CN112962610A - One-time pouring method for large-size raft plate concrete of large petrochemical storage tank bearing platform - Google Patents
One-time pouring method for large-size raft plate concrete of large petrochemical storage tank bearing platform Download PDFInfo
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- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D15/00—Handling building or like materials for hydraulic engineering or foundations
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Abstract
The invention discloses a one-time pouring method for large-volume raft plate concrete of a large petrochemical storage tank bearing platform, which comprises the following steps of: and (3) screening swelling agents: selecting sulphoaluminate expanding agents, lime expanding agents, iron powder expanding agents, MgO expanding agents and composite expanding agents to carry out free expansion tests and limited expansion tests; determining the mixing proportion of concrete; designing concrete formulas inside and outside the expansion band of the bearing platform according to the design result of the mixing proportion of the concrete and the expansion performance test result of the expanding agent; and (5) concrete pouring construction. The large-volume concrete structure has the advantages of high integral rigidity and good quality, and can shorten the construction period and save the cost. The one-time pouring method for the large-volume raft plate concrete of the large petrochemical storage tank bearing platform has the advantages that the integral rigidity of the one-time poured reinforced concrete is high; because no post-cast strip is poured in batches, the integral impermeability is good; the construction period is shortened, the production cost is saved, a post-cast strip and a steel plate water stop strip need to be arranged in batch pouring, the construction period is long, and the production management cost is high.
Description
Technical Field
The invention relates to concrete pouring, in particular to a one-time pouring method for large-volume raft plate concrete of a large-scale petrochemical storage tank bearing platform.
Background
The oil tank construction of China tends to be large-scale, at present, large-scale oil storage bases are mostly in coastal areas, oil tank foundations are mostly soft soil foundations, and although the foundations are tamped and reinforced in the construction process, the foundations of the oil tanks can be settled in different degrees after long-time use. The settling of the tank foundation can have a serious impact on the normal use of the tank. Firstly, the settlement of the soft soil foundation occurs, the oil tank floor generates larger deformation and stress, the deformation can cause leakage along with the prolonging of time, and the tank body can not be normally used. Secondly, large areas of settlement of the foundation can cause large areas of tearing of the tank walls with the fixed topping, resulting in crude oil leakage. The settlement of the foundation can also influence the free lifting of the floating roof, so that the movement of the top cover is out of order, and accidents are caused. Petroleum belongs to flammable and explosive articles, once leakage occurs, fire disasters and environmental pollution are easily caused, the survival and the ecological environment of human beings are seriously influenced, and the production and the national economy are seriously lost.
The concrete for constructing the storage tank bearing platform raft plate with high rigidity has certain resistance to the uneven settlement of the foundation. The storage tank bearing platform has larger load, adopts a concrete bottom plate to bear the load of a building to form a raft foundation, and has good integrity. The concrete for the bearing platform raft plate of the large-scale petroleum storage tank has important significance for ensuring the safety, impermeability and settlement prevention of the petroleum storage tank.
A single 10-ten-thousand-cubic-meter raft plate large-volume concrete storage tank bearing platform is a cylinder with the surface diameter of 80 meters and the thickness of 0.65 meter, the concrete pouring area is more than 5000 square meters, the volume exceeds 3000 cubic meters, and the raft plate large-volume concrete storage tank belongs to large-scale raft plate concrete. The traditional casting method is a secondary casting method using a post-cast strip. The post-cast strip is excellent in overcoming the harmful expansion and contraction possibly generated by temperature contraction, and is widely applied to engineering. But it also has some disadvantages in itself: (1) the post-cast strip goes through the whole structure construction process until the casting is completed, which requires more than one month, and in the period, garbage and sundries are easy to fall into the post-cast strip. In addition, the post-cast steel bars are easy to rust after being exposed for a long time, and a large amount of manpower is consumed for later derusting; (2) before concrete is poured into the post-cast strip, concrete on two sides needs to be chiseled, construction is very difficult, the pouring time interval between some structural concrete and the post-cast strip is several months, the bonding strength of new and old concrete is difficult to guarantee, and most of dry shrinkage of the structural concrete is finished before the post-cast strip is poured due to the difference of the pouring time. Therefore, the post-cast strip concrete is highly susceptible to cracking at the joints of the new and old concrete. The initial purpose of setting up the construction post-cast strip is to prevent the production of concrete crack, but the post-cast strip is handled not well and easily causes two to run through the crack at every post-cast strip department artificially, leads to impervious performance and bulk stiffness to descend.
Disclosure of Invention
The invention aims to provide a one-time pouring method for large-volume raft plate concrete of a large petrochemical storage tank bearing platform.
The invention discloses a one-time pouring method for large-volume raft plate concrete of a large petrochemical storage tank bearing platform, which comprises the following steps of:
and (3) screening swelling agents: selecting a sulphoaluminate expanding agent, a lime expanding agent, an iron powder expanding agent, a MgO expanding agent and a composite expanding agent to carry out a free expansion test and a limited expansion test, and screening the expanding agent which has excellent expansion performance and meets the requirement of concrete performance;
determining the mixing proportion of concrete;
designing concrete formulas inside and outside the expansion band of the bearing platform according to the requirements of limited expansion rate, strength grade and impermeability grade of the concrete of the bearing platform of the storage tank and the combination of the design result of the mix proportion of the concrete and the expansion performance test result of the expanding agent;
and (5) concrete pouring construction.
