CN104947916A - Extra-large area concrete floor structure shrinkage control construction technology - Google Patents
Extra-large area concrete floor structure shrinkage control construction technology Download PDFInfo
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Abstract
The invention relates to an extra-large area concrete floor structure shrinkage control construction technology which effectively controls the extra-large area concrete cracks. When the shrinkage control construction technology is applied, control is mainly performed in the aspects of design and construction technology and comprises design control, material control, construction control and on-site monitoring control. According to the extra-large area concrete floor structure shrinkage control construction technology, the integrality of the floor structure can be effectively ensured, the concrete floor structure durability is improved, construction is reasonably organized, the construction period can be greatly shortened compared with standard arrangement post-cast strip scheme, and the giant economic benefits are brought to engineering projects, particularly industrial projects.
Description
Technical field
The present invention relates to concrete construction process, in particular, the present invention relates to the larger area ground concrete structure both shrinks being applied to the realm of building construction and control construction technology.
Background technology
Along with the development of national economy and the improvement of living standard, people to building functions trend towards variation, complicated.High-rise, super high rise building is ever-increasing while, the building of planar dimension overlength, ultra-wide is also emerging in large numbers rapidly, such as large public building, industrial premises and commercial centre etc.In view of the globality of above-mentioned building structure, using function and the requirement of construction period, ground or the flooring of this type of building require as not establishing shrinkage joint and ater-casting mostly, or shrinkage joint spacing exceedes current specifications requirement.Namely this kind of larger area ground concrete structure is proposed to the requirement of shrinking and controlling construction.
The key problem that larger area ground concrete structure both shrinks controls construction is, to the control producing distress in concrete because deformation constrain stress is excessive.In the past few decades, due to reasons such as economic levels, the domestic engineering relating to overlarge area concrete structure is less, and the engineering of larger area ground concrete structure is less.Thus few to the Crack Control theoretical research of this class formation, cause the design that is all difficult in China's specification, code and even various construction handbook find this class formation concrete and construction method.Engineers and technicians lack the analytical calculation quantitative to this class formation, and can only be undertaken designing and constructing by engineering experience qualitatively, the blindness of this design and construction and not scientific, cause a large amount of wastes and hidden danger in engineering.In view of overlarge area concrete structure in recent years, to shrink the application controlling construction more and more extensive, to the engineering theory research of this respect not enough comprehensively, system and specification, also lack a simple and direct effective design and construction method.
Summary of the invention
One object of the present invention is, provides larger area ground concrete structure both shrinks to control construction technology, carries out simple and direct high-quality control to distress in concrete, improve the construction quality of larger area ground concrete structure.
Concrete technical scheme of the present invention is as follows:
(1) design con-trol
1. utilize late strength of concrete: adopt the lower concrete of strength grade, utilize the concrete later strength of 60 days or 90 days as structural checking computation intensity;
2. reduce the constraint of earth construction: according to formula Y=Ls/S, calculate the restrained degree of concrete slab, in formula:
The about beam ratio coefficient of Y-concrete component, the girth retrained around Ls-concrete slab, the surface area of S-concrete slab;
Reduce the constraint of earth construction, mainly through with under type:
Concrete slab and periphery body of wall and pillar cut off by I, at periphery body of wall pad cystosepiment, increase join oblique reinforcing bar, reinforced mesh in hole surrounding;
II, between layer of concrete and reinforced concrete floor, arranges sliding layer;
3. according to the concrete limit stretching coefficient after following formulae discovery arrangement of reinforcement,
In formula: ε
paconcrete limit stretching after-arrangement of reinforcement, R
f-concrete anticracking design strength, p-sectional reinforcement rate p × 100, d-bar diameter (cm);
Adopt suitable arrangement of reinforcement, improve concrete limit stretching, when reinforcement ratio is constant, adopt minor diameter, closely spaced reinforcing bar; 4. storehouse spacing is jumped according to following formulae discovery:
in formula: [L]-jointless construction jumps storehouse spacing, H-concreting body thickness, the horizontal distortion rigidity (N/mm3) of Cx-outer constraint medium, Δ T
2t ()-length of time, when being t, concrete casting building body was comprehensively lowered the temperature (DEG C), when E (t)-age of concrete is t, and modulus of elasticity of concrete (N/mm2);
(2) control of material
1. cement: Portland cement or the slag cements that should use the same lot number of same manufacturer for same engineering or engineering the same area, the specific area of use cement must not more than 3500 ㎡/kg, and every cubic meter of concrete consumption is at 270 ~ 300kg;
The maximum temperature difference of concrete central temperature and its external surface must not higher than 25 DEG C, and the heat of hydration of concrete batching cement 7d used is not more than 25kj/kg;
2. building stones: adopt that specification is consistent, the multi-angular limestone gravel of continuous grading or cobble, the mud content of building stones controls within 1%, is greater than 5mm clod content ≯ 0.5%;
