter of less than 1.0m is usually significantly lower than that of a large-diameter steel pipe arch, and the problem of shrinkage and void of a steel pipe arch with a diameter of less than 1.0m can be better solved by adopting an expanding agent measure.
While the invention has been shown and described with reference to certain embodiments, those skilled in the art will understand that: various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.
Claims (7)
1. The construction method of the large-diameter steel pipe arch concrete is characterized by comprising the following steps of:
selecting working concrete: adopting self-compacting and non-shrinkage concrete added with a composite expanding agent as the working concrete;
the control step of the waiting time for the working concrete to enter the pump comprises the following steps: keeping the time interval from uniformly mixing the working concrete out of the machine to pumping the working concrete to be 45-120 min;
and (3) controlling the mold-entering temperature of the working concrete: adjusting the mold-entering temperature T of the working concrete according to the daily average air temperature T during construction0(ii) a Wherein, when the daily average temperature T is more than or equal to 25 ℃, the mold-entering temperature T is controlled0Less than or equal to 28 ℃; when the daily average temperature T is more than or equal to 10 ℃ and less than 25 ℃, controlling the mold-entering temperature T0Average temperature less than or equal to daily+8 ℃ and T0Less than or equal to 28 ℃; when the daily average temperature T is less than 10 ℃, controlling the mold-entering temperature T to be less than or equal to 10 DEG C0＜18℃；
The working concrete is put into a mould: firstly, controlling the vacuum degree in a steel pipe arch to be not lower than-0.08 MPa, and then pumping the working concrete into the steel pipe arch until the whole space in the steel pipe arch is filled;
the external heat preservation operation steps of the steel pipe arch are as follows: and carrying out external heat preservation treatment on the outside of the steel pipe arch so as to enable the average temperature drop rate v in 7d after the working concrete temperature peak in the steel pipe arch to be less than or equal to 5 ℃/d.
2. The construction method according to claim 1, wherein in the selection step of the working concrete, the working performance of the self-compacting, non-shrinking concrete meets the requirements of standard JGJ/T283-2012;
the key control indexes of the volume stability performance of the self-compacting and non-shrinkage concrete comprise: firstly, the autogenous volume deformation before final setting is 0.02-0.1 percent, and the test is carried out according to the standard GB/T50448-2015; ② the autogenous volume deformation is more than or equal to 0.02 percent when the self-setting is started at the 3d age, and the test is carried out according to the standard GB/T50082-2009; and thirdly, the autogenous volume deformation is larger than 0 at the age of 90d from the final setting, and the test is carried out according to the standard GB/T50082-2009.
3. The construction method according to claim 1 or 2, wherein in the selection step of the working concrete, the composite expanding agent comprises 0.2-2% of azodicarbonamide plastic expansion component, 30-50% of light-burned calcium oxide clinker, 10-30% of light-burned magnesium oxide clinker and the balance of fine powder, wherein the mass of the composite expanding agent is 100%; wherein the specific surface area of the fine powder is more than 200m2/kg。
4. The construction method according to claim 3, wherein in the selection step of the working concrete, the amount of the composite expansive agent added is 8 to 10% by mass.
5. The construction method according to claim 1, wherein in the step of controlling the mold-entering temperature, the working concrete is cooled by at least one of sunshade storage of raw materials, storage time extension, air cooling, mixing by adding cold water or flake ice, liquid nitrogen cooling, and heat preservation of a loading pump of a transport vehicle; or heating the working concrete by adopting at least one mode of heating raw materials, mixing with hot water and insulating the loading pump of a transport vehicle.
6. The construction method according to claim 1, wherein the outer insulation operation step is performed by winding an insulation material around the outside of the steel pipe arch.
7. The construction method according to claim 6, wherein the thermal conductivity of the thermal insulation material is not more than 0.045W/(m-K) and meets the fire protection requirement of B1 level and above in GB8624-2012, and the thickness of the thermal insulation material is not less than 20 mm.
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