The invention discloses a one-time pouring method for large-volume raft slab concrete of a large petrochemical storage tank bearing platform, wherein the step of carrying out an expansion performance test on an expanding agent comprises the following steps:
the expansion rate of different types of expanding agents is measured by trial preparation, so that the expanding agent meeting the expansion rate limit of the bearing platform concrete is screened out.
The invention discloses a large-volume raft plate concrete one-time pouring method for a large petrochemical storage tank bearing platform, which comprises the following steps of: preparing molding mortar test pieces according to national standards, wherein each group comprises three test pieces, filling prepared mortar into test molds with nail heads at two ends, numbering, placing the test pieces in a curing room for 1d, 3d, 7d, 14d, 21d, 28d, 60d, 90d and 120d from the initial length of the test piece, respectively taking out the length of the test piece, and taking the average value of the three times of testing each test piece for three times.
The invention discloses a large-volume raft plate concrete one-time pouring method for a large petrochemical storage tank bearing platform, wherein an expansion limiting test comprises the following steps: preparing three molded mortar test pieces according to national standards, placing a limited expansion framework into a mortar test mould before filling mortar into the test mould, wherein the limited expansion rate is the same as the free expansion rate test in the test and calculation methods, processing data, taking the average value of the expansion rates of a group of three test pieces as the expansion rate of the group, and taking the average value of the expansion rates of the rest two test pieces as the expansion rate of the group if the expansion rate of one test piece exceeds 30% of the average value, wherein the calculation result is accurate to 0.001%; if two specimens exceed the average value, the expansion ratio at this age is discarded.
The invention discloses a large-volume raft plate concrete one-time pouring method for a large petrochemical storage tank bearing platform, wherein the step of determining the mixing proportion of concrete comprises the following steps:
on the premise of determining the reference mixing ratio, selecting the mixing ratio with the optimal thermal property, physical and mechanical properties and durability by adjusting related parameters, and designing and trial-matching the mixing ratio;
uniformly weighing the raw materials purchased in the same batch of the test concrete, ensuring the consistent performance of the raw materials in each group of tests, adopting the uniform standard for weighing, stirring, vibrating, forming and maintaining the raw materials in each group of tests, and then measuring the slump, the expansion, the 3d strength, the 7d strength, the 28d strength and the 60d strength of the test concrete.
The invention discloses a large-volume raft plate concrete one-time pouring method for a large petrochemical storage tank bearing platform, wherein the concrete pouring construction comprises the following steps:
concrete stirring and transporting: determining the mixing ratio of the concrete inside and outside the expansion zone according to the actual design strength of the bearing platform and the pumping requirement, doping a proper amount of mineral powder to reduce the hydration heat of the concrete, doping a retarder to prolong the initial setting time of the concrete, and controlling the initial setting time of the concrete on site to be 4-8 hours;
concrete pumping and casting and tamping: according to the plane size and the concrete quantity of the bearing platform, the capacity of equipment for supplying and pumping the combined concrete is provided, an automobile pump is configured during the concrete pouring of the bearing platform, and the concrete of the bearing platform is poured and tamped at one time for molding;
and (5) maintenance: temperature observation holes are arranged in a representative area in a large-volume concrete foundation of a bearing platform raft, the internal temperature and the surface temperature of concrete are observed, and the change speed of the surface temperature of the concrete is controlled, so that the difference delta T between the maximum temperature value in the concrete and the surface temperature of the concrete is less than or equal to 25 ℃.
The invention discloses a one-time pouring method for large-volume raft plate concrete of a large petrochemical storage tank bearing platform, wherein the step of controlling the temperature change speed of the surface of the concrete comprises the following steps: after the concrete is initially set, the concrete of the bearing platform is covered by a plastic film in time, then a cotton felt is covered on the plastic film for watering and curing, and after the concrete of the whole bearing platform is completely poured and tamped and the internal and external temperature difference is observed to be less than 25 ℃, the watering and curing of the cotton felt is changed.
The invention discloses a one-time pouring method for large-volume raft plate concrete of a large-scale petrochemical storage tank bearing platform, wherein a temperature observation hole is arranged in a representative area in a large-volume concrete foundation of the bearing platform raft plate, and the observation of the internal temperature and the surface temperature of the concrete comprises the following steps: the concrete pouring method comprises the following steps that 15 temperature observation holes are arranged in a representative area in a base plate foundation of a bearing platform and used for observing the internal temperature and the surface temperature of concrete in different areas, different depths and different time, a thermometer is used for observing the temperature of the concrete of the bearing platform, the first observation is started after 12 hours after the concrete pouring is finished, the observation is performed every 8 hours later, and when the temperature difference in the concrete is more than 25 ℃, heat preservation measures are taken for the concrete, so that the quality of the poured concrete is ensured.
