CN107815938A - A kind of Synthesis Support System of severe cold area concrete extension joint quality control on construction - Google Patents
A kind of Synthesis Support System of severe cold area concrete extension joint quality control on construction Download PDFInfo
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- 238000010276 construction Methods 0.000 title claims abstract description 34
- 238000003908 quality control method Methods 0.000 title claims abstract description 4
- 230000015572 biosynthetic process Effects 0.000 title abstract 2
- 238000003786 synthesis reaction Methods 0.000 title abstract 2
- 238000010438 heat treatment Methods 0.000 claims abstract description 78
- 238000000034 method Methods 0.000 claims abstract description 42
- 238000011161 development Methods 0.000 claims abstract description 28
- 238000012423 maintenance Methods 0.000 claims abstract description 20
- 239000000463 material Substances 0.000 claims abstract description 11
- 238000002360 preparation method Methods 0.000 claims abstract description 10
- 238000012544 monitoring process Methods 0.000 claims abstract description 6
- 239000004793 Polystyrene Substances 0.000 claims description 25
- 229920002223 polystyrene Polymers 0.000 claims description 25
- 239000002985 plastic film Substances 0.000 claims description 24
- 229920006255 plastic film Polymers 0.000 claims description 24
- 238000002156 mixing Methods 0.000 claims description 23
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 20
- 239000004576 sand Substances 0.000 claims description 19
- 238000001723 curing Methods 0.000 claims description 14
- 238000004321 preservation Methods 0.000 claims description 14
- 239000004568 cement Substances 0.000 claims description 13
- 230000036571 hydration Effects 0.000 claims description 13
- 238000006703 hydration reaction Methods 0.000 claims description 13
- 238000009413 insulation Methods 0.000 claims description 11
- 239000004575 stone Substances 0.000 claims description 11
- 229920000742 Cotton Polymers 0.000 claims description 7
- 230000004913 activation Effects 0.000 claims description 6
- 238000004364 calculation method Methods 0.000 claims description 6
- 238000006243 chemical reaction Methods 0.000 claims description 6
- 239000002184 metal Substances 0.000 claims description 6
- 238000013461 design Methods 0.000 claims description 5
- 230000007547 defect Effects 0.000 claims description 3
- 230000000694 effects Effects 0.000 claims description 3
- 239000000126 substance Substances 0.000 claims description 3
- 230000010354 integration Effects 0.000 claims 1
- 239000011505 plaster Substances 0.000 claims 1
- 238000012360 testing method Methods 0.000 abstract description 4
- 238000000205 computational method Methods 0.000 abstract 1
- 238000000275 quality assurance Methods 0.000 description 2
- 238000007789 sealing Methods 0.000 description 2
- 240000005498 Setaria italica Species 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 230000015271 coagulation Effects 0.000 description 1
- 238000005345 coagulation Methods 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 230000005494 condensation Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000007710 freezing Methods 0.000 description 1
- 230000008014 freezing Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
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- 230000002035 prolonged effect Effects 0.000 description 1
- 230000009897 systematic effect Effects 0.000 description 1
Classifications
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- E—FIXED CONSTRUCTIONS
- E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
- E01C—CONSTRUCTION OF, OR SURFACES FOR, ROADS, SPORTS GROUNDS, OR THE LIKE; MACHINES OR AUXILIARY TOOLS FOR CONSTRUCTION OR REPAIR
- E01C11/00—Details of pavings
- E01C11/02—Arrangement or construction of joints; Methods of making joints; Packing for joints
- E01C11/04—Arrangement or construction of joints; Methods of making joints; Packing for joints for cement concrete paving
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- E—FIXED CONSTRUCTIONS
- E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
- E01C—CONSTRUCTION OF, OR SURFACES FOR, ROADS, SPORTS GROUNDS, OR THE LIKE; MACHINES OR AUXILIARY TOOLS FOR CONSTRUCTION OR REPAIR
- E01C11/00—Details of pavings
- E01C11/24—Methods or arrangements for preventing slipperiness or protecting against influences of the weather
- E01C11/26—Permanently installed heating or blowing devices ; Mounting thereof
Abstract
The invention discloses a kind of Synthesis Support System for the severe cold area concrete extension joint quality control on construction for belonging to field of civil engineering.Including：(1) severe cold area concrete extension joint constructing structure；(2) fresh concrete temperature safeguard；(3) concrete heater circuit arrangement；(4) concrete measuring temperature arrangement；(5) concrete heat-insulating maintenance process；(6) heater circuit testing and control project；(7) the concrete strength development course computational methods based on equivalent age.The present invention is the structure type based on concrete extension joint, loading condition and military service performance requirement, is prepared from concrete material, multiple angles such as heating means and embodiment, maintenance measure, strength development monitoring method, the construction quality for systematically ensureing concrete extension joint.By contrasting the relation between equivalent age strength and preparation strength, it can determine that concrete extension joint terminates the time of maintenance or open to traffic；Improve road and bridge construction quality and service life.
