CN113402233B - Mass concrete, preparation method and construction process thereof - Google Patents

Abstract

The invention provides a mass concrete, which relates to the technical field of concrete and comprises the following components in parts by weight: 280-310 parts of cement, 80-140 parts of fly ash, 650-800 parts of fine aggregate, 1050-1150 parts of coarse aggregate, 3-6 parts of additive and 155-165 parts of water. The components and the proportion of the large-volume concrete are matched, so that the components of the large-volume concrete can be optimized, particularly, the flowability of the large-volume concrete prepared by the large-volume concrete is higher by matching with an additive, in addition, in the preparation of the large-volume concrete, the temperature change degree in the preparation process is smaller by controlling the temperature of the raw materials, the influence of the temperature on the large volume is reduced, the construction process is monitored in time in the construction process, the temperature is detected, and the influence of the temperature on the large-volume concrete is avoided.

Description

Mass concrete, preparation method and construction process thereof

Technical Field

The invention relates to the technical field of concrete, in particular to mass concrete, a preparation method and a construction process.

Background

The mass concrete is specified in the 'mass concrete construction standard' of China, the mass concrete with the minimum physical geometric dimension of a concrete structure not less than 1m, or the concrete which is expected to cause harmful cracks due to temperature change and shrinkage caused by hydration of a cementing material in the concrete is called as mass concrete.

The existing preparation process mainly comprises the following steps: the concrete raw material selection, the optimization mix proportion design, the template installation, the pouring, the concrete maintenance and other processes, but large-volume concrete is easy to have surface cracks and telescopic cracks, and the cracks can damage the integrity and the stability of the structure, so that the harmfulness of the structure is extremely high.

Disclosure of Invention

The invention aims to provide mass concrete, a preparation method and a construction process, which have the technical effects of reducing cracks and improving the overall stability and safety by reasonably proportioning raw materials and controlling the preparation and construction of the mass concrete.

The invention is realized by the following technical scheme: the paint comprises the following components in parts by weight:

280-310 parts of cement, 80-140 parts of fly ash, 650-800 parts of fine aggregate, 1050-1150 parts of coarse aggregate, 3-6 parts of an additive and 155-165 parts of water.

In order to better realize the invention, the invention further comprises the following components in parts by weight:

297-302 parts of cement, 100-127 parts of fly ash, 699-749 parts of fine aggregate, 1106-1106 parts of coarse aggregate, 4.82-5.08 parts of additive and 160-161 parts of water.

In order to better realize the invention, the admixture is a water reducing agent and a retarder;

the water reducing agent comprises the following components: black liquor of bamboo pulp fiber, chitosan, calcium lignosulphonate, acrylic monomers, polyoxyalkylene ester unsaturated macromonomers and water.

In order to better realize the invention, further, the preparation of the water reducing agent comprises the following steps:

sa: adding calcium lignosulphonate into the black liquor of the bamboo pulp fiber, heating to 50-60 ℃, and stirring to obtain a first mixture;

sb: and adding chitosan, acrylic monomers, polyoxyalkylene ester unsaturated macromonomers and water into the first mixture, stirring and mixing, and reacting at the temperature of 30-60 ℃ to obtain the water reducer.

In order to better implement the invention, the method further comprises the following steps:

before stirring, the adding temperature of the materials is controlled, and the method specifically comprises the following steps: controlling the water temperature to be 15-18 ℃, the cement temperature to be 34-38 ℃, the fine aggregate temperature to be 24-28 ℃, the coarse aggregate temperature to be 26-30 ℃ and the fly ash temperature to be 29-33 ℃;

and sequentially adding cement, fly ash, fine aggregate, coarse aggregate, an additive and water into the materials with the controlled temperature, and stirring and mixing for 90-120s.