The invention relates to a large-volume raft plate concrete one-time pouring method for a large petrochemical storage tank bearing platform, wherein concrete pouring adopts a pumping concrete construction process, continuous operation is carried out, a natural flowing and inclined plane layering pouring construction method is adopted, the concrete pouring amount per hour is theoretically calculated, whether a pumping concrete machine meets construction requirements is determined, the concrete pouring is carried out according to a parallel flow direction during concrete pouring, the pouring width of the concrete is controlled, so that the actual capacity of the prepared concrete stirring, transporting and pumping machine is met, the concrete is vibrated by an inserted vibrator, the distance between each inserting point of a vibrating bar is controlled to be 400mm, the concrete needs to be secondarily re-vibrated after 30 minutes, the bearing platform concrete is divided by an expansion zone, two pump trucks on two sides are simultaneously constructed, one pump truck on one side is replaced by the concrete on the inner side of the expansion zone in advance before the concrete reaches initial setting for pouring the concrete in the expansion zone, after the concrete is leveled with the concrete in the non-expansion zone, the concrete is replaced by the concrete outside the expansion zone to carry out the concrete pouring construction of the side expansion zone, a dense hole steel wire mesh with the thickness of 0.9mm multiplied by 10mm is arranged at the joint of the expansion zone of the bearing platform and the non-expansion zone, and after the concrete is vibrated, the concrete is firstly scraped by an aluminum alloy ruler according to the elevation; performing secondary vibration before initial setting to close the water collecting crack; before final setting, the concrete is polished twice by a mechanical trowelling machine, so that shrinkage cracks of the concrete are prevented, the elevation of the bearing platform surface is fixed and retested by a level gauge in the concrete tamping process, and the flatness is ensured to meet the design and standard requirements.
The large-volume concrete structure has the advantages of high integral rigidity and good quality, and can shorten the construction period and save the cost. The one-time pouring method for the large-volume raft plate concrete of the large petrochemical storage tank bearing platform has the advantages that the integral rigidity of the one-time poured reinforced concrete is high; because no post-cast strip is poured in batches, the integral impermeability is good; the construction period is shortened, the production cost is saved, a post-cast strip and a steel plate water stop strip need to be arranged in batch pouring, the construction period is long, and the production management cost is high.
Drawings
FIG. 1 is a flow chart of the steps of the one-time pouring method of the large-volume raft slab concrete of the large-scale petrochemical storage tank bearing platform of the invention;
fig. 2 is a schematic view of a temperature observation hole arrangement.
Detailed Description
As shown in fig. 1 and 2, the method for pouring concrete on a large-volume raft slab of a large-scale petrochemical storage tank bearing platform in one step comprises the following steps:
and (3) screening swelling agents: selecting a sulphoaluminate expanding agent, a lime expanding agent, an iron powder expanding agent, a MgO expanding agent and a composite expanding agent to carry out a free expansion test and a limited expansion test, and screening the expanding agent which has excellent expansion performance and meets the requirement of concrete performance;
determining the mixing proportion of concrete;
designing concrete formulas inside and outside the expansion band of the bearing platform according to the requirements of limited expansion rate, strength grade and impermeability grade of the concrete of the bearing platform of the storage tank and the combination of the design result of the mix proportion of the concrete and the expansion performance test result of the expanding agent;
and (5) concrete pouring construction.
The invention discloses a one-time pouring method for large-volume raft slab concrete of a large petrochemical storage tank bearing platform, wherein the step of carrying out an expansion performance test on an expanding agent comprises the following steps:
the expansion rate of different types of expanding agents is measured by trial preparation, so that the expanding agent meeting the expansion rate limit of the bearing platform concrete is screened out.
The invention discloses a large-volume raft plate concrete one-time pouring method for a large petrochemical storage tank bearing platform, which comprises the following steps of: preparing molding mortar test pieces according to national standards, wherein each group comprises three test pieces, filling prepared mortar into test molds with nail heads at two ends, numbering, placing the test pieces in a curing room for 1d, 3d, 7d, 14d, 21d, 28d, 60d, 90d and 120d from the initial length of the test piece, respectively taking out the length of the test piece, and taking the average value of the three times of testing each test piece for three times.
The invention discloses a large-volume raft plate concrete one-time pouring method for a large petrochemical storage tank bearing platform, wherein an expansion limiting test comprises the following steps: preparing three molded mortar test pieces according to national standards, placing a limited expansion framework into a mortar test mould before filling mortar into the test mould, wherein the limited expansion rate is the same as the free expansion rate test in the test and calculation methods, processing data, taking the average value of the expansion rates of a group of three test pieces as the expansion rate of the group, and taking the average value of the expansion rates of the rest two test pieces as the expansion rate of the group if the expansion rate of one test piece exceeds 30% of the average value, wherein the calculation result is accurate to 0.001%; if two specimens exceed the average value, the expansion ratio at this age is discarded.
The invention discloses a large-volume raft plate concrete one-time pouring method for a large petrochemical storage tank bearing platform, wherein the step of determining the mixing proportion of concrete comprises the following steps:
on the premise of determining the reference mixing ratio, selecting the mixing ratio with the optimal thermal property, physical and mechanical properties and durability by adjusting related parameters, and designing and trial-matching the mixing ratio;
uniformly weighing the raw materials purchased in the same batch of the test concrete, ensuring the consistent performance of the raw materials in each group of tests, adopting the uniform standard for weighing, stirring, vibrating, forming and maintaining the raw materials in each group of tests, and then measuring the slump, the expansion, the 3d strength, the 7d strength, the 28d strength and the 60d strength of the test concrete.