Description
Technical Field
The invention belongs to the field of civil engineering, and particularly relates to a comprehensive guarantee system for controlling the construction quality of a concrete expansion joint in a severe cold area. In particular to a heating-heat preservation-strength development comprehensive guarantee system for concrete expansion joint construction in severe cold regions.
Background
When the concrete expansion joint construction is carried out in severe cold areas, the problems of low temperature of concrete entering a mold, slow concrete condensation process and strength development and even freeze-thaw damage caused by low-temperature materials, foundations and atmospheric environments are often faced.
In order to solve the above problems, the conventional measures include raising the concrete discharging temperature by heating the mixing water of the concrete, preventing the heat loss by maintaining the concrete poured into the mold, and accelerating or ensuring the hydration process of the concrete by heating the surface of the concrete. However, the above measures cannot effectively guarantee the development of the overall strength of the concrete poured in the expansion joint, because the low-temperature roadbed can lower the temperature of the concrete at the bottom and the side and hinder the development of the strength. In practical engineering application, the termination of curing or the opening of traffic is often determined according to the resilience value of the concrete surface; at this time, the area with slowly developed strength of the bottom or the side surface becomes a weak area of strength, and if the strength of the area is not enough to bear the external load, the area can be damaged in the stress process, and the integrity, the anti-penetration capability and the service life of the expansion joint are negatively affected.
At present, no overall guarantee scheme aiming at the construction quality of concrete expansion joints in severe cold regions exists at home and abroad, and only some suggested measures are provided in the aspects of mix proportion design, maintenance method, heat preservation measures, strength development and the like of concrete. The American ACI306R specification (concrete construction guide under low-temperature climate conditions) proposes the mold-entering temperature of concrete, the curing time required for resisting one-time freeze-thaw damage, a curing device and a maturity characterization method aiming at the concrete construction in severe cold areas. China's JGJ/T104 regulation (construction regulation in winter of construction engineering) proposes the freezing critical strength, heating maintenance method and application method of equivalent age of concrete for concrete construction under low temperature condition. Although the proposal is helpful for the construction of the concrete expansion joint in severe cold areas, the concrete expansion joint which has small volume and large specific surface area and is poured in the grooved foundation lacks systematic countermeasures and technical guidance; wherein, the definition of the severe cold area refers to a time period of less than 4 ℃ in the daily temperature change process of the area.
Based on the structural form, the load condition and the service performance requirement of the concrete expansion joint, the construction quality of the concrete expansion joint is systematically ensured from a plurality of angles of a concrete material preparation method, a heating method, an implementation mode, a maintenance measure and a strength development monitoring method, and a heating-heat preservation-strength development comprehensive guarantee system for the construction of the concrete expansion joint in a severe cold region is provided.
Disclosure of Invention
The invention aims to provide a comprehensive guarantee system for controlling the construction quality of a concrete expansion joint in a severe cold area, which is characterized in that the comprehensive guarantee system is a heating-heat preservation-strength development comprehensive guarantee system for the construction of the concrete expansion joint in the severe cold area;
the integrated safeguard system includes: (1) a concrete expansion joint construction structure in a severe cold area; (2) temperature guarantee measures of fresh concrete; (3) A concrete heating circuit, a temperature sensor arrangement and a temperature control scheme; (4) a concrete heat-preservation curing method; (5) A concrete strength development process calculation method based on equivalent age; the method comprises the following steps:
1) Severe cold area concrete expansion joint construction structures:
an original concrete roadbed 11 is laid on the foundation 10, and a concrete expansion joint 8 poured by concrete is arranged between two sections of the original concrete roadbed 11; a metal expansion joint 6 is fixed in the middle of the concrete expansion joint 8 by a pin 7 on the metal expansion joint; the insulating layer 9 covers the concrete expansion joint 8; insulating heating wires 1 are regularly arranged in the concrete expansion joint 8, and temperature sensors 2 are arranged at proper positions of the upper part, the middle part and the lower part; the insulated heating wire 1 is connected with a temperature controller 4, and the temperature sensor 2 is connected with a temperature acquisition instrument 3; the temperature acquisition instrument 3 and the temperature controller 4 are respectively connected with the computer 5;
2) Temperature guarantee scheme for fresh concrete
In severe cold areas, materials such as cement, sand and stones for preparing concrete are stored outdoors and are influenced by the surrounding low-temperature environment, and the temperature of the materials is only a few degrees centigrade or less than 5 degrees centigrade, even negative temperature; meanwhile, the sand and stones piled outdoors contain snow blocks and ice blocks under the action of rain, snow and wind; if no proper measures are taken, the prepared concrete is only at a temperature of a few degrees centigrade or less than 10 degrees centigrade; the concrete with the low temperature has slow hydration process, and is characterized by long setting time and slow strength development; if the concrete poured in place further radiates heat to the foundation or the environment, so that the temperature is lower than minus 7 ℃, the hydration of the concrete is terminated, and freeze-thaw damage can be generated;