In order to better implement the invention, the method further comprises the following steps:

before stirring, controlling the adding temperature of the materials, specifically controlling the water temperature to be 17.6 ℃, the cement to be 36.4 ℃, the fine aggregate to be 26.5 ℃, the coarse aggregate to be 28.2 ℃ and the fly ash to be 31.2 ℃;

and sequentially adding cement, fly ash, fine aggregate, coarse aggregate, an additive and water into the temperature-controlled material, and stirring and mixing for 100s.

In order to better implement the invention, the method further comprises the following steps,

s1: checking the steel bars, the protective layer cushion blocks, the embedded parts, the template and the supporting system, and removing garbage in the template;

s2: horizontally transporting the concrete to a construction site by a mixing transport vehicle, and quickly reversing for 60 seconds to discharge the concrete;

s3: pumping concrete to a pouring part, and testing the mold-entering temperature of the poured concrete;

s4: in the pouring process, adding a retarder into the concrete to ensure that the initial setting time of the concrete is more than 8 hours;

s5: the concrete is vibrated and compacted by adopting an inserted vibrating rod, and the concrete is gradually moved upwards from the lower end of a casting layer during vibration;

s6: scraping with a long scraper within 3-4h after pouring, rolling with an iron roller for initial setting, and rubbing with a wooden trowel for compaction;

s7: and (5) concrete curing.

In order to better implement the invention, further, after the S1 inspection is finished, before the pouring, U-shaped cooling water steel pipes are arranged in the template, and after the pouring, the U-shaped cooling water steel pipes are arranged in the bottom plate concrete.

In order to better implement the invention, further, the concrete curing comprises the following steps:

s71: after the concrete is poured, covering the top surface with a plastic film before initial setting;

s72: maintaining for at least 14 days, and checking the integrity of the plastic film.

The invention has the beneficial effects that: according to the invention, through arranging the components of the large-volume concrete and the proportion of the components in a matching manner, the large-volume concrete with more optimized components can be obtained, particularly through arranging the admixture, the flowability of the large-volume concrete finally prepared is stronger, besides, in the preparation of the large-volume concrete, the temperature change degree in the preparation process is smaller through controlling the temperature of the raw materials, the influence of the temperature on the large volume is reduced, the construction process is monitored in time in the construction process, the temperature is detected in time, and the influence of the temperature on the large-volume concrete is further avoided.

Detailed Description

The technical solution of the present invention will be described below with reference to the embodiments of the present invention.

Example 1:

the mass concrete mainly comprises the following components in parts by weight:

280-310 parts of cement, 80-140 parts of fly ash, 650-800 parts of fine aggregate, 1050-1150 parts of coarse aggregate, 3-6 parts of an additive and 155-165 parts of water.

In the long-term experiment process, 297-302 parts of cement, 100-127 parts of fly ash, 699-749 parts of fine aggregate, 1106-1106 parts of coarse aggregate, 4.82-5.08 parts of additive and 160-161 parts of water are preferred.

Specifically, when the fly ash is 25 percent of the mixing amount, the fly ash comprises the following components: 302 parts of cement, 100 parts of fly ash, 749 parts of fine aggregate, 1079 parts of coarse aggregate, 4.82 parts of additive and 160 parts of water, wherein when the mixing amount of the fly ash is 30%, the components are as follows: 297 parts of cement, 127 parts of fly ash, 699 parts of fine aggregate, 1106 parts of coarse aggregate, 5.08 parts of additive and 161 parts of water.

In the embodiment, the cement is general portland cement with low hydration heat, the hydration heat is not more than 250KJ/Kg in 3d, and the hydration heat is not more than 280KJ/Kg in 7 d; when 52.5 strength grade cement is selected, the hydration heat of 7d is preferably less than 300KJ/Kg.

The fly ash mainly has the effects of replacing partial cement in mass concrete, delaying the concentrated heat release of the concrete, reducing the hydration heat of the cement and reducing the internal and external temperatures of the concrete, and preferably selects I-grade or II-grade fly ash, so that the fineness, the loss on ignition, the water demand ratio, the stability, the activity index and the like all meet the technical requirements of the I-grade or II-grade fly ash.

