CN1317219C - Method of controlling expansion of steel pipe concrete precisely - Google Patents

Abstract

The present invention relates to a method for controlling the expansion of steel pipe concrete, particularly to a method for precisely controlling the expansion of steel pipe concrete. The present invention is characterized in that the present invention has the following steps: 1. expansion agent is precisely designed and controlled: (1) an expansion source and raw material of the expansion agent are selected; (2) the component of the expansion agent is precisely designed and controlled; (3) the grain grading of the expansion agent is precisely designed and controlled; 2. material for regulating the relative humidity in the concrete is prepared and selected; 3. the expansion amount of the concrete is comprehensively and precisely designed and controlled: the steel pipe concrete has the mixing proportion that water glue rate is from 0.28 to 0.42; the unit water use quantity is from 175 to 195kg per m<3>; the unit cement use quantity is from 400 to 500kg per m<3>; the sand ratio is from 35 to 42 percent; the mixing quantity of the expansion agent is 10 to 18 percent of the total quality; the mixing quantity of fly ash and cinder is 0 to 20 percent + 0 to 25 percent of the total quality; the total mixing quantity is less than or equal to 25 percent; the mixing quantity of the material for regulating the humidity is 10 to 20 percent of the proportion of the sand use quantity; the mixing quantity of the high-efficiency water reducing agent is 0.8 to 1.8 percent of the total quality. The present invention realizes precise control of the expansion of the steel pipe concrete.

Description

A Method of Precisely Controlling the Expansion of Steel Tube Concrete

technical field

The invention belongs to the field of building materials and relates to a method capable of controlling the expansion of steel pipe concrete.

Background technique

Concrete-filled steel pipe is a composite material made by pouring plain concrete into steel pipes. The composite design principle is: the concrete is tightened by the steel pipe wall, and the strength and toughness can be greatly improved; the steel pipe is filled with concrete, which can improve the stability of the structure. And reduce the amount of steel used; the comprehensive cost performance of the combined material is obviously better than that of the two materials themselves. The key technology is that the core concrete must be closely combined with the steel pipe wall to obtain a composite effect, so as to achieve the designed composite performance. Ordinary concrete has a certain degree of inherent volume shrinkage after hardening, so the core concrete must be designed to have volume expansion and controllable properties. However, various expansive concrete technologies are currently difficult to meet this requirement. The main reason is that the expansion amount is difficult to finely control, and the expansion of concrete is uneven, which may easily cause the concrete to debond from the steel pipe wall to form a cavity, and the composite design performance of steel pipe concrete cannot be exerted. On the one hand, due to the low expansion energy of the current concrete expansive agent, the duration of expansion is short. On the other hand, the steel tube concrete is in a closed environment, and external moisture cannot enter to replenish the moisture consumed by cement hydration. Therefore, in the late stage of cement hydration Swelling agents cannot compensate for shrinkage due to the lack of moisture required for the reaction. In addition, people do not have the concept of finely controlling the expansion, and often do not have the fine design of the expansion at all, nor the technology of precisely designing and controlling the expansion of CFST.

Contents of the invention

In view of the current situation that the expansion of expansive concrete cannot be finely controlled, the purpose of the present invention is to provide a method for finely controlling the expansion of steel pipe concrete.

The technical solution of the present invention is: a method for finely controlling the expansion of concrete filled steel pipe, characterized in that the steps are as follows:

1. Fine design and regulation of expansion agent:

(1) Selection of expansion agent expansion source and raw materials:

In view of the problems that the current concrete expansive agent has low early expansion energy, short expansion stability period, and the closed state of the steel pipe concrete, it is difficult to expand the expansive agent to compensate for the later shrinkage without external water supply. The source is designed to be composed of three kinds of expansion sources of AFt, Mg(OH) ₂ and Fe(OH) ₃ , wherein the AFt expansion source uses different reaction processes generated by different substances to adjust the relationship between expansion speed, expansion and strength, that is, it is designed to be composed of sulfur Aluminate cement clinker and anhydrite provide early expansion source AFt with faster expansion rate and higher expansion energy, and raw alum and anhydrite provide medium-term expansion source AFt with moderate expansion rate and higher expansion energy; The later expansion source Mg(OH) ₂ is designed to be provided by calcined periclase and steel slag with higher RO phase; the later expansion source Fe(OH) ₃ with slower expansion rate is designed to be provided by steel slag with higher RO phase. On the other hand, a certain amount of porous materials such as zeolite powder with a certain porosity are mixed into the expansion agent, so that the water stored in the early stage of hydration will be released due to the pressure difference when the concrete is short of water in the later stage, for the hydration of the expansion component. Swelling occurs, while zeolite powder also provides Al ₂ O ₃ needed for AFT formation.