in order to guarantee or accelerate the strength development rate of the concrete, the mixing water of the concrete is heated to improve the machine-out temperature of the concrete; the temperature of the fresh concrete is increased, so that the initial temperature of the concrete is higher than 5 ℃ after the concrete is poured into a mold and exchanges heat with a foundation and the surrounding environment, and snow blocks and ice blocks in sand can be melted in the mixing process, so that the substances are prevented from remaining in the fresh concrete and forming defects in the later period;
3) Concrete heating circuit, temperature sensor arrangement and temperature control scheme
After concrete is poured into a mold, heat in the concrete can be dissipated to a low-temperature foundation and air, and the existing engineering practice proves that the temperature field distribution of the concrete is that the middle temperature is high, the boundary temperature is low, the upper temperature is high, and the lower temperature is low, so that if the concrete strength of different parts in the concrete expansion joint is synchronously developed, a low-temperature area is heated; the concrete expansion joint heating method comprises the following steps that grids are arranged on a cross section perpendicular to the length direction of a concrete expansion joint in a dividing mode, insulating heating wires are arranged in the center of each grid along the length direction of the concrete expansion joint, the heating range of each insulating heating wire is a prism body arranged on the grid in the dividing mode, each heating wire and a power supply are in a parallel connection state and are independently controlled by a temperature control device controlled by a computer to achieve heating and stopping, and the power of each insulating heating wire enables the prism body to generate the heating capacity of 2 ℃ per hour;
secondly, the arrangement of the temperature sensors in the concrete expansion joint can reflect the temperature field in the concrete expansion joint; the concrete expansion joint is of a prism structure as a whole, after traffic is opened, the action position of wheels is 1 meter away from the edge of the concrete expansion joint, so that the position is used as a monitoring area of a concrete temperature field, the arranged temperature sensors are divided into a middle column and a boundary column according to the symmetry of the concrete expansion joint and the insulated heating wires arranged in the concrete expansion joint, three sensors, namely a bottom sensor, a middle sensor and an upper sensor, are arranged in each column, a computer and a temperature controller are jointly controlled through temperature signals measured by the temperature sensors, the maximum value of the temperature signals measured by all the temperature sensors is used as a target, the insulated heating wires at different positions are switched on or off, heating of set parts is realized, and finally, the concrete at different parts undergoes the same temperature history; the heating circuit is arranged in the concrete, and aims to heat the fresh concrete by means of heat energy converted from external input electric energy so as to raise the temperature of the fresh concrete, thereby ensuring the hydration process of the concrete.
4) Concrete heat-preservation maintenance method
After the concrete is poured into the expansion joint and is vibrated to be dense and plastered, a heat insulation layer is paved on the upper surface of the concrete expansion joint as soon as possible, sealing and curing are carried out, and the concrete measures are as follows: (1) Covering a first layer of plastic film on the upper surface of the concrete expansion joint to prevent the concrete from losing moisture to the outside; (2) Covering a polystyrene board with the thickness of 5 cm on the first layer of plastic film, and preventing the heat in the concrete from dissipating to the air by utilizing the excellent heat-insulating capacity of the polystyrene board; (3) Covering a layer of quilt on the polystyrene board to prevent the heat loss at the joints of the polystyrene board; (4) Covering a second layer of plastic film on the quilt to prevent the moisture in the air from migrating or condensing into the quilt and prevent the heat preservation capacity of the quilt from being reduced; wherein the polystyrene board is an extruded polystyrene board, the fire-proof grade B1 and the heat conductivity coefficient are not more than 0.03W/m.K;
the sizes of the first layer of plastic film, the polystyrene board, the quilt and the second layer of plastic film from bottom to top are sequentially increased; the size of the first plastic film layer at the lowest part is increased by 40 cm in the length direction and the width direction respectively than the concrete expansion joint poured into the mould, and the subsequent polystyrene board is increased by at least 20 cm in the length direction and the width direction respectively than the first plastic film layer, the cotton quilt layer and the second plastic film layer.
5) Concrete strength development process calculation method based on equivalent age
The effect of the temperature history experienced by the concrete on the strength can be examined by an equivalent age method based on the Arrenius formula, wherein k = Ae -(E/RT) Expressed is the relationship between the rate constant of a chemical reaction and the activation energy and temperature; wherein k is a chemical reaction rate constant, A is a frequency factor constant, E is a natural constant, E is activation energy, R is a gas constant, and T is a Kelvin temperature;
the calculated equivalent age is for Arrhenius formula k = Ae -(E/RT) Integrating and converting the temperature experienced by the concrete into the age of 20 ℃, as shown in the following formula,
wherein, t e Is the equivalent age; t is a unit of r Is a reference temperature 293K (kelvin), corresponding to 20 degrees celsius;
t is the temperature experienced by the concrete at different time points (kelvin); t is the time to reach the equivalent age.