3. aggregate: flat-elongated particles content is not more than 10%, aggregate must not with foreign material, during fines is selected, coarse sand, fineness modulus is more than 2.5, mud content controls within 3%, is greater than 5mm clod content and is less than 1%, harmful substance contents < 1.0%;
4. in concrete, water reducing agent, fiber, admixture is added;
(3) construction control
1. concrete slump controls at 140 ± 20mm;
2. before building, the foreign material such as rubbish, earth, wood chip at position are built in cleaning, the pollutant on cleaning reinforcing bar; and checking whether cushion block of concrete bar protective layer is put well, stamp falls to loosen weak sand stone layer and cleans out, and waters fully moistening but ponding must not be had to exist; rainy day forbids to build, and concrete steps are:
I along the direction of concreting, before, during and after arrange 3 road vibrating heads, the 3rd road vibrating head is arranged in placing of reinforcement place, the end or concrete toe place, and rear 1 road vibrating head is arranged in concrete emptying point, road, middle part 1 vibrating head make middle part concrete vibrating closely knit;
II vibrating head moving interval controls at about 200mm, vibrating time 15 ~ 30 seconds, and fast inserting is pulled out slowly, no longer obviously sinks, no longer occurs bubble, surface glows mortar and be as the criterion, insertion about lower-layer concrete 50mm with concrete surface;
III is controlled every block concrete well and is turned back and advance intermittent time of building, and does not occur constuction joint in block;
IV concrete vibration time general control at each point 15 ~ 20s, when concrete surface be level and there is uniform cement paste, no longer include and significantly sink and a large amount of bubble emits time can stop;
V, when after concrete casting to plate top mark height, uses aluminium alloys darby that concrete surface is levelling, pats with wood float, rubs with the hands and smear twice, after concrete initial set, before final set, uses plasterer's trowel to carry out quadric-plastering press polish, and lays plastic sheeting water-preserving curing;
3., when overlarge area concrete structure construction, employing good heat insulating, economic material carry out insulated curing;
When overlarge area concrete structure construction, watering moisturizing, guarantees concrete maintenance more than 14 days under humidified condition;
(4) field monitoring controls
1. reinforcing bar testing element
Reinforcing bar testing element can test the strain and stress of reinforcing bar, and strain testing required precision is not more than 1 μ ε, and range requires at ± 1500 more than μ ε, and stress test required precision is not more than 0.1MPa, and range is at ± more than 400MPa;
2. concrete test element
Concrete test component requirements can test concrete temperature and strain, and temperature test required precision is not more than 0.5 DEG C, and range requires at-20 DEG C ~+110 DEG C, and strain testing required precision is not more than 1 μ ε, and range requires at ± 1500 μ ε;
3. testing element is installed and protection
Testing element installation site is accurate, fixation, concrete test element and structure reinforcing bars and fixed mount metallic object adiabatic, reinforcing bar testing element and bar connecting reliable, the lead-out wire centralized arrangement of all testing elements, in concreting process, must not directly shock-testing element and lead-out wire thereof, when vibrating, oscillating column pump must not touch testing element and lead-out wire thereof;
4. monitoring periods requirement
Also detect for a long time the ess-strain monitoring of concrete temperature strain and reinforcing bar, monitoring time is no less than 45 days;
5. crack treatment measure
Being Ф 10, the dark hole for 10mm along crack@300mm drill diameter, then drying along cleaning in seam both sides 100mm;
The grout nipple going back oxygen clay band fuzz button is fixed in hole, fracture faces with go back oxygen slurry and glass fabric close;
Be coated with suds aerating test, whether inspection leaks gas, and must again close if any gas leakage;
As being in the milk without leaking gas, each grouting point is in the milk successively, if adjacent grout nipple has slurries to spray, namely closes with sebific duct, is then in the milk until all complete successively.
Larger area ground concrete structure both shrinks provided by the invention controls construction technology, preferably, above-mentioned steps (1) in sliding layer adopt waterproofing materials or plastic sheeting, waterproofing materials adopts empty laid process, namely on concrete cushion, directly waterproofing materials is laid, without any need for binding material.
Larger area ground concrete structure both shrinks provided by the invention controls construction technology, preferably, above-mentioned steps (2) in water reducing agent adopt sulfonated polystyrene, Malaysia sulfonate polyoxyethylene ester, admixture adopt coal dust ash, coal dust ash volume be generally no more than 25% of cementitious matter total amount.
Advantage of the present invention and beneficial effect are:
1. larger area ground concrete structure both shrinks provided by the invention controls construction technology, effectively can ensure the globality of earth construction, improve ground using function, control effectively to because concrete shrinkage, temperature action or load etc. act on the distress in concrete caused, improve the functional performancies such as ground waterproof, protection against the tide, high-cleanness, high, improve air purity, ground waterproof, protection against the tide etc., constructing operation is simple and easy, and workmanship is easily guaranteed;
2. larger area ground concrete structure both shrinks provided by the invention controls construction technology, effectively can control overlarge area ground because concrete shrinkage, temperature action or load etc. act on the distress in concrete caused, improve concrete surface structure durability.
3. larger area ground concrete structure both shrinks provided by the invention controls construction technology, in Practical Project, workable comparatively criterion settings ater-casting scheme significantly can save the construction period, can for object of construction production particularly industrial project bring huge economic benefit.