The mineral composition of the sulphoaluminate cement clinker is C ₄ A ₃ S: 50-82%, C ₄ AF: 3-13%, C ₂ S: 5-37%;

The MgO can be MgO obtained by calcining periclase at 950-1050°C;

Described anhydrite can be natural or artificial anhydrite;

The porous material can be zeolite powder with a porosity of 25% to 40%, and its dosage accounts for 10% to 20% of the sum of the raw materials of the expansion agent;

The steel slag may be 400-500m ² /kg and the RO phase K _m (MgO/(FeO+MnO))>1.

(2) Fine design and regulation of expansion agent components:

The ratio of the raw materials of the expansion agent is designed according to the chemical composition in Table 1. At the same time, according to the expansion speed of different expansion sources, the size of the expansion energy and its relationship with the shrinkage and strength of the concrete, the chemical composition of the expansion agent is calculated according to Table 1. In addition to the control, the three indicators of SO ₃ /Al ₂ O ₃ , SO ₃ /MgO and SO ₃ /FeO should be controlled as follows (expressed by mass ratio), namely:

SO ₃ /Al ₂ O ₃ =2~3;

_SO3 /MgO＝4～5;

SO ₃ /FeO=6-8.

Table 1 Chemical composition of expansion agent chemical composition SO ₃ Al ₂ O ₃ CaO MgO SiO ₂ FeO R ₂ O content/% 25～35 10～15 15～35 6～8 15～35 4～6 0.2～0.75

The chemical composition of the above-mentioned finely designed expansion agent is regulated by the ratio of raw materials.

(3) Fine design and control of particle size distribution of expansion agent:

The particle gradation of the expansion agent directly affects its expansion speed and expansion performance. For example, if there is too much fine powder, the dry shrinkage will be large and the expansion drop will be large; if there is too much coarse powder, the expansion speed will be too slow and the expansion rate will be low. The particle gradation of the expansion agent is finely designed according to Table 2:

Table 2 Particle gradation of expansion agent Particle size/μm <45 45～100 100～250 >250 content/% 5～10 35～45 40～55 5～10

2. Preparation and selection of relative humidity adjustment materials inside concrete:

Aiming at the main problem that the steel pipe concrete cannot produce the design expansion due to the lack of water in the later stage, a humidity adjustment material that can store a certain amount of water in advance and release the water when the relative humidity inside the concrete drops sharply is introduced to provide water for the expansion agent to continue to hydrate , compensating for shrinkage and producing expansion.

The raw materials of the humidity regulating material can be mainly composed of CaO, Al ₂ O ₃ , Fe ₂ O ₃ , SiO ₂ , MgO, K ₂ O, Na ₂ O and other raw materials, and the quality range of the chemical composition is: SiO ₂ 55～ 65%, Al ₂ O ₃ 18-25%, Fe ₂ O ₃ 6-10%, CaO+MgO 4-6%, K ₂ O+Na ₂ O 2-5%, loss on ignition 3-5%. Wherein, the ratio between CaO and MgO is arbitrary, and the ratio between K ₂ O and Na ₂ O is arbitrary.

The process flow for the preparation of humidity-adjusting materials is shown in Figure 1. The temperature control conditions of the high-temperature kiln: roasting at 1100-1300°C for 15-20 minutes; Slow cooling at ~400°C, rapid cooling below 400°C; Granule preparation: Use an impact crusher or hammer crusher to crush the bulk material formed by sintering to 2-16mm, and perform special treatment on the surface of the particle to obtain a humidity-adjusting material.

The dosage of the humidity regulating material is 10-20% of the sand consumption.