The invention discloses a large-volume raft plate concrete one-time pouring method for a large petrochemical storage tank bearing platform, wherein the concrete pouring construction comprises the following steps:
concrete stirring and transporting: determining the mixing ratio of the concrete inside and outside the expansion zone according to the actual design strength of the bearing platform and the pumping requirement, doping a proper amount of mineral powder to reduce the hydration heat of the concrete, doping a retarder to prolong the initial setting time of the concrete, and controlling the initial setting time of the concrete on site to be 4-8 hours;
concrete pumping and casting and tamping: according to the plane size and the concrete quantity of the bearing platform, the capacity of equipment for supplying and pumping the combined concrete is provided, an automobile pump is configured during the concrete pouring of the bearing platform, and the concrete of the bearing platform is poured and tamped at one time for molding;
and (5) maintenance: temperature observation holes are arranged in a representative area in a large-volume concrete foundation of a bearing platform raft, the internal temperature and the surface temperature of concrete are observed, and the change speed of the surface temperature of the concrete is controlled, so that the difference delta T between the maximum temperature value in the concrete and the surface temperature of the concrete is less than or equal to 25 ℃.
The invention discloses a one-time pouring method for large-volume raft plate concrete of a large petrochemical storage tank bearing platform, wherein the step of controlling the temperature change speed of the surface of the concrete comprises the following steps: after the concrete is initially set, the concrete of the bearing platform is covered by a plastic film in time, then a cotton felt is covered on the plastic film for watering and curing, and after the concrete of the whole bearing platform is completely poured and tamped and the internal and external temperature difference is observed to be less than 25 ℃, the watering and curing of the cotton felt is changed.
The invention discloses a one-time pouring method for large-volume raft plate concrete of a large-scale petrochemical storage tank bearing platform, wherein a temperature observation hole is arranged in a representative area in a large-volume concrete foundation of the bearing platform raft plate, and the observation of the internal temperature and the surface temperature of the concrete comprises the following steps: the concrete pouring method comprises the following steps that 15 temperature observation holes are arranged in a representative area in a base plate foundation of a bearing platform and used for observing the internal temperature and the surface temperature of concrete in different areas, different depths and different time, a thermometer is used for observing the temperature of the concrete of the bearing platform, the first observation is started after 12 hours after the concrete pouring is finished, the observation is performed every 8 hours later, and when the temperature difference in the concrete is more than 25 ℃, heat preservation measures are taken for the concrete, so that the quality of the poured concrete is ensured.
The invention relates to a large-volume raft plate concrete one-time pouring method for a large petrochemical storage tank bearing platform, wherein concrete pouring adopts a pumping concrete construction process, continuous operation is carried out, a natural flowing and inclined plane layering pouring construction method is adopted, the concrete pouring amount per hour is theoretically calculated, whether a pumping concrete machine meets construction requirements is determined, the concrete pouring is carried out according to a parallel flow direction during concrete pouring, the pouring width of the concrete is controlled, so that the actual capacity of the prepared concrete stirring, transporting and pumping machine is met, the concrete is vibrated by an inserted vibrator, the distance between each inserting point of a vibrating bar is controlled to be 400mm, the concrete needs to be secondarily re-vibrated after 30 minutes, the bearing platform concrete is divided by an expansion zone, two pump trucks on two sides are simultaneously constructed, one pump truck on one side is replaced by the concrete on the inner side of the expansion zone in advance before the concrete reaches initial setting for pouring the concrete in the expansion zone, after the concrete is leveled with the concrete in the non-expansion zone, the concrete is replaced by the concrete outside the expansion zone to carry out the concrete pouring construction of the side expansion zone, a dense hole steel wire mesh with the thickness of 0.9mm multiplied by 10mm is arranged at the joint of the expansion zone of the bearing platform and the non-expansion zone, and after the concrete is vibrated, the concrete is firstly scraped by an aluminum alloy ruler according to the elevation; performing secondary vibration before initial setting to close the water collecting crack; before final setting, the concrete is polished twice by a mechanical trowelling machine, so that shrinkage cracks of the concrete are prevented, the elevation of the bearing platform surface is fixed and retested by a level gauge in the concrete tamping process, and the flatness is ensured to meet the design and standard requirements.
The large-volume concrete structure has the advantages of high integral rigidity and good quality, and can shorten the construction period and save the cost. The one-time pouring method for the large-volume raft plate concrete of the large petrochemical storage tank bearing platform has the advantages that the integral rigidity of the one-time poured reinforced concrete is high; because no post-cast strip is poured in batches, the integral impermeability is good; the construction period is shortened, the production cost is saved, a post-cast strip and a steel plate water stop strip need to be arranged in batch pouring, the construction period is long, and the production management cost is high.
Bulking agent screening
Selecting sulphoaluminate expanding agents, lime expanding agents, iron powder expanding agents, MgO expanding agents and composite expanding agents to carry out free expansion tests and limited expansion tests, and screening the expanding agents which have excellent expansion performance and meet the performance requirements of concrete.