Detailed description of the invention
According to technical scheme of the present invention, when not changing connotation of the present invention, those of ordinary skill in the art can propose multiple frame mode of the present invention.Therefore following detailed description of the invention just illustrating technical scheme of the present invention, and should not be considered as of the present invention all or the restriction be considered as technical solution of the present invention or restriction.
Larger area ground concrete structure both shrinks provided by the invention controls construction technology, controls in construction at larger area ground concrete structure both shrinks, due to concrete shrinkage deformation cause concrete to produce main cause that crack is cracking initiation.Therefore, reduce concrete contraction on the one hand, improving concrete Ultimate Tensile ability on the one hand, is the key preventing concrete from occurring harmful cracks.
For controling effectively to overlarge area distress in concrete, mainly analyzing in design and construction technology controlling and process when using and shrinking and control construction technology, comprising design con-trol, control of material, construction control and field monitoring and controlling, being embodied in:
Early age strength of concrete on the impact of its cracking performance than 28 days after concrete strength even more important, particularly under more severe dehydration condition.The technical measures of any raising early strength not only can not improve early anti-cracking behavior, unfavorable to it on the contrary.Because concrete is at the sclerosis initial stage, ultimate elongation is very low, although modulus of elasticity has obvious increase, resistance to tension improves and not quite, under equal conditions, the stress that the concrete that intensity is higher produces is larger, more easily causes concrete cracking; The concrete that early strength is higher, cement consumption is many, and hydration rate is fast, and shrinkage strain is large, will ftracture once shrink the stretcher strain that oversteps the extreme limit; Creep and to be inversely proportional to intensity, intensity is higher, creeps less, unfavorable to cracking behavior.
So, the concrete that should strength grade be adopted as much as possible lower when design larger area ground concrete structure.Now conventional method is exactly by concrete later strength, namely the intensity of 60 days or 90 days is as intensity during structural checking computation, also using the later strength of concrete 60 days or 90 days as the foundation of Concrete Strength Evaluation, engineering IMM algorithm and design of concrete in work progress.
Facts have proved: the constraint reducing earth construction: according to formula Y=Ls/S, calculate the restrained degree of concrete slab, in formula:
The about beam ratio coefficient of Y-concrete component, the girth retrained around Ls-concrete slab, the surface area of S-concrete slab.
The constraint of the earth construction reduced is mainly manifested in the following aspects:
1. according to engineering practice, when being built by concrete slab and periphery wall barrier, allow periphery concrete relative to periphery body of wall, becoming can the plate of free shrink, can reduce constraint when concrete slab shrinks so largely.Also only cystosepiment need be padded on body of wall during construction.Around hole, Varied section rotation angle position, corner etc. due to variations in temperature and concrete shrinkage, stress can be produced and concentrate and cause crack.For this reason, oblique reinforcing bar, reinforced mesh can be joined in the increasing of hole surrounding.For avoiding the abrupt change of cross section at Varied section place, section transition gradually can be made as Local treatment, increasing simultaneously and joining cracking resistance reinforcing bar, also after concrete meets and jumps storehouse length of time, then in the mode that structure punches, the abrupt change of cross-section can be avoided.
2., under the condition of structure permission, pillar periphery and pillar, when building, cut off by concrete slab.If closely build between concrete slab and pillar, on the one hand when concrete slab shrinks under various effectiveness effect, will produce larger shear stress in pillar, this shear stress makes pillar produce additional bending moment, affects the safety of structure; On the other hand because the constraint of pillar, limit the shrinkage strain of concrete slab, carrying out of aggravation crack.Pillar periphery concrete slab and pillar cut off builds, and construction way is similar to periphery wall barrier to concrete slab, need keep off surrounding at pillar at the time standby cystosepiment of concreting.
3. the interlayer restraint forces size of concrete slab, plays a decisive role in larger area ground concrete structural cracks controls.Common earth construction mainly contains graded sand and stone basic unit, plain concrete cushion layer, reinforced concrete soil padding and surface layer etc., and whether the cracking of main stress layer reinforced concrete floor wherein, whether determines the cracking of whole earth construction.One of effective ways retrained between reducing layer are exactly between plain concrete layer and reinforced concrete floor, arrange " sliding layer ".This " sliding layer " can be served as by waterproofing materials, on the one hand as the main defence line of structurally waterproof, can obviously reduce the shear stress retraining generation between deck on the other hand, thus reduce the restraint stress of reinforced concrete floor.When earth construction does not need to arrange waterproofing course, plastic sheeting also can be adopted to replace.It should be noted that waterproofing materials (as APP modified asphalt waterproof coiled material), construct time should adopt empty laid process, namely direct laying water-proof coiled material in plain concrete cushion layer, and without any need for binding material.
Concrete structure is heterogeneous material, when structure bears pulling force effect, in cross section, each particle is stressed is uneven, there is a large amount of irregular stress concentration points, first these points reach ultimate tension due to stress, cause the plastic strain of local, if there is no reinforcing bar near stress point, finally just occur crack at stress raiser.If there is the reinforcing bar of suitably configuration, the continuation of confined concrete is out of shape by reinforcing bar, thus shares concrete internal stress, postpones the appearance of distress in concrete, improves concrete limit stretching.Suitable arrangement of reinforcement to improve concrete ultimate elongation, and its key is " suitably " two word.Concrete temperature shrinkage fracture is controlled with suitable constructional reinforcement.