The strength development process of the concrete is realized by a logarithm function formula S = a + b × ln (t)Expression, where t is the age under standard conditions, and a and b are constants that can be passed through standard maintenance conditions: the concrete sample cured at the temperature of =20 ℃ and the relative humidity of more than or equal to 95% is fitted out by the strength of the concrete sample tested in the age of 28 days; at the moment, the t value is the age of the concrete sample under the standard curing condition; after a and b in the formula are fitted, the formulaSubstituting the calculated equivalent age into a logarithm function formula 5=a + b in (t), and then obtaining the equivalent age strength;
when the curing is stopped, the strength of the concrete is more than 70 percent of the preparation strength; when the traffic is open, the coagulation strength is 100% of the preparation strength. By comparing the relation between the equivalent age strength and the design strength, the time for stopping the maintenance or opening the traffic of the concrete expansion joint can be determined.
Heating the mixing water for the concrete to ensure that the leaving temperature of the concrete is 20 ℃; the temperature to which the mixing water is heated is calculated by equation (1):
wherein, T i，w The temperature of the heated mixing water is in centigrade degree; m is w 、m b 、m a 、m s The dosage of mixing water, cement, stones and sand is kilogram/cubic meter; c w 、C b 、C a 、C s The specific heat capacities of mixing water, cement, stones and sand are respectively kilojoule/(kilogram DEG C); t is i，b 、T i，a 、T i，s Respectively inquiring the initial temperature of the cement, the pebble and the sand at the temperature of centigrade; t is f The temperature of the mixed concrete after leaving the machine is centigrade.
The cross section perpendicular to the length direction of the concrete expansion joint is provided with grids in a dividing mode, each grid is a square with the length of 100mm and 100mm, and the center of each square is provided with a dielectric layer with the diameter of 3mm and the length resistance of 33 omega/m per meterThe length of the concrete expansion joint is 8m, the specific heat capacity of the concrete is 0.97 kJ/(kg DEG C), the voltage at two ends of the insulating heating wire is 220V, the insulating heating wire is a pure resistance element, and the hydration heat release of the concrete is not considered, so that when the full-power heat release of the insulating heating wire is realized, the heat release quantity Q per hour is shown as formula (2), and the heat release quantity can ensure that the temperature rise value T per hour of the concrete is realized S As shown in formula (3), the design requirement (3.5 ℃/h is more than 2 ℃/h) is met; the general formulas of the formula (2) and the formula (3) are as follows,
in the formula (2), Q is the heat release amount of the heat insulation heating wire per hour, kJ/h, U is the voltage (V) at two ends of the heat insulation heating wire, L is the length (m) of the concrete expansion joint, and R is the resistance (omega/m) of the heat insulation heating wire per meter; 3600 seconds(s) per hour;
t in formula (3) S The temperature rise value of the concrete per hour is DEG C/h; q is the heat release per hour of the heat insulation heating wire, kJ/h; q represents the specific heat capacity of the concrete, kJ/(kg. DEG C); v is the volume of concrete to be heated by the insulated heating wire, m 3 (ii) a Rho is the volume weight of concrete, kg/m 3 。
The invention has the beneficial effects that the construction quality of the concrete expansion joint is systematically ensured from a plurality of angles such as concrete material preparation, heating methods, implementation modes, maintenance measures, strength development monitoring methods and the like based on the structural form, load conditions and service performance requirements of the concrete expansion joint. By comparing the relation between the equivalent age strength and the preparation strength, the time for terminating the maintenance or opening the traffic of the concrete expansion joint can be determined; the construction quality of the road and bridge is improved and the service life of the road and bridge is prolonged.
Drawings
Fig. 1 is a schematic view of a concrete expansion joint construction quality assurance system in a severe cold region.
Fig. 2 is a schematic diagram of a concrete temperature field of a concrete expansion joint in a severe cold region.
Detailed Description
The invention provides a comprehensive guarantee system for controlling the construction quality of a concrete expansion joint in a severe cold area, in particular to a heating-heat preservation-strength development comprehensive guarantee system for the construction of the concrete expansion joint in the severe cold area. The following description is made with reference to the accompanying drawings.