Concrete mix proportion optimization design
The hydration temperature rise of the concrete is controlled, and work is mainly carried out from the aspect of reducing the cement consumption. When the cement consumption is reduced, the physical and mechanical properties of the concrete, especially the strength and workability of the concrete, need to be ensured. On the basis of obtaining the initial mix proportion of the raft large-volume concrete, the existing raw materials in the storage tank construction area are utilized, the hydration heat release of the concrete under different cement using amounts is measured by adjusting relevant parameters, such as the using amount of a cementing material, the mixing amount of an admixture, the sand rate, the mixing amount of an admixture and other indexes, and the influence rule of the cement on the hydration heat release of the concrete is analyzed; and analyzing various performance indexes of the concrete under different mixing proportion conditions, finding out the mixing proportion of the concrete meeting engineering requirements and optimizing the concrete.
One-time pouring technical design and application of large-volume concrete of raft plate of storage tank bearing platform
According to the requirements of limited expansion rate, strength grade and impermeability grade of the concrete of the storage tank bearing platform, the concrete mixing proportion design, the free expansion test of the expanding agent and the result of the limited expansion test are combined to design the one-time concrete pouring technical scheme.
And arranging temperature observation holes in representative areas in the large-volume concrete foundation of the bearing platform raft plate to observe the internal temperature and the surface temperature of the concrete. The variation speed of the surface temperature of the concrete is controlled by covering agricultural film, wet cotton felt and the like on the surface of the poured concrete, so that the difference delta T between the maximum temperature value in the concrete and the surface temperature of the concrete is less than or equal to 25 ℃.
Shrinkage is the general term for the reduction in volume of concrete materials due to physical and chemical effects. The shrinkage of ordinary concrete includes chemical shrinkage, plastic shrinkage, drying shrinkage, self-shrinkage, carbonization shrinkage, temperature shrinkage, creep shrinkage, and the like. The core concrete in steel tube concrete is mainly affected by chemical shrinkage, self-shrinkage and creep shrinkage. The expansion mechanisms of different expanding agents are not completely the same, and the generated substances causing expansion are different, for example, the UEA expanding agent is a calcium vanadium stone which can increase the volume of a solid phase by 2 times and mainly compensate chemical shrinkage and self-shrinkage; the MgO is made of light-burned MgO, the expansion source is brucite which can increase the volume of a solid phase by 1 time and mainly compensate drying shrinkage and temperature shrinkage. The expansion rate of different types of expanding agents is measured by trial preparation, so that the expanding agent meeting the expansion rate limit of the bearing platform concrete is screened out.
The concrete meets the physical and mechanical property requirements of strength, workability and the like required by the construction of a storage tank bearing platform by adjusting the formula, the hydration temperature rise is controlled to avoid cracks, and the expanding agent with a proper proportion is added to resist the contraction of the concrete, so that the stress generated by the contraction of the concrete is balanced with the prestress generated by the expansion of the expanding agent.
According to the principle of the balance between the stress generated by the contraction of the concrete and the prestress generated by the expansion of the expansive concrete, the concrete with different contents of the expansive agent is poured inside and outside the expansive zone. Meanwhile, as the foundation concrete of the storage tank is large in volume, measures must be taken according to the construction process requirements of large-volume concrete, namely any large-volume concrete poured on site, so that the problems of hydration heat and volume deformation caused by hydration heat are solved, cracking is reduced to the maximum extent, the temperature control technology is researched, the difference delta T between the maximum temperature value in the concrete and the surface temperature of the concrete is controlled to be less than or equal to 25 ℃, and cracking on the surface is avoided. Thus, the concrete for the bearing platform raft plate of the storage tank with large integral rigidity and good impermeability is obtained by continuous one-time pouring without a post-cast strip.
Concrete containing expanding agents in different proportions is poured inside and outside the expansion zone according to the principle of the balance of the shrinkage stress of the concrete and the prestress generated by slight expansion of the expansion concrete, the technology is applied to the one-step pouring forming technology of the large-size raft slab concrete without the post-pouring zone of the large-size storage tank bearing platform, the cracking influence caused by the internal stress is eliminated, the raft slab concrete has stronger rigidity and impermeability, secondary construction is avoided, the construction period is shortened, and the benefit is improved.
Screening of expanding agent and research on expansion performance of expanding agent on concrete
Selecting sulphoaluminate expanding agents, lime expanding agents, iron powder expanding agents, MgO expanding agents and composite expanding agents to carry out free expansion tests and limited expansion tests. And determining the grade, the dosage, the total amount of the cementing material and the water-to-gel ratio of the sample cement according to the requirements of the expansion band and the outer concrete of the storage tank bearing platform on the aspects of strength, workability and the like. In order to investigate the influence of the type and the mixing amount of the expanding agent on the expansion performance and reduce the interference of other factors, the fixed cement dosage, the total amount of the cementing material and the water-cement ratio are adopted.
Free expansion test: and preparing three molded mortar test pieces in each group according to the national standard. And (3) filling the prepared mortar into test molds with nail heads at two ends in two layers, and numbering. From the initial length of the test piece, the test pieces are placed in a curing room for 1d, 3d, 7d, 14d, 21d, 28d, 60d, 90d and 120d, the lengths of the test pieces are taken out and measured respectively, and each test piece is tested three times at a time, and the average value of the three times is taken.