So-called " suitably ", in brief, arrangement of reinforcement should be accomplished thin, close.That reacts this relation has following empirical formula:
In formula:
ε
paconcrete limit stretching after-arrangement of reinforcement, R
f-concrete anticracking design strength,
P-sectional reinforcement rate p × 100, d-bar diameter (cm).
The design of overlarge area reinforced concrete structure arrangement of reinforcement should follow minor diameter, closely spaced principle.When reinforcement ratio is constant, adopt minor diameter, closely spaced reinforcing bar, be equivalent to add the surface area that reinforcing bar contacts with concrete, be conducive to the Crack Control of concrete structure.Generally, the reinforcing bar of Φ 8 ~ 14mm and 100 ~ 150mm spacing is adopted to be more reasonable.Should also be noted that structure muscle is joined in increasing, particularly to cavity and pre-buried pipeline place, be the weak link of Crack Control simultaneously.The reinforcement ratio of total cross-section should be not less than 0.3%.
Jumping storehouse spacing i.e. concrete slab, not arranging in ground, shrinkage joint situation, there will not be the maximum of crack to build length, select reasonably construction jumping storehouse spacing to be the prerequisite of Crack Control success or failure.Larger area ground concrete structure both shrinks controls construction, and key is the control to ground structural cracks.Short distance release stress contraction control construction be concrete surface by vertical direction arrange be constuction joint, with constuction joint, larger area ground concrete is divided into some pieces by certain size, adjacent block interval is built (jumping storehouse to build), until first concreting after moderate finite deformation, then connection is built integrally.Be non-linear relation according to temperature shrinkage stress and structure length, utilize early stage (7 ~ 10 days) temperature difference of concrete and shrinkage strain larger, adopt the early stage larger contraction of way reply of short distance release stress, until concrete through the early stage temperature difference compared with super large with after shrinking, each piece of cast connects into entirety, contraction less after reply.Must not there is crack in the concrete after this just requires piecemeal, namely require that the crack minimum spacing of primary concreting block must be less than and jump storehouse spacing in block.
Storehouse spacing is jumped according to following formulae discovery:
in formula: [L]-jointless construction jumps storehouse spacing; H-concreting body thickness; The horizontal distortion rigidity (N/mm3) of Cx-outer constraint medium; Δ T
2t ()-length of time, when being t, concrete casting building body comprehensively lowered the temperature (DEG C); E (t)-age of concrete is when being t, modulus of elasticity of concrete (N/mm2).
To larger area ground concrete structure, when considering late strength of concrete (60 days or 90 days), concrete strength grade is usually between C20 ~ C35.The optional Portland cement of kind of cement, slag cements or coal dust ash concrete.The Primary Reference parameter of the selection of cement type is cement fineness (or specific area) and soundness.Because the size of cement fineness is directly connected to the size of concrete shrinkage degree, engineering practice shows that the fineness of cement is thinner, forms concrete shrinkage larger after hydrated cementitious.Its specific area of cement be used in larger area ground concrete structure must not more than 3500 ㎡/kg.In addition cement also should have steady quality, alkalinity is low, activity good, consumptive use of water normal consistence is little, and uniformity, easy performance are good, and between cement and admixture, compliance is good.The economy of engineering also should be considered, usually preferred Portland cement or slag cements when selecting.The cement of the same lot number of same manufacturer should be used to same engineering or engineering the same area.The consumption of cement should control, and after when ground structural strength, between C25 ~ C35, also employing utilizes late strength of concrete, every cubic meter of concrete consumption is at 270 ~ 300kg.
The principle that larger area ground concrete structural concrete coarse aggregate is selected: particle diameter compared with large, intensity is high, continuous grading is good, linear expansion coeffcient is little, the place of production, specification must be consistent, the multi-angular limestone gravel of continuous grading or cobble.Particle diameter should be determined according to structural thickness and rebar spacing, selects greater particle size as far as possible, because increase aggregate size, decrease water supply volume, concrete contraction and bleeding reduce thereupon, simultaneously due to the minimizing of cement consumption, the heat of hydration of cement reduces, and reduces concrete temperature rise.If but aggregate size is excessive, easily cause concrete segregation.The mud content of stone should be strict controlled within 1%, is greater than 5mm clod content ≯ 0.5%.Aggregate flat-elongated particles content is not more than 10%, and aggregate must not with foreign material.During fines should be selected, coarse sand, fineness modulus is more than 2.5, and mud content controls within 3%, and the clod content being greater than 5mm is less than 1%, and hazardous substances is < 1.0% by weight.In, coarse sand compares with spun yarn, every cubic meter of concrete can reduce water supply volume 20 ~ 25kg, and water/binder ratio is constant, the corresponding minimizing 8 ~ 35kg of cement consumption, thus reduces concrete drying shrinkage, favourable to concrete anticracking.