The content of fine aggregate is less than or equal to 3 percent, the content of mud blocks is less than or equal to 1 percent, the content of chloride ions is less than or equal to 0.06 percent, the content of mica is less than or equal to 2 percent, no sundries are obtained, and medium sand with the fineness modulus of 2.4-2.8 or (the medium sand with 2.4-2.8 is prepared by coarse sand and fine sand according to a proportion) is selected.

The mud content of the coarse aggregate is less than or equal to 1 percent, the mud block content is less than or equal to 0.5 percent, the needle sheet content is less than or equal to 15 percent, the crushing index value is less than or equal to 12 percent, no sundries are obtained, and 5-31.5 mm continuous size fraction crushed stones are selected.

The components are used for preparing mass concrete in the range, and can be used for realizing synergistic complementation, so that the mechanical property of the concrete is optimal, and cracks can not appear in the construction process.

The admixture is a water reducing agent and a retarder:

the water reducing agent consists of the following components of black bamboo pulp fiber liquor, chitosan, calcium lignosulphonate, acrylic monomers, polyoxyalkylene ester unsaturated macromonomer and water.

The preparation method of the water reducing agent comprises the following steps:

the water reducing agent is prepared by the following steps:

sa: adding calcium lignosulphonate into the black liquor of the bamboo pulp fiber, heating to 50-60 ℃, and stirring to obtain a first mixture;

sb: and further adding chitosan, acrylic monomers, polyoxyalkylene ester unsaturated macromonomers and water into the first mixture, stirring and mixing, and reacting at the temperature of 30-60 ℃ to obtain the water reducer.

The main components of the water reducing agent are bamboo pulp fiber black liquor, chitosan, calcium lignosulfonate, acrylic monomers, polyoxyalkylene ester unsaturated macromonomer and water, the bamboo pulp black liquor and the calcium lignosulfonate are mixed in the components, holes are distributed on the cross section of the bamboo pulp black liquor, the water reducing agent has excellent moisture absorption and air permeability, and the longitudinal section of the fiber is provided with strip grooves, so that the bamboo pulp black liquor and the calcium lignosulfonate are subjected to cross-linking reaction to be modified and fully reacted to obtain a first mixture, wherein the optimal reaction temperature is 50-60 ℃ in the reaction process, and the reaction is more fully carried out at the temperature.

And then, stirring and mixing the chitosan, the acrylic monomer, the polyoxyalkylene ester unsaturated macromonomer and water, and carrying out polymerization reaction to modify and reduce the mixture into the water reducing agent of chitosan, thereby achieving the purposes of improving solubility and enhancing fluidity.

In the process of preparing concrete, the bamboo pulp black liquor is adopted and reacts with calcium lignosulfonate to open the activity of the bamboo pulp black liquor, so that the activity of the whole water reducing agent is enhanced, the tension of the water reducing agent is improved through some improvements, the finally obtained water reducing agent surfactant is strong, the water surface tension and the interfacial tension between water and cement can be reduced, the solubility is gradually improved in the releasing process, the cement is easier to wet, and the fluidity of the concrete is improved.

Example 2:

a preparation method of mass concrete comprises the following steps:

before stirring, the adding temperature of the materials is controlled, and the method specifically comprises the following steps: controlling the water temperature to be 15-18 ℃, the cement temperature to be 34-38 ℃, the fine aggregate temperature to be 24-28 ℃, the coarse aggregate temperature to be 26-30 ℃ and the fly ash temperature to be 29-33 ℃;

and sequentially adding cement, fly ash, fine aggregate, coarse aggregate, an additive and water into the materials with the controlled temperature, and stirring and mixing for 90-120s.

The temperature of the concrete in the mold is preferably controlled to be 5-30 ℃, and when the temperature of the concrete in the mold exceeds 30 ℃, the crushed ice blocks are added into the water to reduce the temperature of the concrete in the mold.