Limited expansion test: and preparing three molded mortar test pieces in each group according to the national standard. Before the mortar is loaded into the test mould, the expansion limiting framework is firstly placed into the mortar test mould. The constrained expansion ratio is the same as the free expansion ratio test and calculation method. Processing data, taking the average value of the expansion rates of a group of three test pieces as the expansion rate of the group, and taking the average value of the expansion rates of the rest two test pieces as the expansion rate of the group if the expansion rate of one test piece exceeds 30% of the average value, wherein the calculation result is accurate to 0.001%; if two specimens exceed the average value, the expansion ratio at this age is discarded.
Concrete mix proportion optimization design
On the premise of determining the reference mixing ratio, the mixing ratio with the best thermal property, physical and mechanical properties and durability is selected by adjusting relevant parameters such as the using amount of a cementing material, the mixing amount of an admixture, the sand rate, the mixing amount of an admixture and the like. And carrying out mix proportion design and trial mix according to JGJ55-2000 design regulations on common concrete mix proportion and JGJ/T10-95 technical regulations on concrete pumping construction.
Uniformly weighing raw materials purchased in the same batch of test concrete, ensuring the consistent performance of the raw materials in each group of tests as far as possible, adopting the uniform standard for weighing, stirring, vibrating, forming and maintaining the raw materials in each group of tests, and then measuring the physical properties such as slump, expansion, 3d strength, 7d strength, 28d strength, 60d strength and the like.
According to the requirements of the concrete limited expansion rate, the strength grade and the impermeability grade of the storage tank bearing platform, the concrete formula, the pouring process and the temperature control measures inside and outside the expansion zone of the bearing platform are designed by combining the concrete mixing proportion design and the expansion performance test result of the expanding agent.
The construction process comprises the following steps:
construction preparation → concrete stirring (centralized stirring supply from a stirring station) → concrete stirring transportation (truck transportation) → pumping (pump truck pipe distribution, cloth material) → pouring and tamping (plug-in vibrator tamping) → curing (curing film covering, watering curing).
Concrete mixing and transporting
The mixing proportion (including the replacement proportion of the expanding agent) of the concrete inside and outside the expansion zone is determined according to the actual designed strength and pumping requirement of the bearing platform. Proper amount of mineral powder is doped to reduce the hydration heat of the concrete; the retarder is added to prolong the initial setting time of the concrete, and the initial setting time of the concrete on site is controlled to be 4-8 hours.
Concrete pouring and pumping schematic diagram
According to the plane size and the concrete quantity of the bearing platform, the capacity of the concrete supply and pumping equipment is combined, and two automobile pumps (the length of a material distributing rod is 48-52 m) are arranged during the concrete pouring of the bearing platform.
Concrete pumping and casting and tamping
The casting and tamping of the concrete of the bearing platform are formed by one-time casting and tamping without setting construction joints. The concrete pouring and tamping of the bearing platform adopts a pump concrete construction process, continuous operation and a natural flowing and inclined plane layering pouring and tamping construction method. And (4) theoretically calculating the concrete pouring amount per hour, and determining whether the pumped concrete machinery meets the construction requirements. The concrete is poured according to the parallel flow direction, and the pouring width of the concrete is controlled, thereby meeting the actual capacity of the equipped concrete stirring, transporting and pumping machinery
The concrete is vibrated by adopting an insertion type vibrator, so that the 'fast insertion and slow drawing' is realized, and the distance between each insertion point of the vibrating spear is controlled at 400 mm. Because the slump of the pumped concrete is relatively high, the concrete needs to be subjected to secondary re-vibration after 30 minutes. And when the concrete of the bearing platform is tamped, the expansion zone is used as a boundary, the two pump trucks on the two sides are simultaneously cast, before the concrete reaches initial set, the pump truck on one side is replaced by the concrete on the inner side of the expansion zone in advance to carry out the casting construction of the concrete in the expansion zone, and after the concrete is flushed with the concrete in the non-expansion zone, the pump truck on the other side is replaced by the concrete on the outer side of the expansion zone to carry out the casting construction of the concrete on. The joint of the expansion belt and the non-expansion belt of the bearing platform is provided with a dense-hole steel wire mesh of 0.9mm multiplied by 10 mm.
After the concrete is vibrated, an aluminum alloy ruler is used for scraping according to the elevation; performing secondary vibration before initial setting to close the water collecting crack; before final setting, the concrete is polished twice by a mechanical polisher to prevent the concrete from generating shrinkage cracks. In the concrete pouring and tamping process, the elevation of the bearing table surface is fixed and retested by a level gauge, and the flatness is ensured to meet the design and standard requirements.