Fig. 1 is a schematic view of a concrete expansion joint construction quality assurance system in a severe cold region. The integrated safeguard system shown in the figure includes: (1) a concrete expansion joint construction structure in a severe cold area; (2) temperature guarantee measures of fresh concrete; (3) A concrete heating circuit, a temperature sensor arrangement and a temperature control scheme; (4) a concrete heat-preservation curing method; (5) A concrete strength development process calculation method based on equivalent age; the method comprises the following steps:
1) Severe cold area concrete expansion joint construction structures:
as shown in fig. 1, an original concrete subgrade 11 is laid on a foundation 10, and a concrete expansion joint 8 poured by concrete is arranged between two sections of the original concrete subgrade 11; a metal expansion joint 6 is fixed in the middle of the concrete expansion joint 8 by a pin 7 on the metal expansion joint; the insulating layer 9 covers the concrete expansion joint 8; insulating heating wires 1 are regularly arranged in the concrete expansion joint 8, and temperature sensors 2 are arranged at proper positions of the upper part, the middle part and the lower part; the insulated heating wire 1 is connected with a temperature controller 4, and the temperature sensor 2 is connected with a temperature acquisition instrument 3; the temperature acquisition instrument 3 and the temperature controller 4 are respectively connected with the computer 5;
2) Temperature guarantee scheme for fresh concrete
In severe cold areas, materials such as cement, sand and stones for preparing concrete are stored outdoors and are influenced by the surrounding low-temperature environment, and the temperature of the materials is only a few degrees centigrade or less than 5 degrees centigrade, even negative temperature; meanwhile, the sand and the stones stacked outdoors contain snow blocks and ice blocks under the action of rain, snow and wind; if no proper measures are taken, the temperature of the prepared concrete is below 10 ℃; the concrete with the low temperature has slow hydration process, and is characterized by long setting time and slow strength development; if the concrete poured in place further radiates heat to the foundation or the environment, so that the temperature is lower than minus 7 ℃, the hydration of the concrete is terminated, and freeze-thaw damage can be generated;
in order to guarantee or accelerate the strength development rate of the concrete, the mixing water of the concrete is heated to improve the leaving temperature of the concrete; the temperature of the fresh concrete is increased, so that the initial temperature of the concrete is higher than 5 ℃ after the concrete is poured into a mold and exchanges heat with the foundation and the surrounding environment, and snow blocks and ice blocks in sand can be melted in the mixing process, so that the residual of the substances in the fresh concrete is prevented, and the defects are formed at the later stage.
Based on the reasons, the fresh concrete temperature guarantee scheme provided by the invention is to heat the mixing water of the concrete, so that the leaving temperature of the concrete is 20 ℃. The temperature to which the mixing water is heated is calculated by equation (1):
wherein, T i，w The temperature of the heated mixing water is in centigrade degree; m is w 、m b 、m a 、m s The dosage of mixing water, cement, foxtail millet and sand is kilogram/cubic meter; c w 、C b 、C a 、C s The specific heat capacities of mixing water, cement, stones and sand are respectively kilojoule/(kilogram DEG C); t is i，b 、T i，a 、T i，s Respectively inquiring the initial temperature of the cement, the pebble and the sand at the temperature of centigrade; t is f The temperature of the mixed concrete after leaving the machine is centigrade.
For example, the initial temperature of the concrete prepared by heating the mixing water to 80 degrees Celsius and using cement, gravel and sand with an initial temperature of 3 degrees Celsius is around 18 degrees Celsius (depending on the amount of the materials in the concrete) as calculated by equation (1).
3) Concrete heating circuit, temperature sensor arrangement and temperature control scheme
After the concrete is poured into a mold, the heat in the concrete can be dissipated to the low-temperature foundation and the air, and the existing engineering practice proves that the temperature field distribution of the concrete is that the middle temperature is high, the boundary temperature is low, the upper temperature is high, and the lower temperature is low, so that the temperature field shown in figure 2 is formed; therefore, if the concrete strength of different parts in the concrete expansion joint is synchronously developed, the low-temperature area is heated; the concrete expansion joint is characterized in that an insulating layer 9 covers the concrete expansion joint 8; the section vertical to the length direction of the concrete expansion joint 8 is provided with grids in a scribing way, the center of each grid is provided with an insulating heating wire 1, and the upper, middle and lower proper positions are provided with temperature sensors 2; the insulated heating wire 1 is connected with a temperature controller 4, and the temperature sensor 2 is connected with a temperature acquisition instrument 3; the temperature collector 3 and the temperature controller 4 are respectively connected with the computer 5. The heating range of each insulating heating wire 1 is in the prism of the grid, each insulating heating wire arranged in fig. 1 is independently controlled, each heating wire and a power supply are in a parallel state and are independently controlled by a temperature controller 4 controlled by a computer 5 to realize heating and stopping, and the power of each insulating heating wire is required to enable the prism to generate the heating capacity of 2 ℃ per hour;
secondly, the arrangement of the temperature sensor 2 in the concrete expansion joint 8 should reflect the temperature field in the concrete expansion joint shown in fig. 2; the concrete expansion joint 8 is a prism structure as a whole, after traffic is opened, the action position of wheels is about 1 meter away from the edge of the concrete expansion joint 8, therefore, the position is used as a monitoring area of a concrete temperature field, the arranged temperature sensors 2 are divided into a middle column and a boundary column according to the symmetry of the concrete expansion joint 8 and the insulating heating wires 1 arranged in the concrete expansion joint, three temperature sensors 2 at the bottom, the middle and the upper are arranged in each column, a computer and a temperature controller carry out combined control through temperature signals measured by the temperature sensors, the maximum value of the temperature signals measured by all the temperature sensors is taken as a target, the power supply is switched on or switched off for the insulating heating wires at different positions, heating of set positions is realized, and finally, the concrete at different positions undergoes the same temperature history; the heating circuit is arranged in the concrete, and aims to heat the fresh concrete by means of heat energy converted from external input electric energy, so that the temperature of the fresh concrete is raised, and the hydration process of the concrete is guaranteed.