In the embodiment of the invention, the temperature of the raw materials before production is controlled, specifically, the temperature of the raw materials is measured and controlled, wherein the water temperature is controlled to be 17.6 ℃, the cement is controlled to be 36.4 ℃, the sand is controlled to be 26.5 ℃, the stone is controlled to be 28.2 ℃, the fly ash is controlled to be 31.2 ℃, the mixing proportion of the fly ash is 30 percent, an operator correctly inputs the weight of each raw material in the mixing proportion, idling aggregate is peeled, feeding is carried out after water and impurities are discharged completely, and the mixing time of the concrete is controlled to be 90-120s.

Example 3:

the construction process of the mass concrete comprises the following steps:

comprises the following steps of (a) carrying out,

s1: checking the steel bars, the protective layer cushion blocks, the embedded parts, the template and the supporting system, and removing garbage in the template;

the method comprises the following steps: in concrete transportation, before the tank car receives the materials, the tank body rotates in the same direction to drain the residual water in the tank and then receives the materials, a concrete grade signboard is placed at the position of a cab windshield, and the tank body rotates reversely with the slowest gear in the transportation or waiting process to prevent uneven materials on the upper part, the middle part and the lower part of the concrete in the tank body.

Before concrete pouring, the steel bars, the cushion blocks of the protective layer, the embedded parts, the templates and the supporting system are checked, impurities such as garbage in the templates are clear and clean, the concrete pouring is started, the bottom plates are watered and moistened, meanwhile, drainage channels around the bottom plates are cleaned and dredged, and the smooth drainage in the concrete pouring process is guaranteed.

Before pumping concrete, the whole pipeline is wetted by water, and then cement paste with the same mixing proportion is fed in, so that the wall of the conveying pipe is in a fully wetted state.

S2: horizontally transporting the concrete to a construction site by a mixing transport vehicle, and quickly reversing for 60 seconds to discharge the concrete;

in the pouring process, if the slump loss of the concrete is overlarge, the additive can be used for adjustment so as to meet the requirement of on-site concrete pumping, and if the segregation phenomenon occurs, the concrete must be conveyed to a mixing plant for secondary mixing and can be put into a bin.

S3: pumping concrete to a pouring part, and testing the mold-entering temperature of the poured concrete;

the concrete is pumped to a pouring position, the mold-entering temperature test is carried out on the concrete, the mold-entering temperature test is carried out for no less than 2 times in each shift, and the test is carried out by a special person, and the mold-entering temperature of the concrete is measured in real time after the concrete arrives at a construction site.

S4: in the pouring process, adding a retarder into the concrete to ensure that the initial setting time of the concrete is more than 8 hours;

the concrete is put into a warehouse by a pump, the free falling height of the concrete is not more than 2m, and when the free falling height of the concrete exceeds the free falling height, the concrete is fed by a string barrel or a chute. And (3) realizing continuous casting by adopting a horizontal layering or inclined plane layering method according to the plane size, wherein the casting and tamping time of each layer of concrete is not more than the initial setting time, and the thickness is not more than 300mm. The retarder is added into the concrete, so that the initial setting time of the concrete is more than 8 hours, and cold seams can not appear before the upper concrete layer covers the lower concrete layer. In order to prevent the concrete from generating cold joints during pouring, the most critical measure is to ensure the continuous supply of the concrete, and the combination between the concrete layers does not exceed the initial setting time. Meanwhile, the quantity and the quality of tools for supplying and constructing concrete are ensured, and reliable spare equipment is provided.

S5: the concrete is vibrated and compacted by adopting an inserted vibrating rod, and the concrete gradually moves upwards from the lower end of a casting layer during vibration;

the concrete is vibrated and compacted by adopting a 50-type inserted vibrating rod, the concrete is gradually moved upwards from the lower end of a casting layer during vibration, and the vibration distance is not more than 1.25 times of the vibration radius of the vibrating rod. The thickness of the concrete layer blanking can not exceed 50cm. When the upper layer is vibrated, the concrete is inserted into the lower layer by about 50mm, so that the old and new concrete of the upper and lower layers are tightly combined. The vibrating rod should be pulled out slowly and inserted quickly, the vibrating time should not be too long, and the vibrating rod cannot vibrate excessively or leak. The insertion points are uniformly arranged in a staggered quincunx mode, the space is not more than 1.5R (R is the acting radius of the vibrator), and the vibration time of each insertion point is generally 20-30 seconds. The vibrating spear cannot be in direct contact with the template, the steel bars, the embedded parts and the like.