Concrete temperature control technology
Because the storage tank foundation concrete volume is great, according to bulky concrete construction process requirement: "any in-situ cast mass concrete must be treated to solve the problem of hydration heat and consequent volume deformation to minimize cracking"; the relevant specifications of China indicate that: when the difference delta T between the maximum temperature value in the concrete and the surface temperature of the concrete is less than or equal to 25 ℃, no surface crack is generated. Calculating the temperature difference according to the condition of the basic concrete:
calculation of adiabatic temperature rise versus maximum temperature:
T＝WQ/Cr
in the formula: w-amount of concrete Cement per cubic meter
Q-heat of hydration per kilogram cement
C-specific heat of concrete
r-concrete volume weight
The method comprises the steps of firstly covering an agricultural film on the surface of poured concrete, then fully paving a wet cotton felt layer, so that the surface of concrete of a bearing platform bottom plate is not cooled too fast, improving the surface temperature of the concrete by utilizing the heat dissipated by hydration heat in the concrete, ensuring the surface temperature of the concrete, avoiding temperature difference cracks and shrinkage cracks of the concrete caused by the action of the hydration heat, and further ensuring the construction quality of the concrete.
15 temperature observation holes are arranged in a representative area in the base plate foundation of the bearing platform and are used for observing the internal temperature and the surface temperature of the concrete in different areas, different depths and different time. And observing the concrete temperature of the bearing platform by using a thermometer, starting the first observation 12 hours after the concrete pouring is finished, and observing every 8 hours later. When the temperature difference in the concrete is more than 25 ℃, heat preservation measures are taken for the concrete to ensure the quality of the poured concrete. The distribution position and burying of the temperature observation points are shown in FIG. 3.
After the concrete is initially set, the concrete of the bearing platform is covered by a plastic film in time, and then the plastic film is covered by a cotton felt for watering and curing. And after the concrete of the whole bearing platform is completely poured and tamped, and the temperature difference between the inside and the outside is observed to be less than 25 ℃, changing the watering and maintenance of the cotton felt.
The one-time pouring method for the large-size raft plate concrete of the large-scale petrochemical storage tank bearing platform replaces the traditional secondary pouring method technology to pour the large-size concrete of the storage tank bearing platform raft plate, improves the integral rigidity and the impermeability of the storage tank bearing platform, shortens the construction period and reduces the cost.
By adopting the large-volume raft plate concrete for the large-scale petrochemical storage tank bearing platform, the construction period can be effectively shortened, and the management cost can be saved. The traditional secondary pouring method is used for pouring the petroleum storage tank bearing platform by using the post-pouring belt, and the post-pouring belt can be poured after 42 days of the first pouring. In the period, sundries are easy to fall into the post-pouring belt, and need to be cleaned before pouring again; the post-cast steel bars are easy to rust after being exposed for a long time, and rust removal is needed in later secondary casting; before concrete is filled in the post-cast strip, the concrete on two sides needs to be chiseled, a large amount of manpower is consumed, and the construction cost is increased. On the contrary, the one-time pouring forming without the post-pouring belt avoids the procedures.
The large-volume raft plate concrete for the large petrochemical storage tank bearing platform can improve the integral rigidity and the impermeability of the storage tank bearing platform raft plate concrete and can resist the storage tank safety problem caused by slight uneven foundation settlement. The problem that the drying shrinkage of the secondary pouring post-cast strip concrete is easy to generate cracks at the joint of new and old concrete is avoided by the one-step pouring and forming of the large-volume concrete, and the possibility of petroleum leakage of the storage tank is reduced.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (9)
1. The utility model provides a large-size raft board concrete one-time pouring method of large-scale petrochemical industry storage tank cushion cap which characterized in that includes:
and (3) screening swelling agents: selecting a sulphoaluminate expanding agent, a lime expanding agent, an iron powder expanding agent, a MgO expanding agent and a composite expanding agent to carry out a free expansion test and a limited expansion test, and screening the expanding agent which has excellent expansion performance and meets the requirement of concrete performance;
determining the mixing proportion of concrete;
designing concrete formulas inside and outside the expansion band of the bearing platform according to the requirements of limited expansion rate, strength grade and impermeability grade of the concrete of the bearing platform of the storage tank and the combination of the design result of the mix proportion of the concrete and the expansion performance test result of the expanding agent;
and (5) concrete pouring construction.
2. The method for pouring the large-volume raft slab concrete of the large petrochemical storage tank bearing platform according to claim 1, wherein the performing of the expansion performance test of the expanding agent comprises:
the expansion rate of different types of expanding agents is measured by trial preparation, so that the expanding agent meeting the expansion rate limit of the bearing platform concrete is screened out.
3. The method for pouring the large-volume raft slab concrete on the large petrochemical storage tank bearing platform at one time according to claim 2, wherein the free expansion test comprises the following steps: preparing molding mortar test pieces according to national standards, wherein each group comprises three test pieces, filling prepared mortar into test molds with nail heads at two ends, numbering, placing the test pieces in a curing room for 1d, 3d, 7d, 14d, 21d, 28d, 60d, 90d and 120d from the initial length of the test piece, respectively taking out the length of the test piece, and taking the average value of the three times of testing each test piece for three times.
4. The method for pouring the large-volume raft slab concrete of the large petrochemical storage tank bearing platform at one time according to claim 3, wherein the expansion limiting test comprises the following steps: preparing three molded mortar test pieces according to national standards, placing a limited expansion framework into a mortar test mould before filling mortar into the test mould, wherein the limited expansion rate is the same as the free expansion rate test in the test and calculation methods, processing data, taking the average value of the expansion rates of a group of three test pieces as the expansion rate of the group, and taking the average value of the expansion rates of the rest two test pieces as the expansion rate of the group if the expansion rate of one test piece exceeds 30% of the average value, wherein the calculation result is accurate to 0.001%; if two specimens exceed the average value, the expansion ratio at this age is discarded.