For example, a square of 100mm x 100mm is scribed on the section of a concrete expansion joint, an insulating heating wire with the diameter of 3mm and the resistance of 33 omega/m is arranged in the center of the square, the length of the concrete expansion joint is 8m, the specific heat capacity of the concrete is 0.97 kJ/(kg. DEG C.), the voltage at two ends of the insulating heating wire is 220V, the insulating heating wire is a pure resistance element, and meanwhile, the hydration heat release of the concrete is not considered, the heat release quantity per hour is calculated to be 660kJ by the formula (2) when the heat insulation heating wire generates heat at full power, the heat release quantity can enable the temperature rise value per hour of the concrete to be calculated to be 3.5 ℃/h by the formula (3), and the design requirement (3.5 ℃/h is more than 2 ℃/h) is met. The specific formula (2) and formula (3) are calculated as follows,
formula (2):formula (3):
4) Concrete heat-preservation maintenance method
After the concrete is poured into the expansion joint and is vibrated to be dense and plastered, a heat preservation layer 9 is paved on the upper surface of the concrete expansion joint 8 as soon as possible, sealing and maintenance are carried out, and the concrete measures are as follows: (1) Covering a first layer of plastic film on the upper surface of the concrete expansion joint to prevent the concrete from losing moisture to the outside; (2) The polystyrene board after 5 cm is covered on the first layer of plastic film, and the excellent heat preservation capability of the polystyrene board is utilized to prevent the heat in the concrete from dissipating to the air; (3) Covering a layer of quilt on the polystyrene board to prevent the heat loss at the joints of the polystyrene board; (4) The cotton quilt is covered with a second layer of plastic film to prevent the moisture in the air from migrating or condensing into the cotton quilt and prevent the heat preservation capacity of the cotton quilt from being reduced. (the polystyrene board is an extruded polystyrene board with fire-proof grade B1 and thermal conductivity not more than 0.03W/m.K),
the sizes of the first layer of plastic film, the polystyrene board, the quilt and the second layer of plastic film from bottom to top are sequentially increased; the size of the first plastic film layer at the lowest part is 40 cm larger than that of the concrete expansion joint poured into the mould in the length and width directions, and the subsequent polystyrene board layer is at least 20 cm larger than that of the first plastic film layer, the cotton quilt layer and the second plastic film layer in sequence in the length and width directions.
5) Concrete strength development process calculation method based on equivalent age
The effect of the temperature history experienced by concrete on the strength can be examined by an equivalent age method based on an Arrenius formula, wherein the Arrhenius formula expresses the relationship between the rate constant of a chemical reaction and activation energy and temperature, and is shown in a formula (4):
k＝Ae -(E/RT) (4)
wherein k is a chemical reaction rate constant, A is a frequency factor constant, E is a natural constant, E is activation energy, R is a gas constant, and T is a Kelvin temperature;
the calculated equivalent age is an age in which the temperature experienced by the concrete is converted to 20 degrees celsius as shown in equation (5).
Wherein, t e Is the equivalent age; t is a unit of r Is reference temperature =293K (kelvin, corresponding to 20 degrees celsius); t is the temperature experienced by the concrete at different time points (expressed as kelvin); t is the time to reach the equivalent age.
The strength development course of the concrete can be expressed by a logarithmic function shown in formula (3), wherein t is the age, and a and b are constants which can be fitted by the strength of a concrete sample cured under standard curing conditions (temperature =20 ℃, relative humidity is more than or equal to 95%) in a 28-day age test; at this time, the t value is the age of the concrete sample under standard curing conditions.
S＝a+b*ln(t) (6)
After a and b in the formula (6) are fitted, the equivalent age calculated by the formula (2) is substituted into the formula (6), and the equivalent age intensity can be obtained.
When the curing is stopped, the strength of the concrete is more than 70 percent of the preparation strength; when the traffic is open, the strength of the concrete should reach 100% of the formulated strength. By comparing the relation between the equivalent age strength and the preparation strength, the time for stopping the maintenance or opening the traffic of the concrete expansion joint can be determined.
In addition, for the sake of safety, other strength testing methods, such as a rebound method and a temperature matching maintenance method performed in a laboratory, can be used for testing the strength of the concrete in the expansion joint, so that the confidence of the determination of the termination maintenance or the open traffic of the concrete expansion joint is increased.