3. Comprehensive and fine control of concrete filled steel tube expansion:

In addition to expansion agents and humidity-regulating materials, the expansion of concrete-filled steel tubes is also closely related to the type and amount of cement, the type and amount of admixtures and water-reducing agents, and the strength grade of concrete. Fine control is based on the fine design and control technology of the expansion agent and the technology of the humidity control material, and according to the concrete strength grade, admixture and water reducing agent content and other indicators, the concrete mix ratio (see Table 3) especially the concrete expansion agent The dosage of concrete is carefully designed as follows to achieve optimal matching of cementitious materials, coordinated development of concrete strength and expansion, and fine control of expansion:

(1) Determine the basic dosage of expansion agent according to the gelling material

Make the _SO3 of the "cement + admixture + expansion agent" system equal to 5% to determine the basic amount of expansion agent;

(2) Determine the amount of expansion agent according to the concrete strength grade, admixture and water reducer

The amount of expansion agent = the basic amount of expansion agent × (1+m/25) × [1+log (Ja/β)] × γ

In the formula, m is the total dosage of the admixture (%);

Ja is the dosage of water reducer (%);

β is the influence coefficient of the water reducer. If the water reducer is a naphthalene-based water reducer, then β=0.7; if the water reducer is a polycarboxylate water reducer, then β=0.9;

γ is the influence coefficient of concrete strength grade, if the strength grade ≤ C50, then γ=1, if the strength grade>C50, then γ=1.1. Admixtures refer to fly ash, slag, etc.

Table 3 Mix ratio of steel tube concrete water-binder ratio Unit water consumption (kg/m ³ ) Unit cement consumption (kg/m ³ ) Sand rate (%) Dosage of expansion agent (%) The total amount of fly ash and slag (%) Humidity adjustment material content (%) (as the proportion of sand consumption) Superplasticizer content (%) 0.28～0.42 175～195 400～500 35～42 10～18 0～20+0～25 (total dosage≤25) 10-20 0.8～1.8

Among them, the cement is 32.5, 42.5, 52.5 ordinary silicon cement (Portland cement or fly ash cement or slag cement);

The swelling agent is the above-mentioned swelling agent;

The humidity-regulating material is the above-mentioned humidity-regulating material;

The fly ash is Class II fly ash or Class I fly ash;

The slag is S95 slag or S105 slag;

The water reducing agent is a high-efficiency water-reducing agent, such as a polycarboxylate high-efficiency water-reducing agent;

Water is tap water.

The sand rate is the percentage of fine aggregate in the total amount of aggregate (i.e. fine aggregate and coarse aggregate), in which coarse aggregate is crushed stone with a continuous gradation interval of 5-20mm or 5-25mm or 5-31.5mm ; The fine aggregate is sand with a fineness modulus of 2.3-3.1.

Features of the present invention:

1. The present invention adopts the fine design and control technology of the expansion source, raw materials, chemical components, and particle gradation of the expansion agent, the humidity adjustment material technology, and according to the concrete strength grade, admixture, and water reducing agent content and other indicators , finely design the concrete mix ratio, especially the amount of concrete expansion agent, to achieve the optimal matching of cementitious materials, the coordinated development of concrete strength and expansion, and the fine control of expansion;

2. In the present invention, on the one hand, the expansion source of the expansion agent is designed to be composed of AFT, Mg(OH) ₂ and Fe(OH) _3. Three kinds of expansion sources, on the other hand, a certain amount of zeolite with a certain porosity is mixed in the expansion agent Porous materials such as zeolite powder, so that the water stored in the early stage of hydration is released due to pressure difference when the concrete is short of water in the later stage, which is used for the hydration of the expansion component to generate expansion. At the same time, the zeolite powder also provides the Al ₂ O required for the formation of AFT ₃ .

The present invention adopts the fine design and control technology of the expansion agent, releases moisture in a timely and quantitative manner during the hardening process of the concrete, so that the expansion physical and chemical reaction of the concrete can be carried out normally, and considers the strength level of the concrete, the amount of admixture, The comprehensive fine design and control technology of concrete expansion with the characteristics of water agent type and dosage, etc., realizes the fine control of the expansion of concrete filled steel pipe.