5. The method for pouring the large-volume raft slab concrete of the large petrochemical storage tank bearing platform at one time according to claim 4, wherein the step of determining the mixing proportion of the concrete comprises the following steps:
on the premise of determining the reference mixing ratio, selecting the mixing ratio with the optimal thermal property, physical and mechanical properties and durability by adjusting related parameters, and designing and trial-matching the mixing ratio;
uniformly weighing the raw materials purchased in the same batch of the test concrete, ensuring the consistent performance of the raw materials in each group of tests, adopting the uniform standard for weighing, stirring, vibrating, forming and maintaining the raw materials in each group of tests, and then measuring the slump, the expansion, the 3d strength, the 7d strength, the 28d strength and the 60d strength of the test concrete.
6. The method for pouring the concrete for the large-volume raft slab of the large petrochemical storage tank bearing platform according to claim 5, wherein the concrete pouring construction comprises the following steps:
concrete stirring and transporting: determining the mixing ratio of the concrete inside and outside the expansion zone according to the actual design strength of the bearing platform and the pumping requirement, doping a proper amount of mineral powder to reduce the hydration heat of the concrete, doping a retarder to prolong the initial setting time of the concrete, and controlling the initial setting time of the concrete on site to be 4-8 hours;
concrete pumping and casting and tamping: according to the plane size and the concrete quantity of the bearing platform, the capacity of equipment for supplying and pumping the combined concrete is provided, an automobile pump is configured during the concrete pouring of the bearing platform, and the concrete of the bearing platform is poured and tamped at one time for molding;
and (5) maintenance: temperature observation holes are arranged in a representative area in a large-volume concrete foundation of a bearing platform raft, the internal temperature and the surface temperature of concrete are observed, and the change speed of the surface temperature of the concrete is controlled, so that the difference delta T between the maximum temperature value in the concrete and the surface temperature of the concrete is less than or equal to 25 ℃.
7. The method for pouring the large-volume raft slab concrete of the large petrochemical storage tank bearing platform according to claim 6, wherein controlling the surface temperature change speed of the concrete comprises: after the concrete is initially set, the concrete of the bearing platform is covered by a plastic film in time, then a cotton felt is covered on the plastic film for watering and curing, and after the concrete of the whole bearing platform is completely poured and tamped and the internal and external temperature difference is observed to be less than 25 ℃, the watering and curing of the cotton felt is changed.
8. The method for pouring the concrete of the large-size petrochemical storage tank bearing platform raft plate at one time according to claim 7, wherein a temperature observation hole is formed in a representative area in the large-size concrete foundation of the bearing platform raft plate, and the step of observing the internal temperature and the surface temperature of the concrete comprises the following steps: the concrete pouring method comprises the following steps that 15 temperature observation holes are arranged in a representative area in a base plate foundation of a bearing platform and used for observing the internal temperature and the surface temperature of concrete in different areas, different depths and different time, a thermometer is used for observing the temperature of the concrete of the bearing platform, the first observation is started after 12 hours after the concrete pouring is finished, the observation is performed every 8 hours later, and when the temperature difference in the concrete is more than 25 ℃, heat preservation measures are taken for the concrete, so that the quality of the poured concrete is ensured.
9. The method for one-time pouring of the large-volume raft plate concrete on the bearing platform of the large petrochemical storage tank according to claim 8, wherein the concrete is poured and pounded by adopting a pumping concrete construction process and continuous operation, a natural flow and inclined plane layered pouring and pounding construction method is adopted, the concrete pounding amount per hour is theoretically calculated, whether a pumping concrete machine meets the construction requirements is determined, the concrete is poured and poured according to the parallel flow direction, the pouring width of the concrete is controlled, so that the actual capacity of the prepared concrete stirring, transporting and pumping machine is met, the concrete is pounded by adopting an inserted vibrator, the distance between each inserting point of a vibrating rod is controlled to be 400mm, the concrete is subjected to secondary re-vibration after 30 minutes, the bearing platform concrete is pounded by taking an expansion zone as a boundary, two pump trucks on two sides are simultaneously poured and constructed, one pump truck in one side of the concrete before the concrete reaches initial setting is replaced by the concrete inside the expansion zone for pouring the concrete in the expansion zone, after the concrete is leveled with the concrete in the non-expansion zone, the concrete is replaced by the concrete outside the expansion zone to carry out the concrete pouring construction of the side expansion zone, a dense hole steel wire mesh with the thickness of 0.9mm multiplied by 10mm is arranged at the joint of the expansion zone of the bearing platform and the non-expansion zone, and after the concrete is vibrated, the concrete is firstly scraped by an aluminum alloy ruler according to the elevation; performing secondary vibration before initial setting to close the water collecting crack; before final setting, the concrete is polished twice by a mechanical trowelling machine, so that shrinkage cracks of the concrete are prevented, the elevation of the bearing platform surface is fixed and retested by a level gauge in the concrete tamping process, and the flatness is ensured to meet the design and standard requirements.
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