Claims (3)
1. A comprehensive guarantee system for controlling the construction quality of a concrete expansion joint in a severe cold area is characterized in that the comprehensive guarantee system is a heating-heat preservation-strength development comprehensive guarantee system for the concrete expansion joint construction in the severe cold area;
the integrated safeguard system comprises: (1) a concrete expansion joint construction structure in a severe cold area; (2) temperature guarantee measures of fresh concrete; (3) A concrete heating circuit, a temperature sensor arrangement and a temperature control scheme; (4) a concrete heat-preservation curing method; (5) A concrete strength development process calculation method based on equivalent age; the method comprises the following steps:
1) Severe cold area concrete expansion joint construction structures:
an original concrete roadbed (11) is laid on the foundation (10), and a concrete expansion joint (8) poured by concrete is arranged between two sections of the original concrete roadbed (11); the metal expansion joint (6) is fixed in the middle of the concrete expansion joint (8) by a pin (7) on the metal expansion joint; the heat insulation layer (9) covers the concrete expansion joint (8); insulating heating wires (1) are regularly arranged at the concrete expansion joint (8) and temperature sensors (2) are arranged at proper positions of the upper part, the middle part and the lower part; the insulating heating wire (1) is connected with a temperature controller (4), and the temperature sensor (2) is connected with a temperature acquisition instrument (3); the temperature acquisition instrument (3) and the temperature controller (4) are respectively connected with the computer (5);
2) Temperature guarantee scheme for fresh concrete
In severe cold areas, materials such as cement, sand and stones for preparing concrete are stored outdoors and are influenced by the surrounding low-temperature environment, and the temperature of the materials is only a few degrees centigrade or less than 5 degrees centigrade, even negative temperature; meanwhile, the sand and stones piled outdoors contain snow blocks and ice blocks under the action of rain, snow and wind; if no proper measures are taken, the prepared concrete is only at a temperature of a few degrees centigrade or less than 10 degrees centigrade; the concrete with the low temperature has slow hydration process, and is characterized by long setting time and slow strength development; if the concrete poured in place further radiates heat to the foundation or the environment, so that the temperature is lower than minus 7 ℃, the hydration of the concrete is terminated, and freeze-thaw damage can be generated;
in order to guarantee or accelerate the strength development rate of the concrete, the mixing water of the concrete is heated to improve the leaving temperature of the concrete; the temperature of the fresh concrete is increased, so that the initial temperature of the concrete is higher than 5 ℃ after the concrete is poured into a mold and exchanges heat with a foundation and the surrounding environment, and snow blocks and ice blocks in sand can be melted in the mixing process, so that the substances are prevented from remaining in the fresh concrete and forming defects in the later period;
3) Concrete heating circuit, temperature sensor arrangement and temperature control scheme
After concrete is poured into a mold, heat in the concrete can be dissipated to a low-temperature foundation and air, and the existing engineering practice proves that the temperature field distribution of the concrete is that the middle temperature is high, the boundary temperature is low, the upper temperature is high, and the lower temperature is low, so that if the concrete strength of different parts in the concrete expansion joint is synchronously developed, a low-temperature area is heated; the concrete expansion joint heating method comprises the following steps that grids are arranged on a cross section perpendicular to the length direction of a concrete expansion joint in a dividing mode, insulating heating wires are arranged in the center of each grid along the length direction of the concrete expansion joint, the heating range of each insulating heating wire is a prism body arranged on the grid in the dividing mode, each heating wire and a power supply are in a parallel connection state and are independently controlled by a temperature control device controlled by a computer to achieve heating and stopping, and the power of each insulating heating wire enables the prism body to generate the heating capacity of 2 ℃ per hour;
secondly, the arrangement of the temperature sensors in the concrete expansion joint can reflect the temperature field in the concrete expansion joint; the concrete expansion joint is of a prism structure as a whole, after traffic is opened, the action position of wheels is 1 meter away from the edge of the concrete expansion joint, so that the position is used as a monitoring area of a concrete temperature field, the arranged temperature sensors are divided into a middle column and a boundary column according to the symmetry of the concrete expansion joint and the insulated heating wires arranged in the concrete expansion joint, three sensors, namely a bottom sensor, a middle sensor and an upper sensor, are arranged in each column, a computer and a temperature controller are jointly controlled through temperature signals measured by the temperature sensors, the maximum value of the temperature signals measured by all the temperature sensors is used as a target, the insulated heating wires at different positions are switched on or off, heating of set parts is realized, and finally, the concrete at different parts undergoes the same temperature history; the heating circuit is arranged in the concrete, and aims to heat the fresh concrete by means of heat energy converted from external input electric energy so as to raise the temperature of the fresh concrete and ensure the hydration process of the concrete;
4) Concrete heat-preservation maintenance method