S6: scraping with a long scraper within 3-4h after pouring, rolling with an iron roller for initial setting, and rubbing with a wooden trowel for compacting;

after pouring, the cement slurry on the surface of the mass concrete is thick, the mass concrete is primarily scraped by a long scraping rule within 3-4 hours after pouring, the mass concrete is rolled for 2 times by an iron roller before initial setting, and then is rubbed and compacted by a wooden trowel, so that secondary plastering compaction is carried out after the initial setting and before final setting of the concrete, water collecting cracks are closed, and surface cracks are controlled. If the surface cracks, the wood trowel is used for rubbing and compacting in time, and the water storage curing is preferred under the condition of the regulation.

S7: curing the concrete;

s71: after the concrete pouring is finished, covering the top surface with a plastic film before initial setting;

s72: maintaining for at least 14 days, and checking the integrity of the plastic film.

Concrete curing:

after the concrete is poured, a plastic film is required to cover the top surface immediately before initial setting. After the secondary plastering and compacting, two layers of gunny bags or cotton wool are added on the top surface for covering and curing. If the top surface heat preservation effect can not meet the requirement, measures such as adding sacks and cotton fibers can be adopted to reduce the temperature difference between the surface and the inside of the concrete, and the side surface adopts 15mm plywood which can meet the requirement of heat preservation and maintenance.

And (4) maintaining work, which is under the charge of a specially-assigned person, testing and recording, wherein the duration time of moisture preservation and maintenance is not less than 14 days, the integrity of the plastic film is checked frequently, and the surface of the concrete is kept moist.

The covering thickness is adjusted at any time according to the concrete temperature measurement result, and the covering thickness is reduced as much as possible on the premise that the maximum temperature difference between the inside and the outside of the concrete meets the standard requirement. The temperature-measuring device can be adjusted in time according to the temperature-measuring information of the concrete and the change condition of the weather and the temperature, so that the covering thickness can be reduced in the daytime when the weather is good and the temperature is high, and even the jute bag can be opened in a short time. When the night comes, the gunny bag needs to be covered in time; when the temperature suddenly changes, which is the key moment of maintenance work, attention is paid to weather forecast, and measures should be taken quickly to prevent temperature cracks.

The removal of the heat-insulating covering layer is carried out layer by layer gradually, and when the maximum temperature difference between the surface temperature of the concrete and the environment is less than 20 ℃, the concrete can be completely removed.

Controlling the temperature of concrete:

the rising value of the concrete poured on the basis of the mold-entering temperature is not more than 50 ℃.

The temperature difference between the inner surface and the outer surface of the concrete casting is not more than 25 ℃.

The cooling rate of the concrete casting is not more than 2.0 ℃/d.

The temperature difference between the surface of the concrete casting and the atmosphere is not more than 20 ℃ when the heat preservation covering is removed.

The surface temperature difference, the cooling rate and the environmental temperature of the large-volume concrete pouring body are tested, and after the concrete is poured, the time is not less than 4 times every day and night.

Before pouring, a sunshade, rainproof and windproof multifunctional shed is erected in a foundation construction area by using a steel pipe scaffold and color strip cloth, and the periphery of the shed is sealed by using a thick film. The temperature in the shed can be increased, and the temperature cracks caused by mortar loss in concrete and sudden reduction of the surface temperature due to rainwater can be prevented.