Description of drawings

Fig. 1 is the flow chart of the preparation process of humidity regulating material of the present invention

Detailed ways

Embodiment 1 (C50 steel tube concrete):

Raw materials:

(1) cement,

42.5 Ordinary Portland cement,

(2) expansion agent,

Porous materials such as sulfoaluminate cement clinker, periclase calcined at 950-1050℃, MgO, natural or artificial anhydrite, zeolite powder with a porosity of 25-40%, and a specific surface area of 400-500m ² / kg and RO phase K _m (MgO/(FeO+MnO))>1 steel slag is processed according to the chemical composition of SO ₃ /Al ₂ O ₃ =2.6, SO ₃ /MgO=4.4, SO ₃ /FeO=6 and Table 1 Batching, homogenizing and grinding until the particle gradation reaches the range shown in Table 2, and finally packaging and sealing, the obtained product has large expansion energy, reasonable expansion speed, continuous and stable expansion of concrete, and fine control of expansion components and particle gradation. expansion agent.

(3) Humidity regulating material,

The humidity regulating material is prepared from shale as raw material according to the process flow chart 1, the particle size is 2-7.5mm, and the 24h water absorption rate is 15-20%.

(4) fly ash,

Class I fly ash,

(5) Aggregate: Coarse aggregates are crushed stones with a continuous grading range of 5-20 mm in size, crushing value < 10%, needle flake content < 10%; fine aggregates are fineness modulus of 2.3-3.1 of sand.

(6) Water reducing agent,

Water reducer: polycarboxylate high-efficiency water reducer, water reducing rate 28-30%.

Mixing ratio and performance:

Table 4 C50 concrete filled steel pipe mix ratio and properties (kg/m ³ ) cement water fly ash coarse aggregate sand Superplasticizer expansion agent Humidity Regulating Materials Compressive strength/MPa Initial slump (mm) Slump after 3h (mm) 420 190 80 1083 510 1.3% 55 73 59 220 190

Table 5 C50 Concrete-filled steel tube concrete under 20±3℃ confined expansion ratio (×10 ^-4 ) 7 days 28 days 56 days 90 days 180 days 2.7 3.7 3.8 3.7 3.7

Embodiment 2 (C60 steel tube concrete):

Raw materials:

(3) Cement:

52.5 Ordinary Portland cement,

(4) Expansion agent:

Porous materials such as sulfoaluminate cement clinker, periclase calcined at 950-1050℃, MgO, natural or artificial anhydrite, zeolite powder with a porosity of 25-40%, and a specific surface area of 400-500m ² / kg and RO phase K _m (MgO/(FeO+MnO))>1 steel slag is processed according to the chemical composition of SO ₃ /Al ₂ O ₃ =2.6, SO ₃ /MgO=4.4, SO ₃ /FeO=6 and Table 1 Batching, homogenizing and grinding until the particle gradation reaches the range shown in Table 2, and finally packaging and sealing, the obtained product has large expansion energy, reasonable expansion speed, continuous and stable expansion of concrete, and fine control of expansion components and particle gradation. expansion agent.

(3) Humidity regulating material:

The humidity regulating material is prepared from shale as raw material according to the process flow chart 1, the particle size is 2-7.5mm, and the 24h water absorption rate is 15-20%.

(4) fly ash,

Class I fly ash,

(5) Aggregate: Coarse aggregates are crushed stones with a continuous grading range of 5-20 mm in size, crushing value < 10%, needle flake content < 10%; fine aggregates are fineness modulus of 2.3-3.1 of sand.

(6) Water reducing agent:

Water reducer: polycarboxylate high-efficiency water reducer, water reducing rate 28-30%.