Concrete should lay the heat preservation at concrete expansion joint upper surface as early as possible after pouring the expansion joint and carry out the vibration closely knit and plaster, seals, maintenance, and concrete measure is as follows: 1) Covering a first layer of plastic film on the upper surface of the concrete expansion joint to prevent the concrete from losing moisture to the outside; 2) The polystyrene board after 5 cm is covered on the first layer of plastic film, and the excellent heat preservation capability of the polystyrene board is utilized to prevent the heat in the concrete from dissipating to the air; 3) Covering a layer of quilt on the polystyrene board to prevent the heat loss at the joints of the polystyrene board; 4) Covering a second layer of plastic film on the quilt to prevent the moisture in the air from migrating or condensing into the quilt and prevent the heat preservation capacity of the quilt from being reduced; wherein the polystyrene board is an extruded polystyrene board, the fire-proof grade B1 and the heat conductivity coefficient are not more than 0.03W/m.K;
the sizes of the first layer of plastic film, the polystyrene board, the quilt and the second layer of plastic film from bottom to top are sequentially increased; the size of the first plastic film layer at the lowest part is 40 cm larger than that of the concrete expansion joint poured into the mould in the length and width directions, and the subsequent polystyrene board is at least 20 cm larger than that of the first plastic film layer, the cotton quilt is polystyrene board and the second plastic film layer is cotton quilt in sequence in the length and width directions;
5) Concrete strength development process calculation method based on equivalent age
The effect of the temperature history experienced by the concrete on the strength can be examined by an equivalent age method based on the Arrenius formula, wherein k = Ae -(E/RT) Expressed is the relationship between the rate constant of a chemical reaction and the activation energy and temperature; wherein k is a chemical reaction rate constant, A is a frequency factor constant, a natural constant, E is an activation energy, R is a gas constant, and T is a Kelvin temperature;
the calculated equivalent age is for Arrhenius formula k = Ae -(E/RT) Integration, converting the temperature experienced by the concrete to an age of 20 degrees celsius, as shown in the following formula,
wherein, t e Is the equivalent age; t is r Is reference temperature =293K, corresponding to 20 degrees celsius; t is the temperature experienced by the concrete at different time points (expressed as kelvin); t is the time to reach the equivalent age;
the strength development history of concrete is expressed by a logarithmic function S = a + b l n (t), where t is the age under standard conditions and is a constant which can be passed through standard curing conditions: the concrete sample cured at the temperature of =20 ℃ and the relative humidity of more than or equal to 95% is fitted out by the strength of the concrete sample tested in the age of 28 days; at this time, the t value is a concrete sampleAge under standard maintenance conditions; after the sum in the formula is fitted, the formulaSubstituting the calculated equivalent age into a logarithm functional expression S = a + b × ln (t), and then obtaining the strength of the equivalent age;
when the curing is stopped, the strength of the concrete is more than 70 percent of the preparation strength; when the traffic is open, the strength of the concrete should reach 100% of the formulated strength. By comparing the relation between the equivalent age strength and the preparation strength, the time for stopping the maintenance or opening the traffic of the concrete expansion joint can be determined.
2. The comprehensive guarantee system for the construction quality control of the concrete expansion joint in the severe cold area as claimed in claim 1, wherein the mixing water for the concrete is heated to ensure that the leaving temperature of the concrete is 20 ℃; the temperature to which the mixing water is heated is calculated by equation (1):
wherein, T i，w The temperature of the heated mixing water is in centigrade degree; m is w 、m b 、m a 、m s The dosage of mixing water, cement, stones and sand is kilogram/cubic meter; c w 、C b 、C a 、C s The specific heat capacity of mixing water, cement, stones and sand, kilojoule (kilogram-degree centigrade); t is i，b 、T i，a 、T i，s Respectively inquiring the initial temperature of the cement, the pebble and the sand at the temperature of centigrade; t is f The temperature of the mixed concrete after leaving the machine is centigrade.
3. The system of claim 1, wherein the cross section perpendicular to the length direction of the concrete expansion joint is provided with grids of 100mm x 100mm squaresThe insulating heating wire with the diameter of 3mm and the resistance of 33 omega/m per meter is arranged at the center of the square, the length of a concrete expansion joint is 8m, the specific heat capacity of concrete is 0.97 kJ/(kg DEG C), the voltage at two ends of the insulating heating wire is 220V, the insulating heating wire is a pure resistance element, and the hydration heat release of the concrete is not considered, so that the heat release quantity Q per hour is shown in formula (2) when the full power of the insulating heating wire is heated, and the heat release quantity can enable the temperature rise value T per hour of the concrete to be as high as the temperature rise value T per hour S As shown in formula (3), meets the design requirement (3.5 ℃/h)>, 2 ℃/h); the general formulas of the formula (2) and the formula (3) are as follows,
in the formula (2), Q is the heat release per hour of the heat insulation heating wire, kJ/h, U is the voltage at two ends of the heat insulation heating wire, V and L are the lengths of the concrete expansion joints, m and R are the resistance per meter of the heat insulation heating wire, and omega/m; 3600 seconds(s) per hour;
t in formula (3) S The temperature rise value of the concrete per hour is DEG C/h; q is the heat release per hour of the heat insulation heating wire, kJ/h; q represents the specific heat capacity of the concrete, kJ/(kg. DEG C); v is the volume of concrete to be heated by the insulated heating wire, m 3 (ii) a Rho is the volume weight of concrete, kg/m 3 。
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