The selection key of Admixture is the compliance with cement, because it affects the performance of concrete batching system, to the concrete pore structure of improvement, improves concrete compactness, thus improves cracking of reinforced concrete important role.
Water reducing agent, as concrete important component, is used in a large number in concrete production.Along with the development of water reducing agent research, the kind of water reducing agent also becomes increasingly abundant, from naphthalenesulfonate formaldehyde condensation compound, polycyclic aromatic hydrocarbon sulfonate formaldehyde condensation products and condensate of melamine sulfonate and formaldehyde three kinds develop into the polytype such as current sulfonated polystyrene, Malaysia sulfonate polyoxyethylene ester.The appearance of these novel water reducing agents, make concrete service behaviour better, slump-loss reduces.The diminishing principle of water reducing agent is that after various raw material add water and mix and stir, namely cement granules is wrapped up by moisture film when water reducing agent do not mixed by concrete, and from outward appearance to inner essence, (main component is C from the superficial to the deep to make calcium silicates mineral matter
3s and C
2s etc.) start aquation and hydrolysis, generate calcium silicate hydrate and Ca (OH)
2.These novel substances condense gradually, and this cohesive force is much larger than the wetting capacity to cement granules inside, make aquation and hydrolysis produce retardation.Novel substance is surrounded on around cement granules, decreases aquation surface and the aquation degree of depth of cement granules.When adding water reducing agent, water reducing agent is by absorption peptizaiton, lubrication and humidification, absorption peptizaiton makes " cement--water " system be in metastable suspended state, produce one deck solvent moisture film at cement particle surface simultaneously, free water in Flocculated Cement shape body is discharged, reaches the object of diminishing.
Research shows: mix water reducing agent decapacitation and effectively reduce concrete unit consumption of water, reduces the heat of hydration of cement, improves workability and the mobility of concrete mix.Under the condition of identical concrete strength, cement consumption can also be reduced.
The reason of concrete structure crack mainly contains three kinds: the stress produced in structure under external load effect and the crack caused; The crack that secondary stress causes is produced under external load effect; By being out of shape the crack caused, as the crack that the factors such as temperature, contraction, expansion and differential settlement cause.Wherein especially maximum to be out of shape the crack caused, account for more than 80%.Effectively can resist by suitably increasing constructional reinforcement the crack that external load causes, but for the third crack, especially plastic shrinkage cracks is invalid.
But after mixing fiber, due to fiber distribution in three-dimensional random in concrete, in concrete before there is not crack, can think fiber and concrete material shared tensile stress, and after crack appears in concrete, concrete collective deactivates, fiber prevention concrete is moulded the mechanism split and is in particular in two aspects: (1) plastic crack is always expanded from the primary microcrack place of concrete surface, when the length of microcrack is greater than the spacing of fiber, fiber plays crossing over crack the function served as bridge transmitting load, the tensile stress that crack was born by concrete body is originally transferred to fiber, make the stress field in concrete more continuously with even simultaneously, the stress at microcrack tip is concentrated and is able to passivation, further expanding of crack suffers restraints.(2) fiber has good ductility, ultimate elongation value is large, length is less than the pre-existing fracture expansion of fiber spacing when running into fiber, and fiber generates finer field, crack by forcing it to change bearing of trend or crossing over fiber, enlarges markedly the energy ezpenditure of microcrack expansion.
Single with regard to the prevent-crevice theory of fiber, in unit volume of concrete, the radical of fiber is more, and the spacing of fiber is less, and it is better that effect is split in the resistance of fiber, and the surface area in other words in unit volume concrete after fiber dispersion is larger, hinders that to split effect better.Because the surface area of fiber increases with the increase of fibre fineness, therefore, fibre fineness can be adopted to split the Specifeca tion speeification of ability as the resistance of description fiber.Along with the increase of fibre fineness, under identical volume volume, the spacing of fiber obviously reduces, and the restriction ability of fracture also significantly strengthens.
The cracking resistance effect of fiber shows the time of occurrence having delayed Article 1 plastic shrinkage cracks on the one hand, blocks the appearance that existing crack limits new crack on the other hand, to reach the effect of cracking resistance simultaneously.
Due to the distinguishing feature of admixture, mix the trend that admixture has been modern concrete development in concrete, with regard to the current construction market of China, what in larger area ground concrete structure, admixture was most widely used is coal dust ash.Room test records and confirms with a large amount of engineering practices by experiment: the main filling concrete pellet pores of coal dust ash, and the workability of Concrete Structure, can effectively reduce concrete shrinkage value; Volume is higher, or water-cement ratio is larger, and the amplitude of shrinking reduction is more; The amplitude that early-age shrinkage reduces is higher than the intermediary and later stages.Because the response speed of coal dust ash is quite slow, after therefore replacing clinker cement, the effect reducing autogenous shrinkage is fairly obvious, even if in the later stage, still has certain inhibition.Water-cement ratio is lower, improves effect poorer, and one is because water-cement ratio is lower, and grain spacing reduces, and coal dust ash is more easily excited and participates in reaction; Two is that low water binder ratio is poorer than grog hydrating condition, and after coal dust ash replaces, grog degree of hydration improves.Namely coal dust ash intensity contribution in low water binder ratio cement paste is relatively large.The heat of hydration of flyash is much smaller than cement, and 1/3, the 28 day length of time being about cement the 7 day length of time is about 1/2 of cement.The flyash reduction cement consumption that admixture mixes 15% of cement amount can reduce the heat of hydration about 15%.Flyash surface smoother, water requirement is little, can make to retain in the cement slurry under identical water/binder ratio condition relatively many Free water, thus reduction self-constriction, also have water-reduction simultaneously, concrete unit consumption of water and cement consumption can be reduced, shrink to reduce concrete autogenous volume, what have also slightly expands, and is conducive to anticracking.Coal dust ash volume is generally no more than 25% of cementitious matter total amount.