Proportion and performance

Table 6 C60 concrete filled steel pipe ratio (Kg/m ³ ) and performance cement water fly ash coarse aggregate sand Superplasticizer expansion agent Humidity Regulating Material Compressive strength/MPa Initial slump (mm) Slump after 3h (mm) 460 185 70 1050 650 1.5% 66 77 70 220 200

Table 7 C60 Concrete-filled Steel Tube Concrete at 20±3℃ Confined Expansion Rate (×10 ^-4 ) 7 days 28 days 56 days 90 days 180 days 2.6 3.6 3.5 3.6 3.6

Claims (1)

1. the method for a controlling expansion of steel pipe concrete precisely, it is characterized in that: step is as follows: 1). meticulous design of swelling agent and regulation and control:

(1) swelling agent expansion sources and starting material are chosen: the expansion sources with swelling agent is designed to by AFt, Mg (OH) on the one hand ₂And Fe (OH) ₃Three kinds of expansion sources are mixed porosity and are 25～40% zeolite powder porous material on the other hand in swelling agent; Starting material are: sulphoaluminate cement clinker, and the MgO of periclasite after 950～1050 ℃ of calcination, natural or artificial anhydrite, porosity is 25～40% zeolite powder, 400～500m ²/ kg and RO phase K _mThe slag of (MgO/ (FeO+MnO))＞1; Described sulphoaluminate cement clinker, its mineral composition are C ₄A ₃S:50～82%, C ₄AF:3～13%, C ₂S:5～37%;

(2) meticulous design of swelling agent component and regulation and control:

It is SO that the chemical composition of swelling agent is removed by the quality percentage composition ₃: 25～35%, Al ₂O ₃: 10～15%, CaO:15～35%, MgO:6-8%, SiO ₂: 15～35%, FeO:4～6%, R ₂O:0.2～0.75% control, and press mass ratio: SO ₃/ Al ₂O ₃=2～3; SO ₃/ MgO=4～5; SO ₃/ FeO=6～8 controls;

(3) meticulous design of swelling agent grain composition and regulation and control:

The grain composition of swelling agent is by granularity/μ m:＜45 its quality percentage compositions are 5～10%, its quality percentage composition of granularity/μ m:45～100 is 35～45%, its quality percentage composition of granularity/μ m:100～250 is 40～55%, granularity/μ m:＞250 its quality percentage compositions are 5～10%, carry out meticulous design and control;

2). inside concrete relative humidity is regulated material preparation and is chosen: select the Chemical Composition mass range to exist: SiO ₂: 55～65%, Al ₂O ₃: 18～25%, Fe ₂O ₃: 6～10%, CaO+MgO:4～6%, K ₂O+Na ₂The starting material of O:2～5%, loss on ignition 3～5% utilize rotary kiln roasting 15～20min under 1100～1300 ℃ of conditions; Tapping temperature is controlled at 800～900 ℃, is chilled to 700 ℃, and 700～400 ℃ of slowly coolings are adopted chilling below 400 ℃; Adopt impact breaker or hammer mill to be crushed to 2～16mm after being cooled to room temperature, make the moisture control material of regulating inside concrete relative humidity; The volume of moisture control material is 10～20% of a sand consumption;

3). comprehensive meticulous design of concrete swell increment and control: concrete filled steel tube proportioning: water-cement ratio 0.28～0.42, unit consumption of water 175～195kg/m ³, unit cement consumption 400～500kg/m ³Sand coarse aggregate ratio 35～42%, the shared total mass 10～18% of expansive agent dosage, the shared total mass 0～20%+0 of flyash+fine slag contents～25% and total volume≤25%, moisture control material volume is the ratio 10-20% of sand consumption, the shared total mass 0.8～1.8% of high efficiency water reducing agent volume;

The volume of swelling agent carries out following meticulous design: (1) determines the basic volume of swelling agent according to gelling material: make the SO3 of " cement+adulterant+swelling agent " system equal 5% to determine the basic volume of swelling agent;

(2) determine expansive agent dosage according to strength grade of concrete, adulterant and water reducer:

The basic volume of expansive agent dosage=swelling agent * (1+m/25) * [1+log (Ja/ β)] * γ

In the formula: m is the total volume of adulterant (%);

Ja is water reducer volume (%);

β is the water reducer influence coefficient, if water reducer is a naphthalene water reducer, then β=0.7 is a polycarboxylate dehydragent as if water reducer, then β=0.9;

γ is the strength grade of concrete influence coefficient, if strength grade≤C50, if γ=1 then is strength grade＞C50, then γ=1.1.