In the process of pouring large-volume concrete, a U-shaped cooling water steel pipe is adopted for cooling, the middle part inside the bottom plate concrete is horizontally provided with the U-shaped cooling water steel pipe with the horizontal distance of phi 30 multiplied by 2mm and the length of 1.5m, when the temperature difference in the concrete is higher, the temperature difference is not more than 25 ℃, the temperature of water is introduced for cooling and radiating, the distance between the pipe bottom and the bottom plate bottom is 1500mm, the pipe orifices at two ends are exposed out of the concrete surface by 100mm, the pipe is always in a full water state, according to the temperature measurement result, the water temperature of a water tank is adjusted, the flow rate and the flow speed of the pipeline are controlled, the temperature difference between the internal temperature and the water inlet temperature is not more than 25 ℃, or the water temperature is too low to generate internal crack.

The surface temperature of the concrete, the lower surface temperature of the film and the curing water temperature are measured by thermometers, the internal temperature measurement is measured by an intelligent patrol instrument, nine groups of temperature measuring sheets are arranged, the embedding depth of each group is 0.1m below the upper surface, 0.1m above the middle part and the bottom plate (bottom die), and the concrete is embedded before casting. Measuring the temperature 12 hours after concrete is tamped, measuring the internal temperature and the atmospheric temperature of the concrete once every 2 hours in the temperature rise stage, measuring the internal temperature and the atmospheric temperature once every 8 hours in the temperature decrease stage, making a record, and timely reviewing by technical responsible persons to control the internal and external temperature difference of the concrete to be not more than 25 ℃ at any time. The temperature gradient per meter is not more than 15 ℃. When the temperature difference or the temperature gradient between the inside and the outside approaches the standard requirement, the alarm is given in time and measures are taken immediately.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily think of the changes or substitutions within the technical scope of the present invention, and shall cover the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (4)

1. A mass concrete is characterized in that,

the paint comprises the following components in parts by weight:

280-310 parts of cement, 80-140 parts of fly ash, 650-800 parts of fine aggregate, 1050-1150 parts of coarse aggregate, 3-6 parts of an additive and 155-165 parts of water;

the additive is a water reducing agent and a retarder;

the water reducing agent comprises the following components: black liquor of bamboo pulp fiber, chitosan, calcium lignosulphonate, acrylic monomers, polyoxyalkylene ester unsaturated macromonomers and water;

the preparation of the water reducing agent comprises the following steps:

sa: adding calcium lignosulphonate into the black liquor of the bamboo pulp fiber, heating to 50-60 ℃, and stirring to obtain a first mixture;

sb: adding chitosan, acrylic monomers, polyoxyalkylene ester unsaturated macromonomers and water into the first mixture, stirring and mixing, and reacting at the temperature of 30-60 ℃ to obtain the water reducer.

2. The bulk concrete according to claim 1,

the paint comprises the following components in parts by weight:

297-302 parts of cement, 100-127 parts of fly ash, 699-749 parts of fine aggregate, 1106-1106 parts of coarse aggregate, 4.82-5.08 parts of additive and 160-161 parts of water.

3. The method for producing mass concrete according to claim 1,

the method comprises the following steps:

before stirring, the adding temperature of the materials is controlled, and the method specifically comprises the following steps: controlling the water temperature to be 15-18 ℃, the cement temperature to be 34-38 ℃, the fine aggregate temperature to be 24-28 ℃, the coarse aggregate temperature to be 26-30 ℃ and the fly ash temperature to be 29-33 ℃;

and sequentially adding cement, fly ash, fine aggregate, coarse aggregate, an additive and water into the materials with the controlled temperature, and stirring and mixing for 90-120s.

4. The method for producing mass concrete according to claim 3,

the method comprises the following steps:

before stirring, controlling the adding temperature of the materials, specifically controlling the water temperature to be 17.6 ℃, the cement to be 36.4 ℃, the fine aggregate to be 26.5 ℃, the coarse aggregate to be 28.2 ℃ and the fly ash to be 31.2 ℃;

and sequentially adding cement, fly ash, fine aggregate, coarse aggregate, an additive and water into the temperature-controlled material, and stirring and mixing for 100s.