For strictly controlling concrete-agitating quality, reduce, because communications and transportation causes slump-loss, to affect concrete uniformity, concrete should follow following principle in mixing process:
1) namely the same match ratio of strict implement is ensure raw material constant (the same to place of production, same specification, main performance index close), water-cement ratio constant (error is in allowed band).
2) mixing time is controlled.Mixing time length is directly connected to the indexs such as concrete intensity, workability, and the concrete-agitating time extends 15 ~ 20s than ordinary concrete mixing time.
3) according to temperature condition, build the time situation such as (daytime or night), water content of sandstone change, concrete slump loss; suitably first wife's composition and division in a proportion (water/binder ratio) is finely tuned in time; be strict controlled in prescribed limit with slump when ensureing concreting; concrete not bleeding, do not emanate, guarantee concrete supply quality.
Larger area ground concrete structure requires strict to concrete slump, must control at 140 ± 20mm, engineering construction place from concrete mixing plant transportation range more than 1 hour or transportation condition easily occur block up engineering, should take to set up agitator at the construction field (site).
No matter be adopt commercial concrete or scene to set up agitator all to answer strict implement concrete inspection system, to commercial concrete, during initial construction, per car checks the slump, after steady quality, within 2 ~ 4 hours, checks 1 time.Agitator is set up to scene, reviewer's regular check should be sent to entering pump and going out pump, have in inspection: enter pump temperature, enter the pump slump, go out pump temperature, go out the pump slump.In concrete delivery service, gunnysack should be adopted to cover elephant trunk, and moisturizing of sprinkling water.
Before building, the foreign material such as rubbish, earth, wood chip at position are built in cleaning, the pollutant on cleaning reinforcing bar, and check whether cushion block of concrete bar protective layer is put well.Treatment of construction joints way should be used as process to the block periphery of building before.Namely stamp falls to loosen weak sand stone layer and cleans out, and waters fully moistening but ponding must not be had to exist.Rainy day forbids to build.
Concrete vibrating quality directly has influence on compactness and concrete surface quality after concrete formation, and fully appropriate vibrating can improve concrete capacity against cracking largely, is building in the process of vibrating and should adopt measure:
1) along the direction of concreting, before, during and after arrange 3 road vibrating heads, the 3rd road vibrating head is arranged in placing of reinforcement place, the end or concrete toe place, guarantees the closely knit of concrete lower part; Rear 1 road vibrating head is arranged in concrete emptying point, solves the concrete tamping in top; Middle part 1 road vibrating head makes middle part concrete vibrating closely knit, and promotes that concrete flows.
2) vibrating head moving interval should control at about 200mm, smash 15 ~ 30 seconds time, fast inserting is pulled out slowly, but also no longer obviously should sink depending on concrete surface, no longer occur bubble, surface glows mortar and is as the criterion, and should about lower-layer concrete 50mm be inserted, to eliminate the seam between two layers.Process of vibrating is wanted comprehensively carefully, forbids causing the concrete construction quality such as honeycomb, pitted skin accident because occurring leakage to shake.Vibrating of concrete will be determined people, determine scope.
3) every block concrete of controlling well is turned back the intermittent time of advancing and building, and ensures not occur constuction joint in block, accomplishes compact and orderly operation.
4) concrete vibration time is grasped, longly easily cause concrete disintegration, too short concrete vibrating leakiness, general be level with concrete surface and occur uniform cement paste, no longer include when significantly sinking and in a large number bubble emits and can stop, concrete vibration time general control is at each point 15 ~ 20s.
5) when after concrete casting to plate top mark height, application 2m long aluminium alloys darby is levelling by concrete surface, and it is high to control plate top mark well.Then pat with wood float, rub with the hands and smear twice, at concrete after initial set, before final set, carry out quadric-plastering press polish with plasterer's trowel, and lay plastic sheeting water-preserving curing subsequently.
Mainly be divided into the maintenance of larger area ground concrete structural concrete: concrete heat and moisture preserving maintenance in the insulation of hydration heat of cement temperature rise after concrete initial set and temperature-fall period two stages.The each construction link of reasonable arrangement (as during concrete construction, its roof system has been constructed complete) in construction, allows being in indoor maintenance during concrete curing and being advisable.
Having the good material of heat-insulating property all may be used in concrete insulated curing, when overlarge area concrete structure construction, can adopt good heat insulating with suiting measures to local conditions, economic material makes insulated curing.Conventional heat insulating material has plastic sheeting, straw bag and gunnysack etc.To the watering moisturizing of larger area ground concrete structure, special messenger should be had to be responsible for.Guarantee concrete maintenance more than 14 days under humidified condition.
Larger area ground concrete structure field monitoring main manifestations is the ess-strain to concrete temperature and strain and reinforcing bar.According to the data recorded in observation process, analyze reinforcing bar and concrete stressed and restraint condition, if find there is sudden change or occur abnormal in temperature or strain, then should adjust maintenance measure in time, as increased the number of plies covering gunnysack or the frequency etc. increasing watering.By the maintenance that field monitoring instructs, realize concrete dynamic maintenance.
Reinforcing bar testing element requires the strain and stress testing reinforcing bar, the little 1 μ ε of element strain testing required precision, and range requires at ± 1500 more than μ ε; Stress test required precision is not more than 0.1MPa, and range is at ± more than 400MPa.Require good insulation preformance, waterproof durable, good stability, antijamming capability is strong, and signal long-distance transmission is undistorted, can realize long-term observation etc.
Concrete test component requirements can test concrete temperature and strain, and temperature test required precision is not more than 0.5 DEG C, and range requires at-20 DEG C ~+110 DEG C; Strain testing required precision is not more than 1 μ ε, and range requires at ± 1500 μ ε.Require good insulation preformance equally, waterproof durable, good stability, antijamming capability is strong, can realize long-term observation etc.
Testing element installation site should be accurate, fixation, concrete test component requirements and structure reinforcing bars and fixed mount metallic object adiabatic, reinforcing bar testing element requires with bar connecting reliable, and testing element and bar splice place should be taken measures to eliminate stress concentrated.The lead-out wire of all testing elements should be tried one's best centralized arrangement, and is protected.In concreting process, must not directly shock-testing element and lead-out wire thereof during blanking, when vibrating, oscillating column pump must not touch testing element and lead-out wire thereof.The qualification rate of testing elements all in addition should more than 95%, avoids occurring the excessive or component failure of multi-measuring point test error and cannot obtain desired data.
Concrete variations in temperature and creep and shrinkage are relative long-term processes, construction period concrete temperature strain be also a relative longer process with the monitoring of the ess-strain of reinforcing bar, when structure construction conditions permit, should monitor as far as possible for a long time, and monitoring time must not be less than 45 days.
Because the mechanism of larger area ground concrete structural cracks is very complicated, still may there is visible crack to the larger area ground concrete Structural Engineering of some complex condition, for this kind of quality problems, correct treatment principle should be had.The large multipair structural safety in this kind of crack does not constitute a threat to, but requires and user psychology acceptance from using function, should take measures to repair by fracture.Can adopt with the following method:
1. being Ф 10, the dark hole for 10mm along crack@300mm drill diameter, then totally drying along cleaning in seam both sides 100mm;
2. be fixed in hole with the grout nipple going back oxygen clay band fuzz button, fracture faces with go back oxygen slurry and glass fabric close;
3. be coated with suds aerating test, whether inspection leaks gas, and must again close if any gas leakage;
4. as being in the milk without leaking gas, each grouting point is in the milk successively, if find, adjacent grout nipple has slurries to spray, and namely closes with sebific duct, is then in the milk until all complete successively.
Claims (3)
1. larger area ground concrete structure both shrinks controls construction technology, it is characterized in that, specifically comprises the following steps:
(1) design con-trol
1. utilize late strength of concrete: adopt the lower concrete of strength grade, utilize the concrete later strength of 60 days or 90 days as structural checking computation intensity;
2. reduce the constraint of earth construction: according to formula Y=Ls/S, calculate the restrained degree of concrete slab, in formula:
The about beam ratio coefficient of Y-concrete component, the girth retrained around Ls-concrete slab, the surface area of S-concrete slab;
Reduce the constraint of earth construction, mainly through with under type:
Concrete slab and periphery body of wall and pillar cut off by I, at periphery body of wall pad cystosepiment, increase join oblique reinforcing bar, reinforced mesh in hole surrounding; II arranges sliding layer between layer of concrete and reinforced concrete floor;
3. according to the concrete limit stretching coefficient after following formulae discovery arrangement of reinforcement,
in formula: ε
paconcrete limit stretching after-arrangement of reinforcement, R
f-concrete anticracking design strength, p-sectional reinforcement rate p × 100, d-bar diameter (cm);
Adopt suitable arrangement of reinforcement, improve concrete limit stretching, when reinforcement ratio is constant, adopt minor diameter, closely spaced reinforcing bar;
4. storehouse spacing is jumped according to following formulae discovery:
in formula: [L]-jointless construction jumps storehouse spacing, H-concreting body thickness, the horizontal distortion rigidity (N/mm3) of Cx-outer constraint medium, Δ T
2t ()-length of time, when being t, concrete casting building body was comprehensively lowered the temperature (DEG C), when E (t)-age of concrete is t, and modulus of elasticity of concrete (N/mm2);
(2) control of material
1. cement: Portland cement or the slag cements that should use the same lot number of same manufacturer for same engineering or engineering the same area, the specific area of use cement must not more than 3500 ㎡/kg, every cubic meter of concrete consumption is at 270 ~ 300kg, the maximum temperature difference of concrete central temperature and its external surface must not higher than 25 DEG C, and the heat of hydration of concrete batching cement 7d used is not more than 25kj/kg;
2. building stones: adopt that specification is consistent, the multi-angular limestone gravel of continuous grading or cobble, the mud content of building stones controls within 1%, is greater than 5mm clod content ≯ 0.5%;
3. aggregate: flat-elongated particles content is not more than 10%, aggregate must not with foreign material, during fines is selected, coarse sand, fineness modulus is more than 2.5, mud content controls within 3%, is greater than 5mm clod content and is less than 1%, harmful substance contents < 1.0%;
4. in concrete, water reducing agent, fiber, admixture is added;
(3) construction control
1. concrete slump controls at 140 ± 20mm;
2. before building, the foreign material such as rubbish, earth, wood chip at position are built in cleaning, the pollutant on cleaning reinforcing bar; and checking whether cushion block of concrete bar protective layer is put well, stamp falls to loosen weak sand stone layer and cleans out, and waters fully moistening but ponding must not be had to exist; rainy day forbids to build, and concrete steps are:
I along the direction of concreting, before, during and after arrange 3 road vibrating heads, the 3rd road vibrating head is arranged in placing of reinforcement place, the end or concrete toe place, and rear 1 road vibrating head is arranged in concrete emptying point, road, middle part 1 vibrating head make middle part concrete vibrating closely knit;
II vibrating head moving interval controls at about 200mm, vibrating time 15 ~ 30 seconds, and fast inserting is pulled out slowly, no longer obviously sinks, no longer occurs bubble, surface glows mortar and be as the criterion, insertion about lower-layer concrete 50mm with concrete surface;
III is controlled every block concrete well and is turned back and advance intermittent time of building, and does not occur constuction joint in block;
IV concrete vibration time general control at each point 15 ~ 20s, when concrete surface be level and there is uniform cement paste, no longer include and significantly sink and a large amount of bubble emits time can stop;
V, when after concrete casting to plate top mark height, uses aluminium alloys darby that concrete surface is levelling, pats with wood float, rubs with the hands and smear twice, after concrete initial set, before final set, uses plasterer's trowel to carry out quadric-plastering press polish, and lays plastic sheeting water-preserving curing;
3., when overlarge area concrete structure construction, employing good heat insulating, economic material carry out insulated curing;
When overlarge area concrete structure construction, watering moisturizing, guarantees concrete maintenance more than 14 days under humidified condition;
(4) field monitoring controls
1. reinforcing bar testing element
Reinforcing bar testing element can test the strain and stress of reinforcing bar, and strain testing required precision is not more than 1 μ ε, and range requires at ± 1500 more than μ ε, and stress test required precision is not more than 0.1MPa, and range is at ± more than 400MPa;
2. concrete test element
Concrete test component requirements can test concrete temperature and strain, and temperature test required precision is not more than 0.5 DEG C, and range requires at-20 DEG C ~+110 DEG C, and strain testing required precision is not more than 1 μ ε, and range requires at ± 1500 μ ε;
3. testing element is installed and protection
Testing element installation site is accurate, fixation, concrete test element and structure reinforcing bars and fixed mount metallic object adiabatic, reinforcing bar testing element and bar connecting reliable, the lead-out wire centralized arrangement of all testing elements, in concreting process, must not directly shock-testing element and lead-out wire thereof, when vibrating, oscillating column pump must not touch testing element and lead-out wire thereof;
4. monitoring periods requirement
Also detect for a long time the ess-strain monitoring of concrete temperature strain and reinforcing bar, monitoring time is no less than 45 days;
5. crack treatment measure
Being Ф 10, the dark hole for 10mm along crack@300mm drill diameter, then drying along cleaning in seam both sides 100mm;
The grout nipple going back oxygen clay band fuzz button is fixed in hole, fracture faces with go back oxygen slurry and glass fabric close;
Painting suds aerating test, whether inspection leaks gas, and must again close if any gas leakage, and as being in the milk without leaking gas, each grouting point is in the milk successively, if adjacent grout nipple has slurries to spray, namely closes with sebific duct, is then in the milk until all complete successively.
2. larger area ground concrete structure both shrinks according to claim 1 controls construction technology, it is characterized in that, above-mentioned steps (1) in sliding layer adopt waterproofing materials or plastic sheeting, waterproofing materials adopts empty laid process, namely on concrete cushion, directly waterproofing materials is laid, without any need for binding material.
3. larger area ground concrete structure both shrinks according to claim 1 controls construction technology, it is characterized in that, above-mentioned steps (2) in water reducing agent adopt sulfonated polystyrene, Malaysia sulfonate polyoxyethylene ester, admixture adopts coal dust ash, and coal dust ash volume is generally no more than 25% of cementitious matter total amount.
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| CN110005169A (en) * | 2019-04-12 | 2019-07-12 | 中国启源工程设计研究院有限公司 | A kind of cracking resistance process with stressed seamless terrace |
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